Ecotoxicological assessment of residues from different biogas production plants used as fertilizer for soil

Abstract

Residues from biogas production (RBP) are a relatively new materials, which may be an interesting resource for the improvement of soil fertility. Nevertheless, in spite of the potential benefits from the agricultural utilization of RBP, there is a need of comprehensive estimation of their toxicity. This information is needed to exclude potential negative environmental impacts arising from the use of RBP. Samples of RBP obtained from six biogas production plants with varied biogas production methods were analysed. The samples with and without separation on solid and liquid phases were investigated. The physicochemical properties of the RBP, heavy metals content (Cr, Cu, Ni, Cd, Pb i Zn) and toxicity on bacteria (Vibrio fischeri, MARA test - 11 different strains), collembolans (Folsomia candida) and two plant species (Lepidium sativum and Sinapis alba) was investigated. Toxicity of RBP was examined using Phytotoxkit F (root growth inhibition), collembolan test (mortality, inhibition of reproduction), Microtox® (inhibition of the luminescence of V. fischeri) and MARA test (growth of microorganisms). An especially negative effect on the tested organisms whereas was noted for the liquid phase after separation. In many cases, RBP without separation also showed unfavourable effects on the tested organisms. Liquid phase after separation and non-separated materials caused inhibition of root growth of L. sativum and S. alba at the level of 17.42-100% and 30.5-100%, respectively, as well as the inhibition of reproduction of F. candida with the range from 68.89 to 100%. In most cases, no ecotoxicological effect was observed for solid phase after separation for tested organisms. The solid phase after separation presented the most favorable properties between all investigated RBP. Therefore, it can be a potential material for the improvement of soil properties and for later use in agriculture.

Keywords: Ecotoxicity; Fertilizer; Heavy metals; Liquid phase; Non-separated; Residues from biogas production; Solid phase.