Treatment Of Wastewater From EPS Production By MBR/RO Process

With the increasing shortage of water resources, saving water and improving water utilization ratio have become the problems that brook no delay. At present, the mode of the treatment-discharge in factories is not of benefit to protect environment. To increase water recycling rate and realize sustainable development are becoming the new national policy guidance. In this experiment, MBR/RO process was used for treatment of wastewater from expanded polystyrene (EPS) production at a factory in Tianjin. The feasibility of wastewater treatment and reuse was studied. Some research on treatment of brine water from RO was also carried out.The existing process in this factory was coagulation and sedimentation - hydrolytic acidification - biological contact oxidation. Based on the above, the effluent from different stages was taken as influent of MBR in this pilot-scale experiment. The experimental results showed that when the influent of MBR was the equalization tank effluent, the CODCr of the influent and the effluent was 1453~1936 mg/L, 140~368 mg/L, respectively, and the removal rate was 80%~90%. When the influent of MBR was the hydrolysis acidification tank effluent, the CODCr of the influent and the effluent was 598~1161 mg/L, 32~87 mg/L, respectively, and the removal rate was 88%~96%. When the influent of MBR was the biological contact oxidation effluent, the CODCr of the influent and the effluent was 142~303 mg/L, 40~98 mg/L, respectively, and the removal rate was 70%~75%. The optimum way in process modification is to take the effluent from hydrolysis acidification tank as the MBR influent. The turbidity of the MBR effluent was 0.08 ~0.18 NTU and the sludge density index (SDI15) was fluctuated between 2.1~3.9. MBR effluent could meet the requirement of RO influent water.The influent, effluent and supernatant of MBR were scanned by near ultraviolet spectrum and their organic molecular weight distributions were detected. Hydrolysis acidification can efficiently improve the biodegradability of EPS wastewater. The organic compositions in the MBR effluent are mainly polystyrene of small molecular weight, the organic matter with conjugated double bonds (such as conjugated diene, unsaturated aldehyde, unsaturated ketone), and alkanes. Powdered activated carbon (PAC) can remove organic matter in the brine water from RO process by absorption and 1 mg TOC was removed by 50 mg PAC. NPOC removal efficiency was only 7%~10% by coagulation with ferric chloride and its removal efficiency was not increased with the increases of the coagulant dosage. The organic matter in the brine water is hard to be biodegraded by microorganism and its removal needs more research.