Sludge treatment represents almost half the cost of wastewater treatment at many facilities in the U.S. Although sludge problems are of serious concern everywhere, they are different for different locations. The approach to sludge handling and the solution to problems depends on geography, climate, population, proportion and nature of industrial wastes in the wastewater, and local details (e.g., proximity of hills, rivers, residences, farmland, landfills, strip-minded land). The net result has been different approaches to sludge handling, and great variety in processes and equipment. A breakdown of small community sludge management facilities in the U.S. indicates that the most popular method of sludge stabilization for facilities of less than 1 mgd (0.044 cu m/s) capacity is aerobic digestion, followed closely by anaerobic digestion, primarily at facilities near the high end of the range. The overwhelming choice for dewatering is sand drying beds, and for final disposal, land filling and spreading. These practices have evolved over several decades for a variety of reasons.