Ecotoxicity tests on solid residues from microwave induced pyrolysis of different organic residues: An addendum

•The char fraction obtained from microwave pyrolysis could be added to soils.•Char from pyrolysis of sewage sludge and straw were tested.•No toxic effects were found up to 3 wt% of addition.•The char porosity seems to influence the fresh biomass yield.

Microwave-induced pyrolysis of organic wastes has been demonstrated to be a suitable technology for the production of syngas (H2 + CO). However, there is a need for developing alternatives to manage the residual streams from this process. In this short communication, the use of the solid fraction from microwave-induced pyrolysis as a soil conditioner and its ecotoxic effect on the growth of barley and cress plants have been studied. The porous structure of these chars has been found out to be one of the possible factors related to the germination rates. This alternative has resulted to be highly promising since the toxic effect on plants germination was very limited or non-existing regardless of the municipal waste char composition.