Amelioration of methane yield in cheese whey fermentation by controlling the pH of the methanogenic stage

A two-stage, no-mix anaerobic digester of 145 L capacity was used to investigate the effect of controlling the pH of the methanogenic stage on the biogas production and the pollution potential reduction of acid cheese whey. The digester was operated at a 15-d hydraulic retention time, and a temperature of 35°C. Controlling the pH of the methanogenic stage increased the biogas production rate and methane yield by 77.77 and 289.00%, respectively. Reductions of up to 32.19, 44.44, and 35.86% in the COD, solids and nitrogen were achieved.     

Biogasification of Green and Food Wastes Using Anaerobic-Phased Solids Digester System

The performance of a laboratory-scale anaerobic-phased solid (APS) digester system treating food and green wastes was evaluated at thermophilic condition. The APS system comprised of four hydrolysis digesters and one biogasification reactor. The hydrolysis reactors were operated batchwised at a 12-day retention time, while the biogasification reactor was continuously operated at different hydraulic retention times (HRT). The biogas and methane yields from green waste were determined to be 0.438 and 0.252 L/g volatile solid (VS), respectively, with VS removal of 78%. The biogas and methane yields from food waste were 0.596 and 0.379 L/g VS, respectively, with VS removal of 85%. Hydrogen was produced from hydrolysis reactors during the digestion of food waste. Its content was 30.1% and 8.5% of the biogas produced on the first and second day of digestion, respectively. Hydrogen yield from the whole system was determined to be 0.029 L/g VS representing about 4.9% of the total biogas production from the system. The ratio between the volumes of biogasification and hydrolysis reactors (BR/HR) was found to be a factor that affects the process performance and stability.     

The Performance of Jatropha Curcas Linn. Capsule Husk as Feedstocks Biogas in One Phase Anaerobic Digestion

Jatropa curcas Linn. (JcL) capsule husk was not recommended as biogas feedstocks. However for biorefinery purpose, several technologies have been conducting to solve this problem. This research reported quantity and quality comparison of Dry Husk Jcl (DH-JcL) in one phase system of batch digester compare with semi continuous digester. HDPE drum of 80 L working volume used as digester with 40 days hydraulic retention time. Feeding of DH-Jcl and solvent water was mixed on concentration of 1: 8. Research conclusion showed that semi continuous digester was better than batch digester. Biogas quality showed that methane content can reach 66.61% to 83.15% and biogas quantity in semi continuous digester can reach 0.016 m³ · kg^–1 DH JcL. The result was not in optimize condition yet because ratio number of volatile fatty acids/ alkalinity showed 0.5, it was indicated unstable anaerobic degradation process of DH-JcL.     

Effects of Feedstock Sources on Inoculant Acclimatization: Start-up Strategies and Reactor Performance

Different inoculum sources and acclimatization methods result in different substrate adaptation and biodegradability. To increase straw degradation rate, shorten the digester start-up time, and enhance the biogas production, we domesticated anaerobic sludge by adding microcrystalline cellulose (MCC). During acclimatization, the start-up strategies and reactor performance were investigated to analyze changes in feedstock adaption, biodegradability, and methanogen activity. The effect of the domesticated inoculum was evaluated by testing batch un-pretreated corn stover with a dewatered sludge (DS)-domesticated inoculum as a control. The results showed that (1) using MCC as a substrate rapidly improved microorganism biodegradability and adaptation. (2) MCC as domesticated substrate has relatively stable system and high mass conversion, but with low buffer capacity. (3) Macro- and micronutrients should be added for improving the activity of methanogenic and system’s buffer capacity. (4) Using the domesticated inoculums and batch tests to anaerobically digest untreated corn stover yielded rapid biogas production of 292 mL, with an early peak value on the first day. The results indicated that cultivating directional inoculum can efficiently and quickly start-up digester. These investigated results to promote anaerobic digestion of straw for producing biogas speed up the transformation of achievements of biomass solid waste utilization have a positive promoting significance.     

Single-stage anaerobic codigestion for mixture wastes of simulated Korean food waste and waste activated sludge

Korean food waste was treated with a single-stage anaerobic codigester (SSAD) using waste activated sludge (WAS) generated from a municipal wastewater treatment plant. The stability and performance of the system was analyzed. The C/N ratio was improved with increasing food waste fraction of feed mixture. The pH, alkalinity, and free ammonia nitrogen concentration were the parameters used to evaluate the digester’s stability. The experimentally determined values of the parameters indicated that there were no methane inhibitions in the digester. Digester performance was determined by measuring the total chemical oxygen demand TCOD), volate solids (VS) removal, methane content in biogas, methane production rate (MPR), and specific methane productivity. Methane content in biogas and MPR were significantly dependent on hydraulic retention time (HRT) and ratio of food waste to WAS. The methane content in biogas decreased at shorter HRT or higher organic loading rate (OLR) with increased food waste fraction. Concerning the performance of the codigester, the optimum operating condition of the SSAD was found to be at an HRT of 10 d with a feed mixture ratio of 50% food waste and 50% WAS. A TCOD removal efficiency of 53.6% and a VS removal efficiency of 53.7% were obtained at an OLR of 5.96 kg of TCOD/(m³·d) and 3.14 kg of VS/(m³·d), respectively. A maximum MPR of 1.15 m³ CH₄/(m³·d) and an SMP of 0.37 m³ CH₄/kg of VS_feed were obtained at an HRT of 10 d with a methane content of 63%.     

Methane production in a 100-L upflow bioreactor by anaerobic digestion of farm waste

Manure waste from dairy farms has been used for methane production for decades, however, problems such as digester failure are routine. The problem has been investigated in small scale (1-2 L) digesters in the laboratory; however, very little scale-up to intermediate scales are available. We report production of methane in a 100-L digester and the results of an investigation into the effect of partial mixing induced by gas upflow/recirculation in the digester. The digester was operated for a period of about 70 d (with 16-d hydraulic retention time) with and without the mixing induced by gas recirculation through an internal draft tube. The results show a clear effect of mixing on digester operation. Without any mixing, the digester performance deteriorated within 30-50 d, whereas with mixing continuous production of methane was observed. This study demonstrates the importance of mixing and its critical role in design of large scale anaerobic digesters.     

Methane production in a 100-L upflow bioreactor by anaerobic digestion of farm waste

Manure waste from dairy farms has been used for methane production for decades, however, problems such as digester failure are routine. The problem has been investigated in small scale (1–2 L) digesters in the laboratory; however, very little scale-up to intermediate scales are available. We report production of methane in a 100-L digester and the results of an investigation into the effect of partial mixing induced by gas upflow/recirculation in the digester. The digester was operated for a period of about 70 d (with 16-d hydraulic retention time) with and without the mixing induced by gas recirculation through an internal draft tube. The results show a clear effect of mixing on digester operation. Without any mixing, the digester performance deteriorated within 30–50 d, whereas with mixing continuous production of methane was observed. This study demonstrates the importance of mixing and its critical role in design of large scale anaerobic digesters.     

Combining metal-microbe and microbe-microbe dual direct electron transfer on Fe(0)-cathode of bio-electrochemical system to enhance anaerobic digestion of cellulose wastewater

Considering that cathode of microbial electrochemical system (MES) is a good electrons source for methane production via direct/indirect electron transfer to electroactive microorganisms, and that Fe(0) is also a confirmed electron donor for some electroactive microorganisms through metal-microbe direct electron transfer (DET), Fe(0)-cathode was equipped into an MES digester to enhance cathodic methane production. The results of this study indicated that the potential DET participator, Clostridium possibly obtained electrons directly from Fe(0)-cathode via metal-microbe electrons transfer, then transferred electrons directly to the definite DET participators, Methanosarcina/Methanothrix via microbe-microbe electrons transfer for CH₄ production. In addition, Methanobacterium is another specially enriched methanogen on Fe(0)-cathode, which might obtain electrons directly from Fe(0)-cathode to produce CH₄ via metal/electrode-microbe DET. The increment of conductivity of cathodic sludge in Fe(0)-cathode MES digester (R1) further confirmed the enrichment of electroactive microorganisms participating in DET process. As a consequence, a higher CH₄ production (1205–1508 mL/d) and chemical oxygen demand (COD) removal (79.0%-93.8%) were achieved in R1 compared with graphite-cathode MES digester (R2, 720–1090 mL/d and 63.6%-85.6%) and the conventional anaerobic digester (R3, 384–428 mL/d and 35.2%-41.0%). In addition, energy efficiency calculated indicated that the output energy of CH₄ production was 8.16 folds of electricity input in Fe(0)-cathode MES digester.     

Anaerobic bioconversion of municipal solid wastes using a novel high-solids reactor design

Novel, laboratory-scale, high-solids reactors operated under mesophilic conditions were used to study the anaerobic fermentation of processed municipal solid waste (MSW) to methane. Product gas rate data were determined for organic loading rates ranging from 2.99–18.46 g of volatile solids (VS) per liter (L) per day (d). The data represent the anaerobic fermentation at high-solids levels within the reactor of 21–32%, while feeding a refuse-derived fuel (RDF)/MSW feedstock supplemented with a vitamin/mineral/nutrient solution. The average biogas yield was 0.59 L biogas/g VS added to the reactor system/d. The average methane composition of the biogas produced was 57.2%. The data indicate a linear relationship of increasing total biogas production with increasing organic loading rate to the process. The maximum organic loading rate obtainable with high-solids anaerobic digestion is in the range of 18–20 g VS/L·d to obtain 80% or greater bioconversion for the RDF/MSW feedstock. This loading rate is approximately four to six times greater than that which can be obtained with comparable low-solids anaerobic bioreactor technology.     

Biomethanation of a mixture of salty cheese whey and poultry waste or cattle dung

This paper describes the results of a study aimed at improving the efficiency of anaerobic digestion of salty cheese whey in combination with poultry waste or cattle dung. Best results were obtained when salty cheese whey was mixed with poultry waste in the ratio of 7:3, or cattle dung in the ratio of 1:1, both on dry weight basis giving maximum gas production of 1.2 L/L of digester/d with enriched methane content of 64% and 1.3 L/L of digester/d having methane content of 63% respectively. Various conditions such as temperature and retention time have been optimized for maximum process performance.     

Anaerobic upflow fixed-film bioreactor for biomethanation of salty cheese whey

In order to develop a suitable reactor for the biomethanation of high-strength salty cheese whey, the performance of anaerobic upflow fixed-film reactors packed with different support materials, such as charcoal, gravel, brick pieces, pumicestones, and PVC pieces, has been studied. The charcoal-bedded reactor gave the best performance, with the maximum gas production (3.3 L/L digester/d) and an enriched methane content (69% CH₄). Temperature and hydraulic retention time were optimized, with the ultimate aim of improving biomethanation. Maximum gas production (3.3 L/L digester/d) was achieved at a hydraulic retention time of 2 d at 40°C.     

Two-phase methanization of food wastes in pilot scale

A 5 ton/d pilot scale two-phase anaerobic digester was constructed and tested to treat Korean food wastes in Anyang city near Seoul. The easily degradable presorted food waste was efficiently treated in the two-phase anaerobic digestion process. The waste contained in plastic bags was shredded and then screened for the removal of inert materials such as fabrics and plastics, and subsequently put into the two-stage reactors. Heavy and light inerts such as bones, shells, spoons, and plastic pieces were again removed by gravity differences. The residual organic component was effectively hydrolyzed and acidified in the first reactor with 5 d space time at pH of about 6.5. The second, methanization reactor converted the acids into methane with pH between 7.4 and 7.8. The space time for the second reactor was 15 d. The effluent from the second reactor was recycled to the first reactor to provide alkalinities. The process showed stable steady-state operation with the maximum organic loading rate of 7.9 kg volatile solid (VS)/m³/d and the volatile solid reduction efficiency of about 70%. The total of 3.6 tons presorted MSW containing 2.9 tons of food organic was treated to produce about 230 m³ of biogas with 70% (v/v) of methane and 80 kg of humus. This process is extended to full-scale treating 15 tons of food waste a day in Euiwang city and the produced biogas is utilized for the heating/cooling of adjacent buildings. Author to whom all correspondence and reprint requests should be addressed.     

Codigestion of proteinaceous industrial waste

Organic wastes are increasingly collected source separated, thus requiring additional treatment or recovery capacities for municipal biowastes, organic industrial wastes, as well as agroindustrial byproducts. In this study, we demonstrate that anaerobic digestion is preferentially suited for high-water-containing liquid or pasty waste materials. We also evaluate the suitability of various organic wastes and byproducts as substrates for anaerobic digestion and provide a current status survey of codigestion. Biodegradation tests and estimations of the biogas yield were carried out with semisolid and pasty proteins and lipids containing byproducts from slaughterhouses; pharmaceutical, food, and beverage industries; distilleries; and municipal biowastes. Biogas yields in batch tests ranged from 0.3 to 1.36 L/g of volatile solids_added. In continuous fermentation tests, hydraulic retention times (HRTs) between 12 and 60 d, at a fermentation temperature of 35°C, were required for stable operation and maximum gas yield. Laboratory experiments were scaled up to full-scale codigestion trials in municipal and agricultural digestion plants. Up to 30% cosubstrate addition was investigated, using municipal sewage sludge as well as cattle manure as basic substrate. Depending on addition rate and cosubstrate composition, the digester biogas productivity could be increased by 80–400%. About 5–15% cosubstrate addition proved to be best suited, without causing any detrimental effects on the digestion process or on the further use of the digestate.     

Influence of Hydraulic Retention Time and Reactor Configuration During Fermentation of Diluted Chicken Manure

In this study, single-stage and two-phase semi-continuous thermophilic anaerobic reactors fed with diluted (3 % total solids (TS) and 1.8 % volatile solids (VS)) chicken manure at three different hydraulic retention times (HRTs) were compared interms of biogas production rate, methane content of the produced biogas, and VS and TS removal. Along the study, HRTs of 16, 12, and 8 days were implemented to the single-stage and the two-phase systems. It was observed that the single-stage anaerobic system was superior to the two-phase anaerobic system according to their biogas production rates (517 vs. 356, 551 vs. 359, 459 vs. 386 (mL/g VS_feed)) at all HRTs. On the other hand, methane content of the biogas produced was higher in the two-phase system compared to the single-stage system.     

Comparison of yellow poplar pretreatment between NREL digester and sunds hydrolyzer

Single-stage cocurrent dilute acid pretreatments were carried out on yellow poplar (Liriodendron tulipifera) sawdust using an as-installed and short residence time modified pilot-scale Sunds hydrolyzer and a 4-L bench-scale NREL digester (steam explosion reactor). Pretreatment conditions for the Sunds hydrolyzer, installed in the NREL process development unit (PDU), which operates at 1 t/d (bone-dry t) feed rate, spanned the temperature range of 160 – 210°C, 0.1 – 1.0% (w/w) sulfuric acid, and 4-10-min residence times. The batch pretreatments of yellow poplar sawdust in the bench-scale digester were carried out at 210 and 230°C, 0.26% (w/w) sulfuric acid, and 1-, 3-, and 4-min residence times. The dilute acid prehydrolysis solubilized more than 90% of the hemicellulose, and increased the enzymatic digestibility of the cellulose that remained in the solids. Compositional analysis of the pretreated solids and liquors and mass balance data show that the two pretreatment devices had similar pretreatment performance.     

A Review on Optimization Production and Upgrading Biogas Through CO2 Removal Using Various Techniques

Biogas from anaerobic digestion of organic materials is a renewable energy resource that consists mainly of CH₄ and CO₂. Trace components that are often present in biogas are water vapor, hydrogen sulfide, siloxanes, hydrocarbons, ammonia, oxygen, carbon monoxide, and nitrogen. Considering the biogas is a clean and renewable form of energy that could well substitute the conventional source of energy (fossil fuels), the optimization of this type of energy becomes substantial. Various optimization techniques in biogas production process had been developed, including pretreatment, biotechnological approaches, co-digestion as well as the use of serial digester. For some application, the certain purity degree of biogas is needed. The presence of CO₂ and other trace components in biogas could affect engine performance adversely. Reducing CO₂ content will significantly upgrade the quality of biogas and enhancing the calorific value. Upgrading is generally performed in order to meet the standards for use as vehicle fuel or for injection in the natural gas grid. Different methods for biogas upgrading are used. They differ in functioning, the necessary quality conditions of the incoming gas, and the efficiency. Biogas can be purified from CO₂ using pressure swing adsorption, membrane separation, physical or chemical CO₂ absorption. This paper reviews the various techniques, which could be used to optimize the biogas production as well as to upgrade the biogas quality.     

Evidence of multiple electrohydrodynamic forces acting on a colloidal particle near an electrode due to an alternating current electric field

Total internal reflection microscopy was used to monitor the elevation of 4-7.5 mum diameter particles near an electrode in response to an oscillating electric field with amplitude up to 8.5 kV/m. The media were 0.15 mM electrolyte solutions of HNO(3), NaHCO(3), and KOH, and the frequency band was 40 Hz to 10 kHz. Polystyrene-sulfonate particles were used in bicarbonate and KOH solutions, while polystyrene-amine particles were used in nitric acid. At frequencies less than 500 Hz, large oscillations in elevation at the driving frequency with small superimposed Brownian excursions were observed. At frequencies above 1 kHz, deterministic oscillations in elevation were negligible compared to Brownian fluctuations, which allowed transformation of histograms of elevations into potential energy profiles. The ac field drew the particle closer on average to the electrode in KOH solutions (compared to the no-field average elevation) and the field pushed the particle farther from the electrode in NaHCO(3). In HNO(3) a reversal of average height was observed at a frequency of 300 Hz at 1.7 kV/m with the particle being drawn closer to the electrode at low frequencies and being pushed away at higher frequencies. The reversal reflects two different electrohydrodynamic mechanisms. Analysis of the data at a high frequency (10 kHz) revealed a net force that was attractive in KOH and repulsive in HNO(3). This net force scaled with E(2)omega(-)(1), where E is the amplitude and omega is the frequency.     

In situ Removal of Hydrogen Sulfide During Biogas Fermentation at Microaerobic Condition

In this paper, rice straw was used as a raw material to produce biogas by anaerobic batch fermentation at 35 °C (mesophilic) or 55 °C (thermophilic). The hydrogen sulfide in biogas can be converted to S⁰ or sulfate and removed in-situ under micro-oxygen environment. Trace oxygen was conducted to the anaerobic fermentation tank in amount of 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, or 10.0 times stoichiometric equivalence, respectively, and the control experiment without oxygen addition was carried out. The results showed that the initial H₂S concentrations of biogas are about 3235?±?185 mg/m³ (mesophilic) or 3394?±?126 mg/m³ (thermophilic), respectively. The desulfurization efficiency is 72.3 % (mesophilic) or 65.6 % (thermophilic), respectively, with oxygen addition by stoichiometric relation. When the oxygen feeded in amount of 2～4 times, theoretical quantity demanded the removal efficiency of hydrogen sulfide could be over 92 %, and the oxygen residue in biogas could be maintained less than 0.5 %, which fit the requirement of biogas used as vehicle fuel or combined to the grid. Though further more oxygen addition could promote the removal efficiency of hydrogen sulfide (about 93.6 %), the oxygen residue in biogas would be higher than the application limit concentration (0.5 %). Whether mesophilic or thermophilic fermentation with the extra addition of oxygen, there were no obvious changes in the gas production and methane concentration. In conclusion, in-situ desulfurization can be achieved in the anaerobic methane fermentation system under micro-oxygen environment. In addition, air could be used as a substitute oxygen resource on the situation without strict demand for the methane content of biogas.     

Improved efficiency and stable digestion of biomass in nonmixed upflow solids reactors

A nonmixed upflow solids reactor (USR), which permitted longer solids than hydraulic retention times, was used to study the anaerobic digestion performance of sea kelp (Macrocystis pyrifera). The performance of the USR was compared to that of the continuously stirred tank reactor (CSTR) at different organic loading rates in terms of methane yield, methane production rate, and process stability. Results showed that, although digester performance was markedly affected by kelp compositional variability, methane yields and production rates in the USR were significantly higher than those observed with the CSTR. Results also showed that volatile acid concentrations, which are generally inversely related to digester stability, were significantly lower in the USR than in the CSTR.     

Structure, stability and vibrational spectrum of the hydrogen-bonded complex between HNO3 and H2O. Ab initio and DFT studies

The structure, stability and vibrational spectrum of the binary complex between HONO2 and H2O have been investigated using ab initio calculations at SCF and MP2 levels with different basis sets and B3LYP/6-31G(d,p) calculations. Full geometry optimization was made for the complex studied. It was established that the hydrogen-bonded H2O...HONO2 complex has a planar structure. The corrected values of the dissociation energy at the SCF and MP2 levels and B3LYP calculations are indicative of relatively strong OH...O hydrogen-bonded interaction. The changes in the vibrational characteristics (vibrational frequencies and infrared intensities) arising from the hydrogen bonding between HONO2 and H2O have been estimated by using the ab initio calculations at SCF and MP2 levels and B3LYP/6-31G(d,p) calculations. It was established that the most sensitive to the complexation is the stretching O-H vibration from HONO2. In agreement with the experiment, its vibrational frequency in the complex is shifted to lower wavenumbers. The predicted frequency shift with the B3LYP/6-31G(d,p) calculations (-439 cm(-1)) is in the best agreement with the experimentally measured (-498 cm(-1)). The intensity of this vibration increases dramatically upon hydrogen bonding. The ab initio calculations at the SCF level predict an increase up to five times; at the MP2 level up to 10 times and the B3LYP/6-31G(d,p) predicted increase is up to 17 times. The good agreement between the predicted values of the frequency shifts and those experimentally observed show that the structure of the hydrogen-bonded complex H2O...HONO2 is reliable.