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UBC Theses and Dissertations

Fate of conventional pollutants and persistent pharmaceuticals during single-stage and sequential sludge digestion processes Ahmad, Muneer


The consumption of pharmaceuticals is rapidly increasing each year. Ingested pharmaceuticals are excreted in urine or feces, hence they end up in wastewater. Wastewater treatment plants (WWTPs) are not designed to remove pharmaceuticals and therefore act as a main pathway for pharmaceuticals to enter the environment. Due to the incomplete elimination of pharmaceuticals in WWTPs, many of the most resistant pharmaceuticals accumulate in wastewater sludge. The objective of this research was to study the fate of six pharmaceuticals: azithromycin (AZI), bezafibrate (BZF), carbamazepine (CBZ), diclofenac (DCF), mefenamic acid (MFA), ibuprofen (IBP) and one ibuprofen metabolite 1-hydroxy ibuprofen (1-OH IBP) in single-stage and sequential sludge digestion. The selected pharmaceuticals are refractory and have endocrine disrupting potential (except AZI), while the endocrine disrupting potential of 1-OH IBP is not yet known. A multi-residual analytical method was developed for the determination of selected pharmaceuticals using ultra-performance liquid chromatograph tandem mass spectrometer (UPLC-MS/MS). A comparative study of the selected pharmaceuticals was carried out at thermophilic (TH) temperatures in single-stage conventional anaerobic (AN) and sequential anaerobic/aerobic/anoxic (AN/AERO/ANOX) sludge digestion. Sequential AN/AERO/ANOX digestion showed an advantage in treating pharmaceuticals by either removing them or by decreasing their accumulation compared to single-stage digestion. While CBZ, MFA and DCF showed an accumulation trend in both single-stage as well as sequential digestion systems, the rate of accumulation for MFA was significantly lower (91%) in sequential digestion compared to single-stage digestion (998%). In comparison to single-stage digestion, IBP and 1-OH IBP demonstrated 50% removal and a 34% accumulation in sequential digestion, respectively. Azithromycin showed 27% removal in single-stage and 33 to 35% removal in the sequential digestion systems. Moreover, the use of sequential AN/AERO/ANOX digestion demonstrated secondary benefits over single-stage digestion in conventional digester performance parameters as well. These benefits included reduced ammonia generation (44.5%), improved solids removal (4.2%), reduced corrosive and odor-causing sulfur compounds in the headspace of the digester, and enhanced digestate dewaterability (20%). Overall, the removal efficiencies of most of the pharmaceuticals as well as conventional parameters were improved by increasing the duration of the AERO phase in the second stage AERO/ANOX digester.

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