In the search for sustainable waste management solutions, Sorigué has demonstrated, as part of the Lloval project, that sludge originating from DWTPs can be successfully incorporated into the manufacture of cement. Furthermore, its potential in the ceramics industry as a raw material for the production of thermal insulating clay (Termoarcilla) and non-facing bricks has also been proven. The study was conducted by Nordvert, Sorigué’s specialist waste management company, based on the analysis on sludge samples from two drinking water treatment plants (DWTPs) in Catalonia: Cardedeu and Abrera.
 
In the water purification process, suspended particles precipitate and accumulate at the bottom of the settling tanks. A sludge is formed, which is then thickened and dewatered to increase its concentration. Around 20,000 tonnes of this dewatered sludge, known as “water clarification sludge” is generated in Catalonia each year, 80% of which is managed by the company Nordvert.
 
How to make use of this sludge in a circular economy in a way that is profitable for the industry and does not harm the environment? Researchers found the answer to this question in the sludge’s chemical composition. Thanks to its high concentration of aluminium oxide and silicon oxide, it can replace raw materials used in the cement and ceramics industry with remarkable results.
 
Production of clinker and bricks
 
Added to the other raw materials before entering the kiln, the sludge provides calcium, iron, silicon or aluminium, elements needed for the manufacture of clinker, a key component of cement. A comparison of the quality of the product before and after the incorporation of the sludge demonstrated the material’s stability, making sludge recovery in the cement industry a viable and positive process. 

Further interesting potential lies in the ceramics industry. With the support of the Castellón Institute of Ceramic Technology (ITC), the research determined that the water treatment plant sludge could be used in the manufacture of thermal insulating clay (Termoarcilla) and non-facing bricks. The resulting product has a higher porosity and lightness and possibly improved thermal and acoustic insulation properties. However, this assessment is yet to be established in larger scale manufacturing to deliver conclusive results.
 
Environmental and economic impact
 
Positive environmental and economic impacts have been observed at all stages of sludge recycling and use. Drinking water producers or managers can improve their processes without having to look for new sites and without increasing overall costs.
 
Companies managing sludge have an alternative means of disposal, providing an incentive for its recovery in the cement industry. Lastly, the cement industry can use alternative raw materials, reducing the use of non-renewable resources, quarrying, dust and noise emissions during operations. In addition, due to its chemical composition, the water treatment sludge does not affect the quality of the end product, does not increase atmospheric emissions and does not affect the health of workers. 
 
Included in the Catalan Waste Agency’s 2019 call for projects that promote the Circular Economy with the support of Acció, this study has allowed Sorigué to link three of its business areas: water cycle management, waste recovery and construction. A highly positive impact that can extend all along the production chain, turning waste into a valuable product.