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| Waste type | Waste pretreatment | Enzymatic hydrolysis | Fermentation conditions | Yield of glucose after enzymatic hydrolysis | Microorganism used in fermentation step | Production levels of lactic acid | Yield of lactic acid per glucose consumed | References |
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| Brewer’s spent grain | 1.25% (v/v) sulfuric acid solution in a 1 : 8 g : g solid : liquid ratio, at 120°C for 17 minutes;
2% (v/v) sodium hydroxide solution in a 1 : 20 g : g solid : liquid ratio, at 120°C for 90 minutes | 2.24% (v/v) cellulase (Novozymes) and 1% (v/v) β-glucosidase (Novozymes) using 8% (w/v) substrate, at 45°C and 120 rpm for 72 hours | Inoculum with 10% (v/v) of cell suspension, at 37°C and 60 ×g | 75.0 g/L | Lactobacillus acidophilus ATCC 43121 | 8.9 g/L from AAT BSG 1
12.26 g/L from AAT BSG 1 + yeast extract
17.49 g/L from AAS BSG 2
22.16 g/L from AAS BSG 2 + yeast extract | 0.48 g/g from AAT BSG 1
0.6 g/g from AAT BSG 1 + yeast extract
0.52 g/g from AAS BSG 2
0.61 g/g from AAS BSG 2 + yeast extract | This study |
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| Mango peel | — | — | Coupling of the microbial hydrolysis and fermentation of the carbohydrate substrate into a single step at 35°C under static incubation conditions | — | Consortium of indigenous microorganisms of mango peels | 17.48 g/L | — | [17] |
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| Municipal solid waste (MSW) | 2% (v/v) of H2SO4 (1 : 10 solid-to-liquid ratio) at 124°C for 15 minutes | — | Optimum conditions: initial pH 7.6, 1% v/v inoculum, and 5% (w/v) calcium carbonate buffer at 32°C | 41.3 g/L | Lactobacillus arabinosus B-787,
L. arabinosus B-788,
L. arabinosus B-813,
L. arabinosus B-531,
L. pentosus B-277,
L. pentosus B-473,
L. plantarum USDA 422, and L. xylosus B-4449 | ~17–19 g/L excepted for L. xylosus B-4449 ~6 g/L | From 0.52 g/g to 0.73 g/g | [18] |
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| Brewer’s spent grain | 1.25% (v/v) sulfuric acid solution in a 1 : 8 g : g solid : liquid ratio, at 120°C for 17 minutes;
2% (v/v) sodium hydroxide solution in a 1 : 20 g : g solid : liquid ratio, at 120°C for 90 minutes | Celluclast 1.5 L from Trichoderma reesei (Novozymes, Denmark) | Inoculated with an initial cell concentration of 1.0 g/L; statical incubation at 37°C | 50.0 g/L | Lactobacillus delbrueckii | 7.87 g/L using nonsupplemented BSG hydrolysate
~9 g/L using BSG hydrolysate supplemented with yeast extract | 0.7 g/g | [19] |
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| Corn cobs | 5, 10, and 15% (v/v) of H2SO4 autoclaved at different temperatures for different intervals of time | — | Optimum conditions: 40°C, pH 5-6 | 4.0 (% w/w) | Lactobacillus delbrueckii | 25.62 g/L | — | [20] |
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