UV/iodide advanced reduction process and biological treatments to ofloxacin photo-degradation and mineralization: influence parameters, kinetic, degradation pathway, energy consumption and toxicology

The degradation of ofloxacin (OFL) by ultraviolet (UV) radiation in the presence of iodide was studied as an advanced reduction process (ARP), and followed resulting effluents were biodegraded for further mineralisation in the biological treatment. About 100% degradation of OFL was obtained under the selected condition (OFL: Iodide molar ratio of 2:1 and pH 9.0) after 20 min reaction time. In UV/Iodide ARP, the obtained range for reaction rate constant (kobs) and reaction rate (robs) were from 0.311 to 0.039 min−1, and from 15.55 to 7.94 mg/L.min, respectively. The calculation of the energy consumption (using kinetic model) indicated with increasing OFL concentration from 50 to 200 mg L−1, the amount of energy consumption increases from 0.905 to 7.09 kW per cubic metre of treatment (also it was observed increase from 0.91 to 6.29 kW per cubic metre of treatment using IUPAC model). Intermediate (I) products and possible photodegradation pathways of OFL in the UV/Iodide ARP effluent were analysed after 30 min using GC-MS. Investigations showed after 30 min, most of the intermediates were converted to simple linear compounds such as acrylic acid (I6: C3H4O2), formic acid (I9: CH2O2) and acrylaldehyde (I10: C3H4O), that finally mineralised to CO2, H2O, NH4+ and NH3. Modified Kirby-Bauer disc diffusion test (applied to investigation of bacterial inhibition) was reduced from 33 mm (in initial concentration of OFL without treatment) to 9 mm (after 30 min of reaction). The UV/Iodide effluent reduced the COD by 40.9% after 30 min of reaction. When the biological reactor as post-treatment was operated at a concentration of MLSS 1000 mg L−1, the COD removal efficiency reached to 65.28% (121 to 42 mg L−1) within 11 h. However, by increasing the amount of MLSS to 3000 mg L−1, the COD removal efficiency reached to 84.09% (from 176 to 28 mg L−1) and at the 5000 mg L−1 of MLSS, the COD removal efficiency was 91.52% (from 236 to 20 mg L−1). It can be concluded from this study, although, the UV/Iodide ARP was very effective in breaking down OFL molecules, but it is not cost-effective due to the high time and cost of mineralisation. Therefore, application of the biological reactors as a post-treatment method after UV/Iodide ARP, due to cost-effective, environmentally friendly and the ability to degrade the intermediates produced can be useful.