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1.
In this study, the optimal fermentation type and the operating conditions of anaerobic process in continuous-flow acidogenic reactors was investigated for the maximization of bio-hydrogen production using mixed cultures. Butyric acid type fermentation occurred at pH>6, propionic acid type fermentation occurred at pH about 5.5 with E(h) (redox potential) >-278mV, and ethanol-type fermentation occurred at pH<4.5. The representative strains of these fermentations were Clostridium sp., Propionibacterium sp. and Bacteriodes sp., respectively. Ethanol fermentation was optimal type by comparing the operating stabilities and hydrogen production capacities between the fermentation types, which remained stable when the organic loading rate (OLR) reached the highest OLR at 86.1kgCOD/m(3)d. The maximum hydrogen production reached up to 14.99L/d.  相似文献   

2.
A pilot scale experiment was performed for a year to develop a two-phase anaerobic process for piggery wastewater treatment (COD: 6,000 mg/L, BOD: 4,000 mg/L, SS: 500 gm/L, pH 8.4, alkalinity 6,000 mg/L). The acidogenic reactor had a total volume of 3 m3, and the methanogenic reactor, an, anaerobic up-flow sludge filter, combining a filter and a sludge bed, was also of total volume 3 m3 (1.5 m3 of upper packing material). Temperatures of the acidogenic and methanogenic reactors kept at 20°C and 35°C., respectively. When the pH of the acidogenic reactor was controlled at 6.0–7.0 with HCl, the COD removal efficiency increased from 50 to 80% over a period of six months, and as a result, the COD of the final effluent fell in the range of 1,000–1,500 mg/L. BOD removal efficiency over the same period was above 90%, and 300 to 400 mg/L was maintained in the final effluent. The average SS in the final effluent was 270 mg/L. The methane production was 0.32 m3 CH4/kg CODremoved and methane content of the methanogenic reactor was high value at 80–90%., When the pH of the acidogenic reactor was not controlled over the final two months, the pH reached 8.2 and acid conversion decreased compared with that of pH controlled, while COD removal was similar to the pH controlled operation. Without pH control, the methane content in the gas from methanogenic reactor improved to 90%, compared to 80% with pH control.  相似文献   

3.
Summary A bench scale continuously stirred reactor was used to study the acidogenic phase of the anaerobic fermentation of stillage. The residence time of the effluent in the reactor ranged from 15.7 to 8.2 hours, pH was around 5.0 and temperature was maintained at 35°C. The results indicate that the residence time had no appreciable effect on the production or composition of the organic acids. The main acid products found in the reactor effluent were acetic, propionic and butiric acids.  相似文献   

4.
Production of PHA from starchy wastewater via organic acids   总被引:8,自引:0,他引:8  
Polyhydroxyalkanoate (PHA) was produced from a starchy wastewater in a two-step process of microbial acidogenesis and acid polymerization. The starchy organic waste was first digested in a thermophilic upflow anaerobic sludge blanket (UASB) reactor to form acetic (60-80%), propionic (10-30%) and butyric (5-40%) acids. The total volatile fatty acids reached 4000 mg l(-1) at a chemical oxygen demand (COD) loading rate of 25-35 g l(-1) day(-1). A carbon balance indicates that up to 43% of the organic carbon in the starchy waste went to the organic acids and the rest to biogas, volatile suspended solids and residual sludge accumulated in the reactor. The acid composition profile was affected by COD loading rate: a medium rate around 9 g l(-1) day(-1) gave a high propionic acid content (29% wt) and a high rate around 26 g l(-1) day(-1) led to a high butyric acid content (34% wt). The acids in the effluent solution after microfiltration were utilized and polymerized into PHA by bacterium Alcaligenes eutrophus in a second reactor. Fifty grams of PHA was produced from 100 g total organic carbon (TOC) utilized, a yield of 28% based on TOC, which is comparable with 55 g PHA per 100 g TOC of pure butyric and propionic acids used. PHA formation from individual acids was further investigated in a semi-batch reactor with three acid feeding rates. With a limited nitrogen source (80-100 mg NH(3) per liter), the active biomass of A. eutrophus, not including the accumulated PHA in cells, was maintained at a constant level (8-9 g l(-1)) while PHA content in the cell mass increased continuously in 45 h; 48% PHA with butyric acid and 53% PHA with propionic acid, respectively. Polyhydroxybutyrate was formed from butyric acid and poly(hydroxybutyrate-hydroxyvalerate) formed from propionic acid with 38% hydroxyvalerate.  相似文献   

5.
Zhao QB  Mu Y  Wang Y  Liu XW  Dong F  Yu HQ 《Bioresource technology》2008,99(17):8344-8347
The response of an upflow acidogenic granule-based reactor to the substrate shift from sucrose to lactose was investigated in this study. Experimental results show that it took 60h for the reactor to completely degrade the new substrate. Hydrogen production performance, in terms of H(2) partial pressure, H(2) production rate and H(2) yield, was affected. Acetate, propionate, butyrate, valerate, caporate, ethanol and propanol were present in the reactor effluent, and their distribution changed significantly after the substrate shift. As the substrate was changed, the caproate- and ethanol-type fermentation was weakened, while the propionate-type fermentation was strengthened. Throughout the experiment, the butyrate-type fermentation played an important role. The H(2) yield had a close correlation with both propionate and B/A (butyrate/acetate) in this substrate shift process.  相似文献   

6.
A three-stage process was developed to produce polyhydroxyalkanoates (PHAs) from sugar cane molasses. The process includes (1) molasses acidogenic fermentation, (2) selection of PHA-accumulating cultures, (3) PHA batch accumulation using the enriched sludge and fermented molasses. In the fermentation step, the effect of pH (5–7) on the organic acids profile and productivity was evaluated. At higher pH, acetic and propionic acids were the main products, while lower pH favoured the production of butyric and valeric acids. PHA accumulation using fermented molasses was evaluated with two cultures selected either with acetate or fermented molasses. The effect of organic acids distribution on polymer composition and yield was evaluated with the acetate selected culture. Storage yields varied from 0.37 to 0.50 Cmmol HA/Cmmol VFA. A direct relationship between the type of organic acids used and the polymers composition was observed. Low ammonia concentration (0.1 Nmmol/l) in the fermented molasses stimulated PHA storage (0.62 Cmmol HA/Cmmol VFA). In addition, strategies of reactor operation to select a PHA-accumulating culture on fermented molasses were developed. The combination of low organic loading with high ammonia concentration selected a culture with a stable storage capacity and with a storage yield (0.59 Cmmol HA/Cmmol VFA) similar to that of the acetate-selected culture.  相似文献   

7.
A continuous stirred-tank reactor was used as an anaerobic sludge system and the hydrogen production capabilities of three typical fermentations, in terms of specific hydrogen production rates, were investigated under the same hydraulic retention times (8 h) and influent chemical oxygen demand (5000 mg/L) at 35 °C. The reactor was continuously fed with diluted molasses, while the pH and oxidation reduction potential in the reactor were regulated to control the type of fermentation. The specific hydrogen production rate of the anaerobic sludge reached 2.96 mol/kg mixed liquid volatile suspended solid (MLVSS)/day, (mol•kg MLVSS− 1 d− 1), in ethanol-type fermentation, while 0.57 mol·kg MLVSS− 1 d− 1 in butyric acid-type fermentation, and 0.022 mol·kgMLVSS− 1 d− 1 in propionic acid-type fermentation. The hydrogen production capability of ethanol-type fermentation was 4.11 times greater than that of butyric acid-type fermentation and 148 times that of propionic acid-type fermentation.  相似文献   

8.
The influence of substrate loading rate on fermentative hydrogen (H2) production was studied in biofilm configured sequencing batch reactor using chemical wastewater as substrate. Reactor was operated with selectively enriched anaerobic mixed microflora at different organic loading rates (OLRs; 6.3, 7.1 and 7.9kg COD/m3 day) after adjusting the feed to a pH of 6.0 (acidophilic) to provide suitable environment for acidogenic bacterial function. Variation in H2 production rate was observed with change in OLR [specific hydrogen yield - 13.44molH2/kgCODRday (6.3kgCOD/m3day), 8.23molH2/kgCODRday (7.1kgCOD/m3 day) and 6.064molH2/kgCODR day (7.9kgCOD/m3 day)]. H2 yield showed reasonably good correlation with pH drop [6.3kgCOD/m3 day (R2 - 0.9796), 7.1kgCOD/m3 day (R2 - 0.9973), 7.9kgCOD/m3 day (R2 - 0.9908)]. Increase in OLR showed marked reduction in COD removal efficiency [22.6% - 6.3kgCOD/m3 day; 19.8% - 7.1kgCOD/m3 day and 17.2% - 7.9kgCOD/m3 day].  相似文献   

9.
Two-phase anaerobic digestion of cheese whey was investigated in a system consisting of a stirred acidogenic reactor followed by a stirred methanogenic reactor, the latter being coupled to a membrane filtration system to enable removal of soluble effluent whilst retaining solids. The acidogenic reactor was operated at a hydraulic retention time (HRT) of one day, giving maximum acidification of 52.25% with up to 5 g/l volatile fatty acids, of which 63.7% was acetic acid and 24.7% was propionic acid. The methanogenic reactor received an organic load up to 19.78 g COD/ld, corresponding to a HRT of 4 days, at which 79% CODs and 83% BOD(5) removal efficiencies were obtained. Average removals of COD, BOD(5) and TSS in the two-phase anaerobic digestion process were 98.5%, 99% and 100%, respectively. The daily biogas production exceeded 10 times reactor volume and biogas methane content was greater than 70%.  相似文献   

10.
Two fixed-bed loop reactors were used to evaluate singleand separated-phase anaerobic treatments of a high strength waste-water from ethanol fermentation. The one-phase system consisted of an anaerobic fixed-bed loop reactor containing both acidogenic as well as methanogenic populations allowing a complete conversion of the carbon source into gaseous end products and biomass.The two-phase system consisted of a second fixed-bed loop reactor operated as a methanogenic unit, which was proceeded by a CSTR for acidification, both connected in series allowing sequential acidogenesis and methanogenesis of the organic components. The reactors were operated under steady state and variable process conditions. By gradually increasing the feed supply in both systems, maximum turnover of COD was determined.The separated-phase system consistently gave a better quality effluent with lower suspended solids and total COD. Maximum loading rates and COD elimination of the methanogenic phase of the two-phase system was over two times higher than that of the one-phase system. Process stability was also higher.On overloading the methane reactor of the two phase system accumulation of different fatty acids within the reactor was observed. Hydrogen concentration in the biogas can be used as a reliable indicator for system overloadings. At least, continuous online monitoring of hydrogen in the methanogenic reactor gas should provide a convenient alternative to other analyses for process control.  相似文献   

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