Environmental Significance of Helminth Parasites and Their Removal in Wastewater Treatment Processes

Abstract

Epidemiological surveys  have   reported  important risks  regarding intestinal parasites because of  their  widespread  distribution (Crompton 1989),  their  high  survival  rate  in  the  environment (Shuval  et  al.   1988)  and  their  low  infective dose  (Kowal  1985 Gunnerson et al. 1985). The presence of large  number of helminth  eggs  in various  effluents  used  for agricultural purposes has been reported by several studies (Barbier et al. 1990 Schwartzbrod et al. 1986). Occurrence of helminthes, a human intestinal parasite, in sewage  is of considerable environmental  significance.   In the  past,  the  different helminth  parasites were  distributed only  in some pockets on  earth.  But the migration  of people  and  enormous   production of sewage with  population  explosion  has  resulted   in widespread occurrence of these parasites.  These parasites are  transmitted through  their  resistant life  stages such  as  eggs  and larvae   and  are  responsible  for   infection of  intestine,   illness,  pneumonia,   cough,   eosinophilia,   blood   stained  sputum,  bowel obstruction,  infection of liver,  gall  bladder  and  appendix, vitamin  deficiency and also  occasional death  in both children and  adults. Contaminated articles  like vegetables,  hands, utensils  and dust help in distribution and transmission of parasites.  Sewage treatment plant workers are also  exposed to the infection by helminth  parasites. Strict standards  for the number of eggs are  laid down  by W.H.O. for the reuse  of treated wastewater. Various wastewater treatments processed differ  in their efficiency in the  removal  of highly resistant  helminth  eggs.  In sewage treatment,  most  of the helminth  eggs are  concentrated in the sludge,  which  require further treatment such  as composting,  aerobic digestion and anaerobic digestion. The information  on all  these  aspects are  reviewed in this  paper,  including  the  approaches proposed  by  different workers to  make  the treatment more effective to make sewage and sludge suitable  for safe  reuse  and the suitable monitoring methods developed for the enumeration of helminth  parasites in wastewater and treated effluents and sludge.