[China Aluminum Industry Network] Aluminum is a very active metal. In order to prevent surface oxidation or defects caused by the surrounding environment, aluminum profiles need to be surface treated before use. Through the treatment, a protective film can be formed on the surface of the aluminum profile, and the protective film plays an important role in appearance, corrosion resistance, mechanical strength, and service life extension [1]. Treatment of aluminum surfaces requires the consumption of large amounts of water, and usually 50 to 80 tons of water per ton of aluminum surface treatment. The waste water produced by aluminum surface treatment is mainly acid-alkali wastewater, which contains a large amount of Al3+, SO42- and a small amount of Ni2+, Sn2+, Cr3+, F-, etc. The wastewater is usually treated with acid-base neutralization method. The wastewater is generally acidic and must be neutralized with alkali. During the neutralization process, the formation of hydroxides such as Al3+, Ni2+, Sn2+, and Cr3+ are removed during adsorption and precipitation; and the anions such as SO42- and F- are coagulated. The cations such as Ca2+ and Fe2+ precipitated and were partially removed. The main water-consuming links for surface treatment of aluminum profiles are post-washing processes for the processes of degreasing, alkaline etching, neutralization, and oxidation. The water quality requirements of the above-mentioned links are not too high. The pH of the water after washing, neutralization, and oxidation is required. Above 2, alkaline washing water after the need to be less than pH 12, turbidity is less than 50NTU, Al3 +, SO42-, respectively, less than 500, 2000mg / L to meet the requirements [2]. Therefore, the author uses the coagulation + microfiltration membrane separation and combination process to treat aluminum surface treatment wastewater in order to achieve the purpose of reuse. The effective volumes of the coagulation tank, inclined tube sedimentation tank and filter tank are 30, 50, and 80L, respectively. The microfiltration membrane is made of polyethylene hollow fiber membrane manufactured by Mitsubishi Corporation of Japan. The membrane pore diameter is 0.1 μm, and the membrane diameter is 0.27 mm. 0.42mm, membrane area 2.0m2. The membrane module is placed directly in the filter tank and an air aeration tube is provided below it to function as a flush membrane module. Membrane modules are equipped with solenoid valves at both ends of the outlet pipe to control the system's outlet and anti-aeration with a time controller. 2. Results and Discussion 2.1 Coagulation Sedimentation Test In this study, 25 coagulants of FeCl2, FeCl3, Fe2(SO4)3, AlCl3, and Ca(OH) were selected. In order to increase the degree of compaction of flocs, PAM was selected as a coagulant aid. . Coagulant dosing concentrations were 100, 150, 200, and 250 mg/L, respectively; Coagulant dosing concentrations were 2, 4, 6, and 8 mg/L, respectively. After a comparative test, the optimum dosing amount and flocculating effect of various coagulant/coagulant were obtained. The results are shown in Table 1. From Table 1, it can be seen that the coagulation effect of Ca(OH)2/PAM is significantly better than that of other coagulants. When the mass concentration of Ca(OH)2 was 200 mg/L and the mass concentration of PAM was 4 mg/L, the effluent turbidity after coagulation and sedimentation was 50 NTU. The effluent Al3+ and SO42- were lower than 18, 1500 mg/L, respectively. Shows that the use of a single coagulation and sedimentation treatment of aluminum surface treatment wastewater, barely able to achieve degreasing, alkaline corrosion, neutralization, oxidation and other processes for water quality requirements, but the amount of coagulant dosage, and the water quality is not stable enough. As can be seen from FIG. 2 , the turbidity of the final effluent after filtration by the microfiltration membrane is about 10 NTU, which completely satisfies the requirements for turbidity of the water-washing step after degreasing, alkaline etching, neutralizing, and oxidizing processes. Fan Light,Ceiling Fan Light,Led Ceiling Lamp Light,Led Ceiling Fan JIANGMEN MOSCOT OPTOELECTRONIC TECHNOLOGY CO.,LTD. , https://www.sensorsled.com
In this study, the coagulant and sedimentation test was used to determine the preferred coagulant, coagulant and dosage of the combined process. Then the effect of microfiltration membrane operating factors on the membrane filtration performance and the overall operational effect of the combined process were examined. And conducted a technical and economic analysis. The combined process can achieve the goal of water conservation and pollution reduction, with social, environmental and economic multiple benefits.
1. Test materials and methods 1.1 Test water The equipment used is directly placed next to the integrated wastewater conditioning pool of the aluminum profile surface treatment production line of an aluminum profile plant in Foshan City, Guangdong Province. (In addition to wastewater containing a single type of pollutant such as chromium and nickel After the treatment, it enters the regulating tank and the remaining waste water enters the regulating tank directly. The waste water is taken directly from the integrated wastewater conditioning tank. Its water quality is: Al3+500~600mg/L, SO42-2000~3000mg/L, and turbidity 300~500NTU. pH3~5.
1.2 Test device The test device is shown in Figure 1.
Aluminum Surface Treatment Wastewater Treatment and Reuse Technology 
1.3 Test methods 1.3.1 Coagulant screening test In order to select the appropriate coagulant and coagulant aid, the coagulation effects of various commonly used coagulants were compared through sequential batch tests at the exploratory stage. According to the characteristics of aluminum surface treatment wastewater and follow-up wastewater treatment program needs, the turbidity, Al3+, SO42- removal rate and flocculation settling performance were selected as the measurement indicators to seek for better coagulant and dosage.
Take a few 1000mL beakers, add 500mL of comprehensive adjustment tank wastewater (water temperature and room temperature are around 28 °C), add the measured coagulant, add NaOH powder to adjust the pH to 8.0, and then add metering aids to each beaker Coagulating agent PAM; placed on the six-speed stirrer first stirring 360r/min 1min, then stirring at 150r/min 2min; stand 30min after the supernatant to test flocculation and sedimentation effect.
1.3.2 Coagulation + Microfiltration Membrane Separation Combination Test Coagulant and coagulant aid solution respectively enter the suction line of the inflow pump through the metering valve and enter the coagulation tank after being rapidly mixed with the raw water through the impeller; Inclined-tube sedimentation tank; The supernatant after the separation of sludge and water enters the filtration tank, and the filtered water is obtained through membrane filtration under the suction pump suction action. Inlet and outlet valves work alternately under the control of a time controller. According to the content of suspended solids in the effluent of the coagulation system, the sludge at the bottom of the filter tank is excluded once every 6 to 8 cycles. 
The single coagulation and sedimentation treatment is carried out by adding a sufficient amount of coagulant and coagulant aid so that the flocs that are formed by the colloidal particles suspended in water have good sedimentation performance can be removed. Using the coagulation + microfiltration membrane separation and combination process, the microfiltration membrane separation technology can achieve a solid-liquid separation level of the order of 0.1 μm, and the coagulant and coagulant added do not destabilize the colloidal particles only by compressing the double-layer. Yes, there is no need to form particles that depend on gravity for sedimentation. This not only reduces the amount of coagulant and coagulant, but also increases the range of contaminants that can be removed compared to single coagulation. The experiment did not change the Ca(OH)2 dosage (200 mg/L), but the coagulation aid PAM was only added in half (2 mg/L). The coagulation and microfiltration membrane separation combined process was used to treat the aluminum profile processing wastewater. The processing effect.
2.2 Effect of anti-aeration of microfiltration membrane on membrane filtration performance In this study, the average membrane flux was used as an evaluation index of membrane filtration performance. In order to reduce the degree of membrane fouling and maintain the stability of the membrane filtration performance, a cyclic anti-aeration operation was used to remove the cake layer deposited on the membrane surface. The pressure of anti-aeration was 0.15 MPa, and the time for each counter aeration was 3min. The results of membrane filtration performance change under different operating cycle conditions show that the anti-aeration of the membrane cycle can largely blow off the mudcake layer deposited on the membrane surface, reduce the membrane fouling, recover the membrane flux, and effectively maintain the membrane filtration. The stability of the performance; using filter 30min, anti-aeration 3min way, the cycle of water production can be stabilized at about 40L / (m2 & dot; h).
2.3 Coagulation + Microfiltration Membrane Separation Combined Process Performance Ca(OH)2 and PAM were used as coagulants and coagulant aids. The dosing mass concentration was 200, 2 mg/L, respectively, and the anti-aeration was carried out with 30 min filtration and 3 min. The mode of operation is stable for 2 weeks with an average membrane flux control of 40 L/(m2 ˙h). Coagulation + microfiltration membrane separation combined treatment of aluminum surface treatment of comprehensive wastewater treatment effect shown in Figure 2 and Figure 3. 
As can be seen from Figure 3, although the system influent SO42-fluctuated (mainly caused by irregular discharge part of the degreasing or light bath solution), but the final effluent SO42- stabilized at about 1000mg / L, the resulting calcium sulfate precipitation and hydroxide Adsorption of SO42- by aluminum precipitation may be the main way to remove sulfate radicals in this system; after the treatment process of coagulation+microfiltration membrane separation, the effluent Al3+ is stable at about 8 mg/L. After the combination process, the effluent of the system fully meets the requirements of the water for the washing steps of the degreasing, alkaline etching, neutralization, and oxidation processes on Al3+ and SO42-.
3. Technical and economic analysis Compared with the conventional process, the coagulation + microfiltration membrane separation and combination process for aluminum surface treatment wastewater has the advantages of stable water quality, small project footprint, capital construction and investment, high degree of automation, and convenient operation and management. [3], and the effluent can achieve the purpose of reuse.
Taking the daily treatment and reuse of 1000t waste water as an example, the technical and economic analysis of the process of separation and combination of coagulation and microfiltration membranes was carried out. The capital construction investment was 150,000 yuan, and the equipment cost (film price 150 yuan/m2) was 186,000 yuan. The depreciation expense was (membrane life is 3a, other is 20a) is 0.192 yuan/m3, energy consumption is 0.4 yuan/m3 (electricity fee is 0.8 yuan/(kW˙h)), pharmaceutical cost is 0.133 yuan/m3, labor cost is 0.15 yuan /m3, the total operating cost of the system is 0.875 yuan/m3. Compared to the current water cost of the enterprise of 2.5 yuan/m3 (including 1.3 yuan/m3 for tap water, 0.4 yuan/m3 for wastewater treatment, and 0.8 yuan/m3 for sewage), the economic benefits are very obvious.
4. Conclusions The process conditions for the treatment of synthetic waste water from surface treatment of aluminum profiles using a coagulation + microfiltration membrane separation and combination process are as follows: Ca(OH)2 as coagulant, PAM as coagulant, Ca(OH) The mass concentrations of 2 and PAM were 200 mg/L and 2 mg/L, respectively. The microfiltration membrane separation system was operated with 30 min filtration and 3 min anti-aeration. Under this condition, the system operated stably for 2 weeks. Although the influent water quality changed greatly, the effluent turbidity was stable at about 10 NTU, the Al3+ and SO42- were stable at about 8 mg/L and 1000 mg/L, and the effluent quality completely satisfied the degreasing and alkali corrosion. Water requirements for water washing after processes such as, neutralization, and oxidation. Compared with the conventional treatment process, the coagulation + microfiltration membrane separation and combination process has obvious advantages in technology and is economically feasible.
Aluminum Surface Treatment Wastewater Treatment and Reuse Technology