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

Abstract

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 K b (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 ( R 2 = 0.874 ), and related K b with the pond detention time t and depth H ( K b = 0.682 H – 1.286 t – 0.103 ). The other equation also led to a satisfactory fitting ( R 2 = 0.845 ), but was slightly simpler, depending only on the pond depth ( K b = 0.549 H – 1.456 ).