Enhanced Aerobic Bioremediation
Innovative Technique for In Situ Treatment of Contaminated Surface Waters and Submerged Sediments by Enhanced Aerobic Bioremediation
[Originally published as IECEC – 98 298
33rd Intersociety Engineering Conference on Energy Conversion
Colorado Springs, CO, August 2-6, 1998]
To determine method efficiency, bench-scale and field study wastewater treatment tests are being conducted to enhance water quality by means of the introduction at the water-sediment interface of oxygen and nutrients. The method being examined promotes the growth of aerobic microorganisms that break down the contaminants while creating non-toxic byproducts. Results of our tests will determine efficiency in three areas: as an alternative to toxic herbicides in the treatment of algae blooms in lakes, treatment of hog manure sludge pits to reduce odor and reduce the amount of waste, and to aid human sewage treatment at Publicly Owned Treatment Works (POTWs). The purposes of this paper are to summarize the studies already completed, and describe the work currently underway and indicate the need for future implications and potentialities of our methodology.
1. SOURCE OF WATER POLLUTANTS
The delicate balance of our planet’s fragile aquatic ecosystem is being disturbed at an alarming rate. Industrial, agricultural, and residential effluents enter our waterways polluting these systems with a wide range of organic, metallic and inorganic compounds. In the United States, the Federal Clean Water Act of 19771 gave the Environmental Protection Agency (EPA) legal authority to prosecute polluters which has resulted in a drastic reduction in “point source” pollutants, those whose sources are easily identified from their waste streams.
Concentrated Livestock Operations (CLOs) have been the target of criticism for the production of so-called “non-point source” pollution in our waterways. A “non-point source” of pollution is one in which a discrete origin cannot be identified and is usually the result of many sources. A recent study in North Carolina suggests that such CLOs in just two river basins alone produce 111.31 metric tons of excreted nitrogen and 36.39 metric tons of phosphorus annually.2 The introduction of high concentrations of biologically active nitrogen and phosphorus in the surface waters has resulted in a rapid increase in growth of aquatic algae and plants in estuaries and coastal zones.
Larger and more frequent fish kills are reported every year, such as the one occurring in the summer of 1996 in a tributary of the Chesapeake River, in the United States, in which one billion fish of nineteen different genera were reported killed.3 The overabundance of nutrients, as well as contaminants, in lakes, streams and estuaries has created a crisis for aquatic organisms. The degradation of water quality has resulted from an increase in nutrient concentrations (NO3, PO4), increased oxygen demand (BOD, COD), turbidity and raised bacterial counts (T-Coli, F-Coli). This has resulted in the closure of shellfish bed harvests and a reduction in the number and health of commercial fish populations that spawn in estuarine waters.4, 5 Aside from accidental spills of pollutants, the run-off from agricultural operations has been targeted in recent legislative restrictions on CLOs.6
2. COMPARISON TO EXISTING METHODS OR ENHANCED AEROBIC BIOREMEDIATION METHOD
Existing methods for wastewater treatment are both expensive and damaging to benthic ecosystems, because they kill organisms that are crucial to the delicate food web in the aquatic environment. Current methods of remediating aquatic sediments contaminated with organic pollutants, such as agricultural and residential sewage, fuel oil, PCBs and other industrial chemicals, involve dredging up the sediment, treating it elsewhere, and then returning it to the removal site. Surface water treatments, such as the treatment of lakes for algae blooms, require the addition of poisonous chemical herbicides and pesticides. The need for inexpensive alternative treatments is clearly evident and has encouraged our research into this field.
Most conventional primary and secondary treatment facilities are inadequate in terms of the complete removal of many inorganic and organic chemicals, leading to the eutrophication in lakes, rivers, and bays. Analysis of the recent analysis of hog farm manure which is incorporated into farm soil shows the following high values:
These values do not reflect what will be found in the streams containing agricultural runoff. These values will be diluted by rain and irrigation water and filtered by the soil. The potential for environmental damage exists, if this type of waste is accidentally discharged into waterways undiluted.
The activated sludge method is the most commonly used secondary wastewater treatment system for human waste. After primary treatment in which the majority of solids are settled out of the water column, these solids are diverted into an activated sludge reactor while the overlaying water is sent to an aerobic treatment system before discharge. In the aerobic treatment system, oxygen is supplied to the water by aeration, incorporating either surface aerators or diffusers which utilize a mechanical process requiring energy input, the amount of which is dependent upon the BOD (Biological Oxygen Demand) or COD (Chemical Oxygen Demand). However, the activated sludge chamber that treats the solids portion is devoid of oxygen, and anaerobic degradation is enhanced by an increase in temperature and bacteria and nutrients.
A variation of this method is used in the treatment of concentrated livestock waste such as at hog facilities. The raw waste at these facilities is stored in what are called anaerobic sludge lagoons or pits. These consist of large earthen or cement lined enclosures into which the raw slurry (manure and water) is pumped. The slurry remains in this enclosure, which is usually open to the air, for several weeks or months before it is removed and incorporated into the crop field soil. For the most part these lagoons remain anaerobic even though they are exposed to the air at the water surface. In some cases aerators are used to diffuse oxygen into the lagoon to promote aerobic degradation, which reduces the amount of noxious gases created in the anaerobic breakdown of the manure.
Our studies have shown that utilizing Cellinite Technologies’ time-release tablets for biological degradation provides an efficient method for aerating wastewater sufficiently in cooperation with, or in place of, secondary treatment systems. The incorporation of advantageous microorganisms and various nutrients as well as dissolved oxygen (by the breakdown of hydrogen peroxide) can be added into almost any wastewater environment through the use of time-release tablets specifically designed for that system to reduce BOD and noxious gases and establish a harmonious Eco-balance.
The economy of treatment relies on the efficiency of the wastewater treatment system to provide an environment which supports the activity and growth of a treatment microflora along with factors such as the balance between oxygen and substrate supply. Our system designed under the U.S. Patent # 5,275,9437 can incorporate appropriately required nutrients, micro-organisms and oxygen via hydrogen peroxide to balance the organic and inorganic nature and control the biodegradability of the waste.
Similar studies have also been made by Higa8 in Japan, who combines synthesizing microorganisms with zymogenic microorganisms. He defines zymogenic microorganisms as those that reduce organic matter to a soluble state while creating large quantities of antioxidants. Higa developed his own process of autolysis, in which the digestion of organisms takes place by enzymes naturally present, and utilizes these methods for the break down of agricultural synthetic chemicals, as well as harmful bacteria such as E. coli. He has identified upwards of 80 different strains of microorganisms known to have the capacity to eradicate agricultural chemicals.
In both field and laboratory studies, Cellinite Technologies has now created controlled degradation systems. Successful use of these systems involves the utilization of specific microorganisms, nutrients, and oxygen introduction through time-released aeration capsules for controlled degradation of manure and decaying detritus (plant matter). The changes in physicochemical parameters in a static system and the passage of bacterial pathogens have also been analyzed and demonstrate beneficial results.
3. CONCENTRATED LIVESTOCK MANURE TREATMENT
A recent study in Iowa9 stated that a typical hog production facility (CFO) of 2000 head generates 820,000 gallons of manure per year. Using industry standard calculations, a producer could land apply 3500 gallons per acre; therefore, 235 acres are needed to utilize the manure from this facility. Depending on the crop, some acreage need only be fertilized every other year, so that the land requirement could be 470 acres. In 1996, Iowa produced 24,000,000 hogs or 9,840,000,000 gallons of manure requiring 5,622,857 acres in order to land apply it. This data just covers hog manure, not manure from other livestock. Combining all the types of livestock manure data together, then looking at the area needed to land apply it, one finds that the needed area far exceeds the available land for crops. These figures will only increase as the demand for U.S. pork products goes up worldwide.
Storing it in open-air anaerobic sludge lagoons for a period of time is the typical way in which a hog farm treats its manure. Periodically the surface liquid fraction (supernatant) is then pumped off and sprayed onto crop fields. The solids (sludge) on the bottom of these pits are later removed and tilled into the cropland. Large corporate farms, which have concentrated huge amounts of manure into vast outdoor sludge lagoons, discharge a great deal of noxious gases. These gases, byproducts of anaerobic degradation of the manure, include compounds such as Hydrogen Sulfide, Methane, Ammonia, and Methyl Mercaptan, as well as Carbon Dioxide. These gases are a nuisance to local neighbors and have a detrimental effect on the atmosphere by contributing to global warming. New government restrictions will force farms to convert their treatment systems from anaerobic to aerobic treatment. Typically this would involve large capital expenditure on the part of the farmer to construct batch reactors or to place high-powered electric air pumping systems into their lagoons, to insure aerobic degradation.
4. MANURE TREATMENT EXPERIMENTAL DESIGN
Microbial treatment or “purification” may be regarded as a process by which the pollutants in the raw waste are converted to microbial cell biomass or insoluble substances. This biomass can then be separated from the final end product, which is water containing a suitable BOD, resulting in the satisfactory achievement of the reduction of pollution associated with agricultural wastes.
The treatment we have developed, however, does not rely on mechanical means to aerate the manure. It uses the byproduct of a chemical reaction, hydrogen peroxide, which in solution quickly degrades to molecular oxygen and water, to oxygenate the water. Based on a U.S. patented methodology,7 it uses a timed-release tablet to both oxygenate the water column slowly and introduce aerobic bacteria, enzymes, buffers and additives. These components help to speed up the degradation of the manure and reduce gases which would otherwise have been created during anaerobic degradation. Because our process is aerobic, the noxious gases are not produced,10 thereby reducing the foul odors associated with these pits. The tablets are custom manufactured into layers to incorporate the chemical requirements of a particular situation, such as the inclusion of a phosphate precipitant like ferrous chloride.11 The key to its success is providing a source of molecular oxygen on a continuous basis, gently disturbing the sludge particles at the bottom of the lagoon with oxygen bubbles. The raised particles of sludge create a greater surface area on which the aerobic bacteria can attach, speeding up the degradation process.
In the aerobic environment, the bacterial genera Nitrosomonas and Nitrobacter convert Ammonium Nitrogen to Nitrite then Nitrite to Nitrate. Once the micro-environment at the sediment-water interface is adjusted to promote aerobic bacterial growth (Nitrification), the bacterial portion of the tablet dissolves. As these bacteria mature and reproduce, they consume the sludge without producing noxious gases. There are several odor-reducing steps occurring simultaneously, aside from the aerobic bacterial degradation of the manure. Physically, the rising bubbles of oxygen tend to purge any dissolved gases out of solution by removing them from the manure. Chemically, the dissolution of the dry oxidative alkali raises the pH of the manure, thereby preventing the volatilization of ammonia nitrogen. Such biological treatment degrades the polluting organic matter as a result of the activity of a mixture of microorganisms being cultivated and introduced by our patented methodology. The introduced bacteria, after moving from their suspended state to the growth phase, absorb and consume the existing organic matter as food, provided they have the proper surrounding environment. Our method ensures that the environment is sufficiently oxygenated to promote the growth of the aerobic and facultative anaerobes.
The fundamental principle is that wild microorganisms will multiply if they are provided with the organic matter in sewage and DO (dissolved oxygen). In the process, most of the biodegradable carbon compounds are converted to CO2. In our research we introduce beneficial microorganisms, oxygen and nutrients sufficiently able to repair any imbalance created in a high BOD system.12
5. BENCH-SCALE TEST
An experimental design for the bench-scale testing based on one developed by Dr. Bundy of Iowa State University13 was utilized. These were completed to narrow down the choices between 12 variations of the prototype tablets, containing different concentrations of components, to be used in the field test onsite at the hog farm sludge lagoon. Six reactors were constructed of 4″ diameter PVC 40″ long with an end cap and treaded top cap and pressure relief hose to remove gas produced from the laboratory. The reactors were filled with 5 liters of distilled water and sealed. Fresh hog manure was acquired from a local 1400 head facility that maintains a 125,000-gallon cement lined anaerobic sludge lagoon. The percent moisture of the manure was determined to be 20% using AWWA standard method 2540b.14 Although the “Bundy method” suggests using manure that has been diluted to 4% solids with water, we chose to adjust the test solution to 10% solids. This is because on actual farms the manure supernatants test at between 10% and 20 % solids; our results would thus be closer to the field conditions.
At the start of each test, a one-liter volume of water and manure was added to each container to bring the percent Solids up to 10%. Total liquid volume in each container was 6 liters. The mixture was then stirred with a modified paint stirrer to ensure the homogenization of the sample. A YSI model 6920 probe sonde was used to measure the test parameter. The probe is designed to take readings for depth, temperature, pH, dissolved oxygen, conductivity, total dissolved solids, oxidation-reduction potential, and ammonium-nitrogen at set intervals. The initial interval was set at one minute, but later modified to every 15 minutes over a two-day period. The initial bench-scale test determined that there was a lag time of 22 hours between the saturation of the water with dissolved oxygen and the consumption of the oxygen by the bacteria (Chart #1).
This was followed by a sharp decline in the level of dissolved oxygen down to a hypoxic level below 2.0mg/l. The pH rose from 3.0 to 8.4, preventing the volatilization of ammonia, which does not volatilize at a pH greater than 5.0. After the initial burst of off-gases, there was a noticeable reduction in odor between the control and the treated samples. A modification of the standard methods protocol will be used to quantify the field test results. Registering odor is very subjective and can vary from person to person, so a panel will be used to standardize the results.
Robinson15 also found the benefits of raising pH in a study. He found, in hog waste, that an alkaline pH value (8.5-9.0) could be maintained when the substrate has a high N content. He also found that the maintenance of such pH levels corresponds with a high rate of reduction of O2 demand of the substrate; lower rates of substrate supply led to the production of acid conditions (pH 5.5-6.0).
6. FIELD TEST
The field test of the tablets in the manure lagoon at the hog facility was implemented from 4/9/98-4/16/98. From the bench scale testing a quantity of tablets was added at intervals over a 7-day period. A preliminary sample was taken at the start of the test and one at the end. Test parameters will include pH, Volatile Fatty Acids, COD, BOD, Total solids, Total Volatile Solids, Ammonia Nitrogen, Total Kjeldahl Nitrogen, and Total Phosphorus and Odor . Results are shown in Chart #2.
7. AQUATIC ALGAE REMEDIATION
There has been speculation that agricultural runoff has a detrimental affect on estuarine water quality, leading to the increase in HABs (Harmful Algal Blooms) such as Pfiesteria. In lakes and ponds, herbicides are commonly used to reduce the growth of aquatic weeds. The most commonly used are inorganic copper compounds such as Copper Sulfate. These compounds preventing the production of carbohydrates, thereby tend to block portions of the photosynthetic process, killing the weeds. Organic herbicides, such as Diquat dibromide, also interfere with photosynthetic processes to kill the weeds, but are biologically persistent because they are difficult to biodegrade and may bioaccumulate in the tissues of other aquatic organisms.
Identified therefore in this study is the use of light energy to help to degrade organic pollutants. Solar irradiation is a principal cause of transformation. Midday summer sunlight can operate in a wavelength range of 300-350nm, which produces a photo lux of about 10 to the 15 photons/cm2s. According to Noort18 if each photon induced the transformation of one molecule, and if they are absorbed within the first 100 cm, then the overall transformation rate will be 1m mol/1min. Therefore, research was also conducted to investigate methods to control and manage the rate of photons or, in other words, to identify the various photochemical pathways by enhancing the aquatic environment in order to derive quantitative expressions with relevant molecular properties of (potential) micro-pollutants of the transformation rates relating to photochemical processes.
An equally important factor affecting biological activity in an aquatic environment is the presence or absence of DO (Dissolved Oxygen) in its different parts. A lake receives oxygen from inflows of fresh water, from O2 transfer at the water-air interface, and from photosynthesis. The distribution of oxygen in an aquatic environment is affected by stratification and circulation often caused by wind and temperature variations, and biological activity, all of which plays a significant role in the creation of different aquatic environments. Within an aquatic environment, oxygen is consumed in the respiration of organisms living in the water. As biochemical and organic systems degrade or decompose, additional oxygen is also consumed in the chemical reactions. The DO profile in an aquatic environment is the net result of oxygen availability and oxygen consumption at different depths. While the surface layers are generally well oxygenated, the bottom or lower layers often do not receive sufficient oxygen, especially in a non-circulating system, unless there is downward diffusion through the upper layer of water, photosynthesis (if light penetration permits), or a mass exchange of water through strong circulating patterns.
All herbicides including the colorants cause the death and subsequent decay of the algae and plants. As these dead plants start to decay they cause an increase in the water’s demand on available dissolved oxygen. As DO levels in the water drop below 5.0 mg/L fish health and fecundity are affected. In some cases, this situation has resulted in fish kills. The need for a method of preventing weed production without persistent use of herbicides and without causing fish kills is evident.
In the aquatic environment, the pertinent microenvironments are particulate matter, surface film , the dissolved organic matter, and the water itself. The variations in sunlight directly affect the rate of transformation for organic micro-pollutants as well as the growth rate of algae and plants in aquatic environments. Hence, the various transport and transformation processes determine the organic micro-pollutants in the aquatic environment.
Oxygen depletion nuisances are caused by the release of excessive levels of nutrients into waterways. This enhances eutrophication and then, finally, oxygen depletion. Oxygen depletion can arise from the primary effect of direct organic matter inputs to the lake. In addition, secondary effects of dying plankton and decaying algae can cause sudden death of fishes as well as the release of odors caused by CH4, H2S, and NH3 gases.19 The contemporary approach is to change the direct inputs of organic matter by anaerobic or mechanical waste treatment systems or by rerouting such wastes to other locations such as flowing streams.
A second U.S. Patent Pending technology introduced in this paper is specifically designed to provide a better solution to combat the problems associated with lake eutrophication. With a single timed-release layered tablet, several active steps will occur. First, the outer layer will dissolve, releasing a compound that liberates both oxygen, in the form of bubbles, and a combination of blue and yellow water-soluble dyes. The bubbles act to disperse the dye into the water column, raise the DO level in the water, and loosen particles at the sediment-water interface, causing the tablet to bury itself deeper into the sediment. Next, the inner layers of the tablet disintegrate to release a combination of enzymes, buffers and aerobic and facultative anaerobic microorganisms. The dye acts to block the wavelength of light necessary for photosynthesis. This causes the death of the nuisance algae or plants, which sink to the bottom as they decay. The microorganisms consume the detritus at a high rate, enhanced by the nutrients and enzymes and dissolved oxygen. The high DO level also helps to prevent the fish kills associated with the increased demand created by the decaying plant matter. The source of the oxygen is a dry form of hydrogen peroxide, which in solution quickly degrades to molecular oxygen and water, thus oxygenating the water. Since microorganisms receive O2 from DO in the liquid phase instead of the usual replacement of DO from the atmosphere through a process of stirring or agitation, we introduce it directly into the system; relocation or extensive mechanical processing systems are therefore not required for the gas/liquid interface. The oxygen transfer rate differs depending on the characteristics of the water by such variables as dissolved solids, organics, and surface-active agents. The amount needed can be determined by using the following standard equation:
dc/dt = K(Cs – C1)
Where K=O2 transfer rate; Cs =concentration of dissolved O2 at saturation; C1 = concentration of dissolved O2 at time t.
By placing the time-release tablet in the aquatic environment, the rate of O2 supply and the buffering capacity provided by a body of liquid containing dissolved O2 is able to be in excess of the O2 required for microbial metabolism so that the development of anaerobic conditions is restrained. Thus, we have been able to show that in nonmechanical systemsCfor example, barrier ditches and lagoonsCO2 supply is no longer limited to transfer at the liquid surface. Previous limitations of treatment by the low rate of O2 transfer can be compensated for by an increase in oxygen introduced by time-release tablets which create a reduction in the substrate load.
8. AQUATIC FIELD TEST
A small private pond in New York State is being used for field trials and was tested from 4/21/98 – 5/2/98.