Characterization of water quality among direct and delayed wet -weather flows in an urban combined sewer catchment of Thailand

Abstract

The purpose of this research was to compare five water quality parameters (BOD, TSS, total zinc, TKN, and fecal coliform) in wet-weather flow of a combined sewer catchment against dry-weather flow, while making a distinction between direct and delayed inflow, which has often not been made. Correlations and event mean concentrations (EMCs) were also calculated. A total of 38 samples were collected from Khon Kaen’s combined sewer system between March and August 2015. Concentrations in direct inflow of three parameters: total zinc ( x = 0.24 mg/L, IQR = 0.12-0.34), TSS (240 mg/L, 176-356), and BOD (59.7 mg/L, 42.4-77.8) were higher than delayed inflow ( x = 0.04 mg/L, 36 mg/L, and 23.7 mg/L, respectively). Concentrations of delayed inflow were similar to or lower than dry-weather flow. Pollutant concentrations for particulatebased pollutants were much higher during the direct inflow phase of rain events compared to the delayed inflow phase. Dissolved-phased nutrients, however, were not different.

Keywords

• combined sewer overflow
• event mean concentration
• stormwater
• surface water quality
• urban runoff