Determination of the pollution carrying capacity of way bunut river in metro city using QUAL2Kw modeling and mass balance approach

Abstract

Way Bunut River in Metro City, Lampung, is an important water source for irrigation and tourism. The quality has declined due to untreated domestic wastewater, irrigation effluents, and agricultural runoff. This study evaluates the river’s pollution-carrying capacity and assesses its current water quality status based on applicable standards. The objectives are to analyse water quality parameters (temperature, pH, TDS, TSS, BOD5, DO, and ammonia), estimate the Total Maximum Daily Load (TMDL), and determine pollution status using the Pollution Index (PI). Data were collected from four river segments with five sampling points, representing one point source and four non-point sources. Pollution load capacity was assessed using QUAL2Kw modelling combined with a mass balance approach, while water quality status was determined through PI analysis. The QUAL2Kw model was calibrated with field measurements and applied to three simulation scenarios. Results showed that BOD exceeded Class II standards (Government Regulation No. 22/2021), with TMDL exceedances of -356.75 kg/day in segment 3 and -12.04 kg/day for ammonia. Both current and simulated conditions classified the river as lightly polluted. These findings indicate that Way Bunut River has surpassed its pollutant assimilation capacity, highlighting the need for integrated pollution control measures to ensure sustainable management.