| Biological method is one of the important purification technologies for VOCs,and mass transfer efficiency is a key factor affecting the efficiency of biological method.The macromolecules and strongly hydrophobic organics in VOCs have low mass transfer efficiency between gas phase-liquid phase-biological phase,which seriously affects the biological purification effect.Therefore,improving the mass transfer efficiency of macromolecular and hydrophobic VOCs is the key to improving the efficiency of biological purification of VOCs.In this experiment,hydrophobic toluene was selected as the target pollutant,and rhamnolipid was used as the surfactant to build two identical bio-trickling filter(BTF)systems.The removal efficiency,mineralization rate and biofilm surface hydrophobicity of the two biological trickling filter towers under different operating conditions were determined.The effect of adding rhamnolipid to biological treatment of toluene and the strengthening mechanism of surfactant were comparatively studied.The main findings are as follows:(1)The concentration of rhamnolipid was determined by experiments to be 100mg/L.At this concentration,the efficiency of microbial degradation of toluene was80.1%,and the promotion effect was obvious.Moreover,the amount of rhamnolipid metabolized by microorganisms at this concentration was 0.54 mg,and the degradation rate was lower.(2)After the system was successfully started,it was found that the removal efficiency of BTF1 with the addition of rhamnolipid was significantly better than that of BTF2 with the changes of toluene inlet concentration,gas residence time and inlet oxygen content.The results clarified that adding rhamnolipid in the filter tower can better cope with the effect of changes in experimental conditions on the performance of BTFs.It can not only promote the mass transfer effect of toluene between different phases,but also improve the ability of the whole system to resist load shock.(3)Based on the detection results of GC-MS and the KEGG database,it can be known that the intermediate products of biodegradation of toluene mainly include phenols and ketones.The biological metabolic pathway of toluene waste gas in this experiment was deduced with reference to relevant data: Toluene→Phenol→Ketones→Carbon dioxide.(4)The study found that the changes in the content of extracellular proteins and polysaccharides in BTF1 supplemented with rhamnolipids led to the enhancement of the relative hydrophobicity of the biofilm surface.The relative hydrophobicity of BTF1 biofilm reached 77.3%,while that of BTF2 was 63.1% when the system ran to 120 d.It shows that the addition of rhamnolipid can promote the efficient adsorption of hydrophobic waste gas by biofilm,thereby improving the bioavailability of toluene.(5)16S rRNA technology was used to analyze the microbial communities during the stable operation of the two systems.It was found that at the phylum level,the dominant phyla in the BTF1 system were Proteobacteria and Acidobacteriota,accounting for 62.3% and 9.8%.In the BTF2 system,the dominant phyla were Proteobacteria and Firmicutes,accounting for 56.3% and 9.1%,respectively.At the genus level,the dominant genera in BTF1 and BTF2 were Pseudomonas and Blastocatellaceae,accounting for 44.3%,9.7% and 32.4%,5.2%,respectively.Adding rhamnolipid to the filter tower can promote the enrichment and growth of dominant bacteria.It improved the removal efficiency and operational stability of the system. |
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