1 23 Waste and Biomass Valorization ISSN 1877-2641 Waste Biomass Valor DOI 10.1007/s12649-017-9916-y Effect of the Addition of Biochar and Coffee Grounds on the Biological Properties and Ecotoxicity of Composts Michał Kopeć, Agnieszka Baran, Monika Mierzwa-Hersztek, Krzysztof Gondek & Maria Jolanta Chmiel