Model-based comparison of biological wastewater and sludge treatment combinations for nutrient removal, sludge and biogas production

One of the strategies for reducing the potential environmental and health-related risks associated with wastewater treatment sludge is to select treatment options that would minimize its production while using its beneficial products and meeting effluent discharge standards. In this regard, simulation models can aid in estimating treatment performance, sludge production, and biogas formation. This study evaluates effluent concentrations focusing on nutrients, sludge production, and biogas generation rates for various combinations of wastewater and sludge treatment alternatives for varying strengths of domestic wastewater. Overall, 105 scenarios were simulated for three different wastewater strengths for 35 treatment schemes. Bardenpho-5 (B5) was superior over A2O (A2) in removing nitrogen and phosphorous. Adding primary sedimentation to A2 and B5 models improved sludge and in turn biogas production. Effluent total phosphorus (TP) was usually higher in scenarios with anaerobic sludge digestion. However, struvite precipitation following anaerobic digestion helped reduce total nitrogen (TN) and TP effluent concentrations for all wastewater treatment technologies. Sludge production amounts ranged between 2865 kg/day to 38,709 kg/day (total solids) for an influent flow rate of 100,000 m3/day. Sludge production rates were relatively insensitive to sludge treatment alternatives for extended aeration (EA) compared to conventional activated sludge (AS), A2, A/O (AO), and B5. Generally, the impact of a sludge treatment option was significant for wastewater treatment technologies with higher waste sludge production. Thermal hydrolysis followed by anaerobic digestion provided the lowest sludge production and significantly improved the biogas production.