High-salinity Mustard Tuber Wastewater Treatment And Microbial Community Structure In Bioelectrochemical System

The resource treatment of high-salinity organic wastewater has always been a hotspot and difficulty in environmental research,especially the removal of nutrient in high-salinity wastewater.One technology that uses microorganisms as electrode catalysts to convert pollutants into electricity has attracted great attention.This new technology,called the bioelectrochemical system(BES),has been widely used in the resource treatment of pollutants,such as organic matter,heavy metals,and antibiotics.In recent years,BES has shown potential advantages in the removal of nutrients from low-salinity and low-concentration wastewater.However,under the high-salinity and high-concentration conditions,the removal efficiency and mechanism of nutrients,the evolution of related microbial community structure,and the species distribution of functional bacteria are still unclear.In this study,BES with different architectures(three-chamber microbial desalination battery,two-chamber microbial fuel cell and single-chamber microbial fuel cell)was constructed for high-salinity mustard tuber wastewater(MTWW)treatment to achieve efficient removal of nutrients.The migration and transformation rules and removal mechanism of nutrient in BES were explored.The effects of different environmental factors on the functional microbial community structure that affects the nutrient removal and system performance were investigated.(1)The efficient nutrient removal of high-salinity MTWW was realized in the three-chamber microbial desalination cell(MDC).Through migration,the removal efficiencies of NH₄⁺and PO₄^3-were as high as 99.8%and 99.3%,respectively.The NH₄⁺that migrated to the cathode chamber was further removed through the nitrification-denitrification process,which resulting in 90%of total nitrogen(TN)removal in each power generation cycle.The removal of PO₄^3-that migrated to the anode chamber was poor,which was only 4-11%in each power generation cycle.In addition,the SO₄^2-that migrated to the anode chamber was effectively reduced in the anaerobic environment.The removal of SO₄^2-in each power generation cycle was about 88.1-92.8%.Efficient reduction of SO₄^2-might lower the power generation of the system,thereby adversely affecting the migration and removal of nutrient.The COD removal efficiencies in anode and cathode were excellent,and the average removals were 94.6%and 94.2%in a desalination cycle,respectively.The BMDC showed stable power output for 150 days.OCVs and MPDs were 853 m V and 6.63 W m^-3,864 m V and 7.15 W m^-3,859 m V and 6.70 W m^-3,855 m V and 6.55 W m^-3,and 866 m V and 7.88 W m^-3 on days 20,45,90,125,and 150,respectively.The microbial community analysis showed that the relative abundances of electrgenic bacteria in anode and cathode were 23.18%and 16.50%,respectively,which greatly promoted electricity production and the removal of nutrient.The genera norank?f?Nitrosomonadaceae and norank?f?Xanthomonadaceae were the main nitrifying bacteria in cathode biofilm.The genera Thaurea,unclassified?f?Comamonadaceae,Pseudomonas,Paracoccus,norank?f?Xanthomonadales,norank?f?Saprospiraceae and unclassified?f?Chitinophagaceae were the main denitrifying bacteria in cathode biofilm.(2)Electrode denitrification for nitrogen and phosphorus removal was successfully achieved at the cathode in the dual-chamber microbial fuel cell(MFC)for MTWW treatment.The removal efficiencies of TN and TP were 98.83%and 91.72%,respectively.The electrode denitrification and phosphorus removal system showed good impact resistance to salinity changes.The removal rates of TN were 98.68±1.13%,98.46±1.23%,98.26±0.93%,and 91.55±1.19%at the salinity of 25,30,35 and 40 g L^-1,respectively.The removal efficiency of TP remained stable at around 90%.The analysis of microbial community showed that the high enrichment of electrotrophic denitrifying bacteria in the cathode biofilm has greatly promoted nitrogen removal.Arcobacter,Lentimicrobium,Trichococcus and Caldithrix were the main bacteria that were responsible for electrode denitrification,with the relative abundance of 25.4%.The phosphorus was mainly removed in the form of calcium hydroxyphosphate by chemical precipitation.(3)In the double-chamber MFC,anaerobic activated sludge was used as cathode inoculation to realize simultaneous nitrogen and phosphorus removal,and electricity generation for MTWW treatment.When the dissolved oxygen(DO)concentrations in cathode were 2.0,2.8,3.7,and 4.9 mg L^-1,the NH₄⁺removal rates were 96.1±1.0%,97.6±0.6%,98.3±1.4%,and 98.4±0.8%;TN removal rates were 91.5±1.2%,90.6±0.8%,89.8±1.0 and 87.7±0.6%;TP removal rates were 69.7±0.9%,72.9±1.0%,76.3±0.8%and 80.8±1.0%,respectively.Under different DO concentrations,the anode and cathode COD removals were excellent,which were above 90%.DO had a significant impact on the electricity generation performance of MFC.When the DO were 2.0,2.8,3.7 and 4.9mg L^-1,the maximum output voltages were 284 m V,334 m V,377 m V and 415 m V;OCVs and MPDs were 680 m V and 0.70 W m^-3,723 m V and 0.93 W m^-3,750 m V and 1.19 W m^-3,and 760 m V and 1.45 W m^-3;coulombic efficiencies(CEs)were 11.3±0.9%,13.0±0.6%,15.1±0.8%and 17.8±1.0%,respectively.The microbial community analysis of cathode biofilm showed that Nitrosomonas and SM1A02 were the main autotrophic nitrifying bacteria;Thaurea,Stenotrophomonas,Flavobacterium and Marinobacter were the main heterotrophic nitrifying bacteria.The denitrifying bacteria were mainly composed of Oceanimonas,Saprospiraceae?uncultured(Anaerobic denitrification),and Thauera,Stenotrophomonas,Flavobacterium,Marinobacter(aerobic denitrification),and Thioalkalispira(autotrophic denitrification).The genera Saprospiraceae?uncultured and Flavobacterium were the main bacteria which were in charge of phosphorus removal.(4)The cathode of double-chamber MFC was sequentially inoculated with denitrification and nitrification sludges to construct mixed biofilm electrode for the removal of nutrient from MTWW.When operating in aeration/non-aeration mode under different COD/TN ratios(2.8,5.2,7.5 and 9.8),the removal rate of TN was 100%;and the removal rates of TP were 91.5±0.9%,92.7±0.7%,89.4±0.6%and 91.7±0.8%,respectively.The OCVs under aeration and non-aeration conditions were in the range of718-728 m V and 581-615 m V;MPDs were 0.77-0.87 W m^-3 and 0.25-0.33 W m^-3;the CEs were 14.2±0.4%,14.1±0.7%,13.7±0.6%and 14.2±0.5%,respectively.In addition,the MFC ran stably for 450 days at the COD/TN ratio of 5.2.The preliminary energy balance analysis showed that the MFC obtained a net energy output of 370.29-661.76 k J kg^-1 N.Besides,the microbial community analysis confirmed that SM1A02(autotrophic nitrification)and unclassified?f??Rhodobacteraceae,Halomonas,Thaurea(heterotrophic nitrification)were the main bacterial which were responsible for NH₄⁺oxidation.Denitrifying bacteria,including Oceanimonas,Xanthobacter,Azoarcus(anaerobic denitrification),and Halomonas,unclassified?f??Rhodobacteraceae,Thaurea(aerobic denitrification)had been enriched in cathode biofilm.Xanthobacter,Azoarcus and Thaurea also undertook the task of electrochemical denitrification.Halomonas was responsible for the phosphorus removal.(5)Simultaneous nitrogen and carbon removal and electricity production for MTWWtreatment in single-chamber MFC were realized.When the COD/TN ratios were2.4,5.6,8.7 and 11.1,the NH₄⁺removal rates were 51.41±0.86%,83.98±0.78%,88.92±0.89%,and 93.03±0.86%;the TN removal rates were 51.28±1.12%,83.59±1.02%,88.56±0.69%and 92.59±0.89%,respectively.Under different COD/TN ratios,the OCVs were 547±6 m V,553±5 m V,525±4 m V,and 508±6 m V;the MPDs were 14.91±0.69 W m^-3,15.32±0.54 W m^-3,12.32±0.63 W m^-3 and 9.86±0.71 W m^-3;the CEs were 13.31±0.89%,10.04±0.69%,8.16±0.78%and 8.69±0.85%,respectively.The phosphorus removal was poor under different COD/TN ratios,with the removal rates of16.49±0.96%,15.02±0.26%,15.92±0.78%and 16.03±0.85%,respectively.The microbial community analysis showed that Thaurea,Lentimicrobium,unclassified?f??Rhodobacteraceae and unclassified?f??Rhodocyclaceae were the main denitrifying bacteria in the anode biofilm.The bacteria related to denitrification in cathodic biofilm included heterotrophic nitrifying-aerobic denitrifying bacteria and anaerobic denitrifying bacteria.The genera unclassified?f??Rhodobacteraceae,Thaurea and Paracoccus were the main heterotrophic nitrifying-aerobic denitrifying bacteria.Vitellibacter,unclassified?f??Rhodocyclaceae and Lentimicrobium were the main anaerobic denitrifying bacteria.The distribution of the electrgenic bacteria was as follows:anode biofilms,Thaurea and Lentimicrobium;cathode biofilms,Thaurea,Paracoccus and Lentimicrobium.(6)Considering the pollutant removal efficiency and power generation of different BES systems,the single-chamber MFC was the best optimal BES system for high-salinity MTWW treatment.Although the diversity,absolute abundance and distribution of species of microbial communities in different BES were quite different,the functional microorganism groups involved in the denitrification process were similar.In the high-salinity condition,the heterotrophic nitrification-aerobic denitrification and electrode denitrification microorganisms became the common dominant functional floras in different BES.Thauera,Paracoccus,Lentimicrobium and unclassified?f??Rhodobacteraceae were the key bacteria which were responsible for heterotrophic nitrification-aerobic denitrification and electrode denitrification.