Resumen de Hidrólisis enzimática de la fracción orgánica de los residuos sólidos urbanos: valorización del sólido agotado para la producción de biopesticidas mediante fermentación en estado sólido
Recent European legislation requires the separate collection and the proper management of the organic fraction of municipal solid waste (OFMSW). In the framework of the EU project SCALIBUR (Horizon 2020, grant agreement No 817788), this thesis evaluates the valorization of the OFMSW in a biorefinery-like scenario based on the use of enzymatic hydrolysis to obtain building chemicals that can be further used in fermentative processes. In particular, this work focuses on the use of solid-state fermentation (SSF) as a technology for the production of biopesticides from the solid fraction obtained after an enzymatic hydrolysis of the OFMSW to obtain low molecular weight reducing sugars.
First, the enzymatic hydrolysis was studied using a high-quality OFMSW (low content of impurities). The process was optimized for key operational parameters using a commercial enzymatic cocktail and compared with a tailor-made cocktail from the SCALIBUR project.
Then, the SSF process for the production of Bacillus thuringiensis (Bt) biopesticides from the obtained solid enzymatic hydrolysate was developed at a laboratory scale (0.5 L). Different approaches to control pH, which was identified as a key parameter for the growth of Bt, were tested. The use of urban waste materials as cosubstrates appeared as an efficient and simple strategy to maintain pH near neutrality. 1.6 L scale bioreactors were used to evaluate the effects of non-sterile cosubstrates on process temperature. Despite the higher temperatures reached, the cosubstrate mixtures were more robust in terms of pH stability and steady growth of Bt than the solid hydrolysate. A prototype reactor (22 L) was used to validate the strategy for two cosubstrates: anaerobically digested sewage sludge and anaerobically digested OFMSW. At this scale, the final production of Bt spores, which are associated with biopesticide activity, was slightly reduced but the process remained competitive in comparison to previously published results. Moreover, the strategy was evaluated for the enzymatic hydrolysate of the SCALIBUR project at a 100 L scale although difficulties related to heat accumulation and microbial competition appeared.
Finally, preliminary mass balance and economic evaluation were performed to evaluate the viability of the proposed biorefinery scheme. Despite the high-value bioproducts produced, enzyme cost was a limiting factor. Therefore, alternative biorefinery configurations to reduce this cost are discussed, such as the production of enzymatic cocktails from organic waste.
This thesis presents a novel approach for the valorization of the OFMSW beyond composting and anaerobic digestion, to have a wider number of technological alternatives to reach the sustainability principle of securing resources for future generations.
