Kenichiro Tsukahara

Wet disk milling pretreatment without sulfuric acid for enzymatic hydrolysis of rice straw

Rice straw has recently attracted interest in Japan as a potential source of raw material for ethanol production. Wet disk milling, a continuous pretreatment to enhance the enzymatic digestibility of rice straw, was compared with conventional ball milling and hot-compressed water treatment. Pretreated rice straw was evaluated by enzymatic hydrolysis using Acremonium cellulase and characterized by X-ray diffraction and scanning electron microscopy. Glucose and xylose yields by wet disk milling, ball milling, and hot-compressed water treatment were 78.5% and 41.5%, 89.4% and 54.3%, and 70.3% and 88.6%, respectively. Wet disk milling and hot-compressed water treatment increased sugar yields without decreasing their crystallinity. The feature size of the wet disk milled rice straw was similar to that of hot-compressed water-treated rice straw. The energy consumption of wet disk milling was lower than that of other pretreatments. Thus, wet disk milling is an economical, practical pretreatment for the enzymatic hydrolysis of lignocellulosic biomass, especially herbaceous biomass such as rice straw.

Effect of ammonium addition on methanogenic community in a fluidized bed anaerobic digestion.

After immobilization of anaerobes on carbon felt in a fluidized-bed anaerobic digester at an ammonium concentration of 500 mg N/l, the results of real-time PCR analysis indicated that the cell densities of the immobilized methanogens and bacteria increased compared with those of the free-living methanogens and bacteria in the original anaerobically digested sewage sludge, respectively. The results of the clone analysis of the original sludge suggested that the major methanogens were Methanosaeta sp. and the members of the order Methanomicrobiales, and that after immobilization, these were changed to Methanobacterium and Methanosarcina sp. The results of real-time PCR analysis also showed that the ratio of the Methanosaeta sp. in the methanogenic archaea decreased from 58.2% to 0.3% after the immobilization. Methane production decreased at ammonium concentrations of greater than 6000 mg N/l. The results of real-time PCR analysis indicated that the cell density of the immobilized archaea decreased at ammonium concentrations of greater than 3000 mg N/l. On the other hand, the cell density of the immobilized bacteria did not decrease at an ammonium concentration of 6000 mg N/l, but decreased at that of 9000 mg N/l. The major methanogenic clones immobilized on the carbon felt at an ammonium concentration of 3000 or 6000 mg N/l were Methanobacterium sp. The present results indicated that methanogens were relatively more sensitive to ammonium than bacteria.

Combination of hot compressed water treatment and wet disk milling for high sugar recovery yield in enzymatic hydrolysis of rice straw.

Rice straw has attracted significant interest in Japan as a potential raw material for biorefineries. Combination of hot-compressed water treatment (HCWT) and wet disk milling (WDM) was investigated to improve the enzymatic digestibility of rice straw and enhance sugar recovery yield. Rice straw, cut to <3 mm, was autoclaved at 121, 135, and 150 °C for 60 min, and subsequently treated by wet disk milling. WDM with HCWT at 135 °C for 60 min produced maximum xylose and glucose yields of 79% and 90%, respectively, at 10 FPU/g-substrate cellulase loading. Autoclaving at 150 °C leaked a 35% arabinose effluence in the liquid phase. Hydrolysis via WDM with HCWT required a lower enzyme loading (5 FPU/g-substrate) than either pretreatment process in isolation for >70% xylose and 80% glucose yield. Economical analysis indicate that enzymes cost for ethanol production is reduced by 19-67% by WDM with HCWT.

Thermochemical Liquidization and Anaerobic Treatment of Kitchen Garbage

The pretreatment effect of thermochemical liquidization for anaerobic digestion of kitchen garbage was studied. Model kitchen garbage (dry matter: 11.3%) was thermochemically liquidized at 175°C and 4 MPa with 1 h of holding time. The liquidized garbage was separated into a solid fraction (12.2 wt%) and filtrate (82.9 wt%). The filtrate was anaerobically digested at added volatile solid (VS) concentrations of 1.8–1.9 g/l in a batch system. The biogas yield from the filtrate after 4 d of digestion was 311 ml/g-added VS and the digestion ratio was 67%. The anaerobic treatment of the filtrate indicated fast digestion compared with mechanically disrupted garbage. The diluted supernatant was continuously anaerobically digested by the upflow anaerobic sludge blanket (UASB) method. The range of digestion ratios was 74–75% at an added TOC concentration of 17.0 g/l and an added TOC amount of 1.8–2.8 mg/cm3-granule·d. The solid fraction was suggested to be easily processed to refuse derived fuel, based on its low moisture content. The energy balance of the liquidization and anaerobic digestion treatment process was initially analyzed to be better than direct incineration.

Thermochemical liquidization of anaerobically digested and dewatered sludge and anaerobic retreatment

Abstract The pretreatment effect of thermochemical liquidization for the anaerobic retreatment of anaerobically digested and dewatered sludge was studied. The digested sludge (dry matter; 15.7%) was thermochemically liquidized at 175°C and 4 MPa with a holding time of 1 h. The liquidized sludge was separated by centrifugation to produce a supernatant of 44.7% (w/w) and precipitate of 52.3%. The liquidized sludge and its supernatant were successfully anaerobically digested at the added VS concentrations of 1.6–2.2 g/l. The biogas yield from the supernatant during 8 days of incubation was 339 ml/g-added VS and the digestion ratio was 61% (w/w). The digestion of the supernatant from the liquidized sludge showed a high biogas yield and high digestion ratio. Moreover, the precipitate of the liquidized sludge could be incinerated using a much smaller amount of supplementary fuel than that of the digested sludge.

Microalgal cultivation in a solution recovered from the low-temperature catalytic gasification of the microalga

Microalgal cultivation in a solution recovered from the low-temperature catalytic gasification of the microalga itself was studied. The growth of Chlorella vulgaris in 75-300-fold diluted recovered solution containing phosphate, magnesium ions and micro-elements was comparable to that in the standard culture medium. It was suggested that C. vulgaris could use ammonium in the recovered solution as its nitrogen source and at the same time could provide a source of biomass which was recycled via gasification.

Effects of glucose addition and light on current outputs in photosynthetic electrochemical cells using Synechocystis sp. PCC6714

The effects of glucose addition and light on the current outputs in electrochemical cells using a cyanobacterium Synechocystis sp. PCC6714 were investigated under photo- and chemoheterotrophical conditions. The addition of glucose to the anode solutions of the electrochemical cells resulted in a rapid increase in the current outputs under both light and dark conditions. Although the coulombic outputs were almost the same between under light and dark conditions, the rate of glucose consumption was faster under illumination than in the dark. The total sugar content in the cells of strain PCC6714 increased with the addition of glucose and the total sugar accumulated remained intact during the discharge under illumination, while it decreased gradually in the dark. When the light was switched off after the addition of glucose, the current output markedly increased. The coulombic outputs obtained after darkening were 10 to 80 times larger than that obtained by the addition of glucose under the continuous light or dark conditions. Synechocystis sp. completely incorporated 0.14 mM and 0.42 mM glucose for 1 h and 3 h, respectively, under illumination. There was no difference in the coulombic outputs between 1 h and 12 h illumination times in the electrochemical cells with 0.14 mM glucose. When the light was switched off after 1 h illumination in the electrochemical cells with 0.42 mM glucose, the coulombic output obtained from the electrochemical cell was lower than that in the electrochemical cell with 12 h illumination. This indicates that the current output was produced with higher efficiency with glucose incorporated under illumination than that in the case of glucose incorporated after darkening. The highest coulombic yield of 54% in this experiment was obtained by darkening in the electrochemical cell with 0.14 mM glucose.

Performance of photosynthetic electrochemical cells using immobilized Anabaena variabilis M-3 in discharge/culture cycles

Abstract The performance of photosynthetic electrochemical cells using Anabaena variabilis M-3 immobilized within alginate beads was investigated during repeated discharge and culture cycles of 10-h each. The effect of the light intensity during the culture periods on the duration of the current output and the recovery of endogenous total sugar in the Anabaena cells was examined. Compared with continuous discharge operation, the duration of the current output was extenced by 10 times when the electrochemical cell was operated under 10-h discharge (dark)/culture (light) cycles with a light intensity of 100 W/m 2 during the culture periods. The conversion efficiency of light energy into electricity was about 0.2% under these conditions.

Treatment of liquid fraction separated from liquidized food waste in an upflow anaerobic sludge blanket reactor.

Thermochemical liquidization as a pretreatment for anaerobic digestion of food waste was studied using a laboratory-scale upflow anaerobic sludge blanket (UASB) reactor for a period of 82 d. Model food waste (approximately 90 wt% moisture content) was thermochemically liquidized at 175 degrees C for 1 h. The liquidized food waste was separated into a solid phase (6-10 wt%) and a liquid phase (85-89 wt%). The diluted liquid phase was continuously treated by anaerobic digestion using a UASB reactor at 35 degrees C. The volumetric loading rate was increased stepwise to 6.4-7.2 g total organic carbon (TOC)/l-reactor/d. Methane production was found to be approximately 0.35-0.61 l/g-TOC removed. The range of TOC removal efficiencies was 67-69% at an influent TOC concentration of 10.1-11.1 g/l and a volumetric loading rate of 4.8-5.3 g-TOC/l-reactor/d. This treatment process using an UASB reactor could be suitable for resource recovery from food waste.

Behavior of glucose degradation in Synechocystis sp. M-203 in bioelectrochemical fuel cells.

Glucose metabolism in Synechocystis of M-203 under heterotrophic condition was studied with the electrochemical cells. By the addition of glucose, the voltage output rapidly increased under illumination, and in the dark substantial voltage output was sustained stably for 20 h of discharge. The addition of the glucose analogue 3-O-methyl-d-glucose did not change the current output both in the light and the dark, indicating that added glucose was transported into Synechocystis cells and was consumed to produce electricity. An inhibitor, carbonyl cyanide-m-chlorophenylhydrazone was induced the increase in the current output under illumination, while 3-(3,4-dichlorophenyl)-1, 1-dimethylurea partially inhibited the current output.