Clogging index: A tool to quantify filter bed clogging in horizontal subsurface flow macrophyte-assisted vermifilter

This study aimed to develop a mathematical index for quantifying filter bed clogging in horizontal subsurface flow macrophyte-assisted vermifilter (HSSF-MAVF). The developed clogging index (CI) simulates the porosity reduction in the HSSF-MAVF bed due to the combined actions of deposition of suspended solids, biofilm generation, and plant growth. A series of experiments based on HSSF-MAVF were conducted to examine the key parameters related to clogging of the vermifilter such as hydraulic loading rates (HLR), organic strength (COD), and total suspended solid (TSS) at different operating conditions for the treatment of synthetic dairy wastewaters. The index was then validated using the data collected from the experiments. The predicted CI was observed to be highly capable of replicating the clogging phenomenon, as observed in this experimental study within the error range of 2-8%. Based on the visual observation and value of CI, filter beds can be grouped as unclogged (CI < 25), partially clogged (25 < CI < 40), and clogged (40 < CI). Clogged filter beds with higher CI resulted in a 5-15% reduction in the COD removal performance of HSSF-MAVFs. Moreover, the CI also envisages one to understand the individual contributions of biofilm growth, suspended solid deposition, and plant roots growth on the filter bed clogging during the operation of vermifilter and thus helps in deciding the proper setting of operational conditions to prolong the time of HSSF-MAVF operations within the acceptable range of bed materials clogging. PRACTITIONER POINTS: A mathematical index was developed to quantify clogging of the HSSF-MAVF. Flow is the most sensitive parameter based upon the sensitivity analysis. Dairy wastewater was used for the validation of CI.