MBR Process for Coal Chemical Wastewater Reuse and Treatment
Introduction of MBR sewage advanced treatment process
1.1 Project introduction
The water quality of the MBR system of the advanced sewage treatment project varies greatly, including domestic sewage, biochemical effluent of low-concentration oily sewage, and ultrafiltration backwashing drainage in the desalination and reuse section. The biodegradability of the three water sources is poor.
The water source is mixed by the lift pump in the water distribution corridor and then enters the A/O biochemical stage through the wedge wire drum screen. This stage can better remove the emulsified oil port organic matter in the oily sewage, which is conducive to further advanced treatment in the subsequent MBR stage.
The produced water after biochemical treatment enters the MBR treatment section. The treated effluent is desalted and reused in the water section after passing the test. After its treatment, the produced water is sent to the recycling water pipe network to replace fresh water and advanced treatment areas. Use water to reduce groundwater usage.
Design scale: Design water quality of influent and influent and effluent in MBR section: 410m3/h, as shown in Table 1.
1.2 Process flow and its description
MBR section process flow. Domestic sewage and low-concentration oily sewage biochemical effluent desalination and reuse section ultrafiltration backwash drainage pressure enters the water distribution well in the MBR section, and the sewage is evenly distributed to the two grid canals through the water distribution well. The sewage will flow into the A/O pool after removing the particulate matter and floating matter in the sewage through the drum grille.
The A/O pool consists of two sequences. Pool A is the front denitrification pool, and the heterotrophic denitrifying bacteria in pool A use the organic matter in the incoming water as a carbon source to reduce the nitrite nitrogen and nitrate nitrogen in the mixed solution to nitrogen.
The O tank is a plug-flow aeration tank. The microorganisms in the activated sludge degrade the organic matter in the sewage into CO2 and H2O under aerobic conditions, and oxidize the NH3-N in the sewage into nitrite nitrogen and nitrate nitrogen. .
The mixed solution from the MBR membrane pool is returned to pool A for denitrification. Pool A supplements nutrients, and pool O supplements alkalinity. The effluent from the A/O pool flows into the MBR membrane separation room.
The effluent from the AO pool flows into the MBR distribution channel and then evenly enters the MBR membrane tank to further remove the organic matter in the sewage and separate the sewage from solid and liquid. After the effluent test of MBR production tank is qualified, it enters the UF1 raw water tank through the lift pump of the MBR production tank. The MBR membrane tank mixture is returned to the A/O tank through the activated sludge return pump. The excess sludge is lifted to the original sludge treatment system by the excess sludge pump.
Discussion on the influencing factors of MBR operation
2.1 Sludge concentration changes
Through the analysis of the actual operation data on site, the viscosity of activated sludge gradually increased with the increase of time, and reached a peak of 7-10g/l around 20d.
2.2 Influence of aeration amount
As shown in Figure 1, it can be seen that with the increase of aeration flow rate, the membrane transmembrane pressure difference gradually decreases, and its change is stable after 6m3/h. The change is closely related to the formation of the contamination layer on the membrane surface.
2.3 Influence of filter index
As shown in Figure 2, it can be seen that the filtration index has a great influence on the membrane filtration transmembrane pressure difference, and it is in a stable state when it is less than 1.5. When it is greater than 1.5, the transmembrane pressure difference increases rapidly, indicating that the viscosity of the sludge is greater. The faster the membrane surface is fouled.
2.4 Influence of reflux ratio
The activated sludge return ratio was found in the actual operation process: in the initial stage of operation, a small return ratio should be used to ensure the normal operation of the membrane tank. After 15-20 days, the sludge concentration of the membrane tank and biochemical tank gradually increased. In this case of, increasing the reflux ratio can better ensure the balance of the whole system. However, increasing the sludge concentration of the biochemical system is an effective method to rapidly increase the sludge concentration of the entire MBR system.
2.5 Changes in MBR water production during system operation
After the combined process with MBR, the effluent COD is less than 10mg/L, and the effluent ammonia nitrogen is less than 2mg/L. Compared with the raw water quality in Table 4, the average removal rate reached 94%, and the ammonia nitrogen removal rate reached 95%. The removal rate of oil, sulfide and volatile phenol is basically completely removed, showing a very good treatment effect. Some studies have shown that there are different degrees of short-range nitrification and denitrification and simultaneous nitrification and denitrification while performing traditional denitrification in membrane bioreactors. At the same time, the appropriate sludge concentration and aeration rate ensure that the biofilm on the membrane surface can remove COD and oil in the water to the maximum extent.
The practical application of this project shows that the biochemical + MBR combined treatment process has high treatment efficiency for oily sewage, but the precise setting and control of operating parameters are the key factors for the stable and efficient operation of the entire system. The following experiences and conclusions were obtained:
(1) Sludge concentration, aeration rate, reflux ratio and filtration index are the main factors affecting the operation of MBR system.
(2) In the early stage of operation, the oil content in the raw water should be strictly controlled to be less than 5mg/l. At the same time, the system load should be gradually increased to avoid sudden shocks. Increasing the sludge concentration in the biochemical section is an effective way to increase the sludge concentration in the entire system.
(3) During the operation, it is necessary to gradually explore the best operating parameters of the system, strictly control the debugging and operation process, avoid the occurrence of excessive water production or overtime water production, and regularly perform cleaning procedures to improve the service life of membrane elements. achieve efficient system operation.
(4) During the commissioning and operation stage, the production site should be regularly inspected to detect abnormal operations in time. Regularly sample and test each monitoring parameter of the system to keep abreast of system operation.