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[Display omitted] • ZnCl 2 -activated biochar from sludge successfully adsorbed total NAs in raw OSPW. • Pore filling, hydrogen bonding, and π − π interactions were the adsorption mechanisms. • Biochar had selectivity for NAs with hydrophobic and higher cyclicity characteristics. • Microtox® assay indicated 66% reduction in acute toxicity after biochar treatment. • 91% reduction of bioavailability of organics was observed in OSPW treated with sludge biochar. Large volumes of oil sands process water (OSPW) containing naphthenic acids (NAs) and other contaminants are generated by oil sands operations. For the first time, pristine and zinc chloride-activated biochars from sludge from a municipal wastewater treatment plant are studied in the adsorption of NAs in real OSPW. By using activated biochar instead of pristine biochar, the adsorption capacity (q t) for total NAs (classical and oxidized NAs) increased from 2.3 to 26.6 mg/g. The increase in q t for activated biochar was related to the improvement of surface area from 7.9 to 513 m2/g, the abundance of mesopores (89% of pore volume), and the oxygen-containing surface groups. Equilibrium was reached at 2 h of contact time. Considering the thousands of structures of NAs in the OSPW, the activated biochar presented higher affinity for NAs with higher carbon and double bond equivalency numbers, therefore, NAs with more hydrophobic and higher cyclicity characteristics. Pore-filling, hydrogen bonding, and π-π interactions are the adsorption mechanisms. Thermal regeneration of spent activated biochar was studied, and in the fifth cycle of regeneration, the regenerated biochar had q t of 7.1 mg/g, which was 5 times higher than the adsorption capacity of fresh pristine biochar. Adsorption treatment of OSPW using activated biochar decreased the following parameters: metals Mg (7%), Ca (21%), Sr (27%), and Ba (60%), organic matter by means of DOC (63%) and COD (66%), acute toxicity towards V. fischeri (66%) and bioavailability of organics (91%). These findings promote circular economy as it presents an efficient adsorbent for NAs in OSPW developed from sludge, reducing the environmental impact associated with sludge disposal and allowing the efficient reclamation and reuse of OSPW. [ABSTRACT FROM AUTHOR]

[Display omitted] • BC/ZnO composites were successfully synthesized from wood wastes. • The BC/30 %ZnO composite showed enhanced photocatalytic performance than pure ZnO. • The composite presented good reusability and stability after 4 cycles of use. • First study applied BC/ZnO composite for NAs mixture photocatalytic degradation. • Over 95 % of NAs in mixture were degraded by BC/30 %ZnO after 6 h solar irradiation. Naphthenic acids (NAs) present in oil sands process water (OSPW) have brought increasing environmental concerns due to their potential risk to aquatic and mammalian species. In this study, sustainable biochar zinc oxide (BC/ZnO) composites were synthesized using wood waste with different ZnO content and applied under simulated solar light for the photocatalytic degradation of different NAs for the first time. The best experimental conditions were determined as 0.5 g/L BC/30%ZnO and 4 h of simulated solar irradiation time, achieving 93.7 % degradation of cyclohexanecarboxylic acid (CHA) following the pseudo-first order kinetics. BC, with a porous structure and roughened surface, acted as an excellent platform for ZnO particles and an electron reservoir to inhibit the recombination of photogenerated electron-hole pairs. Hydroxyl radicals (•OH) were identified to play the dominant role in CHA degradation, and the enhanced photocatalytic performance of the BC/30%ZnO composite was proved by more •OH species detected compared to synthesized ZnO. The composite showed good reusability and stability after 4 successive cycles of use, still achieving 92.9 % degradation of CHA. Moreover, this is the first study applying BC/30%ZnO composite for the simultaneous degradation of a complex mixture of eight NAs with significantly different chemical structures. The competition kinetics were observed among different NAs in the mixture, resulted in over 95 % degradation of total NAs after 6 h treatment. By applying wood waste-based BC/ZnO composite with excellent photocatalytic performance in combination with solar light as green energy source, this research highlights a promising sustainable approach for real OSPW remediation. [ABSTRACT FROM AUTHOR]

[Display omitted] • PDS and PMS were successfully activated by UVA LED light to treat real OSPW. • Over 90 % of classical NAs were removed by UVA LED/PDS (1 mM) or /PMS (2 mM) • The UVA LED/PDS (1 mM) was the most cost-effective system to treat OSPW. • Pre-existing immunotoxic and cytotoxic effects were markedly reduced in treated OSPW. • Treated OSPW could potentially be considered for reuse applications. This study investigated for the first time the synergistic effect of coupling persulfate (PDS) and peroxymonosulfate (PMS) with UVA LED light for the treatment of real oil sands process water (OSPW). The performance of the UVA LED/PDS and UVA LED/PMS processes was studied at different oxidant concentrations to remove fluorophore organic compounds and naphthenic acids (NAs), commonly considered significant contributors to the toxicity of raw OSPW. Both systems were highly efficient in eliminating fluorophore organic contaminants and classical NAs (O 2 -NAs) from the matrix; however, concentrations of 1 and 2 mM of PDS and PMS, respectively, were the most suitable conditions to achieve one order of magnitude removal of O 2 -NAs (i.e., 90 %). In addition, oxidized NAs (O 3 - and O 4 -NAs) were moderately degraded under these conditions. Considering economic factors, the UVA LED/PDS (1 mM) system proved to be more cost-effective than the UVA LED/PMS (2 mM) process and a viable alternative to other advanced treatments for OSPW remediation. Moreover, the pre-existing toxic effect of raw OSPW was markedly mitigated after treatment with UVA LED/PDS (1 mM), reducing by 80 % the ability of the matrix to induce pro-inflammatory cytokines in human leukemic monocytic and without significantly affecting the viability of the Staphylococcus epidermidis bacteria. Specifically for the microbial viability assay, the exposure period of the microorganism was exceptionally more extended than those considered in standard bioassays, reinforcing the scientific relevance of the obtained results. Finally, these results suggest a high environmental compatibility of the treated OSPW, making its reuse in further applications safe. [ABSTRACT FROM AUTHOR]

• The photochemical reactions of ferric citrate were used to treat OSPW. • NAs could be effectively degraded by ferric citrate under visible light irradiation. • Photocatalytic activity of ferric citrate was greatly affected by the initial pH of OSPW. • Hydroxyl radical was the dominant reactive species in the process. • The photochemical reactions of ferric citrate could produce both Fe2+ and H 2 O 2 in situ. An environmental-friendly treatment method based on photochemical reactions of ferricarboxylate complexes was developed for the treatment of oil sands process water (OSPW). Without using H 2 O 2 , the classical naphthenic acids (NAs), one of the organic compounds present in OSPW, can be effectively degraded by ferric citrate under visible light irradiation. Photochemical reaction activity of ferric citrate was greatly affected by the initial pH of OSPW. In acidic conditions, ferric citrate exhibited an extremely high degradation ratio of classical NAs, 98.3% (initial pH 3) and 96.8% (initial pH 5). Once initial pH exceeded 5, the degradation ratio of classical NAs in OSPW decreased quickly, and the degradation ratio of classical NAs could reach 65.7% (initial pH 7) and 42.4% (without adjusting pH, initial pH 8.9), respectively. It was found that the structure of NAs had little impact on the removal efficiency of NAs. It was also confirmed through scavenger experiments and reaction mechanism study that hydroxyl radical was the dominant reactive species in the process. The study demonstrated that ferric citrate possesses excellent visible light absorption ability and the photochemical reactions of ferric citrate can produce both Fe2+ and H 2 O 2 in situ , Fenton reagent, which non-selectively degrade NAs of OSPW. [ABSTRACT FROM AUTHOR]