Abstract: Aiming at the problem of treating biogas slurry generated from wet anaerobic fermentation in China’s biogas projects, a technical route of biogas slurry membrane concentration + microbial fermentation for fertilizer production was proposed. Taking a pig manure biogas project in Tongren city, Guizhou province as a case study, through multistage filtration (microfiltration + ultrafiltration + nanofiltration + reverse osmosis) combined with aerobic fermentation technology, the biogas liquid was concentrated six times and converted into high-value liquid fertilizer. The concentrated slurry met the requirments of GB 5084—2021 Standard for Irrigation Water Quality. Product testing demonstrated that the contents of organic matter, humic acid and total nutrients in the concentrated fertilizer were (55.00±1.20) g/L, (10.63±0.25) g/L, and (9.89±0.16) g/L， respectively, far exceeding the requirements of GB/T 40750—2021 Biogas Slurry for Agricultural Use. Heavy metals were either undetectable or below limits, and pathogenic microorganisms, the water-insoluble substance content and odor emission concentration complied with the requirements of GB/T 40750—2021. Field trials showed that by applying concentrated biogas slurry fertilizer through drip irrigation 10 times, each at a dosage of 75 kg/hm2 with a 10-day interval, the sugarcane yield reached 147.15 t/hm2, which was 19.20% higher than that of the chemical fertilizer group, the sucrose content increased by 6.70%, resulting in an average additional income of 34 590 yuan per hectare.Techno-economic analysis confirmed that the investment payback period of the project was only 2.18 years, and it has both environmental benefits and profit potential, providing a feasible path for the resource utilization of biogas slurry in large-scale biogas projects.

Key words: concentrated biogas slurry fertilizer, membrane separation technology, sugar improvement, sugarcane yield, integrated water and fertilizer, circular agriculture