CH4 Production Rate Research Articles

Frequent export of pig slurry for outside storage reduced methane but not ammonia emissions in cold and warm seasons

Manure management is a significant source of methane (CH4) and ammonia (NH3), and there is an urgent need for strategies to reduce these emissions. More frequent export of manure for outside storage can lower gaseous emissions from housing facilities, but the longer residence time may then increase emissions during outside storage. This study examined CH4 and NH3 emissions from liquid pig manure (pig slurry) removed from the in-house slurry collection pits at three different frequencies, i.e., three times per week (T2.3), once per week (T7), or once after 40 days (T40, reference). The slurry from treatments T2.3 and T7 was transferred for outside storage weekly over four weeks, and slurry from treatment T40 once after 40 days, in connection with summer and winter production cycles with growing-finishing pigs. The slurry was stored in pilot-scale storage tanks with solid cover and continuous ventilation. Compared to T40, the treatments T2.3 and T7 increased CH4 emissions during outside storage, but in-house emissions were reduced even more, and the net effects on total CH4 emissions from manure management (housing unit and outside storage) were reductions of 18–41% in summer and 53–83% in winter. The frequent slurry export for outside storage led to more NH3 emissions, except for the treatment T2.3, which has slurry funnel inserts beneath the slatted floor. Measurements of in-vitro CH4 production rates suggested that shorter residence time for slurry in pig houses delayed the development of active methanogenic populations, and that this contributed to the reduction of CH4 emissions.

Constructing CoAl-LDO/MoO3−x S-scheme heterojunctions for enhanced photocatalytic CO2 reduction

Converting CO2 into chemicals and fuels by solar energy can alleviate global warming and solve the energy crisis. In this work, CoAl-LDO/MoO3−x (LDO/MO) composites were successfully prepared and achieved efficient CO2 reduction under visible light. The CoAl-layered double oxides (CoAl-LDO) evolved from CoAl-layered double hydroxide (CoAl-LDH) exhibited a more robust structure, broader light absorption, and improved CO2 adsorption ability. The local surface plasmon resonance (LSPR) effect excited by nonstoichiometric MoO3−x broadened the photo-response range of CoAl-LDO/MoO3−x. In addition, constructing step-scheme (S-scheme) heterojunctions could simultaneously optimize the migration mechanism of photogenerated electrons and holes, and retain carriers with strong redox ability. Therefore, the production rates of CO and CH4 on the optimal LDO/MO composite were 7 and 9 times higher than the pristine CoAl-LDH, respectively. This work hybridizes oxidation photocatalysts and LDO-based materials to optimize the charge separation and migration mechanisms, which guides the modification of LDO-based materials.

Complexity of temperature dependence in methanogenic microbial environments.

There is virtually no environmental process that is not dependent on temperature. This includes the microbial processes that result in the production of CH4, an important greenhouse gas. Microbial CH4 production is the result of a combination of many different microorganisms and microbial processes, which together achieve the mineralization of organic matter to CO2 and CH4. Temperature dependence applies to each individual step and each individual microbe. This review will discuss the different aspects of temperature dependence including temperature affecting the kinetics and thermodynamics of the various microbial processes, affecting the pathways of organic matter degradation and CH4 production, and affecting the composition of the microbial communities involved. For example, it was found that increasing temperature results in a change of the methanogenic pathway with increasing contribution from mainly acetate to mainly H2/CO2 as immediate CH4 precursor, and with replacement of aceticlastic methanogenic archaea by thermophilic syntrophic acetate-oxidizing bacteria plus thermophilic hydrogenotrophic methanogenic archaea. This shift is consistent with reaction energetics, but it is not obligatory, since high temperature environments exist in which acetate is consumed by thermophilic aceticlastic archaea. Many studies have shown that CH4 production rates increase with temperature displaying a temperature optimum and a characteristic apparent activation energy (Ea). Interestingly, CH4 release from defined microbial cultures, from environmental samples and from wetland field sites all show similar Ea values around 100 kJ mol-1 indicating that CH4 production rates are limited by the methanogenic archaea rather than by hydrolysis of organic matter. Hence, the final rather than the initial step controls the methanogenic degradation of organic matter, which apparently is rarely in steady state.

Study Investigates Conversion of Biomethane From CO2 and Biohydrogen

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 22744, “Accelerated Methanogenesis for the Conversion of Biomethane From Carbon Dioxide and Biohydrogen at Hyperthermophilic Conditions,” by Ivy C.C. Hsia, Petronas, and Mohd F.A. Wahab and Nur K.A. Jalil, Universiti Teknologi Malaysia, et al. The paper has not been peer reviewed. Copyright 2023 International Petroleum Technology Conference. Reproduced by permission. _ Methanogenesis is the conversion of CO2 to methane (CH4) using microbes. In the context of CO2 usage, the process of methanogenesis using native microbes from a particular reservoir can be a very slow process without any external intervention. The study detailed in this complete paper investigates the use of agriculture byproducts such as palm oil mill effluent (POME) as substrates, along with potential microbial isolates that can produce biohydrogen at high temperatures. The authors write that stimulation of microbes using POME as substrate with hydrogen (H2)/CO2 supplementation is important in accelerating the rate and yield of CH4 production. Introduction The authors write that a population of microbes isolated from sludge of agriculture wastes, when given proper conditions and nutrients, was able to accelerate the rate of methanogenesis. POME is an agricultural byproduct from which a huge microbial community can be manipulated for methanogenesis, specifically for hydrogen production. This study incorporates the process of dark fermentation, using POME to generate hydrogen required to convert CO2 to CH4 in a syntrophic reaction at hyperthermophilic temperatures. Accounting for both the high reservoir temperatures (above 100°C) common to Malaysia and the temperature-tolerance limit of most microorganisms in general, the authors selected 70°C as the temperature to be studied. They write that, as their team studied a range of different temperatures, anaerobic microbes showed no production of biohydrogen and CH4 above 70°C.

Evaluation of biogas production rate and leachate treatment in Landfill through a water-energy nexus framework for integrated waste management

The aim of this study was to investigate the simultaneous biogas generation and leachate treatment using municipal waste and its polluted leachate at Mashhad landfill in northeast Iran. The research focused on examining the kinetic model of CH4, CO2, CO, H2S and O2 production with and without leachate recirculation (LR) through control/test wells. The findings from both wells showed an increase in logarithmic CH4 production rate, with the coefficient related to the rate of increase in methane concentration ranging from 0/52-0/64 in the control well and 0/47-0/55 in the test well, respectively. Under LR conditions, it was observed that the CH4 production rate was slower, taking an average of 120 minutes to reach 50% concentration, compared to just 15 minutes without LR. Using first-order equations, the CH4 production coefficients were measured to be 2/17 h−1 and 0/9 h−1 for the control and test wells, respectively. The analysis of recirculated leachate revealed a significant decrease (∼30%) in the total volume of leachate with 72% COD removal, which could help manage overloaded leachate problems in the landfill. The COD removal coefficient was found to be 0/036 day−1 in the control well, whereas the test well with leachate recirculation showed a more rapid decrease from 50 g.l−1 to about 14 g.l−1 with a removal coefficient of 0/012 day−1, three times higher than the control well. Additionally, nitrogen content analysis indicated that although the amount of ammonia content increased with LR, the increase was relatively low in comparison to conditions without LR, equivalent to 1394 ppm and 1000 ppm in control and test wells, respectively. This study aligns with the water-energy-nexus concept by offering a sustainable solution for waste management and energy generation, while also addressing water management challenges associated with landfill operations.

Flowable capacitive cathode for efficiency carbon dioxide reduction in photoelectrochemical cell

ABSTRACT Photoelectrochemical (PEC) Cell reduction carbon dioxide (CO2) is a promising avenue for converting CO2 into valuable products. In this work, a flowable electrode with a rotating impeller collector was proposed to enhance the efficiency of the carbon dioxide reduction reaction (CO2RR) in a photoelectrochemical system. Titanium carbide (Ti3C2), with its capacitive properties, serves as a catalyst and is fluidized in the cathode chamber. The frequent contact between the Ti3C2 catalysts and the rotating impeller collector extends the catalytic reaction throughout the catholyte and enhances the efficiency of CO2RR. The feasibility of the design was verified through suspension characterization, CO2 diffusion concentration measurement, capacitance characterization, and experimental factor analysis. The PEC with a flow electrode exhibits CO and CH4 production rates of 1.64 μmol g−1h −1and 9.62 μmol g−1h−1, respectively, which are 3.5 and 7.2 times higher than those of the fixed cathode. The Faradaic efficiency for CH4 reaches 92.4%. Moreover, the collision probability of the flow electrode is 17.7%, which is significantly higher than that of the conventional bubbling fluidized electrode. In addition, the capacitive properties of Ti3C2 particles favor the continuous CO2RR under open circuit conditions, which was verified by an EDS test of Na+. Finally, the operational mechanism of the PEC system is described.

Highly Efficient Photocatalytic CO2 Methanation over Ru-Doped TiO2 with Tunable Oxygen Vacancies

Solar-driven CO2 methanation is an imperative and promising approach to relieve the global warming and environmental crisis, yet remains a great challenge due to the low reaction efficiency, unsatisfactory selectivity and poor stability. In this work, we demonstrate a facile and efficient strategy to prepare Ru-doped TiO2 photocatalyst with tunable oxygen vacancies using the ascorbic acid as a reducing agent for the CO2 methanation reaction. The optimal Ru-TiO2-OV-50 exhibits a remarkable CH4 production rate of 81.7 mmol g−1 h−1 with a 100% CH4 selectivity under a 1.5 W cm−2 light illumination, which is significantly higher than commercial Ru/TiO2 and other reported catalysts. We reveal that the superior photocatalytic CO2 methanation performance is mainly due to the synergistic effect of Ru doping and TiO2 with tunable oxygen vacancies. Impressively, the light rather than thermal effect is confirmed as the main influencing factor by experimental studies. In addition, in situ spectroscopic technology is performed to investigate the CO2 methanation reaction pathway. This work will open an avenue to design and prepare highly efficient photocatalyst with tunable oxygen vacancies for CO2 conversion and other related applications.

Synergistic effects of heterointerface and surface Br vacancies in ultrathin 2D/2D H2WO4/Cs2AgBiBr6 for efficient CO2 photoreduction to CH4

Efficient photocatalytic conversion of CO2 to CH4 is challenging due to the complex eight-electron coupled proton transfer process. Herein, a 2D/2D H2WO4/Cs2AgBiBr6 (HWO/CABB) heterojunction was fabricated specifically through the “top-down” acid cleavage of layered Bi2WO6 (Bi2O2-WO4) into 2D HWO nanosheet, followed by the in-situ “bottom-up” epitaxial growth of 2D CABB on HWO nanosheet. Detailed characterizations revealed that HWO/CABB possessed abundant surface Br-vacancies (VBr) with an ultrathin 2D/2D heterointerface involving Bi-O and Ag-O bonds, facilitating charge transfer via an S-scheme. Density functional theory (DFT) calculations demonstrated that VBr could promote the adsorption/activation of CO2 and reduce the formation energy barrier of CHO* significantly. Therefore, HWO/CABB exhibited an enhanced CH4 production rate of 22.6 µmol·g−1·h−1 (the electron selectivity of 86.1%), approximately 30 times higher than that of pristine CABB. Furthermore, a plausible mechanism of photocatalytic CO2 to CH4 was proposed based on in-situ diffuse reflectance infrared spectroscopy and DFT calculations. This work demonstrates the potential of heterointerface and surface defects in synergistically tailoring CO2 selective reduction on halide perovskite photocatalysts.

Exfoliation of a Two-Dimensional Metal–Organic Framework for Enhanced Photocatalytic CO2 Reduction

A two-dimensional metal-organic framework, FICN-12, was constructed from tris[4-(1H-pyrazole-4-yl)phenyl]amine (H3TPPA) ligands and Ni2 secondary building units. The triphenylamine moiety in the H3TPPA ligand readily absorbs UV-visible photons and sensitizes the Ni center to drive photocatalytic CO2 reduction. FICN-12 can be exfoliated into monolayer and few-layer nanosheets with a "top-down" approach, which exposes more catalytic sites and increases its catalytic activity. As a result, the nanosheets (FICN-12-MONs) showed photocatalytic CO and CH4 production rates of 121.15 and 12.17 μmol/g/h, respectively, nearly 1.4 times higher than those of bulk FICN-12.

Photocatalytic reforming of acetic acid into methane over platinized TiO2 mediated by carbonate radical anion

In this research, Pt-loaded TiO2 was prepared by photodeposition used for acetic acid photocatalytic reforming. CO2 was injected into an acetic acid solution for removing O2 and inducing the formation of CO32–. The production rate of CH4 were higher in a CO2 atmosphere than that in an Ar atmosphere (about 69%). According to electron spin resonance (ESR) analysis, more •CH3 radical was produced in CO2 atmosphere, suggesting that CO2 introduced in acetic acid solution can better promote acetic acid reforming to CH4. On the contrary, the production rate of H2 is higher under an Ar atmosphere than that under CO2, suggesting a peroxidation of acetic acid transferred to H2.

Tunable Interfacial Charge Transfer in a 2D-2D Composite for Efficient Visible-Light-Driven CO2 Conversion.

Photocatalytic CO2 conversion for hydrocarbon fuel production has been known as one of the most promising strategies for achieving carbon neutrality. Yet, its conversion efficiency remains unsatisfactory mainly due to its severe charge-transfer resistance and slow charge kinetics. Herein, a tunable interfacial charge transfer on an oxygen-vacancies-modified bismuth molybdate nanoflower assembled by 2D nanosheets (BMOVs) and 2D bismuthene composite (Bi/BMOVs) is demonstrated for photocatalytic CO2 conversion. Specifically, the meticulous design of the Ohmic contact formed between BMOVs and bismuthene can allow the modulation of the interfacial charge-transfer resistance. According to density functional theory (DFT) simulations, it is ascertained that such exceptional charge kinetics is attributed to the tunable built-in electric field (IEF) of the Ohmic contact. As such, the photocatalytic CO2 reduction performance of the optimized Bi/BMOVs (CO and CH4 productions rate of 169.93 and 4.65µmol g-1 h-1 , respectively) is ca. 10 times higher than that of the pristine BMO (CO and CH4 production rates of 16.06 and 0.51µmol g-1 h-1 , respectively). The tunable interfacial resistance of the Ohmic contact reported in this work can shed some important light on the design of highly efficient photocatalysts for both energy and environmental applications.

Experimental Evaluation of Carrier Materials: A New Wood Ash Filter Material Comparison with Others Used for Ex-Situ Biomethanation

Biomethanation is a prospective method to integrate a renewable solar or wind power grid with a biogas grid, where excess energy can be used to produce hydrogen for the biomethanation of the biogas and produce biomethane. The use of biotrickling filter reactors with appropriate carrier materials for biomethanation is essential for the immobilisation of hydrogenotrophic methanogens on the surface of the packing material. Wood ash filter material use end-of-the-line waste ash as the main raw material for the production of filters. The wood ash filter material is a robust porous material that has good properties in the context of biomethanation. Testing packing materials in constantly operating biotrickling filter reactors would cost too much time and money. The purpose of this study is to compare a novel wood ash filter material with materials that are often applied in the sector. The study uses an effective methodology to test three alternative packing materials for use in a biotrickling filter. The manometric method and BMP test is used to determine the rate of CH4 production. The physical parameters such as bulk-specific surface area (m2 × m–3), external porosity (% vol), and bulk density (kg × m–3), and chemical composition of the novel wood ash filter material are compared to other filter materials commonly used in biomethanation applications. The results of the experiment determine whether the novel wood ash filter material or other tested materials can compete with and even replace some of the materials currently used in biomethanation applications.

Microbial organic matter reduction regulates methane and carbon dioxide production across an ombrotrophic-minerotrophic peatland gradient

Unraveling the mechanistic controls of methane (CH4) cycling in northern peatland ecosystems is crucial for understanding peatland-climate feedbacks. Growing evidence indicates that the microbial reduction of organic matter as a terminal electron acceptor can be a key regulator of CH4 production in peatlands, but the role of microbial organic matter reduction in different peatlands has not been well explored. Using an electron shuttling capacity assay, we investigated the relationship between the microbial reduction of organic matter and anaerobic CH4 and carbon dioxide (CO2) production in peatland soils in three experiments. In the first experiment, we surveyed the importance of microbial organic matter reduction in six soils representing the ombrotrophic-minerotrophic peatland gradient. In the second experiment, we further explored the reduction of solid-phase organic electron acceptors in a minerotrophic fen and compared these results to previously published values from an ombrotrophic bog (the end members of the initial gradient surveyed). Results from these experiments suggest that microbial organic matter reduction suppresses CH4 production, especially in ombrotrophic peat soils, likely helping to explain low CH4 production in bog-like soils. In contrast, the pool of oxidized organic matter was quickly reduced in minerotrophic peat soils which subsequently exhibited higher rates of CH4 production. In the final experiment, we investigated the effect of temperature on microbial organic matter reduction in the same ombrotrophic bog soil, demonstrating that warmer temperatures resulted in both a faster reduction of solid-phase organic matter and an apparent increase in the size of the organic electron acceptor pool that can be reduced by microbes. Future work should explore the drivers of the observed differences in microbial organic matter reduction in different peatland soils to provide a stronger mechanistic explanation for how this process will regulate peatland greenhouse gas dynamics in the face of global change, including increases in temperature.

The Synergistic Promotion Effect of In‐situ Formed Metal Cationic Vacancies and Interstitial Metals on Photocatalytic Performance of WO3 in CO2 Reduction

AbstractMicrostructure modulation of photocatalysts is an effective way to improve photocatalytic performances. The synergistic effect of metal cationic vacancies and interstitial metals on photocatalysts is rarely studied. In‐situ formations of metal cationic vacancies and interstitial metals are achieved in WO3 via acid treatments, resulting from the migration of metal impurities in WO3. Characterizations of structures, components, photo‐responsive and photoelectric properties identify the differences of WO3 photocatalysts via different treatments. The presence of both metal cationic vacancies and interstitial metal impurities exhibits the positive synergistic effect in photocatalytic reaction. Photocatalytic activities in CO2 reduction are enhanced with the high production rates of CO and CH4. Experimental characterizations of WO3 photocatalysts indicate the increased photoinduced electrons and photocurrent intensities, and the decreased electrochemical impedances. Theoretical simulations confirm the changes of electronic structures of WO3. The calculated band gaps of WO3 after acid treatment decrease and the defect energy levels form, which favor the separation and the transfer of photoinduced carriers for the promotion of photocatalytic activities. To utilize the dissolution difference of metals is feasible to fabricate metal cationic vacancies and interstitial metals simultaneously, an option for other metal‐containing photocatalysts with the in‐situ introduced impurities.

Insights into the Electron Transfer Behaviors of a Biocathode Regulated by Cathode Potentials in Microbial Electrosynthesis Cells for Biogas Upgrading.

Bioelectrochemical-based biogas upgrading is a promising technology for the storage of renewable energy and reduction of the global greenhouse gas emissions. Understanding the electron transfer behavior between the electrodes and biofilm is crucial for the development of this technology. Herein, the electron transfer pathway of the biofilm and its catalytic capability that responded to the cathode potential during the electromethanogenesis process were investigated. The result suggested that the dominant electron transfer pathway shifted from a direct (DET) to indirect (IDET) way when decreasing the cathode potential from -0.8 V (Bio-0.8 V) to -1.0 V (Bio-1.0 V) referred to Ag/AgCl. More IDET-related redox substances and high content of hydrogenotrophic methanogens (91.9%) were observed at Bio-1.0 V, while more DET-related redox substances and methanogens (82.3%) were detected at Bio-0.8 V. H2, as an important electron mediator, contributed to the electromethanogenesis up to 72.9% of total CH4 yield at Bio-1.0 V but only ∼17.3% at Bio-0.8 V. Much higher biogas upgrading performance in terms of CH4 production rate, final CH4 content, and carbon conversion rate was obtained with Bio-1.0 V. This study provides insight into the electron transfer pathway in the mixed culture constructed biofilm for biogas upgrading.

Effect of Ag-doping strategies on the Lewis acid/base behavior of mesoporous TiO2 photocatalyst and its performance in CO2 photoreduction

The nanostructure and doping of heteroelements are considered crucial for the photocatalytic reduction of CO2. Herein, we report the development and optimization of a mesoporous photocatalyst for the CO2 photoreduction (CO2PR) reaction through the integration of TiO2 with a CMK-3 template and template removal, followed by a focused study of silver-doping strategies using photodeposition and synchronous doping. Through investigating the effects of the charge-carrier recombination rates and acid/base behavior on CO2PR efficiency and product selectivity, we revealed that the influence on the CO2PR reaction follows the order of Lewis acid sites > Lewis base sites > charge-carrier recombination rates. Our proposed mechanism suggests that the Lewis acid sites regulate H+ production and control the CO and CH4 production rates and selectivity. In addition, we demonstrate irradiation-induced Lewis acid/base behavior of the photocatalyst by NH3-/CO2-temperature programmed desorption. Accordingly, our engineered photocatalyst comprising 1% synchronous Ag-doped mesoporous TiO2 calcinated at 470 °C (S-Ag1.0TC470) exhibited 96% CH4 selectivity and an 11-fold higher production yield than that of commercial P25.

Comparative effect of conductive and dielectric materials on methanogenesis from highly concentrated volatile fatty acids

Various conductive materials and their dielectric counterparts were used to get deeper insights into contribution of direct interspecies electron transfer (DIET) in improving methanogenesis from highly concentrated volatile fatty acids (12.5 g/L). Potential CH4 yield, maximum CH4 production rate and lag phase were significantly (up to 1.4, 3.9 and 2.0 times, respectively) improved with addition of stainless-steel mesh (SM) and carbon felt (CF) compared to both control and dielectric counterparts (p < 0.05). kapp increased by 82% for SM and 63% for CF compared to control (p < 0.05). Short thick pili-like structures up to 150 nm in width were formed only in CF and SM biofilms, however, were more abundant for SM. Ureibacillus and Limnochordia specific for SM biofilms, and Coprothermobacter and Ca. Caldatribacterium for CF biofilms, were considered electrogenic. Promotion of DIET by conductive materials is governed by many factors, including specificity of electrogenic groups to material surface.

Ir-CoO Active Centers Supported on Porous Al2 O3 Nanosheets as Efficient and Durable Photo-Thermal Catalysts for CO2 Conversion.

Photo-thermal catalytic CO2 hydrogenation is currently extensively studied as one of the most promising approaches for the conversion of CO2 into value-added chemicals under mild conditions; however, achieving desirable conversion efficiency and target product selectivity remains challenging. Herein, the fabrication of Ir-CoO/Al2 O3 catalysts derived from Ir/CoAl LDH composites is reported for photo-thermal CO2 methanation, which consist of Ir-CoO ensembles as active centers that are evenly anchored on amorphous Al2 O3 nanosheets. A CH4 production rate of 128.9 mmol gcat⁻ 1 h⁻1 is achieved at 250 °C under ambient pressure and visible light irradiation, outperforming most reported metal-based catalysts. Mechanism studies based on density functional theory (DFT) calculations and numerical simulations reveal that the CoO nanoparticles function as photocatalysts to donate electrons for Ir nanoparticles and meanwhile act as "nanoheaters" to effectively elevate the local temperature around Ir active sites, thus promoting the adsorption, activation, and conversion of reactant molecules. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) demonstrates that illumination also efficiently boosts the conversion of formate intermediates. The mechanism of dual functions of photothermal semiconductors as photocatalysts for electron donation and as nano-heaters for local temperature enhancement provides new insight in the exploration for efficient photo-thermal catalysts.

Surface engineering of full-spectrum sunlight-driven CdS/NaYF4: Yb, Er for boosting photocatalytic CO2 reduction reaction

The utilization of the Near-infrared (NIR) light accounting for about 52% in solar energy is meaningful and promising to enhance photocatalytic CO2 reduction reaction (CO2RR). In this study, an efficient ultraviolet-visible-near-infrared (UV-Vis-NIR) -activated photocatalyst for CO2RR is constructed by an in-situ surface heterojunction engineering, which is composited of nanosized CdS decorating on the up-conversion component of hexagonal NaYF4: Yb, Er (NYFYE). The as-obtained CdS/NYFYE composite photocatalyst not only shows significant CO2 reduction activities under NIR light but also exhibits a greatly boosted CO and CH4 production rate under simulated sunlight, in which the corresponding 3 h yields of CO and CH4 over CdS/NYFYE are ca. 2.7 and 4.3 times higher than that of pure CdS, respectively. Benefiting from the strong up-converted energy of NYFYE and the efficient energy transfer in the interfacial contact, the photocatalytic CO2RR can be effectively strengthened by the full spectrum of sunlight. Furthermore, the plausible photocatalytic mechanism for CO2RR over CdS/NYFYE is proposed. This work provides a feasible strategy for designing a new photocatalyst with utilization of sunlight and a durable structure to obtain high-efficiency CO2 reduction.

Impact of municipal solid waste landfill leachate on biogas production rate

Landfills/open dump sites are the final disposal facilities for municipal solid waste (MSW). These sites undergo continuous process of biochemical reactions and anaerobic degradation, which make them prone to generation of landfill gas (LFG) and leachate. Worldwide, the quantitative and qualitative assessment for leachate treatment and management has been a growing concern. The present study investigated the physico-chemical characteristics and heavy metal parameters for fresh, 3-month, 6-month and 3-year old landfill leachate samples. The total dissolved solids (13280 mg/l), alkalinity (13000 mg/l), chemical oxygen demand (42000 mg/l) and total organic carbon (16500 mg/l) was found to be maximum in 3-year old leachate sample. While, the 3 and 6-month old leachate samples had maximum heavy metal concentration. The attempt was also made to identify the key parameters responsible to enhance biogas production yield from different ages of MSW. The substrate combinations of MSW and 3-year old leachate samples was prepared at varying proportion. The study was performed in three cycles and the volume of leachate diffused in each cycle was kept constant. The control samples with no leachate diffusion was also prepared to compare the percentage increase in biogas production rate. It was found that the cumulative methane (CH4) production from fresh (358 ml/g) and 3-month old MSW (273 ml/g) was maximum, and the overall percentage increase was 43% and 32%. It was also conclusive that the excess leachate diffusion of >15 ml results in low calcination behaviour and CH4 production rate. The response surface methodology was used to correlate and validate independent input variables (volatile solids, C/N ratio and leachate concentration) responsible for maximum CH4 yield.