Membrane bioreactors for water reclamation.

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Membrane Science

Background:

• Singapore utilizes dual membrane technology (MF/UF RO) for producing high-grade NEWater from secondary treated sewage.
• Membrane bioreactor (MBR) technology presents significant potential for enhancing water reclamation productivity and quality.

Purpose of the Study:

• To assess the technical feasibility of MBR systems for water reclamation in Singapore.
• To compare different submerged membrane systems and gain operational experience, including membrane cleaning.
• To evaluate MBR performance against existing water treatment technologies.

Main Methods:

• Three MBR plants, each with a 300 m3/day capacity, were constructed and commissioned.
• Submerged membranes of three types were tested: plate sheet (0.4 µm), hollow fiber (0.4 µm), and hollow fiber (0.035 µm).
• Permeate quality was analyzed using TOC measurements, Gas Chromatography-Mass Spectrometry (GC-MS), Gas Chromatography-Electron Capture Detector (GC-ECD), and High-Performance Liquid Chromatography (HPLC).

Main Results:

• All three MBR systems produced permeate quality equivalent to or exceeding conventional ultrafiltration (UF) tertiary treatment.
• MBR permeate exhibited approximately 2 mg/l lower Total Organic Carbon (TOC) than UF permeate.
• Trace organic contaminant levels in MBR and UF permeates were found to be in a similar range.
• MBR power consumption was less than 1 kWh/m³.
• A dynamic membrane or gel layer formed on the submerged membrane surface, contributing to lower permeate TOC.

Conclusions:

• MBR technology is technically feasible for advanced water reclamation in Singapore.
• The formation of a dynamic membrane is crucial for achieving low TOC levels in MBR permeate.
• MBR systems offer an efficient and effective alternative for producing high-quality reclaimed water.