Biological Treatment Of Acidic Selenium And Cadmium Wastewater With Limited Carbon Source Wastewater And The Microorganisms Community Characteristics

Selenium usually coexists with other heavy metal ions（such as Cd（II））in acidic wastewater,which has a low pH（pH 2.0 to 5.0）and the concentration of organic carbon source is very limited.At present,the research on the biological treatment of selenium and cadmium wastewater generally requires higher external carbon source,which increases the treatment cost.The main aim of this work was to evaluate the simultaneous removal of Se（IV）and Cd（II）of acidic wastewater with limited carbon source by activated sludge and anaerobic granular sludge.The Se（IV）and Cd（II）removal mechanism were investigated by scanning electron microscope and x-ray energy dispersive spectroscopy（SEM-EDS）,high solution transmission electron microscopy（HRTEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,fourier transform infrared spectroscopy（FTIR）and dynamic light scattering（DLS）analyses.The structure characteristics of microbial community in activated sludge and anaerobic granular sludge were analyzed by high-throughput sequencing technology.The main conclusions are as follows:（1）Sequencing batch reactor（SBR）inoculated with activated sludge was used to treat low carbon source（50-100 mg/L）acidic（pH 4.0）,selenium（3.6 mg/L）and cadmium（5.6 mg/L）contained wastewater.Under the influent COD of 100 mg/L,selenium（97.50±3.25%）and cadmium（98.07±1.53%）in acid wastewater can be effectively removed.Protein and polysaccharide in EPS can promote the removal of Se（IV）and Cd（II）.SEM-EDS,HRTEM,XPS and FTIR analyses indicated that reduction and adsorption were the main mechanisms for Se（IV）and Cd（II）removal;the average size of Se（0）and Cd Se nanoparticles on the surface of microorganisms was 4 nm;the functional groups of-OH,C-O,C=O and O-C=O play an important role in the biological removal of Se（IV）and Cd（II）.（2）The analysis of activated sludge microbial community showed that Proteobacteria and Bacteroidetes were the dominant phyla,which had strong ability to remove Se（IV）and Cd（II）;Clostridium＿sensu＿stricto＿1,Pseudomonas and Zoogloea have strong ability to remove Se（IV）and Cd（II）.（3）Sequencing batch reactor（SBR）inoculated with anaerobic granular sludge was used to treat acidic（pH 4.0）,selenium（7.9 mg/L）and cadmium（11.2 mg/L）contained wastewater.Under the influent COD of100 mg/L in period I（1～40 cycles）,the cadmium average removal efficiency was 96.67±2.70%.While in the first 16 cycles,of phase I,the average removal efficiencies of total Se and Se（IV）were 97.07±3.17%and 98.86±1.84%,respectively.Under the influent COD is 50 mg/L in phase II（41～100 cycles）,the cadmium and selenium removal efficiencies were not ideal.SEM-EDS、DLS、XRD、FTIR and XPS analyses indicated that reduction and adsorption were the main mechanisms for Se（IV）and Cd（II）removal;the average particle sizes of Se（0）and Cd Se nanoparticles on the surface of microorganisms were 491 nm（phase I）and 370 nm（phase II）,respectively;the functional groups of C-O,C=O,O-C=O,-NH₂ and-N≡O played an important role in the biological removal of Se（IV）and Cd（II）.（4）The results of bacterial community analysis of anaerobic granular sludge showed that Proteobacteria,Synergistota and Firmicutes were the dominant bacteria at the phylum level.While Burkholderiae,Comamonadaceae and Pseudomonadaceae,which have the ability to remove Se（IV）and Cd（II）,were dominant at the family level in the anaerobic granular sludge.The analysis of archaea community structure showed that Methanosaeta and Methanobacterium had strong tolerance to selenium and cadmium.This study confirmed the feasibility of microbial removal of selenium and cadmium from low carbon source（100 mg/L）acid wastewater,which can provide reference for the treatment of limited carbon source acid selenium and cadmium wastewater and the study of microbial characteristics.