Optimisation of chemical oxygen demand removal from animal house wastewater using central composite design

Abstract In the developing world, most animal farmhouses dispose of their wastewater without treatment and that creates conditions for the spread of diseases. To discourage this practice, there is the need to provide relatively simpler wastewater treatment options. Thus, this research work sought to optimise the chemical oxygen demand (COD) removal efficiency of a simple anaerobic digester by determining the optimum concentrations of rhamnolipid biosurfactant and potassium phosphate buffer needed to make the anaerobic digester remove COD efficiently. The central composite design was used for the optimization study. In the one factor at a time experiment, increasing the concentration of the potassium phosphate buffer from 1.07 g/l K2HPO4 + 0.53 g/l KH2PO4 to 1.37 g/l K2HPO4 + 0.83 g/l KH2PO4 increased the COD removal efficiency of the anaerobic digester from 19.3 to 24.7%. Also, increasing the concentration of rhamnolipid from 80 to 320 mg/l increased the efficiency of the digester from 24.2 to 26%. The percentage COD removal was highly improved (> 85%) in the optimisation study when both rhamnolipid and buffer were combined at high levels (+ 1). The model built from the central composite design reflected a good fit of the data obtained with R 2 of 82.5% and a p value of 0.000. This study therefore demonstrated that a simple anaerobic digester can be used to remove COD in wastewater by optimising the concentrations of rhamnolipid and potassium phosphate buffers in the treatment system.