Earlier this year UKWIR published a study entitled Circular Economy – Water Treatment Sludges, which aimed to assess the current uses and marketplace for water sludges. The work forms part of UKWIR’s Big Question 11 – how do we embed and maximise a sustainable circular economy within the water sector by 2050?
The report estimated production at 115000 tonnes of dry solids per year, with most ferric-treated sludge disposed of to sewer, while alum-treated is applied to land. But among the key conclusions were that the volumes produced are poorly understood, while data on data on composition and its implications is limited, and management efforts are thus disjointed.
Of the current applications, ferric sludges are sometimes used for H2S removal in anaerobic digestion. Other uses are largely non-biological, e.g. in ceramics or construction materials, in coagulant recovery or for special uses like flame retardants.
The most promising routes were identified as coagulant recovery and use in removal of phosphorus (P) from wastewater; while others included H2S removal, or as an adsorbent for biogas cleaning after drying and thermal processing of the sludge. Potential regulatory issues include compliance with End-of-Waste and REACH requirements.
EBNet’s Anaerobic Fermentation WG welcomed the report. “This is an underexplored area. The processes identified are mainly physico-chemical and the report understandably focuses on chemicals recovery, rather than on the biological component. This material is even more challenging to deal with than wastewater biosolids because of the high inorganic content; but still represents a potential resource for valorisation in a sustainable bioeconomy. Options could include direct use as a feedstock, utilisation of the material’s chemical properties within biorefinery processes, or use as carbon and energy source in recovery of metals, for example in bioelectrochemical systems”.
The full report is available to read on UKWIR’s Reports webpage.