Simulation-based analysis of full-scale implementation of energy neutral wastewater treatment plants

Abstract

Achieving an energy-positive operation is critical to meet the sustainability paradigm for wastewater management. While there is interest in developing energy positive schemes, a comprehensive analysis on full-scale implementation of such schemes is lacking. We used advanced simulation techniques to evaluate a low-energy treatment scheme capable of increasing resource recovery, while simultaneously meeting typical effluent limits (total N [TN] ≤ 3 mg/L; total P [TP] ≤ 1 mg/L). Major components of the treatment scheme include anaerobic membrane bioreactors (BOD/TSS removal), polymeric anion exchangers (P removal) and mainstream anammox process (N removal). Simulation results indicate the potential for reduction in net treatment energy requirement by about 0.46 kW h/m3 (∼ 94 %) compared to a conventional activated sludge system. Energy recovery through biogas combustion (0.29 kW h/m3) was about 90 % of the total energy required for treatment. Sludge production was reduced by 49 % using mainstream anaerobic configurations, while 55 % of the influent COD was recovered as biogas. Sensitivity analysis indicated that dominant parameters controlling energy production and consumption include temperature, influent COD, electric efficiency of combined heat and power (CHP) engine. Determination of solution space for energy self-sufficiency indicated that the proposed treatment scheme could reach a break-even point at 544 mg/L COD and 38 % electric efficiency of the CHP engine. Our analysis helped identify potential challenges for full-scale implementation and determination of operational strategies to overcome these challenges. We believe that our advanced simulation-based analysis provides a platform that utilities can apply to make decisions to achieve sustainable wastewater management.