Environmental Science & Engineering - www.esemag.com - May 2004
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St. John's installs low-pressure membrane system

By C. Russell Davis

Left: Hollow fibre microporous membranes, approximately 0.5 mm in diameter, are at the heart of the CMF-S system. Right: Artist’s rendering of a largescale Memcor CMF-S unit, which is similar to the one that will be installed at St. John’s.

St. John’s, Newfoundland, is one of the oldest cities in North America. Located on the Northeast Avalon Peninsula, the St. John’s Urban Region is home to almost 200,000 people.

Three regional water treatment plants (WTPs) serve the population: Bay Bulls Big Pond, Petty Harbour Long Pond and Windsor Lake. The regional authority owns, operates and maintains Bay Bulls; the city, Petty Harbour and Windsor Lake. The city is also responsible for various pumping stations, meter chambers and pressurereducing valves throughout the distribution system.

A boil water advisory, issued in August 2001, helped spur the city to investigate ways of better treating its surface water. St. John’s previously used conventional screening, chlorination and pH adjustment as the sole means of treating water at both Windsor Lake and Petty Harbour, and was unable to meet proposed regulatory treatment requirements.

The city consulted Newfoundland Design Associates Ltd. and its specialist process consultant, CH2M HILL, of Toronto. The consultants recommended a four-month pilot study at the larger of the two plants, Windsor Lake, which provides approximately 60,000 of St. John’s residents with fresh drinking water.

At the study’s conclusion, the city decided to design and build a 70- megalitre per day (MLD) Memcor® continuous microfiltration submerged (CMF-S) system from USFilter. The plant is expected to be complete in fall 2005. The CMF-S will ensure total compliance with provincial and national water treatment regulatory requirements.

A view of the chlorination plant that is currently treating St. John’s drinking water. The 70-MLD membrane plant will be built where the photographer is standing.

The city of St. John’s follows Provincial Standards for Bacteriological Quality of Drinking Water as well as Federal Guidelines for Canadian Drinking Water Quality. St. John’s regularly collects samples, which are tested for total coliform and fecal/E.coli at the Public Health Laboratory.

Although similar to USFilter’s proven CMF technology, the Memcor CMF-S system differs slightly in design in that it uses a vacuum design, resulting in a smaller system footprint, lower capital investment and annual operating cost savings.

Hollow fibre microporous membranes, approximately 0.5mm in diameter, are at the heart of the CMF-S system. These bundled membranes form filter modules connected by a patented interlocking mechanism that reduces external plumbing requirements.

During normal operation, the feed passes from the outside of the membrane into the centre, exiting as filtrate. Suspended solids, colloidal particles, fecal bacteria and enteric viruses, Giardia lamblia, Cryptosporidium, heavy metal particulates and their hydroxides, algal blooms, and yeast cells collect on the outside surface of the hollow fibre.

The main treatment units at St. John’s will include both primary and backwash recovery CMF-S units, along with corrosion control and final disinfection. The backwash recovery units will increase the overall plant recovery to 99.6 percent, reducing the wastewater volume to less than 0.5 MLD.

The CMF-S system is equipped with features designed to simplify plant operation and maintain membrane integrity, including a service access platform, an advanced membrane integrity test system and an onsite, operator-friendly module repair system and procedure.
C. Russell Davis is technical sales manager for USFilter Memcor Products.
Contact: daviscr@usfilter.com

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