Characteristics Of M-Cresol Degradation By Pseudomonas SP. And Its Aerobic Denitrification

Phenol and its methylated derivatives m-， o-and p-cresol arerepresentative phenolic compounds which are widely detected in effluents ascharacteristic pollutants in many industrial processes, including coalconversion, oil refineries, dyeing, petrochemicals. With respect to phenol,m-cresol exhibits more hazardous effects on the environment and humanbeings even at lower concentration. Therefore, Discharge standard ofpollutants for municipal wastewater treatment plant(GB18918—2002)stipulates that the m-cresol discharge is limited sternly under0.1mg/L tonatural water in China. In addition, phenolic wastewater also containsconsiderable nitrogenous compounds which could lead to eutrophication innatural waters if they are discharged without treatment. Given all that，aerobic denitrifiers show an outstanding advantage to treat phenolicwastewater, since they have capacity to degrade phenolic compounds andremove nitrogen simultaneously. An aerobic denitrifying strain, Pseudomonas sp., was isolated from atreatment system for coking wastewater. The characteristics of degradation ofm-cresol by the strain were investigated at different conditions, and the optimalconditions for m-cresol-degrading via aerobic denitrifying were specified as:shaking speed of180r/min, C/N=7, temperature30℃and initial pH7.0,where Pseudomonas sp. was able to utilize360mg/L m-cresol to the most in78h. With m-cresol concentration increasing, it exhibited stronger inhibitioneffect on cell growth. Also the inhibitory effect m-cresol was stronger than thatof phenol. During the aerobic incubation, phenol hydroxylase and catechol2,3-dioxygenase was synthesized by Pseudomonas sp. induced by solesubstrate m-cresol, which confirmed that the ring was cleaved via meta fissionin the m-cresol-degrading process. M-cresol was degraded by co-degradationof O2respiration and aerobic denitrification. In the co-metabolism systemcomprising with m-cresol and sodium acetate, the biodegradation of m-cresolwas accelerated distinctly by sodium acetate.During the aerobic incubation, simultaneous reduction of nitrate andaccumulation of nitrite were observed with Pseudomonas sp. utilizing m-cresolas sole carbon source. In the denitrification medium with initial360mg/Lm-cresol and40.0mg/L nitrate,87.8%nitrate nitrogen was removed out within78h, and nitrate nitrogen remained4.21mg/L with accumulation rate above12.0%. Besides, both nitrite reductase and periplasmic nitrate reductase wereexpressed in the isolate during the whole nitrogen removal process of the strain. Sodium acetate promoted the denitrifying potential of the strain Pseudomonassp., thus nitrate nitrogen and nitrite nitrogen almost could be removed.With m-cresol as the sole carbon and energy source for Pseudomonas sp.at initial concentration0~360mg/L, the Haldane，s equation was used toinvestigate cell growth dynamic. The parameter values were: μmax=0.202h-1,Ks=9.85mg·L-1, Ki=101.91mg·L-1. The cell growth kinetics was welldescribed by the Haldane kinetic models. Furthermore, when Pseudomonas sp.grown on the mixture culture of m-cresol and phenol, the characteristics of cellgrowth and substrates interaction were studied. The results showed that lowconcentration phenol (0~150mg/L) accelerated the biodegradation ofm-cresol. Conversely, m-cresol released strong inhibition onphenol-degrading even at very low concentration. The different biodegradationrates were result of competition between acceleratory effect and inhibitoryeffect which existed all along in dual-substrate biodegradation.