A review of carbon recovery in sewage treatment and analysis of product options for a typical water recycling plant†

Carbon recovery and sustainable management of sewage sludge from wastewater treatment plants were reviewed regarding the technical and market supply potentials, environmental, economic, and social benefits, and technology readiness. The findings were used in a case study of a 75 000 PE water recycling plant to evaluate the potential benefits of implementing the most promising technological solutions via a triple bottom line approach. Implementation of rotating belt filtration for cellulose recovery in primary treatment would reduce the energy required for aeration, the sludge volume and thus the sludge management burden. Recovery of protein from the waste activated sludge would provide net revenue. Volatile fatty acid (VFA) extraction from the acidogenic phase of anaerobic digestion was economically sound. Co-digestion of food waste with the sludge would enhance VFA production or biogas generation, depending on the target product. Microalgal treatment of the digestate liquor would enable purification of the biogas through CO₂ fixation and generate biomass which could be returned to anaerobic digestion for biogas production. Conversion of the biosolids to biochar would lead to net generation of revenue due to cost savings for transportation and land application, the biochar is useful for adsorption, catalysis and soil amendment for nutrients and sequestering CO₂. Integration of promising recovery technologies into wastewater treatment would reduce sludge volume and create value-added products, and also reduce the environmental impact and health risks. However, integration must address the obstacles in terms of economy, value chain development, environment and wellbeing, as well as societal and policy limitations.