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- "Civilization and Sludge: Notes on the History of the Management of Human Excreta" by Abby A. Rockefeller
- Sludge safe if properly managed; report criticizes sludge fertilizer, By Daniel Cusick, Register Staff Reporter
- Sludge-Fertilizer: Contaminating Ground Water, By David Swanson, Staff Writer
- Treatment Alternatives
“The Natural Way” - Preliminary Proposal for an Integrated Technologies Wastewater Treatment Pond System for Los Osos, California
September 1, 2000
by Nelson Environmental Inc., 101 Dawson Road, Winnipeg, Manitoba, Canada, R2J 0S6
Tel: 204-949-7500, Fax: 204-237-0660,
Email: mhildebrand@nelsonenvironmental.com
Contact: Martin Hildebrand, P. Eng., ManagerIntroduction to Nelson Environmental Inc.
The function of Nelson Environmental Inc. is to provide long term cost effective, ecologically friendly wastewater treatment through:
· technology
· design and construction
· operation and maintenance
· system leasing and financing optionsNelson Environmental Inc. and associated companies have 75 years of construction and 35 years of wastewater design experience. Hundreds of systems have been installed in the USA and Canada over the last 35 years.
Our wastewater treatment methodology is to develop systems that:
· are long term cost effective
· simple in design and construction
· are ecologically friendly
· can accommodate the present and future needs of the communityNelson Environmental retains the rights to the Air Diffusion System (ADS) fine bubble aeration concept. This technology is used to provide oxygen and mixing in the wastewater to enhance the biological activity which is required for treating the wastewater. The ADS system simulates the mechanics of a slowly rolling river in a series of lagoons. A natural, slowly rolling river has a tremendous capacity for treating contaminated waters through mixing and rolling oxygen to the sludge layer on the bed of the river where aerobic bacteria convert the sludge to water, carbon dioxide and a small quantity of inert ash. Combining this technology with others such as bacterial augmentation and biofiltration results in a simple, low maintenance system that produces excellent water quality.
Project Overview
The water to be treated is the wastewater produced primarily from municipal wastewater. At present the homes located in Los Osos utilize septic tanks and leach fields to dispose wastewater. There are concerns that these practices have lead to excessive nitrates being infiltrated into the groundwater system. The objective of constructing a central wastewater treatment facility is to abandon the use of the leach fields and pipe the water to the new facility. Septige from the septic tanks would be hauled periodically to the treatment plant.One of the key issues in the selection of appropriate technologies for the wastewater treatment facility is the stringent requirement of discharged effluent having less than 7 mg/l of total nitrogen. Through the combination of technologies and appropriate design, this water quality can meet using a low maintenance ponding system.
In order to provide optimal treatment while optimizing land use, the following system would be utilized.
1) primary solids screening
2) ADS aerated Primary lagoon (Cell#1) with bacterial augmentation for minimizing sludge production
3) ADS aerated Secondary lagoon (Cell#2)
4) ADS aerated Nitrification/ micro denitrification lagoons (Cell#3a and #3b) equipped with Aquamats biofiltration technology and bacterial augmentation for optimizing nutrient removal
5) Denitrification ponds (Cell#4a and #4a) equipped with Aquamats biofiltration and bacterial augmentation for optimizing nutrient removal
6) ADS aerated Living Rock filters for final solids removal and nutrient polishing
ADS Aerated Primary Lagoon (Cell#1)
Approximately 75% of the total system sludge accumulation will occur in cell#1. The complete system is designed to handle a minimum 20 years of sludge accumulation. For sludge removal, the aeration tubing can simply be disconnected from the header lines and removed (by hand) from the cell. After sludge removal the lines are placed back in the cell and reconnected to the header.
The diffuser lines are placed on the bottom of the cells perpendicular to the flow of the wastewater. Through the rise of the bubbles, and subsequent mixing, convection cells are created between the lines. Not only does the water rise with the bubbles, the solids settle out through the downward motion of the water between the diffuser lines where the circulation loop is completed. When the solids reach the bottom of the lagoon, additional oxygen for biodegradation is provided through the bottom laid diffusers. This process results in minimal organic bottom sludge accumulation. The environmental impact and cost of sludge removal, disposal and treatment can be minimized with this system. There is no requirement for daily sludge handling with an ADS aerated lagoon system. Eliminating daily sludge handling also minimizes health risks to the operators.
Sludge reducing soil and water bacteria will be added to the lagoon with a continuous feed system. A preactivation system will be used to maximize the efficiency and reproduction rates of the bacteria.
Cell#1 has a mixing rate of 17 minutes. This rapid turnover maximizes contact time between oxygen, organic reducing aerobic bacteria and the water resulting efficient odor free BOD removal. Cell#1 will reduce BOD concentrations by 65 to 70%. The retention time is 14.3 days at design flow.
Because of the long retention time, the mixing capability of the aeration system the effluent recirculation, and the high residual dissolved oxygen levels, this system can handle fluctuations in loads and flows such as septige dumping without being upset.
Because the system is a complete aerobic process, no odors are produced. The air introduced through the linear air diffusers at the bottom of the lagoon provides life giving oxygen to the bacteria and micro-organisms at the sludge water interface resulting in the aerobic conversion of the sludge to carbon dioxide, water, and inert ash, none of which smell.
BOD5 is reduced to carbon dioxide, water, and inert ash by natural bacteria, which receive their oxygen supply from air provided through the aeration diffusers. Because the aeration bubbles not only provide oxygen but also mix the water, the oxygen is evenly distributed throughout the water body. The bubbles produced by the air diffusers are less than 3 mm in diameter and rise at approximately 0.25m/s. The small bubble size results in tremendous total surface area per cubic metre of air introduced into the system. This combined with the slow rate of bubble rise contributes the phenomenal efficiency of the system. Because of low sludge production in the system, retention time is retained for long term BOD5 removal.
Fecal coliform (FC) destruction is a direct function of dissolved oxygen levels, mixing and exposure to sunlight. Because of the high mixing rate produced by the diffusion system the wastewater is continually being brought to the surface where ultraviolet rays form the sun destroy the fecal coliform. Because of suspended solids, color and turbidity, the depth of penetration of the UV rays for fecal coliform reduction is very shallow in wastewater. If the water is not continually mixed to the surface, poor FC destruction occurs. In cell #1 the diffusion system mixes the complete cell every 17 minutes which means that each drop of water in the entire water column is exposed to sunlight approximately 43 times during 12 hours of daylight.
The continuous mixing results in significantly lower algae production than conventional passive wastewater stabilization ponds. The oxygen introduced into the system channel nutrients to microorganisms instead of algae. Lower algae production results in lower suspended solids in system effluent. The Nelson Environmental system design does not rely on algae or natural surface aeration for providing oxygen to the wastewater.
ADS Secondary Lagoon (Cell#2)
Additional BOD and suspended solids removal occurs in Cell#2. Cell #2 is mixed every 30 minutes to allow for settlement of finer particles that passed through from the aggressively circulated Cell#1. The retention time is 9.8 days for Cell#2. Cell#2 will reduce BOD concentrations by 55 to 60%. Effluent concentrations leaving cell#2 will have BOD concentrations less than 30 mg/l which is critical in the nitrification process in cell #3a and #3bADS aerated Nitrification/ micro denitrification lagoons (Cell#3a and #3b)
Cells #3a and #3b are primarily for nutrient removal. Nutrient removal only occurs efficiently when BOD levels are reduced below 30 mg/l in a lagoon setting. The lagoon is aerated to provide oxygen to the nitrifying bacteria which convert ammonia to nitrite and nitrate. The aeration system also provides continuous water circulation past the biofiltration curtains. Fixed media biofiltration is provided by Aquamats® biofiltration curtains. The curtain material provides surface area throughout the water column for bacterial growth. The unique design of Aquamats® provides pore spaces in the fabric that are anoxic. These regions provide optimum conditions for the growth of denitrifying bacteria. In essence two very different processes (one requiring aerobic conditions and the other requiring anoxic conditions) are contained in microclimates in the same lagoon.
Natural nitrifying soil and water bacteria will be applied to the lagoon with a continuous feed system. As in cell #1 a preactivation unit will be utilized.
Aquamats® have been used extensively in the aquaculture industry to reduce nutrients and improve water quality.
Denitrification ponds (Cell#4a and #4a)
Although Cells#4a and 4b are primarily for denitrification (anoxic conditions) several lines of ADS aeration tubing will be implemented to allow for flexibility in producing either anoxic conditions (without aeration) or aerobic conditions (with aeration). Aquamats® biofiltration curtains will also be utilized in this pond. A pipe from cell#1 to cells 4a and 4b will provide the necessary carbon (if required) for the nitrification process. These cells also operate in parallel.
ADS aerated Living Rock filter (Cell#5a and $5b)
An ADS living rock filter will be utilized to provide final polishing for solids removal in addition to being a second stage fixed media for final nutrient polishing. The two rock filters will operate in parallel. ADS aeration tubing is placed in perforated pipe underneath the rock filter to provide oxygen to the nitrifying bacteria as well as to provide a means of cleaning the filter. As with the biofiltration curtains, anoxic microclimates also exist within the Living Rock Filter which contain appropriate strains of bacteria for denitrification.
The total land area required for the lagoon system approximately 31.5 acres. A minimum area of 35 acres should be allowed for buildings, parking lot and any headworks.
Influent Design Parameters
BOD5 (mg/l) 220
TSS (mg/l) 200
flow (mgd) 1.7
design population 17,000
assume 25 mg/l total N entering cell# 3a and #3b.Effluent Design Parameters
BOD5 (mg/l) <10 (assumed)
TSS (mg/l) <20 (assumed)
Total N (mg/l) <7 (specified)Nutrient removal with Integrated Lagoon System
This preliminary design combines various technologies that all have proven track records. Hundreds of ADS aerated lagoon systems have been installed across the USA, Canada and into Mexico over the past 35 years. Many of these systems have had a design life of well over 20 years including several that are over 30 years old. Sludge removal frequency averages approximately 20 to 25 years. The ADS systems are well known for their efficiency in operation and the low maintenance requirements. The flexibility of the ADS system allows for easy implementation in lagoons of various depths, configurations and functions as demonstrated with this preliminary design. ADS lagoon configurations vary from 1 to 4 cell systems. Treatment efficiencies generally vary in accordance with the number of cells.
Total N is typically not monitored in aerated lagoon systems. Generally ammonia is the only N related parameter that is monitored, and in some cases even ammonia is not considered to be critical in the effluent. Some communities do however occasionally monitor total N and ammonia. The following is a brief summary of several ADS aerated lagoon systems which periodically monitor nutrients:
1) Caroline, Alberta, Canada
Caroline has a two cell continuous discharge ADS aerated lagoon system which treats standard municipal wastewater. No biofiltration or bacterial augmentation is presently being utilized in this system. Typical winter discharge TKN is 15 to 20 mg/l (0.5 C water with ice cover). Summer discharge is ranges from 2 to 10 mg/l with water temperatures ranging from 5 C to 20 C. Discharge BOD and TSS levels have averaged 15 mg/l based on monthly data averaged over 9 years of operation.
2) Fairmont Hotsprings, British Columbia, Canada
Fairmont has a single cell aerated lagoon with discharge to a storage cell. BOD and TSS have averaged 12 and 14 respectively over 14 years of test data. System has been in operation for 20 years. No sludge removal has been required throughout this time. TKN in effluent tested over a two year period ranged from 6.5 to 7.81 mg/l. No biofiltration or bacterial augmentation is utilized in this system.
3) Quail Creek, Oklahoma
Quail Creek has a three cell aerated lagoon system and has stocked to lagoons with fish as a method of nutrient removal. TKN levels in the discharge are typically less than 3 mg/l with BOD and TSS levels at 6 and 12 mg/l respectively.
4) Grainger, Iowa
Grainger utilizes a 2 cell aerated lagoon system with a constructed wetlands for final polishing. TKN is not tested but ammonia levels are generally average 2.5 mg/l. Ammonia typically ranges from 40 to 60% of TKN. The TKN levels could therefore be estimated to between 4.2 and 6.3 mg/l.
5) Melcher – Dallas, Oklahoma
Melcher-Dallas has been awarded the “Operations and Maintenance Excellence” award from the EPA for its 2-cell ADS aerated lagoon system. Ammonia testing conducted through 3 consecutive years between the months of May and October resulted in an average of 2.1 mg/l. Using the same 40% to 60% NH3 of TKN the resulting TKN value would be 3.5 to 5.3 mg/l.
6) Hamel, Illinois
Hamel utilizes a 3 cell ADS aerated lagoon combined with a Living Rock Filter. NH3 levels in the effluent water range from 0.1 to 2 mg/l during ice free months. This would correspond to TKN values of less than 0.2 mg/l to a maximum of 5 mg/l.
Through the above examples we demonstrate that 7 mg/l total N is indeed achievable with an aerated lagoon system. None of the above systems utilize bacterial augmentation on a regular basis or Aquamats® biofiltration technology. All of the systems are located in climates that are more severe that that of Los Osos.
Aquamats® biofiltration
Aquamats® biofiltration units are used primarily as a fixed media system for nutrient control in the aquaculture industry. Through extensive lab and field testing, total N removal rates per square meter of mat have been developed at various temperatures.
The Aquamats® system is designed to remove up to 18 mg/l N at design flow at minimum water temperatures of 6 degrees C. Based on the assumption that approximately 25 mg/l N will enter cells#3a and #3b the effluent quality will be 7 mg/l. The aerated living rock filter, which has proven to be tremendously successful is considered a redundant system for N removal.
Bacta-Pur® bioaugmentation
The nitrification and denitrification processes are very sensitive to numerous conditions. By bioaugmentation a balanced community of nitrifying and denitrifying bacteria is assured. Bioaugmentation also controls soluble organics to which the process is very sensitive. Preactivation of the bacterial mixture increases the size of the community of the beneficial microorganisms prior to bringing the cultures in contact with the wastewater to be treated.
Bioaugmentation in this preliminary design is not given a specific N removal rate, it is looked upon only to optimize the performance of the Aquamats®.
Bioaugmentation for sludge minimization has proven to extremely effective in numerous sewage lagoon applications. Hamel, Illinois for example reduced sludge depths in the lagoon (23 year old sludge by 10 to 20 inches over the entire lagoon in a 3.5 month program. Using the bacteria on a continuous basis starting with a new system such as Los Osos will significantly extend the internal sludge retention capacity of the lagoon system.
Based on the individual success of the above technologies and in some cases even better success when two or more of the systems are combined we are very confident that 7 mg/l total N discharge can be consistently attained with this preliminary system design.
The excellent water quality produced combined with no sludge handling required for the design life of the system makes this integrated pond system a viable alternative to a mechanical sewage treatment plant.
Operation and Maintenance requirements
The operators of the majority of ADS systems do not have any formal education or training. On average, one hour per day would be spent operating and maintaining the system. Because the Los Osos system combines numerous technologies, we suggest that one full time operator would be appropriate.
Cost Analyses
Treatment Plant site- Land 35 acres -$3,675,000
Mitigation land - $1,500,000
Subtotal Land Costs - $5,175,000
Base Capital Estimate (includes 15% contingency) - $7,500,000
Additional Collection System - $100,000
Additional odor control - $0
Additional Water Feature Cost - $0
Additional Drainage Creek Improvements - $300,000
Additional Biosolids Recycling facilities - $0
Subtotal – Capital Costs: Construction - $7,900,000
Salvage Value – Land -$1,281,665
Total Present Worth Capital
Cost-Effective Wastewater Treatment Process for Removal of Organics and Nutrients
Long Live the Bacteria! Bacteria have two great advantages in wastewater treatment: high metabolism and high reproduction rates. Figure 4 shows research results regarding the growth of microorganisms in an aerobic treatment environment of municipal wastewater. The influent wastewater typically carries 1 to 2 million bacteria per liter. After 2 days, the bacteria population reaches a maximum of about 70 million per liter!Additionally, the high rate of metabolism assures a fast reduction of organic pollutants (the food source for bacteria). Figure 5 shows the high rate of metabolic production compared to the mass of the bacteria vs. other forms of life. As a rule of thumb, the smaller the microorganism, the greater the metabolic production per biomass. The reason is that smaller-size microorganisms have more surface area per unit of weight. The size of surface area determines the intensity of metabolic functions. Thus, bacteria have the greatest metabolic "throughput" per unit of weight, and therefore are most efficient in reducing BOD.
With a higher sludge age, more complex microorganisms such as flagellates and ciliates grow. These microorganisms often feed on each other (e.g., ciliates feed on bacteria). This has the undesirable effect of not further reducing the influent BOD load, while still requiring significant aeration energy to maintain these life forms. Thus, for BOD reduction, a high sludge age is undesirable.
Generally, bacteria reproduce by cell division, called binary fission. The time required for each fission is referred to as the generation time. With bacteria, the generation time is the shortest of any life form, often less than 30 minutes. Thus, the likelihood of developing mutations that are capable of disintegrating various pollutants, while being resistant to adverse conditions is quite high.
While a great amount of pollutant removal is achieved in the adsorption stage by means of physical processes, the adsorption stage additionally takes advantage of the described properties of bacteria. The sludge age is only a few hours, resulting in a biomass that consists of bacteria only, as shown in Figure 4. For example, if the sludge age in the adsorption stage is five hours, more than ten generations of bacteria will grow. This results in a significant selection process of the bacteria that are best adapt at degrading the wastewater influent. The mutations that are most resistant to the toxic components of the wastewater (and best at dealing with pollutants with shock loads that may occur in the sewage collection system from time to time) will survive and create a very valuable population of microorganisms.
From the adsorption stage, the effluent enters an intermediate clarifier where excess sludge and return sludge is withdrawn. The supernatant then passes on to the second treatment stage, called the Bio-Oxidation Stage. This stage benefits from the high treatment efficiency in the adsorption stage. Furthermore, it has been shown that the adsorption stage significantly reduces the concentration of difficult-to-decompose chemical compounds. To some degree, such compounds actually convert to simpler, more easily digested BOD. This conversion reduces the treatment burden in the second stage, particularly if denitrification is required.
These advantages relating to the adsorption stage can be realized only in a dual-sludge system in which the microbial eco-system of the initial adsorption stage is strictly kept separate from the microbial eco-system of subsequent treatment stages.4 More specifically, this means that only the supernatant from the clarifier of the adsorption stage flows into the bio-oxidation stage, while the return activated sludge streams recycle sludge only within each stage. Figure 6 shows a photographic image of the microorganisms in the bio-oxidation stage. Compared to the bacterial population in the absorption stage (see Figure 3), the microbes here are dominated by higher life forms.
Contrary to dual-sludge designs, typical single-sludge treatment processes cannot keep the microbial environments between treatment steps distinctly separate. Instead, mixed cultures of bacteria and higher microorganisms co-exist in the activated sludge of a single-sludge system, with bacteria being metabolized. Due to the resulting lower bacteria concentration, longer retention times are required to reduce BOD. In addition, the existence of ciliates and other higher microorganisms cause more oxygen to be consumed per BOD removed.
Nitrogen Removal
Biological nitrogen removal consists of two steps: nitrification in an aerobic environment, followed by denitrification in an anoxic environment. The nitrifying bacteria, or "nitrifiers," require high sludge ages as their generation time is 2 to 3 days. The sludge age in the second stage of the AB Process typically ranges from 8 to 20 days. This yields a diverse ecosystem of microorganisms, including 10 to 20 percent autotrophics. These autotrophic microorganisms thrive in an aerobic environment and convert ammonia to nitrate. In the subsequent denitrification step, this nitrate is converted to elementary nitrogen, that leaves the treatment tank in a gaseous form.
Denitrification is the more difficult process step to achieve as it requires the simultaneous presence of a biodegradable carbon source and nitrate. In the anoxic environment of a denitrification stage, heterothropic bacteria use the oxygen of the nitrate to breathe, and the carbonaceous matter as a food source. It has been shown that denitrification is dependent on the following key variables:Carbon substrate type and concentration
Dissolved oxygen concentration
Alkalinity and pH
TemperatureOf these variables, the most critical is the type and concentration of carbon substrate. A great benefit of the selective removal of refractory substances in the adsorption stage is that easily biodegradable BOD and COD enters the second treatment stage. The denitrifying bacteria grow rapidly, utilizing this food source and the oxygen of the nitrate molecules.
A critical design parameter for achieving the desired nitrogen removal is the BOD/COD removal efficiency in the adsorption stage. Theoretically, denitrification requires a BOD:N ratio > 3. A higher BOD:N ratio increases the stability of the denitrification performance. Thus, to achieve a high degree of denitrification and stable performance in the bio-oxidation stage, BOD/COD removal efficiency in the adsorption stage should be low. On the other hand, high BOD/COD removal in the adsorption stage is desirable, as it is achieved at low cost per gram BOD removed.
The AB Process has proven to be very amenable to process optimization for nitrogen control. During on-going operations, the BOD removal efficiency in the adsorption stage may be varied within a wide range depending on the requirements for nitrification and denitrification in the subsequent bio-oxidation stage. Empirical tests have shown that design BOD removal efficiencies in the adsorption stage from 50 to 70 percent assure high nitrogen removal in the bio-oxidation stage. An additional benefit of the process dynamics in the adsorption stage is nitrogen removal by virtue of biomass growth that is withdrawn as waste sludge from the treatment process. As a rule of thumb, for every 100 g of BOD removed, 5 g of nitrogen becomes part of the cell mass, which is withdrawn from the treatment system as sludge. This effect reduces the amount of nitrogen that needs to be removed by means of nitrification and denitrification, which results in smaller treatment volume requirements in the bio-oxidation stage.
Phosphorus Removal
Phosphorus, like nitrogen, is an important ingredient of bacterial growth. In order to process 100 g of BOD, the bacteria require about 1 gram of phosphorus to create bacterial cell mass. The phosphorus is an energy source for bacteria.
Biological phosphorus removal is based on the phenomenon called "luxury uptake." This effect is observed when certain microorganisms, primarily acinetobacter, are subject to anaerobic conditions, followed by aerobic conditions. Under anaerobic conditions, acinetobacter experience a stress due to a lack of oxygen. They release phosphorus and take on soluble COD. In the subsequent aerobic zone, the same microbes take on additional phosphorus to replenish the energy resources. In what may be interpreted as a "preventive measure," the microbes take on 2p;5 times more phosphorus than required for biosynthesis. The microbes effectively prepare themselves for future stress situations (i.e., low O2 concentrations) by storing more-than-normal amounts of phosphorus in the form of polyphosphates as an energy source.In the AB process, the anaerobic-aerobic sequence may be achieved by subjecting the return sludge streams of both the adsorption and bio-oxidation stages to anaerobic conditions, while portions of the treatment tanks of both stages provide the aerobic environment. Thus, the luxury uptake occurs within the main treatment zones. In the subsequent clarifier of either stage, waste and return sludge consisting of biomass with a high phosphorus content is withdrawn, thus lowering phosphorus concentration in the effluent.
Besides utilizing the effect of luxury uptake of phosphorous, the AB Process achieves additional phosphorus removal through adsorptive mechanisms from the wastewater in the adsorption stage. This is dependent on the concentration in the influent. The higher the influent phosphorus concentration, the greater the phosphorus elimination.
Depending on the phosphorus maximum contamination level (MCL) the treatment plant has to meet, additional precipitation of phosphorus is often the most cost-effective way to reduce total phosphorus in the effluent to less than 2 to 3 mg/l. For instance, iron salts may be added to the bio-oxidation stage to remove additional phosphorus.
An alternative approach is the precipitation of phosphorus in the supernatant of gravity thickeners. In a typical wastewater treatment plant design, return activated sludge and waste sludge may pass a gravity thickener. Since within a short period of time anaerobic conditions develop in the thickener, phosphorus is released into the supernatant. Thus, the supernatant may have a phosphorus concentration many times greater than that of the raw wastewater. Before returning the supernatant to the treatment zone, precipitation may be used to sufficiently lower overall phosphorus levels to meet permit requirements.
Shock Absorption Performance
Research and practical applications have shown that the adsorption stage serves as an effective buffer against fluctuations in organic load, acidity and toxic loads.
Empirical evidence has proved that refractory and difficult-to-biocompose substances are disproportionately removed from the wastewater and withdrawn in the waste sludge. This lowers stress on the biomass in the second treatment stage, and therefore results in better overall treatment performance of the plant.Further research discovered an even more significant phenomenon: COD removal efficiencies increase with higher COD concentrations in the influent of the adsorption stage. The result is a buffering effect of the adsorption stage against fluctuations in COD. Thus, the second treatment stage receives a much more uniform waste stream resulting in better treatment performance. This counter-intuitive phenomenon has been researched at four full-scale AB plants in Germany, and a linear relationship has been established between COD influent concentration and the COD elimination rate (Figure 7).
The coefficient that describes the slope of this linear relationship varies with the peculiarities of the influent of the specific wastewater treatment plant. For example, at the Pulheim municipal treatment plant the COD removal efficiency increased from 45 to 65 percent, while the COD load in the influent increased from 600 to 1200 mg/l. Thus, effluent COD concentrations of the adsorption stage varied only from 330 to 420 mg/l in this example.
A similarly impressive buffering effect has been observed in the case of acidic and alkaline shocks of the influent to the adsorption stage. For example, the 80 mgd Krefeld municipal WWTP treats a significant amount of industrial wastewater, that varies significantly in pH. For illustration purposes, Figure 8 shows the pH of the influent to the adsorption stage, the effluent of the intermediate sedimentation tank, and the effluent of the final sedimentation tank. During the 3-day observation period, the adsorption stage suffered a very strong acidic shock (pH = 1) on day one, followed by influent with a pH between 3 and 4 for several hours during day two.
These significant fluctuations in pH are essentially non-discernible in the effluent of the adsorption stage as well as final sedimentation stage. The excellent pH-buffering effect indicates that the bacteria have a very effective defense mechanism. The reason is likely to be the high proportion of procaryotic microorganisms in the sludge of the adsorption stage. These microbes are known to adjust more rapidly to changing and extreme environments than eucaryotes.
At the Loerach municipal treatment plant, alkaline shocks were common. Influent to the adsorption stage typically exceeded a pH of 10, and frequently hit a pH of 14. Similar to the experience in Krefeld, the adsorption stage buffered the pH very well, and the alkaline impact was not discernible in the final plant effluent.
Robustness Against Toxic Shocks
The activated sludge of the adsorption stage also withstands shocks of toxic substances very well. This is illustrated by Figure 9 that shows the oxygen concentration profiles of the A stage and the B stage in the Krefeld POTW for a given day. A load of poisonous substances reached the effluent around 5 pm, and resulted in a steep increase of the oxygen concentration in the adsorption stage. This indicates reduced respiration of the microbes during this period of constant aeration due to significant damage to the microbial population.
Within less than four hours, the microbial population recovered, as indicated by the drop in free oxygen towards 9 pm on the test day. Furthermore, the damage of the toxic load to the bio-oxidation stage has been almost non-detectable, as is indicated by the relatively flat oxygen concentration profile.This speedy recovery of the biomass in the adsorption stage can be explained by the following properties of the microbial population:
- A wide-ranging
biochemical potential coupled with distinct "job sharing."
High selection and mutation capacity that leads to the development of microbes adapted to the characteristics of the wastewater to be treated.
An effective survival mechanism supported by short generation time and high adaptability. - A high
level of resistance to changes in the environment as well as stabilizing
characteristics that assure return to original bio-conditions after
ceasing the shock condition.
In summary, the AB Process is an innovative and cost-effective biological wastewater treatment process that holds promise for effective treatment of municipal and industrial wastewater, including biological nutrient removal. The cost-effectiveness increases with higher organics loads, making it ideal for municipal wastewater with a high content of industrial wastewater. Furthermore, the ability to overcome shock loads from toxic materials or organics, and the ability to smooth out pH fluctuations allow application of the process in situations that may not have previously been considered for biological wastewater treatment.
References
Schulze-Rettmer, Jawari, "Ueber die Mechanismen der Eliminierung von organischen Substanzen aus dem Abwasser durch belebten Schlamm." Z. f. Wasser und Abwasser-Forschung, 11. Jahrgang, Nr. 6/78. Reimann, K.: Adsorption und echter Abbau bei Belebtschlamm. Z. f. Wasser- und Abwasser-Forschung 2, 1969.
Malz, F.; Bili, V., "Ueber biologische und chemische Verfahrensschritte in sehr hoch belasteten Belebungsstufen und deren Wirkung auf die Elimination von Abwasserinhaltsstoffen," Abwassertechnik Heft 2, 1992.
Diering, B., "Einstufige oder zweistufige biologische Klaerwerke," Korrespondenz Abwasser, Heft 2, 1980.
About the Authors:
Professor Botho Boehnke, Ph.D., has been conducting research on wastewater treatment technologies for more than three decades. He has been the head of the Institute of Municipal Wastewater Management at the RWTH Aachen in Germany.
Dr. Bernd Diering is president of Diering VMBH in Aachen, Germany.Dr. Stefan W. Zuckut is president of AP Technologies, Inc. in Los Angeles, Calif.
Special thanks to Dr. Botho Boehnke, Dr. Bernd Diering and Dr. Stefan W. Zuckut of Water Engineering & Management for providing a copy of this article to CASE.
Civilization and Sludge: Notes on the History of the Management of Human Excreta
by Abby A. Rockefeller, Founder and President of the ReSource Institute for Low Entropy Systems, Boston, Massachusetts
Disposal of human excreta and industrial wastes by means of the water-carriage system of sewerage has been the preferred method of management of these wastes for more than a century in all industrialized nations of the world. The pollution of water bodies caused by this practice led to treatment of the centrally collected sewage. Treatment of sewage led, in turn, to the production of sludge. Sludge consists not only of human excreta and industrial wastes, but of a myriad of nonpoint source wastes as well. Although sewage sludge was officially treated as a hazardous material by the environmental protection agencies of the sewered nations of the world, these same agencies nonetheless allowed it to be disposed of by dumping into the ocean and major inland bodies of water, by land filling, and by incineration. Environmental damage to ocean ecosystems, air, and groundwaters caused by these practices aroused opposition from environmental groups. Between the late 1970s and early 1990s, a policy shift by the environ-mental protection agencies changed the classification of sludge from hazardous material to fertilizer, and, through banning ocean dumping and curtailing land filling and incineration, mandated, instead, land application of sewage sludge. The hazards associated with the decision to dispose of sludge by putting it on the land is now the subject of increasing controversy among policymakers, scientists, and citizens’ groups. Ms. Rockefeller can be reached at 104 Irving Street, Cambridge, MA 02138.
People have been “civilized” - have been settled as opposed to nomadic or hunting-and-gathering - for a mere ten thousand years. And most of us Homo sapiens sapiens remained “uncivilized,” in this narrowly meant sense of living without the advantages or constraints of a settled abode, for probably at least the first half of that ten thousand year period.
Before people became “citizens” living in “cities,” these smartest alecks of the animal world deposited their excreta - their urine and feces - on the ground, here and there, widely dispersed, in the manner of all other land creatures. Of course, some groups, such as the cats, bury their feces and urine in shallow holes. But the effect of surface deposit or shallow burial is the same: ready access by the decomposer creatures in the soil to the nutrients and stored energy in the excreta; ready cycling through life of the elements necessary to it, attended by an incremental enrichment and diversification of the forms of life.
This meant keeping the nutrients characteristic of excreta in the cycle of soil-to-bacteria-to-plants-to-animals-to-soil. The soil and its communities of life long ago grabbed hold, so to speak, of this major source of nutrients. Keeping these nutrients - especially the major, or “macro,” ones such as nitrogen and phosphorus - locked up in the cycles of the land, besides making the land-based life cycles nutrient-rich, kept them out of the waters of the Earth. The lakes, rivers, streams, ponds, oceans, and aquifers were consequently relatively nutrient-poor—what we call “pure.” Aquatic life forms evolved in precise relation to such pure waters, so that the characteristic of macro-nutrient scarcity has become, gradually but absolutely, crucial to the health of the species and the ecosystems of the aquatic environment.
When we speak of “healthy” eco-systems, we mean stable ecosystems: that is, both tending toward diversity and not subject to cataclysmic drops in diversity. Such conditions, also called balanced, create relationships - ever more intricate relationships - that increasingly locate the inorganic elements necessary to life in cycles that make those inorganic elements increasingly available to life. The more extensive these relationships, the more consis-tently available the nutrient-elements will be to the life forms within those relationships. Expanding diversity of life forms is, relatively speaking, a low entropy enterprise. The more diverse the forms of life, the more matter and energy are kept available for use, or “work,” and the less they are lost to use or work through either irretrievable dissipation or unresolvable mixing.
So, when we talk of “pure” water, we do not mean pure in the chemical sense. We mean, rather, a dynamic balance between the non-living macro-nutrient--scarce matter and the living organisms in water; a balance whereby the relationships of life forms to one another, perhaps developed over the course of a couple of billions of years, are, though always changing, never-theless (excepting cataclysmic events), always stable, expanding in diversity, and healthy.
It is not that life will disappear in waters suddenly enriched by an infusion of macro-nutrients. (Nitrogen and phosphorus, both called macro-nutrients because most plants need large quantities in order to grow, are also sometimes called “limiting factors” since, when they are scarce, the growth of plants - such as algae - not accustomed to nutrient-poor waters, is limited.) But the effect of sudden infusions of any of the macro-nutrients will be to reduce the diversity of life in any body of pure water. We call waters polluted that look like pea soup - so full are they with living algae - because we understand that even a very great abundance of a single form of life in, say, a lake doesn’t mean that all’s well with the life system in the waters of that lake.
And, indeed, all is not well - much is, in fact, dreadfully wrong - with most of the waters on Earth. What happened to make this so? In brief, there was a sudden infusion (sudden compared to the slow pace of evolution) of nutrients into the Earth’s waters—in the form of water-borne human excreta. What follows touches on of how water came to be used to transport human excreta, how bodies of water came to be used as the recipient dumps for the water-borne excreta, and what environmental effects have been associated with the chain of behavioral and technological developments resulting from these practices.
Much of the history of human behavior is before our eyes in living societies today, the history of our excretory practices not excepted. It is likely that all practices ever associated with the disposition of excreta continue in some societies still. The patterns of settled community behavior early split into two courses: one that unambiguously assumed there to be in human excreta a fertilizer value to agriculture, and one that did not regard it as having such a value or that was at least ambivalent about its value.
It was, to be sure, agriculture that “caused” civilization: in its simplest and in its most elaborate forms, civilization altogether depends on agriculture. This dependence, however, has not inspired all agricultural societies, with reverence for the economy of the cycles on which agriculture is dependent. Especially uneven has been awareness of the economy of giving back to the soil in the form of excreta what has been taken out in the form of food. The cultures that did consistently employ their own manure in agriculture were primarily Asian. Much has been written about the longevity of these civili-zations and the significance of the persistent use of human manure to that longevity (King 1927).
Those settled cultures that do not - and did not - connect human manure with sustainable agricultural productivity followed, and still follow, a fairly stand-ard pattern of “development” of their “sanitation” habits. Urinating and defecating on the ground’s surface in the manner of pre-civilized days, but in the immediate vicinity of their dwellings, is the first phase. This soon becomes unviable - that is, too unpleasant - due to the increasing density of the settlers, which leads to the creation of the community pit. When privacy of excretory functions comes to be deemed important, then comes the pit privy, the privacy structure on top of the hole in the ground.
This “outhouse,” on account of the smell, is placed at a distance from the dwelling. The odor caused by concentrating excreta in one spot in the manner of the pit latrine - an olfactory offense that causes many to choose the bushes - is legendary for its unpleasantness. But stink aside, and contrary to what some people think, the pit latrine - with or without the privacy struc-ture - is not, and never was, environmentally viable. The pit toilet causes two related troubles - waste and pollution: waste through loss of the unretrieved nutrients in the excreta and pollution of the ground waters by those same wasted nutrients. The pit privy is not, from an environmental point of view, anywhere near as damaging as the flush toilet, but the kind of damage it caused - and still causes - is of a piece with the kind caused by the string of technologies, flush toilet included, that evolved in response to the pit privy’s inadequacies.
European societies were for centuries ambivalent in their attitude toward their own excreta. Was it a fertilizer source for agriculture or a nuisance to be “got rid of”? Before the advent of piped-in water, human excreta was deposited in cesspools (lined pits with some drainage of liquids) or vault privies (tight tanks from which there is no drainage) in the backyards of European towns. The “night soil” - human manure collected at night - was removed by “scavengers” and either taken to farms or dumped into streams and rivers or in “dumps” on the land. In Europe, there was, in other words, no consistent perception of the agricultural value of these materials: not as in Asian cultures, where the husbanding of human excreta was (until very recently) unexceptional and routinized.
Five hundred years before Christ, Rome already had in place a system both for bringing in pure water through its famous aqueducts and for the removal via sewers of fouled water that included water-borne excreta from public toilets and from water closets in the homes of the rich (Pliny the Elder 1991; Mumford 1961). But until the middle of the 19th century, most of Europe prohibited the use of sewers for the disposal ‘of human excreta. Sewers consisting of open gutters or sometimes covered trenches in the center or sides of streets had long been in use in European cities, but only for the drainage of rain run-off and for city filth. However, householding transgres-sors used the sewers to dump their kitchen slop water, and - to save on the cost of paying scavengers - the contents of chamber pots and overflowing cesspools. And when going all the way to the farm was an inconvenience or an extra expense for professional cesspool scavengers, they too took surrep-titious advantage of the sewers to dump the product of their nightly labors. The putrefying matter in these stagnant ditches moved along only when it rained enough (hence the name “storm” sewers), and digging them out with shovels was the job of the “sewermen” (Reid 1991).
The “water closet” (so-called to distinguish it from the “earth-closet,” an early species of compost toilet much favored by 19th century environmen-talists) afforded the enormous convenience of simultaneously putting the toilet in the house while getting the excreta out of the house. The so-named “flush” toilet had been known to the privileged at the height of the Roman era and since the 18th century in northern parts of Europe. But this pivotal technology, symbol of civilization still, came to widespread use only after piped-in water had been made available to the major cities in Europe and the United States. The first waterworks in the United States was installed in Philadelphia in 1802. By 1860 there were 136 systems in the U.S., and by 1880 the number was up to 598 (Tarr and Dupuy 1988). The convenience of a constant water supply stimulated the adoption of residential water fix-tures - baths and kitchen sinks as well as flush toilets - dramatically increas-ing the per capita use of water on average from three to five gallons per person per day to 30 and even 100 gallons per person per day.
Of course, once water was in great quantities piped into homes, it had to be piped out again, and the first “logical” place to pipe it, including the flush water from water closets, was backyard cesspools. These cesspools, which hitherto had received the contents of chamber pots - urine and feces - only, now regularly overflowed with fecally polluted water, and a new level of horrendous odors and the spread of water-borne diseases was the imme-diate result.
Thus the system of cesspools and vault privies, which had been to some extent effective in avoiding pollution of waterways through their periodic cleanout by scavengers and the at least partial returning of human manure to farms, was overwhelmed by the pressure created by the new availability of running water. The next “natural” step in the solve-one-problem-at-a-time approach was to connect the cesspools to the sewers, thereby moving the sewage from overflowing cesspools into the open sewers of city streets. The result: epidemics of cholera. In 1832 20,000 people died of cholera in Paris alone (Reid 1991). Wherever and whenever this combination of piped-in water, flush toilets, and open sewers has appeared in the world, epidemics of cholera have followed.
By the middle of the 19th century, the diseases spawned by the convenience of running water and the flush toilet gave rise to a demand for the construction of sewers that would carry the sewage not only out of and away from the home, but away from the city as well. This demand entailed the evolution of the ditch-type storm sewer into the closed-pipe water-carnage system of sewerage. The wastewater itself was in this system the medium of transpor-tation, so a large and regular supply of water was a built-in requirement to keep the wastes moving in the pipes (Tarr arid Dupuy 1988). (Today, efforts to conserve water by promoting the use of low-flush toilets - 1.6 gallons vs. five to seven gallons - have led to plugging up of sewers engineered for a minimum hydraulic flow of five gallons per flush. To deal with this problem, owners of these “water-conserving” toilets have been instructed to flush two or three times per use.)
The water-carriage system of sewerage introduced a new set of problems and, about these problems, a new set of debates among sanitary engineers in Europe and the United States. The engineers were divided again between those who believed in the value of human excreta to agriculture and those who did not. The believers argued in favor of “sewage farming,” the practice of irrigating neighboring farms with municipal sewage. The second group, arguing that “running water purifies itself’ (the more current slogan among sanitary engineers: “the solution to pollution is dilution”), argued for piping sewage into lakes, rivers, and oceans. In the United States, the engineers who argued for direct disposal into water had, by the turn of the 19th century, won this debate. By 1909, untold miles of rivers had been turned functionally into open sewers, and 25,000 miles of sewer pipes had been laid to take the sewage to those rivers (Tarr and Dupuy 1988).
In the cities with water-carriage sewers, cholera epidemics abated. However, in cities downstream from those dumping raw sewage into the river, death rates from typhoid soared. This led to the next debate: whether to treat the sewage before dumping it into the recipient bodies of water or whether to filter the drinking water downstream. Health authorities argued that sewage should be treated before disposal into any bodies of water, but the sanitary engineers preferred filtration by the next town down the river. The engineers prevailed, and indeed, in those cities with filtered water, deaths from typhoid then dropped dramatically (Tarr and Dupuy 1988).
The practice of “purifying” water polluted with sewage from upstream in order to make drinking water safe downstream, rather than treating sewage where it is produced, persisted until the middle of the 20th century. By then, the rate of industrial development had been enormous, and every industry wanted cheap disposal of its wastes. And since the public was paying, this was cheap as could be. Industries’ demand for more sewering to serve their own disposal needs stimulated the industrialized nations of the world to allocate vast sums of money for massive sewer construction programs.
To the nutrient burden on recipient waters from human excrement, then, was added a new and ever increasing flow of industrial waste, much of it toxic. Wherever on the globe there were sewers, the recipient rivers, lakes, and streams were discovered to have become unacceptably filthy, and in response came pressure to treat the sewage before it entered those waters. And so began the “treatment” phase of the get-rid-of-it approach to dealing with wastewa-ter now consisting of human excrement mingled with all industrial wastes transported by water.
The first step in the effort to clean up the sewage before sending the effluent into the river is termed “primary treatment.” From the point of view of improving water quality, it is a crude method, consisting of little more than settling and screening the sewage to remove the largest and most aesthetically offensive objects: all nutrients and chemicals not tied up in dead cats and intact feces remain in the water.
The next stage, called “secondary treatment,” includes some biological stabilization through forced aeration of the sewage, and chemical flocculation and precipitation of some of the phosphates deriving from laundry detergents. But in spite of the great energy and financial cost of this form of treatment, the effluent reaching the recipient bodies of water continues to be rich in nitrates and phosphates. (These nutrients, as noted above, are called limiting factors. When they are present in water, they cause an explosive growth of algae, which in turn causes lakes to die of eutrophication as the decaying algae robs the water of its oxygen.) Industrial pollutants, such as toxic chemicals and heavy metals, are not addressed by this level of treatment.
So engineering ingenuity developed another, yet more complex, yet more energy intensive and expensive form called “tertiary” or “advanced waste-water treatment.” Because of its enormous cost it has been difficult to get American taxpayers to fund this level to any great extent. But even where funded, treatment remains incomplete: some nitrates, some heavy metals, and many toxic chemicals continue to evade tertiary treatment and remain in the water.
Central collection and treatment of sewage cannot be said to have succeeded in solving the underlying problem of water pollution caused by using water to transport wastes. The problem is deeper and systemic. The trouble with the treatment approach to managing the pollution caused by water carnage of excreta and the by-products of industry lies only partly in the inadequacy of even the most advanced processes. Though the trouble may seem to have been ameliorated because this bay or that river is less polluted than it was without wastewater treatment, the pollutants that were in the water have simply been reorganized and concentrated in a new form: sludge.
Sludge is the dewatered, sticky black “cake “ consisting of every waste material capable of being sent down the drains of homes and industries and into the sewers, and which the treatment process is able to get back out again.
Sludge is the dewatered, sticky black “cake” consisting of every waste material capable of being sent down the drains of homes and industries and into the sewers, and which the treatment process is able to get back out again. If sewage can be said perfectly to exemplify a high entropy process of matter lost through irretrievable dissipation, sludge is the quintessential example of disparate matter lost to use through unresolvable homogenization.
In the United States Federal Register (Volume 55, Number 218, November 9, 1990), the United States Environmental Protection Agency (EPA) says of sludge:
The chemical composition and biological constituents of the sludge depend upon the composition of the wastewater entering the treatment facilities and the subsequent treatment processes. Typically, these constituents may include volatiles, organic solids, nutrients, disease-causing pathogenic organisms (e.g., bacteria, viruses, etc.), heavy metals and inorganic ions, and toxic organic chemicals from industrial wastes, household chemicals, and pesticides.
This short list of what sludge “may include” is shorthand for the enormous list of constituents that can actually be present in it. For instance, of the 100,000 or so organic and inorganic chemicals produced and used in indus-trialized nations, a huge number will end up in the sewers. One thousand new ones are produced every year and are added to the cocktail of synthetic substances affecting life processes. Those pollutants that are put in the sewers - and that are removed from the wastewater by the treatment proc-ess - will end up in the sludge. There are the heavy metals which, though they are micro-nutrients crucially needed in tiny amounts for growth of life, are toxic to life when they cross the threshold firmly established in the cells of life. There are organochlorines estrogen mimicars, the best known of which are DDT, chlordane, aipha-hexachlorocyclohexane, 2,4,D, PCBs, and dioxin. There are halogenated aliphatic (chain) hydrocarbons, aromatic (ring) hydrocarbons, chloro- and nitro-aromatic hydrocarbons, phthalates, halogenated ethers, and phenols.
Sludge safe if properly managed; Report criticizes sludge fertilizer
03/28/2000
By DANIEL CUSICK
Register Staff ReporterA group of Grand Bay citizens fighting a program that uses treated human sewage as farm fertilizer welcomed a report Monday by a U.S. inspector general that criticizes federal regulators for poor oversight of the practice.
The report, released by Nikki L. Tinsley, inspector general of the U.S. Environmental Protection Agency, says that regulators have not put ample resources into ensuring that the fertilizer wastes are being handled safely and properly.
The report gained attention last week before the U.S. House of Representatives Committee on Science, which is seeking to address public concerns about the use and regulation of the sewage sludge, also called "class B biosolids."
In Grand Bay near the Mississippi state line, a Maryland-based firm called Bio Gro has been spraying biosolids on farm fields for more than a decade. The sludge, about 98 percent water and 2 percent solids, comes from two sewage-treatment plants operated by the Mobile Area Water and Sewer System. It is rich in nitrogen and can improve the growth of pasture grasses.
While useful as fertilizer, residents living around the Grand Bay fields where the sludge is used have complained about odors and heavy truck traffic on home-lined roads. They also are concerned about possible exposure to bacteria, pathogens and other harmful organisms that could be living in the sludge. Some say the sludge may be responsible for skin rashes, respiratory problems and other medical conditions.
Gary Schaefer, head of a newly formed group called Citizens Against Pollution, said Monday that the report strengthens his organization's contention that health concerns about the sludge have been overlooked by the EPA and the Alabama Department of Environmental Management.
EPA officials in Washington, D.C, said they are reviewing the report and will try to address its concerns. But they insisted that the government's rules on biosolids are sufficient to protect human health.
"I don't know what the agency's ultimate response will be" to the report, said John Walker, head of the EPA's biosolids program implementation team. "The application of biosolids to land is very low risk. As a priority matter, EPA has said we need to put more of our regulatory efforts in other areas."
Officials with Bio Gro and the Mobile water and sewer board also have said that the sludge is safe if properly managed. But to allay public fears, the sewer system has pledged to increase soil and water monitoring in areas where the biosolids are being applied.
Walker said the EPA also is working to develop voluntary standards for handlers of biosolids that would ensure that the sludge is handled in an environmentally safe manner. Those standards, however, would not be enforceable by law.
While the EPA has come to rely on state environmental agencies to help regulate the use of biosolids, Alabama lacks any formal program. The state simply approves land that can receive biosolids. All other regulation is left to federal regulators.
Mike Hom, a biosolids regulator with EPA's Southeast regional office, said recently that the agency has only two full-time people assigned to regulate more than 700 sewage-treatment plants that dispose of biosolids on farm fields.
Sludge-Fertilizer: Contaminating Ground Water
By DAVID SWANSON
Staff WriterAs discussed in the March 16 Culpeper News, the tenants in four houses owned by Wayne Lenn and his brothers in Culpeper County have been without safe water at least since December.
The Lenns have now returned from wintering in Florida and plan to have Leazer Drilling Co. Inc. drill a new well on the property in Stevensburg. As soon as they do so, Wayne Lenn said, they will pour cement down the old well and also down an even older one on the site has not been used for years.
One of the tenants, Doyne Shrader, has had some tests done on the contaminated water, but he has not yet had one done to identify whether the fecal coliform in it is human or from cattle or other animals.
Shrader and his neighbors began noticing problems with their water late last year after biosolids were applied to land adjacent to where they live. Lenn now says sludge use is the “about the only logical” explanation for the contamination.
Joiner Micro Labs in Warrenton can reportedly perform a test that determines the source of fecal coliform, but the accuracy of the testing is uncertain. A professor at JMU is reportedly able to do DNA testing to make this determination more reliably.
Shrader is considering having both such tests performed.*****
On March 19 James Burns, the local Health Department’s district director, wrote to Shrader warning against using the water from his well but advising against doing additional tests of it. Burns wrote that the well was definitely contaminated, “probably by surface water entering the well . . . . I do not recommend further testing of this well, but the new well should be tested.”
Failing to follow this advice, Shrader had some tests done the last week in March. Joiner Labs tested the well water and found MPN 80/100 ml for total coliform bacteria (meaning that the most probable number of organisms is 80 in every 100 ml of water). The test found MPN 8/100 ml for E. coli. An acceptable level in drinking water for coliform bacteria, including E. coli, according to the Health Department, is zero.
Joiner Labs also tested a sample of sludge from the Lenn farm adjacent to the tenants’ homes and found MPN 9 per gram for E. coli. A sample of soil taken 10 feet from the well in the direction of the sludge was found to contain MPN <2 per gram for E. coli. Robyn Joiner explained that this means none was detected, but it is not necessarily absent.
On March 28, Shrader said, Suzanne Haldin-Coates of the Health Department told him that BioGro, the firm that applied the sludge on the Lenn farm, had applied for the permit on Lenn’s behalf to dig a new well. Charles Shepherd of the Health Department confirmed on Tuesday that “BioGro applied on Lenn’s behalf as his agent. They were the ones that had Mr. Lenn’s telephone number. They were the ones that could contact him.”
Shrader also said he has developed a rash on his left leg, beginning in March. He is continuing to have medical testing done.
On April 3, Shrader said, the Lenns had returned from Florida and had poured chlorine down the well but had not yet contacted him. The next day, Shrader says, Wayne Lenn called him.
Shrader says that Lenn suggested he move out and that Shrader told him he was “financially and physically incapable” of it. Then Lenn reportedly said he would have to consult with BioGro.
Contacted this week, Lenn said he has been waiting for days for Leazer Drilling Co. to show up and dig a new well. Mark Bannister, at Leazer, said the well will be drilled by the end of this week or the beginning of next.
“Circumstantial evidence,” Lenn said, “points heavily to contamination from the sludge. That’s about the only logical [explanation], but there seems to be no test that can prove it.” Lenn said he had never heard of tests to identify fecal coliform as of human origin.*****
Lenn said he charges tenants rent that is “$100 under the market,” and that before he left for Florida in late January, he told his tenants he would give them $100 per month to buy water. “As soon as my back was turned they decided they wouldn’t pay the rent.” The tenants all stopped paying rent as of January.
Lenn said he had never heard of ground water getting into the well in years past, and that if he’d known the well casing was cracked he could have replaced it a year ago and avoided the contamination.
In response to his tenants’ (and the Health Department’s) complaints that they couldn’t reach him for months, Lenn said, “Aw, hell’s bells. The mail is forwarded! Didn’t you know the postal service has been forwarding mail for 150 years?”
Lenn said he has evicted the tenants from one house, following a disagreement over rent. Asked whether others would be evicted, Lenn laughed loudly and said, “Call back in a couple of weeks.”
Shrader said that he did not know the mail was being forwarded and that he has always paid cash because he has no check book. He said the Health Department had told him in early March the tenants would get free rent plus bottled water.
Shepherd said, “That’s what I was told by Pamela Gratton of BioGro . . . . Where BioGro got the information I don’t know.”
Lenn does not think his tenants have had it very bad. He laughed uproariously through much of his conversation with the Culpeper News.
“Grocery stores are full of bottled water,” he said. What about showers? “They’ve been taking showers all along.” But they shouldn’t have been, according to the Health Department.
To that, Lenn laughed and said, “Chicken and hamburger are full of E. coli. . . . It was none of my fault. . . . The more we bend over backwards to help those who need to live in modest-priced housing, the more we get screwed.”
Lenn called back to say, “Ask all the tenants why in the world didn’t they move out . . . . Not one of them has a security deposit. . . . If they didn’t have the money to move, they would have had it by the second month of not paying rent.” (Shrader’s response to this was that he’s had the expense of hauling water and eating out.)
Lenn called back again to say, “We farmed all our life for a living, and I am very partial to doing everything I can to help farmers. The reason I did nothing to the well prior to going south was I thought it would clear itself up after a liner was put in, and the [bacteria] count went down from 1,600 to 2.
“I thought if I gave up the well it might hurt farmers’ use of the sludge. I still want to do anything I can not to destroy farmers’ ability to use the sludge, because it’s such a help. If a few tenants have to wash behind their ears with a dishrag for a few days, I’m going to be with the farmers.”
Asked whether BioGro is paying for the new well, Lenn declined to answer.
Shrader and other residents have been discussing with Ted Korth, a Charlottesville lawyer, various possible courses of action.*****
Shrader said he has not yet heard back from Laurie Reynolds of the EPA, who told him she would look into this matter on March 20. Nor has he heard from Bill Chase (D-Stevensburg) or any of the other Culpeper supervisors, though Chase told him at last week’s board meeting that he was sorry for not returning his calls and would eventually be in touch with him.
Shrader has been in touch with residents of Grand Bay, Ala., who have formed a group called Citizens Against Pollution Inc. to oppose the dumping of sludge there by BioGro. Gary Schaefer, a member of the group, describes illnesses to humans and dead dogs.
“Pamela Gratton got up at a meeting,” he said, “and said she spent all day in the field with the trucks and never smelled anything. Three people jumped up and just went berserk.”
Schaefer said that he has mailed a video of violations to the EPA. He describes the EPA as extremely powerful. “[Federal Department of Transportation] regulations say [sludge is] hazardous material to transport, but EPA overrules DOT.”The Handshys
Scott and Lori Handshy, who live in Stevensburg, next to a property where sludge has been applied, had the tests done at Joiner labs on Shrader’s water as well as on their own and that of a neighbor, Pat Lake.
They are also having tests done out of state on Shrader’s water for heavy metals and viruses. Scott Handshy said that several groups are helping to pay for the tests, including one called the National Sludge Alliance and another called People Against Toxic Sludge Inc.
The Joiner tests on the Handshys’ well tested positive for total coliform bacteria but negative for E. coli. A stream on the site tested MPN 300/100 ml for E. coli.
Desiree Lopasic of the Health Department came out, at the Handshys’ request, and tested their water. She found MPN <2 for fecal coliform in the Handshys’ water and also in that of Pat Lake.
Lake said Joiner’s test had found bacteria in her well, which she found hard to believe since she has had good water for many years. She said that both Lopasic’s test and another done at Environmental Systems Services, a private company in Culpeper, found no fecal coliform.
Lake said she was very much relieved. However, the tests may not contradict each other, if -- as seems to be the case -- Joiner tested for total coliform and the other labs tested only for fecal coliform.
Health Department standards require the absence of any coliform bacteria. Coliform bacteria is an indicator of the probable presence of pathogens.The Settles
Sherri and Larry Settle live in a house near Beauregard Farms, a 3,082-acre farm near Brandy Station where sludge is applied. Beauregard is owned by Johanna Quandt and her family -- very wealthy Germans who are reportedly the main stockholders in BMW -- and managed by Jim Bowen.
The Settles blame sludge for the death in January of their Great Dane, who drank water in the fields at Beauregard. Sherri Settle was admitted to the hospital for two days herself and diagnosed with an intestinal virus on Jan. 28-29, something she said she’d never had before. She has also, she said, developed “pink, scaly stuff” on her trunk and legs where the water touches her in the bathtub. Settle said that she has seen her water come out of the tap black “like charcoal.”
Recently, Settle said, her water has cleared up. But, she noted that no geese have come to the lakes on Beauregard Farm this spring, as they did in previous years.
Bowen said that sludge was applied on 500 of the property’s 3,600 acres last year and on another 500 this winter, with more to come. Bowen said that six to eight neighbors had signed waivers of distance restrictions (county law requires that sludge be kept 400 feet from occupied dwellings), and that for about 12 rentals on the property there was no need for waivers.
“Nobody’s complained to me,” Bowen said.
Asthma, allergies, and sludge odor
Diane Reno is a Stevensburg resident with asthma and allergies who says she still suffers whenever she has to drive through areas that were sludged last November.
“It has a musty, moldy smell, and I’m highly allergic to mold . . . . When I come through that area I have to use an inhaler. I get headaches.” Reno said her granddaughter and son-in-law also get headaches from being in sludged areas.
“I don’t know why the board won’t listen to us and find out what’s in this stuff. . . . We’re not opposing farmers. I have 40 acres. We’re from farming families. We just don’t want it to end up killing people.
“. . . . They say it’s psychological. It’s not psychological. I have to use my inhaler. I feel like I can’t breathe. . . . I liked it here until that stuff started being spread.”
There are a number of technologies which are presently used to recover energy from waste. These technologies have a wider usage than treatment of sewage sludge, but the descriptions here emphasise on the use of these technologies in relation to sludge:
- Anaerobic digestion
- Composting
- Dedicated incineration
- Thermal drying with incineration of the refuse-derived fuel (RDF)
- Other treatment & disposal options for sludge
Anaerobic digestion - works by feeding the sludge to an enclosed reaction tank where naturally occurring bacteria degrade the organic material. The end product is biogas and stabilized sludge. The biogas can be converted to both electricity and heat. There are no actual problems related to anaerobic digestion other than the problem of disposing of the digested sludge. The normal outlet is as a fertiliser to agricultural land but where not enough suitable land is available, sludge can be incinerated.
Benefits
* odour control
* reducing the solids content
* reducing the numbers of pathogens
* producing biogas as a by-product
The microbial process of anaerobic digestion
The influent sludge will contain a variety of organic and inorganic material. Of the organic material in the sludge, only a part will be readily degradable in the anaerobic digestion process. Sugars, lipids, protein, and even some organic chemical compounds will be used as substrates for the anaerobic bacteria. Lignin, a constituent of paper, will not be degraded anaerobically, and neither will a range of synthetic chemicals that are present in domestic sewage.
Bacterial degradation of organic material. Three groups of bacteria are involved in the anaerobic digestion: the hydrolytic and fermentative bacteria, the acetogenic bacteria, and the methanogenic bacteria. The hydrolytic and fermentative bacteria will break down polymers like cellulose and proteins. Cellulose will be hydrolysed to smaller sugars. Sugars are fermented to long and short chain organic acids. The acetogenic bacteria will use the resulting compounds from the hydrolysis and fermentation, e.g. they will use long chain organic acids as a substrate and produce short chain organic and carbon dioxide. The methanogenic bacteria are the most sensitive and slow growing of the three groups of bacteria. The methanogenic bacteria use the products of the acetogenic bacteria as a substrate for methanogenesis, the production of methane. Once the methanogenic population has build up, a balance should exist between the methanogenic and acetogenic populations which is essential for both populations, and is therefore essential for the stability of the process.
Microbial requirements. In order to have a successful anaerobic digestion with quick removal of organic material, stable gas production and sufficient reduction in the number of pathogens, the bacteria must have optimal growth conditions. Most important is the control of temperature and substrate availability. Temperature optima for the anaerobic bacteria exist in the mesophilic (30-37°C) and the thermophilic (50-65°C) range. Substrate availability depends on the organic loading of the influent sludge. If the influent sludge is very thin, i.e. has got a low organic loading, the flow rate through the digester can cause wash out of the methanogenic population.
Design and operation
A lot of research has gone into finding the optimal design for an anaerobic digestion system. The solution chosen will depend on the amount of sewage sludge to be treated.
Mesophilic or thermophilic digestion. Anaerobic digestion at thermophilic temperatures has proven to be feasible, but only very few plants run at thermophilic temperatures. The thermophilic process has a greater conversion of volatile solids to gas and an increased rate of digestion, but has got a reduced process stability and a greater heat requirement. The higher risk of having problems with maintaining a stable thermophilic digestion and problems with odours from thermophilic digestion, are the reasons why digestion at mesophilic temperatures is by far the most common (ref.15).
Single-stage or two-stage digestion. In a conventional single-stagedigestion system, all phases during the anaerobic degradation takes place in the same reactor, even though the microbial requirements of the different phases are not the same. In a two-stage digestion system, phase optimisation is possible. This leads to increased stability and higher biogas production due to more volatile solids being degraded (ref.3; ref.18; ref.17). However, the relatively small increase in efficiency may not justify the increased cost of two-stage digestion (ref.3). Another advantage of two-stage digestion can be utilised if the primary stage is a thermophilic stage which provides pasteurisation of the sludge. The secondary step should be mesophilic because that will eliminate problems with odours which can be a problem for thermophilic digestion (ref.19).
Requirements to influent sludge. Dry solids content - Before feeding to the digestion tank, the raw sludge undergoes a thickening process. A thickness of 8% dry solids is desirable, and under 2.5% dry solids the performance of the digestion is reduced. A low solids concentration will lead to a short retention time and thereby a potential wash out of the methanogenic population. The thickness of the sludge is also important for its mixing properties, and it influences the volume of sludge that requires heating up to the digestion temperature (ref.5).
Inhibitory compounds
The anaerobic bacteria can be inhibited by a number of compounds, and reduced digestion efficiency can be a result of inhibitory compounds present in the sewage. Potentially inhibitory compounds include heavy metals, chlorinated organic substances, pesticides, and detergents. Due to industrial effluent control, it is unlikely that these compounds will be present in the sewage in inhibitory concentrations (ref.5; ref.26)
Digestion tank. The digester is an enclosed tank with attached heating and mixing systems. In recent years, the most common choice of design has been pre-fabricated digesters constructed of glass-coated steel panels with an external insulation layer (ref.5; ref.15). The digesters can be equipped with a floating roof for gas collection or a separate gas holder. In Germany and USA egg-shaped digesters are commonly used (ref.5). The egg-shape is ideal for providing complete mixing of the entire volume and the shape has a decreasing effect on the build-up of scum in the digester (ref.11; ref.16).
Heating. Anaerobic digestion is normally carried out at mesophilic temperatures and a heating system must be capable of maintaining the entire volume at 35°C, even at low temperatures in winter.
Maintaining the temperature at 35°C is not only important to achieve an efficient digestion process, it is also a requirement if the sludge is disposed of to agricultural land. The DoE Code of practice for Agricultural Use of Sewage Sludge (ref.10) has set requirements for different sludge treatment methods to achieve acceptable levels of pathogen reduction. (See Application of treated sludge to agricultural land.) For mesophilic anaerobic digestion the sludge for agricultural use must have been treated at least 12 days at 35°C.
Digester heating is normally supplied through, directly or indirectly, thecombustion of the produced biogas. Traditionally, the heating was supplied by burning biogas in a hot water boiler and transferring the heat by use of heat exchangers. Depending on how the biogas is utilised, there can be other ways of recovering heat for the digestion. If the gas is used in dual-fuel or gas engines for power generation, it is possible to recover engine heat for digester heating. Spark-ignition engines for CHP are normally able to provide all the needed heat for digestion (ref.5; ref.15).
Mixing. The digester should be completely mixed to ensure efficient digestion.
Firstly, the mixing brings the raw influent sludge in contact with actively digesting sludge. It speeds up the digestion that the already existing bacterial population is brought into contact with new substrate. Secondly, the mixing ensures a uniform temperature throughout the digester. And thirdly, the mixing prevents accumulation of grit in the bottom of the digester and the build up of a scum layer on the top. Without a uniform environment in the digester, there would be pockets of sludge not degrading properly, potentially leading to undigested sludge leaving the digester and a decreased digestion rate.
Types of mixing systems
Different types of systems are used, either mechanical mixing systems or gas mixing systems. Most modern plants use gas recirculation systems where digester gas is recirculated to diffuse through the sludge. Mechanical mixing systems are cheaper, but because of the very high cost of taking a digester out of use in case of maintenance or repair, the mechanical mixing systems are not cheaper in use than gas mixing systems (ref.5; ref.15). A new mixing system, draft-tube mixers, are energy efficient, and their use is recommended especially for egg-shaped digesters (ref.31).
Energy recovery
The production of biogas provides an easy possibility of energy recovery. The biogas is a mixture of methane (60-70%) and carbon dioxide (30-40%). Other gases like hydrogen sulphide, nitrogen, hydrogen and water vapour, are present in small amounts. The calorific value of the gas depends on its methane content, at 70% methane content it is approximately 23,380 kJ m-3 (ref.5).
The gas can be converted to energy for use in the treatment itself and excess electricity can be exported to the grid. Surplus biogas after use of gas for heating of the digester can be utilised in different ways. Some possibilities are:
* combined heat and power generation (CHP)
* export of gas either as raw gas or refined
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