A chemical plant in Tuas, Singapore, faces the problem of meeting the required standards for discharging their wastewater into public sewers. To ensure the quality of Singapore’s limited water resources, the treatment and discharge of industrial wastewater into public sewers are regulated by the Sewerage and Drainage Act and the Sewerage and Drainage (Trade Effluent) Regulations by the National Environment Agency. Typical conventional activated sludge (CAS) processes produce an effluent quality with COD exceeding 4,000 mg/L, reaching 10,000 mg/L at times, which exceeds discharge regulations.
The design of the wastewater treatment plant uses PoroCep® MBR membranes which is combined with an anaerobic and oxic biological process. After biological treatment in the anaerobic tank, the COD can be reduced to less than 2,000 mg/L and a further reduction to less than 600mg/L after the oxic tank. The MLSS concentration in the oxic tank is controlled above 5,000 mg/L, while the MLSS in the membrane tank is generally within the range of 7,000 – 11,000 mg/L.
With the above MBR process, the wastewater treatment plant can treat 1,500m3 of chemical wastewater per day, with the effluent quality meeting Trade Effluent requirements.
6 POR102-1020 skids are installed, where the skids are arranged into 2 trains with 3 skids per train. The operating flux is about 12 LMH.
The membrane system is operated on a cycle of 9 minutes of filtration followed by 1 minute of relaxation. The clean in place for the membranes includes maintenance cleaning (MC) and recovery cleaning (RC). Both are used as a preventive measure to combat membrane fouling. MC is conducted on a weekly basis while RC is conducted every 180 days. When one train is in MC or RC, the other train remains in operation.
Wastewater from the chemical plant enters the equalization tank and passes into the anaerobic tank. Anaerobic digestion takes place, where microorganisms break down biodegradable material in the absence of oxygen. The wastewater is then directed into the oxic tank to further reduce BOD and COD. The mixed liquor is finally directed into the membrane tank to separate sludge and water. The permeate water is then directly discharged into the public sewerage system.
The PoroCep® MBR process has achieved a consistent and high quality effluent with low COD and turbidity levels to meet discharge requirements.