Enhanced Anaerobic Biodegradation Of Phenol By Redox Mediators

Phenol, a kind of high toxic substances, is one of priority pollutants in China. Although the anaerobic degradation has many advantages compared to the aerobic degradation, slow degradation rate has always been the bottleneck. According to some reports, quinones can accelerate anaerobic transformation. So the characteristics with respect to the anaerobic degradation of phenol by Shewanella sp. XB or actived sludge were studied by using phenol as the sole electron donor and the quinones as redox mediators.The characteristics of phenol anaerobic degradation by Shewanella sp. XB were studied. The experimental results showed that when the nitrogen source was ammonium chloride without an electron accpetor, phenol could be degraded via anaerobic fermentation. And the addition of quinones and riboflavin improved the degradation rates of phenol degradation. When0.005mM riboflavin,0.01mM AQDS and0.3mM AQS were used, the degradation rates were1.24,1.35,1.41folds of that of the control assay, respectively. Ammonium chloride was replaced with nitrate as the sole electron acceptor. When the dry weight of XB was30mg/L and the C/N ratio was13.3, phenol could be totally exhausted. Additionally, when various redox mediators, i.e. riboflavin (3μM), AQDS (0.01mM), AQS (0.05mM), and LQ (0.01mM),2-methy-1.4-naphthoquinone (0.1mM) were added, the degradation rates were1.82,2.3,2.16,2.11and1.36folds of that of the control assay, respectively. So the redox mediator could accelerate the biodegradation of phenol under nitrate reducing condition. In addition, the GC-MS demonstrated one of the intermediate products of phenol degradation was catechol, which in fact was the aerobic degradation metabolite. It was inferred that O2was produced during the denitrification process, which made the phenol degraded through the aerobic pathway. In addition, according the amount of phenol degraded under the nitrate reducing condition, it was concluded that the process of the phenol anoxic degradation was the combination of the aerobic and anaerobic degradation.The characteristics of phenol nitrate-dependent degradation by unacclimatizated activated sludge were sudided. Results showed that when the concentration of MLSS was2g/L and C/N ratio was6, the phenol could be totally degraded coupled with the reduction of nitrate. It was also noted that there was little nitrite of the effluent. The effect of Shewanella sp. XB on phenol degradation by activated sludge was investigated. It showed that when the dry weight concentration of XB was30mg/L in the sludge system, the degradation rate was1.94folds of that of control assay. And the effects of the redox meditors were also studied. When the intial phenol concentration was different, the most appropriate RM concentration was different. While phenol concentration was200mg/L, the phenol degradation rate was the highest when the concentration of riboflavin, AQS, AQDS was0.01mM,0.01mM,0.03mM. The degradation rates were0.70、0.64、1.41times faster than that of the assay without redox mediators. When the phenol concentration was300mg/L, the addition of0.03mM riboflavin,0.05mm AQS and0.05mM AQDS improved the phenol degradation rate obviously. The degradation rate was1.79,1.21,1.7folds of that of control assay. Compared to them, AQS showed little positive effect.