An experimental apparatus was constructed to perform hybrid solid anaerobic digestion batch processing of the organic fraction of municipal solid waste. The preliminary process was carried out with a high total solids concentration of about 33% w w−1 and with an initial organic load of about 340 kg VS kg−1. The fresh organic fraction to inoculum ratio used to enhance the anaerobic process start-up was 0.910 kg VS kg VS−1. The process was conducted by spreading the percolate on top of the mixture. The percolate was stored in a separate section of the apparatus with a mean hydraulic retention time of about 1 day. During the process, acetate, butyrate and propionate in the percolate reached concentrations ranging from 3000 to 11 000 mg L−1. In spite of these high concentrations, the biomethane produced from both the solid and the percolate was quite high, at about 210 NL kg VS−1. The digestate obtained at the end of the run showed rather good features for being classified as an organic fertilizer according to Italian law. However, a residual phytotoxicity level was detected by a standardized test showing a germination index of about 50%.