Escherichia coli enumeration was monitored from
the 35th day. The input load averaged at 3.54×107
CFU/
100 mL. After 49 days of experiment, there were, in the
output effluent treated by S, only 2.4×103
CFU/100 mL
of E. coli corresponding to an abatement of 99.99%
while there was 1.75×107
CFU/100 mL of E.coli in the
output effluent treated by P (Table 2). According to
several authors (Sharma et al,. 1985; Bomo et al., 2003),
the elimination of bacteria is controlled by filtration
and adsorption. These mechanisms depend on grain
size, clogging of filter, pH, and bacterial concentration.
The better elimination of bacteria by S compared to P
can be explained by their difference of accessible
surface. S and P have both high specific surfaces.
However in the case of P, most of this surface is inside
micro and macro pores and is therefore mostly not
accessible to a fast flow of water. The surface available
for bacteria to be adsorbed is thus less than with S.
Microbiological removal obtained with S was
interesting because, results were in the range of
reduction (1-3 log10) obtained by Potts et al. (2004) in
the lysimeter sand. The WHO (1989) standard
recommended for the reuse of treated wastewater for
irrigation of cooked crops (Coli.F <104
CFU/100 mL)
was reached.
During the experiment, the output effluent COD
was unstable partly because of input effluent
fluctuation. So results were presented as percentage
of abatement. The input effluent COD recorded a range
of 172. 14 to 1042.34 mg/LO2
with an average value of
601.48 mg/LO2
. It can be observed in Fig. 2a, that after
one week of operation, 90% of this load was cut down
by the S treatment and remained above this value
during the rest of the experiment. In order to achieve
this performance, SP mixture treatment required an
additional week of operation. Performance with P was
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