Post-treatment of real municipal wastewater effluents by means of granular activated carbon (GAC) based catalytic processes: A focus on abatement of pharmaceutically active compounds.

Pharmaceutically active compounds (PhACs) widely present in urban wastewater effluents pose a threat to ecosystems in the receiving aquatic environment. In this work, efficiency of granular activated carbon (GAC) - based catalytic processes, namely catalytic wet peroxide oxidation (CWPO), peroxymonosulfate oxidation (PMS/GAC) and peroxydisulfate oxidation (PDS/GAC) at ambient temperature and pressure were studied for removal of 22 PhACs (ng L-1 level) that were present in secondary effluents of real urban wastewater. Concentrations of PhACs were measured using Ultra Performance Liquid Chromatography - Triple Quadrupole Mass Spectrometry (UPLC-QqQ-MS/MS). Catalytic experiments were conducted in discontinuous mode using up-flow fixed bed reactors with granular activated carbon (GAC) as a catalyst. The catalyst was characterized by means of N2 adsorption-desorption isotherm, mercury intrusion porosimetry (MIP), elemental analysis, X-ray fluorescence spectroscopy (WDXRF), X-ray diffraction (XRD), thermal gravimetry and differential temperature analyses coupled mass spectrometry (TGA-DTA-MS). Results indicate that the highest efficiency in terms of TOC removal was achieved during CWPO performed at optimal operational conditions (stoichiometric dose of H2O2; TOC removal ~ 82%) followed by PMS/GAC (initial PMS concentration 100 mg L-1; TOC removal ~73.7%) and PDS/GAC (initial PDS concentration 100 mg L-1; TOC removal ~ 67.9%) after 5 min of contact time. Full consumption of oxidants was observed in all cases for CWPO and PDS/GAC at contact times of 2.5 min, while for PMS/GAC it was 1.5 min. In general, for 18 out of 22 target PhACs, very high removal efficiencies (> 92%) were achieved in all tested processes (including adsorption) performed at optimal operational conditions during 5 min of contact time. However, moderate (40 - 70%) and poor (< 40%) removal efficiencies were achieved for salicylic acid, ofloxacin, norfloxacin and ciprofloxacin, which can be possibly attributed to insufficient contact time. Despite high efficiency of all studied processes for PhACs elimination from urban wastewater effluent, CWPO seems to be more promising for continuous operation.

A comparison of photolytic, photochemical and photocatalytic processes for disinfection of recirculation aquaculture systems (RAS) streams.

The development of technologically advanced recirculation aquaculture systems (RAS) implies the reuse of water in a high recirculation rate (>90%). One of the most important phases for water management in RAS involves water disinfection in order to avoid proliferation of potential pathogens and related fish diseases. Accordingly, different approaches have been assessed in this study by performing a comparison of photolytic (UV-LEDs) at different wavelengths (λ = 262, 268 and 262 + 268 nm), photochemical (UV-LEDs/H2O2, UV-LEDs/HSO5- and UV-LEDs/S2O82-) and photocatalytic (TiO2/SiO2/UV-LEDs and ZnO/SiO2/UV-LEDs) processes for the disinfection of water in RAS streams. Different laboratory tests were performed in batch scale with real RAS stream water and naturally occurring bacteria (Aeromonas hydrophyla and Citrobacter gillenii) as target microorganisms. Regarding photolytic processes, higher inactivation rates were obtained by combining λ262+268 in front of single wavelengths. Photochemical processes showed higher efficiencies by comparison with a single UV-C process, especially at 10 mg L-1 of initial oxidant dose. The inactivation kinetic rate constant was improved in the range of 15-38%, with major efficiency for UV/H2O2 âˆ¼ UV/HSO5- > UV/S2O82-. According to photocatalytic tests, higher efficiencies were obtained by improving the inactivation kinetic rate constant up to 55% in comparison with a single UV-C process. Preliminary cost estimation was conducted for all tested disinfection methods. Those results suggest the potential application of UV-LEDs as promoter of different photochemical and photocatalytic processes, which are able to enhance disinfection in particular cases, such as the aquaculture industry.

Removal of natural organic matter (NOM) from water by ion exchange - A review.

Natural organic matter (NOM) is present in underground and surface waters. The main constituents of NOM are humic substances, with a major fraction of refractory anionic macromolecules of various molecular weights. The NOM concentration in drinking water is typically 2-10 ppm. Both aromatic and aliphatic components with carboxylic and phenolic functional groups can be found in NOM, leading to negatively charged humic substances at the pH of natural water. The presence of NOM in drinking water causes difficulties in conventional water treatment processes such as coagulation. Problems also arise when applying alternative treatment techniques for NOM removal. For example, the most significant challenge in nanofiltration (NF) is membrane fouling. The ion exchange process for NOM removal is an efficient technology that is recommended for the beginning of the treatment process. This approach allows for a significant decrease in the concentration of NOM and prevents the formation of disinfection byproducts (DBPs) such as trihalomethanes (THMs). This article provides a state-of-the-art review of NOM removal from water by ion exchange.