In the wastewater engineering field organic pollution is measured by the weight of oxygen it takes to oxidize it chemically, referred to as the "chemical oxygen demand" (COD). COD is basically a measure of organic matter content or concentration. The best way to appreciate anaerobic wastewater treatment is to compare its COD balance with that of aerobic wastewater treatment, as shown in figure 4 below.

Figure 4: Comparison of the COD balance during anaerobic and aerobic treatment of wastewater containing organic pollution

The COD in wastewater during anaerobic treatment is highly converted to methane, which is a valuable fuel. Very little COD is converted to sludge. No major inputs are required to operate the system. Nevertheless it depends on stable preconditions as i.e. temperature to make the process stable.

The COD in wastewater during aerobic treatment is highly converted sludge, a bulky waste product, which costs lots of money to get rid of in developed countries with less area, but can be of interest as low-cost fertilizer in developing countries if the sludge is not contaminated. Elemental oxygen has to be continuously supplied by aerating the wastewater. The process itself can be more stable.