Study On Simultaneously Aerobic-anaerobic Degradation Of PCP In Wastewater With Microaerobic Granules

Pentachlorophenol (PCP) is a toxic and hardly biodegradable xenobiotic and widely used as biocide and wood preserving-agent. Large quantities of PCP are also produced by some industry processes. It has been placed on the Priority List of Pollutants by the U.S. Environmental Protection Agency and our country. Sequence anaerobic-aerobic technology was approved to be the most efficient PCP removal technology , but aerobic and anaerobic processes were separated timely and spatially. In this paper, a promising technology - microaerobic granule was proposed to treat PCP containing waste water.Firstly, cultivation of microaerobic granules was studied. Disaggregated and whole anaerobic granules were taken as inoculum, respectively. Granules formed through flocculent sludge disaggregated after acclimation with PCP due to loosen structure. Culture and acclimation with PCP were simultaneously conducted when whole anaerobic granules was taken as inoculum. With time on, degradation of waste water was increasing. Good capability microaerobic granules was formed at last. Compared to anaerobic granules in literature, PCP could be mineralized completely with microaerobic granules, and no lower chlorophenols accumulated.Granulation mechanism of flocculent lied in upper layer was studied, emphasizedly. Before mature granules formation, three-frame structure formed by filamentous bacteria, bridge formed by two value metal cations and conglutination of extracellular polymers (ECPs) played important roles. After mature granules formation, effect of cellular dehydration caused by proton translocation became most important in granules growing up, but effects of two value metal cations and ECPs were also important. This period is similar with modification process of lower layer granules.After simultaneously aerobic-anaerobic system was established, effects of restrictive ecological factors such as dissolved oxygen (DO) concentration, pH, oxidation-reduction potential (ORP), PCP loading rate and concentration of glucose on the system were studied firstly under dynamic condition. Experimental results show, increasing of DO concentration in microaerobic range was in favor of PCP mineralization, but DO concentration beyond this range, disadvantage effects might occur. PCP and CODcr removal rates decreased when pH was lower than 6.7 or higher than 7.5. Decrease of ORP made for degradation of PCP, TeCP and TCP, while made...