Effects of volatile fatty acids in biohydrogen effluent on biohythane production from palm oil mill effluent under thermophilic condition

Background: Biohydrogen effluent contains a high concentration of volatile fatty acid (VFA) mainly as butyric, acetic, lactic and propionic acids. The presence of various VFAs (mixture VFAs) and their cooperative effects on two-stage biohythane production need to be further studied. The effect of VFA concentrations in biohydrogen effluent of palm oil mill effluent (POME) on methane yield in methane stage of biohythane production was investigated. Results: The methane yield obtained in low VFA loading (0.9 and 1.8 g/L) was 15­20% times greater than that of high VFA loading (3.6 and 4.7 g/L). Butyric acid at high concentrations (8 g/L) has the individual significantly negative effect the methane production process (P b 0.05). Lactic, acetic and butyric acid mixed with propionic acid at a concentration higher than 0.5 g/L has an interaction significantly negative effect on the methanogenesis process (P b 0.05). Inhibition condition had a negative effect on both bacteria and archaea with inhibited on Geobacillus sp., Thermoanaerobacterium thermosaccharolyticum, Methanoculleus thermophilus and Methanothermobacter delfuvii resulting in low methane yield. Conclusion: Preventing the high concentration of butyric acid, and propionic acid in the hydrogenic effluent could enhance methane production in two-stage anaerobic digestion for biohythane production.

Application of palm pressed fiber as a carrier for ethanol production by Candida shehatae TISTR5843

Palm pressed fiber (PPF) is a clean and renewable lignocellulosic material. The PPF and delignified PPF (DPPF) were used as a carrier for immobilization of Candida shehatae TISTR5843 in bioethanol production. PPF was pre-treated by milling to obtain small particles, whereas DPPF was the delignification of PPF using NaClO2. C. shehatae TISTR5843 was grown in modified yeast extract- malt (YM) medium at 30 +/- 2ºC on an orbital shaker at 150 rpm for batch and repeated batch fermentation. In the batch system, immobilized cells on a small size, less than 0.5 mm, of DPPF (sDPPF) gave the maximum ethanol production of 11.5 g L-1 at 24 hrs cultivation period. The ethanol concentration and ethanol yield of sDPPF were 6.2 percent and 6.8 percent higher (ethanol production 11.5 g L-1, ethanol yield 0.47 g g-1) than those of free cells (ethanol production 10.8 g L-1, ethanol yield 0.44 g g-1) after 36 hrs of cultivation. In contrast, the small size of PPF (sPPF) was selected as a carrier in repeated batch fermentation for cost effectiveness. The ethanol productivity of immobilized yeast cells in repeated batch fermentations was 45.2-51.6 percent greater than that obtained from batch fermentations. The immobilized cells on sPPF improved the ethanol production and could be reused 4 times with retaining the activity of 93 percent. In conclusion, PPF is a potential carrier in the immobilization system. The pre-treatment of PPF increases the surface area that enhances cell adsorption and ethanol production by C. shehatae TISTR5843.

Enhance 1, 3-propanediol production from crude glycerol in batch and fed-batch fermentation with two-phase pH-controlled strategy

The batch fermentation of 1,3-propanediol (1,3-PD) by Klebsiella pneumoniae SU6 at different crude glycerol concentration (40-100 g l-1), pH (6.5-7.5) and temperature (31-40ºC) combined with two-phase pH-controlled strategy was investigated. Effect of feeding rate (0.10-0.15 L h-1) was studied in fed-batch fermentation. In batch fermentation, the optimal condition was 60 g l-1 crude glycerol, pH control at 6.5 and cultivation temperature at 37ºC. The maximum 1,3-PD of 20 g l-1, the yield of 0.34 g 1,3-PD g-1 glycerol consumed and the productivity of 1.25 g l-1 h-1 were achieved at 16 hrs cultivation. The by-products were acetic acid and succinic acid at 2.7 and 1.1 g l-1, respectively. Two-phase pH-controlled strategy gave better results (24.95 g l-1 1,3-PD and 1.78 g l-1 h-1 productivity) than constant pH-controlled strategy (20 g l-1 and 1.25 g l-1 h-1, respectively) at 16 hrs incubation. In fed-batch fermentation, the maximum 1,3-PD of 45.35 g l-1 was achieved at constant feeding rate of 0.1 L h-1. The yield and productivity were 0.44 g g-1 and 1.94 g l-1 h-1, respectively. The fed-batch fermentation with constant feeding at 0.1 L h-1 with two-phase pH-controlled strategy gave 2.2 folds higher 1,3 PD concentration than the batch fermentation with two-phase pH-controlled strategy. This demonstrated the great impact of combination of pH control and feeding strategies in fed-batch fermentation on enhancing 1,3-propanediol production.

Effect of temperature and initial pH on biohydrogen production from palm oil mill effluent: long-term evaluation and microbial community analysis

Anaerobic sludge from palm oil mill effluent (POME) treatment plant was used as a source of inocula for the conversion of POME into hydrogen. Optimization of temperature and initial pH for biohydrogen production from POME was investigated by response surface methodology. Temperature of 60ºC and initial pHof 5.5 was optimized for anaerobic microflora which gave a maximum hydrogen production of 4820 ml H2/l-POME corresponding to hydrogen yield of 243 ml H2/g-sugar. Total sugar consumption and chemical oxygen demand (COD) removal efficiency were 98.7 percent and 46 percent respectively. Long-term hydrogen production in continuous reactor at HRT of 2 days, 1 day and 12 hrs were 4850 +/- 90, 4660 +/- 99 and 2590 +/- 120 ml H2/l-POME, respectively. Phylogenetic analysis of the mixed culture revealed that members involved hydrogen producers in both batch and continuous reactors were phylogenetically related to the Thermoanaerobacterium thermosaccharolyticum. Batch reactor showed more diversity of microorganisms than continuous reactor. Microbial community structure of batch reactor was comprised of T. thermosaccharolyticum, T. bryantii, Thermoanaerobacterium sp., Clostridium thermopalmarium and Clostridium NS5-4, while continuous reactor was comprised of T. thermosaccharolyticum, T. bryantii and Thermoanaerobacterium sp. POME is good substrate for biohydrogen production under thermophilic condition with Thermoanaerobacterium species play an important role in hydrogen fermentation.

Nutrient optimization for production of polyhydroxybutyrate from halotolerant photosynthetic bacteria cultivated under aerobic-dark condition

Three halotolerant bacterial strains; Rhodobacter sphaeroides ES16 (the wild type) and the two mutant strains of R. sphaeroides ES16, namely N20 and U7, were cultivated in glutamate-malate (GM) medium and screened for production of polyhydroxybutyrate (PHB). The mutant strains N20 and U7 were found to accumulate PHB (53.9 and 42.0 percent of DCW, respectively) 3.6 and 2.8 times higher than the wild type strain (19.5 percent of DCW), respectively. R. sphaeroides N20 were selected for studies on the effects of nutrient and environmental conditions on PHB accumulation. The optimal condition was 4 g/l acetate, 0.02 g/l (NH4)2SO4, C/N ratio of 6:1, 1.0 g/l K2HPO4, 1.0 g/l KH2PO4 and 3 percent NaCl with initial pH at 7.0. Under this optimal condition, the maximum PHB accumulation increased from 53.9 percent to 88 percent of DCW and 9.11 ± 0.08 g/l biomass, 8.02 +/- 0.10 g/l PHB concentration were achieved after 60 hrs cultivation at 37ºC. These results are the highest values ever obtained from photosynthetic bacteria reported so far.

Application of statistical experimental methods to optimize medium for exopolymer production by newly isolated Halobacterium sp. SM5

The study investigated on medium optimization for production of exopolymer by a newly isolated bacterium, Halobacterium sp. SM5, using the mixture design and response surface method. The mixture experiment was designed by setting five parameters at the lowest and highest of concentrations: pseudo components design containing 0.15-0.25 glucose, 0.15-0.25 yeast extract, 0.35-0.45 MgSO4·7H2O, 0.1-0.2 vitamin casamino acid and 0.02-0.06 KCl. The results of the mixture design revealed that the effect of nutrients or elements on the exopolymer produced by the strain SM5 were in the order of MgSO4·7H2O > yeast extract > vitamin casamino acid > KCl > glucose, respectively. The suitable medium recipe for enhancement the exopolymer production was 7.43 g/l glucose, 12.38 g/l yeast extract, 17.33 g/l MgSO4·7H2O, 9.9 g/l vitamin casamino acid and 2.48 g/l KCl. The exopolymer to be produced by the strain SM5 was 2.25 g/l, which was higher than that obtained in the original medium (1.3 times). The yield of exopolymer was 2.13 g/l to be obtained in medium containing 7.43 g/l glucose, 11.37 g/l yeast extract, 22.28 g/l MgSO4·7H2O, 7.44 g/l vitamin casamino acid and 0.99 g/l KCl which was predicted by response surface methodology. However, under an experiment, the yield of exopolymer was 2.08 + - 0.0020 g/l.