Performance And Mechanism Of Cr(Ⅵ) Removal From Water By Biological Method Using Corn Cob As Carbon Source

With the continuous development of China’s industrialization,the problem of Cr(Ⅵ)pollution in water has become more and more serious,causing widespread concern.Microbiological method is considered to be one of the most promising Cr(Ⅵ)remediation technology due to its advantages of low energy consumption,environmental friendliness and reusability.However,the lack of carbon source is an important factor limiting the treatment performance of wastewater containing Cr(Ⅵ),and it is difficult to control the addition amount of external liquid carbon source,which is easy to lead to secondary pollution.Therefore,in recent years,the substitution of solid-phase carbon source for traditional liquid-phase carbon source mediated microbial has gradually become the focus of many researchers,among which agricultural waste is more popular because it is cheap and easily available as one of the options of solid-phase carbon source.In this study,the Cr(Ⅵ)removal performance of microbial system with corn-cob as solid carbon source was investigated,and the reduction and removal path and mechanism of the bioreduction were clarified.At the same time,the Cr(Ⅵ)removal performance,distribution of microorganisms and reaction mechanism along the reactor also were analyzed.The main conclusions are as follows:(1)The corn-cob contained abundant organic carbon,which could be used by microorganisms.It suggested that 286.76±6.22 mg/L of dissolved organic carbon could be continuously released by 1 g corn-cob,which could provided sufficient carbon source for the Cr(Ⅵ)bioreduction process.At the same time,Corn-cob has good structural durability and long-term carbon release efficiency,and the removal load of Cr(Ⅵ)per unit mass of corn cob can reach 28 mg/g.(2)The optimal operating conditions of the system were corn-cob dosage 5.0g/L,initial Cr(Ⅵ)concentration 10 mg/L,and initial p H 7.0.The reduction of Cr(Ⅵ)by microorganisms was an enzyme-mediated process.Cr(Ⅵ)can be reduced both extracellular and intracellular,and the extracellular reduction process dominated by membrane-related enzymes.(3)Compared with the uniformly packed reactor system(CQM),the gradient packed reactor system(CQG)enhanced the Cr(Ⅵ)removal rate at the inlet end of the corn-cob packed bed reactor,and promoted the CQG system to show higher tolerance and resistance to the change of Cr(Ⅵ)influent load.(4)Cellulomonas and Clostridium were abundant in both CQM and CQG systems,but there was another chrome-reducing bacterium(Delftia)with a relatively high proportion in CQG system.At the same time,corncob cellulosic degrading bacteria and heterotrophic Cr(Ⅵ)reducing bacteria played a synergistic role in different reaction chambers of the reactor to achieve a continuous and effective reduction and removal of Cr(Ⅵ).This study showed that corn-cob can be used as an economical and efficient solid-phase carbon source mediated microorganism to achieve Cr(Ⅵ)bioreduction,providing a new economical carbon source material for the biological treatment technology of Cr(Ⅵ)-containing wastewater.