Temperature-dependent sorption of naphthalene, phenanthrene, and pyrene to low organic carbon aquifer sediments

Abstract

Sorption experiments were conducted with naphthalene, phenanthrene, and pyrene on low organic carbon sediments at 4 and 26 °C using batch and column techniques. Experimental controls ensured the absence of biologic and photolytic activity and colloid-free solution supernatants. Equilibrium distribution coefficients ( K d ) increased 1.1−1.6 times with a decrease in temperature of 22 °C. Fraction instantaneous sorption ( F ) values did not change significantly with a decrease in temperature of 22 °C. Desorption rate constants ( k 2 ) decreased 1.2−2.6 times with a decrease in temperature of 22 °C. Times to equilibrium were at least 40 h. The magnitude of observed K d and k 2 values and the effect of temperature on K d (e.g., low enthalpy of sorption) are consistent with sorbate partitioning between the aqueous phase and small amounts of organic matter ( f oc = 0.02%) on the sediments. The temperature dependence of K d and k 2 may be small as compared to the effects of heterogeneities in field-scale aquifer systems. Thus, thermal gradients may not be of major importance in most saturated subsurface regimes when predicting solute transport. However, aquifer remediation pump-and-treat times could be decreased because increased temperature decreases both retardation and tailing.