Residence time distribution and disinfection of secondary effluents by infiltration percolation

Infiltration percolation is used as a tertiary treatment in order to meet the WHO's microbiological standards applying to unrestricted agricultural wastewater reuse. Faecal coliform removal, Afc, was investigated in laboratory columns and on a 565 m2 pilot plant. Δfc observed in laboratory columns was shown to be closely related to water detention time distribution, DTD. The relationship between Δfc and DTD, which has been determined from column tests, allowed a good prediction of the disinfection performances of the pilot plant for hydraulic loads of 0.54 and 0.66 m/d. For 0.82 m/d, the maximum load that could be tested on the plant, the mean faecal coliform removal was more than 1 log. unit higher than predicted. These unexpected good performances, though calling for more comprehensive explanation, speak for the widespreading of a reliable and cost-effective extensive technique.