Abstract

Development of UVC advanced oxidation photolysis combined with membrane electro- bioreactor for simultaneous removal for emerging contaminants and reduction of by-products

The continuous discharge of emerging contaminants (ECs) to the aquatic ecosystem generate concerns due to their unpredictable risks to human and environment. The presence of ECs in source water attributed to the conventional wastewater treatment facilities which are not fundamentally designed to completely eliminate these micropollutants at low concentrations.
The aim of this research was to enhance the wastewater treatment to the level of its potential reuse as a source of water. The investigations were conducted at lab and pilot scale in 8 phases and several stages. Initially, the removal of selected ECs was optimized. Subsequently, the by-product formation and their identification were conducted. Then, the study focused on the by-product removal. In subsequent phases, the optimal technological parameters were verified in natural conditions, at the pilot scale in AOP (advance oxidation process) and AO-MEBR (membrane electro-bioreactor) facilities. Such approach permitted to study the removal of sulfamethoxazole (SMX), 17- alpha ethynyl estradiol (EE2), caffeine (CAF) and paracetamol (PCM) from various aqueous solutions (DI water, river water, effluent after wastewater treatment, and wastewater). A developed model investigated the effect of technological parameters on pharmaceuticals’ removal efficiency and on by-product abatement.
The results showed superior removal efficiency (99%) by both UV/H2O2 AOP and UV/O3 AOP of SMX, PCM, CAF and EE2 in comparison to sole UVC photolysis (30-40%). UV/O3 AOP demonstrated an elevated rate and removal by 10-15% higher than ozonation alone. The target ECs such as SMX, PCM were removed by more than 80% in effluent and more than 90% in river water during 60 minutes. The differences in the ECs and their byproducts removal from various aqueous matrices were discussed from the matrix properties perspectives, particularly non-target constituents (EfOM, NOM and sacavengers) present at different amounts in target matrices. The influence of operational parametrs (oxidant and UV doses, exposure time, pH) was defined, where particular usefulness of Surface Response Methodology was underlined. Overall, the SMX and by-products’ abatement (99.99%) in different matrices by AO-MEBR hybrid system was evident.
Four major SMX by-products (BP-99, BP-270, BP-288, BP-172) identified by LC-MS-MS, revealed longer lifetime and stability even after parent SMX ion removal. By applying optimal technological parameters, i.e. pH, oxidant dose and aeration rate, the by-products amounts were successfully controlled. Degradation mechanisms, reaction pathway and evolution of by-products during treatment in various aqueous solutions were conducted. Particular attention was paid on the effect of OH scavenging, the role of non-target constituencies, operation parameters, as well as aeration and superoxide radicals. Furthermore, the toxicity was decreased and energy consumption for target pollutant removal was minimized (20-25%).
The AO-MEBR system not merely improved the quality of effluent with respect to refractory organic pollutants, but also likely promoted by-products and toxicity mitigation as well as saving energy leading to improved potential of water recovery from sewage.