| The phenols in the wastewater are the dominant phenolic pollution source in waterbody. Coal gasification wastewater is a typical refractory industrial wastewater with high concentration of phenols and poor biodegradability. The complex phenl ic compounds have been regarded as the organic contaminants to be removal and controlled for the first consideration in coal chemical industry wastewater treatment. Large amounts of toxic compounds in the wastewater would cause serious environmental pollution if treated inappropriately. In recent years, some common problems have been found in coal gasification wastewater treatment plant at home and abroad, such as unsatisfactory treatment performance, poor stability of the system and high cost. The wastewater treatment has been the bottleneck which restricts the virtuous development of coal chemical industry.In the present study, the research progress of bioaugmentation(Biological multiplication technique) and modified A/O(Anoxic-Oxic technique) process in coal gasification wastewater treatment was studied. Bioaugmentation strengthened the accumulation of model pollutants in activated sludge by adding powder activated carbon(PAC), further promoting the mass transfer process in the sludge floc and enhancing the biodegradation of pollutants. The experimental results showed that the apparent degradation rate constants of hydroquinone, phenol and resorcin increased 11%, 20% and 13% respectively. COD and total phenols were rapidly degraded in the first two chambers of bioaugmentation and maintained at low concentration in the following chambers. Concentrations of COD and total phenols in the effluent of bioaugmentation were less than 200 mg/L and 30 mg/L respectively. The degradation rates of COD and total phenols in the second chamber were the highest among all the chambers.Total phenols had adverse effect on nitrification. Whtn total phenols increased from 30 to 300 mg/L, COD, total phenols and ammonia removal efficiencies decreased from 98%, 99% and 50% to 58%, 66% and 5% respectively.Modified A/O process enhanced the nitrification. Concentrations of COD, total phenols and ammonia in the effluent of modified A/O process were significantly lower than that of conventional A/O during both startup and steady operat ion, whether the influent total phenols of 50 or 300 mg/L. The advantage was of more significance when the operation tended to be stabler.Total phenols also had inhibitory effect on denitrification. Whtn total phenols concentration increased from 50 to 200 mg/L, COD, total phenols and nitrate removal efficiencies decreased from 98%, 99% and 90% to 85%, 90% and 60% respectively. Finally, COD, total phenols and nitrate removal efficiencies were only 75%, 75% and 38%.Nitrate removal efficiency decreased with the decline of COD/NO3-N(5:1, 4:1, 3:1, 2::1 and 1:1), the corresponding removal efficiencies were 70-80%, 55-60%, 40%, 25-30% and 15-20% respectively. When the C/N of real coal gasification wastewater was lower than 2:1, which had restricted the denitri fication process dramatically, step feed(distribution ratio 70%:30%) was beneficial to optimize the C/N in anoxic I and anoxic II. COD, total phenols, ammonia and nitrate in the effluent were 60-80 mg/L, <10 mg/L, <5 mg/L and 100 mg/L respectively, and TN removal efficiency was higher than 40%.In the practical project, bioaugmentation-modified A/O process was built up to treat real coal gasification wastewater. COD and total phenols removal efficiencies in bioaugmentation reached to 80% and 90% during the stable operation, with the ammonia and TN in the effluent of 10 mg/L and 200 mg/L. COD and total phenols removal efficiencies were 50% and 67% in modified A/O, and ammonia and TN in the effluent were stable at 3 mg/L and 60 mg/L. The total removal efficie ncies of COD, ammonia and TN in bioaugmentation-modified A/O process achieved to 99%, 80% and more than 95% respectively. |
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