The Navajo Tribal Utility Authority has agreed to bring six wastewater treatment facilities into compliance with the federal and Navajo laws in...
Products in Action
The AQUA 2000 Project is a build-own-operate-transfer (BOOT)
project, delivered and operated by Vivendi Water Australia. It includes the
construction and operation for 25 years of a water treatment scheme for the
Coliban Water Authority in Victoria, located in southeastern Australia.
The project is composed of three water treatment plants
(WTPs), the largest of which, at Sandhurst, uses a Memcor® continuous
microfiltration-submerged (CMF-S) system by USFilter (Vivendi Water's sister
At a capacity of 33 million gallons a day (126 mL/day),
Sandhurst WTP is the largest microfiltration plant in the world for potable
water treatment. An extensive amount of work went into designing, selecting and
testing the system, to achieve the performance measures set by Coliban Water
for all possible raw water conditions and to verify the system's economic
The performance measures included --
quality targets to remove taste, odor, algal toxins,
pathogens, disinfection byproducts and other chemical
and pressure of supply;
maintenance of lifetime assets.
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The raw water is supplied from three reservoirs located in a
large catchment linked by a channel system. Both gravity and pump systems are
used to feed the plants. During
the process validation period, it was observed that taste and odor compounds
(MIB and geosmin) were close to or above the threshold value of 5mg/L.
Originally thought to occur only briefly throughout the year,
these high values have persisted for long periods throughout the year.
Treated Water Quality
The specification for the treated water from the treatment
plants was designed to meet existing guidelines and anticipate future
regulations in drinking water.
Penalties are imposed for excursions from any of the 25
specifications including taste and odor, color, iron, radon, continuous 2- to
5-micron particle removal and 4-log reduction for Cryptosporidium.
There is no contractual relief due to unforeseen changes in
raw water quality.
The raw water entering the Sandhurst WTP is first screened,
then dosed with lime and carbon dioxide to stabilize the water and prevent
corrosion. Liquid aluminum chlorhydrate is added to coagulate particulates,
metals and color.
Microfiltration membranes provide a physical barrier,
removing particles down to 0.2 micron, including coagulated impurities,
protozoa and particles.
The Memcor CMF-S system consists of eight cells (six duty
cells, two stand-by cells), each containing 576 submerged membrane modules.
Water enters each cell and is drawn through the outside of the porous membranes
to the inside by a filtrate pump (one filtrate pump per cell), producing
These cells are backwashed intermittently using filtrate and
air to scrub the fiber surface. Periodic chemical cleaning is performed when
the maximum transmembrane pressure (TMP) is reached.
The microfiltration system's integrity is tested daily using
the Memcor pressure decay test (PDT), a fully automated and highly sensitive
integrity test system. If any leaks are detected, the membranes are isolated or
pin-repaired during the next scheduled maintenance period.
The filtrate from the Memcor CMF-S system is then pumped to
ozone contact tanks. Ozone is generated on-site using air or liquid oxygen. The
ozone acts as an oxidant, disinfecting and destroying algal toxins and breaking
down the complex organic material to simpler forms for the downstream
The ozonated water is then applied to an upflow biological
activated carbon (BAC) filter vessel, using coal-based carbon, with an empty
bed contact time of 15 minutes. The BAC reduces organic carbon level in the
water, eliminates taste and odor compounds and blue-green algae toxins
resulting in high-quality, stable water.
Lime is added to control the final pH and provide corrosion
protection. Chlorine and ammonia are dosed to provide chlorination disinfection
to ensure the treated water retains its quality within the distribution system.
Testing of the Memcor CMF-S system on this site began in
1998 during the bidding process. Once Vivendi Water was awarded the project,
the testing was scaled up to a simulation of the complete process over an
extended period of time.
The Process Verification Plant was started in October 1999
and continued to operate up to and beyond the commissioning of the full-scale
plant in the spring of 2002. The Process Verification Plant has provided
long-term data on the operation of the process on this feed stream, and has
proved a great tool in ensuring the proper design of the large-scale plant.
The Sandhurst WTP is now supplying high-quality, potable
water to the Bendigo area of Victoria, Australia. Water quality is monitored
continuously through the process to ensure water quality parameters are
The plant will be accredited and operated to satisfy quality
and environmental management systems ISO 9002 and 14001, while meeting some of
the most challenging finished water quality standards in the world.