The use of sewage sludge in the production of ceramic floor tiles

Abstract

Scientists proved that municipal sewage sludge contains many dangerous pathogens, toxic heavy metals, endocrine disruptors, drains, storm water runoff, hospitals, and industrial plants. Sewage sludge represents an extremely high ecological hazard to the environment. Due to the increasing amount of sludge generated from the wastewater treatments plants a strong demand for environmentally and effective safe reuse has arisen. One potential use of that waste is its incorporation in the production of ceramic tiles. The main aim of present work was to study the possibility of usage of this hazardous waste in floor ceramic tiles industry. A dried sludge waste was added in percentages from 5% up to 35% to a standard floor tile mix, molded, pressed uniaxially at 30MPa and then fired at temperatures reaching 1150°C for 15 min soaking time. The properties of both green and fired tiles were investigated as function of percent waste added. The vitrification parameters, which are linear firing shrinkage, water absorption, apparent porosity, and mechanical property, were determined and compared with ISO standards. Fired samples of the proposed mixtures were investigated by scanning electron microscope (SEM). It was possible to obtain tiles that abided by ISO standards for maximum addition of 7% sludge fired at 1150°C (for water absorption<10%), and 10% sludge or 5% sludge for tiles fired at 1150°C and 1100°C, respectively (for water absorption>10%), which are recommended for both their economic and environmental benefits.