Disposal of sewage sludge is a common problem. Often the waste is dumped into waterbodies, severely polluting them. A better option may soon be available if a team of Korean ceramic researchers has its way: it is suggesting sludge be used to make cement.

Scientists at the Seoul-based Korea Institute of Ceramic Engineering and Technology led by Woo-Teck Kwon say the organic part of the sludge may serve as fuel for manufacturing cement and the inorganic components such as oxides of silicon, aluminium and iron can be the raw material for the clinker.

However, one problem with this application is the high phosphate and chloride content of sludge. While the desirable chloride content in cement raw mix is 400 parts per million (ppm), the same in sludge can by anything from 300-10,000 ppm. Similarly, phosphate content in the sludge can be 2,000 ppm, which is several times higher than what an ideal cement mix can have.

The scientists investigated how much phosphate and chloride can be allowed in the sludge without compromising the quality of the cement produced or affecting the kiln. They found if applied in limited quantities (up to 2 per cent by weight), phosphate and chloride cancel out each other's negative impact, leaving the quality of cement somewhat untouched. Their findings appeared recently in the online materials science journal, Azojomo.