Exploration of ammonia stripping coupled adsorption-membrane filtration process for treating kitchen waste biogas slurry

The potential contamination of biogas slurry generated from the anaerobic digestion of kitchen waste (KW) poses a considerable challenge to its safe and effective utilization as a fertilizer. To tackle this problem, a novel route termed “AS-BC” was developed, integrating ammonia stripping (AS), biochar adsorption, and ceramic membrane filtration (CMF) for comprehensive pollutant mitigation. A stepwise optimization was carried out, comparing biochar adsorption investigation, the AS process, and the combined AS + CMF process. Results indicated that the AS process possessed the maximum total ammonia nitrogen (TAN) removal of 86.21% at an airflow rate of 40 L/min. The combined AS and CMF process with 0.1 μm membrane had best performance for total phosphorus (TP) with removal efficiencies of 80.45%–87.98%. Under the optimal biochar addition condition of 5 g/L with a particle size of 0.25–0.85 μm, the adsorption pretreatment effectively removed 0.41 g/g of soluble chemical oxygen demand (SCOD), prevented nutrient loss, and substantially enhanced pollutant removal efficiency in the subsequent CMF process. Compared to other routes, the route AS-BC achieved higher total nitrogen (TN), TAN, TP, and SCOD removal efficiency of 91.42%, 91.49%, 89.54%, and 76.34% from the raw biogas slurry, respectively. Moreover, the route AS-BC demonstrated its cost-effectiveness in producing nutrient-rich concentrated slurry suitable for use as fertilizer. The route AS-BC was proved to comprehensively remove various indicators from the KW biogas slurry while generating economically reuse by-products during the membrane filtration process. This study offers valuable insights into the trade-offs between AS performance enhancement and pollutant mitigation, pinpointing essential routes for future research and practical improvements.