pH-control modes in a 5-L stirred-tank bioreactor for cell biomass and exopolysaccharide production by Tremella fuciformis spore

The effect of pH-control modes on cell growth and exopolysaccharide production by Tremella fuciformis was evaluated in a 5-L bioreactor. The results show that the maximal dry cell weight (DCW) and exopolysaccharide production were 23.57 and 4.48 g L⁻¹ in pH-stat fermentation, where the maximal specific growth rate (μ_max) and specific production rate of exopolysaccharide (P_P/X) were 1.03 and 0.24 d⁻¹, respectively; under pH-shift cultivation, the maximal DCW and exopolysaccharide production were 30.57 and 3.90 g L⁻¹, where the μ_max and P_P/X were 1.21 and 0.06 d⁻¹. Unlike batch fermentation, maximal DCW and exopolysaccharide production merely reached 15.04 and 2.0 g L⁻¹, where the μ_max and P_P/X were 0.86 and 0.05 d⁻¹, respectively. These results suggest that a pH-stat strategy is a more efficient way of performing the fermentation process to increase exopolysaccharide production. Furthermore, this research has also proved that the three-stage pH-control mode is effective for cell growth.     

Integrated hydrogen production process from cellulose by combining dark fermentation, microbial fuel cells, and a microbial electrolysis cell

Hydrogen gas production from cellulose was investigated using an integrated hydrogen production process consisting of a dark fermentation reactor and microbial fuel cells (MFCs) as power sources for a microbial electrolysis cell (MEC). Two MFCs (each 25 mL) connected in series to an MEC (72 mL) produced a maximum of 0.43 V using fermentation effluent as a feed, achieving a hydrogen production rate from the MEC of 0.48 m³ H₂/m³/d (based on the MEC volume), and a yield of 33.2 mmol H₂/g COD removed in the MEC. The overall hydrogen production for the integrated system (fermentation, MFC and MEC) was increased by 41% compared with fermentation alone to 14.3 mmol H₂/g cellulose, with a total hydrogen production rate of 0.24 m³ H₂/m³/d and an overall energy recovery efficiency of 23% (based on cellulose removed) without the need for any external electrical energy input.     

A kinetic evaluation of anaerobic treatment of swine wastewater at two temperatures in a temperate climate zone

A static granular bed reactor (SGBR) was used to treat swine wastewater at 24 and 16 °C. At 24 °C, the organic loading rate (OLR) was 0.7-5.4 kg COD/m³ day and the average chemical oxygen demand (COD) removal efficiency was 88.5%, respectively. Meanwhile, at 16 °C, the OLR was 1.6-4.0 kg COD/m³ day and the average COD removal efficiency was 68.0%, respectively. The SGBR acted as a bioreactor as well as a biofilter. After backwashing, the recovery of COD removal was not a function of an OLR but recovery time, while that of TSS removal was not a function of either recovery time or the OLR. The maximum substrate utilization rate (k_max) ratio was 1.89 between 24 and 16 °C, and the half velocity constant (K_s) ratio was 1.22, and the maximum specific growth rate (μ_max) ratio was 4.71. In addition, the temperature-activity coefficient in this study was determined to be 1.09.     

Potential for methane production from anaerobic co-digestion of swine manure with winery wastewater

This work examines the methane production potential for the anaerobic co-digestion of swine manure (SM) with winery wastewater (WW). Batch and semi-continuous experiments were carried out under mesophilic conditions. Batch experiments revealed that the highest specific methane yield was 348 mL CH₄ g⁻¹ COD added, obtained at 85.4% of WW and 0.7 g COD g⁻¹ VS. Specific methane yield from SM alone was 27 mL CH₄ g⁻¹ COD added d⁻¹. Furthermore, specific methane yields were 49, 87 and 107 mL CH₄ g⁻¹ COD added d⁻¹ for the reactors co-digesting mixtures with 10% WW, 25% WW and 40% WW, respectively. Co-digestion with 40% WW improved the removal efficiencies up to 52% (TCOD), 132% (SCOD) and 61% (VSS) compared to SM alone. These results suggest that methane can be produced very efficiently by the co-digestion of swine manure with winery wastewater.     

Performance and spatial community succession of an anaerobic baffled reactor treating acetone-butanol-ethanol fermentation wastewater

An anaerobic baffled reactor with four compartments (C1-C4) was successfully used for treatment of acetone-butanol-ethanol fermentation wastewater and methane production. The chemical oxygen demand (COD) removal efficiency was 88.2% with a CH₄ yield of 0.25 L/(g COD_removed) when organic loading rate (OLR) was 5.4 kg COD m⁻³ d⁻¹. C1 played the most important role in solvents (acetone, butanol and ethanol) and COD removal. Community structure of C2 was similar to that in C1 at stage 3 with higher OLR, but was similar to those in C3 and C4 at stages 1-2 with lower OLR. This community variation in C2 was consistent with its increased role in COD and solvent removal at stage 3. During community succession from C1 to C4 at stage 3, abundance of Firmicutes (especially OTUs ABRB07 and ABRB10) and Methanoculleus decreased, while Bacteroidetes and Methanocorpusculum became dominant. Thus, ABRB07 coupled with Methanoculleus and/or acetogen (ABRB10) may be key species for solvents degradation.     

Green and economical production of propionic acid by Propionibacterium freudenreichii CCTCC M207015 in plant fibrous-bed bioreactor

Propionic acid production by Propionibacterium freudenreichii from molasses and waste propionibacterium cells was studied in plant fibrous-bed bioreactor (PFB). With non-treated molasses as carbon source, 12.69 ± 0.40 g l^-1 of propionic acid was attained at 120 h in free-cell fermentation, whereas the PFB fermentation yielded 41.22 ± 2.06 g l^-1 at 120 h and faster cells growth was observed. In order to optimize the fermentation outcomes, fed-batch fermentation was performed with hydrolyzed molasses in PFB, giving 91.89 ± 4.59 g l^-1 of propionic acid at 254 h. Further studies were carried out using hydrolyzed waste propionibacterium cells as substitute nitrogen source, resulting in a propionic acid concentration of 79.81 ± 3.99 g l^-1 at 302 h. The present study suggests that the low-cost molasses and waste propionibacterium cells can be utilized for the green and economical production of propionic acid by P. freudenreichii.     

Fermentative hydrogen production from fresh leachate in batch and continuous bioreactors

This research for the first time investigated hydrogen production from the fresh leachate originated from municipal solid wastes. We found that fermentation of the leachate generated H₂ and was very much enhanced in the presence of extra phosphate in the batch reactor. The continuous expanded granular sludge bed (EGSB) reactor started to generate H₂ at day 20 and continued to 176 days with 120 mg/l of extra phosphate present. The highest chemical oxygen demand (COD) removal efficiency (66.9%) was achieved at liquid up-flow velocity of 3.7 m/h and hydraulic retention time of 12 h. Under proposed optimal operation conditions, the mean H₂ production rate reached up to 2155 ml/(l day). We also found that over 80% liquid metabolites were acetic acid and ethanol, suggesting the ethanol-type fermentation was dominant in the bioreactor. These findings indicate that the fresh leachate can be used as the source for continuous hydrogen production.     

Acidogenic fermentation of vegetable based market waste to harness biohydrogen with simultaneous stabilization

Vegetable based market waste was evaluated as a fermentable substrate for hydrogen (H₂) production with simultaneous stabilization by dark-fermentation process using selectively enriched acidogenic mixed consortia under acidophilic microenvironment. Experiments were performed at different substrate/organic loading conditions in concurrence with two types of feed compositions (with and without pulp). Study depicted the feasibility of H₂ production from vegetable waste stabilization process. H₂ production was found to be dependent on the concentration of the substrate and composition. Higher H₂ production and substrate degradation were observed in experiments performed without pulp (23.96 mmol/day (30.0 kg COD/m³); 13.96 mol/kg COD_R (4.8 kg COD/m³)) than with pulp (22.46 mmol/day (32.0 kg COD/m³); 12.24 mol/kg COD_R (4.4 kg COD/m³)). Generation of higher concentrations of acetic acid and butyric acid was observed in experiments performed without pulp. Data enveloping analysis (DEA) was employed to study the combined process efficiency of system by integrating H₂ production and substrate degradation.     

Experimental studies and mathematical modeling of an up-flow biofilm reactor treating mustard oil rich wastewater

Bioremediation of lipid-rich model wastewater was investigated in a packed bed biofilm reactor (anaerobic filter). A detailed study was conducted about the influence of fatty acid concentration on biomethanation of the high-fat liquid effluent of edible oil refineries. The biochemical methane potential (BMP) of the liquid waste was reported and maximum cumulative methane production at the exit of the reactor is estimated to be 785 ml CH₄ (STP)/(g VSS added). The effects of hydraulic retention time (HRT), organic loading rate (OLR) and bed porosity on the cold gas efficiency or energy efficiency of the bioconversion process were also investigated. Results revealed that the maximum cold gas efficiency of the process is 42% when the total organic load is 2.1 g COD/l at HRT of 3.33 days. Classical substrate uninhibited Monod model is used to generate the differential system equations which can predict the reactor behavior satisfactorily.     

Treatment of poultry slaughterhouse wastewater in hybrid upflow anaerobic sludge blanket reactor packed with pleated poly vinyl chloride rings

In this study, the performance of 5.4 L hybrid upflow anaerobic sludge blanket (HUASB) reactor for treating poultry slaughterhouse wastewater under mesophilic conditions (29-35 °C), was investigated. After starting-up, the reactor was loaded up to an OLR of 19 kg COD/m³ d and achieved varied TCOD and SCOD removal efficiencies of 70-86% and 80-92%, respectively. The biogas was varied between 1.1 and 5.2 m³/m³ d with the maximum methane content of 72%. The maximum methane yield was 0.32 m³/kg COD_removed at an OLR of 9.27 kg COD/m³ d. Black matured granules of size between 2.5 and 5 mm were observed at the end of 225 d operation. RTD study showed the flow behavior was in mixed regime at the end of performance study. Step wise polynomial regression analysis was fitted well. Methanobacterium and Methanosaeta bacteria were dominant at the end of start-up whereas Methanosarcina, Cocci and rods were predominant at the end of performance studies.     

Biohydrogen and methane production by co-digestion of cassava stillage and excess sludge under thermophilic condition

Thermophilic anaerobic hydrogen and methane production by co-digestion of cassava stillage (CS) and excess sludge (ES) was investigated in this study. The improved hydrogen and subsequent methane production were observed by co-digestion of CS with certain amount of ES in batch experiments. Compared with one phase anaerobic digestion, two phase anaerobic digestion offered an attractive alternative with more abundant biogas production and energy yield, e.g., the total energy yield in two phase obtained at VS_CS/VS_ES of 3:1 was 25% higher than the value of one phase. Results from continuous experiments further demonstrated that VS_CS/VS_ES of 3:1 was optimal for hydrogen production with the highest hydrogen yield of 74 mL/g total VS added, the balanced nutrient condition with C/N ratio of 1.5 g carbohydrate-COD/g protein-COD or 11.9 g C/g N might be the main reason for such enhancement. VS_CS/VS_ES of 3:1 was also optimal for continuous methane production considering the higher methane yield of 350 mL/g total VS added and the lower propionate concentration in the effluent.     

Butyric acid fermentation in a fibrous bed bioreactor with immobilized Clostridium tyrobutyricum from cane molasses

Butyrate fermentation by immobilized Clostridium tyrobutyricum was successfully carried out in a fibrous bed bioreactor using cane molasses. Batch fermentations were conducted to investigate the influence of pH on the metabolism of the strain, and the results showed that the fermentation gave a highest butyrate production of 26.2 g l⁻¹ with yield of 0.47 g g⁻¹ and reactor productivity up to 4.13 g l⁻¹ h⁻¹ at pH 6.0. When repeated-batch fermentation was carried out, long-term operation with high butyrate yield, volumetric productivity was achieved. Several cane molasses pretreatment techniques were investigated, and it was found that sulfuric acid treatment gave better results regarding butyrate concentration (34.6 ± 0.8 g l⁻¹), yield (0.58 ± 0.01 g g⁻¹), and sugar utilization (90.8 ± 0.9%). Also, fed-batch fermentation from cane molasses pretreated with sulfuric acid was performed to further increase the concentration of butyrate up to 55.2 g l⁻¹.     

The role of phase separation and feed cycle length in leach beds coupled to methanogenic reactors for digestion of a solid substrate (Part 1): Optimisation of reactors' performance

A two-phase system composed by a leach bed and a methanogenic reactor was modified for the first time to improve volumetric substrate degradation and methane yields from a complex substrate (maize; Zeamays). The system, which was operated for consecutive feed cycles of different durations for 120 days, was highly flexible and its performance improved by altering operational conditions. Daily substrate degradation was higher the shorter the feed cycle, reaching 8.5 g TS_destroyed d⁻¹ (7-day feed cycle) but the overall substrate degradation was higher by up to 55% when longer feed cycles (14 and 28 days) were applied. The same occurred with volumetric methane yields, reaching 0.839 m³ (m³)⁻¹ d⁻¹. The system performed better than others on specific methane yields, reaching 0.434 m³ kg⁻¹ TS_added, in the 14-day and 28-day systems. The UASB and AF designs performed similarly as second stage reactors on methane yields, SCOD and VFA removal efficiencies.     

3-Phenyllactic acid production by substrate feeding and pH-control in fed-batch fermentation of Lactobacillus sp. SK007

3-Phenyllactic acid (PLA), which is produced by some strains of lactic acid bacteria (LAB), is a known antimicrobial agent with a broad spectrum. Batch and fed-batch fermentation by the strain Lactobacillus sp. SK007 for PLA production have been reported. With batch fermentation without pH-control, PLA production yield was 2.42 g L⁻¹. When fed-batch fermentation by Lactobacillus sp. SK007 was conducted in 3 L initial volume with pH-control at 6.0 and intermittent feeding, which was developed after fermentation for 12 h and every 2 h with 120 mL 100 g L⁻¹ PPA phenylpyruvic acid (PPA) and 50 mL 500 g L⁻¹ glucose each time, PLA production yield reached 17.38 g L⁻¹. The final conversion ratio of PPA to PLA was 51.1%, and the PLA production rate was 0.241 g L⁻¹ h⁻¹. This indicated that PPA was the ideal substrate for PLA fermentation production, and fed-batch fermentation with intermittent PPA feeding and pH-control was an effective approach to improve PLA production yield.     

Using cheese whey for hydrogen and methane generation in a two-stage continuous process with alternative pH controlling approaches

This study focuses on the exploitation of cheese whey as a source for hydrogen and methane, in a two-stage continuous process. Mesophilic fermentative hydrogen production from undiluted cheese whey was investigated at a hydraulic retention time (HRT) of 24 h. Alkalinity addition (NaHCO₃) or an automatic pH controller were used, to maintain the pH culture at a constant value of 5.2. The hydrogen production rate was 2.9 ± 0.2 L/Lreactor/d, while the yield of hydrogen produced was approximately 0.78 ± 0.05 mol H₂/mol glucose consumed, with alkalinity addition, while the respective values when using pH control were 1.9 ± 0.1 L/Lreactor/d and 0.61 ± 0.04 mol H₂/mol glucose consumed. The corresponding yields of hydrogen produced were 2.9 L of H₂/L cheese whey and 1.9 L of H₂/L cheese whey, respectively. The effluent from the hydrogenogenic reactor was further digested to biogas in a continuous mesophilic anaerobic bioreactor. The anaerobic digester was operated at an HRT of 20d and produced approximately 1 L CH₄/d, corresponding to a yield of 6.7 L CH₄/L of influent. The chemical oxygen demand (COD) elimination reached 95.3% demonstrating that cheese whey could be efficiently used for hydrogen and methane production, in a two-stage process.     

Kinetic behaviour of waste tyre rubber as microorganism support in an anaerobic digester treating cane molasses distillery slops

The kinetics of anaerobic digestion of cane molasses distillery slops was investigated using a continuous-flow bioreactor which contained waste tyre rubber as support, to which the microorganisms became immobilized. Hydraulic retention times (HRT) ranging from 1 to 10 days were investigated at an average influent chemical oxygen demand (COD) concentration of 47.7?g/l. The maximum substrate utilization rate, k, and half saturation coefficient, K _L, were determined to be 1.82?kg COD_removed/kg VSS day and 0.33?kg COD/kg VSS day. The yield coefficient, Y, and sludge decay rate coefficient, K _d, were also determined to be 0.06?kg VSS/kg COD_removed and 0.05?day^-1, respectively. Methane production was maximum (6.75?l/l day) at a 2 day HRT corresponding to a biomass loading rate of 2.578?kg COD/kg VSS day. Biogas yield ranged between 0.51?l/g COD (HRT=2 days) and 0.25?l/g COD (HRT=1?day). In addition, the methane percentage in the biogas varied between 70.5% (HRT=10?days) and 47.5% (HRT=1?day). The close relationship between biomass loading rate and specific substrate utilization rate supported the use of Monod equations. Finally, the experimental values of effluent substrate concentration were reproduced with deviations equal to or less than 10% in every case.     

Performance and characterization of a newly developed self-agitated anaerobic reactor with biological desulfurization

The continuous operation of a newly developed methane fermentation reactor, which requires no electricity for the agitation of the fermentation liquid was investigated, and the extent of the biological desulfurization was monitored. Inside the reactor, the continual change in the liquid level and the self-agitation, occurring between 5 and 16 times every day, distributed the organic load near the inlet port of the reactor, as well as providing a nutrient supply to the hydrogen sulfide oxidizing bacteria. At different COD_Cr loading rates (5, 7, 10 kg m³ d⁻¹), the reactor achieved a biogas production yield of 0.72-0.82 m³ g⁻¹-TS, a COD_Cr reduction of 79.4-85.5% and an average of 99% hydrogen sulfide removal. This investigation demonstrated that the self-agitated reactor is comparable in digestion performance to the completely stirred tank reactor (CSTR) investigated in a previous study, and that the desulfurization performance was significantly enhanced compared to the CSTR.     

Effect of nutrient limitation and two-stage continuous fermentor design on productivities during "Clostridium ragsdalei" syngas fermentation

The effect of three limiting nutrients, calcium pantothenate, vitamin B₁₂ and cobalt chloride (CoCl₂), on syngas fermentation using “Clostridium ragsdalei” was determined using serum bottle fermentation studies. Significant results from the bottle studies were translated into single- and two-stage continuous fermentor designs. Studies indicated that three-way interactions between the three limiting nutrients, and two-way interactions between vitamin B₁₂ and CoCl₂ had a significant positive effect on ethanol and acetic acid formation. In general, ethanol and acetic acid production ceased at the end of 9 days corresponding to the production of 2.01 and 1.95 g L⁻¹ for the above interactions. Reactor studies indicated the three-way nutrient limitation in two-stage fermentor showed improved acetic acid (17.51 g g⁻¹ cells) and ethanol (14.74 g g⁻¹ cells) yield compared to treatments in single-stage fermentors. These results further support the hypothesis that it is possible to modulate the product formation by limiting key nutrients during C. ragsdalei syngas fermentation.