Macrophyte-assisted Vermi-filtration for the on-site treatment of food-analysis laboratory wastewater: a first assessment under Sri Lankan conditions

Abstract

Research and testing laboratories generate wastewater during routine operations, which is mostly discharged into the environment without adequate treatment, leading to environmental pollution. Cost-effective vermi-filtration technology can be a promising approach for treating laboratory wastewater. This study evaluated a macrophyte-assisted vermifilter for treating wastewater from the food-analysis laboratories of the Industrial Technology Institute (ITI), Sri Lanka. Three laboratory-scale sub-surface vertical-flow columns were operated in parallel for eight weekly batches at a feeding rate of 10 mL min⁻¹ and a seven-day hydraulic retention time: a control without biota, a vermifilter inoculated with Eisenia fetida (VF), and a vermifilter additionally planted with Canna indica (VF+CW). Chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and pH were monitored; functional groups were screened by Fourier-transform infrared (FTIR) spectroscopy, and earthworm populations were tracked. Mean COD removal increased from 60.2 ± 30.3% (control) to 71.6 ± 22.9% (VF) and 72.1 ± 25.1% (VF+CW). Mean TN removal was low (8.1, 11.0, and 24.9%, respectively), and TP removal was moderate but highly variable (35.8–40.0%). One-way ANOVA indicated that differences among units were not statistically significant for any parameter (COD: F = 0.52, p = 0.60; TN: F = 1.02, p = 0.38; TP: F = 0.02, p = 0.98). Earthworm numbers rose from 100 to 275 (VF) and 300 (VF+CW) over eight weeks, and the planted unit showed reduced effluent volume, no clogging, and no odor. The biological units removed a visible oil layer, which was absent from the control effluent. The findings show that vermifiltration is a promising, robust route for reducing organic load in food-laboratory wastewater, while nutrient polishing requires process intensification.