Selected Information - Proposed Research

The design of rapid gravity filters (RGF) is often driven by process suppliers' in-house approach and not substantially influenced by the client. Historically, design criteria have tended to be conservative and based on what has gone before. Recent work by WRc has shown that the approach taken to filter design, whether for refurbishment or new build, can impact markedly on capital and operating

costs and maintainability. There is a need for a fundamental review of design principles and technology for rapid filters. This is particularly relevant given the increasing implementation in the UK of dual media (sand/anthracite) filtration and combined air-water backwashing.

Key issues that need to be examined include: the relative merits of different filter floor designs; the applicability of relatively deep/coarse monomedia sand filters; and the relative merits of options for minimising the loss of filter media during washing.

The project will provide detailed guidance to those refurbishing existing filters or procuring new ones.

Benefits to Clients

• Reduced OPEX through reduced usage of wash water and reduced media losses.
• Reduced CAPEX for new builds through minimisation of filter dimensions.

Work Programme

1. A detailed review of design practice through liaison with water companies, consultants and filter refurbishers.
2. Audits of selected operational filtration systems to evaluate the influence of design on backwash performance.
3. Audits of examples of filtration processes that use a relatively deep, coarse, sand bed in contrast to processes that use relatively shallow beds.
4. Undertake modelling to demonstrate the influence of design on key aspects of performance (e.g. minimising wash water, minimising loss of media).

Project Output

• Detailed and practical guidelines to support those responsible for either filter refurbishment or new builds.
• Dissemination workshop to ensure effective implementation of project findings.

Related Work

• Alternative Filtration Media, CP326, 2009.
• Optimising Filter Backwashing, CP334, 2009*.
• Numerous single client projects to test filtration media characteristics, 2006 - 2008.

*This project will build on CP334 which identified a need to look at and challenge the design principles that govern the reliability and operating costs of rapid filtration processes.