3.3 Conditioning

In many cases, stabilized sludge may be applied directly to land. If it is desired to land apply stabilized sludge in liquid form, sludge from anaerobic digestion, aerobic digestion, lime stabilization, chlorine oxidation, or pasteurization may be transported to the land-application site via a pipeline or tank truck. If the sludge is to be applied to land in solid form or if the land-application site is located a considerable distance from the wastewater treatment plant and it is desired to reduce transportation costs, it may be necessary to dewater the sludge. The product of the dewatering process is a sludge that has the mechanical properties of a solid. To facilitate sludge dewatering, the sludge must be conditioned.

Conditioning is the treatment of sludge to facilitate water removal. Conditioning prior to dewatering involves the chemical and/or physical treatment of sludge to enhance water removal and to improve solids capture. Most sludge conditioning systems employ inorganic chemicals, organic polymers, or heat. It should be noted that since conditioning always has an effect on the efficiency of the dewatering process that follows, any evaluation of the conditioning process must take into account the capital, operating, and maintenance costs for the entire conditioning/dewatering system. These costs must include the impact of sidestreams on other plant processes, the plant effluent, and the resulting air quality [38,80].

A primary objective of chemical conditioning is to increase the sludge particle size by combining smaller particles into large aggregates. Chemical conditioning is a two-step process...