In developed countries, municipal wastewater treatment has historically used aerobic biological processes like
activated sludge. Anaerobic processes have been used only to treat sludge resulting from aerobic processes, as well as
high-strength industrial wastewaters. In aerobic processes, organic compounds combine with oxygen to form carbon
dioxide and water. In this conversion, much energy is lost to air – about 20 times as much as with an anaerobic process. In
contrast, anaerobic processes produce methane, which can be used as a renewable energy source. In recent years,
anaerobic reactor technology has advanced, and studies have demonstrated that anaerobic processes can be used
successfully to treat low-strength wastewaters, including municipal wastewaters. This allows a valuable renewable energy
resource to be tapped. In general, anaerobic systems can remove 75-95% biochemical oxygen demand (BOD), and 70-
98% chemical oxygen demand (COD), and up to 100% total suspended solids (TSS). Capital costs, operational costs and
energy requirements are typically lower for anaerobic processes compared to aerobic systems, even if the anaerobic
systems must include post-treatment processes to achieve water quality standards. Anaerobic municipal wastewater
treatment can be particularly attractive for developing countries, which are confronting rapidly increasing water pollution
problems. This paper will:
1. provide an overview of anaerobic and aerobic treatment processes, including anaerobic system limitations that
have been overcome by recent advances.
2. discuss benefits and limitations of anaerobic wastewater treatment processes compared with aerobic processes.
3. summarize recent studies of anaerobic processes for treating municipal wastewater.