Enumeration and survival studies on Helminth eggs in relation to treatment of anaerobic and aerobic sludges in Jordan

Abstract

This research involved survey, laboratory and field studies. First, an evaluation of the present status of intestinal parasitic infections was made in the Jordanian population. Second, laboratory investigations were conducted on the development of a new technique to detect the viability of Ascaris eggs. Third, field studies were carried out to investigate the survival and occurrence of indigenous parasite eggs and indicator pathogens in domestic waste sludges in Jordan. Field investigations were also conducted on the effect of open natural drying beds on the inactivation of parasite eggs and bacterial pathogens. The results of this study and a survey of available literature indicated a need for a universally accepted definition of a "viable" Ascaris egg. A staining technique for detecting Ascaris egg viability was developed in conjunction with research studies of Ascaris eggs in sludge. The vital stain Crystal violet showed high correlation with the incubation method, and was more precise than the other stains tested. Crystal violet showed the best spontaneous detection of changes in egg viability and, within certain limits, it was found to be a strong indicator of the state of egg viability; furthermore it did not show any evidence of toxicity. In the staining method, Crystal violet stain is added directly to an egg preparation and observations are then made immediately using a light microscope. The results are available in only 10 minutes, compared to the 30 days required for the Incubation method. Since only stained or unstained eggs were observed, the method is less subjective than the Incubation method. In order to evaluate the versatility of the staining method, the effect of UV light and temperature was also investigated. The ultimate disposal of domestic wastewater treatment plant sludges has been recognised recently as a problem in Jordan, and has never previously been investigated from the point of view of pathogen survival and transmission. This study showed that a huge volume of sludge (36,600 m3 dry weight basis) accumulated from 1985-1993 in six anaerobic ponds, now requires desludging, treatment and disposal. Anaerobic pond sludges displayed some physico-chemical similarities to digested primary sludge.....This research concludes that sludge drying beds can be an effective method for inactivating parasite eggs, particularly in warmer geographic locations, and thus the treated sludge can be considered safe in terms of parasite transmission for application to agricultural land. Ascaris eggs had degenerated when the percentage of total solids was recorded as more than 88%; this took a shorter time in sand than in gravel drying beds. The inactivation of Ascaris eggs in drying beds is probably due to more factors than desiccation alone. Temperature, oxygen content, solar radiation, exposure time, mould activity, type of sludge, type of media etc., may also affect survival of the eggs. Anaerobic pond sludge bacterial counts showed higher resistance to desiccation and treatment conditions in drying beds compared with oxidation ditch sludge.