The development of nutrient-removal processes (abridged) - Discussion

The earliest references to the loss of nitrogen and phosphorus in activated -sludge systems indicated an awareness, but no particular interest, in the use of biological processes for the removal of nutrients. The development o f extended-aeration processes in general, and of channel systems in particu lar, intensified the interest in denitrification as a means of reducing nit rogen in an effluent. Observations of simultaneous nitrification and denitr ification led to the proposal of separate anoxic zones for optimal nitrogen removal. The discovery that biological nitrogen and phosphorus removal cou ld be synergistic, led to an explosion of processes, differing in all but t he basic underlying biochemistry, for the removal of both nitrogen and phos phorus. The development of computer models, to accurately describe the comp lex and inter-related reactions, makes it possible to fully exploit biologi cal systems to achieve cost-effective nutrient removal.