Advanced energy and phosphorus recovery of concentrated organic sludge by the integration of a high-solid anaerobic membrane bioreactor and hydroxyapatite-based partial nitritation/anammox process: Performance and techno-economic analysis

• A high-solid AnMBR was combined with HAP-PNA process for organic sludge treatment. • Energy production reached 100.2 kWh with a net energy neutrality coefficient of 1.73. • Revenue from electricity and HAP sales was 2,658 and 121 JPY/m 3 , respectively. • Net GHG emissions was 2.23 kg-CO 2 eq/m 3 for the integrated system. • The innovative system reduced energy costs by 37.7 % and GHG emissions by 52.5 %. Organic sludge (OrS) is a valuable source of energy and nutrients generated in wastewater sector, and the recycling treatment has significant potential to generate economic benefits, reduce environmental impacts, and transform sludge treatment plants into resource recovery facilities. One cubic meter of concentrated OrS contains 39.6 kg of total suspended solids, 158 g of phosphorus, and 361 g of ammonia nitrogen. This study offers a sustainable solution by integrating a high-solid anaerobic membrane bioreactor with a hydroxyapatite (HAP)-based one-stage partial nitritation/anammox process. The system enabled simultaneous high-efficiency anaerobic digestion for energy recovery, low greenhouse gas (GHG) emissions, and efficient phosphorus recovery. The electricity cost and GHG emissions were 57.7 kWh and 29.9 kg-CO 2 eq, respectively, when treating 1 m 3 of concentrated OrS, while energy production reached 100.2 kWh, yielding a net energy neutrality coefficient of 1.73. Compared to conventional treatment processes, this combined system achieved reductions of 37.7 % in energy consumption and 52.5 % in GHG emissions. The annual capital and operating costs were 21.4 million JPY, with potential revenue from electricity production and HAP sales estimated at 26.4 million JPY per year if the system were scaled to a full-sized sludge treatment plant. This indicates the potential of the sludge-to-resource treatment system to offset operational costs, achieve net revenue, and realize a circular economy.