Promotion Effect Of Filamentous Bacteria On Bioleaching Of Heavy Metals From Contaminated Sediment

In this work I have carried out bioleaching experiment of heavy metal contaminatedsediments from zhuzhou xiawan harbor by Acidithiobacillus ferrooxidans and FilamentousBacteria and investigated the effect of filamentous bacteria on the removal rate of heavymetals. Results indicated that filamentous bacteria could alleviate the toxic effect of lowmolecular weight organic acids on Acidithiobacillus ferrooxidans and promote the removal ofheavy metals. Hence, it is feasible that the filamentous bacteria might be used for bioleachingof sediment contaminated with metals coupled with organic compounds because it has apromotion effect on the removal of heavy metals.The bioleaching process may be defined as the solubilization of metals fromsolid substrates either directly by the metabolism of leaching bacteria or indirectly bythe products of metabolism．Bioleaching processes are based on the ability ofmicroorganisms to transform solid compounds and result in soluble and extractableelements which can be recovered. Metal solubilization from solid wastes or othersolids is achieved through a variety of acidophilic and chemoautolithotrophic bacteria such asAcidithiobacillus ferrooxidans and AcidiAcidithiobacillus thiooxidans. It has been paid greatattention in recent years due to its low cost and high efficiency and good dehydrationcapability after bioleaching. Bioleaching has proved to be a possible way to remove heavymetals from metal contaminated materials such as anaerobically digested sewage sludge,contaminated river sediment，spent nickel-cadmium batteries， tannery sludge and incineratorfly ash．The process of bioleaching by Acidithiobacillus ferrooxidans has been inhibited by avariety of parameters. In which dissolved organic matters particularly small molecular weightorganic acids have a strong inhibitory effect on the oxidation of ferrous ions byAcidithiobacillus ferrooxidans. Most of the current study only investigate the removal effectof heavy metals by bioleaching but a majority of sediments have been contaminated withmetals coupled with organic compounds.Sediments of Zhuzhou Xiawan harbor was seriously polluted by heavy metals. The maximum concentration of Cu, Cd, Pb, Zn reached460mg/kg,100mg/kg,1040mg/kg,4000mg/kg respectively, greatly higher than the Environmental Quality Standard. Futhermore, theconcentration of dissolved organic matters was relatively high, a mass of small molecularweight organic acids may be produced during bioleaching and consequently affect theremoval of heavy metals.Influence of small molecular weight organic acids on the oxidation of ferrous ions wasstudie during the bioleaching. We also investigated the effect of filamentous bacteria on theremoval rate of heavy metals. Results indicated that filamentous bacteria could alleviate thetoxic effect of low molecular weight organic acids on Acidithiobacillus ferrooxidans andpromote the removal of heavy metals. pH could reduce to less than2within5days ofbioleaching and ferrous iron was completely oxidized in4days with10%of the inoculumscontaining filamentous bacteria. Removal efficiencies of76.3%for Cu,92.5%for Cd,52.6%for Pb, and88.5%for Zn were obtained after10days of bioleaching. The time needed forachieving the greatest removal efficiencies advanced for1～2days. The promotion effect onremoval of Pb was the most evident in all4kinds of heavy metals as the removal efficiencyhas doubled. Hence, it is feasible that the filamentous bacteria might be used for bioleachingof sediment contaminated with metals coupled with organic compounds because it has apromotion effect on the removal of heavy metals.