Adsorption performance of Ni(II) by KOH-modified biochar derived from different microalgae species.

[Display omitted] • Chlorella sp. biochar modified with KOH is superior candidate for Ni(II) removal. • Zero-charge point of 6.87 was obtained for the biochar pyrolyzed under 600 °C. • Microalgae species diversity for biochar preparation to adsorb Ni(II) was revealed. • Ni(II) adsorption was comprehensively optimized via response surface methodology. • 100 % Ni(II) removal was achieved with small biochar dose of 0.5 g/L. Microalgae biochar is potential adsorbents to remove heavy metals from wastewater due to abundant functional groups, high porosity and wide sources, but performance is not fully developed since it depends on microalgae species attributing to distinct morphology and biomass compositions. Here, two microalgae species Chlorella Pyrenoidosa and Scenedesmus Obliquus were used for biochar preparation via KOH-modification, biochar properties and their influences on Ni(II) adsorption were investigated. Ni(II) adsorption performances responding to biochar properties and operating conditions were upgraded via progressive optimization and response surface methodology. Together, adsorption isotherms and kinetics were analyzed to obtain significant factors for Ni(II) removal. As results, 100 % of Ni(II) removal was achieved under 100 mg/L initial Ni(II) concentration as pH was higher than the biochar zero-charge point of 6.87 with low biochar dosage (0.5 g/L), which provides an efficient approach for heavy metal removal from wastewater with microalgae biochar. [ABSTRACT FROM AUTHOR]