Thermophilic aerobic biological wastewater treatment

The following review article will serve to elucidate the existing state-of- the-art and breadth of technical understanding related to thermophilic aero bic biological wastewater treatment. The advantages of this technology incl ude rapid biodegradation rates, low sludge yields, and excellent process st ability. Substrate utilization rates reported in the technical literature a re 3-10 times greater than that observed with analogous mesophilic processe s, and sludge production rates are generally similar to anaerobic treatment processes. As such, thermophilic aerobic treatment has been used to biodeg rade wastewaters from the pulp and paper industry, livestock production, an d many other miscellaneous waste streams. Thermophilic aerobic processes ar e particularly advantageous fdr the treatment of high-strength wastewaters that can fully benefit from the rapid biodegradation rates and low sludge y ields. High-strength wastewaters also contain the necessary energy content to facilitate autothermal operation such that exogenous heat input is not r equired. A theoretical energy balance is presented which predicts that COD removals of 20,000-40,000 mg l(-1) coupled with an oxygen transfer efficien cy of 10-20% are necessary for autoheating to thermophilic temperatures. Of the bacteria likely to proliferate in thermophilic aerobic bioreactors, re latively unique and specific nutritional requirements are common. In partic ular, thermophilic Bacillus spp. commonly exhibit a growth requirement for methionine. Most researchers have reported that thermophilic bacteria fail to aggregate, making biomass separation from the treated effluent a key des ign criterion. Further work on thermophilic aerobic treatment processes is also needed to identify optimum operating conditions, and determine the bes t method to accommodate the oxygen uptake rates of these systems. (C) 1999 Elsevier Science Ltd. All rights reserved.