Waste stream, microbial degradation

Bioremediation is defined as the use of microorganisms or microbial processes to degrade environmental contaminants. Bioremediation has numerous applications, including cleanup of groundwater, soils, lagoons, sludge, and process waste streams. 

Microbial degradation is potentially the most important pathway for removal of PCAs in waste streams, yet much remains to be learned about transformation rates under various conditions as well as the products of degradation. In general, studies suggest that biodegradation of PCAs does occur, and is influenced by chlorine content and carbon chain length. 

In the case of oxygen-depleted streams, such as typically occur downstream of wastewater outfalls, the flux of O2 is from the atmosphere into the streams. In a stream with steady, uniform flow and no sources or sinks of oxygen other than the atmosphere, an oxygen deficit decays exponentially with downstream travel time. The classic Streeter-Phelps model, discussed in Section 2.5, considers not only dissolution of O2 into a stream but also simultaneous O2 consumption due to microbial degradation of organic waste within the stream. By tradition, the reaeration coefficient in Streeter-Phelps modeling is designated fCoj. 

You need to purify a waste water stream containing a recalitrant compound, trichloroethene, present in fairly high concentrations, 100 yuM (13 ppm). If one can deliver this waste water into a well mixed tank (i.e., a continuously stirred tank reactor or CSTR) virtually saturated with methane at 500 yuM and oxygen at 1000 yuM and all other nutrients needed for microbial growth on methane, then one can build up a methanotroph population capable of degrading the trichloroethene by cometabolism to innocuous substances like C02 and H20 before the water is discharged. 

Chemical pollution is the diversion of chemical elements from the natural biogeo-chemical cycles. The carbon, nitrogen, and phosphate in municipal wastes released to streams and lakes are removed from the soil-plant cycle, which is the source of the nitrogen and much of the phosphate. If those substances were instead put back directly into the soils from whence they came, much less pollution would result. Air and water only slowly convert their wastes back into their natural sites in plants and soils. Soil, on the other hand, has enormous surface area and microbial catalytic activity plus oxygen and water with which to deactivate pollutants. Soil degrades most... 

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