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Comparison of Advanced Oxidation Pre-treatment Processes for Degradation of bisphenol A in Wastewater Sludge

D.P. MOHAPATRA¹*, S.K. BRAR¹, P. TREMBLAY², R.D. TYAGI¹, R.Y. SURAMPALLI³

¹INRS-ETE, Université du Québec, 490, Rue de la Couronne, Québec, Canada G1K 9A9

²Phytronix Technologies, 4535 boulevard Wilfrid Hamel, Quebec, Canada, G1P 2J7

³ US Environmental Protection Agency, Kansas City, USA, KS 66117

Abstract

The growing population, urbanization and modernization has led to the release of toxic organic compounds into the environment, including the endocrine disrupting compounds (EDCs). These compounds and many of their metabolites end up in the environment as a result of emission from production sites and direct disposal from households- detected in wastewater (WW) and wastewater sludge (WWS) across Canada. The biggest problem associated with these compounds is their detection (ng or pg level) mainly in media with complex matrix. Bisphenol A (BPA) has been identified as EDC by the U.S Environmental Protection Agency (EPA) and World Wide Fund for Nature (WWF). According to Environment Canada, BPA is a high priority organic compound for assessment of human health risk as it is considered to present greatest potential for human exposure (GPE) and has been classified by other agencies on the basis of reproductive toxicity.

In present study, a comparision of three pre-treatment methods, including ultrasonication (US), Fenton's oxidation (FO), ferro- sonication (FS) and partial ozonation (OZ) were assessed in terms of increase in solubilization of WWS and simultaneous degradation of BPA. The analysis of BPA in wastewater sludge was carried out by using LC-MS-MS and LDTD-MS-MS method. Higher degradation of BPA was observed in ozonation pre-treatment followed by Fenton's oxidation and ferro-sonication processes as compared to ultrasonic processes. The increased suspended solids (SS), volatile suspended solids (VSS), chemical oxygen demand (COD) and soluble organic carbon (SOC) solubilization during OZ, FO and FS pre-treatment processes as compared to US pre-treatment processes was due to acid hydrolysis and partial oxidation (hydroxyl radicals) of cells and organic matter leading to enhanced lysis or disintegration of sludge cells. The contact of efficiency of pre-treatment methods for solubilization and BPA degradation was OZ>FS>FO>US and OZ>FS>FO>US, respectively. The faster degradation of BPA during ferro-sonication pre-treatment as compared to Fenton is believed to be due to the higher efficiency for the production of OH^• radicals as well as due to the ultrasonic physical and chemical processes. In addition, the effect of rheological parameters (viscosity and particle size) and zeta potential on degradation of BPA in raw and different pre-treated sludges were also investigated. The results showed that decrease in viscosity and particle size and increase in zeta potential resulted in higher degradation of BPA. Lower viscosity and particle size increased mass transfer rate of BPA causing higher reaction rate and its partitioning, leading to degradation within the medium. As the size of the flocs decreased with increasing zeta potential, overall availability of sorbed BPA molecules to react with OH^• radicals increased resulting in higher degradation of BPA. However, the three phenomenon namely, increase in zeta potential, decrease in viscosity and particle size occurred simultaneously within the media leading to increased reaction rate and partitioning of BPA thus causing its higher removal from raw sludge.

Keywords: Bisphenol A; pre-treatment; rheology; wastewater sludge; zeta potential