Research On Influencing Factors Of Iron Dissolution In Biological Sponge Iron System

The traditional biological iron method improves the purification capacity of activated sludge by adding iron salts to generate iron flocculation substances.However,due to the limited strengthening effect,complicated process and high investment and operating costs,it is relatively few in practical applications.The Fe⁰-bioferric method is to put Fe⁰ into the biochemical reactor to dissolve Fe²⁺through electrochemical corrosion and biocorrosion,and oxidize it to Fe³⁺through O₂,iron oxidizing bacteria and other substances.Shortcomings.As a special zero-valent material,sponge iron can be used as a biological carrier because of its loose micropores.When it is put into a biochemical reactor,a Fe⁰/O₂system will be formed.In the environment,chemical and biological effects will dissolve iron ions and participate in Fenton-like.Reaction,Fe²⁺catalyzes H₂O₂ to produce·OH,and·OH oxidizes and decomposes organic matter into small molecules through electron transfer and other means,effectively decomposing organic matter that is difficult to degrade It is not conducive to the progress of Fenton-like reaction,so it is particularly important to control iron dissolution.In this paper,the loose microporous zero-valent iron metal sponge iron was introduced into activated sludge with good degradation effect on ciprofloxacin to form a biological sponge iron system.The pH value of wastewater influent,sludge concentration,dissolved oxygen,The influence of sponge iron dosing method and organic load on the dissolution of sponge iron.Using the AUTOLAB electrochemical workstation and Nova1.10 software,the measured Tafel curve and its electrochemical parameters were processed and analyzed to obtain the corrosion rate.The corrosion rate was used to characterize the dissolution rate.Afterwards,the SBR reactor was used to continue the parallel test.The iron leaching amount was tested and analyzed,with Fe²⁺and TFe as the evaluation indicators,and then the effect of Fe²⁺on the degradation of ciprofloxacin and COD produced by the strong oxidizing substances（H2O2,·OH）involved in the Fenton-like effect was analyzed.Profloxacin characterizes the degradation effect of the biological sponge iron system on refractory organic matter,and the following conclusions are obtained:（1）The corrosion rate increases with the increase of sludge concentration,dissolved oxygen,and organic load,and decreases with the decrease of pH.The corrosion rate of sponge iron with carrier（composite carrier）is higher than that of sponge iron（single carrier）.The corrosion rate should be fast.（2）According to Tafel electrochemical parameter analysis,the sponge iron corrosion dissolution is mainly subjected to the electrochemical action under the combined action of anode activation dissolution and cathode oxygen diffusion control.In the biological sponge iron system,sponge iron is subject to electrochemical corrosion and microbial corrosion.Hydrogen evolution corrosion occurs under anaerobic and extremely acidic solutions.Oxygen absorption corrosion occurs under aerobic and solution neutral and alkaline conditions.Dissolved oxygen is sufficient,and oxygen corrosion occurs.In the biological sponge iron system,the sponge iron corrosion accounts for about 15%of the electrochemical corrosion,and the microbial corrosion accounts for about 85%.The electrochemical effect gradually increases,and the microbial effect gradually weakens.（3）The iron leaching amount increases with the increase of sludge concentration and dissolved oxygen,and increases with the decrease of pH;the iron leaching amount of higher organic load is larger;the iron leaching amount of sponge iron with carrier is larger.There are various forms of iron ions after leaching.The anaerobic and extremely acid conditions are mainly present in the supernatant in the form of ions.Most of the iron ions in the aerobic and alkaline conditions are oxidized in the form of precipitates or flocs.Part of the iron ions in the supernatant and the mixed solution participate in the Fenton-like reaction to degrade organic matter.（4）（1）The lower the pH,the faster the corrosion rate,the greater the iron dissolution rate and the amount of dissolution,the more strong oxidizing substances generated by Fenton-like action,the higher the degradation rate of ciprofloxacin,but strong acid condition deactivates sludge flocs,the degradation effect of CIP is ranked as pH=6>pH=7>pH=9>pH=4,the highest degradation rate of CIP is 95.65%;（2）The higher the sludge concentration,the faster the sponge iron corrosion rate,The greater the amount of dissolution,the more strong oxidizing substances produced by Fenton-like effect,the better the degradation effect of ciprofloxacin,the degradation effect is ranked as sludge concentration 5.0g/L>3.0g/L>1.2g/L>0.0g/L,the maximum degradation rate of CIP is80.1%;（3）The sponge organic iron with high organic load has a faster corrosion rate than iron with low organic load,the iron dissolution amount is larger,the stronger the Fenton-like effect,the highest degradation rate of CIP is 91.9%,the degradation effect The order is COD=1200mg/L>COD=2000mg/L>COD=800mg/L;（4）The use of a composite carrier accelerates the corrosion rate and increases the amount of iron dissolution.Due to the inhibitory effect of antibiotics on biological activity,the restriction is expanded Biological activity makes the sponge iron with carrier addition method slightly degrade the CIP than the direct addition of sponge iron.The CIP degradation rates are 79.55%and77.27%respectively;（5）The higher the DO,the faster the sponge iron corrosion rate,The greater the amount of dissolution,the more strong oxidizing substances produced by Fenton-like effect,the better the degradation effect of CIP,the order is DO 6-7mg/L>DO3-4mg/L>DO 0-1mg/L,the highest degradation rate of CIP is 92.05%.Different conditions in the biological sponge iron system are closely related to the iron dissolution rate,iron dissolution amount and the degradation of refractory organic matter.