Estimation of greenhouse gas generation in wastewater treatment plants--model development and application.

A comprehensive mathematical model has been developed to estimate greenhouse gas (GHG) emissions by wastewater treatment plants (WWTP) resulting from on-site and off-site activities. The contribution of individual processes to the production of GHGs in a typical hybrid treatment system for food processing wastewaters has been determined. The results show that the recovery of biogas and its reuse as fuel have a remarkable impact on GHG emissions and reduce the overall emissions by 1023 kg CO(2)e d(-1) from a total of 7640 kg CO(2)e d(-1) when treating a wastewater at 2000 kg BOD d(-1). Furthermore, the recovery of biogas and its combustion may be used to cover the entire energy needs of the treatment plant for aeration, heating and electricity generation while creating emissions credit equal to 34 kg CO(2)e d(-1). The off-site GHG emissions resulting from the manufacturing of material for on-site usage were identified as the major source of GHG generation in hybrid treatment systems. These emissions account for the generation of 4138 kg CO(2)e d(-1), or 62% of the overall GHG emissions when biogas recovery is carried out. The inclusion of GHG emissions from nutrient removal as well as off-site processes in the overall GHG emissions of WWTPs increased the accuracy and completeness of this estimation, lending support to the novelty of the present study.