ABSTRACT
Microbiological systems for the treatment of wastewaters were developed around the late 1890s, initially for treatment of human waste and later for treatment of industrial wastes. The first treatment systems were run in “batch mode”; wastewater was held in reactors containing rocks. Although the microbial nature of the process was not clearly understood initially, it is now known that microbes grow in biofilms attach to the rocks, utilize carbon and nitrogen compounds in the waste as a food source, and thus reduce the oxygen demand the wastewaters would exert when released to the environment. To increase the amount of wastewater that could be treated and decrease problems associated with clogging, two continuous processes were developed in the early 1900s — trickling filters [1] and activated sludge [2]. These processes continue to dominate wastewater treatment systems to the modern day.
