Maize cob waste pre-treatments to enhance biogas production through co-anaerobic digestion with OFMSW.

In the present work, the enhancement of biogas and methane yields through anaerobic co-digestion of the pre-hydrolised Organic Fraction of Municipal Solid Wastes (hOFMSW) and Maize Cob Wastes (MCW) in a lab-scale thermophilic anaerobic reactor was tested. In order to increase its biodegradability, MCW were submitted to an initial pre-treatment screening phase as follows: (i) microwave (MW) irradiation catalysed by NaOH, (ii) MW catalysed by glycerol in water and alkaline water solutions, (iii) MW catalysed by HO with pH of 9.8 and (iv) chemical pre-treatment at room temperature catalysed by HO with 4 h reaction time. The pre-treatments cataysed by HO were performed with 2% MCW (wMCW/v alkaline water) at ratios of 0.125, 0.25, 0.5 and 1.0 (wHO/wMCW). The pre-treatment that presented the most favourable balance between sugars, lignin, cellulose and hemicellulose solubilisations, as well as low production of phenolic compound and furfural (inhibitors), was the chemical pre-treatment catalysed by HO, at room temperature, with a ratio of 0.5 wHO/wMCW (Pre1). This Pre1 was then optimised testing reaction times of 1, 2 and 3 days at a different pH (11.5) and MCW percentage (10% w/v). The optimised pre-treatment that presented the best results, considering the same criteria defined above, was the one carried out during 3 days, at pH 9.8 and 10% MCW w/v (Pre2). The anaerobic reactor was initially fed with the hOFMSW obtained from the hydrolysis tank of an industrial AD plant. The hOFMSW was than co-digested with MCW submitted to the pre-treatment Pre1. In another assay, hOFMSW was co-digested with MCW submitted pre-treatment Pre 2. The co-digestion of hOFMSW + Pre1 increased the biogas yield by 38.9% and methane yield by 29.7%, when compared to the results obtained with hOFMSW alone. The co-digestion of hOFMSW + Pre2 increased biogas yield by 46.0% and CH yield by 36.3%. In both cases, the methane content obtained in the biogas streams was above 66% v/v. These results show that pre-treatment with HO, at room temperature, is a promising low cost way to valorize MCW through co-digestion with hOFMSW.