Characteristics And Mechanism Of Heavy Metal/Selenite Treatment By Selenite Reducing Bacteria

Selenium and selenium-containing compounds are widely existed in the natural environment.Human activities such as mining,coal burning,glass manufacturing,and the petroleum industry have accelerated the migration and accumulation of selenium species.The selenium pollution in surface and groundwater have threated the health of humans and other organisms.Microbiological treatment of selenium-containing wastewater has attracted researchers' attention because of its feature of low energy consumption and has no secondary pollution.However,selenium-containing wastewater is usually contains various heavy metals.Since microorganisms have limited tolerance to heavy metals,this method has certain limitations in practical applications.Selenite was reduced by the Bacillus cereus strain CC-1,which was isolated and kept by our laboratory previously.In this study,the biogenic selenium nanoparticles were firstly purified by NaOH treatment.The surface biomass was largely removed according to the results of SEM and EDS.The purified selenium nanoparticles were then used to adsorb lead ions,and the effects of adsorption time,lead ion concentration,pH,and sodium chloride concentration on the lead adsorption capacity were investigated.It was found that when the concentration of selenium nanoparticles was 250 mg·L-1,the adsorption capacity increased with the increase of lead concentration;when the lead ion concentration was 40 mg·L-1,the adsorption reaction reached equilibrium at 480 min,and the adsorption capacity was 139.7 mg·g-1.Increasing the pH and sodium chloride concentration resulted on the decrease of adsorption capacity.In addition,the experiment also explored the adsorption capacity of the nanoparticles for various metal ions,such as zinc,copper and cadmium.And the selective adsorption characteristics for the coexistence solution of multiple metal ions was explored.It was found that selenium nanoparticles have good adsorption properties for heavy metal ions such as zinc and cadmium.In addition,this study also investigated the simultaneously lead ions and selenite removal capacity of strain CC-1.There is no obvious effect on the growth of CC-1 when the lead ion concentration is 0.1-1 mmol·L-1.When the strain CC-1 was directly incubated with lead ion and selenite,lead selenide nanoparticles were generated.Subsequently,it was found that the concentration change of selenite or lead ions effects the removal rate of both ions and the products morphology and crystal phases.It was found that the addition of lead ions would inhibit the reduction of selenite.Even when the concentration ratio of selenite to lead ions was 1:5,the removal rate of lead ions can still reach more than 90%.As the increasing concentration of lead ions,the morphology of the products changes from a rod-like structure with length longer than 1 ?m to dispersed particles less than 10 nm.Finally,the tolerance and reduction mechanism of CC-1 to lead ions,selenite,and coexistence of the two was explored through transcriptome sequencing and analysis.