Project Appreciation and Objectives
Sand is used universally as a filtration medium in drinking water treatment. Many alternatives are available that have approval for use in drinking water filtration. These include sustainable products (e.g. recycled glass), also quarried and "engineered" materials (e.g. expanded clays). Various claims are made as to the benefits of specific products relative to sand, in order to justify a greater initial material cost. For deep bed filtration, the claims include: greater particle removal efficiency; more effective cleaning of bed, leading to smaller backwash water requirements; longer operating life. Some products could also be used for slow sand filtration. There is a need to understand the true relative benefits of the various commercial products for specific water treatment applications.
This project undertook an independent review of the availability, specification, whole life cost and performance of alternative filtration media.
Benefits to Clients
- Identification of filtration media with superior performance and lower whole life costs than conventional media.
- Identification of sustainable filtration products as part of a wider environmental policy.
- The environmental and/or other claimed benefits of alternative filtration media, from sustainable, quarried and "engineered" sources, were identified.
- Potential applications and expected advantages were established. Gaps in knowledge requiring further investigation were identified.
- Laboratory testing to verify specifications (e.g. size distribution, voidage, density, attrition rate) and specific aspects of performance (e.g. surface activity and adsorption properties).
- Selected media were tested at pilot scale. Performance relative to sand were assessed from, e.g.: ripening time, solids capacity; particle removal efficiency; adsorption; backwash requirements for effective cleaning. Successful materials were recommended for evaluation at full scale possibly as a final phase to project.
Technical support was provided by Caroline Fitzpatrick, Head of Env. Eng. Group at UCL.
- A report detailing the options for alternative media, their availability, approximate cost, claimed performance as well as gaps in knowledge.
- A comprehensive report on the detailed results of laboratory and pilot scale testing of media identified during Phase 1. Alternatives that have clear advantages over conventional materials were recommended for full scale evaluation.
- A workshop to review the benefits of alternative media.
Related WRc Work
- Extensive testing of filtration sand and support gravel for Garside Sands Ltd., using upgraded plant facility , Major utility, 2006
- Testing of alternative media eg ferric hydroxide adsorbent and pumice, Media suppliers, 2001-2004
- Media testing during process audits, numerous utility clients, 1990 - present