Water quality and TMDL determinations for the Chaopraya River, Thailand

Water quality, loadings of Biochemical Oxygen Demand (BOD), and Total Maximum Daily Loads (TMDL) of BOD for the Chaopraya River, Thailand were determined. The results showed that BOD loadings in the lower, middle, and upper river portions in 2014 were 172,326, 178,537, and 46,045 kg/d, respectively. Aquaculture and domestic wastewaters were major sources of BOD loadings. The TMDL of BOD were 284,230, 80,717, and 48,279 kg/d for the lower, middle, and upper Chaopraya, respectively in the wet season; and they were 42,866, 40,124, and 10,211 kg/d for the associated river portions, respectively in the dry season. High negative correlations between DO and BOD concentrations were detected. However, the DO concentrations at some river portions did not meet the values for the specified water classes although the BOD loadings were reduced until they met the TMDL of BOD for the associated river portions.