In recent years biofouling from native (bryozoans, sponges) and non-native (Cordylophora) animals has increased in UK water treatment works (WTW). A survey of six UK water companies and eight WTWs revealed that these taxa were more widespread and abundant than previously recognised. Primary problems related to the occlusion of underfloor nozzles and tailpipes in rapid gravity filter beds (RGFs). These cost the UK water industry £1.49 m between 2005 and 2009. Additional impacts came from skin irritation to operatives from sponge spicules and the potential for elevated bacterial pathogen levels. Sponges penetrated the furthest through the water treatment process, reaching the point of final chlorination at one WTW. A monitoring plate study showed pronounced seasonality in fouling, with most taxa peaking in mid to late summer before a winter die-off. Control options, including the use of chlorine, and the importance of resistant stages for each taxon are discussed.

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