Methods for reducing the infection hazard of waste-water sludge

The most commonly used disposal practices for digested sewage sludge in the United States of America are disposal to landfill, agricultural use, incineration and disposal to the ocean. About a quarter of the sludge produced is used for agricultural purposes. The US Congress has been strongly urging more beneficial use of waste-water and waste-water sludge. However, plant location and other consideration, such as the high metals content of many sludges, make it unlikely that the proportion of sludge used on the land will increase markedly in the near future. A portion of the sludge used on the land must be attenuated in content of infectious material below that obtained by conventional digestion processes. One method for reducing infection hazard is high-energy irradiation. However, this method must compete with other methods such as pasteurization, long-term lagooning, thermophilic anaerobic digestion and thermophilic aerobic digestion. The high-energy irradiation method offers several advantages, particularly high reliability, but its cost must be competitive with other methods to gain acceptance. (author)