Novel Biofilm Reactors Using For Remediation Of Arsenic Contaminated Water And Their Molecular Basis Study

Arsenic contamination in groundwater and acid mine drainage(AMD)is a severe environmental problem faced by humanbeings.Two populations of arsenite-oxidizing microorganisms which were enriched respectively from neutral soil sample and acid soil sample from the tailing of the Shimen realgar mine was used to generate biofilms on the surfaces of perlites to construct two types of biofilm reactors.The one constructed with the microorganisms from the neutral soil sample is used for remediation of arsenic contaminated groundwater,the other constructed with microorganisms from acid soil sample is used for oxidizing arsenite in AMD.The first one is able to completely oxidize 1.1 mg/L As(?)dissolved in simulated groundwater(pH 6.8~7.0)into As(V)within 10 min;after 140 days of operation,approximately 20 min were required to completely oxidize the same concentration of As(?).Analysis for the 16 S rRNA genes of the microbial community showed that Bacteroidetes and Proteobacteria are dominant in the reactor.Six different bacterial strains were randomly isolated from the reactor.Function and gene analysis indicated that all the isolates possess arsenite-oxidizing activity,and five of them are chemoautotrophic.Further analysis showed that a large diversity of AioAs and two types of RuBisCOs are present in the microbial community.This suggests that many chemoautotrophic arsenite-oxidizing microorganisms were responsible for quick oxidation of arsenite in the reactor.We also found that the reactor is easily regenerated and its number is readily expanded.To the best of our knowledge,the arsenite-oxidizing efficiency,which was expressed as the minimum time for complete oxidization of a certain concentration of As(?)under a single operation,of this bioreactor is the highest among the described bioreactors;it is also the most stable,economic and environment-friendly.The second reactor is operated to oxidize As(?)in synthetic acid mine drainage at pH 4.0.It is able to oxidize 120 mg/L As(?)in synthetic AMD to As(V)in 24 hours.When As(?)concentration decreased to 20 mg/L,4.5 hours are needed to oxidize As(?)completely.The arsenic-oxidizing ability of the reactor under different pH conditions was also investigated.At pH 3.5,it took 6.5 hours to oxidize all 20 mg/L As(??)in synthetic AMD;at pH 3.0,after 18 hours' operation,there is still 6 mg/L As(?)remaining for oxidizing in the synthetic AMD.A transpatent first order kinetic model was used to get a more quantitative assessment of As(?)oxidation rates of the reactor under different working conditions.Rate constant(kobs)decreased as the pH changed from 4.0 to 3.0,which may be due to the acid in the water restrained the activity of the oxidase of the bacteria in the biofilm reactor.Images of environmental scanning electonical microscopy showed that condese boifilms formed on the surface of perlites,suggesting that As(?)oxidizing occuring in the reactor was carried out by biofilm generated from a population of microorganisms.Analysis for the 16 S rRNA genes of the microbial community showed that Proteobacteria is dominant in the reactor.Further analysis showed that a relatively small diversity of AioAs are present in the microbial community.This suggests arsenic-oxidizing microbes living in acid conditions are much less than those living in neutral conditons.To our knowlegde,this biofilm reactor is the first used for remediation of arsenic in acid mine drainage by oxidizing the As(?)in the synthetic acid mine drainage.Taken together,two types of arsenic oxidizing biofilm reactors generated from the microbial population from neural soil and acid soil.The arsenic-oxidizing ablility,molecular basis of both reactors were investigated.