Advanced oxidation pre-treatment of benzalkonium chlorides prior to biological treatment.
Adnan Hossain Khana, Jing Wana, Mark Sumarahb, Sheila M. Macfiec, Madhumita B. Raya,*.
aDepartment of Chemical and Biochemical Engineering, University of Western Ontario, London, ON, N6A 5B9, Canada.
bAgriculture and Agri-Food Canada, London, ON, N5V 4T3, Canada.
cDepartment of Biology, University of Western Ontario, London, ON, N6A 5B7, Canada.
Benzalkonium chlorides are a common group of antibacterial cationic surfactants that are found in wastewater effluents and biosolids. Widely used benzyl dimethyl dodecyl ammonium chloride (BDDA) and benzyl dimethyl tetradecyl ammonium chloride (BDTA) are biodegradable but their mixtures are persistent to biodegradation. The research evaluated an advanced oxidation treatment (AOT) as a pre-treatment to enhance the biodegradability of a BDDA and BDTA mixture and to reduce toxicity for further biological treatment of mixtures. Chemical oxidation using ozone and hydrogen peroxide at different pH was tested and the experimental conditions were optimized using a central composite design (CCD). Preliminary experiments showed that pH played an important role for the removal of the BDDA and BDTA mixture at initial concentrations of 50:25 mg L–1 in presence of ozone and hydrogen peroxide (Fig. 1). A synergistic effect of increased removal rate was observed by adding hydrogen peroxide to ozone, although hydrogen peroxide by itself did not degrade BDDA but partially degraded BDTA (≤ 25%) during the same treatment time. Optimization of AOT using CCD showed greater than 90% removal of the initial BDDA and BDTA mixture at pH 10 or above with 150 mg L–1 hydrogen peroxide and 0.8 mg L–1 ozone. Intermediates formed during AOT are being analyzed by HPLC-MS. To evaluate AOT as a pre-treatment prior to biological treatment, the biodegradability of the pre-treated effluent, in which 90% of the parent BDDA: BDTA mixture was removed, is being determined using the ratio of biological oxygen demand to chemical oxygen demand and a toxicity test is being performed using fresh water algae species.
Keywords: Advanced oxidation treatment; benzalkonium chloride; cationic surfactants; benzyl dimethyl dodecyl ammonium chloride; benzyl dimethyl tetradecyl ammonium chloride.
Fig.1. Percentage removal of benzalkonium chlorides over time. The AOTs were conducted at different pH, temperature (°C), O3 concentration in liquid phase (mg L–1) and H2O2 concentration in mg L–1; (a) BDDA and (b) BDTA.