Lake Erie Continuous Microfiltration Plant, Canada

In July 2002, after evaluating extensive proposals from five membrane system manufacturers, the Municipality of Chatham-Kent Public Utilities Commission in Ontario, Canada, awarded US Filter Corporation (now a subsidiary of Siemens) a US$1.7m contract to provide the first microfiltration plant to treat water from Lake Erie.

In May 2000, Chatham-Kent developed a master plan specifically to address future water and wastewater servicing issues in the region. Part of the plan was to focus on two of the region's existing conventional water treatment plants that draw water from Lake Erie.

In order to consolidate operations and provide for future water requirements, the plants needed to be upgraded or replaced. During the design of the new plant, five membrane system manufacturers were asked to submit proposals for review.

US Filter was selected to supply the membrane technology because of its "best overall life cycle cost while meeting the prerequisite water quality standards".

The bid selection criteria was based on the quality of the water, capital, operating and membrane replacement costs, and experience of the manufacturer.

Continuous microfiltration (CMF)

The Memcor CMF system provides six million gallons of water per day to over 10,000 residents in the Ontario area. The new South Chatham-Kent Water Treatment Plant will service the area of south Chatham-Kent including the communities of Blenhiem and Erie Beach.

"The US Filter Continuous Microfiltration Plant was commissioned in spring 2003."

Consulting engineers for the Municipality of Chatham-Kent, Totten Sims Hubicki Associates (TSH), provided the project management for the scheme. TSH is now known by its parent company AECOM.

The CMF technology incorporates a patented air / liquid backwash to remove inorganic or organic contaminants greater than 0.2 microns and prevents them from entering the hollow fibre membranes that form the CMF barrier. The direct-flow (outside-in) filtration through the PVDF oxidant-resistant membrane fibres provides an efficient use of membrane area and ensures the removal of contaminants from the raw water source.

The new plant also includes activated carbon for taste and odour control, and chlorine for disinfection. The microfiltration unit was finally commissioned in spring 2003.

Microfiltration treatment process

The Memtek Microfiltration treatment process begins with the transfer of wastewater to one or more reaction tanks followed by controlled addition of pretreatment chemicals to precipitate the contaminants to filterable particles. Reactions are monitored and controlled automatically and continuously. The chemically pretreated wastewater then flows to the concentration tank.

From there, the water is pumped continuously through the 1in tubular membrane filtration modules at a high fluid velocity. At the normal operating pressure (20psi-40psi), clean water is forced through the pores of the membrane while the contaminated particles remain suspended in the recirculated stream.

"The concentration of the wastewater slurry is typically maintained between 2% to 5% solids."

The turbulence of the recirculated slurry prevents the contaminants from accumulating on the membrane surface, thereby maintaining high and continuous filtration rates. The filtration piping also includes a back-pulse mechanism that reverses the flow of filtrate to maintain higher flow rates and extend the time between cleaning cycles.

The clean water (membrane filtrate) flows by gravity from the membrane modules to a drain, storage tank or the final neutralisation tank. Clean, neutralised filtrate is often used for non-critical rinses and applications. The filtrate is ideally suited for further processing by reverse osmosis for water recycle. The concentration of the wastewater slurry is typically maintained between 2% to 5% solids.

Under normal operating conditions, a portion of the slurry is periodically removed from the system, usually to a filter press that produces a dry (30% 40%) solids cake for disposal. Filtrate from the press is returned to the feed system for reprocessing.

System cleaning

Every E-Series filtration system includes a convenient integral cleaning loop consisting of a pump, two tanks and the necessary piping and valving to permit in-place cleaning of the membrane modules. No disassembly is required and cleaning normally requires less than two hours after 60-100 hours of operation.

US Filter

In 1999, US Filter Corporation was acquired by Vivendi Environnement company, North America's largest water company providing water and wastewater systems and services to commercial, industrial, municipal and residential customers. In 2003, the company changed its name to Veolia Environnement, the independent company of Veolia. US Filter was acquired by Siemens in 2004.