Modelling of coliform removal in 186 facultative and maturation ponds around the world

The paper presents a very extensive evaluation of the coliform decay in facultative and maturation ponds, based on data from 186 different ponds in the world. The ponds encompass a very wide diversity in terms of physical and operating conditions, covering most situations encountered in practice. The median values for the coliform removal efficiencies were 1.8 log units (98% removal) for primary facultative ponds, 1.0 log units for secondary facultative ponds (90% removal) and 1.2 log units (94% removal) for each maturation pond in the series. Two equations to be used for design purposes were derived for estimating the die-off coefficient Kb (dispersed flow, 20 °C) in facultative and maturation ponds. The first equation led to a slightly better fitting with the observed logarithm of the effluent coliform concentrations (R2=0.874R2=0.874), and related Kb with the pond detention time t and depth H   (Kb=0.682H–1.286t–0.103). The other equation also led to a satisfactory fitting (R2=0.845R2=0.845), but was slightly simpler, depending only on the pond depth (Kb=0.549H–1.456).