The Effect Of Ferrous Ion On Anaerobic Digestion And Aerobic Biological Denitrification

Anaerobic biological fermentation and aerobic biological denitrification are both the important parts of the wastewater biological treatment technology.These technologies are utilized by sewage treatment plants mostly.Anaerobic and aerobic treatment processes have matured with the progress of technology,but also need to be improved on processing efficiency.Iron as a type of microelement in activated sludge plays an irreplaceable role in the microbial cell.Iron is not only the active site of enzyme in cell,but the important element for cellular homeostasis and boosting metabolism.It has major operation significance to study the role of iron in the wastewater biological treatment.Comparative experiments of adding iron were made by anaerobic fermentation reactor and aerobic bioreactor.Influents of bioreactors are laboratory-made solution.It is necessary to reasonably regulate the operation of the reactor.To investigate the effect of Fe²⁺on anaerobic fermentation,the conditions of ion concentration and sucrose concentration had changed in the experiment,with examining and analyzing of the change of physical and chemical properties on reactors,and combining with fluorescence spectra.Aerobic biological denitrification experiment includes two stages:carbon source and no carbon source experiments.The reactors both inoculated mature aerobic sludge.To investigate the effect of Fe²⁺on nitrification and denitrification by changing ferrous ion concentration in reactors,this study analyzed nitrogen removal efficiency by determining nitrogen indexes,and explored the process of aerobic granulation by determining particle size.Relevant conclusions of the study are the following:?1?The removal rate of COD was increased from 86.3%to 90.6%with increasing Fe²⁺ concentration while COD of influent was decreased from 438.15 mg·L^-1 to 332.79mg·L^-1and the sucrose concentration of effluent was decreased from 15 mg·L^-1to 2.5mg·L^-1 under the condition of anaerobic digestion.COD of effluent had increased to some extent with increasing the sucrose concentration and decreasing the Fe²⁺concentration.?2?pH of effluent increased while adding Fe²⁺.The date of serious acidification had been postponed 11d on the UASB which had a higher concentration of Fe²⁺compared with control group when the anaerobic fermentation process was inhibited.Take the sludge which reactors running 80d and 124d respectively to measure.The iron source was 24772.6 mg·kg^-1 and 13096.9 mg·kg^-1 respectively.Continuous addition of source of iron will cause iron accumulation in activated sludge.The results revealed that iron could accumulate in anaerobic activated sludge by adding in reactor consistently.The iron content of effluent from the UASB reactor was always less than 1 mg·L^-1.?3?Adding iron could promote the degradation of fatty acid,with accelerating the degradation of acetic acid and the accumulating of propionic acid.Water-soluble Fe²⁺which has absorption could reduce the concentration of SS.Upon light microscope analysis,the granular sludge which adding iron was bigger than the control group one.The result showed that iron could promote accumulation in activated sludge.?4?By three-dimensional fluorescence method,it was parsed out that the dosing of water containing iron source material has four phosphors:tryptophan;tyrosine;coenzyme F₄₂₀;fulvic acid-like.The changing situation of each fluorophore could correspond with physicochemical property.The study showed the addition of Fe²⁺had largely improved the efficiency of anaerobic fermentation.?5?Aerobic biological denitrification experiments processed in SBR reactors denitrogenation by adding organic carbon source sodium acetate.Adding Fe²⁺promote the efficiency of the degradation of ammonia nitrogen and the production of nitrate nitrogen.The addition of Fe²⁺had slightly improved the efficiency of anaerobic fermentation.The degradation of COD on SBR reactors could reach upon 80%,and the removal rate on the experimental group was higher than the control group.The result showed that Fe²⁺is conducive to the removal of organic matter.Upon light microscope analysis,the granular sludge which adding iron was bigger than the control group one.The result showed that iron could promote accumulation in activated sludge.?6?When the concentrations of Fe²⁺were set to 0.002mg·L^-1,0.5mg·L^-1 and 1 mg·L^-1,respectively,the ammonia nitrogen removal rate were 98.4%?99%?99.2%,total nitrogen removal rate were 37.5%?37.3%?37.6%.Fe²⁺has little influence on the degradation of total nitrogen.The production of nitrate nitrogen and nitrite nitrogen increased slightly,however in general,the effect of Fe²⁺is not obvious.After adding Fe²⁺,Zeta potential of effluent became lower then the potential of influent while the potential difference of influent and effluent increased.It is suggested that Fe²⁺improve the aerobic sludge granulation.This conclusion has been well established in the granular size.With increasing Fe²⁺concentration,D50 of granule sludge was enhanced.