Temperature Effect On Microbial Activity,and Heavy Metals Bioavailability During Co-Bioevaporation Process

Bioevaporation is a novel technology for treating highly concentrated organic wastewater.The continuous co-bioevaporation process had a significant removal performance on food waste(FW)and concentrated landfill leachate(CLL).The microbial community structure and biological enzyme activity have close relation with the efficiency of bio-evaporation using microbial metabolic activity to achieve the ideal removal effect of pollutants.In addition,the bioevaporation process is accompanied by dynamic changes in sludge bed temperature.Therefore,it is significance to study the effect of temperature on the succession of microbial communities and key enzyme activities during bioevaporation.At the same time,as the CLL is continuously added,the heavy metal content in the matrix will accumulate on a turn-by-turn basis.Therefore,exploring changes in bioavailability of heavy metals during the bioevaporation process is of great significance in effectively assessing and controlling the environmental risks of heavy metals.The objective of the present work was to gain a comprehensive insight into the temperature effect on enzymatic activity,microbial community and heavy metals bioavailability during co-bioevaporation process.In this aim,the 5 cycles co-bioevaporation process was divided into seven stages(beginning,warming stage(30 ~oC,50 ~oC),top-temperature,cooling stage(50 ~oC,30~oC),ending).Three hydrolases(i.e.,protease,urease and phosphatase)and dehydrogenases were selected to analysis the enzyme activity in different temperature stages of the 5 cycles co-bioevaporation process.Bacterial community composition and structure were analyzed using High-throughput sequencing data.The in-situ distribution of Live/Dead bacteria on the sludge particles was observed by the confocal laser scanning microscopy(CLSM).In addition,Cu,Zn,Pb,Ni,Hg,Fe,Cr,Cd and As were selected as the model heavy metals to measure the concentration and speciation,moreover,the bioavailability of heavy metals was also analyzed.The results showed that temperature had a great impact on the release of dehydrogenase,protease,urease and phosphatase.The maximal dehydrogenase activity appeared at 30-50 ~oC in the warming stage.The maximal hydrolytic activity of microorganisms on macromolecular organic compounds(protein,urea and phosphorus-containing organic compounds)appeared at about 50 ~oC in the thermophilic phase.It was also found that Proteobacterica(1.3%-52.7%),Actinobacterica(4.8%-63.5%)and Firmicutes(32.6%-85.9%)were the dominant bacterial phyla during the entire co-bioevaporation process.Bacterial community structure was reconstructed in different temperature stages of co-bioevaporation process.Among all bacteria,Pseudomanas(uncultured_Tiopseudomonas,unclassified_Pseudomonas)preferred to grow in mesophilic phase,whereas thermophilic Bacillus and thermophilic actinomycetes were the dominant genus in thermophilic phase.Meanwhile,the image of bacterial in-situ distribution suggested that bacteria mainly gathered around the surface and pores of the sludge particles for aerobic metabolism.Bacteria were mainly gathered together on the surface and pores of the sludge particles for aerobic metabolism.The decreasing value of C_a/C_T showed the co-bioevaporation process could effectively reduce the bioavailability of heavy metals.