Electroplating wastewater treatment membrane separation technology
The water quality of electroplating wastewater is complex, containing various heavy metal ions such as nickel, zinc, and chromium, as well as organic matter, ammonia nitrogen, acid, and alkali pollutants, and the treatment process is complex, which is the focus of environmental supervision.
At present, the electroplating wastewater treatment and discharge standards are strict, and the reuse requirements are high. The traditional physicochemical + biological treatment process is difficult to meet the strict electroplating wastewater discharge requirements. It is urgent to upgrade the traditional treatment process. Therefore, the electroplating wastewater treatment process is updated and improved. Must do.
Membrane separation technology is efficient and pollution-free and has been widely used in domestic sewage and landfill leachate treatment in my country. There are few reports on the large-scale application of electroplating wastewater treatment. This article intends to introduce the application of membrane technology in practical engineering.
Application of MBR in the upgrading of electroplating wastewater treatment facilities
Membrane Bioreactor (MBR) is a new high-efficiency sewage treatment process that organically combines membrane separation technology and sewage biological treatment process. MBR is regarded as the “Best Available Technology” in the treatment and reuse of municipal sewage and industrial wastewater.
The MBR system can completely trap the microorganisms in the bioreactor, realize the complete separation of the hydraulic retention time of the reactor and the sludge age, and has high removal efficiency for organic matter and ammonia nitrogen, and the effluent can be directly reused.
A medium-sized electroplating enterprise mainly has production processes such as surface treatment, electroplating, and spraying, and the amount of wastewater produced is 2600m3/d. In the existing wastewater treatment, pretreatment wastewater, cyanide-containing wastewater, chromium-containing wastewater, mixed wastewater, and comprehensive wastewater are treated by the quality and are treated by conventional physicochemical process + hydrolysis acidification + contact oxidation process.
However, due to the high content of organic matter in the wastewater, the terminal biochemical treatment process cannot meet the electroplating wastewater discharge standards, so the electroplating wastewater treatment facilities are actively upgraded.
After the renovation, the workshop wastewater pretreatment facilities and classified collection pipelines were re-optimized. In response to the problem of excessive COD in effluent, the original hydrolysis acidification + contact oxidation process section was transformed into an anoxic tank + MBR process. All wastewater was pretreated and entered into the newly modified biochemical process section, and the wastewater was subjected to advanced membrane separation treatment. The schematic diagram of the membrane separation process is shown in Figure 1.
The MBR process uses an integrated built-in membrane. The sludge concentration in normal operation is 5000mg/L, the sludge age is 7d, the membrane filtration flux is 0.65m3 (m2·d), and the online cleaning frequency is 1 time per week.
Compared with the traditional activated sludge method, MBR operates under high volumetric load and low sludge load, resulting in less excess sludge production, less sludge particle size, and increased oxygen diffusion rate.
Therefore, the MBR process enhances the removal ability of organic matter and replaces some functions of the original hydrolysis and acidification process. The increased oxygen-deficient process section also ensures the removal of total nitrogen. After the stable operation of the process, the effluent treated by the wastewater treatment system meets the standard in Table 3 of the Discharge Standard for Electroplating Pollutants (GB21900-2008), and the treatment effect of the MBR system is shown in Table 1.
The transformed wastewater treatment facility has the characteristics of process modularization, a high degree of automation, and easy operation. After the normal operation of the MBR system, the removal effect of organic matter and ammonia nitrogen is remarkable, and it also has an adsorption effect on some heavy metals, which can ensure the water quality of the effluent is stable and up to the standard.
Therefore, membrane bioreactors can be used as a technical choice for electroplating wastewater treatment.
Application of UF/NF/RO membrane integration technology in electroplating wastewater reuse
Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF), and Reverse Osmosis (RO) membrane separation technologies have reached a practical stage in the field of wastewater reuse. For specific classification and functions, see figure 2.
In the field of membrane application, the development of membrane integration technology is the main focus at present, which integrates various membrane technologies and combines membrane collections with various separation properties, namely membrane integration technology. Common membrane integration processes include NF/RO membrane purification of seawater, MBR/UF-RO treatment of domestic sewage, and MF/UF-NF/RO multi-stage membrane filtration process to treat trace pollutants.
In recent years, my country has also made progress in the application of membrane integration technology to electroplating wastewater treatment and resource recovery.
In an electroplating park, due to the limited water use requirements of the EIA approval documents, in order to meet the needs of expanding production scale, it is necessary to deepen the degree of wastewater reuse and carry out deep wastewater reuse projects.
The amount of wastewater produced in the park is 3000m3/d, and the reuse rate is 60%. After the demonstration, the comprehensive reuse rate is designed to be 80%.
In the process application, the original reused water treatment facilities are integrated, and after multi-media filter + UF filtration pretreatment, three-stage NF-RO-RO filtration, and concentration, the filtered water achieves the purpose of efficient recycling.
After the comprehensive treatment of electroplating wastewater, the process effluent enters the reuse treatment system. The colloid and suspended solids in the influent can be removed by the multi-media filter + UF pre-filtration pretreatment, and then the filtrate is introduced into the three-stage complete set of membrane separation devices in turn. The first-stage nanofiltration freshwater is removed to the pure water preparation system or directly stored and reused. The concentrated water enters the second-stage reverse osmosis system, the second-stage reverse osmosis freshwater returns to the raw water collection tank, the concentrated water enters the third-stage reverse osmosis system, and the third-stage reverse osmosis freshwater returns to the original water collection tank. In the secondary reverse osmosis raw water tank, the tertiary concentrated water enters the terminal treatment collection tank, and after the process of micro-electrolysis oxidation + Fenton oxidation + physicochemical coagulation sedimentation + aerated biological filter, the wastewater is discharged to the standard.
The first-stage nanofiltration freshwater is removed to the pure water preparation system or directly stored and reused. The concentrated water enters the second-stage reverse osmosis system, the second-stage reverse osmosis freshwater returns to the raw water collection tank, the concentrated water enters the third-stage reverse osmosis system, and the third-stage reverse osmosis freshwater returns to the original water collection tank. In the secondary reverse osmosis raw water tank, the tertiary concentrated water enters the terminal treatment collection tank, and after the process of micro-electrolysis oxidation + Fenton oxidation + physicochemical coagulation sedimentation + aerated biological filter, the wastewater is discharged to the standard.
The system membrane pretreatment process is the characteristic of the membrane integrated device. In the process of applying the UF membrane, through the filtration of colloids and macromolecular organic matter, it is helpful to achieve the goal of deep purification of wastewater, and it also reduces the need for subsequent membranes. fouling or membrane blockage issues.
The pore size of the nanofiltration membrane (0.5~5nm) is between reverse osmosis and ultrafiltration, and it has a charged nano-scale microporous structure. The retention effect of inorganic salts mainly depends on the strength of the charge effect of the membrane onions. The separation characteristics of nanofiltration membranes can effectively separate and remove multivalent heavy metal ions from water.
The pore size of the reverse osmosis membrane is below 0.1~1nm. It is mainly based on the semi-permeable membrane principle of the reverse osmosis membrane. Because the reverse osmosis membrane only allows water molecules to pass through under high pressure, it does not allow potassium, sodium, calcium, zinc, viruses, etc. Bacteria pass through, so it can get high-quality pure water.
Because the nanofiltration membrane with a high water recovery rate is used in the front stage, and the reverse osmosis concentrated water in the latter stage is returned to the front stage as the nanofiltration influent, the whole system can achieve a high water recovery rate, and the actual operation wastewater recovery rate can reach more than 80%.
The parameter design of different modules of the membrane integrated system is based on the reuse water standard, and the distributed control system is applied to the complete set of membrane separation equipment to effectively achieve the goals of decentralized control and centralized monitoring. and can achieve the goal of controlling the energy consumption of the effluent water quality system at all levels.
According to the characteristics of the complete set of membrane separation devices and the different quality requirements of the reclaimed water in the workshop, UF/NF/RO is not only an organic whole but also three independent systems.
Therefore, in the actual process of wastewater treatment, when a single device needs to be suspended for performance maintenance and troubleshooting, the scope of influence will be reduced to a single membrane unit and will not affect other membrane units, so the goal of continuous wastewater treatment can be achieved. It has the effect of stable operation.
To sum up, due to the urgency of water environment quality issues and the increasingly stringent sewage standards, the use of composite technology and multi-stage membranes to strengthen the treatment of electroplating wastewater can not only meet the standard treatment requirements but also reuse water resources, which is the development of treatment technology. direction.
The application of the MBR process can provide a technical guarantee for the treatment of the organic matter in electroplating wastewater. The application of UF/NF/RO integrated membrane technology can realize the production and reuse of electroplating wastewater, meet the goal of clean production, and meet the requirements of wastewater recycling.