Experimental Study On Treatment Of PTA Wastewater By Two-phase Anaerobic Digestion

Purified terephthalic acid(PTA)is an important chemical raw material,mainly used in the production of chemical products such as polyester resins,polyester fibers and insulating paints.During the production of PTA,a large amount of organic wastewater containing aromatic compounds is generated.The wastewater has the characteristics of high pollutant concentration,large fluctuations in water quality and p H value,and high effluent water temperature.At the same time,the aromatics in the wastewater are highly biologically toxic,and direct emissions is extremely harmful to the environment.They must be effectively treated to meet standards before discharge.Among them,terephthalic acid(TA)and p-toluic acid(PA)are generally considered to be the most difficult biodegradable pollutants in PTA wastewater,and biodegradability of PA is worse than TA.Due to the large fluctuations in water quality and quantity,the single-phase UASB has a poor effect in PTA wastewater treatment,mainly due to the inhibitory and toxic effect of high concentrations of aromatic organic compounds on microorganims.The fisrt-stage UASB can be used as a hydrolytic acidification stage to remove the easily degradable organics,and play a certain effect on the degradation of refractory organic compounds,thereby improving the biodegradability of the PTA wastewater and providing convenience for the biological degradation in the secondary UASB reactor.Therefore,in this study,a two-phase upflow anaerobic sludge bed(UASB)was developed to treat the PTA wastewater.The potential of carbon and biochar carriers to promote rapid start-up and efficient operation of the reactor was also investigated.The study examined the long-term operating performance of the two-phase UASB reactors,the removal of specific pollutants,microbial community structure,the physicochemical properties of different carriers,and the effect on sludge granulation,in order to continuously optimizing the biological treatment of PTA wastewater.Firstly,the performance of two-phase UASB reactors for PTA wastewater treatment was determined.The results showed that the two-phase UASB reactor can effectively treat PTA wastewater,with an average COD removal rate of more than 90%,and the average biogas production of 14.24 m L/(g COD·d)in the first phase UASB,and27.95 m L/(g COD·d)in the second-phase.Among the three specific pollutants,BA showed the best removal efficiency,followed by TA and PA,with average removal efficiency of 100%,97.99%,and 92.07%,respectively.The highest relative abundance of microbial phylum in the first-stage UASB reactor was Euryarchaeota,with a relative abundance of 29.1%,followed by Proteobacteria,with a relative abundance of 26.6%.The highest relative abundance in the secondary UASB reactor was Proteobacteria(25.0%),Candida(19.4%),and Curvularia(11.8%).The richness and diversity of the microbial community in the secondary UASB reactor were higher than those in the primary one.In order to improve the removal efficiency and gas production in the treatment of PTA wastewater by the two-phase UASB reactor,the effect of different carrier addition was investigated.The results showed that the average COD removal rates of the reactors with addition of waste carclazyte,iron-carbon,and biochar were 87.84%,83.67%,and85.42%,respectively,which were slightly lower than 90.14% of the control reactor.However,the carriers were beneficial to improve biogas production.Compared with the control reactor,the average biogas production increased by 2.0 times,3.3 times,and 2.7times,respectively.Adding carriers improved the abundance of hydrolytic acidifying bacteria and methanogens,and promoted the bioconversion of short-chain fatty acids and methanogenesis performance.The particle size of sludge was increased by adding carrier to some extent,but the sludge granulation in UASB reactor was not realized.In summary,the two-phase UASB reactor can effectively treat PTA wastewater,and the addition of waste carclazyte,iron-carbon and biochar carriers can greatly improve the biogas production.Further exploration is needed in accelerating reactor start-up and sludge granulation.