ECOTOXICOLOGY OF DIGESTATE ON EARTHWORM (Eisenia fetida): BEHAVIOURAL MARKERS (Avoidance and Growth)

ABSTRACT

Cattle rumen feedstock is a relatively new idea in biogas production; however residual digestate from such anaerobic digestion (AD) is increasingly used in Africa. The study aims at assessing the ecotoxicological impact of the cattle rumen digestate application (processed digestate) under laboratory conditions on earthworms from the short term and at investigating under laboratory conditions. Ecological quality of digestate, used as fertilizers for agricultural use, was assessed through an acute ecotoxicological bioassay testing the earthworm Eisenia fetida (OECD222/). No mortality occurred inside soil mixed with processed digestate. E. fetida avoided the soil surface and burrowed into the processed digestate soil in 28minutes. While E. fetida showed no avoidance towards the processed digestate products. A clear weight gain of up to 25 % was observed only E. fetida in 5.0, 10.0 and15.0%. The bacterial isolates in the processed digestates were identified to be Bacillus subtilis, Enterobacter aerogenes, Escherichia coli and Serratia marcescens. The identification of microbial isolates from the processed digestates with capacity to promote plant growth further revealed that the digestates could serve as alternative to inorganic fertilizers without any long-term detrimental effect to the soils and non-target organism like E. fetida.