[Show abstract][Hide abstract] ABSTRACT: This study investigated the effects of sugar composition and hydraulic retention time (HRT) on continuous hydrogen fermentation. Continuously-stirred tank reactors (CSTRs) were inoculated with heat-treated digester sludge and fed with 15 g/L of glucose, galactose and galactose: glucose mixture (8:2 ratio-simulating the hydrolysate composition of macroalgae) at HRTs of 6-24 h. Peak hydrogen production rate (HPR) and hydrogen yield (HY) of 4.49 L/L/d and 1.62 mol/mol glucoseadded were attained while using glucose as feedstock at HRTs of 6 and 18 h, respectively. Meanwhile, galactose provided a peak HPR and HY of 2.35 L/L/d and 1.00 mol/mol galactoseadded during the HRTs of 12 and 24 h, respectively. In case of mixed sugars (galactose 8: glucose 2) the production performances were inferior to the sole sugar conditions due to the low substrate utilization of less than 65%, which showed a maximal HPR and HY of 2.75 L/L/d and 0.48 mol/mol carbohydrateadded at the HRTs of 6 and 18 h, respectively.
Full-text · Article · Dec 2014 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: This work presents the effect of acid-pretreatment on H-2 fermentation of food waste with detailed microbial information by next generation sequencing. The pretreated food waste at pH 1.0-4.0 was cultivated under mesophilic conditions without external inoculum addition. From the food waste acid-pretreated at pH 1-3, H-2 yields in the range of 1.37-1.74 mol H-2/mol hexose(added) were achieved, attaining the highest value at pH 2. Clostridium sp. such as Clostridium acetobutylicum ATCC 824 and Clostridium perfringens occupied more than 70% of total number of sequences at pH 1-3. On the other hand, in the control (no pretreatment) and at pH 4, lactic acid bacteria such as Lactobacillus and Streptococcus were found to be the dominant genus (>90% of total number of sequences), resulting in a low H-2 yield. In addition, the effect of substrate concentration on H-2 fermentation was investigated, and the maximum H-2 productivity was estimated to be 27.2 L H-2/L/d by Andrew's model. Copyright
Full-text · Article · Oct 2014 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: Background
Biological fermentation routes can provide an environmentally friendly way of producing H2 since they use renewable biomass as feedstock and proceed under ambient temperature and pressure. In particular, photo-fermentation has superior properties in terms of achieving high H2 yield through complete degradation of substrates. However, long-term H2 production data with stable performance is limited, and this data is essential for practical applications. In the present work, continuous photo-fermentative H2 production from lactate was attempted using the purple non-sulfur bacterium, Rhodobacter sphaeroides KD131. As a gradual drop in H2 production was observed, we attempted to add ethanol (0.2% v/v) to the medium.
As continuous operation went on, H2 production was not sustained and showed a negligible H2 yield (< 0.5 mol H2/mol lactateadded) within two weeks. Electron balance analysis showed that the reason for the gradual drop in H2 production was ascribed to the increase in production of soluble microbial products (SMPs). To see the possible effect of ethanol addition, a batch test was first conducted. The presence of ethanol significantly increased the H2 yield from 1.15 to 2.20 mol H2/mol lactateadded, by suppressing the production of SMPs. The analysis of SMPs by size exclusion chromatography showed that, in the later period of fermentation, more than half of the low molecular weight SMPs (< 1 kDa) were consumed and used for H2 production when ethanol had been added, while the concentration of SMPs continuously increased in the absence of ethanol. It was found that the addition of ethanol facilitated the utilization of reducing power, resulting in an increase in the cellular levels of NAD+ and NADP+. In continuous operation, ethanol addition was effective, such that stable H2 production was attained with an H2 yield of 2.5 mol H2/mol lactateadded. Less than 15% of substrate electrons were used for SMP production, whereas 35% were used in the control.
We have found that SMPs are the key factor in photo-fermentative H2 production, and their production can be suppressed by ethanol addition. However, since external addition of ethanol to the medium represents an extra economic burden, ethanol should be prepared in a cost-effective way.
Full-text · Article · May 2014 · Biotechnology for Biofuels
[Show abstract][Hide abstract] ABSTRACT: To improve the sustainability of microalgae as a bioenergy feedstock, lipid-extracted microalgae (LEM) are often further treated by anaerobic digestion (AD). However, the residual chloroform used for extracting lipids as a solvent could inhibit this process, an aspect that has not been studied to date. In this study, the inhibitory effect of chloroform on H 2 and CH 4 production was investigated by performing batch tests. To prepare the feedstock, Chlorella vulgaris was ultrasonicated and the supernatant was discarded after centrifugation. In case of H 2 production, it was found that the H 2 yield fell to almost half that of the control (15.6 mL H 2 /g COD added) at 100 mg CHCl 3 /L. The reason for the decrease of the H 2 yield with the increase of chloroform level was due to the change of metabolites from acetate and butyrate to lactate via a non-hydrogenic reaction. In comparison with H 2 production, a much more severe inhibitory effect of chloroform on CH 4 production was observed. The inhibitor concentration (IC 30, 60, and 90) on H 2 production was 138, 319, and 622 mg CHCl 3 /L, respectively, while concentrations of 15, 37, and 86 mg CHCl 3 /L were obtained on CH 4 production. When the chloroform concentration was !25 mg/L on CH 4 production, more than 2 g COD/L of organic acids remained, resulting in a decrease of CH 4 yield. These findings indicate that the residual chloroform in LEM should be seriously considered to prevent possible microbial inhibition when designing a process for additional energy recovery from microalgae via AD. ScienceDirect journal h ome page: www.elsevier.com/loca te/he i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 9 (2 0 1 4) 1 9 2 5 6 e1 9 2 6 1
Full-text · Article · Apr 2014 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: In the present work, lactic acid (LA) production performance with granulation was investigated at various hydraulic retention times (HRTs), 8-0.5h. Glucose was used as a feedstock, and anaerobic mixed cultures were inoculated in an up-flow anaerobic sludge blanket reactor. As HRT decreased, the average diameter and hydrophobicity of the granules increased from 0.31 to 3.4mm and from 17.5% to 38.3%, respectively, suggesting the successful formation of granules. With decreasing HRT, LA productivity increased up to 16.7gLA/L-fermenter/h at HRT 0.5h. The existence of rod-shaped organisms with pores and internal channels at granule surface was observed by scanning electron microscope. Next generation sequencing revealed that Lactobacillus was the dominant microorganism, accounting for 96.7% of total sequences, comprising LA-producing granules.
Full-text · Article · Mar 2014 · Bioresource Technology
[Show abstract][Hide abstract] ABSTRACT: The release of silver (Ag) nanoparticles (NPs) into sewage streams has heightened concerns about potential adverse impacts on wastewater treatment processes. Here, we show that the rate constants of both biological nitrification and organic oxidation decreased exponentially with an increase in the Ag NP concentration, but nitrification was more severely inhibited than the organic oxidation even at low Ag NP concentrations (<1 mg Ag L(-1)) in batch experiments. The long-term exposure effects of Ag NPs on activated sludge bacteria were evaluated in sequencing batch reactors (SBRs) fed with two different substrates favoring heterotrophic and autotrophic bacteria. From a continuous operation for 50 days, it was found that heterotrophic bacteria in the organic removal process have higher tolerance to Ag NPs than do nitrifying bacteria. The effects of Ag NPs on the microbial community in both SBRs were analyzed using 16S ribosomal ribonucleic acid (rRNA) gene sequences obtained from pyrosequencing. The results showed that the level of microbial susceptibility is different for each type of microorganism and that the microbial diversity decreased dramatically after continuous exposure to Ag NPs for 50 days, resulting in a decrease of wastewater treatment efficiency.
No preview · Article · Feb 2014 · Journal of Environmental Science and Health Part A Toxic/Hazardous Substances & Environmental Engineering
[Show abstract][Hide abstract] ABSTRACT: In the present work, alkali-treated sewage sludge (SS) was used as a seeding source for H2 fermentation of food waste leachate (FWL). The role of alkaline treatment of SS was to suppress the activity of non-H2-producers in SS and also to enhance the solubility of SS. The effect of pretreatment pH and FWL:SS ratio on H2 production was crucial, by changing the pH conditions and selecting the dominant species. High pretreatment pH and high SS content resulted in high initial pH conditions. The highest H2 yield of 2.1 mol H2/mol hexoseadded was achieved at pretreatment pH 10 and a mixing ratio of FWL:SS = 3:5. At these conditions, the initial pH was 7.9, and cultivation pH was maintained within the reported optimum range of 5.5-6.5 during fermentation. It was found that pretreatment pH 9 was not strong enough to suppress the activity of non-H2-producers in SS, in particular, lactic acid bacteria (LAB). Microbial analysis results confirmed that LAB such as Lactobacillus sp. and Enterococcus sp. were the dominant species at pretreatment pH 9 while Clostridium sp., the main anaerobic H2-producers, were dominant at pretreatment pH 10.
Full-text · Article · Nov 2013 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: In the present work, we introduced a novel approach for microbial fatty acids (FA) production. Photosynthetic bacteria, Rhodobacter sphaeroides KD131, were cultivated in a continuous-flow, stirred-tank reactor (CFSTR) at various substrate (lactate) concentrations. At hydraulic retention time (HRT) 4d, cell concentration continuously increased from 0.97g dcw/L to 2.05g dcw/L as lactate concentration increased from 30mM to 60mM. At 70mM, however, cell concentration fluctuated with incomplete substrate degradation. By installing a membrane unit to CFSTR, a stable performance was observed under much higher substrate loading (lactate 100mM and HRT 1.5d). A maximum cell concentration of 16.2g dcw/L, cell productivity of 1.9g dcw/L/d, and FA productivity of 665mg FA/L/d were attained, and these values were comparable with those achieved using microalgae. The FA content of R. sphaeroides was around 35% of dry cell weight, mainly composed of vaccenic acid (C18:1, omega-7).
No preview · Article · Aug 2013 · Bioresource Technology
[Show abstract][Hide abstract] ABSTRACT: "Solubilization (SCOD/TCOD, chemical oxygen demand (COD), %)" is generally used as an indicator for the pretreatment effectiveness in anaerobic digestion (AD) of excess sludge. In the present work, ultrasonic (irradiation 5-60min) and alkaline pretreatments (pH 9-13) were applied to excess sludge individually and in combination. Biological methane potential tests were carried out using the whole part of pretreated sludge and only the soluble fraction. Although solubilization increased with pretreatment intensity increase, methane production was inconsistent with increased solubilization, due to the lower methane yield of soluble fraction. While the soluble fraction obtained under mild pretreatment condition (pH 9+ultrasonication 5min) showed 91% of methane yield, it was only 61% in case of severe pretreatment condition (pH 13+ultrasonication 60min). 25.8% of the pretreated sludge at (pH 13+ultrasonication 60min) consisted of soluble but non-biodegradable portion. These findings demonstrate that increased solubilization does not always result in enhanced AD efficiency.
No preview · Article · Jun 2013 · Bioresource Technology
[Show abstract][Hide abstract] ABSTRACT: In the present work, a continuous photo-fermentative hydrogen (H2) production from lactate was attempted at various hydraulic retention times (HRTs) (48–120 h). Electron balance was made at each operating conditions to elucidate different performances. At 120 h HRT, H2 production was negligible, while 42% and 52% of substrate electrons diverted towards cell growth and soluble microbial products (SMPs), respectively. After changing HRT to 96 h, H2 yield jumped to 2.3 mol-H2/mol-lactateadded with less SMPs production and minimal cell growth. The highest H2 production rate of 260 mL-H2/L-fermenter/d was also achieved at 96 h HRT. When HRT was further shortened to 72 and 48 h, H2 yield dropped to 1.4 and 0.2 mol-H2/mol-lactateadded, respectively. While almost all of the lactate was degraded at <72 h HRT, only 65% of the lactate was consumed at 48 h HRT. From 200th day, the feedstock was changed to lactate-rich acidified food waste, which was obtained via one-day fermentation of food waste and subsequent centrifugation. At 2 g chemical oxygen demand/L, substrate conversion efficiency reached 35%, which was slightly lower than that of feeding pure lactate. SMPs were found to be mainly consisted of low molecular weight compounds (<500 Da), and the majority of organic matters were aromatic proteins at 120 h HRT and it was shifted to humic-like region in 96 h HRT.
No preview · Article · May 2013 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: The present work reports the first ever evaluation of the biological CH4 potential (BMP) of starfish, classified as invasive species. Since starfish contain a large amount of inorganic matter, only the supernatant obtained through grinding and centrifugation was used for BMP test. By applying response surface methodology, the individual and interactive effects of three parameters, inoculum/substrate ratios, substrate concentrations, and buffer capacities on CH4 production were investigated, and the maximum CH4 yield of 334mL CH4/g COD was estimated. In addition, continuous CH4 production was attempted using a two-stage (acidogenic sequencing batch reactor+methanogenic up-flow anaerobic sludge blanket reactor (UASBr)) fermentation process. Acidification efficiency was maximized at 2days of hydraulic retention time with valerate, butyrate, and acetate as main acids, and these were converted to CH4 with showing 296mL CH4/g CODadded. Overall, the two-stage fermentation process could convert 44% of organic content in whole starfish to CH4.
No preview · Article · Feb 2013 · Bioresource Technology
[Show abstract][Hide abstract] ABSTRACT: Rhodobacter sphaeroides evolves H2 by nitrogenase under photoheterotrophic growth conditions. The maximum accumulation level of H2 increases by up to 60% when the culture medium, in which succinate and ammonium ion are the major carbon and nitrogen sources, is supplemented with ethanol at 0.5% (vol/vol). Such an effect by ethanol is not observed when ammonium ion is omitted from the medium. Ethanol is not used as a carbon source under the conditions examined, and the utilization of succinate and ammonium ion by cell is not affected by ethanol. The nitrogenase activity in the presence of ethanol, which is approximately 60% higher compared with that determined in its absence, is regulated at the level of nif transcription since the similar increase in the β-galactosidase activity of nifH-lacZ fusion was reproducibly observed under the same conditions. Interestingly, nifA transcription also increased similarly in the presence of ethanol. Neither glnB nor glnK interruptions abolished the ethanol-mediated enhancement of H2 evolution. Thus, the presence of ethanol results in the enhancement of nitrogenase expression of R. sphaeroides through the increase of NifA expression in a manner independent of GlnB and GlnK.
No preview · Article · Nov 2012 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: In this study, a novel three-stage (lactate-+photo-H(2)+CH(4)) fermentation system was developed, which converts food waste to H(2) and CH(4), with an emphasis on achieving high H(2) yield. The system begins by first fermenting food waste to lactate, rather than acetate and butyrate, using indigenous lactic acid bacteria. Lactate fermentation effluent was then centrifuged, and the supernatant was used for H(2) production by photo-fermentation, while the residue was used for CH(4) production by anaerobic digestion. Overall, via the three-stage fermentation system, 41% and 37% of the energy content in the food waste was converted to H(2) and CH(4), respectively, corresponding to the electrical energy yield of 1146MJ/ton-food waste, which is 1.4 times higher value than that of previous two-stage dark (H(2)+CH(4)) fermentation system. The H(2) yield based on hexose input was 8.35mol H(2)/mol hexose(added), the highest value ever reported from actual organic waste.
No preview · Article · Oct 2012 · Bioresource Technology
[Show abstract][Hide abstract] ABSTRACT: In this study, we investigated various cultural and operational factors to enhance electricity generation in a microbial fuel cell (MFC) using Geobacter sulfurreducens. The pure culture of G. sulfurreducens was cultivated using various substrates including acetate, malate, succinate, and butyrate, with fumarate as an electron acceptor. Cell growth was observed only in acetate-fed medium, when the cell concentrations increased 4-fold for 3 days. A high acetate concentration suppressed electricity generation. As the acetate concentration was increased from 5 to 20 mM, the power density dropped from 16 to 13 mW/m2, whereas the coulombic efficiency (CE) declined by about half. The immobilization of G. sulfurreducens on the anode considerably reduced the enrichment period from 15 to 7 days. Using argon gas to create an anaerobic condition in the anode chamber led to increased pH, and electricity generation subsequently dropped. When the plain carbon paper cathode was replaced by Pt-coated carbon paper (0.5 mg Pt/cm2), the CE increased greatly from 39% to 83%.
Full-text · Article · Oct 2012 · Journal of Microbiology and Biotechnology
[Show abstract][Hide abstract] ABSTRACT: The effect of culture conditions on photo-H2 production was investigated using the photosynthetic bacterium Rhodobacter sphaeroides KD131. When the initial cell concentrations were either below or above a threshold of 0.56 g-dcw/L, the H2 production decreased due to an imbalance between the biomass and the substrate. Malate- and succinate-fed cultures exhibited the highest substrate conversion to H2 production, whereas more than 85% of the substrate was utilized for cell growth in acetate- and butyrate-fed cultures. Compared with (NH4)2SO4, glutamate as a nitrogen source was more appropriate for the initial H2 production, but inhibited H2 evolution during extended cultivation due to released NH4+ ion. Even though the KD131 strain grew well under slightly acidic conditions, the pH value should be maintained in a neutral range in order to enhance H2 production. The highest H2 yield of 3.65 mol-H2/mol-succinate was achieved when the KD131 strain grew in the succinate–glutamate medium with an initial cell concentration of 0.56 g-dcw/L and the pH level controlled to 7.5.
Full-text · Article · Oct 2012 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: The information on continuous operation and the use of actual waste as a feedstock are essential for the practical application of photo-fermentative H2 production. For the first 200 days, continuous H2 production from lactate was attempted using purple non-sulfur (PNS) bacteria, Rhodobacter sphaeroides KD131, under an illumination of 110 W/m2. During the continuous operation, 30% of the fermenter volume was replaced by fresh feedstock once a day, and substrate concentration was gradually increased from 5 mM to 30 mM. H2 production was negligible at 5 mM, which was ascribed to the fact that the electrons contained in lactate were mostly consumed for cell growth and soluble microbial products (SMPs) production. As lactate concentration increased, H2 production gradually increased and reached a maximum at 20 mM, showing a substrate conversion efficiency (SCE) of 38%, a H2 yield of 2.3 mol H2/mol lactateadded, and a H2 production rate of 309 mL H2/L-fermenter/d. Further increases of lactate concentration resulted in a drop of H2 production (<1.0 mol H2/mol lactateadded). When the feedstock was changed to actual waste obtained from a 1-day lactate fermentation of food waste, stable H2 production was maintained, but showed a decreased SCE of 24%. It was speculated that the low performance was due to the fact that actual waste contained not only pure lactate but also other organic compounds that could not be utilized by PNS bacteria. In addition, compared to feeding with pure lactate, the electron consumption to the cell growth was higher in feeding with actual waste, which led to the lower performance.
No preview · Article · Oct 2012 · International Journal of Hydrogen Energy
[Show abstract][Hide abstract] ABSTRACT: A frequently used fermentation manner in lactic acid (LA) production, batch fermentation by pure cultures, has a limited practicability: low volumetric productivity and high energy consumption. In this study, continuous LA fermentation was performed in a completely stirred tank reactor at 12h HRT, inoculated with anaerobic digester sludge. Glucose (25 g COD/L) was used as a feedstock and temperature was increased from 35 to 60°C. LA production significantly increased from 50°C, which was negligible up to 45°C, with obvious bacterial community change. At 50 and 55°C, LA production was maximized, reaching 23 g COD/L, corresponding to 92% LA conversion efficiency. Pyrosequencing analysis showed that microbial diversity was simplified at 50-60°C, and the sequences closely related with Bacillus coagulans became predominant, followed by Lactobacillus fermentum. An LA-producing upflow ananerobic sludge blanket reactor was successfully developed, which enhanced the productivity up to 4.8 gLA/L/h by shortening HRT to 4h.
No preview · Article · May 2012 · Bioresource Technology
[Show abstract][Hide abstract] ABSTRACT: Hydrogen(H2)-producing bacterial community structures of the dark fermentation system in a batch reactor were investigated during 48 h by analyzing 16S rRNA gene sequences obtained from pyrosequencing. Organic wastes composed of food waste and sewage sludge were used as a feedstock. After heat treatment (90 °C for 20 min) of the feedstock, H2 was naturally evolved under anaerobic mesophilic conditions, showing a H2 yield of 2.26 mol H2/mol hexoseadded. The bacterial community structure of the initial inoculum (microbial community at the starting point (0 h)) combined with heat treated food waste and sewage sludge was mainly comprised of Proteobacteria and Bacteroidetes. After 6 h operation, the sequences that belong to other groups except Firmicutes decreased dramatically and were not observed at all in the latter samples. Clostridium spp., which were negligible in the inoculum, took over the main bacterial community by taking charge of H2 production. Among the phylum Firmicutes, the sequences closely related with Clostridium sordellii ATCC 9714T, Clostridium perfringens ATCC 13124T, and Clostridium butyricum ATCC 19398T became predominant in the time series within 48 h. Overall, the results showed how fast the Clostridium spp. overwhelmed the bacterial community in dark fermentative H2 production conditions, where they were at a negligible amount at the start.
No preview · Article · May 2012 · International Journal of Hydrogen Energy