Study On The Effectiveness And Mechanism Of Anaerobic Bioreduction Of Cr(?) Enhanced By Sludge Lysate

As an essential industrial material,chromium(Cr)is widely used in industrial manufacturing,leading to its inevitable release into the surrounding environment.The effects of chromium-containing wastewater on the environment and human beings are well known.Biological method is the main method for the treatment of low and middle concentrations of chromium-containing wastewater.It has the advantages of environmental protection,low cost,high efficiency and no secondary pollution.However,the problem of insufficient carbon source is often accompanied during the actual process of biological treatment.An external carbon source is often required to ensure high biological efficiency.This study proposed use of excess sludge lysate containing multiple organic substances enhanced Cr(?)biological treatment process:that is,the use of easily degradable organic matters as a cometabolic substrate and electron donor improve the activity of biological metabolism;humic acid organic matters as complexation adsorbents and redox mediators enrich metabolic pathways and accelerating Cr(?)degradation,and realize the resource utilization of excess sludge and efficient removal of Cr(?).The excess sludge is pretreatment by the thermal and alkali process to prepared sludge lysate(SL).The SL was added to Cr(?)anaerobic bioreduction system to investigate its effect on Cr(?)bioreduction.The results showed that when Cr(?)concentration was 20.4 mg/L,51.5 mg/L and 98.2 mg/L respectively,the removal rate of Cr(?)in the bioaugmentation group increased by 26.6%,55.8% and 29.6%compared with the control group without SL.When Cr(?)concentration was27.44±4.570 mg/g in the per unit of wet sludge,about 87.8% and 49.0% of the total Cr was distributed among activated sludge in bioaugmentation and control group,respectively.In both groups,intercellular Cr accounted for 87.2% and 46.5% of the total Cr.It is indicated that the existence of the SL enhances the anaerobic biological reduction of Cr(?)and causes more Cr(?)to be reduced and immobilized in the cell.Furthermore,humic acid(SHA)was extracted from SL was added to the anaerobic bioreduction system of Cr(?)to investigate its bioaugmentation mechanism of Cr(?)anaerobic bioreduction.The results showed that 98.21 mg/L Cr(?)was completely reduced after 24 h with a removal rate increased by 34.3%compared with that of the control group without SHA in the presence of 300 mg/L SHA.The results of elemental analysis showed that the O/C and H/C of SHA were0.52 and 1.69 respectively,indicating that it contains more oxygen-containingfunctional groups and can be adsorbed and complexed with pollutants in the environment.The results of three-dimensional fluorescence spectroscopy and fluorescence quenching analysis showed that SHA can adsorb and complex with Cr(?),and the amount of adsorption and complexation is 34.4 mg/g.The results of electrochemical activity measurement showed that the cyclic voltammetry curve of SHA has obvious oxidation-reduction symmetry peaks.And in the presence of different concentrations of SHA,the redox potential of Cr(?)anaerobic bioreduction system was about 10 mV-70 mV lower than that of the control group.It indicated that SHA has the properties of redox mediators.In addition,the high-throughput sequencing results showed that the abundance of electroactive bacteria such as Acinetobacter,Pseudomonas and Arcobacter increased in the Cr(?)anaerobic bioreduction system containing SL.Electrochemically active bacteria could utilize the additional redox mediators to move metabolically produced electrons to cell surfaces to further accelerate electron transport.It is further proves that the redox mediators of SHA.SHA enhances the anaerobic bioreduction process of Cr(?)by the adsorption and complexation reaction with Cr(?)and acting as a redox mediator,which increases the microbial degradation pathway of Cr(?).