Abstract
The implementation of an efficient and sustainable management of the organic fraction of municipal solid wastes (OFMSW) is a topic of intensive discussion in EU countries. Recently, the OFMSW has been investigated as a potential substrate for the production of lactic acid (LA) through fermentation. Nevertheless, none of the reports available in the literature covers all the stages of the conversion process. The present research article is a comprehensive study which includes the upstream, fermentation and downstream for the conversion of OFMSW into LA. Several batches of OFMSW were analysed for the evaluation of sugars released and LA content before the fermentation. Fermentations were performed to study the effect of hydrolysate quality on the LA production using Bacillus coagulans A166. Purification of LA, based on electrodialysis, was carried out after pilot scale fermentation of OFMSW hydrolysates. Results showed that variations in the concentrations of sugars and LA are observed from batch to batch of OFMSW. More specifically, LA can reach high concentrations even before the substrates are hydrolysed, limiting the potential applications of the final product due to low enantiomeric purities. In general, fermentations of the hydrolysate were efficient, with conversion yields of 0.65 g g−1 without the addition of extra nutrients. Downstream is still a challenging stage of the process. A LA recovery of 55% was obtained, with the most significant losses observed during the micro- and nanofiltrations. Overall, a conversion of 10% from OFMSW substrate (dry basis) to LA was achieved.Graphic
Highlights
The implementation of an efficient and sustainable management of the organic fraction of municipal solid wastes (OFMSW) is a topic of intensive discussion in EU countries
Such variations can result in considerable changes in the composition of carbohydrates available for fermentation
As explained by Probst et al [14], the OFMSW is an ideal substrate for the proliferation of lactic acid bacteria (LAB)
Summary
The implementation of an efficient and sustainable management of the organic fraction of municipal solid wastes (OFMSW) is a topic of intensive discussion in EU countries. OFMSW are used for the production of energy by incineration or biological treatment through biogas or compost production [2, 3]. Even though these practices have significantly decreased the amount of waste sent to landfills, they fail to meet the sustainability standards of the EU, which target a complete exploitation of waste streams for the production of value-added products [1]. In order to improve microbial conversions, the complex carbohydrate fraction needs to be first broken down i.e. hydrolysed, a step which has been established as the most significant part in the biogas production process [13]
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