Substrate removal kinetics and performance assessment of a vermifilter bioreactor under organic shock load conditions

In the present study, the effect of short-term organic shock loads (675, 799, 1,084 and 1,410 mg COD/L) on the treatment performance of a pilot-scale vermifilter (VF), employing an epigeic earthworm Eisenia fetida and treating synthetic domestic wastewater is investigated. The effect of organic shock loads on the performance and stability of vermifiltration reactor was evaluated to identify its feasibility in actual field conditions. Prior to the application of each organic shock load, normal loading conditions were maintained to achieve the pseudo steady state (PSS) conditions. The results showed satisfactory endurance against imposed organic shock loads with negligible reduction in chemical oxygen demand (COD) removals and it was almost similar to PSS condition with removal efficiencies of ∼ 66, 71, 67 and 68%, respectively. The experimental COD data fit well to first-order kinetic model, with a regression value of 0.95. At the end of all shock loads, the nutritional analysis of vermicompost obtained from the top layer of VF, showed increased concentration of total nitrogen (∼31 g/Kg) and total phosphorus (29 g/Kg). Besides, an augmented earthworm biomass, ∼23.2% on weight basis and ∼22% on number basis, was observed at the end of the study.