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Technique Microbiology: The Key To Wastewater Treatment Using a novel sewer collection bioaugmentation process, wastewater goes from liability to asset. by Bulbul Ahmed, Andrew Newbold, and Rich Schici he biological treatment of wastewater relies mainly on a consortium of heterotrophic and autotrophic bacteria. The fecal bacteria that are constantly intro- duced into the collection system are not the optimal bacteria for degrading the contaminants present in wastewa- ters. The soil bacteria that are introduced through inflow and infiltration are more effective at degrading the wastes and can contribute to stabilizing the downstream wastewater treatment process; however, the flux of these organisms into the sewer system is not enough to contribute to significant degradation in the sewer system under normal conditions. Collection sys- tem bioaugmentation aims to introduce high concentrations of specific soil bacteria into the outer reaches of the sewer sys- tem and amplify the beneficial effects of soil bacteria in the col- lection system. The downstream impact of this treatment serves to improve the condition of the collection system by reducing odor and degrading fats, oils, grease (FOG), as well as reduc- ing organic loadings to waste water treatment plants (WWTPs) and increasing the efficiency and effectiveness of the waste- water treatment process. T Background Direct releases of domestic, municipal, or industrial wastewater into surface waters degrade the condition of the natural aquatic environment and can pose serious threats to human health. Biological treatment processes are still the mainstay for degrading most of wastewater contaminants after pre- treatment (e.g., screening and settling) since it is the most effective process in contaminant degradation, cost effective, and it is eco-friendly compared to the physiochemical processes. Advanced chemical and/or biological treatments, such as chemical precipitation or tertiary filtration are often required before reuse or discharge into ecologically sensitive waters. In a biological process, indigenous microorganisms (mainly bacteria) are the key to removing contaminants such 10 Water Online The Magazine, Wastewater Edition ■ wateronline.com as organics (chemical oxygen demand [COD]), and nutrients (nitrogen/phosphorous) from wastewater. Figure 1: The environment in the sewer line. Wastewater Bacteria And Their Metabolisms Fecal heterotrophic and natural autotrophic bacteria are the indigenous microorganisms introduced into the biologi- cal wastewater treatment processes. Heterotrophic bacteria degrade readily biodegradable COD (rbCOD) in wastewater by using it as an electron donor for respiration. They respire using oxygen, nitrate, or sulfate, as an electron acceptor under aerobic, anoxic, or anaerobic conditions, respec- tively. The main respiration products are carbon dioxide, nitrogen gas, sulfide, and bio- mass. Heterotrophic bacteria also degrade rbCOD through the fermentation processes under anaerobic conditions and generate the fermenta- tion products of carbon diox- ide and biomass. Autotrophic nitrifiers oxidize ammonia to nitrate or nitrite for energy and use alkalinity as a carbon source. Anaerobic respiration using sulfate is undesirable in a wastewater treatment process since the respiration product sulfide creates nuisance odors and is also toxic to human health. Furthermore, the sulfide oxidation in the sewer atmosphere generates sulfuric acid, which is corrosive to the sewer infrastructure. In addition, heterotrophic bacteria secrete enzymes to hydrolyze hydrolysable particulate COD to rbCOD, which then can be used as an electron donor for cellular metabolism. Current Microbiology And Wastewater Treatment Approximately 99.9% of fecal bacteria are strict anaerobes and the rest are either aerobes or facultative anaerobes. Fecal bacteria are more susceptible to the changes in wastewater characteristics and environmental conditions such as tem- perature, pH, chemistry, etc. Heterotrophic and autotrophic bacteria are the main contributors in wastewater treatment.