A comparison of biofilm and suspension methods in removing heavy metals (chromium) from industrial wastewater with Scenedesmus obliquus and Chlorella vulgaris
Mohsen Mohebi, Mohammad Gholami Parashkoohi, Ahmad Mohammadi
Abstract
The study investigated the factors influencing chromium absorption by the microalgae species S. obliquus and C. vulgaris using an ANOVA approach. The analysis revealed significant independent effects of contact time, temperature, pH, density, algal species, and production methods, as well as notable interactions among these factors. Under standardized conditions of pH 7, 105 min of contact time, a temperature of 25 °C, light intensity of 3500 lux, and a density of 60, S. obliquus showed the highest chromium absorption. The biofilm production method was consistently more effective than the suspension method for both species. At a pH of 5, C. vulgaris outperformed S. obliquus , achieving maximum absorption rates in both production methods. The study also found that higher temperatures facilitated increased chromium absorption, peaking at 27.5 °C for suspension and 26.5 °C for biofilm methods, with S. obliquus demonstrating superiority. Significant interactions resulted in the combination of the biofilm method and S. obliquus yielding the best absorption rates at specified conditions. Density trends indicated decreasing absorption rates for both microalgae at densities of 30 and 40, but S. obliquus later exhibited a reversal of this trend, unlike C. vulgaris . Contact time results indicated increased absorption from 60 to 115 min, but a decline afterwards, with S. obliquus again leading. The optimal conditions for chromium absorption were identified as pH 5, temperatures around 26–28 °C, with particular density levels, highlighting the importance of production method in enhancing absorption rates for both microalgae species.