Accumulation of arsenic in drinking water distribution systems

The tendency for iron solid surfaces to adsorb arsenic is well-known and has become the basis for several drinking water treatment approaches that remove arsenic. It is reasonable to assume that iron-based solids, such as corrosion deposits present in drinking water distribution systems, have similar adsorptive properties and could therefore concentrate arsenic and potentially re-release it into the distribution system. The arsenic composition of solids collected from drinking water distribution systems (pipe sections and hydrant flush solids), where the waters had measurable amounts of arsenic in their treated water, were determined. The elemental composition and mineralogy of 67 solid samples collected from 15 drinking water utilities located in Ohio (7), Michigan (7), and Indiana (1) were also determined. The arsenic content of these solids ranged from 10 to 13 650 microg of As/g of solid (as high as 1.37 wt %), and the major element of most solids was iron. Significant amounts of arsenic were even found in solids from systems that were exposed to relatively low concentrations of arsenic (<10 microg/L) in the water.     

Optimization of data-acquistion rates in time-correlated single-photon fluorimetry

Four different operating configurations of a time-to-amplitude converter were examined for performance in the time-correlated single-photon fluorimetric experiment. Parameters considered were the intensity/count linearity, maximum data rate, and decay distortion. The inverted configuration with an interactive source was optimum. This arrangement combined total linearity with a 37-kHz conversion rate and did not distort the fluorescence decay. In addition, the pulse-height analyzer could severely limit the overall system data rate and could destroy the TAC intensity/count linearity.