• Energy Research

This work reports on production of ethanol with simultaneous fixing of nitrogen (N2) using the anaerobic bacterium Zymomonas mobilis DSM 473. A batch fermentation with an initial glucose concentration of 50 g L-1, an initial pH of ∼5.5, an inoculum size of 10% by volume and a N2 feeding rate of 50 mL min-1 without mechanical agitation was found to provide the highest ethanol productivity (0.401 g L-1 h-1). Ethanol yield on glucose exceeded 97% of the theoretical maximum. The nitrogen content of the microbial biomass was 10.4% w/w at 65 h and all of it was derived by fixation of dinitrogen. Repeated-batch fermentations were investigated for ethanol production using simultaneous nitrogen fixation. A 2-cycle repeated-batch fermentation lasting 71 h gave a maximum ethanol yield on glucose of 0.475 g g-1 and an ethanol productivity of 0.675 g L-1 h-1. The yield (0.415 g g-1) and productivity (0.638 g L-1 h-1) were reduced in a 3-cycle repeated batch operation lasting 94 h. The need to fix nitrogen did not reduce the final achievable ethanol concentration, or the ethanol yield on glucose, relative to fermentations provided with fixed nitrogen, but did reduce the ethanol productivity by ∼82% because less cell mass was produced.

Two continuous stirred tank reactors (CSTRs) each fed with palm oil mill effluent (POME), operated at 37oC and 55oC, respectively, were investigated for their performance under varies organic loading rates (OLRs). The 37oC reactor operated successfully at a maximum OLR of 12.25 g[COD]/L/day and a hydraulic retention time (HRT) of 7 days. The 55oC reactor operated successfully at the higher loading rate of 17.01 g[COD]/L/day and had a HRT of 5 days. The 37oC reactor achieved a 71.10% reduction of chemical oxygen demand (COD), a biogas production rate of 3.73 L of gas/L[reactor]/day containing 71.04% methane, whereas the 55oC reactor achieved a 70.32% reduction of COD, a biogas production rate of 4.66 L of gas/L[reactor]/day containing 69.53% methane. An OLR of 9.68 g[COD]/L/day, at a HRT of 7 days, was used to study the effects of changing the temperature by 3oC increments. The reactor processes were reasonably stable during the increase from 37oC to 43oC and the decrease from 55oC to 43oC. When the temperature was increased from 37oC to 46oC, the total volatile fatty acid (TVFA) concentration and biogas production was 2,059 mg as acetic acid/L and 1.49 L of gas/L[reactor]/day at day 56, respectively. When the temperature was reduced from 55oC to 40oC, the TVFA concentration and biogas production was 2,368 mg as acetic acid/L and 2.01 L of gas/L[reactor]/day at day 102, respectively. By first reducing the OLR to 4.20 g[COD]/L/day then slowly increasing the OLR back to 9.68 g[COD]/L/day, both reactors were restored to stable conditions at 49oC and 37oC respectively. The initial 37oC reactor became fully acclimatized at 55oC with an efficiency similar to that when operated at the initial 37oC whereas the 55oC reactor also achieved stability at 37oC but with a lower efficiency

Kinetic parameters for growth and extracellular 5-aminolevulinic acid (ALA) production of Rhodopseudomonas palustris KG31 under light and dark conditions in a medium containing volatile fatty acids (VFA) as the carbon sources were estimated using a Gompertz model. The lag phase for growth and the maximum specific growth rate under microaerobic-light cultivations were 7.29-12.49 h and 0.038-0.094 h(-1), respectively, whereas under aerobic-dark cultivations, they were 2.03-14.25 h and 0.016-0.022 h(-1), respectively. The lag phase for extracellular ALA production and the maximum specific extracellular ALA production rate under microaerobic-light cultivations (15.72-24.74 h and 0.222-0.299 h(-1), respectively) were better than those obtained under aerobic-dark cultivations (24.57-44.84 h and 0.103-0.215 h(-1), respectively). The biomass and the extracellular ALA yields of 39.66-56.25 gDCW/l/mol C, and 148.47-245.75 μM/mol C, respectively, under microaerobic-light cultivations were higher than of those obtained under aerobic-dark conditions. An enhancement of extracellular ALA production under aerobic-dark conditions revealed that the ALA yield was markedly increased 8-fold (48.36 μM) by the addition of 10mM succinate, 4.5mM glycine, and 15 mM levulinic acid (LA). By controlling dissolved oxygen (DO) and pH values, a maximum extracellular ALA yield of 66.38 μM was found. The degradation rate of ALA in the culture broth was closely related to the pH value.

A sequential two-step treatment with peracetic acid (PA) and alkaline peroxide (AP) at mild temperatures (20-35°C) removed more than 98% of the lignin from oil palm empty fruit bunch (EFB) fiber. For each kilogram of EFB fiber treated, 200-250g of a solids fraction and 120-170g of a precipitate fraction were recovered after the treatment. Subsequent enzymatic hydrolysis (45°C, 72h) of the recovered solids (excluding the precipitate) resulted in a glucose yield of 629.8±0.5g per kg of the original dry EFB biomass. Enzymatic hydrolysis of untreated EFB yielded only 3.0±0.0g glucose per kg of dry EFB. Therefore, the PA-AP pretreatment enhanced glucose recovery from EFB by nearly 210-fold. The total treatment time was 93h (a 9h PA treatment at 35°C, a 12h treatment with AP (20°C, 4% NaOH), 72h of enzymatic hydrolysis).

Chlorella sp. TISTR 8990 was cultivated heterotrophically in media with various initial carbon-to-nitrogen ratios (C/N ratio) and at different agitation speeds. The production of the biomass, its total fatty acid content and the composition of the fatty acids were affected by the C/N ratio, but not by agitation speed in the range examined. The biomass production was maximized at a C/N mass ratio of 29:1. At this C/N ratio, the biomass productivity was 0.68gL(-1)d(-1), or nearly 1.6-fold the best attainable productivity in photoautotrophic growth. The biomass yield coefficient on glucose was 0.62gg(-1) during exponential growth. The total fatty acids (TFAs) in the freeze-dried biomass were maximum (459mgg(-1)) at a C/N ratio of 95:1. Lower values of the C/N ratio reduced the fatty acid content of the biomass. The maximum productivity of TFAs (186mgL(-1)d(-1)) occurred at C/N ratios of 63:1 and higher. At these conditions, the fatty acids were mostly of the polyunsaturated type. Allowing the alga to remain in the stationary phase for a prolonged period after N-depletion, reduced the level of monounsaturated fatty acids and the level of polyunsaturated fatty acids increased. Biotin supplementation of the culture medium reduced the biomass productivity relative to biotin-free control, but had no effect on the total fatty acid content of the biomass.

Abstract Thermal and acid hydrolysates of oil palm empty fruit bunch and other lignocellulosic substrates contain glucose, xylose, and acetic acid as the main components. In using such hydrolysates for photofermentive production of biohydrogen, the gas yield is highly dependent on the composition of the mixed carbon substrate. Batch photofermentation experiments were used to investigate the effect of the composition of the mixed carbon (glucose G, xylose X, and acetic acid A) on growth and hydrogen production by the bacterium Rhodobacter sphaeroides S10. Anaerobic fermentations were carried out at 35 °C under an incident light level of 14.6 W/m2. The mixed carbon composition strongly influenced hydrogen and biomass production. Depending on the composition of the mixed substrate: the cumulative hydrogen volume ranged from 0.99 to 2.33 L H2/L medium; the conversion efficiency ranged from 21% to 45%; and the biomass yield on substrate ranged from 0.28 to 0.47 g DCW/g (G + X + A). Based on the conversion efficiency, the optimal substrate for hydrogen production was a mixture of 5 mM glucose, 18 mM xylose and 7 mM acetic acid. This combination gave a cumulative hydrogen volume of 2.33 L H2/L medium. The hydrogen yield was 3.56 mol H2/mol mixed substrate and the substrate specific hydrogen production rate was 7.26 mL H2/g mixed substrate h. The conversion efficiency and the lag period of hydrogen production were 45% and 13 h, respectively.

Abstract Oil palm empty fruit bunches (EFB) are a lignocellulosic by product generated by palm oil mills. Delignified EFB fiber is a potential source of inexpensive hemicellulose, a substrate that is easily hydrolyzed to sugars for use in diverse biotechnological processes. The conditions for maximized selective removal of lignin from EFB fiber via separate treatments with alkaline peroxide and peracetic acid, were established such that the loss of hemicellulose was kept to a minimum. The amount of a reagent used in delignification, the temperature and the length of treatment, were optimized using a combination of Box–Behnken experimental design and the response surface method. Treatments with peracetic acid always left behind more hemicellulose and removed more lignin compared with the treatments involving alkaline peroxide. Under the best conditions (20 cm3 peracetic acid per g EFB, 35 °C, reaction time of 9 h), hemicellulose, cellulose and acid insoluble lignin constituted (dry weight basis) nearly 36%, 47% and ∼16%, respectively, of the treated acetone-washed extractive-free EFB fiber. Approximately 53% of the lignin was removed, but nearly all the hemicellulose was retained.

5-Aminolevulinic acid (ALA) and the biomass of photosynthetic bacteria, Rhodopseudomonas palustris KG31, have very high potential for development and exploitation as bioherbicide and biofertilizer respectively. In this work, the effects of two precursors and an inhibitor of aminolevulinic dehydratase (ALAD) added to the VFA culture medium on the production of ALA and biomass were investigated. The experimental runs were carried out according to a Box-Behnken design. The precursors were added to the medium at the beginning of cultivation, while the inhibitor was added after 24 h. Statistical analysis indicated that levulinic acid (LA) has a positive effect on ALA production while glycine has a negative effect on biomass production. In order to enhance both ALA and biomass products, the most suitable medium was VFA medium supplemented with 3.0 mM glycine and 10 mM LA, giving ALA and biomass of 182.91 microM and 3.1 gDCW/l within 54 h.

The microalgae Chlorella protothecoides UTEX 25, Chlorella sp. TISTR 8991, and Chlorella sp. TISTR 8990 were compared for use in the production of biomass and lipids under photoautotrophic conditions. Chlorella sp. TISTR 8990 was shown to be potentially suitable for lipid production at 30°C in a culture medium that contained only inorganic salts. For Chlorella sp. TISTR 8990 in optimal conditions in a stirred tank photobioreactor, the lipid productivity was 2.3 mg L(-1) h(-1) and after 14 days the biomass contained more than 30% lipids by dry weight. To attain this, the nitrogen was provided as KNO(3) at an initial concentration of 2.05 g L(-1) and chelated ferric iron was added at a concentration of 1.2 × 10(-5) mol L(-1) on the ninth day. Under the same conditions in culture tubes (36 mm outer diameter), the biomass productivity was 2.8-fold greater than in the photobioreactor (0.125 m in diameter), but the lipid productivity was only 1.2-fold higher. Thus, the average low-light level in the photobioreactor actually increased the biomass specific lipid production compared to the culture tubes. A light-limited growth model closely agreed with the experimental profiles of biomass production, nitrogen consumption, and lipid production in the photobioreactor.