Biological Purification Pathway Of Dichlorobenzene And Performance Enhancement

Volatile organic compounds?VOCs?,which have strong photochemical activities,are main precursors to cause urban grey haze,ozone pollution and photochemical smog.Chlorinated volatile organic compounds?CVOCs?are the major components of VOCs,it would produce toxic by-products when treated by physical-chemical methods,in contrast,the biological purification technology showed obvious advantages in reducing toxic by-products.The hydrophobicity and difficulty in biodegradation of CVOCs are the key factors which limited the development and application of biological purification technology.Therefore,researches and developments of efficient and stable biological removal technology aim at hydrophobicity and difficulty in degradation of CVOCs:improving of mass transfer rate of CVOCs between different phases and enhancing the adaptability of microorganism's degradation and microbial activity are important aspects for enhancing biological purification of hydrophobic and refractory CVOCs.In this study,the typical CVOCs,1,2-Dichlorobenzene and 1,3-Dichlorobenzene,were selected as the target pollutants,the strains named Bacillus cereus DL-1 and Brevibacillus agriDH-1 were inoculated to purify the 1,2-dichlorobenzene and1,3-dichlorobenzene respectively.The growth and degradation kinetics were elucidated by GC?GC/MS?IC and enzymology technology,and the degradation pathway of dichlorobenzene removal was alsofurther studied.On this basis,rhamnolipid,Fe³⁺and Mg²⁺wereadded to the bio-removal system to investigate the strengtheningmechanism through analysis of biological indicators,chemical indicators and surface characteristics of bacteria.The enhanced performance of removal of gaseous dichlorobenzene was studied by adding rhamnolipid,Fe³⁺and Mg²⁺in the biotrickling filters.The main results and discussions in this study are listed as follows:?1?Firstly,the growth kinetics of Bacillus cereus DL-1 and Brevibacillus agriDH-1 for 1,2-dichlorobenzene and 1,3-dichlorobenzene are consistent with Haldane-Andrews model and the purification process meets pseudo-first-order degradation kinetics model.Furthermore,it is found that the intermediates of 1,2-dichlorobenzene degradation include chlorobenzene,benzene,phenol and2-chlorophenol,and the main intermediates of 1,3-dichlorobenzene are chlorobenzene andphenol.Thedegradationprocedureof1,2-dichlorobenzeneand1,3-dichlorobenzene withBacillus cereus DL-1 and Brevibacillus agri DH-1 strains follows the specific path of"dechlorination before opening the loop",that is to say the benzene ring is ortho open-loop,which happened after dechlorination.?2?The optimal concentration of rhamnolipid,Fe³⁺and Mg²⁺were 120 mg/L,4mg/L and 2 mg/Lrespectively for enhancing 1,3-dichlorobenzene removal.All of the three additives,rhamnolipid,Fe³⁺and Mg²⁺,can increase the content of polysaccharides and proteins EPS in DL-1 bacteria,the biological activity of catechol-1,2-dioxygenase(C₁₂O)was also enhanced.Rhamnolipid significantly increased the cell hydrophobicity and decreased Zeta potential of strain DL-1.The experiments results of fourier transform infrared spectrum analysis showed that hydrogen bonds were formed between rhamnol hydroxyl groups and amino acids on the surface of bacteria when rhamnolipid was solely added,which significantly increased the cell hydrophobicity,decreased the Zeta potential of strain DL-1,enhanced the capture ability of bacteria for hydrophobic substances and strengthened the interphase mass transfer between matrix and solution.?3?When the additive was added as a combination(rhamnolipid+Fe³⁺,rhamnolipid+Mg²⁺,Fe³⁺+Mg²⁺and rhamnolipid+Fe³⁺+Mg²⁺),the secretion of DL-1bacteriaproteinincreasedandtheenzymaticactivity ofcatechol-1,2-dioxygenase was improved compared to the sole additive.The addition of combination of Fe³⁺and Mg²⁺leads to the decreasing of critical micelle concentration of rhamnolipid and 17.40 times increasing of 1,2-dichlorobenzene apparent solubility,and enhances the contact between DL-1 strain and1,2-Dichlorobenzene.FTIR and XPS results showed that the functional groups of EPS in DL-1 bacteria had complexation reactions with metal ions Fe³⁺and Mg²⁺,and the presence of rhamnolipid promoted the interaction among oxygen-containing functional groups and metal ions(Fe³⁺and Mg²⁺).The interaction between metal ion(Fe³⁺or Mg²⁺)and functional group on the surface of DL-1 bacteria is enhanced when Fe³⁺and Mg²⁺are exist simultaneously.?4?The addition of 120 mg/L rhamnolipid,4 mg/L Fe³⁺and 2 mg/L Mg²⁺can improve the performance of biotrickling filter for 1,2-dichlorobenzene removal,the start-up time was shortened by 5 days,the removal efficiency in the startup phase is increased by about 11%.In steady operation stage,the removal efficiency wasincreased by 14.84%,and removal capacity of BTF wasincreased above to 8.20g/?m³·h?,the proportion of dominant bacterial species Bacillus cereus DL-1 in the reactor was increased by 6.11%.The addition of 170 mg/L rhamnolipid and 2 mg/L Mg²⁺can improve the performance of biotrickling filter for 1,3-dichlorobenzene removal,the start-up time was shortened by 7 days,the removal efficiency in the startup phase is increased by about 7.98%.In steady operation stage,the removal efficiency and removal capacity of BTF were improved,the removal efficiency was increased by 10.70%and the removal load was increased by 8.09 g/?m³·h?respectively,the proportion of dominant bacterial species Bacillus cereus DL-1 in the reactor was increased by 9.26%.In this thesis,surfactant-coupled metal ions are used to enhance the performance of biologically purified hydrophobic and refractory VOCs.This study can improve the technical system of biological purification for hydrophobic and refractory VOCs,and provide theoretical and technical support for regulating and controlling the biological purification performance for hydrophobic and refractory VOCs waste gas.