BOD load analysis and management improvement for the Chao Phraya River Basin, Thailand

The loads of biochemical oxygen demand (BOD) in the Chao Phraya River Basin (CPRB), Thailand were analyzed in terms of how they were generated (BOD_gen), stocked in the environment (BOD_en-stock), and discharged into the Chao Phraya River (BOD_CPR) using material flow analysis. BOD_gen from the industrial sector was the highest; however, BOD_en-stock and BOD_CPR from this point source were not significantly higher than those from the domestic sector. BOD_gen, BOD_en-stock, and BOD_CPR from swine farming and aquaculture across the river basin were lower than those from the domestic and industrial sectors. Of the total 251,884 tons per year (t/year) BOD_CPR, 49,614 t/year were in the upper river section, 35,976 t/year in the middle river section, and 166,294 t/year in the lower river section. These amounts were more than the carrying capacities of the relevant river sections (i.e., 7230 t/year, 18,380 t/year, and 37,851 t/year of the BOD loads for the upper, middle, and lower river sections, respectively). The first priority in BOD reduction in the CPRB should emphasize domestic wastewater by increasing wastewater treatment efficiency and onsite installations of wastewater treatment systems, while the second should be on paddy fields and other nonpoint sources. Specific best management practices may be considered, e.g., creating constructed wetlands or preserving riverbank vegetation as natural swales to alleviate BOD discharge from agricultural activities into water sources.