Australian Microfiltration System is World's Largest For Potable Water Treatment

Nov. 12, 2002
Products in Action

About the author: For more information, phone USFilter Memcor at 800-547-1202.

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 company).

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 performance.

The performance measures included --

* Water quality targets to remove taste, odor, algal toxins, pathogens, disinfection byproducts and other chemical contaminants;

* Volume and pressure of supply;

* Reliability;

* Environmental compliance; and

* Ongoing 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.

Process Configuration

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 filtered water.

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 biological treatment.

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.

System Performance

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 maintained.

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.

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