Estimation of greenhouse gas emissions from a hybrid wastewater treatment plant

An elaborate model was developed to estimate on-site and off-site greenhouse gases (GHGs) generated from wastewater treatment plants (WWTPs). The model was applied to a hybrid treatment system (five-stage Bardenpho processes) treating 5500 m3 d−1 of municipal wastewater with 200 mg L−1 influent biochemical oxygen demand (BOD). A sensitivity analysis was performed to predict the potential variability of GHG emissions from the WWTP. On-site GHG emissions related to biochemical reactions at the system were estimated to be 8264 ± 678kgCO2e d−1. The major source of on-site GHG emissions was the first aeration tank, and these were caused by the release of dissolved and accumulated GHGs by air-blowing. Off-site GHG emissions related to electricity consumption, chemical production, and transportation were estimated to be 4591 ± 576 kgCO2e d−1. Off-site production of chemicals to be used on-site was identified as the primary source of the off-site GHG emissions. The recovery of biogas and its reuse as electricity reduced the overall GHG emissions. The results obtained from the newly developed model (10.6 kgCO2e·kg−1BOD) were 2.83-4.24 times greater than those obtained from previous studies. From the results of this study, an appropriate methodology is proposed to accurately estimate GHG emissions from WWTPs and tactics are outlined for reducing GHG emissions without reducing the quality of treated wastewater.