Carbon-nitrogen nexus changed by improved organic carbon pre-concentration and autotrophic deammonification to improve wastewater treatment energy self-sufficiency

Abstract

Achievement of energy self-sufficiency for wastewater treatment plants (WWTPs) requires comprehensively understanding the impacts of process design on energy consumption and generation. A stoichiometric model revealed the effects of organic preconcentration (PreC) and sidestream/mainstream autotrophic deammonification (S&M-ANA) on carbon-nitrogen nexus and accordingly energy efficiency. PreC unit not only increased energy generation by enlarging organic feed amount for AD (anaerobic digestion), but also decreased energy consumption by reducing aeration requirement. ANA indicated potentials to save organics for energy recovery. However, its advantages on energy self-sufficiency (ES) were conditional requiring high PreC combination. The specific energy consumption was reduced from 0.373 kWh/m3 to 0.228 kWh/m3, while energy generation increased from 0.106 kWh/m3 to 0.403 kWh/m3 for moderate strength wastewater (500 mg/L COD). M-ANA (73.5%–88.4%) achieved more nitrogen removals than S-ANA (17.1%–22.7%). Even without S&M-ANA, the theoretical energy self-sufficiency increased to as high as 98.0% by just recovering organic matters via high efficiency PreC. These results provided strategies to improve WWTPs energy efficiency based on process layout design with improved organic pre-concentration recovery and autotrophic deammonification.