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- 16 January 2008 -

Introduction to membranes: manufacturers' comparison: part 3

In part three of his overview of the different manufacturers found in the field of membranes for water and wastewater treatment, Graeme Pearce looks at membranes based on the outside feed format.

This article is the ninth in a series of articles describing membrane filtration technology used for water and wastewater treatment. Previous articles have provided an introduction to the field and examined the basics of membranes, modules, process design, and operation in water and wastewater applications. The series then looked at a comparison of manufacturers' products, of which this article is the third part. This article examines products with an outside feed configuration. The series will then conclude with a review of MBR technology and products.

Outside feed formats

The fourth article in this series discussed the pros and cons of inside and outside feed formats, and of pressure driven and submerged membrane configurations. The seventh article went on to provide an overview of manufacturers' products, and discussed the benefits of different approaches with reference to specific offerings. This article will review the outside feed format products in more detail.

There are three main international suppliers offering outside feed format technology, and several new entrants or regional players. Most of the products are based on polyvinlydifluoride (PVDF). The largest supplier both in this group, and in the whole UF/MF market for water and wastewater, is Zenon, who exclusively offers submerged products. Pressure driven outside feed (PDO) formats are offered by two of the market leaders, Pall and Siemens, with their Memcor product range, and several smaller players. The PDO format forms the largest proportion of the overall water and wastewater market sector with a 40% share. Memcor also have a submerged product range. Submerged products from Zenon and Memcor account for 30% of the market. In the review, the market leaders will be discussed in order of market share, and then the new entrants and smaller players will be discussed in alphabetical order.

Information for the review has been primarily taken from the websites of the companies involved or from material that they have submitted. The review does not provide a comprehensive description of the complete range of the companies' products, but attempts to provide highlights and general guidance. It should be noted that there are frequent developments and product enhancements, since the market is still evolving.

Zenon

Zenon is long established in the membrane market and is notable for its promotion of the submerged format, the membrane bioreactor, and PVDF fibre chemistry. PVDF goes well with the requirements of submerged products and MBR since the fibre is flexible, making it compatible with air scour, and highly resistant to chlorine.

Zenon was purchased by GE in 2006, to make a group with one of the most comprehensive offerings in the marketplace, covering product and system design, as well as project finance and operation.

The original Zenon product was based on the ZW 500 range, a supported fibre developed during the 1990s primarily for wastewater applications. The fibre is used in a vertical cassette, and has an impressive record for integrity and life, but was too expensive for large scale water treatment applications. In 2002, Zenon introduced the ZW 1000, a horizontal format cassette, which uses a thinner unsupported fibre.

Significant development has taken place in the field of process design and operation to optimise the performance and operating cost with respect to air and chemical use. The submerged concept can have an important advantage with regard to tolerance of a high solids loading, and does not require shells to encapsulate the membrane fibre. However, the lack of containment on the feed side can make chemical cleaning expensive, so it is best used with relatively low flux to give low fouling rates.

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