| Recently,a large amount of coking wastewater,generating from coal gas purification,coal coking,and refining processes of chemical products in the coke plant,leads to serious environmental impact.According to the statics,the production of coking wastewater in China is about 1.8*108t per year.Even though many different methods could be used to treat the wastewater,a certain amount of them is drain off into the environment and finally pollute earther's surface water bodies.As we know,coking wastewater is one of the most refractory wastewaters,which contains large quantities of complex,recalcitrant,highly concentrated,and toxic organic pollutants such as aromatic compounds,and nitrogen-,oxygen-,and sulfur-containing heterocyclic compounds,etc.And most components of them in the coking wastewater are toxic,carcinogenic,and mutagenic and may have long-term ecologic impacts.In general,phenol,pyridine,and quinoline are the key components of the coking wastewater.As we know,the biodegradation of many compounds is the process which needs electron donors,for example,denrification,mono-oxygenation,di-oxygenation,reductive dechlorination etc.Therefore,there is a competetion for electron donors among them,when two or more compounds are simultaneous biodegradation.In this thesis,the internal circulation baffled biofilm reactor(ICBBR)and vertical baffled bioreactor(VBBR)were used to study the distribution of electon donors during two or three of the main components simultaneous biodegradation in the coking wastewater(Pyridine,Quinoline,Phenol).We have tested them in the simulated wastewater and actural coking wastewater.Four main parts of experiment were taken:competition for electrons between pyridine and quinoline during their simultaneous biodegradation;competition for molecular oxygen and electron donor between phenol and quinoline during their simultaneous biodegradation;simultaneous biodegradation of pyridine,quinoline and phenol;and the distribution of electron donors duing pyridine and quinolin simultaneous biodegradation under actural coking wastewater as background.Pyridine and quinoline removal rates decelerated during simultaneous biodegradation,compared to separate biodegradation,as they competed for intracellular electron donors(2H).The first mono-oxygenation of quinoline(from quinoline to 2HQ)always was faster than the first mono-oxygenation of pyridine(from pyridine to 2HP),and the difference was accentuated with pyridine and quinoline were biodegraded simultaneously due to the competition for 2H.Competition also existed between mono-oxygenations of 2HP and 2HQ,and the 2HP removal rate was faster than the rate for 2HQ,even though the rate for quinoline was faster than pyridine.Adding exogenous electron donor accelerated all mono-oxygenations in proportion to the amount of donor added,but the increments were greater for quinoline due to its higher affinity for intracellular electron donors than pyridine.The first two steps of phenol and quinoline biodegradations are mono-oxygenations requiring O2 and intercellular electron donor(2H).Batch experiments documented mutual inhibition between phenol and quinoline,because they competed for O2,2H,or both during simultaneous biodegradation.Phenol removal rates always were faster than for quinoline,whether independent or simultaneous biodegradation.Simultaneous biodegradation also led to the transient accumulation of phenol's first mono-oxygenation product,catechol.Low DO was a limiting factor for phenol and quinoline biodegradations,as both rates slowed significantly for DO ? 3 mg/L,compared to DO>5 mg/L:A DO concentration of 0.5 mg/L led to 89%and 65%slower removal kinetics for phenol and quinoline,respectively.Although addihg succinate as an exogenous electron donor was able to alleviate competition when the DO was 4?5 mg/L,it had no benefit for a DO ? 3 mg/L.Thus,significant DO limitation could not be overcome by addition of more donor.The results have practical significance for improving the treatment efficiency of industrial wastewater containing multi-component organic pollutants that require oxygenation reactions.For example,a strategy that involves adding or creating an exogenous electron donor may be effective only when DO is not significantly rate limiting for the initial oxygenation reactions.The biodegradation rate of phenol is faster than quinoline's and pyridine's,no matter independent biodegradation or simultaneous biodegradation.So phenol is more biodegradable than quinolin and pyridine.From the Monod,we can see that the mono-oxygenase responsible for the phenol mono-oxygenation had better affinity for its substrate than the affinity of quinoline's and pyridine's.In the actual coking wastewater as the background,pyridine and quinoline had similar trend for their removals,although the rates were slower than that in the synthetic wastewater for pyridine(but not quinoline),because actual coking wastewater contains other compounds that may have competed for electron donors or had an inhibitory effect.Pyridine and quinoline removal rates obviously were accelerated when 0.3 mM succinate was added.Thus,the principles of competition of the electron donor remained true for pyridine and quinoline biodegradations in actual coking wastewater.Since competition for intracellular electron donor is an important factor for the biotreatment of many wastewaters containing multiple aromatic compounds,the trends seen here for pyridine and quinoline ought to be significant for a wide range of industrial wastewaters. |
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