| The coal gasification wastewater(CGW) contains high concentration of phenolic compounds, ammonia and refractory organic compounds. Due to the hash characteristics of the wastewater, the issue of disposal and treatment is the bottle neck, which is highly related with the development of coal chemical industry and the living environment of human. Nowadays, the “Zero liquid discharge” standard means a more stringent discharge standard for the nitrogen removal process treating CGW. However, inhibitive organics in the CGW would easily inhibit the nitritation process, and the limited biodegradable compounds resulted in the lack of carbon resource for the denitrification, which leads to the poor performance in nitrogen removal process. In order to resolve the tough technical problem, this subject employed the short-cut biological nitrogen removal(SBNR) reactor and studied the effect of inhibitive organics in the anaerobically treated CGW- phenol, p-cresol, indole and alkanes on the nitritation and denitrification process in SBNR. After conducting research on the adsorption of inhibitive organics with activated carbon and the bioregeneration, a method to remove the inhibitive organic compounds was found. Therefore, powdered activated carbon treatment(PACT) process combined with SBNR process, namely PACT-SBNR, was developed to remove the ammonia and total nitrogen(TN) in the anaerobically treated CGW. And the combined process was also applied in the full-scale plant. In order to cope with the carbon resource shortage occurring in the application, the combined process was improved by adding the GAC(Granular activated carbon) pre-adsorption compartment, namely GAC-PACT-SBNR. The superiority of its efficient utilization of the biodegradable componens in the raw wastewater was investigated.This paper conducted the research on start-up and the influence factors of SBNR. By controlling p H at 7.5~8.0, temperature at approx. 30℃, DO of 0.8~1.5mg/L, sludge retention time(SRT) of 15 d, the ammonia conversion rate and nitrite accumulation rate were 95.2% and 10.9mg NO2ˉ-N/(g VSS·h), respectively. With sodium carbonate or methanol as external carbon resource, the TN removal efficiency was achieved high to 97%. The influence factors test indicated that dissolved oxygen(DO) was the key influence factor for SBNR. DO controlled at low concentration(0.8 ~ 1.5mg/L) was crucial to ensure good performance of SBNR.After inducing inhibitive organic compounds- phenol, indole, p-cresol, long chain alkanes in anaerobically treated CGW into SBNR, it was found that both the ammonia conversion rate and nitrite reduction rate declined to different extent. For the same compound, the higher the concentrations, the stronger inhibition were detected. Inducing less inhibitive compounds, less time was needed to eliminate the inhibition of ammonia oxidation bacteria activity and to recover the SBNR process. In order to obtain good performance in SBNR, the concentrations of phenol, p-cresol, indole and alkanes need to be controlled below 50mg/L, 50mg/L, 5mg/L and 5mg/L, respectively.This study found that powdered activated carbon(PAC) and GAC showed large adsorptive capacity for the inhibitive compounds- phenol and indole. Freundich and Langmuir adsorption isotherm for the adsorption process revealed that the activated carbons preferentially adsorbed phenol rather than indole. When employing the mixture of phenol and indole, PAC exhibited much higher adsorption capacity for indole in the presence of phenol. The activated carbon loaded with inhibitive compounds can be bioregenerated, resulting in a lasting adsorptive capacity. Therefore, the PAC-activated sludge combined system could be used prior to SBNR process to remove and degrade the inhibitive organics, ensuring high removal efficiency of TN in SBNR.The PACT-SBNR combined process was developed and the PACT system was started up. COD and total phenol(TPh) removal rates of 80.2% and 90.3% were achieved under optimal operation condition, i.e. Hydraulic retention time(HRT) of 24 h, PAC dosage of 1.0g/L, DO of 4mg/L, MLSS of 4000mg/L, under with the PACT achieved highest COD and TPh removal efficiency. The phenol, p-cresol, indole and alkane in the effluent were 1.6mg/L, 2.8mg/L, 3.2mg/L and 0mg/L, respectively. Accordingly, the SBNR process achieved high nitrogen conversion rate and TN removal rate, with ammonia and TN concentration of 4.3mg/L ' 17.8mg/L in the effluent, achieving the effluent standard. In the engineered research, by controlling PACT at DO of 4mg/L, PAC concentration of 1.0g/L, HRT of 24 h and controlling SBNR at DO of 0.8~1.5mg/L, p H 为 7.5~8.0, SRT of 15 d, temperature of 30~35℃, the COD, ammonia, TPh and TN was of 27.9~89.9mg/L, 0~4.2mg/L, 0~5.0mg/L, 3.7~18.0mg/L, respectively, achieving the effluent standard.In order to solve the problem of carbon resource shortage in the full-scale plant, the PACT-SBNR combined process was improved by installing an adsorption compartment filled with GAC. The GAC-PACT-SBNR process was operated with GAC outlet as carbon resource for the dinitrification process in SBNR. In light of the adsorptive property of GAC, the compounds in CGW was re-distributed and the biodegradable organic components can be used for the denitrification process in SBNR, therefore reducing the demand for the external carbon resource. When the GAC compartment showed high COD and TPh removal rate, the TN removal efficiency in SBNR was as high as 68.8%~75.8%, which was 30% higher than the one without carbon resource. The GAC-PACT-SBNR combined process offered a more reasonable way to re-distribute the organic components in the raw wastewater and resolve the problem of carbon resource.By developing the PACT-SBNR and GAC-PACT-SBNR combined process, this study realized the efficient removal for both the inhibitive organic compounds and TN, solved the tough problem in the nitrogen removal for CGW, and put forward a new method for wastewater treatment in the field of coal chemical industry. |
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