Modelling of pollutants removal in Integrated Vermifilter (IVmF) using response surface methodology

Abstract

Mathematical models of vermifiltration are not only valuable tools for design and optimization of the processes, but could be also employed for output prediction and system control. In this work, Response Surface Methodology (RSM) technology has been applied to evaluate both individual effect of different parameters as well as their interaction effect simultaneously on system performance. A two stage integrated Vermifilter (IVmF) consisting of Eisenia fetida and Canna indica was developed with vertical flow (VF) system as first stage unit and horizontal flow (HF) system as second stage unit. Box-Behnken Design (BBD) model was implemented for optimization of BOD removal in treatment process. HLR, biodegradable organic strength and VF unit active layer depth were considered as the major affecting factors on performance of the filter. Subsurface flow mode was selected in operation as earthworm may not survive for long time in submerged condition. According to developed model, the optimal conditions (numerical optimization technique) for achieving maximum BOD removal for the designed system were at influent concentration of 1701.00 ​mg/L, HLR of 0.39 ​m 3 /m 2 /d 1 and active layer depth of 34.40 ​cm. Experimental BOD removal of 86.45% was obtained against predicted value of 87.08% at optimum condition. Above data can be used for the implementation of vermifiltration system in field scale with minimal deviation. Growth rate of Eisenia fetida was tracked which shows 20.29%–27.82% increase in earthworm population. Similarly, Canna indica number increased from initial number of 3 to final number 13–18 in different experimental conditions. • A RSM based BBD model was utilized to optimize the biodegradable organics removal. • Macrophyte Canna indica and earthworm Eisenia fetida worked symbiotically to remove pollutants. • 87.08% BOD was removed in optimized condition. • Earthworm number increased 20.29–27.82% and number of Canna indica increased 4–6 times.