Emerging contaminants (ECs) are chemicals that are currently unregulated due to limited understanding of health effects and limited data regarding occurrence. Wastewater treatment plants (WWTP) receive many ECs as components of influent waste and the removal of organic contaminants, such as ECs, occurs primarily by sorption to sludge. Therefore, it is important to develop measures of sorption behavior by ECs to sludge. This study evaluates sorption of three ECs: 3-tert-butyl-4-hydroxyanisole (BHA) a synthetic antioxidant, 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyrane (HHCB) a polycyclic musk, and chlorpyrifos a organophosphate insecticide.
Twenty-four hour laboratory-scale sorption experiments were conducted for each compound individually and then in combination, which allowed the quantification of sorption onto wastewater sludge and the affects of multiple compounds. ECs in both the liquid and solid phases were analyzed using a gas chromatograph with flame ionization detector (GC/FID).
Isotherms of individual sorption behavior followed a linear trend (R2>0.9) for individual ECs, while Kd averaged 2,689 L kg−1, 27,786 L kg−1 and 31,402 L kg−1 for BHA, chlorpyrifos and HHCB, respectively. Sorption behavior for BHA was linear during combined studies with Kd of 1,766 L kg−1 or a decrease of 34%, while HHCB and chlorpyrifos followed non-linear isotherm models. Synergistic effects were observed with spike concentrations ≥25 mg L−1 for HHCB and ≥20 mg L−1 for chlorpyrifos. Kd values ranged from 16,984–6,000,000 L kg−1 for HHCB and 19,536–3,000,000 L kg−1 for chlorpyrifos. These distribution coefficients differed substantially from previously published values, mainly because few studies used sludge as the sorption media. Results suggest that HHCB and chlorpyrifos may be contained in the sludge unlike BHA, which is more available in the aqueous phase. Future investigations should evaluate WWTP processes for degrading ECs to harmless products and releases of ECs from sludge.
- emerging contaminants
- partition coefficient
- wastewater treatment
- © IWA Publishing 2009