Enhancing Circular Bioeconomy through Aerobic Granular Sludge: Experimental Insights into Nutrient Recovery from Kitchen Waste Leachate
Abstract
Kitchen waste leachate is a variable, nutrient-rich liquid stream generated during the collection, storage, and processing of food waste. While it significantly increases the organic load, ammonium, phosphate, suspended solids, oils, and fermentation products are very troublesome in the treatment process; it also provides for the recovery of carbon, nitrogen, and phosphorus. This review critically analyzes the use of aerobic granular sludge (AGS) as a biological platform to improve circular bioeconomy strategies for recovering nutrients from kitchen waste leachate. The review combines leachate characteristics, granulation mechanisms in AGS, microbial nutrient pathways, experimental evidence, and integration pathways with downstream technologies for leachate recovery. The difference between pollutant removal and resource recovery is discussed, as is the fact that conventional nitrogen and phosphorus removal may not yield reusable products. The advantages of AGS treatment include compact dimensions, superior settleability, high biomass retention, and the simultaneous occurrence of carbon degradation and nitrification, anoxic and anaerobic microenvironments, and phosphorus accumulation. But high organic loading, ammonia inhibition, fats, salinity, influent inconsistency, and granule instability remain significant challenges. For recovery-oriented AGS systems, it is therefore beneficial to combine pretreatment, fermentation, struvite precipitation, ammonium recovery, membrane separation, or biomass valorization. Nutrient mass balances, product safety, pilot-scale validation, assessment of greenhouse gas(es) (GHG), and techno-economic analysis should be given greater importance in future research. In general, AGS is a potential bridge between biological treatment and nutrient circularity in sustainable food waste management systems, and between decentralized urban resource recovery and future cities.