The potential of raw sewage sludge in construction industry – A review

Abstract

Excess sewage sludge produced in any municipal or industrial wastewater treatment plant becomes a serious problem due to its increasing amount. This increase is related to the improvement of treatment technologies, expansion of sewage systems and the development of new industrial plants. The implementation and development of new technologies related to the utilization of sewage sludge is currently based on treating it as a substrate. Construction is an industry branch where sewage sludge, as well as other waste materials, can be used. The use of sewage sludge in building materials eliminates some of the expensive and energy-intensive stages of utilization, and the final product obtained is often stable and safe. This is confirmed, among other research regarding strength properties, water resistance, frost resistance and heavy metal leaching, especially when the amount of sewage sludge in solidified samples is low. The main purpose of the article is to present the latest methods of using sewage sludge (dried, dehydrated, and raw) in building and construction materials. Methods of producing low-strength materials for landfilling purposes have also been described.The stabilization of sewage sludge with binding additives improves the end product's durability compared to standard solutions (dewatering). The use of sludge in concrete and mortars mixes is usually associated with a reduction in their strength compared to mixtures without sludge. The binder in the mixture is responsible for the strength of concrete or mortar. Sintering sewage sludge to make ceramic products (bricks, tiles) and lightweight aggregates is a promising approach, but in comparison to other methods such solutions require more energy expenditure. Nevertheless, the obtained products are stable and their durability, while lower than that of the control samples, still qualifies them for applications in construction.Due to the different physicochemical properties of sludge, the methods of its management should be designed separately. It is therefore difficult to select one general and the most optimal method of management of sludge in building materials, but on the basis of the presented review, the authors indicate that one of the best methods of management is sintering sewage sludge into lightweight aggregates.