Water & Wastewater Treatment

4 WWT PUMP AND VALVE SUPPLEMENT 2019 In Focus: renewable energy I t has been a decade since the Environment Agency's Report (SC070010/R5) on 'Renewable energy potential for the water industry'. At the time, in the Figure 5.2 graph showing 'Renewable energy output by water company', two giant towers stood out (Severn Trent Water and Thames Water), with other outputs barely visible. On the one hand, much has changed. We are, for example, supplying the mixing system for Yorkshire Water's impressive new £57 million energy and recycling facility near Huddersfield, which is being built by J Murphy & Sons Ltd. But on the other hand, across the UK, there are no end of digesters still sitting there, offering that very 'Renewable energy potential for the water industry' – not being mixed properly – and therefore not realising that potential. And why so? It's not going out on a limb to suggest that most are approxi- mately one third full of grit. What a waste. These digesters are structurally sound and do not need to be replaced – but these tired old existing mixing systems are never going to turn 'Renewable energy potential for the water industry' into reality. 'Tired old mixing system' is perhaps a tad unfair. Because no doubt about it, these existing mixing systems do mix – for what they were designed for - as part of a waste treatment process – but significantly, not as a process to enhance gas yields, where all the potential is just waiting. Retrofit At Nigg, near Aberdeen, Scottish Water haven't waited. Two partly underground cast in-situ digesters (17m x 20m) are now served by our externally-mounted mixing system. This type of retrofit, whether it be for steel or concrete tanks, is very straightforward. The previous mixing system was problematical and under-performing, whereas now, for easy maintenance, all parts of the system are easily accessible from the outside of the tank. Getting the right mix The water industry has an aspiration to achieve 20 per cent of energy use from renewable sources by the end of 2020. But is it enough? Here, Paul Davies of pump and mixer manufacturer Landia, looks at renewable energy potential. For Scottish Water at Nigg, each digester has been retrofitted with Landia's digester mixing system.

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