Optimization of chitosan coagulant from dry legs of giant freshwater prawn, Macrobrachium rosenbergii in aquaculture wastewater treatment using response surface methodology (RSM)

The environmental impacts of aquaculture wastewater and biowaste from shellfish processing have become a major challenge to aquaculture expansion and sustainability. There is need to develop measures for the wastewater treatment and proper recycling of the biowaste. In this study, dry legs of giant freshwater prawn (Macrobrachium rosenbergii) were chemically processed into chitin and chitosan for use as coagulant in the coagulation/flocculation of real aquaculture wastewater. Box-Behnken design in response surface methodology (RSM) was used to establish the optimum operating conditions of chitosan dosage, pH, and settling time for removal of turbidity and colour. Statistical models were generated for the independent variables after which the model was validated. Results showed that dry legs of M. rosenbergii are mainly composed of minerals (76.36%) with low level of chitin (9.29%) and chitosan (7.02%). With 80% solubility and 91% degree of deacetylation (DDA), the smooth and none porous chitosan showed great potential of a good coagulant. This study recorded that dosage (5 mg/L), pH (5) and settling time of 11.25 min successfully removed 93.84% turbidity while 99.89% colour removal was achieved at 20 mg/L at 7.5 pH and 30 min settling time. The high level of minerals in the legs was responsible for the low chitin and chitosan yields while high turbidity and colour removals were attributed to the solubility and DDA.