Faculty of Engineering, Universiti Teknologi Brunei, Tungku Highway, Gadong, BE 1410, Brunei Darussalam

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Abstract: Simulated rainfall experiments were conducted at sites representing parking lots, restaurants and residential blocks in a typical commercial complex of a humid tropical city to investigate wash-off and buildup processes of BOD₅, ammonia, phosphate, fecal coliforms and total coliforms. It was found that the mass buildup of the studied pollutants is basically independent of the type of land use in the same area. The experiment further revealed that the maximum concentrations of the pollutants, Cm, do not necessarily occur at t=0. Instead, they more occurred between t=5-10 minutes after the beginning of the wash-off process. Thus, the exponential decay function can well replicate the pollutographs only from C=Cm. Accordingly, wash-off coefficients ranging from 0.08-0.15 mm-1 respectively for BOB₅, nutrients and coliforms were suggested based on the experimental data. Parameters of the exponential buildup function suggested by Novotny were also identified for BOD₅, ammonia, phosphate, respectively, using the experimental data, whereas growths of fecal and total coliforms were replicated by the logistic growth model. The parameters obtained for the buildup functions are deemed to be applicable to the humid tropical urban areas similar to where the experiment was conducted. The findings of this study are useful when the pollutant buildup and wash-off dynamics are introduced into urban stormwater quality models.

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