Dewatering Sludge Using Electrokinetic Geosynthetics

Abstract

Many industries create sludges as a waste product. Dewatering of these fine grained slurries is often problematic and the traditional outlets of lagoons or landfill may pose stability and environmental contamination issues. Sludges may be mineral based or organic based. Mineral based sludges created by mining processes are currently deposited into lagoons. These tailings are often very soft and poorly consolidated thus they may create an environmental hazard and even pose a severe safety threat, particularly in seismically active areas. The treatment and disposal of organic based sludges (sewage sludge) is one of the most problematical issues affecting waste water treatment in the developed world. The traditional outlets for sewage sludge are to spread it on agricultural land, or to form a cake for deposit to landfill or incineration. In order to create a sludge cake, water must be removed. Existing dewatering technology based on pressure can only remove a very limited amount of this water because of the way in which water is bound to the sludge particles or flocs. Sewage sludge lagoons, although smaller than tailings ponds still pose an environmental hazard or impede redevelopment. Several researchers have shown that electrokinetic dewatering of sludge is more effective than conventional hydraulically driven methods. Electrokinetic dewatering involves the application of a D.C Voltage across the sludge, driving water under an electrical gradient from positive (anode) electrode to negative (cathode) electrode. However, there have been several reasons why this technique has not been adopted in practice, not least because the, normally metallic, anode rapidly dissolves due to the acidic environment created by the electrolysis of water. This paper will describe experimentation using electrokinetic geosynthetics (EKG): polymer- based materials containing conducting elements. These have been used to minimise the problem of electrode corrosion and create a sludge treatment system that can produce dry solids contents in excess of 30%. It will suggest different options for the treatment of sludges both in situ in sludge lagoons and windrows, and ex situ as a treatment process using adapted filter press technology.