High Concentrated Polyester Resin Wastewater Treatment By A Combined Coagulation And A/O/A/O Process

With the rapid development of polyester industry, highly concentrated toxic polyester resin (PR) wastewater has been produced in large quantities, which not only restricts the sustainable development of related industry, but also brings serious wastewater pollution to surroundings. The existing PR wastewater treatment processes have the disadvantages of complicated units, high investment and operating cost, high energy consumption, low organic loading rate and so on. Therefore, a new method is needed for cost-effective techniques of PR wastewater treatment.In the present study, a cost-effective method, consisting of coagulation and A/O/A/O-MBR was carried out to treat PR wastewater in a pilot-scale. The primary aim of this paper was to evaluate the feasibility of the combined novel process for PR wastewater treatment. Specifically, the optimum condition of coagulation as well as the pollutants removal performance in the A/O/A/O-MBR system was investigated.In addition, organics composition in the raw wastewater and subsequent different processes was in detail characterized. What’s more, the primary functional microbial populations involved were explored. The obtained results will provide profound role in the application of "coagulation-A/OA/O" method for PR wastewater treatment. The primary results of this study are summarized as follows:(1)The effects of FeCl3, A12(SO4)3, PFS and PAC on the performance of coagulation was investigated and PFS showed the best performance. Single factor experiment revealed that the optimum conditions were:pH value of 8.0, PFS dosage of 1000 mg/L, PAM dosage of 10 mg/L, stirring intensity of 350 r/min, reaction time of 25 min and sedimentation time of 10 min. Under this condition, the removal rate of turbidity and COD was about 90% and 20%, respectively. FTIR analysis results proved that coagulation process can reduce the content of phenols, aromatics and aliphatic alkane compounds, and completely remove aldehydes and ketones.(2) A/O/A/O-MBR technology for PR wastewater treatment was successfully constructed and evaluated in a pilot-scale test. The results suggest that the steady performance was achieved as follows:temperature and MLSS in anaerobic tanks was around 25℃ and 10000 mg/L. DO, temperature, MLSS and SV30 in aerobic pool was higher than 1.4 mg/L,26～30℃,2000 mg/L and 60% or so, respectively. When pH and COD concentration of raw PR wastewater were 2-4 and 32000 mg/L,the optimum and maximum tolerable COD concentration in influent was 9000 mg/L and 12500 mg/L. The effluent COD and NH4+-N concentration lower than 500 mg/L and 35 mg/L could be achieved at HRT of 12.8 d,with the COD removal efficiency of 95%. The effluent quality was superior to the second level criteria of "urban sewage discharged into the sewer water quality standards" (CJ343-2010).(3)Based on preliminary results, a simulation bioreactor was designed to enhance the organic pollutants removal performance of A/O/A/O technology, and its potential removal mechanism was also explored. When the inlet COD was below the maximum tolerable concentration of 14000 mg/L, the COD and PTA concentration in effluent averaged 500 mg/L and 21.4 mg/L with removal efficiencies higher than 95.5% and 95.3%. Phenol was also completely removed. In the final effluent, epoxy alkane and esters constituted the major refractory organic pollutants were with relative content of 76.21% and 9.22% respectively. With the elevated of COD concentration in the influent, the bacterial community diversity and species abundance in four reactors were considerablely different and showed a decreasing tendency. Clostridia, Bacteroidia, Saprospirae were the major microbial population in anaerobic reactors while Saprospirae, Alphaproteobacteria and Betaproteobacteria were the dominant species in aerobic reactors. In addition, the family like Comamonadaceae, Cryomorphaceae, Chitinophagaceae, Rhodocyclaceae had a positive correlation with phenol, PTA and COD removal The successful inoculation and enrichment of dominant bacteria in each unit attributes to the good performance of A/O/A/O bioreactor.