A comparative study on the inhibitory effects imposed on earthworms by brewery and rice mill wastewater

Abstract

Of late, vermifiltration (VF) technology has gained major attention from researchers as a sustainable wastewater treatment alternative in which the treatment of wastewater has been driven by earthworms (EWs). Apart from parametric effects, the composition, biodegradability/complexity, hydraulic and organic loading rates (HLR/OLR), and the concentration of organics present in wastewater exhibit inhibitory effects on EWs, declining the treatment efficiency of vermifilters (VFs), which have not been adequately explored. Hence, the present study dealt with the assessment of such inhibitory effects on the survival, growth, and reproduction of EWs using four kinds of wastewater. Results indicated that EWs sustained the flow of rice mill, real brewery, synthetic brewery, and the mixture of real brewery and domestic wastewater for 5–11, 11–21, 20–40, and 23–45 d, respectively, before reaching 50% mortality, at the HLR of 8–4 m3/m2-d. For each wastewater, the lowest HLR (4 m3/m2-d) yielded the highest growth of EWs. The mixture of real brewery and domestic wastewater provided the most favorable conditions for the reproduction of EWs, ensuring the highest number of cocoons (8–12 nos./EW) and juveniles (11–26 nos./EW) produced per EW, followed by synthetic brewery (cocoon: 3–9 nos./EW; juvenile: 5–18 nos./EW), real brewery (cocoon: 2–7 nos./EW; juvenile: 2–12 nos./EW), and rice mill wastewater (cocoon: 1–5 nos./EW; juvenile: 2–8 nos./EW), with the HLR varying inversely with the reproduction rate of EWs. Hence, the mixture of real brewery and domestic wastewater portrayed the least biological inhibition on EWs, whereas rice mill wastewater had the highest. Outcomes of the present study revealed that the VF technology is best suited for remediating the mixture of real brewery and domestic sewage, can substantially remediate synthetic brewery wastewater, and may treat real brewery and rice mill wastewater after an appropriate pretreatment. The premixing of real brewery wastewater with rapidly biodegradable and low-strength domestic sewage at a specific volumetric ratio improved the treatability of the former using the VF technology attributed to the enhanced biodegradability and reduced organic strength of the wastewater mix.