Production of polyhydroxyalkanoates (PHAs) by Bacillus megaterium using food waste acidogenic fermentation-derived volatile fatty acids

Figures & data

Figure 1. Scheme showing the integration of VFAs production through acidogenic fermentation of food waste using membrane bioreactors with PHAs production by Bacillus megaterium ATCC 14,945 through shake flask experiments together with factors studied and analyses carried out in this work

Figure 2. Profile of carbon source concentration (a), absorbance (b), and pH (c) during cultivation of Bacillus megaterium ATCC 14,945 in medium containing glucose, acetic acid, butyric acid, iso-butyric acid, and caproic acid as single carbon sources

Table 1. Characterization of the VFAs-rich stream derived from acidogenic fermentation of food waste that was used in this study

Composition	Value (g/L)
Acetic acid	2.1–2.4
Caproic acid	1.8–2.0
Butyric acid	1.2–1.4
Iso-butyric acid	0.08–0.1
Valeric acid	0.2–0.3
Iso-valeric acid	0.1–0.2
Propionic acid	0.5–0.6

Figure 3. Profiles of VFAs concentration, absorbance, and pH during cultivation of Bacillus megaterium ATCC 14,945 in three different cultivation media: a) Minimum Salt Medium (MSM) with a mixture of synthetic VFAs; b) MSM with VFAs from acidogenic fermentation; and c) VFAs-rich stream as produced from acidogenic fermentation of food waste

Figure 4. Cell mass (a) and PHAs (b) concentrations obtained during cultivation of Bacillus megaterium in medium containing glucose, acetic acid, butyric acid, iso-butyric acid, and caproic acid as single carbon sources

Table 2. Comparison of PHAs yields on a cell mass weight obtained in this work and in previous published studies

Microorganisms	Carbon substrate and concentration (g/L)	PHA type & yields (%)	Cultivation type	Reference
Bacillus megaterium ATCC14945	Glucose, 5 g/L	PHB, 10%	Batch	This work
	Acetic acid, 5 g/L	PHB, 9%
	Butyric acid, 5 g/L	PHB, 11.2%
	Caproic acid, 1.8–2 g/L	PHB, 9.2%
	a mixture of synthetic VFAs	PHB, 10%
	a mixture of VFAs from AD, 7 g/L	PHB, 8.6%
Bacillus cereus	Glucose, 5 g/L	PHB, 13.7%	Batch	[75]
Bacillus thuringiensis	Glucose, 5 g/L	PHB, 11.3%	Batch	[76]
Bacillus cereus SPV	Glucose, 20 g/L	PHB & PHV, 38%	Batch	[61]
Bacillus megaterium DSM 90	Propionic acid, 1.5 g/L
	PHBV, 33.7%	Batch	[77]
Ralstonia eutropha	Acetic acid, 5 g/L	PHB, 29.3%	Batch	[78]
	Butyric acid, 5 g/L	PHB, 31.9%
Cupriavidus necator	Acetic acid, 15 g/L	PHB, 34%	Fed-batch	[79]
	Butyric acid, 25 g/L	PHB, 19%

Figure 5. Cell mass (a) and PHAs (b) concentrations obtained during cultivation of Bacillus megaterium ATCC 14,945 in three different medium recipes: a) Minimal Salt Medium (MSM) containing a mixture of synthetic VFAs; b) MSM with VFAs from acidogenic fermentation; and c) VFAs-rich stream as produced from acidogenic fermentation of food waste

Figure 6. Comparison of FTIR spectra obtained from the analysis of PHAs extracted from bacterial cell grown in VFAs-rich stream from acidogenic fermentation of food waste (a) and of a commercial PHB sample (b)

Table 3. DSC results of PHAs extracted from bacterial cell grown in VFAs-rich stream originated from acidogenic fermentation of food waste and that of a commercial PHB sample

Sample	Tm (^oC)	$\mathrm{\Delta }\mathit{H}$ (J/g)	Xc (%)
Extracted PHAs	133.15–145.42	18.71	12.81
Commercial PHB	148.89–161-62	74.09	50.74

Figure 7. Comparison of DSC profiles between PHAs extracted from bacterial cell grown in VFAs- rich stream from acidogenic fermentation of food waste (a) and a commercial PHB sample (b)

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