Study On Denitrification Via Nitrite Under Normal Temperature

The thesis centers on denitrification via nitrite.Some studies on treatment performance,influence factor,sludge character and kinetics were performed under normal temperature,using a Sequencing Batch Reactor(SBR),a Upflow Sludge Blanket Reactor(USB) and a Air Lift Reactor-Upflow Sludge Blanket Reactor,aiming to provide appropriate condition and technics parameter for biological nitrogen removal from waste water.Results of SBR experiments showed that influent loading should be controlled within 0.192gNO₂^- -N/gMLSS.d,or else sludge turned deteriorated after enduring free nitrous acid to some degree.Inhibition arose when concentration of free nitrous acid reached 0.032mg/L.PH value had a great effect on treatment performance of denitrification via nitrite.Suitable range of pH value was between 7.7 and 8.6 and the optimal pH value was 8.2.Nitrogen could be continuously removed when C/N ratio was beyond 1.94.Starting specific substrate degradation rate rose with C/N ratio rising,but it hardly increased when C/N ratio was higher than 3.11.Saturation constant Ks of C/N ratio was 9.36mg/mg by kinetic analysis on experimental condition.Inhibition type of free nitrous acid belonged to substrate inhibition and reaction was completely inhibited when its concentration reached 0.13mg/L.Kinetic constant of inhibition was 536.9mg/L.Results of USB reactor experiments showed that the highest removal loading reached 0.97gNO₂^- -N/L·d when HRT was 1.9h,C/N ratio was 2.95 and influent loading was 1gNO₂^- -N/L·d.The treatment performance depended on the quantity of carbon source on the premise that influent loading was less than maximal removal loading of the reactor,or else the increase of carbon source had little effect.Influent loading should be controlled within 1.28gNO₂^- -N/L·d.If it exceeded maximal removal loading of the reactor,sludge turned deteriorated and was beyond retrieve.Granular sludge was cultivated after the reactor had been operating for six months.But it began to break up and mineralize content was high as velocity of flow rising.The activity of sludge was reduced.The morphology and section characteristics of granular sludge was observed through scan electron microscope.The major element of mineralize was Ca.Some studies on nitrite accumulation in nitrification process in air lift reactor were performed in this experiment.Treatment performance of combined process of nitrification-denitfification was also studied by combining air lift reactor with upflow sludge blanket after it had been operating for six months.The results showed that when concentration of influent ammonia was more than 98mg/L and free ammonia reached 7mg/L,concentration of effluent nitrite started to rise and over 50%of nitritation rate(NO₂^- -N/NO_x^- -N)could be achieved.When sludge loading was close to 0.53kgNH₄⁺N/kgMLSS·d,ammonia removal rate was quite high and nitritation rate was maximum.But when sludge loading reached 0.85kgNH₄⁺N/kgMLSS·d,ammonia removal rate fell and the conditiori couldn't be improved according to increasing DO and reducing loading.There was obvious granular sludge in upflow sludge blanket reactor.Treatment performance of ultimate effluent turned good obviously when carbon source was enough(C/N ratio was over 3).