Impact of Organic Loading Rate and Earthworms on Dissolved Oxygen and Vermifiltration

Abstract

In order to facilitate an affordable, sustainable, and technologically viable alternative to traditional brewery wastewater remediation technologies, vermifiltration was explored in this study. The impacts of high organic loading rates (OLRs) on removal of organics and nutrients from a vermifilter and their relationship with earthworm inoculation rates were the principal focus. The current study also investigated the role of dissolved oxygen (DO) in vermifiltration. To conduct this study, OLRs ranged 2.25–11.25 kgCOD/m3·d, while earthworm numbers varied 0–10,000 per m3. The average effluent DO was in the range 0.8–0.9 mg/L from biofilters and 1.5–2.1 mg/L from vermifilters. A chemical oxygen demand (COD) removal efficiency of 92%–96% and a NH4+-N conversion efficiency of 81%–85% were observed when OLRs ranged 2.25–3.15 kgCOD/m3·d and earthworm density (EWD) ranged 5,000–10,000·NO3−-N generation was also observed to be in parity with NH4+-N conversion from the system. The impact of DO on COD removal, nitrification, and denitrification was found to be significant. A maximum total nitrogen (TN) removal efficiency of 24% was observed at an EWD of 10,000. Unlike nitrogen removal, phosphorous removal was mostly dependent on adsorption due to dolochar and fine soil particles produced by earthworms. Maximum removal efficiencies of 61% and 44% were observed for PO43−-P and total phosphates (TP), respectively. The results obtained indicate that DO plays a crucial role in vermifiltration and that EWD and OLR play pivotal roles in maintaining DO in the effluents obtained from vermifiltration.