Water & Wastewater Treatment

In the know Getting to grips with trickling filters It's all about the media Reduced energy usage is just one reason to choose trickling filtration for wastewater treatment RIchaRd MannIng, Managing diRectoR, gea 2H WateR tecHnologies A trickling filter is a fixed-growth, biofilm treatment system. Trick- ling filters typically include a dis- tribution system, containment structure, media, underdrain, and ventilation The wastewater is distributed at the top of the filter – using rotating dis- tributor arms powered by electricity or hydraulics – and "trickles" downward over the media which provides a sur- face for the growth of bacteria and other micro-organisms that feed on the organ- ic pollutants. Oxygen is introduced into the system to convert organic matter into harmless by-products. With the cor- rect design and configuration, trickling filters can meet wastewater treatment requirements for BOD removal, nitrifica- tion or denitrification. Trickling filters can be integrated into any wastewater treatment opera- tion. As treatment needs evolve, exist- ing assets and treatment systems can be adapted or upgraded with minimum cost and disruption to the treatment capacity. They can be used to provide a supplementary 'special treatment' stage to meet new standards dictated by legis- lation. It is also possible to add trickling filters onto an existing activated sludge system to provide low-cost, energy- efficient nitrification. It's all about the media Structured, plastic media is the ideal biofilm carrier. It is highly durable, has a large surface area and the high void space needed to minimise clogging and ensure a free-flowing oxygen supply, and to create efficient nitrification towers. Plastic media is resistant to rot, fungi and most dissolved chemicals. Fil- ters can be reused and, when no longer required, plastic media can be recycled. However, using the most appropriate type of plastic media in the correct con- figuration for a particular process is the key to a successful plant. Factors such as organic loading, surface area, void volume and distribution characteristics are all vitally important in ensuring ap- plication and system performance. Similarly, wetting rate, organic load, ammonia load, temperature of the wastewater, and desired effluent quality all play a part in determining the type and volume of media needed. (see 'The media' box out) applications: Roughing filters/primary reduction of BOD Trickling filters are an effective option to reduce the load coming into the ex- isting works. Vertical media is ideal for applications with a particularly heavy www.wwtonline.co.uk | WWt | august 2014 | 35 the process

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