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| Computer rendering of Ontario's latest membrane facility designed by CG&S, the 10 ML/d Parry Sound WTP (now under construction). |
By Martin Gravel, P.Eng., CH2M Gore & Storrie Limited
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| Computer rendering of Ontario's latest membrane facility designed by CG&S, the 10 ML/d Parry Sound WTP (now under construction). |
The continuing rise in the use of membrane technologies for municipal drinking water treatment can be described as nothing short of a revolution. Before the 1990s, membranes were considered a "boutique" process, generally used for reverse osmosis (RO) desalting plants and specialized nanofiltration (NF) applications. For surface water treatment, where large-pore ultrafiltration (UF) and microfiltration (MF) membrane processes are most effective, high capital and operating costs meant that UF/MF technologies were applicable only to small projects.
Times have changed and technologies have evolved. Fuelled by recent regulatory changes demanding increased drinking water quality, the cumulative capacity of UF/MF plants has increased from below 50 ML/d in 1994 to nearly 1,000 ML/d in 1999. In fact, individual plants are now being developed with capacities of more than 150 ML/d.
This exponential growth can be attributed to several factors, most significantly the development of the hollow-fibre membrane and the now-strong competition among membrane equipment suppliers. Competition has driven costs down and provided owners and engineers with favourable economics for new membrane plants.
Concurrently, confidence levels in the engineering and design of membrane plants have increased. Gone are the days when only the best (that is, easy to treat) surface waters were evaluated for membrane applications and the process was "membranes only". Designs for treatment plants now include membranes coupled with other traditional processes such as taste and odour control, colour removal (enhanced coagulation), iron and manganese removal, arsenic removal, and pH adjustment.
Integrated systems that may include UF/MF membrane pre-treatment for tighter NF or RO membranes are also becoming more common in water-reclamation-type projects. For our neighbours to the south, one of the recent developments is the emerging membrane market for indirect potable reuse applications such as surface supply augmentation (SSA) and groundwater recharge (GR). In short, the learning curve is flattening out for designers of treatment plants who want to incorporate membrane processes.
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| UF/MF membrane treatment has grown exponentially in the 1990s. |
Membrane suppliers are also responding technically, rounding out their product mix to meet highly competitive environments and specific treatment needs. In fact, the secrecy surrounding the development of new membrane products is akin more to James Bond movie plots rather than the traditionally slower-paced municipal equipment supply industry. With increased competition and as the technology continues to develop, it is becoming even more important for owners and consultants to identify differentiators between one membrane and another. Technical issues such as membrane-fibre integrity, chlorine resistance, nominal pore sizes (microfiltration to ultrafiltration), and immersed or pressurized system design can sometimes conflict with cost issues such as warranty, performance guarantees, and membrane-module replacement costs.
The increasing complexity and diversity of membrane technology selection can be a minefield for those who lack specialized engineering resources and hands-on experience. The CG&S approach has been to select membrane equipment based on an evaluated-bid basis that also takes into account all operational costs over a 20-year period. Finally, there is nothing more satisfying for membrane products buyers than testing out the technology beforehand; a demonstration or pilot program is the safety blanket for any successful application.
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