Application of (V)UV/O₃ technology for post-treatment of biologically treated wastewater: A pilot-scale study

For the first time, high energy VUV photons and generation of O₃ by (V)UV lamps were applied together for removal of active pharmaceutical ingredients (APIs) from biologically treated wastewater (BTWW) in pilot-scale. The core of the pilot container unit was a photoreactor assembly consisting of six photoreactors, each containing a low-pressure Hg lamp (UV dose of 1.2 J/cm² and 6.6 J/cm² at 185 nm and 254 nm, respectively). BTWW was irradiated (4.75 min residence time) by (V)UV light in presence of in situ photochemically generated O₃ from coolant air of the lamps. Experiments were conducted at the site of two wastewater treatment plants. Out of seven target APIs (namely carbamazepine, ciprofloxacin, clarithromycin, diclofenac, metoprolol, sitagliptin, and sulfamethoxazole), 80-100% removal was accomplished for five and 40-80% for two compounds. Two degradation products of carbamazepine were detected. Degradation products of other target compounds were not found. The applied O₃ dose was 30-45 μg O₃/mg dissolved organic carbon. Inactivation of up to log-4.8, log-4.5 and log-3.8 could be achieved for total coliform, Escherichia coli and Enterococcus faecalis, respectively. SOS Chromotest indicated no genotoxicity nor acute toxicity. Generation of neither NH₄⁺, NO₂^- nor NO₃^- was observed during post-treatment. Electric energy per order values were calculated for the first time for (V)UV/O₃ treatment in BTWW with a median value of 1.5 kWh/m³. This technology can be proposed for post-treatment of BTWWs of small settlements or livestock farms to degrade micropollutants before water discharge or for production of irrigation water. Further studies are essential in pilot-scale for other applications.