The removal of Escherichia coli from the sand beds reached 2-log
at the hydraulic loading rate of 100, and 150 L m2 day1 and only
1-log removal at the hydraulic loading rates from 200 to
800 L m2 day1. This study could not
find Entamoeba histolytica
and Giardia lamblia in the samples. We found that such effluent
showed an excellent quality as for its turbidity values (Table 5).
There amount of 5 NTU was only surpassed at the hydraulic loading
rate of 800 L m2 day1.
The concentration of total suspended solids showed an average
of 22
19 mg L1. This value was much lower than the threshold of
35 mg L1 established by the European laws (Directive 91/271/
EEC). The straining mechanism was chosen to be the main one, as it
contributes to the removal of incoming TSS within the
filter media.
In this mechanism, particles larger than the
filtering media pores
are mechanically strained out. Other mechanisms may also coexist