Removal of contaminants of emerging concern from urban wastewater in novel algal-bacterial photobioreactors

Highlights: • This work evaluated the removal of ECs in novel AX-HRAP and ANA-AX-HRAP PBRs. • Triclosan and propylparaben showed total elimination during ANA-AX-HRAP set-up. • REs > 90% were obtained for ibuprofen and salicylic acid in the ANA-AX-HRAP PBR. • Naproxen was the most recalcitrant with eliminations rates below 52% in all cases. • Biodegradation and sorption were hypothesized as main removal mechanisms. -- Abstract: This work evaluates the removal of five pharmaceuticals and personal care products, i.e., ibuprofen, naproxen, salicylic acid, triclosan and propylparaben, from urban wastewater under two novel algal-bacterial photobioreactor settings. The first configuration (phase A) consisted of an anoxic-aerobic photobioreactor operating at a hydraulic retention time (HRT) of 2 d at different concentrations of total organic carbon (TOC) (90 mg L⁻¹–200 mg L⁻¹). In the second configuration (phase B) an anaerobic step was introduced before the anoxic tank to set a photosynthetic A₂O process. In this phase, the HRT varied between 3 and 4 d and the TOC was kept constant at 200 mg L⁻¹. In addition, the impact of external aeration in the aerobic photobioreactor was assessed. The maximum removals for ibuprofen, naproxen, salicylic acid, triclosan and propylparaben (94 ± 1%, 52 ± 43%, 98 ± 2%, 100 ± 0%, 100 ± 0%, respectively) were recorded during phase B. In phase A, low TOC concentrations triggered higher ibuprofen and naproxen removals likely due to the high contribution of biological oxidation on their removal. In phase B, total or very high removal efficiencies were observed for ibuprofen, propylparaben and triclosan independently on the operating conditions. In contrast, the removal efficiency of naproxen and salicylic acid decreased when the HRT dropped from 4 to 3 d in the absence of external aeration, which suggests that biodegradation played a key role in their removal. In addition, sorption might have contributed to the elimination of triclosan and propylparaben from the wastewater.