Sewage sludge as sustainable resource for lightweight aggregate

Overview

Concrete is the most widely used construction material and, due to its high utilization, has led to the depletion of natural resources, such as conventional aggregates. Many countries in the world are also facing a shortage of high-quality natural aggregates to support local construction needs. Researchers in the construction industry have been developing a more sustainable approach in order to mitigate this issue. One such approach is the reuse of different solid waste materials including sewage sludge, oil-palm-boiler waste, oil palm shell (OPS), palm oil fuel ash (POFA), Ground Granulated Blast-furnace Slag (GGBS), Metakaolin, RHA, tires, and fly ash to produce artificial lightweight aggregates (LWA).

Two major forms, natural LWA and artificial LWA, can be grouped into LWA. The primary source for natural LWA, such as pumice and scoria, is volcanic origin. Artificial LWA, on the other hand, can be produced by thermal treatment of natural materials, industrial by-products, waste materials, etc.

Sewage sludge is an unavoidable by-product of wastewater treatment and can be abundantly found in all over the world. Insufficiencies of landfill sites and rigorous environmental regulations have created disposal problems of sludge. Most of the sludge is disposed of by landfilling and spreading on agricultural land as a fertilizer. All these disposal methods are directly related to the environmental impact such as air, river, sea and groundwater pollution. Studies have been carried out by many researchers to investigate the promising use of sludge and sludge ash as sustainable construction materials. The reuse of sewage sludge into construction materials not only improves disposal problems but also has economic, ecological and energy-saving advantages.