Reuse of fresh water sludge in cement making J.R. Pan, C. Huang and S. Lin Institute of Environmental Engineering, National Chiao Tung University, Hsinchu, Taiwan 30039, Chinese Taiwan (E-mail: jrpan@mail.nctu.edu.tw; cphuang@mail.nctu.edu.tw) Abstract With the increasing demand for high quality water, a large quantity of chemical agent must be added in the water purification process, which in turn generates enormous amount of fresh water sludge. Of all the options for sludge disposal, sludge reuse has been considered most economical and environmentally sound. This study evaluated the possibility of incorporating fresh water sludge in the making of Portland cement through the sintering process. The goal was to search for the optimal condition to maximize the replacement of clay with the fresh water sludge. Characteristics of fresh water sludge were collected and analyzed. The analysis showed that water source and water treatment process dominate the characteristics, particularly the chemical composition of the fresh water sludge. The fresh water sludge was mixed with the cement clay in various percentages, from 0% to 100%, as raw material for cement-making. The effects of its addition on the sintering condition and the quality of cement were evaluated. The analysis of the clinkers showed that the addition of the fresh water sludge did not change the phase form and the f-CaO content of the cement. The compressive strength of the masonry increased with the increasing addition of fresh water sludge. All cement products made from various replacement ratios met the Chinese National Standard of first degree Portland cement. Keywords Cement; fresh water sludge; sintering; sludge reuse Introduction Fresh water sludge (FWS) is an inevitable by-product of the water purification process. The current annual FWS production in Taiwan is approximately 120 thousand tons, which needs to be properly disposed of. Of all the options for FWS treatment, land disposal has been the most popular mode. However, because of the difficulty in acquiring landfill sites, sludge reuse has become the current trend (1). A practical sludge reuse strategy must be simple and inexpensive, and its product must have market value. Because the inorganic chemical composition of the FWS is similar to that of the clay, researchers have considered to recycle sludge and sludge ash in building and construction material. Reuse of sludge or sludge slag as raw material for brick has been investigated (2–6). Other studies have made sludge into synthetic aggregates by firing in high temperature (7–9). These methods consume more energy in burning and melting the sludge than the normal procedures need. Sludge recycles in cement industry can be a practical alternative in that the cement kiln is virtually an incinerator, in which not only the liquid waste can be utilized as fuel in the cement kiln, but also the solid waste can be used as fuel and the raw material for cement. Tay and Show (1991) have utilized dewatered sludge mixed with lime to make cementi- tious material. T. Onake (2000) has reported that the dried sewage sludge pellet can work as raw materials and fuel in the production of Portland cement without any odor and dust emissions problems. Espinosa and Tenorio (2000) have also indicated that the addition of galvanic sludge up to 2.0 wt% didn’t affect the phase form of cement clinker and the leaching tests of metals were below the standard limit. Because the FWS is virtually non- hazardous, chemical composition of the inorganic sludge is similar to the clay used in cement producing, incorporation of FWS in cement production should be a practical approach. Water Science and Technology Vol 50 No 9 pp 183–188 © 2004 IWA Publishing and the authors 183