Mechanisms for Parasites Removal in a Waste Stabilisation Pond |
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Authors: | Roberto Reinoso Saúl Blanco Linda A Torres-Villamizar Eloy Bécares |
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Institution: | 1.Environmental Research Institute,University of León,León,Spain;2.Department of Biodiversity and Environmental Management, Faculty of Biological and Environmental Sciences,University of León,León,Spain |
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Abstract: | A waste stabilisation pond (WSP) system formed by two anaerobic ponds, a facultative pond and a maturation pond was studied
from December 2003 to September 2004 in north-western Spain in order to evaluate its efficiency in the removal of faecal indicator
bacteria (total coliforms, Escherichia coli, faecal streptococci), coliphages, helminth eggs and protozoan (oo)cysts (Cryptosporidium and Giardia). Furthermore, sediment samples were collected from the bottom of the ponds to assess the settling rates and thus determine
the main pathogen removal mechanisms in the WSPs system. The overall removal ranged from 1.4 log units for coliphages in the
cold period to 5.0 log units for E. coli in the hot period. Cryptosporidium oocysts were reduced by an average of 96%, Giardia cysts by 98% and helminth eggs by 100%. The anaerobic ponds showed significantly higher surface removal rates (4.6, 5.2 and
3.7 log (oo)cysts/eggs removed m−2 day−1, respectively) than facultative and maturation ponds. Sunlight and water physicochemical conditions were the main factors
influencing C. parvum oocysts removal both in the anaerobic and maturation ponds, whereas other factors like predation or natural mortality were
more important in the facultative pond. Sedimentation, the most commonly proposed mechanism for cyst removal had, therefore,
a negligible influence in the studied ponds. |
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