Isolation And Characterization Of Benzene-degradaing Heterotrophic Nitrifying Strain

The treatment of organic sewage with bad biodegradability is an emphasis and difficulty in wastewater processing both at word and abroad. Benzene is a usual organic compound in industrial sewage, such as oil chemical industry, coking plants. It is one of priority control pollutants in many country and organizations. Even the concentration of benzene is very low, it does serious harm to biomass for its toxic properties. The wastewater containing benzene becomes a very serious problem in the world because its high volatility, transfer ability and carcinogenicity. Biological treatment of wastewater containing benzene is more suitable and economic, therefore the biological treatment has become research priorities. The key of this method is to isolate microorganism that have the higher capacity of benzene degradation.This study isolated a strain which could utilize benzene and NH+4-N as its only carbon and nitrogen source, respectively, as well as research its different benzene degradation and nitrogen metabolic rule.Typical results are shown below: (1) Active sludge was collected from coking-plant wastewater ponds in lab and used to isolate a strain which colud simultaneous remove benzene and nitrogen. Based on the strain’s physio-biochemical characteristics and the analysis of its16S rDNA gene sequence, the strain is identified to be a Pseudomonas sp strain and renamed as Pseudomonas sp BN5.(2) By measuring and comparing benzene degradation and NH4+-N removal efficiency of the strain, a series of factors like temperature, pH, C/N are studied systematically. About70.86%of ammonium and100%of benzene was removed after72h of incubation at initial benzene and ammonium concentration of52.37mg/L and16.13mg/L, respectively. During nitrogen metabolism, only small amount of NO3--N was observed. Futhermore, the research also investigate the utilization of different nitrogen source (Nitrite/nitrate) to understand the nitrogen removal pathway of Pseudomonas sp. BN5. Strain Pseudomonas sp. BN5showed both NO2--N and NO3--N utilization ability under aerobic conditions, with34.23%and45.6%removal efficiency after72h for nitrite and nitrate, respectively. To investigate the strain’s possible nitrogen metabolism pathway, the research preliminary study on the enzyme activities of HAO, NR, NiR was conducted under aerobic conditions.The results indicated that the tested enzymes were all successfully expressed in strain Pseudomonas sp. BN5, the possible nitrogen metabolic pathway for strain BN5was:NH4+-N→NO2--N→NO3--N→N2O/N2. (3) Under the optimal condition，the process of strain Pseudomonassp. BN5degradation was investigated using Monod kinetic model was appliedto simulate the degradation process of benzene degradation metabolism.Thebenzene degradation dynamic equation is μs=0.53S/(11.07+S), R2=0.987, whichindicated that fitted curve had a good correlation with test measured. Accordingto the material balance of the process, we can draw the growth dynamic thestrain is μx=0.57S/(11.07+S).