| A large amount of aluminum-containing wastewater had been produced during aluminum mining,electrolytic industry and aluminum-based coagulants production and application.These aluminum-containing wastewater entering the sewage biological treatment system will hinder the formation of cell membrane,slow down the growth rate of bacteria and change the microbial community structure,thus affect the flocculation and denitrification effect of activated sludge.In this study,the effects of Al3+ concentration on pollutant removal efficiency were investigated.The changes of sludge flocculation sedimentation were researched and extracellular polymeric substances(EPS)composition and structure were analyzed by three-dimensional excitation emission matrix(3D-EEM)and Fourier transform infrared spectrometer(FTIR).Sludge microstructure was determined by scanning electron microscopy-energy dispersive spectrometry(SEM-EDS).High-throughput sequencing was used to analyze microbial community structure,reveal the influence of Al3+ concentration on sludge properties and reaction mechanism in A2O process,and provide technical support for wastewater treatment plant containing aluminum.The results showed that low concentration of Al3+(<10 mg/L)promoted floes aggregation and improved sludge activity and flocculation,which was beneficial to the removal of COD,TN and ammonia nitrogen.When Al3+ concentration was 10 mg/L,removal efficiency of COD,TN and ammonia nitrogen was the highest(94.5%,86.7%and 99.5%).The sludge activity was the strongest,and the dehydrogenase activities in anaerobic,anoxic and oxic zones were 38.7,41.3 and 40.9 mg TF/(L·h),respectively.The nitrification activity of sludge was 12.12 mg O2/g(MLSS)·h and the flocculation ability(FA)in anaerobic,anoxic and oxic zones were 36.0,45.0%and 44.7%,respectively.When Al3+ concentration was 30 mg/L,Zeta potential of anaerobic,anoxic and oxic sludge were highest and they were-18.2,-17.3 and-25.4 mV,respectively.The addition of Al3+ could promote the secretion of loosely bound EPS(LB-EPS)and tightly bound EPS(TB-EPS)and increase protein(PN)concentration and polysaccharide(PS)concentration.When Al3+ concentration was 10 mg/L,PN/PS ratios in anaerobic,anoxic and oxic zones were the highest(PN/PS ratios of LB-EPS were 6.3,10.7 and 1.9,and PN/PS ratios of TB-EPS were 0.51,0.53 and 0.47).The tryptophan-like fluorescence peaks were detected in the LB-EPS and TB-EPS when Al3+ was not added.When Al3+ concentration was 10 mg/L,the fluorescence peaks of fulvic acid-like and tryptophan-like began to appear.The FTIR analysis showed that the addition of Al3+ had little efifect on the structure of LB-EPS and TB-EPS functional groups.The physicochemical properties and physical structure of sludge was changed with the increase of Al3+ concentration.When Al3+ concentration was increased to 10 mg/L,sludge particles became tight,and the coexistence of coarse,medium and fine particles was more obvious.The addition of Al3+ increased the adsorption sites of activated sludge.The sludge was mainly mesoporous structure,and the specific surface area was the smallest when Al3+ concentration was 10 mg/L,and the specific surface areas of sludge in the anaerobic,anoxic and oxic zones were 5.0,7.1 and 9.8 m2/g,respectively.The addition of Al3+ replaced trace Fe3+ with a large atomic radius in the microorganisms.The microbial community structure of sludge was similar under anaerobic,anoxic and oxic conditions.When Al3+ concentration was 0mg/L,the similarity between oxic zone and anoxic zone was the highest.When Al3+ concentration was 10 mg/L,the similarity was the highest between anaerobic zone and oxic zone.When the Al3+ concentration was 40 mg/L,the similarity was the highest between anaerobic zone and anoxic zone.The addition of aluminum salt directly affected the microbial community structure.Proteobacteria and bacteroidetes were the dominant phyla,and betaproteobacteria and rhizobiales were the dominant order.These bacteria played an important role in removing pollutants from wastewater.The changes of pH significantly affected the composition of EPS.Alkaline conditions were more conducive to the removal of COD,TN and ammonia nitrogen than acidic conditions.Higher acids and lower bases could promote the secretion of EPS,PN and PS.The presence of Al3+ might stimulate microbial growth and enhance the ability of microorganisms in sludge to resist pH shocks. |
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