Integrating dairy manure for enhanced resource recovery at a WRRF: Environmental life cycle and pilot-scale analyses

Abstract

The Twin Falls, Idaho wastewater treatment plant (WWTP), currently operates solely to achieve regulatory permit compliance. Research was conducted to evaluate conversion of the WWTP to a water resource recovery facility (WRRF) and to assess the WRRF environmental sustainability; process configurations were evaluated to produce five resources-reclaimed water, biosolids, struvite, biogas, and bioplastics (polyhydroxyalkanoates, PHA). PHA production occurred using fermented dairy manure. State-of-the-art biokinetic modeling, performed using Dynamita's SUMO process model, was coupled with environmental life cycle assessment to quantify environmental sustainability. Results indicate that electricity production via combined heat and power (CHP) was most important in achieving environmental sustainability; energy offset ranged from 43% to 60%, thereby reducing demand for external fossil fuel-based energy. While struvite production helps maintain a resilient enhanced biological phosphorus removal (EBPR) process, MgO₂ production exhibits negative environmental impacts; integration with CHP negates the adverse consequences. Integrating dairy manure to produce bioplastics diversifies the resource recovery portfolio while maintaining WRRF environmental sustainability; pilot-scale evaluations demonstrated that WRRF effluent quality was not affected by the addition of effluent from PHA production. Collectively, results show that a WRRF integrating dairy manure can yield a diverse portfolio of products while operating in an environmentally sustainable manner. PRACTITIONER POINTS: Wastewater carbon recovery via anaerobic digestion with combined heat/power production significantly reduces water resource recovery facility (WRRF) environmental emissions. Wastewater phosphorus recovery is of value; however, struvite production exhibits negative environmental impacts due to MgO₂ production emissions. Bioplastics production on imported organic-rich agri-food waste can diversify the WRRF portfolio. Dairy manure can be successfully integrated into a WRRF for bioplastics production without compromising WRRF performance. Diversifying the WRRF products portfolio is a strategy to maximize resource recovery from wastewater while concurrently achieving environmental sustainability.

Keywords: life cycle assessment; modeling; resource recovery; wastewater treatment.