Study On Influence Factors Of Degradation Of Quinoline Under Denitrification Condition

As a typical nitrogenous heterocyclic compound,quinoline is moderate toxic,carcinogenic and mutagenic.However,it is of a great significance on modern industry.With the fast development of society and population,the amount of quinoline wastewater discharged into the environment is becoming larger and larger.Because of the easy transportation,certain water solubility,certain evaporation to air with vapour and refractory characteristic of quinoline,it is a potential harzard compound to people and ecotope.Denitrification,which plays an important role on removal of organic and nitrogenous pollutants simultaneously under anoxic condition,is a important process of biological removal of nitrogen.pH and C/N are two important controlling indicators during denitrifying treatment of wastewater,Ca²⁺/Mg²⁺?calcium and magnesium ions?,which improve hardness of water,widely exist in many kinds of natural water bodies and wastewaters.It is of a great significance that study the effects of initial p H,C/N and Ca²⁺/Mg²⁺ on denitrifying degradation of quinolineIn this study,quinoline was used as carbon source and sodium nitrate as nitrogen source.The effects of initial pH,initial C/N and Ca²⁺/Mg²⁺ dasages on denitrifying degradation of quinoline were studied.The main results from this study are follows:?1?The optimum initial pH value was 7.5.concentrations of quinoline,nitrate and nitrite can be reduced to minimum values at any initial pH value?in the experimental range?,while CODs were still surplus in the end of rections.The surplus CODs were varied from initial pH value: with the initial pH value increased,the surplus COD become lower.?2?The changing rules of pH were correlated with initial pH during the denitrifying degradation of quinoline,In neutral and basic environment,pH value decreased at first and then increased during the denitrifying degradation of quinoline.The higher the initial pH was,the greater the magnitude of p H decline was.While in acidic environment,pH value kept increasing during the whole process.The magnitude of pH increment was greater when the initial pH became lower.?3?Neutral and weak basic environment was optimum for the degradation of quinoline and reduction of nitrite.The degradation of quinoline and the reduction of nitrite were inhibited under both the acidic and basic environment.The effect of acid on denitrification than alkalinity did.In the basic environment,the inhibition of nitrite reduction was stronger than the inhibition of quinoline degradation.On the contrary,the inhibition of nitrite reduction was weaker than the inhibition of quinoline degradation in acidic environment.?4?The variation between final pH value and initial pH value was related to initial pH value.The amout of increasement of pH value became smaller or the amout of decreasement of p H value became lager with the initial pH became higher.The drop of pH was due to the hydroxylation of quinoline.Increasement of pH value resulted from denitrification.All these properties constituted a set of regulatory mechanism which adjusted pH value to a suitable range for the survival of microorganisms when system encountered acidic and basic environment.?5?The optimum of initial C/N was 4,while the proper initial C/N was 3-4.Both low and high initial C/N was disadvantageous to the degradation of quinoline,COD,nitrate and nitrite.Low initial C/N had a large effect on quinoline specific degradation rate while affected nitrate specific degradation rate little,High initial C/N had a little effect on quinoline specific degradation rate while affected nitrate specific degradation rate a lot.Low initial C/N had a larger effect on COD and NO₃^--N+0.6NO₂^--N specific degradation rate than high initial C/N did.?6?The optimum dosage of Ca²⁺/Mg²⁺ was 10 mg/L.High concentration of Ca²⁺/Mg²⁺ did not improve denitrificaon apparently but increace MLVSS which decrease specific degradation rate while low concentration of Ca²⁺/Mg²⁺ improved denitrification apparently.Low concentration of Ca²⁺/Mg²⁺ affected degradation of COD,quinline and nitrate,but had no effect on nitrite.Nitrite did not accumulate duiring the whole process when Ca²⁺/Mg²⁺ dosages was low.System appeared red intermediates with the degradation of quinoline when Ca²⁺/Mg²⁺ dosage was 0 mg/L.However,certain phenomenon did not appear at other Ca²⁺/Mg²⁺ dosages.?7?Low concentration of Ca²⁺/Mg²⁺ resulted in reduction of sludge concentration,High concentration of Ca²⁺/Mg²⁺ was in favor of increase of sludge concentration.MLVSS,which present microorganism concentration,keep stable for a long time when Ca²⁺/Mg²⁺ dosage was 1 mg/L.So it can be regarded that 1 mg/L Ca²⁺/Mg²⁺ was the minimun concentration to keep denitrifying system long-term stable running.