Coagulation–flocculation of aquaculture effluent using biobased flocculant: From artificial to real wastewater optimization by response surface methodology

Coagulation–flocculation is currently the best practice for aquaculture effluent treatment, and biobased compounds are emerging as coagulant/flocculants. This study aimed to characterize the bioflocculant produced from Serratia marcescens and applied it to treat artificial turbid water (kaolin substrate) and real aquaculture effluent using the combination of one variable at a time (OVAT) and response surface methodology (RSM) analyses. The bioflocculant produced by S. marcescens was characterized as anionic flocculant with isoelectric point at pH 1.7 and 13.3. At pH 7, its protein content was 1.3 μg/mL, and its total carbohydrate level was 0.53 mg/L. The bioflocculant consisted of various carboxylic acids and enzyme intermediates, indicating the presence of polysaccharides and protein. Comparison of optimized treatment conditions between OVAT and RSM showed that rapid mixing speed, slow mixing time, and sedimentation time were the most influential factors for coagulation–flocculation. The aquaculture effluent required lower rapid mixing speed (125 rpm) and shorter sedimentation time (39 min) than artificial wastewater (160 rpm and 67 min, respectively). The low performance of the bioflocculant in treating aquaculture effluent was due to the more complex characteristics of real aquaculture effluent compared with those of kaolin substrate. Environmental implications: The characterization of bioflocculant produced by Serratia marcescens in terms of its protein level, total carbohydrate content, and isoelectric point has never been reported. The obtained results may provide an insight into the potential of this compound to substitute widely used chemical flocculants with reliable performance. The findings may also be used as a basis to upscale coagulation–flocculation from being applied to artificial wastewater in the laboratory to treating real wastewater, especially with the use of biobased compounds.