Effect of Molecular Dissociation and Sorbent Carbonization on Bisolute Sorption of Pharmaceuticals by Biochars

Abstract

Understanding the sorption behavior of mixtures of pharmaceuticals is critical for predicting their environmental behavior and for risk assessment. Experiments on ketoprofen (KTP) and triclosan (TCS) sorption by wheat straw-derived biochars at 300 °C (WS300) and 700 °C (WS700) in single solute and bisolute systems were conducted to probe the sorption mechanisms. The results of the single solute sorption indicated that WS700 with higher degree of carbonization had higher sorption coefficient (K _d) and nonlinearity than WS300. In a bisolute system, no competitive effect was observed for partition of neutral KTP and TCS in the noncarbonized phase of WS300, but they competed for the adsorptive sites on the carbonized phase of WS300 and WS700 for sorption, in which π-π interaction is proposed as the main mechanism. The competition in the bisolute system varied with degree of dissociation of KTP and TCS, and led to a lower and less nonlinear sorption compared with that in the single solute system. TCS was more competitive than KTP due to its higher hydrophobicity, and sorption inhibition of KTP was enhanced with increasing TCS concentration. Degree of both molecular dissociation and sorbent carbonization should be considered in bisolute sorption of organic pollutants by biochars.

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