ExxonMobil was looking for a biological process with the following characteristics:

• Higher quality effluent than conventional activated sludge, due to value opportunity in reusing water as cooling water makeup

• More automated operation, due to limited operational resources

• Smaller footprint, due to limited available plot space. 

ExxonMobil considered the membrane bioreactor (MBR) process as a potential solution, if shown to be operable on the plant's current feed waste water.  

In 2005 ExxonMobil contracted the Center for Advanced Water Technology (CAWT, a division of Singapore Utilities International) to conduct a laboratory MBR pilot test of the MBR process in treating the ExxonMobil Chemical Plant waste water.  The test proved the feasibility of the MBR process with a flat sheet membrane, providing suitable effluent quality with a reasonable membrane maintenance frequency over a two month operation at flux of 12 liters/m²/hr (lmh) of membrane surface area.  When the flow was increased to 15 lmh, required membrane maintenance increased dramatically due to fouling.  While 12 lmh is much lower than most municipal MBR designs and does increase the size of the membrane tanks relative to higher flux designs, the technology still met the criteria stated above to a sufficient extent to continue evaluation of MBR on a larger scale.

In 2006, ExxonMobil executed another contract with CAWT to conduct a field pilot test of the MBR process on site at the ExxonMobil Singapore Chemical Plant on Jurong Island .  ExxonMobil and CAWT selected Siemens Water Technologies' Petro® MBR submerged hollow fiber technology for the field test.  A pilot plant was constructed locally, delivered to the Jurong Island location, and commissioned on 1 August 2006 with a goal of collecting sufficient data to determine MBR feasibility for the new project.  The required fast-track test plan was deemed feasible, considering there was acclimated seed from the existing activated sludge plant.

The pilot plant was a stand alone system with facilities for all biological as well as membrane processes needed to test the system on site.  In addition, the pilot system was equipped with typical instrumentation, a Process Logic Controller (PLC) and commercial-scale membrane module to collect the relevant data necessary to confirm process efficiency, robustness, reliability, and scale up. 

The first two weeks of the pilot testing were for commissioning and acclimation/thickening of the mixed liquor in the pilot unit.  The system was started at a flux rate of 6 lmh to allow full biological treatment of the relatively high strength waste before contact with the membrane.  Full target design flow providing 12 lmh average daily flux rates was achieved during week 6 of the test and was run through week 15 of the program without need for cleaning in place (CIP) of the membrane.  Optimization of the flux limited the required membrane maintenance to two - 15 minute maintenance cleanings each week.

The pilot plant test resulted in a design hydraulic retention time (HRT) of 15 hours, split 5 hours and 10 hours between anoxic and aerobic sections, respectively.

Pilot operation has provided the following effluent quality to date, at a flux of up to 13 lmh on an average daily basis.

	COD	TKN	TSS	NH3-N	Total N	Oil & grease
MIN Removal	94.5%	92.2%	91.1%	91.4%	63.0%	33%
MAX Removal	98.0%	99.8%	99.5%	99.9%	93.2%	95%
MEAN Removal	96.6%	97.5%	95.1%	99.1%	77.8%	74%
90% confidence	95.9%	95.2%	92.0%	99.2%	73.4%	94%

The pilot testing program further evaluated the required biological design parameters such as SRT and HRT.  ExxonMobil selected the MBR technology for the Singapore expansion and is presently evaluating design proposals for EPC award.