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Application of iron-carbon microelectrolysis in wastewater treatment

1. Mechanism of action of iron-carbon microelectrolysis
       1.1, micro-electrolysis working principle:
       General principle: Iron-carbon micro-electrolysis is based on the galvanic cell reaction in electrochemistry. When iron and carbon are immersed in the electrolyte solution, since there is a 1.2V electrode potential difference between Fe and C, a myriad of microbattery systems are formed, and an electric field is formed in the working space. The new ecological divalent iron ions produced by the anodic reaction have strong reducing ability, can reduce certain organic substances, and can also make certain unsaturated groups (such as carboxyl-COOH, azo-N=N-) The key is opened to decompose part of the refractory cyclic and long-chain organic matter into biodegradable small molecular organic substances to improve biodegradability. In addition, divalent and trivalent iron ions are good flocculants, especially the new divalent iron ions have higher adsorption-flocculation activity, and adjusting the pH of the wastewater can make the iron ions become flocculent precipitates of hydroxides. Adsorption of suspended or colloidal fine particles and organic polymers in the sewage can further reduce the chromaticity of the wastewater, and at the same time remove some organic pollutants to purify the wastewater. The cathodic reaction produces a large number of new ecological [H]] and [O]. Under acidic conditions, these active components can undergo redox reaction with many components in the wastewater, causing the organic macromolecule to undergo chain catalysis degradation. Eliminate the color of organic wastewater and improve the biodegradability of wastewater.
       Iron carbon primary battery reaction:
       Anode: Fe - 2e → Fe2+ E(Fe/Fe2+) = 0.44V
       Cathode: 2H+ + 2e → H2 E(H+/H2) = 0.00V
       When aerobic is present, the cathodic reaction is as follows:
       O2 + 4H+ + 4e → 2H2O E(O2) = 1.23V
       O2 + 2H2O + 4e → 4OH- E (O2/OH-) = 0.41V
       1.2, the general micro-electrolysis reaction is: the iron atom and the carbon atom are next to each other or form a galvanic cell reaction. This iron-carbon contact is not conducive to the transfer of electrons, and the charge efficiency is low, so the removal efficiency of organic matter in the wastewater is generally low. At the same time, when the iron carbon is layered, it will be more detrimental to the removal of organic matter.
       1.3. The iron-carbon-containing micro-electrolysis reaction is: the primary battery reaction formed by the iron atom and the carbon atom being mutually contained. This iron-carbon contact does not have the problem of delamination of iron and carbon, so it is more conducive to the transfer of electrons, higher charge efficiency, and higher removal efficiency of organic matter in wastewater.
2. Progress in the application of iron-carbon microelectrolysis technology in wastewater treatment
       2.1. Application in the treatment of printing and dyeing wastewater
       As a new wastewater treatment method, iron-carbon micro-electrolysis technology was originally applied to the treatment of printing and dyeing wastewater, and achieved good results. The organic pollutants in printing and dyeing wastewater mainly come from dyes and dyeing and finishing additives. In recent years, due to the continuous advancement of printing and dyeing technology and the continuous emergence of new organic synthetic dye products, printing and dyeing wastewater has low pH, deep color, high toxicity and biodegradability. Poor sex and other characteristics. Therefore, the treatment of iron-carbon microelectrolysis for printing and dyeing wastewater reflects the incomparable advantages of other processes.
       After testing, two different printing and dyeing wastewaters with a chroma of 300 times, a COD of 602 mg/L, a pH of 9.76 and a color of 700 times, a COD of 1,223 mg/L and a pH of 5.76 were studied. The ratio is 1:1, the pH is about 3.0, and the reaction time is 20-30 min. The removal rate of chromaticity can reach more than 95%, and the removal rate of COD can also reach 60-70%.
       The printing and dyeing wastewater was treated by iron-carbon microelectrolysis. The results showed that the pH was 3, the contact time was 20-30 min, the chroma removal rate was over 90%, and the COD removal rate was also about 60%.
       For printing and dyeing with high COD or high effluent requirements, the simple treatment with iron-carbon micro-electrolysis does not meet the effluent requirements, and is often combined with other advanced oxidation treatment processes as a pretreatment for biological treatment. The printing and dyeing wastewater with a raw water COD of 11000 mg/L, a pH of 6, and a chromaticity of 8000 times was pretreated by iron-carbon microelectrolysis. When the iron powder has a particle size of 18 mesh and the coke particle size is 2 to 4 mm, iron powder and The coke ratio is 1:1. When the residence time in water is 60-90 min, the decolorization rate is over 90%, and the BOD/COD value is increased from 0.23 to 0.59, which greatly improves the COD removal rate of subsequent biological treatment.
2.2. Application in papermaking wastewater treatment
       Papermaking wastewater is mainly derived from cooking, washing, sieving and bleaching in the pulping process. Wastewater contains a lot of biodegradable substances such as lignin. Many papermaking enterprises can not discharge water pollutants such as CODCr and chromaticity after physicochemical treatment and secondary biochemical treatment. First-class standard.
       The effluent color of the papermaking black liquor treated with white rot fungi-anaerobic-aerobic biological method is too high, and the COD can not reach the standard. The iron-carbon microelectrolysis reaction column is used to decolorize and remove COD. At normal temperature, the mass ratio of iron to carbon is 2:1, the initial pH is between 4.5 and 5.5, the reaction time is 30~40min, and the final chroma and COD removal rates are 94.2% and 68.9%, respectively. The effluent reaches the industry emission standard. .
       The enhanced iron-carbon micro-electrolysis is used to deeply treat the secondary effluent of pulp and paper, and an appropriate amount of H2O2 is added into the iron-carbon micro-electrolysis reaction system to form Feenton reagent for Fe2+ and H2O2 produced by electrolysis, and synergistically with iron-carbon microelectrolysis. After strengthening the micro-electrolysis reaction, the pH value of the water is adjusted to neutral by Ca(OH)2, and Fe(OH)2 and Fe(OH)3 flocs are formed with Fe2+ and Fe3+ in the electrolyte, and further CODCr in the water is trapped. The Fe2+ and Fe3 and SO42+ plasmas in the water are removed, and the chromaticity of the solution is further improved. The results show that when the initial pH value of the solution is 3.0, the dosage of activated carbon is 8.0g/L, the cast iron filings are 40.0g/L, H2O2 is 7.17mmol/L, and the reaction time is 60min, the input amount of Ca(OH)2 is 8.0g. At /L, the total CODCr and chroma removal rates reached 75% and 95%, respectively, reaching the national standard for water pollutant discharge in the paper industry (GB3544— 2001).
2.3. Application in coking wastewater treatment
       At present, the main treatment processes of coking wastewater in China are mainly A/O and A-A/O processes, but the effluent contains high concentrations of ammonia nitrogen, highly toxic CN and organic substances that are difficult to biodegrade, which have inhibitory effects on microorganisms. Therefore, some people use micro-electrolysis technology to pre-treat and deep-process A2/O influent or effluent separately, and finally make the effluent reach the national first-class emission standard. The experimental study on the pretreatment of coking wastewater by iron-carbon microelectrolysis and Fenton reagent combined with oxidation was carried out. The optimum process conditions were determined by single factor experiment. The ratio of iron to carbon was 4, and the dosages were 300mg/L and 75mg/L respectively. The removal rate of COD, NH3-N and CN- was 61.2%, 74%, 56.2% and 74.3%, respectively, when the amount of H2O2 was 1000 mg/L, the pH was 3, and the reaction time was 20 min. The B/C ratio increased from 0.189 to 0.387, greatly reducing the organic load of subsequent biological treatments and increasing the efficiency of biological treatment.
2.4. Application in pharmaceutical wastewater treatment
       At present, the main problems faced by pharmaceutical wastewater treatment are many types of pollutants, high concentration and complex composition, and large impact load. The presence of antibiotics in some wastewaters inhibits the growth of microorganisms during biochemical treatment, and has poor biodegradability and high chroma.
       The engineering practice shows that the iron-carbon micro-electrolysis method has a good removal effect on the COD and chromaticity of the pharmaceutical wastewater of various components, and the B/C is improved.