Sludge dirty secret or black gold?
Culturally, the notion of sewage sludge has connotations of a dirty secret, rather than a valuable commodity. Even the name itself seems to suggest something to be got rid of, rather than reclaimed.
Yet the Office of Fair Trading's recent and highly thought-provoking market study into organic waste treatment paints sewage sludge not as an unwanted by-product but as potential black gold. It could be years before the barriers the OFT identified to creating a truly level market playing field can be sufficiently removed. The question is, can this vision stimulate the water industry – by which I mean both sewage undertakers and suppliers - to innovate its sludge processes in the meantime?
The OFT report got me thinking that we are now much more used to treating domestic and industrial waste as a resource to be sorted, separated, reused and recycled. Sludge has valuable components - energy, soil conditioners, nutrients and metals. Of course, it has been reused in agriculture for many years and is increasingly reclaimed for power generation.
But will we one day see Wastewater treatment works – or other combined organic waste plants – as "sludge factories" producing valuable products, rather than as plants charged to deal efficiently as possible with unending waste supply at lowest cost?
Hydro's sludge technologies focus on mechanical handling in the pre-treatment and primary settlement phases. So you might think there was little scope for refining sludge into a more valuable ‘product' at this stage. Yet, increasingly we are responding to customer demands to produce more and better quality sludge earlier in the process.
The growing uptake by major UK water companies using Zickert Sludge scraping technology in primary settlement tanks, for example, is demonstrating the value of more efficient reclamation of primary sludge early to provide a product with a higher calorific value for incineration. We've also recently launched the Meva Counter Pressure Screw and Screw Wash Press, together promising shredded screenings with 50 – 60% DS content, ideal for incineration.
For now, the attraction in these technologies lies in better operating efficiency and reduced disposal costs. As we redefine sludge as a resource, alongside other waste streams and create more favourable regulatory conditions, I hope our industry can respond by innovating to optimise its value at every stage of the treatment process.
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