We will present the progress of the LIFE MERLIN project which entails sludge & waste resource recovery (and circular economy!) and energy optimisation by implementing co-digestion with liquid trade waste and indigenous sludge pre-treatment. This is being implemented at scale on 2 sites (Murcia and Alicante) where co-digestion has been running for several years. Through this innovation project we are taking it one step further to enhance digester volume usage, but also building robustness and tightened control over the process through a smart control system. Our presentation will include: - Process to seek out and evaluate potential substrates and selection method - Process design : how to dose and where depending on pre-existing works - Operation: monitoring parameters, control, substrate traceability and management - Lookahead: replicability enablers and barriers identified