Enhancement Of Anaerobic Phenol Degradation By Catalytic Biocarriers

Phenol, a kind of toxic substances, is of great concern due to its environmental issues and health risk. Nitrate, as one of the most common pollutants, is widely distributed in water with toxic organics. The degradation of denitrification through simultaneous reaction between nitrate and toxic organics under anaerobic conditions was benefit to remediate combined pollution in water. However, anaerobic biodegradation of phenol was a time-consuming process, reflected by the limit of electrons transfer. Redox mediators were studied to be oxidized and reduced reversibly, thereby conferring the capacity to serve as electron carriers in multiple redox reactions. Therefore, the anaerobic bioreactors with different catalytic biocarriers were investigated, and the most effective strategy for phenol treatment was established. In addition, the cell model of phenol degradation was elucidated according to the analysis of intermediates and mechanism of degradation.After the acclimation period of the anaerobic bioreactors (200days), the contrastive results of the removal of phenol, CODcr and NO3--N indicated that R3filled with quinone-modified polyurethane foam (Q-PUF) showed the most obvious technical advantage. The remaining phenol in the effluent water was only about14.0mg/L, and the removal efficiencies of CODCr and NO3’-N were85.3%and83.7%, respectively. The PCR-DGGE results showed that Shewanella, Pseudomonas and Aromatoleum were considered as the dominant bacterial species. The morphological analysis of scanning electron microscope (SEM) demonstrated that most of the individuals were bacillus in the activated sludge. Additionlly, the close integration of microorganism and immobilized carrier could contribute to direct contact between the bacteria and immobiled mediators.The batch experiments of phenol anaerobic degradation indicated that all of the humic acid (HA) species and aquatic natural organic matter (NOM) acted as redox mediators could accelerate the anaerobic degradation of phenol. Pahokee Peat Humic Acid (PP-HA) showed the most obvious enhancement of phenol anaerobic degradation, the degradation efficiency of phenol was increased18.5%after cultivation for36h. Moreover, the reduction efficiency of nitrate was also improved by4-10%in the presence of HA and NOM under denitrification conditions. Furthermore, the results showed that the performance of phenol anaerobic biodegradation was enhanced by humic acids, suggesting that combination of humic acids (environmental concentration) and catalytic biocarrier could be more beneficial to improve the efficiency of phenol anaerobic degradation.10mg/L PP-HA was supplemented as an additional redox mediator in anaerobic bioreactors system (R3), the results showed that the efficiencies of phenol, CODCr and nitrate in the effluent water were approximate95%,95%and90%, respectively, after40days of incubation.The genus Shewanella distributed widely in various settings and detected as dominant bacterium in above-mentioned bioreactors was selected to investigate the effects of redox mediators on phenol anaerobic degradation. According to the experimental results and relative literatures, a possible degradation cell model of phenol in the presence of mediators was proposed.These results may provide a guideline for us to better understand the phenol mineralization in natural and artificial environments and to develop efficient biotreatment strategies of phenol pollutions.