Potential for parasitic disease transmission with land application of sewage plant effluents and sludges

Land application of sewage plant effluents and sludges is being considered by planners because of environmental problems arising from alternative approaches and as a means of recovering the soil enrichment qualities of sewage effluents and sludges. A review of the literature shows that primary and secondary treatment, anaerobic sludge digestion, and routine disinfection (chlorine or ozone) do not destroy completely parasitic forms. Because of their weight most cysts and eggs are found in the sludge. Sludge digestion does destroy protozoan cysts but not all metazoan eggs. These cysts and eggs are extremely resistant in field conditions and some can persist infective for long periods. Documented disease transmission to humans from land application programs is related only to use of raw, not treated, sewage on land. Some animal disease transmission has been found related to untreated and partially treated sewage. Those who have examined sewage plant effluents and sludges for parasitic cysts and eggs have found them present. The most commonly reported species are: E. histolytica, Ascaris lumbricoides, Trichuris trichiura, Hymenolepis spp, Taenia sp. Enteroblus vermicularis, Ancylostoma and Necator . Destruction of all pathogenic forms can be assured by adequate heating of material to pasteurization temperatures of 60°C or more for 30+ min. Direct heating or composting can accomplish this. Parasitic disease transmission can be reduced by controlling the types of land to which these sewage plant products are applied. Parasitic disease transmission should be considered in developing the technology and/or management approaches to land application of sewage plant products for soil enrichment purposes.