Vol.:(0123456789) 1 3 Waste and Biomass Valorization https://doi.org/10.1007/s12649-020-01077-3 ORIGINAL PAPER Efect of Microbial Inoculation on Lipid and Phenols Removal During the Co‑composting of Olive Mill Solid Sludge with Green Waste in Bioreactor Youness Bouhia 1,2  · Karim Lyamlouli 2  · Loubna El Fels 1,3  · Zeroual Youssef 4  · Yedir Ouhdouch 1,2  · Mohamed Hafdi 1,2 Received: 27 November 2019 / Accepted: 20 April 2020 © Springer Nature B.V. 2020 Abstract In Mediterranean countries, the olive oil industry generates the most important agro-industrial wastewater, which results in the production of a highly toxic sludge following efuent decantation, thus endangering the environment. In this investigation, an optimized composting process via microbial inoculation is suggested as to alleviate the toxicity of olive mill solid sludge (OMS-Sludge) through addressing its high polyphenol and lipid content. The composting assay was carried out in a bioreac- tor using mixtures of sludge and green wastes, with or without microbial inoculation, namely: E1 (49% sludge + 49% green waste + 2% thermophilic Inoculum), and E2 (50% sludge + 50% green waste). After 4 months of composting the inoculation had afected at signifcantly (p < 0.05)pH, EC and total organic carbon degradation compared to control. Furthermore, HPLC analysis revealed that OMS-Sludge composting signifcantly diminished the polyphenol content (95% and 85% for E1 and E2, respectively), and the lipid content (90% and 81% for E1 and E2, respectively). More importantly, microbial inoculation resulted in a signifcant composting efciency, which was corroborated by a decomposition rate 65% for E1 compared to 62% for E2. In-planta assays showed that both the lipid and polyphenol contents werestrongly correlated with the sludge phytotoxicity with respect to seed germination, which was demonstrated by a substantial improvement of the germination index of Cabbage (64.44%), Turnip (86.58%) and Cress seeds (120.85%). Overall, enhancing the composting process through microbial inoculation resulted in a signifcant alleviation of the initial mixture phytotoxicity, and proved to be an efcient strategy for OMS-Sludge valorization. * Mohamed Hafdi hafdi.ucam@gmail.com 1 Laboratory of Microbial Biotechnologies, Agrosciences and Environment, Faculty of Science Semlalia, Cadi Ayyad University, 40000 Marrakesh, Morocco 2 Mohammed VI Polytechnic University (UM6P), AgroBioScience Program, Benguerir, Morocco 3 Higher Institute of Nursing Professions and Health Technics, Marrakech-Saf, Morocco 4 Situation Innovation Group - OCP Group, 24025 JorfLasfar, Morocco