Degradation Of Terephthalic Acid In PTA Wastewater By A Photocatalytic-biocoupled System

As one of the important components in the petrochemical industry,the purified terephthalic acid（PTA）industry occupies a very important position in country’s national economy.The treatment of PTA wastewater has also become a difficult problem in industry governance.Terephthalic acid（TA）is the main component in PTA wastewater,which is a refractory organic pollutant and has a great impact on the water environment.Photocatalysis-biocoupling technology is an emerging treatment method,which provides a new idea for the treatment of refractory TA.In this paper,a photocatalytic-biocoupled degradation system was constructed using the photosensitive material nano-Ti O₂ as the photocatalyst,polyurethane sponge as the carrier,and activated sludge as the biological seed source,and the mechanism and degradation mechanism of photocatalytic and microbial degradation of TA in the coupled system were explored.The main conclusions are as follows:（1）The nano-Ti O₂ was loaded on the sponge carrier by the sol-gel method,and the optimal operating conditions for photocatalytic degradation of TA under UV light irradiation were discussed:the carrier dosage was 5%,the aeration rate was 1.0 L/min,the initial p H was 7,and the light intensity is 390 Lux,the degradation rate of TA reaches 41.95%after 4 h,and the B/C value of wastewater reaches 0.46,which has good biodegradability and is beneficial to subsequent biodegradation experiments.（2）Analysis of TA degradation efficiency of the photocatalytic-biocoupled system:using the coupled system of photocatalysis first and then biodegradation,when the TA concentration is 10 mg/L and the hydraulic retention time is 10h,the results show that the TA degradation rate and the COD removal rate are the highest respectively 92.95%and 88.27%.Compared with photocatalysis alone,the degradation rate of TA was increased by 51%.The effects of coexisting substrates on TA degradation rate were analyzed,and the results showed that the addition of HAc,BA and p-TA to TA degradation inhibition rate was 9.65%,16.5%and22.5%,respectively.The analysis of the physical and chemical properties of the sludge showed that with the increase of TA concentration and the addition of coexisting substrates,the physical and chemical properties of the sludge deteriorated,and the prolongation of the hydraulic retention time was beneficial to improve the physical and chemical properties of the sludge.（3）Analysis of the degradation mechanism of TA:The contribution of photocatalytic radicals to TA degradation in descending order is:·OH>h⁺>·O₂^-.According to the analysis of intermediate products by GC-MS,TA generates 2-HTA under the action of·OH and oxygenase,after which three degradation pathways are separated,namely photocatalytic pathway A:2-HTA in OH,O₂^-and h⁺Under the attack,short-chain alkanes,alkenoic acids and lower carboxylic acids are formed successively,which are finally removed.Biological pathway B:2-HTA is first converted to protocatechuic acid,followed by tricarboxylic acid.Photocatalytically coupled biological pathway C:2-HTA generates 2-hydroxybenzoic acid under the action of decarboxylase,followed by oxidation,esterification and ring opening.（4）Observation of biological activity by CLSM found that the relative activities of microorganisms and biodegradation at 2h and 6h before the reaction were 96%,49%and 89%,respectively.In terms of the overall characteristics of the microbial community,TA and the intermediates produced by photocatalysis changed the community structure.At the phylum level,Proteobacteria and Bacteroidota adapted to changes in the environment,and their relative abundances increased from 11.66%and 2.36%in the original sludge to 48.37%and 31.93%in the biological reaction 6h.At the genus level,Norank＿f＿Microscillaceae,Flavobacterium,Thauera,Zoogloea and Azoarcus became the dominant genera.（5）Degradation of actual PTA wastewater using a photocatalytic-biocoupled system.The research showed that the removal rates of TA and COD reached 35.1%and 76%.At the same time,the biodegradability of the actual wastewater after the photocatalytic reaction is improved.FTIR and EEM analysis showed that complex organic compounds such as aromatic compounds（carboxylic acid compounds,alcohols and phenols）in the effluent of the system were degraded into small molecular substances,indicating that the system had good degradation ability to actual wastewater.