Bioaugmentation In Sewer Network Reduces Sludge Production
This article describes the effectiveness of bioaugmentation in the sewer network as a strategy to reduce sludge production.
Sludge is an obvious by-product generated from the physical, chemical and biological treatment processes of a wastewater treatment plant (WWTP) as shown in Figure 1. Sludge management, which includes treatment, hauling, and disposal, is one of the biggest burdens facing municipal plants. The costs of sludge management account for 55% of the total WWTP operating cost and 35% of the capital cost.
In some cases, sludge treatment may be required to minimize odor emissions during transportation or to reduce and stabilize the remaining sludge organic contents. Due to high sludge management costs and the availability of disposal sites, it is vital to find new technologies that can reduce sludge production.
The Sewer Network
As an integral part of wastewater system, the sewer network contains similar treatment capabilities as a biological reactor designed for the WWTP. The relative fraction of organics or chemical oxygen demand (COD) (i.e., readily biodegradable COD (rbCOD), fast hydrolysable COD (fhCOD), and slowly hydrolysable COD (shCOD), in raw wastewater affects the efficacy of biological treatment systems because bacteria cannot utilize hydrolysable substrate directly. As wastewater travels through the sewer network, the biochemical process of hydrolysis has the potential to change the influent wastewater quality. By increasing rbCOD through hydrolysis of the hydrolysable substrate, it is possible to reduce the influent load (i.e., TSS, COD, BOD, TKN) entering the WWTP through microbial processes.
The biochemical transformations in the sewer network are initiated by indigenous microorganisms (mostly heterotrophic
bacteria). Fecal materials are the main source of indigenous bacteria in the wastewater, but they are not robust (i.e., not spore former) under changing environments in the sewer line (i.e., aerobic, anoxic, anaerobic, high or low temperature, pH fluctuation and toxicity). Establishing more sustainable microbiology in the sewer network can overcome the limitations of the indigenous bacteria, improve the raw wastewater quality, and reduce the influent load to WWTP.
One technology uses an external source of bacillus bacteria added into the collection system in accordance with an engineered plan. The microbiology reduce the volume of sludge produced by degrading organic carbon in the sewer, solids inventory within the plant, and solids in aerobic and lagoon digestion processes. In-Pipe Technology Company, Inc (IPTC) introduces a blend of specialized, facultative, spore forming bacteria (up to 108 times greater than indigenous sessile bacteria in wastewater) into the outer reaches of the sewer network in order to establish more sustainable microbiology in the sewer network to improve raw wastewater quality, control Fats, Oil, and Grease (FOG), and reduce influent load to the WWTP.
IPT’s bioaugmentation process consists of the continual addition (twenty-four hours-a-day, seven days-a-week) of high concentrations of naturally-occurring, non-pathogenic bacteria at multiple points within the collection system in order to (1) grow throughout the surface of the sewer pipes and thereby dominate the sewer biofilm with beneficial bacteria, (2) improve the ability of the sewer biofilm to degrade (improve the wastewater quality and/or reduce the organic load to the WWTP) the organic material, and (3) take advantage of the retention time of the wastewater within the sewer, allowing the added bacteria additional time to degrade the waste.
There are several mechanisms of reducing sludge production in a biological wastewater treatment processes such as (i) increase the degradability of the hydrolysable or inert substrate, (ii) increase the cell decay or lysis, (iii) increase the cell maintenance energy, and (iv) decrease the biomass yield. The bacillus formulation include common heterotrophic soil bacteria that are specifically selected and formulated to effectively degrade a wide variety of organic compounds found in wastewater.
These organisms provide increased conversions of existing sewer processes through hydrolysis due enzymes production that break 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. Adding bioaugmentation to the sewer 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. Several plant processes benefit from the above mentioned IPT biological processes.