Environmental impact analysis of anaerobic fermentation biogas treatment process based on LCA for food wastes

Using the Life Cycle Assessment (LCA) method, with 1 ton of food waste as the functional unit, the LCA system boundary was constructed, covering the entire process of raw material acquisition, collection and transportation, pretreatment, mesophilic anaerobic fermentation, and digestate treatment. Combined with measured data and the East Asia regional adapted inventory of the Ecoinvent3.0 database, the CML 2001 evaluation system was adopted to quantify 7 types of environmental impact categories: abiotic depletion potential (ADP), global warming potential (GWP), acidification potential (AP), human toxicity potential (HTP), photochemical ozone creation potential (POCP), eutrophication potential (EP), and aerosol quality potential (AQP). The environmental impacts of the digestate treatment mode and 6 optimized processes of a large-scale food waste biogas project in Jinhua City, Zhejiang Province were systematically evaluated. The results show that the comprehensive environmental impact potential value of the "ammonia stripping + biochar + membrane separation" mode is -1.835×10^-11, which is 6.93% lower than that of the sewage treatment benchmark mode (-1.716×10^-11). This mode enhances NH₄⁺-N recovery (the recovered product is ammonium sulfate) through pH 10.5-11.0 regulation, and the effluent NH₄⁺-N removal rate reaches 92.32%. Membrane separation technology combined with biochar adsorption achieves soluble chemical oxygen demand (SCOD) and total phosphorus (TP) removal rates of 71.51% and 91.82%, respectively, and has the best inhibitory effect on EP (-6.977×10^-12). Compared with the sewage treatment mode (unit energy consumption 5.553×10⁵ kJ/t), it saves energy by 406.80% (unit energy consumption 3.63×10⁵ kJ/t). Both the "ammonia stripping + biochar + membrane separation" and "ammonia stripping + microalgae" modes reduce the concentration of NH₄⁺-N in biogas slurry compared with the sewage treatment mode through pH regulation, and their comprehensive potential values are better than the sewage treatment mode, confirming that NH₄⁺-N recovery is the core path to control eutrophication. Sensitivity analysis shows that the increase in collection and transportation distance will aggravate the deterioration of GWP and AP indicators, while increasing the proportion of biogas power generation substitution to 100% can reduce EP and AP by 30%～50%. Therefore, economic and environmental benefits can be improved through measures such as path optimization, electric energy substitution for vehicles, and biogas self-power generation. The research results provide a systematic decision-making framework based on LCA for the environmental management of anaerobic fermentation projects, and have important reference value for achieving the construction goal of "Zero-Waste City".