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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]