Enhanced Biodegradation Of Polycyclic Aromatic Hydrocarbons In Coking Wastewater

There are many kinds of organic matters in the industrial coking wastewater,Polycyclic Aromatic Hydrocarbons(PAHs)are the most important toxic pollutants in coking wastewater,and their carcinogenic,teratogenic and mutagenic toxicity have attracted wide attention.As a kind of hydrophobic organic pollutant,a higher concentration of PAHs in coking effluent are enriched in sludge during coking wastewater treatment.After treatments with traditional methods of landfill,composting and incineration,coking sluge with PAHs cause secondary pollution to the water,soil,crops and atmospheric environment.Phenol is the main pollutant in coking wastewater and carbon source which can be utilised by degrading bacteria.In this paper,the aerobic sludge in a coking wastewater treatment plant is selected as a biodegradable microbial source,a novel strain of bacteria Stenotrophomonas sp.N5 was isolated to treat the PAHs contaminated sites,which could utilise high molecular weight PAHs(HMW PAHs)as sole carbon and energy source.The research results include:(1)We conducted the single factor experiment and response surface methology(RSM)experiment,three key factors of the degradation experiment utilising carbon source of BaP were optimized: the incubation temperature,the initial pH value and the inoculum size.In addition to this,a total of 17 experiments were designed based on the design principle and response surface analysis of Box-Behnken center.The experimental conditions of BaP degradation were optimized by five zero tests.The effective inspection was obtained through variance analysis,the significance of the model,the factors of significant interactions between factors,optimum condition was obtained: incubation temperature,35.1?;initial pH value,7.5;inoculum size,9.4%.Under the above conditions,an excellent degradation efficiency of BaP 19.4% by strain N5 was achieved.(2)In the optimal culture conditions,naphthalene,phenanthrene and fluoranthrene were used as the representative compounds of PAHs with different benzene rings.With the initial concentration of 50mg/L,the degradation rates of three PAHs was 3.28 mg/(L·d),2.53 mg/(L·d),0.96 mg/(L·d),respectively,strain N5 was able to degrade 0.62 mg/(L·d)of benzo[a]pyrene(20 mg/L)in 22 days.At the same time,the Electronic Transport System Activity(ETSA)value was measured as an indicator of the degradation potential in the incubation period.(3)The co-metabolic effect of phenol,glucose and rhamnolipid on the biodegradability of BaP was investigated,the results showed that compared with the control(48.2%),51.9%,60.9% and 53.0% degradation eficiency of BaP were observed after adding the three substrates respectively,the ETSA values increased 1.18 times,1.69 times and 1.39 times respectively.The degradation efficiency of BaP increased to 64.9% and 68.2% after addition of phenol+rhamnolipid and glucose+rhamnolipid as dual co-substrates.The data showed that there was a potential synergy between rhamnolipid and other carbons,and phenol as the main pollutant in coking wastewater can be served as existing co-substrate and play a positive role in promoting bioavailibility of PAHs.On this base,a multiplier effect can be achieved by adding biosurfactant into raw coking wastewater.