Differences in length:breadth ratios (in the range of 1:1 to 6:1) and depths (from 1 to 2 m) had little effect on the performance and effluent quality (i.e. BOD, SS and FC) of secondary facultative ponds. Shallow maturation ponds (0.4 m) were more efficient at microbiological disinfection than deeper ones and could actually reduce land area requirements. KT values for faecal coliforms, salmonellae and rotavirus differed from one another in the same ponds and for different pond types. The Marais design equation for predicting faecal coliform numbers in pond effluents, although not perfect, does provide a reasonable design approach for systems containing more than two ponds in series.

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