I. Introduction and differentiation of iron-carbon microelectrolysis process

1. What is iron-carbon micro-electrolysis:

It refers to a wastewater treatment process in which the weak current of iron and charcoal spontaneously generated in the electrolyte solution decomposes the pollutants in the wastewater.

When the iron filings and carbon particles are immersed in the acidic wastewater, due to the electrode potential difference between the iron and the carbon (0.9 to 17 V), numerous micro-primary cells are formed in the wastewater. These microbatteries are made of iron having a low potential as an anode, and carbon having a high potential as a cathode, and an electrochemical reaction occurs in an aqueous solution containing an acidic electrolyte. A large number of primordial Fe2+ and new ecological [•H] produced in the field have extremely high chemical activity, which can change the structure and characteristics of many organic substances in wastewater, and cause the organic matter to break chain and open ring.

The iron-carbon micro-electrolysis process is a combination of oxidation, reduction, electro-precipitation, flocculation, adsorption, bridging, sweeping and co-precipitation.

2. What is the optimal PH range for iron-carbon microelectrolysis?

The optimal use range of iron-carbon microelectrolysis is 3~4. In this PH range, the annual consumption of high-temperature sintered iron-carbon micro-electrolytic filler is 10%-15% (individual manufacturers will talk about the suitable PH range of their fillers). It is 5-7, which is not in accordance with the reaction principle of iron-carbon micro-electrolysis. Therefore, the main principle of this kind of filler for wastewater treatment is the adsorption of activated carbon in iron-carbon, which is not achieved by the principle of true micro-electrolysis.

3. Advantages of iron-carbon microelectrolysis process:

Wide application range, good treatment effect, low cost, convenient operation and maintenance, no need to consume power resources, fast reaction speed, stable treatment effect, no secondary pollution, improved biodegradability of wastewater, chemical precipitation and phosphorus removal, It can be used to remove heavy metals by reduction, and can also be used as pretreatment for biological treatment, which is conducive to sludge sedimentation and biofilming. At present, the mature industries are: chemical, pharmaceutical, dyes, pigments, rubber additives, phenolic resins, electroplating, circuit boards, landfill leachate, printing and dyeing, coal chemical industry, etc.

4. Where did the iron and charcoal go during the reaction:

In the high-temperature sintered iron-carbon micro-electrolytic filler, iron and carbon are not present in the form of large particles, but exist in the form of a total structure in which iron is converted into divalent iron ions in the wastewater and precipitated by subsequent flocculation; As the dissolution of iron continues to fall off, the extremely fine carbon particles after detachment will adsorb pollutants into the sedimentation tank and flocculate and precipitate.

5. What is high temperature sintered iron-carbon micro-electrolytic filler:

The high-temperature sintered iron-carbon micro-electrolytic filler is an integrated alloy structure formed by melting iron powder, carbon powder, catalyst and other components through high temperature (over 1300 ° C), so the physical strength of the filler is strong (≥600kg/cm2); The pore structure provides a large specific surface area and a uniform water and gas passage for the micro-electrolysis reaction, and provides a larger current density and a better catalytic reaction effect for wastewater treatment.

6. How to distinguish whether the iron-carbon micro-electrolytic filler is high-temperature sintering:

By beating or performing related tests: high-temperature sintering micro-electrolytic fillers are not easily broken. Non-high temperature sintered micro-electrolytic fillers are very easy to break and even break when broken.

Porosity detection, can be thrown into the water to see the amount of bubbles generated: high-temperature sintered micro-electrolytic filler has a true porosity, and the porosity reaches 65%, after throwing into the water, the amount of bubbles is large, uniform, long-lasting; strong ability. The non-high temperature sintered micro-electrolytic filler has almost no porosity, and after being thrown into the water, there is almost no bubble amount; the unit filler has a weak ability to treat sewage.

Whether it is a real alloy structure: After sanding the filler with sandpaper or cutting the filler with a die-cutting machine, the high-temperature sintered iron-carbon micro-electrolytic filler has obvious metal Guanze, which is a true alloy structure. The non-high temperature sintered iron-carbon micro-electrolytic filler is polished or die-cut, and the metallic luster of the alloy structure is observed every day.

7. Why use high-temperature sintered iron-carbon micro-electrolytic filler:

The selection of high temperature sintered iron-carbon micro-electrolytic filler is the key to ensure the normal operation of micro-electrolysis process. The high-temperature sintered iron-carbon micro-electrolytic filler does not appear to be knotted or passivated during use. Its physical strength of 1000kg/cm2 is sufficient to withstand the pressure of 20m water column and the erosion of the filler by acidic wastewater, and non-high temperature sintered iron carbon does not appear. High-temperature sintering of iron-carbon micro-electrolytic fillers must be used for the pulverization, passivation, and slab formation of the filler in the water column pressure and the erosion of acidic wastewater.

8. Why does the high-temperature sintered iron-carbon micro-electrolytic filler need not be replaced:

Iron and charcoal are consumed at the same time, and the ratio of iron to char in the filler is not changed, so the consumption of the filler during the reaction is only a quantitative change, not a qualitative change. Therefore, as the filler is consumed, only a new filler needs to be added. In the case of the influent PH3 to 4, the annual consumption of the high-temperature sintered iron-carbon microelectrolytic filler is 10% to 15%.

2. Research progress and application status 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 microelectrolysis 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, forming an electric field 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 reactions with many components in the wastewater, causing the organic macromolecules to undergo chain-breaking degradation, thereby eliminating The color of organic wastewater improves 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 electron transfer, 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 first 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 synthetic dyes, the 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 color 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 over 95%, and the removal rate of COD can also reach 60-70%.

The 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 water demand, the simple treatment with iron-carbon micro-electrolysis can not meet the requirements of water discharge, and often combined with other advanced oxidation treatment processes as pretreatment for biological treatment. The printing and dyeing wastewater with a raw water COD of 11000mg/L, a pH of 6, and a chromaticity of 8000 times is 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. The wastewater contains a lot of hard-to-biodegradable substances such as lignin. Many papermaking enterprises can not discharge the water pollutants of the national paper industry after the first-level physicochemical and secondary biochemical treatment. First-class standard.

Aiming at the phenomenon that the effluent color of the papermaking black liquor treated with white rot fungi-anaerobic-aerobic biological method is too high, and COD can not reach the standard, the study of decolorization and COD removal of effluent by iron-carbon microelectrolysis reaction column is found. 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. .

Advanced treatment of secondary effluent from pulp and paper is carried out by enhanced iron-carbon microelectrolysis. The appropriate amount of H2O2 is added to the iron-carbon microelectrolysis 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 the CODCr in the water is further captured. 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).