Helminth ova control in sludge: a review

Sludge reuse for agricultural production or soil reclamation is a common practice in several countries, but it entails risks if not properly performed. One such risk is the dissemination of helminthiases diseases. As a consequence, international criteria and national standards set values to limit their content in biosolids. However, little information is available on how to inactivate helminth ova from sludge, particularly when a high content is involved as is the case in the developing world. Moreover, treatment criteria are based on a limited number of studies dealing with local characteristics that, when applied to the conditions in developing countries, produce poor results. This is because design criteria were developed for Ascaris (a kind of helminth) while sludge contains a variety of genera. In addition, much information on helminth ova was produced a long time ago using inaccurate analytical techniques. This paper summarizes research and recent technical information from the literature concerning: (a) the general characteristics of helminth ova; (b) the common helminth ova genera found in sludge; (c) the main removal and inactivation mechanisms, (d) the processes that have proven effective in practical conditions at inactivating helminth ova; and (e) analytical techniques used to enumerate these pathogens.