NIRS-aided monitoring and prediction of biogas yields from maize silage at a full-scale biogas plant applying lumped kinetics

The aim of this study was to apply near-infrared spectroscopy (NIRS), available biogas plant data and lumped degradation kinetics to predict biogas production (BPr) of maize silage. A full-scale agricultural biogas plant was equipped with NIRS-metrology at the feeding station. Continuously NIR-spectra were collected for 520 d. Substrate samples were analyzed by means of feedstuff analysis. Biogas potential of the samples was calculated from the laboratory analysis results and for a sample-subset practically assessed by “Hohenheim biogas tests”. NIRS-regression-models for all mentioned parameters were calibrated. Continuously gathered spectra, NIRS-models, actual plant-feeding data and degradation kinetics were used to calculate time-series of theoretically expectable BPr. Results were validated against measured gas quantity. Determination coefficients between calculated and measured BPr were up to 58.2%. This outcome was mainly due to the positive correlation between BPr and input amount since the substrate was very homogeneous. The use of NIRS seems more promising for plants with stronger substrate heterogeneity.     

Effect of mixing on biogas production during mesophilic anaerobic digestion of screened dairy manure in a pilot plant

The effect of mixing on biogas production of a 1.5‐m³ pilot continuous stirred tank reactor (CSTR) processing screened dairy manure was evaluated. Mixing was carried out by recirculation of reactor content with a mono pump. The experiment was conducted at a controlled temperature of 37±1°C and hydraulic retention times (HRTs) of 20 and 10 days. The effect of continuous and intermittent operation of the recirculation pump on biogas production was studied. At 10 days of HRT, the results showed a minimal influence of recirculation rate on biogas production and that continuous recirculation did not improve reactor performance. At 20 days of HRT, the recirculation rate did not affect reactor performance. Combination of low solid content in feed animal slurry and long HRTs results in minimal mixing requirements for anaerobic digestion.     

The future of anaerobic digestion and biogas utilization

One of the common tendencies of animal production activities in Europe and in developed countries in general is to intensify the animal production and to increase the size of the animal production units. High livestock density is always accompanied by production of a surplus of animal manure, representing a considerable pollution threat for the environment in these areas. Avoiding over-fertilization is not only important for environmental protection reasons but also for economical reasons. Intensive animal production areas need therefore suitable manure management, aiming to export and to redistribute the excess of nutrients from manure and to optimize their recycling.     

Batch and continuous biogas production from grass silage liquor

Herein batch and continuous mesophilic anaerobic digestion of grass silage liquor was studied. The continuous process was carried out in Armfield digesters with an OLR ranging from 0.851 to 1.77 kg COD m⁻³ day⁻¹. The effect of recirculation of effluent from the digester was investigated using different OLRs of grass silage liquor feed. These results showed that as the OLR increased, the methane yield decreased for the reactor with no recycle and increased for the reactor with recycle. However, the COD removal for both digesters was nearly the same at the same OLR. Overall these studies show that grass silage liquor can produce a high quality methane steam between 70% and 80% and achieve methane yields of 0.385 m³ kg⁻¹ COD.     

Potential errors in the quantitative evaluation of biogas production in anaerobic digestion processes

Errors that are commonly made in the quantification of biogas from anaerobic digestion experiments were investigated.For liquid displacement gasometers where a barrier solution separates the biogas and the atmosphere, inaccuracy due to gas diffusion was examined experimentally. Acidified saturated saline solution was the most suitable barrier solution, as biogas characteristics changed least with time. Using acidified or tap water caused considerable biogas losses and should therefore be avoided where biogas is stored before measurement.Errors associated with volume calculation from three common liquid displacement gasometer types were investigated theoretically. Corrections that must be made to obtain gas volumes at standard temperature and pressure when using this equipment are discussed. Regarding experimental errors, gasometer designs where displaced liquid is weighed to determine the volume are the most versatile since errors depend mainly upon balance sensitivity. Using liquid heights to calculate volume requires appropriate sizing of the gasometer relative to the volume of gas measured.The calibration of a low flow gas meter was investigated and an approximately linear variation with flow rate was found; hence in situ calibration is advised for this type of instrument. Correction for atmospheric conditions should be performed in real time to reduce errors.     

Feasibility of biogas production from anaerobic co-digestion of herbal-extraction residues with swine manure

The objective of this work was to examine the feasibility of biogas production from the anaerobic co-digestion of herbal-extraction residues with swine manure. Batch and semi-continuous experiments were carried out under mesophilic anaerobic conditions. Batch experiments revealed that the highest specific biogas yield was 294 mL CH₄ g⁻¹ volatile solids added, obtained at 50% of herbal-extraction residues and 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Specific methane yield from swine manure alone was 207 mL CH₄ g⁻¹ volatile solid added d⁻¹ at 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Furthermore, specific methane yields were 162, 180 and 220 mL CH₄ g⁻¹ volatile solids added d⁻¹ for the reactors co-digesting mixtures with 10%, 25% and 50% herbal-extraction residues, respectively. These results suggested that biogas production could be enhanced efficiently by the anaerobic co-digestion of herbal-extraction residues with swine manure.     

Development of a pilot scale anaerobic digester for biogas production from cow manure and whey mix

This paper presents results from anaerobic digestion of cow manure and whey mix. A pilot scale anaerobic digester, 128 l in volume, has been developed, to operate under batch and fed-batch conditions. The versatile and unique characteristics of the instrument allowed testing the methane production directly in the farm. The digester performance was evaluated with two calibration tests, the main for a period of 56 days. The study test was divided into three phases, one for each type of feeding operation (batch, fed-batch, batch). The initial phase of digestion resulted in 57 l-CH₄/kg-VS, the second phase had a yield of 86.6 l-CH₄/kg-VS and the third one had a production of 67 l-CH₄/kg-VS. The total methane yield was equal to 211.4 l-CH₄/kg-VS. Using the obtained pilot plant results to a real scale diary production cycle, it was possible to evaluate an electricity production equal to 8.86 kwh per 1 t/d. The conducted tests did show that there is a good potential to the use of a cow manure and whey biomass mix for biogas production.     

Ethanol production from maize silage as lignocellulosic biomass in anaerobically digested and wet-oxidized manure

In this communication, pretreatment of the anaerobically digested (AD) manure and the application of the pretreated AD manure as liquid medium for the simultaneous saccharification and fermentation (SSF) were described. Furthermore, fermentation of pretreated maize silage and wheat straw was investigated using 2 l bioreactors. Wet oxidation performed for 20 min at 121 °C was found as the most suitable pretreatment conditions for AD manure. High ammonia concentration and significant amount of macro- and micro-nutrients in the AD manure had a positive influence on the ethanol fermentation. No extra nitrogen source was needed in the fermentation broth. It was shown that the AD manure could successfully substitute process water in SSF of pretreated lignocellulosic fibres. Theoretical ethanol yields of 82% were achieved, giving 30.8 kg ethanol per 100 kg dry mass of maize silage.     

Effects of thermo-chemical pre-treatment of grass silage on methane production by anaerobic digestion

Dried grass silage (GS) was pre-treated at different NaOH loading rates (1%, 2.5%, 5% and 7.5% by volatile solids (VS) mass in grass silage) and temperatures (20 °C, 60 °C, 100 °C and 150 °C) to determine effects on its bio-degradability in terms of the hydrolysis yield and degradation of ligno-cellulosic materials for biogas production. At 100 °C and the four NaOH loadings, up to 45% of the total COD was solubilised and up to 65.6%, 36.1% and 21.2% of lignin, hemicellulose and cellulose were removed, respectively; biological methane production potentials obtained were 359.5, 401.8, 449.5 and 452.5 ml CH?/g VS added, respectively, being improved by 10-38.9% in comparison with untreated GS. VS removals following anaerobic digestion were 67.6%, 76.9%, 85.3%, 95.2% and 96.7% for untreated GS and GS treated at the four NaOH loadings, respectively. 100 °C and the NaOH loading rate of 5% is recommended as a proper GS pre-treatment condition.     

Anaerobic digestion of food waste in a hybrid anaerobic solid–liquid system with leachate recirculation in an acidogenic reactor

Recirculation of the leachate in the acidogenic reactor was proposed to enhance anaerobic digestion of food waste in the hybrid anaerobic solid–liquid (HASL) system. Recirculation of the leachate in the acidogenic reactor provided better conditions for extraction of organic matter from the treated food waste and buffering capacity to prevent excessive acidification in the acidogenic reactor. It ensured faster supply of nutrients in the methanogenic reactor in experiment. The highest dissolved COD and VFA concentrations in the leachate from the acidogenic reactor were reached for shorter time and were 16,670 mg/l and 9450 mg/l in control and 18,614 mg/l and 11,094 mg/l in experiment, respectively. Recycling of the leachate in the acidogenic reactor intensified anaerobic digestion of food waste and diminished time needed to produce the same quantity of methane by 40% in comparison with anaerobic digestion of food waste without recirculation.     

Optimization of biogas production from cattle manure by pre-treatment with ultrasound and co-digestion with crude glycerin

Biogas production by co-digestion of cattle manure with crude glycerin obtained from biodiesel production was studied after pre-treatment of the cattle manure or mixtures of cattle manure with different amounts of added glycerin with ultrasound. Batch experiments with 1750 mL of medium containing 1760 g of screened cattle manure or mixtures of cattle manure (screened or ground) and 70-140 mL or crude glycerin were incubated under mesophilic and thermophilic condition in stirred tank reactors. Under mesophilic conditions, the addition of 4% glycerin to screened manure increased biogas production by up to 400%. Application of sonication (20 kHz, 0.1 kW, and 4 min) to a mixture of manure + 4% glycerin increased production of biogas by up to 800% compared to untreated manure. The best results were obtained under thermophilic conditions using sonicated mixtures of ground cattle manure with 6% added glycerin (348 L methane/kg COD removed were obtained).     

Integration of on-farm biodiesel production with anaerobic digestion to maximise energy yield and greenhouse gas savings from process and farm residues

Anaerobic co-digestion of residues from the cold pressing and trans-esterification of oilseed rape (OSR) with other farm wastes was considered as a means of enhancing the sustainability of on-farm biodiesel production. The study verified the process energy yields using biochemical methane potential (BMP) tests and semi-continuous digestion trials. The results indicated that high proportions of OSR cake in the feedstock led to a decrease in volatile solids destruction and instability of the digestion process. Co-digestion with cattle slurry or with vegetable waste led to acceptable specific and volumetric methane productions, and a digestate low in potentially toxic elements (PTE). The results were used to evaluate energy balances and greenhouse gas emissions of the integrated process compared with biodiesel production alone. Co-digestion was shown to provide energy self-sufficiency and security of supply to farms, with sufficient surplus for export as fuel and electricity.     

Performance and kinetic evaluation of anaerobic moving bed biofilm reactor for treating milk permeate from dairy industry

High strength milk permeate derived from ultra-filtration based cheese making process was treated in an anaerobic moving bed biofilm reactor (AMBBR) under mesophilic (35 °C) condition. Total chemical oxygen demand (TCOD) removal efficiencies of 86.3–73.2% were achieved at organic loading rates (OLR) of 2.0–20.0 g TCOD L⁻¹ d⁻¹. A mass balance model gave values of methane yield coefficient (Y_G/S) and cell maintenance coefficient (k_m) of 0.341 L CH₄ g⁻¹ TCOD_removed and 0.1808 g TCOD_removed g⁻¹ VSS d⁻¹, respectively. The maximum substrate utilization rate U_max was determined as 89.3 g TCOD L⁻¹ d⁻¹ by a modified Stover–Kincannon model. Volumetric methane production rates (VMPR) were shown to correlate with the biodegradable TCOD concentration through a Michaelis–Menten type equation. Moreover, based on VMPR and OLR removed from the reactor, the sludge production yield was determined as 0.0794 g VSS g⁻¹ TCOD_removed.     

Interactions between Clostridium beijerinckii and Geobacter metallireducens in co‐culture fermentation with anthrahydroquinone‐2, 6‐disulfonate (AH2QDS) for enhanced biohydrogen production from xylose

To enhance biohydrogen production, Clostridium beijerinckii was co‐cultured with Geobacter metallireducens in the presence of the reduced extracellular electron shuttle anthrahydroquinone‐2, 6‐disulfonate (AH₂QDS). In the co‐culture system, increases of up to 52.3% for maximum cumulative hydrogen production, 38.4% for specific hydrogen production rate, 15.4% for substrate utilization rate, 39.0% for substrate utilization extent, and 34.8% for hydrogen molar yield in co‐culture fermentation were observed compared to a pure culture of C. beijerinckii without AH₂QDS. G. metallireducens grew in the co‐culture system, resulting in a decrease in acetate concentration under co‐culture conditions and a presumed regeneration of AH₂QDS from AQDS. These co‐culture results demonstrate metabolic crosstalk between the fermentative bacterium C. beijerinckii and the respiratory bacterium G. metallireducens and suggest a strategy for industrial biohydrogen production. Biotechnol. Bioeng. 2013; 110: 164–172. © 2012 Wiley Periodicals, Inc.     

Ethanol production from paper sludge by simultaneous saccharification and co‐fermentation using recombinant xylose‐fermenting microorganisms

Simultaneous saccharification and co‐fermentation (SSCF) of waste paper sludge to ethanol was investigated using two recombinant xylose‐fermenting microbes: Zymomonas mobilis 8b and Saccharomyces cerevisiae RWB222. S. cerevisiae RWB222 produced over 40 g/L ethanol with a yield of 0.39 g ethanol/g carbohydrate on paper sludge at 37°C, while similar titers and yields were achieved by Z. mobilis 8b at 30°C. Both S. cerevisiae RWB222 and Z. mobilis 8b exhibited decreasing cell viability at 37°C when producing over 40 g/L ethanol. A high ethanol concentration can account for S. cerevisiae RWB222 viability loss, but ethanol concentration was not the only factor influencing Z. mobilis 8b viability loss at 37°C. Over 3 g/L residual glucose was observed at the end of paper sludge SSCF by Z. mobilis 8b, and a statistical analysis revealed that a high calcium concentration originating from paper sludge, a high ethanol concentration, and a high temperature were the key interactive factors resulting in glucose accumulation. The highest ethanol yields were achieved by SSCF of paper sludge with S. cerevisiae RWB222 at 37°C and Z. mobilis 8b at 30°C. With good sugar consumption at 37°C, S. cerevisiae RWB222 was able to gain an improvement in the polysaccharide to sugar yield compared to that at 30°C, whereas Z. mobilis 8b at 30°C had a lower polysaccharide to sugar yield, but a higher sugar to ethanol yield than S. cerevisiae. Both organisms under optimal conditions achieved a 19% higher overall conversion of paper sludge to ethanol than the non‐xylose utilizing S. cerevisiae D5A at its optimal process temperature of 37°C. Biotechnol. Bioeng. 2010;107: 235–244. © 2010 Wiley Periodicals, Inc.     

Electricity generation from the treatment of wastewater with a hybrid up‐flow microbial fuel cell

The performance of a prototype up‐flow single‐chambered microbial fuel cell (MFC) for electrical power generation using brewery wastewater as fuel is reported. The designed reactor consisted of three zones, namely a lower anaerobic digestion zone, a central MFC zone, and an upper effluent clarifier zone. Tests were conducted in batch mode using a beer wastewater as the fuel/electron donor (COD concentration: 430 mg/L) and mixed consortia (both sewage microflora and anaerobic sludge) as a source of electrogenic bacteria. A stable current density of ～2,270 mA/m² was generated under continuous polarization with a constant external resistance (0.01 kΩ) and cell polarization gave a peak power density of 330 mW/m² at a current density of 1,680 mA/m². Electrochemical impedance analysis showed that the overall internal resistance of the reactor was quite low, that is, 8.0 Ω. Cyclic voltammetric analysis of the anodic biofilm at low scan rate revealed quite complex processes at the anode, with three redox peaks, at potentials of 116, 214, and 319 mV (vs. NHE). Biotechnol. Bioeng. 2010;107: 52–58. © 2010 Wiley Periodicals, Inc.     

Intergeneric yeast fusants with efficient ethanol production from cheese whey powder solution: Construction of a Kluyveromyces marxianus and Saccharomyces cerevisiae AY‐5 hybrid

Due to its high content of lactose and abundant availability, cheese whey powder (CWP) has received much attention for ethanol production in fermentation processes. However, lactose‐fermenting yeast strains including Kluyveromyces marxianus can only produce alcohol at a relatively low level, while the most commonly used distiller yeast strain Saccharomyces cerevisiae cannot ferment lactose since it lacks both β‐galactosidase and the lactose permease system. To combine the unique aspects of these two yeast strains, hybrids of K. marxianus TY‐22 and S. cerevisiae AY‐5 were constructed by protoplast fusion. The fusants were screened and characterized by DNA content, β‐galactosidase activity, ethanol tolerance, and ethanol productivity. Among the genetically stable fusants, the DNA content of strain R‐1 was 6.94%, close to the sum of the DNA contents of TY‐22 (3.99%) and AY‐5 (3.51%). The results obtained by random‐amplified polymorphic DNA analysis suggested that R‐1 was a fusant between AY‐5 and TY‐22. During the fermentation process with CWP, the hybrid strain R‐1 produced 3.8% v/v ethanol in 72 h, while the parental strain TY‐22 only produced 3.1% v/v ethanol in 84 h under the same conditions.