Study on the treatment process of paint wastewater.

Abstract: On the basis of the study of microelectrical and H2O2 oxidation, the paper puts forward a treatment scheme using micro-electrolyte chemical oxidation method for coated paint wastewater, and the optimal micro-electrolyte reaction conditions and oxidation conditions are determined by experiments. The experimental results show that the method can reduce the ρ (CODcr) of raw water from 4000mg/L to 100mg/L, the CODcr removal rate of wastewater is >95%, and the discharge water can meet the discharge standard. In this study, the problems of microelectration scheme are analyzed, and some solutions are put forward

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coating is one of the most important parts of wastewater discharge in the process of steel drum manufacturing. The wastewater mainly comes from the washing water in the production process, the paint room wastewater, commonly known as paint waste water. This type of paint wastewater contains degreasing (degreasing) agent, rust remover, phosphate agent, etc., the main pollutants are CODcr, BOD5, petroleum, acid, alkali, total phosphorus, Cr6 plus, Pb2 plus, Zn2 plus, etc., its biodegradation performance is poor, if discharged directly, it will have a serious impact on the water environment. In this study, the paper studies this kind of paint wastewater and proposes to treat this kind of water by microlysal-chemical oxidation method, so that it can meet the emission standards stipulated by the state.
1 Process Research
1.1 Basic Principles
Microelectrulation is a low-power Fe and a high-power C in wastewater composed of a large number of primary batteries, iron as an anode corrosion, carbon as cathode. These tiny primary batteries form a difference in the likee, producing electrode reactions and a series of reactions that cause organic matter and inorganic contaminants in wastewater to be treated from the wastewater. The main roles are electric field action, Fe's reduction effect, the oxidation effect of the new ecology, filtration, adsorption, coagulation and so on.
chemical oxidation is mainly under the influence of chemical oxidants, so that the organic matter in wastewater is further degraded to a stable inorganic salt with little impact on the natural environment. For wastewater treated by microlytic reactor, the wastewater contains a certain amount of Fe2, Fe3, can catalytic oxidant H2O2, the release of redoxion can be relatively high OH free fundamentals. Under the joint action of OH free agent and H2O2 oxidants, the organic matter in wastewater is degraded.
1.2 main instruments and pharmaceutical
experimental instruments: HJ-6A type number display thermostat, pH instrument, WGZ-200 turbidity meter.
: cast iron chips, activated carbon, 30% H2O2 solution, PAM and so on.
1.3 unit and process
This experimental device uses a cylindrical cylindrical glass microelectrical reaction column with an internal diameter of 90 mm and a length of 1 m. The column is filled with microelectrical fillers consisting of activated iron chips and activated carbon. After the micro-electrolytic reaction column treatment of water, and then further oxidation treatment, and finally add alkali-adjusted pH value of 8 to 8. 5, so that it generates precipitation, in order to remove the water Fe2 plus, Fe3 plus, reduce the water-like CODcr and color. The overall process used in the experiment is shown in Figure 1.
2 experimental results and discussion
2.1 microelectrectration experiment
on the basis of consulting literature and preliminary experiments, the study selected microelectrectrative filler Fe/C volume fraction ratio of 1:1. In order to determine the best process conditions, this study experimented with the pH and reaction time of the water in the water with the greatest effect on the treatment effect.
2.1.1 Determination of the pH of infilled water
take a certain volume of microelectrectrectrectrectrectration fillers, adjust a certain amount of coated paint waste water to different pH conditions, respectively, microelectrectration test, the results are shown in Figure 2. As can be found from the figure, the removal rate of CODcr is more than 85% when the pH is 2.5 to 3.5. When the pH is greater than 3.5, the processing effect is worse. The reason for the analysis may be that when the pH is high, the iron chips are passivated, affecting the processing effect. Therefore, when the activated carbon microelectration method is treated with paint wastewater, the pH of the infringing water should be adjusted to 2.5 to 3.5 as the best.
the optimal reaction time of 2.1.2
the removal rate of CODcr was different according to the dwell time of the original wastewater in the microelectrical reaction column. The effect of reaction time on CODcr removal rate is shown in Figure 3. As can be seen from the figure, the removal rate of CODcr will increase with the extension of reaction time, but increase to a certain extent, the removal rate of CODcr will decrease. Considering this and the reaction time is too long, it will cause excessive consumption of iron chips, reduce the life of the microlyzing reaction column, increase the amount of sludge, in economic practicality is not possible, so determine the optimal reaction time of 60 to 70min.
based on the best experimental conditions determined by the above static experiments, dynamic microelectration reaction experiments are carried out. Adjust the flow of water so that its stay time in the column is 60 to 70min, the pH of infested water is 2.5 to 3.5, at this time the CODcr mass concentration of water is 323.8 mg/L.
2.2 oxidation test
the waste water is treated by microelectration before oxidation test is carried out. Take a certain amount of microelectrectration, adjust the pH, use HJ-6A-type number display thermostat to heat the water sample to 50 degrees C, according to each liter of wastewater add 30% H2O24 mL of the addition of H2O2. After the reaction, the pH is adjusted with sodium hydroxide solution of 8 to 8.5, a small amount of PAM can be added, and the CODcr can be measured by filtering solution.
In order to further determine the feeding method of oxidants, a certain amount of water samples were taken, and under the conditions of temperature of 50 degrees C, pH of 5 and reaction time of 20min, H2O2 was tested using multiple cast and addition methods (one, two, three and four). In multiple casts, 5min intervals are made between the two. The experimental results showed that the removal rate of CODcr was 54.10%, the total CODcr removal rate was 55.10%, the total CODcr removal rate was 59.03% in three and CODcr removal rate was 60.91%. It can be seen that the effect of multiple cast and add processing is better than one cast plus. A cast extra time, produce a large number of bubbles, and in batches of extra time, there are fewer bubbles. This is because a one-time cast plus H2O2, H2O2 can not completely oxidize the organic matter in the water sample, partially in the form of gas overflow, and batch add-on can avoid the loss of H2O2, improve its utilization rate.
2.3 Microelectrical-Chemical Oxidation Experiment
Under the best experimental conditions determined, a certain amount of raw wastewater was taken for micro-electrolyte-chemical oxidation stability experiment, with two measurements 24h apart, and the experimental results were found in Table 1.
3 Conclusion and discussion
3.1 Conclusion
(1) When treating electrophoresis wastewater by activated carbon/iron chip microelectrolysis, the optimal operating parameters are: the volume fraction ratio of activated carbon/iron chip is 1:1, the infested pH is 2.5 to 3.5;
(2) when using hydrogen peroxide water oxidation microelectrative water, the best operating parameters are: 30% H2O2 solution of the injection and addition of 4 mL per liter of wastewater, oxidation temperature of 50 degrees C, pH of 5, reaction time of 20 min, cast and H2O2 using multiple injection and addition method, CODcr removal rate of more than 60%.
(3) the use of micro-electrolyte-chemical oxidation treatment paint wastewater effect is good, the total COD removal rate of more than 95%. And experiments show that the treatment stability is good, the water discharge effect is not large fluctuations, CODcr removal effect is also very good, has been far lower than the class of three-level emission standards (ρ (CODcr) <500mg/L), this method is applicable to a small number of high concentrations of organic wastewater.
3.2 Problems and improvement measures
At present, the reactor of the microelectrical process is an upright traditional microelectrical reaction column, although the technology has been put into industrialization, but many tests have proved that the reactor still has the following problems:
(1) filler block. The most common fillers in the microelectrolyzing reaction column are steel chips and cast iron chips, which affect the processing effect due to the generation of insoluble substances such as Fe (OH) 2 and Fe (OH) 3, which lead to the phenomenon of filler plate knotting, ditch flow and other problems.
(2) filler replacement. In a microlyzing reactor, iron chips are constantly consumed. When the iron chip is reduced to a certain extent, it will affect the treatment effect of internal electrolyte, so the iron chip must be replenished. If iron chips are directly cast into the reactor, iron chips and carbon particles cannot be fully mixed, which will affect the treatment effect of microelectrulation. If all the fillers are cleared and reloaded with a good mix of new fillers, the process is not only very heavy workload, but also requires a large site, implementation difficulties.
(3) reactor is blocked. With the growth of microelectrical reaction column running time, more and more suspended matter will be gathered in the filler, coupled with the thick set of metal hydroxide, easy to block the filler pores, affecting the treatment effect of water, so it is possible to periodically reverse. Due to the high density of iron chips, the need for very large flushing strength, so engineering applications must be equipped with larger equipment, increased investment.
, in view of the above shortcomings of microelectrical treatment of industrial sewage, the process was improved in this study (Figure 4).
Change the upright micro-electrolyte reaction column to a horizontal horizontal micro-electrolyte reaction column, and add imperfectation machine to make it rotate at a uniform speed, while the micro-electrolyte reaction column leaves a certain proportion of space, so that the filler can roll in the reaction column, so as to avoid the blockage and knot of the filler Block; because the process only consumes iron chips, carbon does not consume, in the micro-electrolyte reaction column wall proportionally open a certain number of holes, easy to regularly increase iron chips, increase fillers, open the holes;
addition, the microelectrical reactor can be designed as a mechanical agitation, which can destroy the inert layer of the iron chip surface and avoid precipitation clogging. And the strong stirring speed up the reaction speed, can accelerate the production of Fe2 plus, which is good for the subsequent process of coagulation precipitation.
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