Three hundred thousand tons per year of water works sludge are produced in Korea. End disposal of the sludge is mainly based on recycle such as supplementary material for cement kiln, raw material for construction materials and fill material. The dry clarifier sludge organic content is about 30% and the major elements determined are aluminum(about 14%), iron(about 4%), potassium(1.8%), and manganese(0.5%). The recovery of coagulant has high economic advantage and recommended as a suitable treatment option for the disposal of water works sludge. Chemically, coagulant(aluminum) recovery from the water works sludge is a simple process. This process is however, somewhat complicated by pH control in the mixture of dewatered clarifier sludge and sulfuric acid solution. Also, the thickened water works sludge(TWS), which is withdrawn from the bottom of the thickener in water works plant, is difficult to dewater. In addition coagulation is used to remove total phosphorus(T-P) from municipal wastewater in oder to strengthening discharge water quality standard for T-P in municipal wastewater treatment plant(MWTP). Nevertheless it has the drawback of producing a large amount of sludge which together with the coagulants such as alum and polyaluminum chloride used to treat T-P in municipal wastewater increases the operating cost. Reject water originates from the dewatering of digested sludge in the MWTP. It contains heavy metals and large amounts of nutrients such as phosphorus and nitrogen. Traditionally, reject water is recycled back to the main flow line on of the MWTP. Although this method seems to be simple, it also has its drawbacks. First of which is the increase in the load of the MWTP as the reject water characteristics is very much different from the normal municipal wastewater. The objective of this study is to investigate the effectiveness of thickened water works sludge as an adsorbent of phosphorus from the reject water. In this study, batches of experiments were conducted to investigate the effect of dosage of TWS for reject water on its phosphorus adsorption properties. Increasing the TWS dosage to 30%(vol/vol), T-P and COD of reject water decreased to 55% and 20% respectively. Experimental results show that the potential of the TWS as coagulant in phosphorus and organic matter immobilization, thus converting they from rejector water to a useful material in pollutant control.

Since water works sludge have a high aluminum content, recycling aluminum has become a significant environmental issue. Generally, the method of recovery of aluminum from water works sludge are acid digestion, alkalization, ion exchange and membrane separation. However aluminum hydroxide may be dissolved in strong acidic and alkaline media due to its amphoteric nature. So, the traditional acidification and alkalization methods still being explored. Chemically, aluminum recovery from the water works sludge is a simple process. The acid digestion is however, somewhat complicated by pH control in the mixture of dewatered water works sludge (DWS) and sulfuric acid solution. Under strong acidic condition, probe of pH meter, which is a key part of a pH meter, can be easily damaged. Also it is not easy to control pH during the process of mixing DWS and acid solution because high concentration of total solid are present in the mixture. Furthermore, the moisture content of DWS is very serious change. Most of the previous studies have mainly focused on the adsorption properties of dewatered alum sludge; little attention has been put on how to improve its phosphorus adsorption capacity. In this study, batches of experiments were conducted using DWS, artificially controlling moisture content (64~78%), to investigate the effect of concentration of sulfuric acid on pH of the sludge for pH control without pH meter in the coagulants recovery process. The water content of DWS was measured in 30 minutes using Infrared Moisture Determination Balance (FD 660, Kett). Experimental results show that the concentration of sulfuric acid for acidification of DWS is higher with higher water content of that.