Modelling of a novel near zero energy for a wastewater treatment plant with OXY-Biogas power cycle

With the increase of population in the world, there have been tremendous increases in energy and water con-sumption which has made the Water Energy Nexus (WEN) an important consideration in the past several years. Moreover, energy consumption increased by a factor nine in the last century, and there is a close connection between water and electricity production - electricity production is one of the main sources of CO2 emissions in the world. In order to conserve water, energy, and CO2 emissions, a novel multigeneration net zero energy wastewater treatment plant has been modelled and developed by integrating an oxy-biogas power cycle with a wastewater treatment plant (WWTP). The proposed system is a combination of an activated sludge, anaerobic digester, oxy-biogas power cycle, and a Rankine cycle. The final product of the activated sludge is used to feed the power cycles in order to produce energy. The produced CO2 from the combustion chamber has been recycled and combusted in the combustion chamber with the biogas and pure oxygen. Several parametric studies have been conducted to investigate their effects on the thermodynamic efficiencies and self-sufficiency ratio. While wastewater strength, effluent biochemical oxygen demand, and dissolved oxygen concentration have been varied in the WWTP, turbine inlet temperature, combustion pressure, and CO2 return ratio have been chosen as the decision variables for the power cycle since they play key roles in both power requirement for wastewater treatment and power production from the oxy-biogas turbine cycle. The strength of untreated domestic waste-water has been found to be the most important factor among the decision variables. In addition, combustion pressure has shown to play a significant role, with the maximum self-sufficiency ratio and efficiencies occurring with combustion pressures in the range of 15 to 20 bars. Overall exergy efficiencies varied from 19.38% to 32.59%, and self-sufficiency ratios changed from 82.29 to 132.4%. Moreover, more than 95% of the CO2 has been captured and recycled in the combustion chamber. This work is the first study which evaluated the integration of an oxy-biogas combustion model not only to produce power but also a nearly zero emission free WWTP. Furthermore, a fundamental analysis of energy and CO2 saving for each state in the US have been calculated using the proposed system. It was found that, if the system outlined in this study was utilized in all activated sludge based WWTPs in the US, a total energy and CO(2)e emission savings of 10,409 GWh/yr and 3,553 kilotons/yr, could be obtained, representing 0.28% and 0.24% of the total electricity supply and annual CO(2)e emissions from electricity production. This study suggests that an energetically self-sufficient WWTP with near zero emission is plausible.

Automated summary

With the increasing population and consumption of energy and water, the Water Energy Nexus (WEN) has become an important consideration. A novel multigeneration net zero energy wastewater treatment plant has been developed, which integrates an oxy-biogas power cycle with a wastewater treatment plant to conserve water, energy, and CO2 emissions.