Knowledge: Application of MBR in the upgrading of electroplating wastewater treatment facilities

Application of MBR in the upgrading and transformation of electroplating wastewater treatment facilities, a metal in Yuyao City, Zhejiang Province, mainly engaged in hardware and plastic partselectroplating Surface processing company, with a daily wastewater output of 250m/d (10h/d in a single shift).

Due to the different types of pollutants in the wastewater discharged by the electroplating workshops, the quality of wastewater varies greatly. The existing wastewater treatment facilities of chemical oxidation/reduction pretreatment + two-stage reactive precipitation treatment are difficult to treat the wastewater. Treated into compliance discharge. Therefore, the author designed an upgraded new wastewater treatment plan under the premise of continuing to use the existing wastewater treatment facilities and processes.

The new plan emphasizes classified collection and qualitative pretreatment, and then flows into a comprehensive adjustment tank, a two-stage reaction sedimentation tank, and then adds a membrane separation wastewater advanced treatment process in the follow-up. Figure 1 shows the electroplating wastewater treatment process of the company’s new combined membrane separation after upgrading and transformation.

As shown in Figure 1, the various waste water produced includes comprehensive cleaning waste water, chromium-containing waste water, nickel-containing waste water, organic waste water and domestic waste water. After being collected separately, they are chemically oxidized with different process parameters. Reduction treatment, preliminary precipitation treatment, and then enter the newly modified inclined tube sedimentation tank for two-stage reaction sedimentation treatment, and the supernatant of the sedimentation tank is sent to the MBR facility for processing. The process parameters of the upgraded two-stage inclined tube sedimentation tank and MBR are shown in Table 1.

Because of the modularization of the equipment of the MBR system and a small footprint, it is relatively easy to implement the upgrading and transformation of traditional wastewater treatment projects using MBR. Compared with the traditional activated sludge (CAS) method, MBR can maintain high sludge concentration and high volume load, with low sludge yield, no sludge expansion, and it can control MBR to operate in a good condition.

Usually, according to the system structure of the processing unit, MBR has a negative pressure type with a membrane downstream pump for vacuuming, which is an integrated (or submerged) membrane bioreactor (IMBR) and a membrane upstream pump that separates the driving force. There are two types of pressurized membrane bioreactors (splitted membrane bioreactor, SMBR) that separate the driving force of the waste water.

Because IMBR is a negative pressure operation, the pressure applied to membrane filtration is much lower than that of pressurized SMBR. Therefore, in order to obtain a certain membrane flux, IMBR should be equipped with a large pore diameter MF membrane. However, SMBR can not only use a large pore size or even a finer pore size MF membrane, but also can configure the pore size to have a molecular size. For UF membranes with different cutting molecular weight characteristics, the water quality of the corresponding SMBR treated water is much better than that of IMBR.

This project is based on the purpose of wastewater purification treatment and discharge. As shown in Figure 1 and Table 1, the designed MBR process is an enhanced ABMBR system consisting of an aerobic biochemical treatment tank (AB) and IMBR two biochemical treatment units. Through this system, the biodegradable organic pollutants in wastewater can be degraded into CO2, H2O and other inorganic substances to the greatest extent under the action of aerobic microorganisms and facultative microorganisms before membrane filtration.

The design and operation of the wastewater treatment renovation project show that the membrane used in the IMBR in the system is a hollow fiber MF membrane with a larger pore size (0.1μm), and the COD value of the water separated by the membrane is almost as good as when it enters the membrane filter. The effluent of the oxygen tank is equivalent, and it is the characteristics of the membrane configured in the system that the MF membrane has almost no effect on the removal of COD from the wastewater.

However, the effluent of the aerobic tank is filtered by the MF membrane unit, which greatly improves the removal effect of pollutants in the wastewater and the separation efficiency of solid-liquid, and can be used as primary reuse. As shown in Table 1, the turbidity of the effluent separated by the membrane filter is significantly reduced to <1.0NTO, and the effluent quality is improved to be higher than that of the discharged water in Table 2 in my country’s new version of the "Emission Standard for Electroplating Pollutants" (GB21900.2008) Water quality.

Usually the operating cost of IMBR is lower than that of SMBR, but the primary issue for the success of the wastewater treatment process is the regulation of the water purification effect and process parameters, especially for the MBR process that treats high-concentration wastewater, which depends on innovation Wastewater treatment technology and scientific operation management. The terminal ABMBR strengthening process and operation technology of this renovation project ensured that the treatment of electroplating wastewater has achieved the expected effect.