Abstract

The active layer of a vermifilter (VF) is composed of woodchips that contain heterotrophic bacteria and worms capable of removing organic matter. However, there is no information on heterotrophic microbial kinetics related to oxygen uptake rate (OURend), specific oxygen uptake rate (SOURend), and heterotrophic biomass yield (YH) as they relate to evaluating the removal of COD (chemical oxygen demand) and BOD5 (biochemical oxygen demand) from wastewater. The goal of this study was to assess the heterotrophic activity of the active layer of a full-scale VF that treats rural wastewater. In addition, the effects of seasonality and earthworm density were determined. Heterotrophic activity was evaluated with a respirometer using active layer (wood chip) samples with earthworm densities of 1105 f 982 earthworm/m3 (Zone A) and 7221 f 1699 earthworm/m3 (Zone B), in fall-winter and spring-summer. The results show that the VF has a YH of 0.47 f 0.1 and a growth rate (mu max) of 0.05 f 0.04 d- 1. The YH value was 0.39 in fall-winter and 0.54 in spring-summer, while the mu max value was 0.07 d-1 in fall-winter and 0.02 d- 1 in spring-summer. OURend and SOURend increased 95 % more in spring-summer than in fall-winter and a 64 % more in Zone B than Zone A. This increase in heterotrophic activity corresponds to increases of 15.6 % in COD removal and 12.2 % in BOD5 removal in spring-summer. These results indicate that seasonality and earthworm density affect kinetic parameters such as OURend and SOURend. Finally, the measurement of kinetic parameters allows the COD and BOD5 removal efficiency of a VF to be estimated.