Analysis of the stability of high-solids anaerobic digestion of agro-industrial waste and sewage sludge.

The pilot-scale high-solids anaerobic digestion (HS-AD) of agro-industrial wastes and sewage sludge was analysed in terms of stability by monitoring the most common parameters used to check the performance of anaerobic digesters, i.e. Volatile Fatty Acids (VFA), ammonia nitrogen, pH, alkalinity and methane production. The results reflected similar evolution for the parameters analysed, except for an experiment that presented an unsuccessful start-up. The rest of the experiments ran successfully, although the threshold values proposed in the literature for the detection of an imbalance in wet processes were exceeded, proving the versatility of HS-AD to treat different wastes. The results evidence the need for understanding the dynamics of a high-solids system so as to detect periods of imbalance and to determine inhibitory levels for different compounds formed during anaerobic decomposition. Moreover, the findings presented here could be useful in developing an experimental basis to construct new control strategies for HS-AD.