Application case of membrane water treatment in landfill leachate treatment

2022-08-24

　　Membrane separation technology is a kind of water treatment technology, which mainly uses the different permeability of water molecules and pollutants to separate them under the action of external forces, which greatly improves the separation efficiency。According to the membrane surface pore size, membrane separation technology is usually divided into microfiltration, ultrafiltration, nanofiltration, reverse osmosis。With the continuous development of membrane separation technology, the combined application of different membrane technologies has played an increasingly important role in the field of water treatment。

　　Membrane bioreactor (MBR) is a kind of process which combines the traditional activated sludge process with MF/UF，It has the characteristics of high pollutant removal efficiency and less mud production.NF is a pressure-driven membrane process between RO and UF，The molecular weight is between 200 and 1000，It can trap some low molecular weight organic matter，And lower energy consumption than RO，The combination of NF and MBR can further improve the removal rate of pollutants，Ensure high effluent quality requirements。

　　At present, MBR-NF combined process is mainly used in the field of landfill leachate and printing and dyeing wastewater advanced treatment。Now share an application case of MBR+NF+RO in the treatment of mixed leachate from landfills and incinerators。

　　Design principle:

　　The mixed leachate of landfill and incineration plant has high suspended matter in the water and high concentration of COD, ammonia nitrogen and other pollutants。According to the characteristics of mixed leachate in landfill and incineration plant, it is proposed to adopt the pre-treatment process of initial precipitation +UBF reaction tank to reduce the pollutants in sewage。A two-stage A/O MBR process was used to remove nitrogen and carbon from leachate。In addition, NF+RO is used as the advanced treatment process。As a further guarantee of the water。

　　Process flow:

　　Sewage → regulating tank → primary settling tank → intermediate tank → two-stage UBF → degassing tank → degassing settling tank → two-stage A/O tank → UF → NF → RO → standardized discharge outlet。Sludge → sludge thickening tank → sludge dewatering → dry sludge transport of concentrated liquid → concentrated liquid storage tank → reuse/recharge。

　　Case study:

　　The leachate generated by garbage is collected and flowed to the regulating tank, and the bottom of the tank is set up with a submersible agitator to stir the leachate, prevent the precipitation of suspended matter, and play a role in homogenizing quality and quantity, which can reduce the impact load on the subsequent process。After that, the leachate is sent to the primary sedimentation tank through the action of the sewage lifting pump。

　　The wastewater treated by the primary sedimentation tank enters the primary and secondary UBF anaerobic reaction tanks，Utilizing the metabolic properties of anaerobic microorganisms，Without the need to supply external energy，Reduced organic matter is used as hydrogen acceptor，It produces methane gas, which has energy value，Thus achieving the removal of organic matter，And the purpose of getting clean energy。

　　The effluent enters the two-stage A/O MBR. The A/O pool has a high ability to remove organic matter, and the nitrification liquid of the aerobic pool returns to the anoxic pool. After denitrifying bacteria, most of the nitrogen-containing substances in the water are converted into nitrogen, thus having the ability to remove nitrogen。After treatment, the effluent is pumped into the tubular ultrafiltration membrane system for mud-water separation, and the intercepted sludge is returned to the A/O tank。Because the tubular ultrafiltration membrane has A high interception capacity, on the one hand, it can intercept organic matter, on the other hand, it can intercept activated sludge, so that the sludge concentration in the A/O pool reaches 10 ~ 15g/L, so the biochemical has a high organic matter removal capacity and nitrogen removal capacity。

　　The ultrafiltration liquid is sent to the nanofiltration system through the primary nanofiltration pump, and the organic pollutants, bivalent ions and chroma are removed by the booster pump and circulating pump, and the recovery rate of the clean water side is improved。

　　After the pressure boost of the pump, the nanofiltration water enters the reverse osmosis system for further treatment. Through the high interception capacity of the reverse osmosis system for salt and organic matter, the soluble small molecule organic matter, chloride ion, nitrate ion and other pollutants in the leachate are further removed, and the effluent is recycled through the standardized discharge outlet。

　　The sludge from the primary sedimentation tank, the first and second stage UBF anaerobic reaction tank, and the first and second stage A/O tanks enters the sludge thickening tank and is pumped by screw pump into the centrifugal dehydrator for dewatering treatment. After dewatering, the sludge with water content below 80% is transported and disposed of, and the filtrate generated in the dewatering process returns to the regulating tank。The concentrated liquid is collected from the concentrated liquid storage tank and then reused or refilled。