Carbon and nitrogen removal by Chlorella sp. and Scenedesmus sp. suspended and immobilised in non-toxic silica gel in leather processing wastewater

ABSTRACT Microalgae have been effectively used as a nutrient removal method in wastewater treatment. However, the harvesting microalgae step is a major hurdle to the industry. In this study, the silica non-toxic sol–gel is used as a matrix to immobilise microalgae. Non-toxic silica gel matrix was synthesised by tetraethoxysilane (TEOS) derived alcohol free route. This study aims to evaluate the effect of microalgae immobilisation in non-toxic silica gel to remove tanneries wastewater pollutants. The experiments were conducted by applying immobilised Scenedesmus sp. and Chlorella sp. in three concentrations in leather processing wastewater during 72 h of cultivation. The morphology of immobilisation was evaluated by optical microscopy, SEM and Zeta Potential analysis. The rate removals of total nitrogen (TN), total organic carbon (TOC) and Inorganic Carbon (IC) in comparison to immobilised and suspended microalgae were evaluated by the influence of the immobilisation, type of microalgae and microalgae concentration. For both microalgae, immobilisation showed promise for removing these nutrients. The immobilised Chlorella sp. at the initial concentration of 5.84 ± 0.975 mg.L−1 (I-Ch2) had the highest removal by immobilised microalgae, with an uptake of 20.82% of AN, 18.44% of TN, 30.42% of TOC and 64.73% of IC.