(86e) Evaluation of Treatment of An Ethylene Plant Waste Water with a Membrane Bioreactor

 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.

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.