Variations of Arsenic Species Concentrations in Riverbed Sediments Induced by Geothermal Wastewater Drainage: A Case Study at the Yangbajing Geothermal Field, Tibet, China

Abstract

The high-temperature geothermal fluids from the Yangbajing field, a world famous geothermal field in Tibet, have been used for electricity generation. The geothermal wastewaters generated by the Yangbajing power plants with arsenic (As) concentrations up to 3.18 mg/L, were drained immediately into the Zangbo River, the major surface water in the study area, which markedly increased the arsenic concentration of river waters at the nearest downstream of the wastewater draining exit of the first power plant. However, along the flow direction of the Zangbo River, the arsenic concentrations in river waters were declining sharply. Further inspection shows that the concentrations of ionically bound As, strongly adsorbed As, and total As in riverbed sediments of the Zangbo River were also affected by the drainage of geothermal wastewaters, indicating that they may serve as one of the sinks of arsenic with geothermal source. In other words, after arsenic from geothermal wastewaters entered the Zangbo River, the adsorption of arsenic on riverbed sediments could lower the arsenic concentrations of river waters, which was helpful for reducing the health threat of arsenic on local residents with the Zangbo River as drinking water source.