Study On The Degradation Characteristic Of Phenanthrene In Electricity-anaerobic Biological Coupling System

Phenanthrene is a representative kind of polycyclic aromatic hydrocarbons (PAHs). It has ahigh concentration in the soil and water polluted by oil. The stable chemical properties andlow solubility of phenanthrene make it difficult to be utilized by microorganism. Now theresearch of phenanthrene aerobic degradation has made great achievements, but the anaerobicdegradation like the metabolic pathways and key enzymes is still unclear.Electricity-biological coupling method is a hotspot, and has achieved good effect in dealingwith wastewater contain nitrobenzene, dye and phenol recently. However, the research ofelectricity-anaerobic biological coupling system and this system used for dealing with nosubstituent groups PAHs are rarely reported.In this study, phenanthrene is utilized as the research object, anaerobic granular sludge isutilized as the inoculation sludge, electricity-anaerobic biological coupling system is builtafter laboratory cultivation and domestication, then the factors including degradation time, pH,sludge concentration, current, phenanthrene concentration and Cd2+are inverstigated throughbatch experiments, the metabolic mechanism of phenanthrene and the interaction mechanismbetween electricity and anaerobic microbial are discussed at last. The results are as follows:(1) At the temperature351℃, pH8.0, sludge concentration5gTSS/L, phenanthrene initialconcentration20mg/L, the removal rate of phenanthrene and COD in electricity-anaerobicbiological coupling system (current is2mA) is the best, followed by anaerobic biological,electrolysis is the worst. The removal rate of phenanthrene and COD are99.4%and91.5%,96.7%and81.1%,25.1%and22.6%, respectively.(2) The appropriate current can improve the removal rate of pollutants. When temperatureis351℃，pH is8.0，sludge concentration is5.4gTSS/L，phenanthrene concentration is20mg/L, current is1mA，and degradation time is48h, the removal rate of phenanthrene andCOD can achieve99.9%and92.1%, respectively。But when the current exceeds a certainvalue (4mA), anaerobic digestion rate would be lower than the one without current, biologicalenvironment would be worse, acid-base would be out of balance along with the increase ofcurrent, and the removal rate of organic would reduce quickly.(3) Cadmium has effect on phenanthrene degradation, when cadmium concentrations is lessthan50mg/L, it can promote the degradation of Phenanthrene. However, high cadmiumconcentration (>50mg/L) has inhibitory effect on phenanthrene degradation.(4) The degradation of phenanthrene is the outcome of combined action of intracellularenzyme and intracellular enzyme. At the same time，granular sludge can adsorb phenanthrene, and the adsorption capacity decreases with the increment of processing time. There is adynamic adsorption equilibrium between dissolved phenanthrene in water and adsorbedphenanthrene by the granular sludge.(5) It is an extremely complex process of using electricity-anaerobic biological couplingsystem metabolizes phenanthrene. Dimethyl phthalate, m-phenethyl-benzonitrile,4-hydroxy-9-fluorenone, phthalic acid isononyl ester and benzothiophene are the mainintermediate products. Microbial degradation of phenanthrene plays a main role in the processthat wastewater containing phenanthrene is treated by electricity-anaerobic biologicalcoupling system, and the electric current can not only stimulate microbial growth andmetabolism, but also oxidize and remove phenanthrene.