Ceramic Building Materials: An Alternative in Disposal of Sewage Sludge

Abstract

The increased sewage sludge production from domestic wastewater treatment plants, has become a serious environmental problem. In Portugal the principal way of disposal, is on agricultural land, however this way is unsuitable, not only because land is limited, but also because there are strict regulations in terms of location, categorised site, gas emission, leachate escape, etc. The high organic content of sewage sludge makes it a waste with a considerable calorific value; the inorganic content usually 10 to 30 % is mainly silt and clay minerals. This paper presents results regarding the use of sewage sludge and pore agent additives (mainly forest waste). The development of heavy clay materials as an alternative solution for sludge disposals. Addition of sewage sludge prove to be a way of waste recycling and energy saving The benefits and difficulties to both brick manufacturer and environmental protection are pointed-out. Physical, chemical and mineralogical composition of sewage sludge, forest waste and clay are studied. The influence of such additives on the brick final properties such as mechanical strength, shrinkage, specific gravity and water absorption are presented. Special focus was given to the environmental risk which might ensue from the utilisation of the new material by performing among others, leaching tests, in order to measured the leachability of inorganic substances from the ceramic matrixes. The leaching tests performed were single and sequential batch tests and, in general, they suggest that municipal sewage sludge within the typical heavy metal content could be incorporated within the brickmaking process with absent on negligible leaching potential.