The Effect And Mechanism Of Bioaugmentation With Microalgal Bacterial Consortia On The Treatment Of Piggery Digestate

Microalgae-based system was promising,which can not only remove nutrients from wastewater,but also can produce algal biomass as an important raw material for biodiesel and animal feed.Moreover,this system can absorb and utilize carbon dioxide to reach carbon neutrality.Most of the studies focused on the effect of microalgae-based system on wastewater treatment,while little attention was paid to the mechanism of microorganisms in the system.In this paper,the inoculation scheme of functional bacterial agent in microalgal bacterial consortia was optimized,and the suitable operation conditions for the optimized microalgal bacterial consortia was explored.Under the suitable operation conditions,the feasibility of continuous operation of the microalgal bacterial consortia for piggery digestate treatment was verified,and the bioaugmentation mechanism of the optimized microalgal bacterial consortia was revealed.The main results are presented as follows:1)The inoculation scheme of functional bacterial agents for the optimized microalgal bacterial consortia was obtained,and the bioaugmentation mechanism was revealed.The inoculation of functional bacterial agents especially nitrifying bacteria improved the efficiency of piggery digestate treatment by microalgae-based system.The microalgal bacterial consortia inoculated with nitrifying bacteria and Desmodesmus sp.CHX1 was feasible for piggery digestate treatment,reaching high inorganic nitrogen removal which was 1.74 times of the mono-microalgae system.In microalgal bacterial system,the main ammonia removal pathway was the assimilation of microalgae instead of the nitrification of bacteria,because the microalgal biomass was 2.70 times of the mono-microalgae system.High-throughput sequencing showed that the richness of microbial community decreased but the evenness increased in microalgal bacterial system,which indicated that the structure of bacteria community was stable.The dominant genera Sphingobacterium,Flavobacterium and Comamonas were beneficial to promote the growth of microalgae as well as improve the nutrients removal.2)The suitable initial nitrogen conditions for microalgal bacterial consortia were explored,and the characteristics of microbial community under different nitrogen conditions were analyzed.The microalgae growth was inhibited when initial ammonium concentration was higher than 420 mg/L.When the initial ammonium and nitrate concentration were 420mg/L and 47 mg/L in piggery digestate,the performance of microalgal bacterial consortia was the best with stable bacterial community,high biomass production and high nutrients removal.The total chlorophyll concentration was 44.49 mg/L,the ammonium removal rate was 38.92 mg/L/d and the nitrate removal rate was 11.77mg/L/d.The dominant genera unidentified_Cyanobacteria and Paenibacillus improved the removal efficiency of nitrogen and the flocculation of microalgal bacterial consortia.3)The suitable illumination conditions for microalgal bacterial consortia were explored,and the characteristics of microbial community under different illumination conditions were analyzed.When the light period and intensity were 24 h and 8000 Lux,the efficiency of piggery digestate treatment was the highest.The efficiency of photosynthesis in microalgae and unidentified_Cyanobacteria were improved by the increase of light period.The relative abundance of unidentified_Cyanobacteria,total chlorophyll concentration and ammonia removal reached best under 24 h illumination,which were54.24% and 24.32 mg/L and 49.18%,respectively.Some bacteria were sensitive to illumination,so the dark period improved the richness of bacterial community in microalgal bacterial consortia.Microalgae in piggery digestate grew well under the light intensity from 5000 to 25000 Lux,and the structure of bacterial communities were similar attributing to the shading effect of microalgae.When the light intensity was8000 Lux,the biomass production and nutrients removal were the highest.The total chlorophyll concentration was 32.33 mg/L,and the removal of ammonium,nitrate,nitrite and total phosphorus were 100%,97.51%,91.26% and 95.98%,respectively.The dominant genera were Paenibacillus ? Castellaniella and unidentified_Cyanobacteria.4)The feasibility of the optimized microalgal bacterial consortia for continuously piggery digestate treatment under the optimized operation conditions was verified,and the changes of bacterial community structure and function under different influent nitrogen centrations were revealed.When ammonium loading was 240 mg/L,the efficiency of piggery digestate treatment was the highest with the total inorganic nitrogen removal was 45.62 mg/L/d,and the effluent reached emission standards.The ammonium loading was the most important factor affecting the microbial community structure and function in a photoreactor for piggery digestate treatment.When ammonium concentration was excess,the diversity of bacterial community was higher,and the community function was more complex with two indicator function modules for nitrification and denitrification.The microalgal bacterial consortia was suspend under low ammonium loading(130-330 mg/L),and the main pathway of ammonia removal was assimilation of microalgae.The microalgal bacterial biofilm was formed under high ammonium loading(420-550 mg/L),where Nitrosomonas proliferated in large numbers with high efficiency of ammonia oxidation.Moreover,the dominant genera Thauera,Comamonas and Arenimonas contributed to the formation of microalgal bacterial biofilm.The above results provided theoretical and practical significance for application of microalgal bacteria consortia in piggery digestate treatment.