Bouhoum K., Amahmid O., Habbari Kh. and J. Schwartzbrod (1997) Fate of
helminth eggs and protozoan cysts in an open channel receiving raw wastewater
from Marrakech . Rev. Sci. Eau 10 (2) : 217-232. [article in french]
Original title: Devenir des oeufs d'helminthes et des kystes de protozoaires
dans un canal a ciel ouvert alimenté par les eaux usées de
The use of wastewater in agriculture in what is called "sewage farming" is
becoming more widespread, particularly in countries with a severe shortage
of water resources. Wastewater from the city of Marrakech is used for irrigation
without any treatment. Nevertheless, the wastewater runs into an open channel
of 2 km before being used. Thus, the fate of helminth eggs and protozoan cysts
in this channel is of great importance for public health. The effluent studied
carries wastewater from highly populated residential areas (Sidi Youssef Ben
Ali, la Médina...). The primary channel originating from this effluent
runs for 2 km with a variable width of 0.7 to 5.5 m in a clay soil. Secondary
ramifications on the channel are used for irrigation. Water and sediment samples
were collected at different locations on the channel twice monthly for five
months (April-August). One litre wastewater samples and 10 g sediment samples
were collected, at all stations on the channel. The samples were analysed using
the concentration method of Teleman-Rivas as modified by Bailenger (1962) because
of its reliability and low cost. Helminth eggs were then counted on MacMaster
cells after addition of saturated saccharose solution to the samples. Protozoan
cysts were quantified using a Thoma cell after addition of Lugol solution to
Results of water analyses are expressed as the number of cysts or eggs per
liter of wastewater and results for sediments are expressed as the number of
cysts or eggs per gram of dry matter.
- Wastewater samples from the effluent contained helminths as well as protozoa.
All wastewater samples contained protozoan cysts. Among three species of
protozoa identified, two were pathogenic: Entamoeba histolytica, Giardia sp.
and one saprophytic Entamoeba coli. All water samples contained
helminth eggs. Analyses for helminth egg revealed the presence of Nematodes
(Ascaris, Trichuris, Enterobius) and Cestodes (Hymenolepis, Moniezia).
This results mainly from Ascaris eggs that were encountered in all
water samples. The concentration of helminth eggs in the sewage was much
less than the protozoan cysts. In terms of densities, protozoan cysts were
in the range 6.9 x 10[exp]4 to 2.0 x 10[exp]5 cysts /L with an average of
1.6 x 10[exp]5 cysts/L. Pathogenic protozoa represent 49 % of total cysts.
The wastewater at the beginning of the channel contained from 102 to 238
helminth eggs/L with an average of 145 helminth eggs/L. Nematode eggs represented
72 % of total helminth eggs. Ascaris eggs dominated in the water samples
with 75.6 eggs/L representing 52 % of total helminth eggs. The densities
of protozoan cysts as well as helminth eggs in wastewater samples decreased
dramatically along the open channel. Protozoan cysts dropped from 1.6 x 10[exp]5
cysts/L at the beginning of the channel to 2.7 x 10[exp]4 cysts/L at a distance
2 km in the open channel. Pathogenic protozoa decreased from 8.1 x 10[exp]4
cysts/L to 1.0 x 10[exp]4 cysts/L for the same distance. The average of helminth
eggs also dropped from 145 eggs/L to 33 eggs/L. Ascaris eggs showed
the highest decrease from 76 eggs/L to 12 eggs/L. The genus Trichuris showed
the lowest decrease from 11 eggs/L to 6.8 eggs/L.
- Analyses of sediment samples revealed the presence of all protozoan cysts
and helminth eggs. Contrary to water samples, sediments samples showed an
increase of all egg and cyst concentrations along the open channel. Protozoan
cysts progressively increased from 1.7 x 10[exp]4 cysts/g at 80 m in the
open channel to 1.4 x 10[exp]5 cysts/g at 2 km distance in the channel. Helminth
parasites also increased from 9.6 eggs/g to 78 eggs/g for the same distance.
This increase of helminth eggs and protozoan cysts resulted from the decrease
of water flow velocity which caused their sedimentation. Parasites settle
out of the water column because of their own weight and because they adsorb
to particles accelerating their settling. Among all parasites Ascaris eggs
settle out first before all other nematode eggs. Ascaris eggs were
detected at 80 m in the open channel while Enterobius eggs were not
observed until 560 m in the channel. Trichuris eggs were not observed
in any sediment sample. Trichuris eggs are more easily carried by
the water flow because of their hydrodynamic fusiform shape which may explain
their absence in sediment samples. In conclusion, the parasitic quality of
a domestic wastewater in Marrakech showed significant improvement after 2
km in an open channel. Both helminth eggs and protozoan cysts showed significant
removal percentage of 77 % and 83 % after 2 km running in the open channel.
The best percent removal of protozoan cysts was observed for pathogenic protozoa
with 88 % for Entamoeba histolytica and 87 % for Giardia sp.
For helminth eggs, Ascaris eggs showed the highest removal percentage
with 85 % while Trichuris showed the lowest with 37 %. However, the
concentration of helminth eggs and protozoan cysts, after the sewage flows
over a distance of 2 km in the open channel, are still higher than the guidelines
of the W.H.O. (1989) for the use of wastewater in agriculture (less than
one nematode egg per litre). These wastewaters require further treatment
before they can be used for irrigation.
Wastewater channel, helminth eggs, protozoan cysts, wastewater, sediment,
J. Schwartzbrod, Département de Microbiologie, WHO Collaborating Centre,
Faculté de Pharmacie, 5 rue Albert Lebrun, 54000 Nancy, FRANCE
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