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, ∆fc, was investigated in laboratory columns and on a 565 m pilot plant. ∆fc observed in laboratory columns was shown to be closely related to water detention time distribution, DTD. The relationship between ∆fc 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.