The application of a diagnostic methodology for the identification of hydraulic design deficiencies affecting pathogen removal

Abstract

An intensive diagnostic methodology designed to evaluate microbiological removal deficiencies related to design defects was applied to a two-stage waste stabilisation pond system in Colombia. This evaluation included intensive monitoring of a range of physico-chemical parameters, an integrated assessment of faecal coliform removal and simultaneous hydraulic tracing of surface flow using oranges. The dispersion/advection effects and the hydraulic regime through the facultative pond were defined using a bacteriophage. This methodology facilitated the identification of the hydraulic flow patterns and short-circuiting together with the age distribution of the pond effluent. Observed differences between surface and sub-surface flow patterns were attributed principally to the fact that wind action opposed the natural input-output energy flow path. The concentration of phage leaving the pond in 6 hours represented 1% of the original dose, confirming the finding that a 2-log reduction of pathogen indicators could not be achieved. Three stages of intervention were identified as necessary for the performance to be improved to the level at which WHO reuse targets would be met.