A novel strategy for synthetic microbial community conversion of liquid pig manure into microbial fertilizer

The pig industry generates copious amounts of liquid pig manure (LPM), which poses a great challenge to the environment; conventional treatment of the manure is often time-consuming and inefficient. We developed a novel technique for converting LPM into liquid microbial fertilizer with two steps: (1) screened ammonia nitrogen-degrading strains and synthetic microbial communities (SynCom) were used in combination with H₂O₂ for the biological deodorization of LPM; and (2) the bio-deodorized and autoclaved LPM was then inoculated with screened SynCom2 to produce liquid microbial fertilizers. The results of bio-deodorization demonstrated that both single ammonia nitrogen-degrading strains and SynCom1 reduced over 90% of the odor and GHGs emissions (NH₃, H₂S, CO₂ and CH₄) from LPM, and decreased the pH, chemical oxygen demand (COD), ammoniacal nitrogen (NH₄⁺-N) and EC to varying extents. The SynCom1 was able to completely eliminate malodorous volatile organic compounds (p-methyl phenol) from LPM, outperforming single ammonia nitrogen-degrading strains. The deodorized LPM treated with SynCom2 exhibited high levels of nutrient concentration (31.58 g/L of total carbon and 3.81 g/L of total nitrogen), microbial biomass (up to 1.92 × 10¹⁰ CFU/mL), plant safety and maturity (germination index > 100%), indicating suitability as microbial fertilizer. Cultivation experiments demonstrated a significant increase of over 70% in shoot length, root length, fresh weight and dry weight of rice seedlings when microbial fertilizers were applied in black soil. Overall, our study provided a valuable direction for the development of potential industrial applications.