Water companies in the United Kingdom have been dealing with seasonal algal blooms for many decades, with escalating costs as bloom occurrences have increased markedly with elevated demand on water supply. Environmentally friendly water treatment solutions, such as ultrasound and barley straw, are defined as those that use less energy and chemicals. Barley straw has been used quite extensively by certain UK water companies, and results are generally positive. Ultrasound has only recently been used as a treatment for algal removal, with limited results from several successful trials finding cyanobacteria to be the most susceptible algal group at field scale, with results also indicating susceptibility in other algal groups; however, energy costs are higher than barley straw. Ultrasound has been extremely successful at removing bacteria in wastewater treatment; therefore, ultrasound should be considered as an in-works solution where its effectiveness would be enhanced while reducing energy requirements.Algal bloom control using barley straw and ultrasound D. Purcell et al.

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The zebra mussel, Dreissena polymorpha, is a major biofouling pest of water treatment works, irrigation systems and power stations in Europe and North America. This paper documents current problems associated with zebra mussels in English waterworks. Questionnaires and manual surveys conducted between 2001 and 2003 have revealed that over 30 water treatment works in England suffer problems associated with zebra mussels. Hundreds of tonnes of mussels are being removed each year from raw water intakes, pipelines and reservoirs. Problems have increased in. the last five years, due to a spread in the range of zebra mussels around England and the cessation of chemical treatment at the intakes of many treatment facilities during the 1990s. The importance of taking control of zebra mussels into account in planning new water supply schemes is highlighted.

An electrocoagulation-flotation (ECF) pilot plant was designed, built and operated to evaluate its performance in comparison with a pilot scale conventional dissolved air flotation (DAF) system for treating lowland surface water in the UK. Treatment performance was assessed principally in terms of changes in dissolved organic content (DOC) and system running cost. On average, the decrease in DOC, UV-254 and colour was 10-15% with ECF at pH ca. 7.8 and current densities of 2-5 A m-2 (equivalent dose range of 1-5 gAl(III) m-3). Acidification of the influent (pH 8.4 down to 7.5) decreased only DOC and increased apparent current efficiencies for Al dissolution above unity. Passivation of the aluminium electrodes by Al(III) (hydrous) oxides caused difficulties in maintaining a steady dissolved Al(III) concentration and also increased specific electrical energy consumptions. Treated water quality with ECF was as good as that with DAF at lower equivalent coagulant doses (< 5 gAl(III) m-3), but was less so at higher coagulant doses. The pilot-plant DAF system appeared to be more expensive in terms of its running cost for the conditions used; the cost ratios of DAF to ECF were between 3:1 and 5:1, respectively, for an equivalent treatment performance.

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