Abstract
Source-sorted organic portion of municipal solid waste (bio-waste) can be fermented to lactic acid, a platform chemical widely used in the production of biodegradable polymers, green solvents and chemicals. In the present study, fermentation of bio-waste using lactic acid producing bacterium (LAB) Lactobacillus delbrueckii was investigated. Results showed that adding 10% (v/v) of L. delbrueckii as LAB inoculum along with pH adjustment to 6.2 had the highest lactic acid yield (0.65 g/g total sugars). Nevertheless, pH adjustment without bio-augmentation could also result in relatively high yield of lactic acid (0.57 g/g total sugars). Furthermore, enzymatic hydrolysis was applied to boost the lactic acid production slightly increasing the yield to 0.72 g/g total sugars. Thus, fermentative production of lactic acid can be achieved without the addition of enzymes to reduce production costs. Overall, the results indicate that bio-waste could be a suitable substrate for the production of lactic acid.
Highlights
Lactic acid (LA) or 2-hydroxypropionic acid is the simplest hydroxycarboxylic acid and perhaps the most widely occurring in nature
The microbial analysis of bio-waste was not performed in the current study, it is well-known that Lactobacilli are present in households and fresh organic residues (Mayrhofer et al, 2006; Partanen et al, 2010)
It was previously identified that Lactobacillus plantarum, Lactobacillus brevis, and their closest relatives Lactobacillus mudanjiangensis, Lactobacillus yonginensis, Lactobacillus paucivorans, Lactobacillus malefermentans, and Lactobacillus mixtipabuli are among the most dominant bacteria in food wastes (Probst et al, 2013)
Summary
Lactic acid (LA) or 2-hydroxypropionic acid is the simplest hydroxycarboxylic acid and perhaps the most widely occurring in nature. Due to the presence of two reactive functional groups –one hydroxyl (–OH) and one carboxyl (– COOH)—lactic acid can undergo a variety of chemical conversions to produce e.g., acrylic acid (via dehydration), 1, 2-propanediol (via hydrogenation), acetaldehyde (via decarboxylation), 2, 3pentanedione (via condensation), and poly lactic acid (PLA). LA can be produced via chemical or microbial fermentation routes. LA of high optical purity (e.g., over 98–99% of L-LA) is required for the production of PLA. The fermentative route offers several advantages over the chemical synthesis such as simple operation, utilization of low-cost renewable feedstocks, mild pressure and temperature conditions and reduced risk of contamination, low energy consumption, and better environmental performance (Alves de Oliveira et al, 2018; Singhvi et al, 2018)
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