Incineration of Textile Sludge for Partial Replacement of Cement in Concrete Production: A Case of Ethiopian Textile Industries

Abstract

The rapid growth of textile industries in Ethiopia plays an important role in economic development. However, the sludge from these wastewater treatment plants, which is not an integral part of the treatment process, is often considered hazardous as it is contaminated with heavy metals of dyestuffs and chemicals. The customary transfer routines such as landfilling and incineration may not be suitable because the leachate from the landfilling destinations and the buildups from the incinerators lead to optional contamination. Moreover, such transfer choices are not financially practical. Therefore, there is a growing need to look for various applications of sludge handling for sustainable development. This study attempts to find out an environmentally friendly solution for the management of the textile sludge by incinerating the sludge and using it for partial replacement of cement in concrete production. Concrete is a composite material formed by the combination of cement, sand, coarse aggregate, and water in a particular proportion so that concrete produced meets the needs regarding its workability, strength, durability, and economy. Typical textile sludge was having high heavy metal contents as per the United States Environmental Protection Agency (USEPA) guideline and should be properly disposed of. The sludge upon incineration at 625°C for four hours gives 78.1% moisture content, 61.2% volatile organic matter, and 59.6% inorganic ash content. The main reactive oxide elements such as SiO2, Fe2O3, CaO, and Al2O3 were found to be 18.51, 3.19, 23.87, and 12.73% by weight in the ash. The calorific value determined from the dried sludge were found to be 1973 cal/gm. Concrete block was manufactured by replacement of cement with 10, 20, 30, 40, and 50% incinerated textile sludge ash, and the manufactured block was evaluated in terms of their compressive strengths, leaching behavior, and water absorption. The replacement cement by the ash increases the hydration time reduced, and up to 20%, sludge ash incorporation in the concrete mix design gives the designed compressive strength. Eventhough water absorption increases with increasing content of the incorporation of the ash, for the 20% replacement of cement, the lethal concentration of heavy metals was obtained to be below the permissible limit set by USEPA. Consequently, the experiment work indicates that the potential use of textile sludge ash for cement concrete gives the possibilities of reduction of heavy metal contamination to surroundings upon sludge disposal, reduces the use of raw materials for producing cement and reduces environmental pollution during cement production.