COD removal index - A mechanistic tool for predicting organics removal performance of vermifilters

The present study was aimed at developing a mathematical COD removal index (CRI) based on the key variables of vermifiltration such as hydraulic retention time (HRT), organic concentration and earthworm density (EWD). In the maiden attempt of framing such an index, many experimental runs were conducted by varying the COD strength of the wastewater from 2.0-4.0 kg/m³, EWD and HLR were from 0 to 10,000 earthworms/m³ and 1.8-4.5 m³/m²·d, respectively. The sensitivity analysis of the developed CRI reveals that the EWD, bedding volume, concentration of organics and the flow applied to the vermifilter can immensely affect the model response. However, flow applied to the system is observed to be the most sensitive among other parameters incorporated in the model. In addition, from the sensitivity analysis, it was also revealed that the removal efficiencies were observed to increase with the increase in CRI values in the COD range of 0.2-6.0 kg/m³. In addition, the plot between the reported removals from literatures on vermifiltration of domestic wastewater and CRI values yielded an R² value of 0.76. Such a high correlation suggests that the developed CRI index can be applied for other wastewaters also. The results of this study indicate that the developed index can successfully be applied in determining and predicting organics removal from vermifiltration of wastewaters.