Sir, – Fintan O’Toole’s article on the lack of sewage treatment plants around the country (“Everywhere you look, Ireland has stark physical deficits”, Opinion & Analysis, Weekend Review, August 12th), and the excellent letter from the Soil/Food Research Group of Maynooth University (August 28th), both highlight our old-fashioned attitude to human sewage – a waste problem.
It would be a great leap forward if we could banish the word waste from our vocabulary, and fully embrace the idea of a circular economy. Human (or bovine or poultry) sewage/manure becomes a resource, a “free” supply of nutrients.
Yes, indeed they can be used by farmers in place of bags of fertiliser. But much more is feasible, depending on scale.
The Beckton sewage treatment works in London (the largest in Europe) separate the solids, and send the liquids off for treatment. The solids are dried, then burnt – the heat produced dries the next batch and generates electricity.
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The ash produced is then used to make lightweight blocks for building, and they are good insulation too.
While that may be only feasible at a big scale, surely Dublin, with an increasing population, must be suitable.
At smaller scales could there not be biomethane generation? Feed the gas into heating community buildings, the schools, hospitals, and churches, or small electricity generators. The residue after methane generation can still be used as fertiliser.
Surplus liquid still has nutrient value. After treatment through a living reed bed or willow filtration systems (some examples on the Uisce Éireann website) this can be fed back into rivers with no harmful effects. The reeds and willow can be harvested and burnt or composted. Any carbon-based material can be burnt anaerobically to generate biochar, a soil-improving carbon holding product. Acres of reed beds or willow are also excellent for wildlife, so we also help biodiversity too.
A resource, not waste. – Yours, etc,
STEPHEN BUTLER,
Palmerstown,
Dublin 20.