Enhanced biomethanation of kitchen waste by different pre-treatments

Five different pre-treatments were investigated to enhance the solubilisation and anaerobic biodegradability of kitchen waste (KW) in thermophilic batch and continuous tests. In the batch solubilisation tests, the highest and the lowest solubilisation efficiency were achieved with the thermo-acid and the pressure–depressure pre-treatments, respectively. However, in the batch biodegradability tests, the highest cumulative biogas production was obtained with the pressure–depressure method. In the continuous tests, the best performance in terms of an acceptable biogas production efficiency of 60% and stable in-reactor CODs and VFA concentrations corresponded to the pressure–depressure reactor, followed by freeze–thaw, acid, thermo-acid, thermo and control. The maximum OLR (5 g COD L−1 d−1) applied in the pressure–depressure and freeze–thaw reactors almost doubled the control reactor. From the overall analysis, the freeze–thaw pre-treatment was the most profitable process with a net potential profit of around 11.5 € ton−1 KW.