Reduction of Wastewater Sludge Pathogens Using Heat Treatment

Municipal wastewater sludge contains valuable and recoverable resources which have been used in agriculture over a long period of history. However, the potential spread of human diseases due to the presence of pathogenic microorganisms in wastewater sludge has been recognized by modem man. The risk of diseases coupled with altered aesthetic values and various economic considerations have greatly decreased the use of sludge in agriculture. During the past few years, it has been recognized that this decline in agricultural uses of sludge is not only wasteful, but ultimately leads to pollution of our land, water and air. Therefore, laws have been enacted to regulate the disposal of sludge and to promote its utilization in agriculture. The only natural waste components of wastewater sludge present in sufficient concentration to constitute a health hazard are pathogenic microorganisms. When human excreta becomes a part of sewage, it is often mixed with toxic chemicals from industrial waste. However, the amount of toxic chemicals in sewage that does contain a high percentage of industrial waste can often be considerably reduced or eliminated by industrial source control. For these reasons, safe utilization of most sewage products should require only the removal or inactivation of pathogenic microorganisms. These organisms are often concentrated in sludge as a result of entrapment with larger particles. Pathogens are thus a normal component of sludge and cannot be reduced by source control. The Clean Water Act of 1972 was enacted to improve the quality of the nation\u27s water supplies. As a result, a byproduct of sewage treatment, known as sludge, has increased in quantity as wastewater treatment throughout the nation has improved and expanded. An increasingly important problem is the fate of sludge that is produced. Sludge dumping on the oceanic continental shelf is being phased out. Incineration is not only costly but also causes air pollution and creates a solid waste that must be buried in a landfill. It is estimated that nearly 50% of the costs of sewage treatment plants are already directed toward sludge management (Vesilind. 1974). It is impossible to recover even a portion of these costs if sludge is simply buried in a landfill or dumped in the ocean. Disposal of sludge has become a major concern of many treatment facilities. With the increased cost of transportation, lack of available sites and stringent rules imposed by the Environmental Protection Agency (EPA) on landfills, many utility owners are looking for new options. An attractive alternative, rapidly gaining in popularity, is the beneficial use of sludge as a soil amendment. Sludge has been shown to be an excellent organic amendment for soils and it is also a source of nutrients and minerals for plants. Land application of sludge represents a significant and rapidly increasing option for disposal of sludge produced in the United States. The EPA the primary Federal agency responsible for sludge management is encouraging the beneficial use of sludge wherever environmentally feasible. Estimates suggest that as much as 40% of the municipal sludge generated in the United State is currently applied to land (EPA 1984). The use of sludge as a soil amendment is attractive only when it is not causing any potential health risks. Microorganisms such as bacteria, virus, protozoa and parasites can cause diseases. Land application of sludge creates a potential for human exposure to these organisms through direct and indirect contact. To protect human health from these organisms that sludge contains, the government is now regulating the land application of sludge. The relative public health risk associated with the beneficial use of sludge is directly related to the extent of public exposure. Risk increases if the sludge is used on food chain crops or in public access areas. Therefore, proper treatment of sludge and establishment of management practices are essential before sludge is applied to land