Greenhouse Gas Emission and Energy Consumption in Wastewater Treatment Plants: Impact of Operating Parameters

Greenhouse gas (GHG) emission and energy consumption were estimated in wastewater treatment plants using an elaborate mathematical model that included coagulation/flocculation, anaerobic digester, nitrification/denitrification, and biogas recovery. The examined treatment systems used aerobic, anaerobic, and hybrid biological processes. The impact of pertinent operating parameters including reactor temperature, solid retention time (SRT), primary clarifier underflow rate, and biochemical oxygen demand concentration on GHG emission and energy consumption were investigated, leading to the identification of controlling operating parameters and adequate strategies to reduce GHG emission and energy consumption. The overall GHG emission was 3152, 6051, and 6541kg CO2-equivalent/day, while the estimated energy consumption amounted to 4028, 2017, and 3084MJ/day in the three examined systems, respectively. Parametric studies showed that the best strategy to reduce GHG emission and energy consumption would result from 12% increase in the bioreactor temperature in the aerobic system, 10% increase of the bioreactor temperature and five days increase of SRT in the anaerobic system, and 10% increase of temperature and five days reduction of SRT in the anaerobic bioreactor of the hybrid system. Additional reductions in the GHG emission and energy consumption would result from 50% increase of the primary clarifier underflow rate.