Effect of tapering on the performance of waste stabilization ponds

A model for wastewater degradation in a tapered waste stabilization pond was derived as a modified Bessel function by materials balance approach. Based on hypothetical data, the tapered model gave lower faecal bacteria removal than the conventional (rectangular) model for various values of dispersion number, die-off rate coefficient, average width and shape factors. The above results were corroborated by data collected from two laboratory ponds operated in parallel; one having a tapered and the other a rectangular surface area. The latter gave slightly higher hydraulic efficiency and BOD5 removal. Besides, faecal bacteria removal was significantly lower in the tapered pond than in the rectangular pond at 0.10 level of significance. Calculated faecal bacteria reduction using the tapered model was in good agreement with measured data with coefficient of correlation and standard error of 0.904 and 0.014, respectively. Effects of tapering on ponds with respect to construction cost, operational and maintenance ease and accuracy of estimated design parameters are also discussed.