CONCLUSION
The treatment performance depended on the types
of filters. Pozzolana took a longer time to set, showed
unstable efficiency and a performance drop after the
6th week probably due to clogging. While a good level
of treatment was achieved with the sand after only one
week of experiment. Sand provided good removal of
microorganisms and a good conversion of organic
nitrogen into mineral nitrogen easily assimilated by crop
plants. Sand infiltration promoted a healthy
development of the biofilm that degrade organic matter.
However, biomass growth, accumulation of suspended
solids should be monitored to prevent clogging. This
monitoring could be achieved by COD measurement.
Sand and mixture sand-pozzolana presented similar
results. This suggests that the abatement took place in
the part of the columns. Sand treatment allowed
elimination of pathogen bacteria while preserving the
wastewater nutritional quality. The use of treated
wastewater will lead to reducing the cost of fertilizer
and conservation of freshwater resource. Considering
this result, the sand was retained for further experiments
the field in Djibouti.