mL Of CH4 Research Articles

The Potential of Bioaugmentation-Assisted Phytoremediation Derived Maize Biomass for the Production of Biomethane via Anaerobic Digestion.

Anthropogenic behaviors are causing the severe build-up of heavy metal (HM) pollutants in the environment, particularly in soils. Amongst a diversity of remediation technologies, phytoremediation is an environmentally friendly technology that, when coupling tolerant plants to selected rhizospheric microorganisms, can greatly stimulate HM decontamination of soils. Maize (Zea mays) is a plant with the reported capacity for HM exclusion from contaminated soil but also has energetic importance. In this study, Zea mays was coupled with Rhizophagus irregularis, an arbuscular mycorrhizal fungus (AMF), and Cupriavidus sp. strain 1C2, a plant growth-promoting rhizobacteria (PGPR), as a remediation approach to remove Cd and Zn from an industrial contaminated soil (1.2 mg Cd kg-1 and 599 mg Zn kg-1) and generate plant biomass, by contrast to the conservative development of the plant in an agricultural (with no metal pollution) soil. Biomass production and metal accumulation by Z. mays were monitored, and an increase in plant yield of ca. 9% was observed after development in the contaminated soil compared to the soil without metal contamination, while the plants removed ca. 0.77% and 0.13% of the Cd and Zn initially present in the soil. The resulting biomass (roots, stems, and cobs) was used for biogas generation in several biomethane (BMP) assays to evaluate the potential end purpose of the phytoremediation-resulting biomass. It was perceptible that the HMs existent in the industrial soil did not hinder the anaerobic biodegradation of the biomass, being registered biomethane production yields of ca. 183 and 178 mL of CH4 g-1 VS of the complete plant grown in non-contaminated and contaminated soils, respectively. The generation of biomethane from HM-polluted soils' phytoremediation-derived maize biomass represents thus a promising possibility to be a counterpart to biogas production in an increasingly challenging status of renewable energy necessities.

Optimizing the Biochemical Methane Potential (BMP) of Food Waste

Recent advances in anaerobic digestion has resulted in expansion of sustainable methods for use of waste as energy resources. Conventional methods prove to be uneconomical and environmentally impractical. Moreover, the microbial consortia in anaerobic digestion are temperature dependent and therefore requires investigations on temperature optimization. Therefore, the recent experimental study is being undertaken with the objective in order to assess the effect of temperature on anaerobic biodegradation of food wasted from a hostel campus. The effect of temperature on methane generation rate has also been investigated. The anaerobic digestion study under psychrophilic, mesophilic and thermophilic temperature conditions has been carried out and compared in order to assess the optimum methane production conditions. All the experimental study for anaerobic digestion of food waste has been carried out at optimum F/M (food to mass) ratio of 0.75. The cumulative highest methane production is observed to be 33, 50 and 65 mL of CH4 in reactor R1, R2 and R3 with initial food waste COD dosage of 100, 150 and 200 mg, respectively under mesophilic temperature conditions. The highest biochemical methane potential (BMP) value of 0.94, 0.95 and 0.93 gCH4-COD/gCOD fed in reactor R1, R2 and R3 respectively, under mesophilic temperature conditions. It been observed that for maximum methane generation rate constant of 0.62 d-1 were observed under thermophilic conditions thus has to be highly accelerative process but overall conversion of organic matter to methane is less as compared to mesophilic temperature conditions, this is because free ammonia concentration increases with increasing temperature, by influencing the equilibrium. However, mesophilic conditions provide a more stable environment for the anaerobic digestion process. This may be due to the fact that temperature fluctuations can disrupt the microbial activity and slow down the process, but mesophilic conditions provide a stable environment for the microorganisms to thrive. Therefore, the mesophilic temperature range provides a balance between high reaction rates, stability, and cost-effectiveness, making it the optimal temperature range for anaerobic digestion of food waste. The obtained results in present study will be helpful in implementing on full-scale anaerobic solid waste digesters for enhancing the methane generation under mesophilic temperature conditions with high organic matter removal. Also, under thermophilic conditions the energy requirement for heating proves to be uneconomical.

Термофильное сбраживание бытовых пищевых отходов

In mesophilic conditions, anaerobic digestion is the most common in the world. However, thermophilic fermentation has several advantages due to the growth rate of microorganisms and the reactions they produce, as well as the degradation of deep organic matter due to an increase in the solubility of organic compounds. Increasing the temperature of the process makes it possible to neutralize the remnants of pathogenic organisms (viruses, bacteria, helminth eggs), which are necessary for the further use of fermented biomass as a biofertilizer. An effective inoculum is selected for the process of anaerobic co-fermentation of food waste and excess activated sludge. The optimal ratio of inoculate and substrate is determined to start the process of anaerobic digestion. Experiments with flasks and laboratory biogas reactors demonstrate that fermentation of OSV with food waste can significantly increase the rate and consumption of biogas. The optimal ratio of OSV and food waste in a mixture of coenzymes is 50/50, depending on the total content of organic substances in the mixture. The maximum rate of methanogenesis is observed in mixtures of I/C 70/30 and I/C 55/45 (after 18 days) and 156 ml of CH4 and 178 ml of CH4, respectively. This indicates the stability of the anaerobic process. It is shown that after pretreatment and activation of the landfill, the organic part of solid household waste, food waste and wastewater can be used to start the process of anaerobic digestion in anaerobic reactors.

Effect of temperature and the Carbon-Nitrogen (C/N) ratio on methane production through anaerobic co-digestion of cattle manure and Jatropha seed cake

Anaerobic digestion is a method of agricultural residue transformation used in bioenergy, making these activities energy efficient. However, it can be limited on a larger scale by the availability and diversity of organic residues related to carbon-nitrogen (C/N). Therefore, the anaerobic co-digestion of bovine manure and Jatropha seed cake (Jatropha curcas) were evaluated, with three different C/N ratios, under two conditions: mesophilic (30ºC) and thermophilic (50ºC). Biodigesters were mounted with three replicates for each C/N ratio. The highest production of CH4 was registered after 30 days of processing in the thermophilic condition (C/N 25:1) with 633.95 ± 5.59 mL of CH4 g-1 VS. In contrast, the lowest production was in the mesophilic condition (C/N 20:1) with 208.66 ± 2.61 mL of CH4 g-1 VS. The feasibility of co-digestion of agricultural residues in the production of CH4 as a possible bioenergetic alternative in short periods was demonstrated.

Methane Production from Carbondioxide in Polluted Areas Using Graphene Doped Ni/ NiO Nanocomposite via Photocatalysis

Background: Photocatalysis for the production of solar fuels and particularly to perform CO2 reduction with a sufficiently high efficiency depends to the presence of H2 and absence of H2 O using graphene doped Ni/ NiO nanocomposite. Objective: To examine the methane production from carbondioxide in polluted areas using graphene doped Ni/ NiO nanocomposite via photocatalysis with the use of dimethylaniline and xylene as electron donors. Methods: With 2 mg/l graphene doped Ni/ NiO nanocomposite with a Ni content of 19% wt from 786 μmol/h CO2 gas 563 μl CH4 /g Ni.h was obtained at 160oC temperature and the quantum yield was detected as 1.99%. It was found that H2 O has a negative influence on the photocatalytic activity. Under continuous flow operation, water molecules were easier desorbed from the graphene doped Ni/NiO photocatalyst Results: The maximum CH4 production rate was 650 μl/h for 2.4 mg of graphene doped Ni/ NiO nanocomposite after a detectione time of 17 min. Dimethylaniline and xylene were used as electron donors and 1.2 ml/l dimethylaniline and 0.9 ml/l xylene enhanced the CH4 productions by 8% and 12% as quenching factor. Conclusion: Photocatalysis methods was effected for methane production from carbondioxide in polluted areas using graphene doped Ni/ NiO nanocomposite with the use of dimethylaniline and xylene as electron donors.

Experimental characterization and assessment of bio- and thermo-chemical energy potential of dromedary manure

The aim of this study was to determine the bio- and thermo-chemical characteristics of dromedary (Camelus dromedaruis) manure to be used for renewable energy generation and greenhouse gas (GHG) mitigation. Lactating and pregnant dromedary manure samples were collected from a dromedary milk production farm and were tested. A comprehensive experimental analysis was conducted for the sampled manure to determine key parameters, including organic and nutrients content, ions, heavy metals, in addition to X-ray diffraction and fluorescence characterization. The bio-methane potential was measured in batch anaerobic digestion (AD) assays, while the energy content was determined through a bomb calorimeter. The experimental results showed that the bio-methane production ranged between 129 and 160 mL of CH4 per gram of volatile solids (VS) of dromedary manure. On the other hand, the measured calorific values of dromedary manure ranged between 12.18 and 13.60 MJ kg−1. A feasibility study was carried out for bio- and thermo-chemical waste-to-energy systems for dromedary manure management. The assessment showed that an AD-based manure management system could potentially mitigate GHG emissions; with a unit emission of 0.52 kg kWh−1 of CO2 eq compared to 0.61–0.91 kg kWh−1 of CO2 eq from conventional fossil fuel combustion. Results showed that, compared to AD, incineration would be more viable for dromedary manure management, in terms of economic revenue and energy recovery.

Mesophilic Semi-Continuous Anaerobic Digestion of Strawberry Extrudate Pretreated with Steam Explosion.

The production of strawberry concentrate produces a side stream after extrusion that is commonly landfilled. This strawberry extrudate (SE), of lignocellulosic character, contains valuable bioactive compounds such as sugars and phenols. Thermal treatments, such as steam explosion, are currently used for the valorisation of agricultural lignocellulosic wastes due to their ability to impact the structure of the lignocellulose and hemicellulose present in these wastes, favouring the disruption of fibrous material. Steam explosion has already been shown as a promising technology for phenol recovery from SE. Biogas is an additional valuable resource that might be produced from thermally pretreated and de-phenolised SE. This study assessed the influence of a steam-explosion pretreatment and the subsequent recovery of phenolic compounds from the long-term operation of a semi-continuous anaerobic digester of pretreated SE. The anaerobic digestion of SE steam exploded at 220 °C for 5 min and de-phenolised was stable at an OLR of 0.5 g of volatile solids (VS)/(L·d), which permitted a specific production rate of 135 ± 11 mL of CH4/(g of VS d). The system was not able to operate at an OLR of 1 g of VS/(L·d), which resulted in a failure of the process. Despite the inhibition threshold of phenolic compounds not being achieved, the inhibition of the anaerobic digestion process at an OLR of 1 g of VS/(L·d) was most likely due to the overloading of the system. This was indicated by the accumulation of soluble organic matter and volatile fatty acids. The increase in the propionic acid concentration up to 1300 mg/L when operating at OLRs higher than 0.5 g of VS/(L·d) could be the main factor responsible for the inhibition. An economic evaluation showed that the proposed approach (steam explosion, phenol recovery, and anaerobic digestion) would offer positive benefits, taking into account the high phenolic recovery (0.90 g of gallic acid equivalents/kg of extrudate) and the low sales price of the phenol extract, i.e., EUR 0.610/g of gallic acid equivalents, needed to reach zero net profit.

Pyrolysis and anaerobic digestion of the Egeria Densa biomass in different pretreatment conditions for potential use as a substrate in the generation of bioproducts

In recent years, the interest in clean and sustainable energy technologies has grown significantly. As an alternative to fossil fuels, organic raw materials can reduce the emission of pollutants and greenhouse gases, positively impacting the environment. Submerged aquatic plants, such as Egeria densa, have become an interesting alternative. Due to the high capacity for proliferation and its physicochemical characteristics, E. densa has potential in the generation of bio-oil and biogas for thermochemical and biological processes, respectively. Here, the authors study the pyrolysis of lignocellulosic biomass and the feasibility of methane gas production through anaerobic digestion, after different pretreatments. The design of experiments (DOE) was used to investigate mass loss, biogas yield, and extractives content. Changes in surface morphology (coloration, roughness, and porosity), during pretreatment steps, were evaluated by colorimetric assays and scanning electronic microscopy. The kinetics of biogas production was modeled through a first-order equation. According to DOE results, the degradation of lignocellulose and the efficiency of methane production were favored by the alkaline pretreatment. The maximum yield of methane at 35 °C was 231.82 mL of CH4 g−1 (VS). Changes in the chemical constitution of biomass pretreated with acid, via thermochemical strategy, were observed in colorimetric and microstructural tests, justified by the increase in the concentration of extracts. The maximum mass loss was 80 % (pyrolysis) after biomass was submitted to an acid catalyst. The results showed that the physically-chemically pre-treated aquatic macrophyte E. densa is a renewable source in bio-oil and methane production.

Cyanobacterial Biomass Produced in the Wastewater of the Dairy Industry and Its Evaluation in Anaerobic Co-Digestion with Cattle Manure for Enhanced Methane Production

The unique perspective that microalgae biomass presents for bioenergy production is currently being strongly considered. This type of biomass production involves large amounts of nutrients, due to nitrogen and phosphorous fertilizers, which impose production limitations. A viable alternative to fertilizers is wastewater, rich in essential nutrients (carbon, nitrogen, phosphorus, potassium). Therefore, Arthrospira platensis was cultivated in 150 mL photobioreactors with 70% (v/v) with the wastewater from a dairy industry, under a regime of light:dark cycles (12 h:12 h), with an irradiance of 140 μmol m−2 s−1 photon. The discontinuous cultures were inoculated with an average concentration of chlorophyll-a of 13.19 ± 0.19 mg L−1. High biomass productivity was achieved in the cultures with wastewater from the dairy industry (1.1 ± 0.02 g L−1 d−1). This biomass was subjected to thermal and physical treatments, to be used in co-digestion with cattle manure. Co-digestion was carried out in a mesophilic regime (35 °C) with a C: N ratio of 19:1, reaching a high methane yield of 482.54 ± 8.27 mL of CH4 g−1 volatile solids (VS), compared with control (cattle manure). The results demonstrate the effectiveness of the use of cyanobacterial biomass grown in wastewater to obtain bioenergy.

Comparison of furfural and biogas production using pentoses as platform

Coffee cut-stems (CCS), a biomass with high lignocellulosic content, is a coffee crop waste after bean harvesting. The main application of this material is as fuelwood for farmers, disregarding their carbohydrate content for biotechnological processes. In these terms, this work aims to compare three process scenarios for the experimental valorization of C5 fraction from CCS to produce biogas and furfural with and without the ethanol production from remaining C6 fraction under biorefinery concept. Therefore, an experimental stage was performed to obtain these products, based on a previous diluted acid pretreatment. The hydrolysate fraction was used to produce furfural and biogas, achieving yields of 0.34 g of furfural/g xylose and 81.1 mL of CH4 per gram of volatile solids. Concerning the solid fraction after acid pretreatment, it was used to produce ethanol with a previous enzymatic hydrolysis. After fermentation, 0.47 g of ethanol/g of glucose (92% of the theoretical yield) was obtained. These experimental results were fed to simulation models in order to compare three scenarios in technical, economic and environmental terms. As the main results, from technical point of view, the biogas production presents the lowest energy requirements. From the economic perspective, the furfural production presents a prefeasibility at the base scale of processing (e.g., 12.5 ton h−1). Meanwhile, the biogas scenario needs a processing capacity >22.5 ton h−1 to achieve the economic prefeasibility. In the biorefinery case, the positive economic performance is found at processing scales above 83 ton h−1. This work concludes that the C5 sugars platform is identified as a potential alternative for the generation of furfural and biogas, however, in this case a multiproduct biorefinery system is not always the best option to valorize biomass given the very high scale required and the economic indicators.

Deciphering the effects of temperature on bio-methane generation through anaerobic digestion.

Anaerobic digestion (AD) is a sustainable wastewater treatment technology which facilitates energy, nutrient, and water recovery from organic wastes. The agricultural and industrial wastes are suitable substrates for the AD, as they contain a high level of biodegradable compounds. The aim of this study was to examine the AD of three different concentrations of phenol (100, 200, and 300mg/L) containing wastewater with and without co-substrate (acetate) at four different temperatures (25, 35, 45, and 55°C) to produce methane (CH4)-enriched biogas. It was observed that the chemical oxygen demand (COD) and phenol removal efficiencies of up to 76% and 72%, respectively, were achieved. The CH4 generation was found higher in anaerobic batch reactors (ABRs) using acetate as co-substrate, with the highest yield of 189.1μL CH4 from 500μL sample injected, obtained using 200mg/L of phenol at 35°C. The results revealed that the performance of ABR in terms of degradation efficiency, COD removal, and biogas generation was highest at 35°C followed by 55, 45, and 25°C indicating 35°C to be the optimum temperature for AD of phenolic wastewater with maximum energy recovery. Scanning electron microscopy (SEM) revealed that the morphology of the anaerobic sludge depends greatly on the temperature at which the system is maintained which in turn affects the performance and degradation of toxic contaminants like phenol. It was observed that the anaerobic sludge maintained at 35°C showed uniform channels leading to higher permeability through enhanced mass transfer to achieve higher degradation rates. However, the denser sludge as in the case of 55°C showed lesser permeability leading to limited transfer and thus reduced treatment. Quantitative real-time PCR (qPCR) analysis revealed a more noteworthy change in the population of the microbial communities due to temperature than the presence of phenol with the methanogens being the dominating species at 35°C. The findings suggest that the planned operation of the ABR could be a promising choice for CH4-enriched biogas and COD removal from phenolic wastewater.

Inhibition Effect of Sodium Concentrations on the Anaerobic Digestion Performance of Sargassum Species

The effect of variable sodium concentrations on the anaerobic digestion performance of Sargassum sp. was investigated, and the variation in bacterial and archaeal communities was analyzed by high-throughput gene sequencing. Results showed that the maximum methane yield of 290.41 ± 34.21 mL of CH4 g–1 of volatile solids was obtained at a sodium concentration of 4.42 g L–1, increased by 38.1% compared to the control group. Meanwhile, higher volatile fatty acids production was observed at the sodium concentration of 4.42 g L–1. The inhibitory concentration values of 10%, 50%, and 90% occurred at the sodium concentrations of 6.3, 11.3, and 18.7 g L–1, respectively. The hydrolytic, acidogenic, and acetogenic bacteria and the hydrogenotrophic methanogens could normally metabolize at sodium concentrations of 2.46–24.08 g L–1, whereas the acetoclastic methanogens were severely inhibited at sodium concentrations greater than 20.15 g L–1. The microbial community structure showed that Paludibacter and Fibrobacter pl...

Macroalgae Laminaria digitata and Saccharina latissima as Potential Biomasses for Biogas and Total Phenolics Production: Focusing on Seasonal and Spatial Variations of the Algae

Laminaria digitata (L. digitata) and Saccharina latissima (S. latissima) are the most common species of macroalgae in the north Atlantic and north Pacific. Because of their interesting composition, they have recently attracted attention as useful biomass for various purposes such as for biochemicals and bioenergy production. Nevertheless their composition varies according to the season and to the local environmental conditions. Therefore, in this study different samples harvested throughout a year and in different locations in Denmark were analyzed. The aim of the study was identifying the best period of the year and location to cultivate macroalgae for biofuels and biochemical production. Therefore, the biogas potential and the total phenolics profile for L. digitata and S. latissima were determined. The total phenolics were determined as they may represent an interesting bioactive compound, due to their significant health benefits. The highest methane yield (358.9 ± 5.1 and 285.0 ± 19.1 N mL of CH4 g –1 of volatile solids for L. digitata and S. latissima, respectively) and total phenolic content (TPC) content (47.4 ± 0.0 mg of TPC g–1 of dry matter for L. digitata) were recorded in summer when the sugar level and the light intensity reached their maximum.

Novel Nickel Aluminate-Derived Catalysts Supported on Ceria and Ceria–Zirconia for Partial Oxidation of Methane

In this work novel nickel catalysts based on nickel aluminate deposited on ceria-based supports (CeO2 and Ce0.13Zr0.87O2) were investigated for the partial oxidation of methane. The good catalytic behavior of the CeO2-based sample under moderate (38400 mL of CH4 g–1 h–1 and stoichiometric feed) and severe (60000 mL of CH4 g–1 h–1, an O/C molar ratio of 0.8, and prolonged time on stream (30 h)) reaction conditions was mainly assigned to the small particle size (about 10 nm) that was achieved after the high-temperature reduction of the spinel and its notable redox properties. CeAlO3 formation was found to have a negative effect on the catalytic performance, which was more pronounced for the Ce0.13Zr0.87O2-supported catalyst. This negative impact could be controlled by the introduction of La2O3 since this promoter reacted with alumina to give LaAlO3 instead of CeAlO3 and favored carbon gasification in the vicinity of nickel particles.

Pretreatment of Rice Straw for the Improvement of Biogas Production

Improvement of biogas production by pretreatment of rice straw with 0.25 and 0.5 M sodium carbonate at 90, 110, and 130 °C and for 1, 2, and 3 h was investigated, and promising results were obtained. All treated and untreated rice straws were digested under mesophilic conditions (37 °C). Increasing the concentration of sodium carbonate showed significant improving effects, whereas the treatment time showed less impact. The best results, obtained by pretreatment with 0.5 M sodium carbonate at 110 °C for 2 h, resulted in the production of 292 mL of CH4 per gram of VS, whereas untreated rice straw produced 130 mL of CH4 per gram of VS. Compositional, SEM, and FTIR analyses confirmed that structural modification, lignin removal, and cellulose crystalline reduction are responsible for the improvement.

Microbiological and biogeochemical properties of the Caspian Sea sediments and water column

The work presents the results of investigation of microbial and biogeochemical processes at the water-sediment interface in the samples of three Caspian Sea profiles obtained during the 39th cruise of RV “Rift” in May–June 2012. The decrease in suspended Corg content from the surface to the bottom resulted from the activity of aerobic heterotrophic microorganisms. Autotrophic methanogenesis occurred in anoxic water of deep-sea depressions, where methane concentrations were up to 2.2–3.75 μL CH4 L−1, which was an order of magnitude higher than in the aerobic water column (0.04–0.32 μL CH4 L−1). Methanogenesis was accompanied by a considerable decrease in δ13C of suspended Corg (−26 to −30‰). The numbers of microbial cells in the water column varied from 40 to 3200 × 103 cells mL−1. The results of microbiological and biogeochemical investigation demonstrated that, in spite of the absence of connection with the ocean and other specific features, the Caspian Sea has the characteristics of a typical marine basin.

Microbiological and isotopic geochemical investigation of Lake Kislo-Sladkoe, a meromictic water body at the Kandalaksha Bay shore (White Sea)

Microbiological, biogeochemical, and isotopic geochemical investigation of Lake Kislo-Sladkoe (Polusolenoe in early publications) at the Kandalaksha Bay shore (White Sea) was carried out in September 2010. Lake Kislo-Sladkoe was formed in the mid-1900s out of a sea gulf due to a coastal heave. At the time of investigation, the surface layer was saturated with oxygen, while near-bottom water contained sulfide (up to 32 mg/L). Total number of microorganisms was high (12.3 x 10(6) cells/mL on average). Light CO2 fixation exhibited two pronounced peaks. In the oxic zone, the highest rates of photosynthesis were detected at 1.0 and 2.0 m. The second, more pronounced peak of light CO2 fixation was associated with activity of anoxygenic phototrophic bacteria in the anoxic layer at the depth of 2.9 m (413 μg C L(-1) day(-1)). Green-colored green sulfur bacteria (GSB) predominated in the upper anoxic layer (2.7-2.9 m), their numbers being as high as 1.12 x 10(4) cells/mL, while brown-colored GSB predominated in the lower horizons. The rates of both sulfate reduction and methanogenesis peaked in the 2.9 m horizon (1690 μg S L(-1) day(-1) and 2.9 μL CH4 L(-1) day(-1)). The isotopic composition of dissolved methane from the near-bottom water layer (δ13C (CH4) = -87.76 per thousand) was significantly lighter than in the upper horizons (δ13C (CH4) = -77.95 per thousand). The most isotopically heavy methane (δ13C (CH4) = -72.61 per thousand) was retrieved from the depth of 2.9 m. The rate of methane oxidation peaked in the same horizon. As a result of these reactions, organic matter (OM) carbon of the 2.9 m horizon became lighter (-36.36 per thousand), while carbonate carbon became heavier (-7.56 per thousand). Thus, our results demonstrated that Lake Kislo-Sladkoe is a stratified meromictic lake with active microbial cycles of carbon and sulfur. Suspended matter in the water column was mostly of autochthonous origin. Anoxygenic photosynthesis coupled to utilization of reduced sulfur compounds contributed significantly to OM production.

Improved Anaerobic Digestion by the Addition of Paper Tube Residuals: Pretreatment, Stabilizing, and Synergetic Effects

This study deals with the addition of paper tube residuals to a nitrogen-rich mixture of organic waste obtained from industrial and municipal activities. This nitrogen-rich mixture, called buffer tank substrate (BTS) in the following text, is used in a large-scale biogas plant. The effects were investigated in semi-continuous co-digestion processes, and variations in operational conditions were studied. The addition of paper tubes had stabilizing effects, prevented the failure of the process, and made it possible to decrease the hydraulic retention time from 25 to 20 days. Furthermore, synergetic effects were found, with 15–34% higher methane yields, when paper tubes were co-digested with BTS. Moreover, steam explosion pretreatment of the paper tube waste with the addition of 0–2% NaOH was evaluated by batch digestion experiments. Increasing the NaOH concentrations used in the pretreatment resulted in increasing methane yields, with the highest of 403 N mL of CH4 g–1 of volatile solids (VS) corresponding to an increase by 50% compared to that when untreated paper was digested (268 N mL of CH4 g–1 of VS). The long-term effects of this best pretreatment were further investigated by continuous co-digestion experiments, leading to a higher methane yield when pretreated paper tubes were used in the co-digestion process compared to untreated.

Factors controlling the activity of the microbial community of the alkaline Lake Beloe (Transbaikal Region)

In this work, the main environmental factors determining the functioning of the microbial community of the alkaline low-mineralized Lake Beloe during the annual cycle were studied. High numbers of phototrophic and heterotrophic microorganisms (up to 107 cells/mL) and high rates of bacterial processes of organic matter (OM) production and destruction were observed. The highest rate of dark CO2 assimilation (up to 0.43 mg C dm−3 day−1), as well as the peak intensities of the terminal processes of sulfate reduction and methanogenesis (up to 1.81 mg S dm−3 day−1 and 0.96 μL CH4 dm−3 day−1, respectively), detected at the end of summer, were comparable to the rates of these processes detected in the bottom sediments of most soda lakes of the Transbaikal Region. Principal Component Analysis (PCA) allowed us to estimate the effect of environmental factors on the functioning of the microbial community of the alkaline Lake Beloe. Four main components, explaining 98% of variations, were detected. The first one (PC1) explained 63.5% of the seasonal variations and represented the temperature factor consisting of the temperatures of air, water, and bottom sediments. Water temperature and pH were the main contributors to the second component (PC2) and determine 26.2% of the seasonal variations. The PC3 (silt temperature and the concentration of organic matter) and PC4 (salt concentration) components were less important and explained only 6.5 and 2.2% of the variations, respectively.

Speciation of heavy metals in sewage sludge after mesophilic and thermophilic anaerobic digestion

AbstractTwo types of sewage sludge anaerobic digestion were carried out: mesophilic and thermophilic. Metal speciation analysis was performed revealing some changes in the chemical form of the metals during the stabilization process of sludge. After both methane fermentation processes, a comparable level of organic matter distribution was obtained (≈ 40 %). The amount of produced methane during thermophilic and mesophilic digestion was 560 mL of CH4 and 580 mL of CH4 from 1 g of removed organic matter, respectively. Low concentration of heavy metal ions in the liquid phase of sludge was observed. Metal ions precipitated and remained bound throughout the stabilization process. No accumulation of heavy metals in the mobile fractions of sludge (exchangeable and carbonate) was observed for either digestion process. The highest increase of zinc, copper, nickel, cadmium, and chromium concentration was observed in the organic-sulfide fraction, whereas the highest increase of lead was found in the residual fraction.