| In recent years,the research of phosphate reduction process focuses on the phosphine discovery and its detection means.The research in the application of phosphate reduction process to remove phosphorus from wastewater is just the beginning.Related research is still not perfect and contradictory phenomenon existses.The phosphate reduction reaction mechanism is not yet clear,generally regarded as the result of microbial action.Therefore,the in-depth study of the phosphate reduction process become the priority of dephosphorization technology breakthrough.First,Anaerobic sludge was cultivated and domesticated 90days in the UASB reactor.The COD removal efficiency was 87.99%,the phosphate removal efficiency was 59.49%,the phosphate removal speed was 21.11mg/(L·d),which was preferable sewage treatment efficiency.The MLSS and MLVSS were reduced in the earlier stage,then reach steady,a small amount of rise in the later period,the clarity of outlet water was better.The sludge proliferation was existed in the system and its amount was small.The resulting gas was detected by gas chromatographic analysis and chemistry detection,which was identified as phosphine.This can confirm the truth that the phosphate reduction process was came to pass.And the sludge with phosphate-reducing bacteria was domesticated success.The method of the secondary cold trap-gas chromatography adopted to identify the gas produced are phosphine,which served as the final product of the phosphate reduction reaction.Then,another method of the chemical absorption-antimony molybdenum spectrophotometry adopted to detect the gas produced,which indicates the accumulation at a certain level of phosphine.The Upflow Anaerobic Sludge Blanket(UASB)was worked as the dynamic reactor and a series of wide-necked bottles were worked as the static reactor to study the operation of the phosphate reduction reaction.The following content were performed on the process parameters of the phosphate reduction reaction.1.The precursor materials of the phosphate reduction reaction were studied.The six kinds of inorganic phosphorus source,that yellow phosphorus simple substance,sodium hypophosphite,sodium phosphite,potassium dihydrogen phosphate,dipotassium hydrogen phosphate,sodium hexametaphosphate,respectively,could produce phosphine,which can be the available phosphorus source of the phosphate-reducing bacteria.However,phosphate reduction efficiency was different.Based on the phosphate removal efficiency,which worked the best was potassium dihydrogen phosphate,the best phosphate removal efficiency was 69.72%.Based on the phosphate removal speed,which worked the best was sodium hypophosphite,the best phosphate removal speed was 5.76mg/(L d).Based on the amount of phosphine produced,which worked the best was sodium hypophosphite,the best phosphine produced was 401.1?g.According to the reaction process of phosphorus balance analysis,phosphate reduction reaction may be a slow process,the phosphorus in the low valence can be restored into phosphine easier.2.The sources of nitrogen and its concentration ratio of the phosphate reduction reaction were researched.When the ammonium salt was the single nitrogen source,its optimum N/P ratio was 4/1,the best phosphate removal efficiency was 79.03%.Insufficient ammonium would lead to stagnation of the phosphate reduction reaction,however,excess ammonium did not promote or inhibit the effect of the phosphate reduction system.Therefore,ammonium is one of the prerequisite nutritional factors for phosphate-reducing bacteria.When nitrate added in the system,ammonium existed simultaneously,its optimum N/P ratio was 1/1.The phosphate reduction reaction was promoted at this time,the best phosphate removal efficiency was 83.33%.Its equalized N/P ratio was 2/1.Promoting effect and inhibiting effect kept the balance at this time.Exceeds the equilibrium state,nitrate excess would inhibit the phosphate reduction reaction,the higher the concentration,the more obvious the inhibitory effect.3.The sources of carbon and its concentration ratio of the phosphate reduction reaction were researched.Under the anaerobic condition,in the six kinds of inorganic carbon source,that methanol,ethanol,sodium formate,sodium acetate,glucose,starch,respectively,the preferably phosphate removal efficiency were methanol and ethanol,which was 82.28%.When glucose worked as carbon source,its optimum C/P ratio was 120/1,which the best phosphate removal efficiency was 79.78%,and produced phosphine 82.0 ?g.Under the anoxia condition,the preferably phosphate removal efficiency were methanol and ethanol,which was 84.57%.When glucose used as the carbon source,the optimum reaction C/P ratio was 16/1,which the best phosphate removal efficiency was 87.06%,and produced phosphine 101.6 ?g.Low COD concentration would not be able to make the reaction to the end,high COD concentration would make the environment acidification and promote phosphate reducing bacteria inhibited by obligate anaerobe bacteria.4.The best temperature of phosphate reduction reaction was 31?.The phosphate removal efficiency was 69.72%.The phosphate removal speed was 4.45mg/(L d)at the 12th hour of system operation and was 3.92mg/(L d)at the 24th hour.It produced phosphine 82.0 ?g.In the actual process,the temperature fluctuations which can be controlled between 28? to 31?.The low temperature(ambient temperature below 11 ?)could lead to system collapse,the high temperature(ambient temperature above 37 ?)can lead to bacterial inactivation.5.The best pH value was 8.0.At this time,the phosphate removal efficiency was 70.12%,and it produced phosphine 93.3?g.The pH value was 7.5 took the second place.The phosphate removal efficiency was 69.72%,and it produced phosphine 82.0?g.The excessively high or low pH value(above 8.0 or below 6.0)would hinder the phosphate reduction reaction.Extreme pH value will destroy the physiological and biochemical properties of the microorganism and made it inactivated.Whatever,extreme pH value changes in the interspecific interactions between microorganisms or environmental conditions resulting in reduced efficiency.6.The best oxidation-reduction potential for phosphate reduction was from-130mV to-170mV in an anoxic environment.Anaerobic conditions could also made phosphate-reducing bacteria survive,but the aerobic environment would hinder the phosphate reduction reaction.Finally,the sewage treatment would been tested by phosphate reduction process to enter into the domestic sewage treatment.A perfect process effect could been got,in which the concentration of COD and ammonia can meet the A level of first class stand of the urban sewage treatment plant pollutant discharge standard(GB18918),in spite of phosphate cannot.The oxygen or anaerobic environment for the phosphate reduction process is more suitable than aerobic environment,so this process can be the main process in the anaerobic pool or anoxia pool of the A2O process to do dephosphorization. |
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