Simulation of arsenic partitioning in tributaries to drinking water resevoirs

Abstract

Arsenic released by bottom sediments was determined by experiments in which the sediments were artificially re-suspended using a particle entrainment simulator (PES) to simulate river conditions. Sediment cores were collected from various tributaries to drinking water reservoirs in Connecticut spiked with arsenic, and run in the PES at simulated bed-flow shear stresses from 0.0 to 0.6 N/m(2). Under equilibrium conditions, the dissolved fraction of arsenic was found to range from 8.3 to 22.1 microg/l, which in most cases exceeded EPA Maximum Contaminant Level (MCL) of 10 microg/l. Experimental results from these simulations have shown that bed-flow shear stress causes an increased concentration of dissolved arsenic, most notably at shear stresses of 0.4, 0.5, and 0.6 N/m(2). For the solid phase under equilibrium, the concentrations of arsenic ranged between 71 and 275 mg/kg. The average concentration of arsenic on the solid phase as well as partitioning coefficient values (K (p)) were highest at initial shear stress. This was attributed to the higher fraction of colloidal material and finer organic particles in the suspended solid mixture. Particles of such nature proved to have higher affinity to arsenic. K (p) values were determined from PES data and were found to range from 4,687 to 24,090 l/kg. However, on a mass load basis, the amount of arsenic found in suspended sediment increased with the increase of shear stress. Similarly, the amount of arsenic in the solid phase increased significantly for sites with high Volatile Organic Carbon (VOC) content. Because of the influence of Total Suspended Solids (TSS) and VOC concentrations on K (p), the use of the PES is more appropriate in obtaining K (p) values that would be found under real stream conditions when compared to the traditional way of measuring K (p) using a jar study technique.

Remobilization of heavy metals during the resuspension of Liangshui River sediments using an annular flume

“…As can be seen from Table 3, the K D values for heavy metals reduced as the velocity increased from 0.15 to 0.35 m/s during the resuspension, with the exception for Ni at 0.35 m/s, which was consistent with previous study [23]. One possible explanation for this phenomenon is that finer particles (silt/clay fraction), which enrich more heavy metals compared with sand fraction, decreased as the velocity increased ( Table 2).…”

“…Another possible reason is the change of TOC in SPM. According to previous studies [23], K D values for heavy metals are typically high in organicSPMs. In this study, the TOC of SPM decreased from 96.79 to 84.77 g/kg as the velocity increased from 0.2 to 0.35 m/s (Table 2), which is in accordance with the descending order of the K D values.…”

Remobilization of Phosphorus from Sediments of Taihu Lake during Periods of Simulated Resuspension

“…Partition Coefficient. The partition coefficient (K d ) defines the degree of partitioning between dissolved and particulate phases, and is an important parameter to simulate the transport dynamics of dissolved and particulate forms of contaminants (Alkhatib and Berna, 2008). It is calculated as follows (eq 2):…”

Distribution of heavy metals in the water column, suspended particulate matters and the sediment under hydrodynamic conditions using an annular flume

“…A reasonable explanation for this observation is that the entrainment of larger size particles with lower contaminants into the overlying water at higher velocity diluted the heavy metal concentration (Kim et al, 2004). Another possible reason may be due to their redistribution into the water column, resulting from the loss of adsorption sites on particles as the SPM concentration increased (Alkhatib and Berna, 2008), which is supported by the increase in soluble heavy metals at higher velocity as shown in Fig. 4.…”