The tide of “development” gathering pace in developing countries has resulted in the production of increasing quantities of wastewaters. This inevitably necessitates a reappraisal/reassessment of wastewater technologies. This study demonstrates the role of simple physical modelling approaches in evaluating/appraising the technical performance of hoppered peripheral-feed (spiral-flow) clarifiers -- which clarifiers have enormous scope for use in small plants in developing countries. The study focuses on the optimization of local geometrics and hydrodynamics for the purposes of improving overall performance in hoppered spiral flow clarifiers. It is concluded that for a defined set of clarifier global geometry and loading conditions, an optimum race width and inlet nozzle diameter exist. The optimum values of these parameters for a defined conceptual prototype are presented. It is further concluded that the mere variation of either the race width or the inlet nozzle diameter significantly affects the hydraulic detention and solids removal interrelationships in hoppered spiral flow clarifiers. Under the conditions of this study, a 50% reduction in inlet nozzle diameter resulted in an incredible more than 50% loss in hydraulic efficiency. Overall, the possibility of significantly increasing clarifier capacity and/or overall performance by simply optimizing local geometrics and hydrodynamics has been demonstrated via a well tested and friendly methodology.

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