The study of low-cost techniques for the tertiary
treatment of wastewater is of global interest; above all
low-energy techniques that do not require the use of
chemicals. In this study, a wastewater treatment technology
based on the filtration by a zooplanktonic population
(
Daphnia magna) is studied in controlled laboratory and
mesocosm experiments for different hydraulic retention
times (HRT). The efficiency of the treatment is evaluated
in terms of particle removal efficiency. From laboratory
experiments, HRT over 12 h and
Daphnia concentrations
above 50 individuals l
-1 guarantee a particle removal
efficiency greater than 30 %. However, low HRT of 6 h
would require
Daphnia concentrations above 70 individuals
l
-1 in order to obtain a particle removal efficiency of
20 %. The minimum removal efficiency of 2 % was for
HRT = 3 h, independent of the
Daphnia concentration. In
the mesocosm, the growth of
Daphnia individuals
enhanced
Daphnia magna filtering rates and higher
removal efficiencies than those in the laboratory for the
same HRT range. In the mesocosm experiments
E. coli
concentrations were reduced to a maximum of 2 logarithmic
units. A balance equation model is proposed to predict
particle removal efficiencies for varying HRT.
