In-Pipe Technology’s (IPT) bioaugmentation process converts the collection system into an active part of the wastewater treatment process. IPT converts the passive sewer system into a significant treatment step by utilizing miles of existing pipe to start the process of breaking down wastewater as it travels to the wastewater treatment plant (WWTP). Biochemical processes (i.e., biodegradation and/or bioconversion based on the availability of an electron acceptor) in the collection system provide increased additional capacity within the plant, forestall costly upgrades, and extend the life of existing infrastructure. IPT offers sustainable solutions to collection system and WWTP challenges without additional energy input and capital expansion.
The engineering and scientific community have recognized that sewers are large biological reactors because they support cell growth, produce biomass, and degrade and/or convert wastewater constituents (i.e., organics) (Jahn et al., 1998). While sewers are often seen as merely a means of conveyance to the wastewater treatment plant, they actually provide similar treatment capabilities analogous to:
a trickling filter, i.e: the attached growth process of sewer biofilm, and
activated sludge, due to suspended growth processes in the bulk water phase of the waste stream
To transform a passive conveyance system into an active part of the treatment process, IPT introduces a specific blend of nonpathogenic, spore-forming (US patent 5578211) bacillus bacteria at strategic locations throughout the sewer collection system using a patented technology (US patent 5788841) that intensifies the activity of the existing biofilm and suspension bacteria, and out-competes non-beneficial bacteria for nutrients. This process of external microbial addition is known as bioaugmentation.
Metabolic Pathways of IPT Facultative Microbes
The availability of oxygen as an electron acceptor in a gravity sewer depends on the Dissolved Oxygent (DO) of the influent wastewater, air-water mass transfer of oxygen, and DO consumptions by microorganisms (Gudjonsson et al., 2002). Anaerobic conditions mainly exist in force mains and reach anaerobic condition <500m from the source (Tanaka et al., 2002; Tanaka et al., 1998). IPT bacteria will first consume the available DO under aerobic conditions - and the rate of that consumption will also depend on the availability of the readily biodegradable substrate. Under anoxic conditions, IPT bacteria will shift their metabolism by accepting nitrate/nitrite as the electron acceptor. In the absence of external electron acceptors such as oxygen (aerobic respiration) or nitrate or nitrite (anaerobic respiration), some facultative organisms can grow anaerobically by fermenting sugars (Nakano, 1997). Fermentative bacteria are capable of performing a variety of oxidation- reduction reactions involving organic compounds. Most bacteria within fixed film processes and suspended growth processes are facultative anaerobes and these organisms perform many significant roles in the degradation of waste. Bacillus bacteria, which fall into this group of organisms, degrade soluble organic compounds and contribute to denitrification (Gerardi, 2003).
In fermentation, NADH (nicotinamide adenine dinucleotide, reduced) generated by glycolysis cannot be reoxidized by electron transport systems. Instead, NAD is generated with endogenous electron acceptors produced during the metabolism of pyruvate, while ATP (Adenosine triphosphate), or energy, is generated by substrate-level phosphorylation unlike the case of respiration, in which protein is used to drive ATP synthesis. Pyruvate is an enzyme involved in glycolysis. It catalyzes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to ATP, yielding one molecule of pyruvate and one molecule of ATP. Phosphorylation is the addition of a phosphate (PO4) group to a protein or other organic molecule (Nakano, 1997).
Bacillus grows anaerobically by fermentation either when both glucose and pyruvate are provided or when glucose and mixtures of amino acids are present (Nakano, 1997).
There are many alternative electron acceptors in the matrix of wastewater and metabolites that Bacillus can use. The bacteria will use multiple electron acceptors in its efforts to remain vegetative and alive. IPT microbes can utilize a variety of possible electron acceptors for anaerobic growth, including intermediate metabolites produced during the degradation of organic carbon compounds. One limitation of this understanding is that Oxygen, Nitrate, and Sulfate are the primary acceptors talked about in wastewater manuals. Oxygen and Nitrate provide the most energy to the organism; the others are less efficient but will support growth. Sulfate is the only one documented to have limited usefulness to anything except the sulfate reducing bacteria. Most bacteria do not have the enzyme systems necessary to utilize sulfate as an electron acceptor.
By-products from the conversion of organic matter in the sewer with IPT are nitrogen gas (nitrification & denitrification), CO2 (aerobic respiration), water, and biomass (from growth). The creation of new biomass starts with the conversion of organic matter into a soluble format that bacteria can metabolize for growth or other usable forms of energy (Metcalf & Eddy, 2003).
Changes to the Native Biofilm
While there is no generally accepted rate model for substrate removal by microorganisms (Logan, 1987), mass transfer, boundary layers, and velocities are several mechanisms that are hypothesized for the growth of the biofilm related to IPT treatment. All biofilm present in the various portions of the collection system follow standard growth, detachment, and re-growth processes. A genetically engineered (controlled) biofilm, built with a defined and controlled biological population, has a more homogeneous structure than ‘wild’ sewer biofilm, is usually thinner in size, more uniform in construction.
Biofilm structures often have 3-D architecture, with internal void areas for liquid flow, solid phase growth mass, and other channels (Logan, 1987). These create pathways for food & nutrients to flow into the biofilm structure for transport into the cells, and for metabolic by- products out into the water phase for transport to the next part of the biofilm for further transformations. Wild sewer biofilms continuously grow and slough in rhythmic cycles and are often influenced by environmental impacts of water temperature change and hydraulic conditions.
When the biofilm sloughs, material is released and moves downstream. As the biofilm grows with the addition of In-Pipe bacteria, the 1mm think microscopic community will populate with Bacillus bacteria and degrade organic material including carbon, nitrates or nitrites, and other nutrient sources (cellulose, starch, protein, etc).
These organisms provide increased conversions of existing sewer processes through hydrolysis due to enzyme production that breaks down slowly-biodegradable materials (cellulose, starch, etc.)
This process makes the materials more bio-available (rbCOD), which allows the organisms to transport the material into the cell structure as smaller molecules for use within the cell. Enzymes produced include: amylase, cellulase, chitinase, maltase, mannanase, xylanase, proteases, lipase, nucleases and phosphatase. This process relies on competition between bacteria for survival. In their attempt to dominate the sewer system, the bacteria reduce fungicidal and pathogenic organisms by secreting antibiotics and toxins such as bacitracin, surfactin, polymyxin, difficidin, subtilin, and mycobacillin.
Therefore, the domination of the bacteria not only reduces nonbeneficial microbial activity, but also uses the cell lysate as a food source for metabolism. Since the organisms are facultative, they are compatible with all environmental condition in the sewer network (i.e., aerobic, anoxic and anaerobic) and do not require the presence or absence of dissolved oxygen (DO) in order to function. Carbon transformation under low oxygen and anaerobic conditions yields less biomass per pound of carbon transformed. Each pound of organic material transformed in the sewer during transit reduces the net sludge production at the treatment plant. For example, The City of Portage, IN started the bioaugmentation program in September 2010 and within four months biomass yield decreased ~14% from 1.3 to 1.1 lbs sludge/lbs influent BOD.
Under nutrient limited condition or extreme environmental stress, the bacteria form a spore to protect them from the unfavorable environment. However, sporulation is an energy intensive process that results from the absence of nutrients available for growth. When nutrient limitations become too severe for the maintenance of the bacterial cells, these sporeforming bacteria cannibalize other cells and feed off of the resulting solubilized nutrients to delay sporulation.
In addition to the positive effects of improved influent quality and reduced influent load, the In-Pipe process vastly increases the total quantity of active and beneficial bacteria entering the wastewater treatment plant. The active and beneficial new biomass entering the plant reduces the time required within the treatment process for organics and nutrient removal.
Reduction in BOD and TSS
Biochemical Oxygen Demand (BOD) is a chemical test for determining the amount of dissolved oxygen needed by aerobic organisms to break down organic material present in a given wastewater sample at certain temperature over a specific time period (Metcalf & Eddy, 2003). Removing BOD in the sewer creates a substrate for other organisms consumed in enzymatic reactions. Bacillus excrete enzymes that break down recalcitrant organic matter and create more bio-available food sources for other bacteria to continue the microbial life cycle. Reducing Total Suspended Solids will create some biosolids within the sewer; however, In-Pipe’s continual addition of Bacillus allows a gradual repopulation of the sewer biofilm by bacteria that are more efficient at degradation of organics than the bacteria that are present in natural, untreated conditions. While this material will pass into the plant or remain within the sewer system, the degradation will continue as the organic solids (carbon) are metabolized in situ. Since the Bacillus bacteria flow in the same direction as the new soluble material from the conversion of TSS, solids do not accumulate over time. Our experience and past performance resulted in increased solids destruction in the sewer and the plant.
Conventional wastewater microbiology requires a certain food to microorganism ratio (F:M). IPT bacteria are not constrained by this ratio because they are characterized as ‘r-strategists’, with the ability to survive in low food conditions, multiply quickly when food and nutrients are available, and do not require a specific level of DO to perform (Gray, 1968). The conditions in the plant can be modified and less biomass inventory can be carried in the Mixed Liquor (Lower MLSS) to effectively treat the reduced influent organic load. Bacillus cells at the beginning of the sporulation pathway may delay entering the dormant phase by killing their siblings and feeding on the released nutrients (Rinaldi, 2003).
IPT bacteria suppress the presence of filamentous bacteria, many of which are present due to levels of Fats, Oils & Grease (FOG), which favors filamentous growth with the attendant production of surfactants, causing foaming and poor settling. Supplemental applications of IPT bacteria within the plant quickly helps reduce the amounts of FOG and other material, and minimizes the impact of the shortiterm influent spikes and filamentous bacteria in the plant.
Process Aeration Energy
Energy is conserved by changes to process aeration as Bacillus bacteria enter the plant in greater numbers and shift the total WWTP microcosm to more aerobically capable bacteria. As influent load decreases, air delivery can decrease to maintain a lower D.O. without losing effluent quality. For example, D.O. in the range of 1-2ppm provides lower levels of effluent Total Nitrogen as shown on the IPT DO chart (Figure 5). The chart contains two curves, one for influent load (green) and the second for TN (red). The curves illustrate the complex relationship between changes in
wastewater composition, operation of the plant, and effluent quality.