A Roadmap for Achieving Energy-Positive Sewage Treatment Based on Sludge Treatment Using Free Ammonia

This letter proposes an innovative roadmap for achieving energy positive sewage treatment based on sludge treatment using free ammonia (FA, i.e., NH3). This FA technology is able to enhance anaerobic energy recovery in the form of methane via pretreatment of primary sludge and/or secondary sludge. It can also achieve stable mainstream nitrogen removal via nitrite instead of nitrate, thereby increasing organics availability for energy recovery. Energy evaluation suggests that the FA technology could transform sewage treatment plants from energy consumers (energy consumption at 0.27 kWh/m(3) sewage treated) to energy exporters (energy export at 0.14 kWh/m(3) sewage treated). Economic and environmental evaluations indicate that the FA technology would reduce sewage treatment cost and CO, emission by $0.0.56/m(3) sewage treated and 0.40 kg CO2/m(3) sewage treated, respectively. This FA technology is a sustainable and closed-loop technology, which requires negligible chemical/energy input with FA being a byproduct of sewage treatment. It is also easy to implement in any existing and new sewage treatment plants by adding a simple sludge mixing tank.