Residence time distribution and disinfection of secondary effluents by infiltration percolation

Infiltration percolation is used as a tertiary treatment in order to meet t he WHO's microbiological standards applying to unrestricted agricultural wa stewater reuse. Faecal coliform removal, Delta fc, was investigated in labo ratory columns and on a 565 m(2) pilot plant. Delta fc observed in laborato ry columns was shown to be closely related to water detention time distribu tion, DTD. The relationship between Delta fe and DTD, which has been determ ined from column tests, allowed a good prediction of the disinfection perfo rmances 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 un expected good performances, though calling for more comprehensive explanati on, speak for the widespreading of a reliable and cost-effective extensive technique. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights rese rved.