Green coagulants recovering Scenedesmus obliquus: An optimization study

The recovery of microalgae by means of coagulation-flocculation is efficient, simple and low operating costs. The addition of coagulants makes it possible to destabilize the microalgae surface loads and recover their biomass. Chemical coagulants can contaminate the environment and negatively affect human health. Thus, the exploration of natural coagulants, such as Moringa oleifera and Guazuma ulmifolia, are innovative. Thus, this study aimed to evaluate the efficiency of biomass separation from the microalgae Scenedesmus obliquuos by means of coagulation-flocculation. M. oleifera and G. ulmifolia were used in order to optimize the variables dose, pH and settling time, through a central composite rotational design, which presented recovery efficiencies above 80.0% and 60.0%, respectively. In relation to M. oleifera, optimum regions were obtained for biomass recovery at both pH 4.0 with a dose of 40.0 mg L−1 and pH 9.0 with a dose of 80.0 mg L−1, both in 30 min of settling times. For G. ulmifolia, an optimum dose of 30.0 mg L−1 at pH 4.0 with a 3 min settling time demonstrated that this new coagulant for microalgae recovery has potential for application. Thus, these natural coagulants are promising and can be used in coagulation-flocculation to recover biomass from Scenedesmus obliquuos and, thus, minimize the use of synthetic or metallic products. •Coagulation and biomass separation from Scenedesmus obliquuos were studied.•Dose, pH and settling time were optimized using natural coagulants.•Recovery efficiencies above 80% (M. oleifera) and 60% (G. ulmifolia) were reached.•Optimum regions was found to promote greater recovery.