Enhancement of nutrients recovery and cell metabolism in piggery anaerobic digestate by the co-cultivation of indigenous microalgae and bacteria

For energy-efficient treatment of anaerobic digestate by biological methods, we constructed the native microalgae-bacterial symbiosis systems (Chlorella sp.-Lysinibacillus sp. and Chlamydomonas sp.-Shinella sp.), as well as investigated their nutrient removal, biomass output and chemical composition, and microbial activity during anaerobic digestate treatment. Co-cultures of microalgae and bacteria promoted the synthesis of unsaturated fatty acids, enhanced the tolerance of microorganisms to toxic substances in wastewater, improved photosynthesis of microalgae, and reduced cell mortality. Specifically, bacteria promoted the growth and metabolism of microalgae and further improved the carbon reduction capacity of the system by 22.37%. A ratio of 50:1 in group Chlorella sp.-Lysinibacillus sp. was obtained for the best performance on biomass yield (0.85 g‧L⁻¹) and pollutant removal efficiencies: TOC (48.67%), IC (85.19%), NH₄⁺-N (98.55%), TN (80.35%) and TP (40.62%). The group Chlamydomonas sp.-Shinella sp. achieved the highest biomass yield (1.05 g‧L⁻¹) and the maximum pollutant removal (TOC: 39.05%, IC: 85.92%, NH₄⁺-N: 97.82%, TN: 83.32%, TP: 39.25%) at a ratio of 20:1. This study provides an environmentally-friendly strategy with low carbon emission and energy consumption for anaerobic digestate purification.