Generation Rate Constant Research Articles

Relativistic coupled-cluster simulation of the kinetics of the hydrolysis of uranium hexafluoride

Uranium hexafluoride ( UF 6 ) is used ubiquitously in the nuclear fuel cycle. Its spontaneous hydrolysis in the presence of atmospheric moisture is well known but the associated reaction mechanism is poorly understood. Here a computational study was undertaken with the aim of characterizing the rate-limiting step of the hydrolysis of UF 6 under dry conditions. Toward this end, we began by examining the convergence of various energy contributions to the atomization enthalpy ( Δ H at ) of UF 6 and its hydrolysis product, UO 2 F 2 . This enabled a refinement of our previous composite method, resulting in a composite method with improved accuracy that also scales well by leveraging existing massively-parallel codes. We find that extremely high levels of theory are required to obtain Δ H at within experimental error bars, in agreement with the literature. Having calibrated our composite scheme, we proceed to investigate approximations appropriate for computing accurate binding energies and barrier heights on the potential energy surface governing the hydrolysis of UF 6 . In combination with high-accuracy relative energies, a master equation approach is used to generate rate constants, and comparisons are made with recent measurements [Richards et al., RSC Adv., 2020, 10, 34729]. Based on kinetic and equilibrium arguments, we conclude that the hydrolysis of U F 6 , when proceeding under very dry conditions, is unlikely to be initiated via U F 6 + H 2 O → UF 5 OH + HF type reactions. Finally, computed equilibrium constants and rate coefficients are tabulated for the temperature range 300–1800 K.

Anaerobic digestion of herbal waste: a waste to energy option.

Herbal waste produced during the manufacturing of herbal products is a potential feedstock for anaerobic digestion due to high amount of organic matter that can be transformed into biogas as an energy resource. Therefore, the present study was undertaken to convert herbal waste produced during the manufacturing of common of Ayurveda products into biogas through anaerobic digestion process using batch test study under controlled mesophilic temperature conditions of 35°C with food to inoculum ratio of 0.75. The maximum biomethane potential (BMP) of 0.90 (gCH4COD/g CODfed) and sludge activity of 0.70 (gCH4-CD/gVSS) was exhibited by WS herbal waste owing to its high chemical oxygen demand (COD) of 4g/g and better solubilization potential of the organic matter showing change in volatile suspended solids (ΔVSS) of 79%. On the other hand, the waste derived from the TA herb, exhibited the least biogas yield of 0.55 (gCH4COD/g CODfed) and sludge activity of 0.40 (gCH4-CD/gVSS), albeit with higher organic matter present. This was due to the possible hindrance of waste solubilization by the presence of lignin. The waste derived from VVL and PE showed intermediate BMP and sludge activity. The methane generation rate constant (k), a key indicator of the biodegradation potential, was also evaluated. The k values showed similar trend as of BMP values ranging from 0.081 to 0.15 d-1 thus indicating the influence of presence of lignin and the change in ΔVSS. The present study proves anaerobic digestion to be an alternative treatment method to be a milestone for management of herbal wastes and can be successfully implemented on real-scale systems.

Complementary Field and Laboratory Batch Studies to Quantify Generation Rates of Perfluoroalkyl Acids in a Contaminated Agricultural Topsoil with Unknown Precursors

AbstractSoil microbiome changes and generation rates of per‐ and polyfluoroalkyl substances (PFAS) precursors were studied in a contaminated agricultural field using a combination of field and laboratory batch microcosm studies. 16S rRNA gene amplicon sequencing was used to track how microbial community composition changed over time, while perfluoroalkyl acids (PFAA) generation rates were quantified using a combination of field and batch incubations combined with the direct total oxidizable precursor (dTOP) assay. The study site in Brilon‐Scharfenberg, North Rhine‐Westphalia, Germany, has PFAS contamination in the topsoil (0 to 30 cm) originating from compost. Generation rate constants of these short‐chain PFAA estimated from batch incubations (0.12 to 0.75 1/year) were higher but similar to rate constants from the fields (0.05 to 0.22 1/year). Long‐term field mass discharge data (2009 to 2023) suggest that at least 60 years are needed to remove 99.99% of short‐chain PFAA and their precursors. 16S rRNA gene amplicon sequencing data revealed a major impact of PFAA on the biodiversity of soil microorganisms, with batch‐incubated contaminated soils showing higher richness and diversity indexes than field control soils. However, most of these impacts occurred at lower taxonomical ranks and did not seem to have a prominent impact on the overall structure of the autochtonous microbial communities of the soils where PFAA were produced and accumulated. Overall, our findings demonstrate that well‐controlled aerobic batch test combined with the results of dTOP assay are a suitable approach for estimating short‐chain PFAA generation rates. Additionally, our research suggests that the complete removal of PFAA precursors from topsoil will take decades.

Evaluation of the Methane (CH4) Generation Rate Constant (k Value) of Municipal Solid Waste (MSW) in Mogadishu City, Somalia

Landfills are the third largest source of the greenhouse gas methane, contributing to 25% of global warming. Therefore, the characterization of national municipal solid waste (MSW) and estimation of methane generation rate are very important for the solid waste management (SWM) toward sustainable development goal no. 13, climate action. This study presents (a) an assessment of daily MSW generation, (b) the characterization of MSW, and (c) an evaluation of the methane generation rate constant (k value) in Mogadishu, Somalia. The MSW samples were collected from three (3) sampling zones (Zones 1, 2, and 3; 204 households) and weighted (kg). Next, the waste generation per person per day was estimated. The MSW characterization includes sorting (based on plastic/polythene, food wastes, wood, metals, yard waste, paper/cardboard, textile, glass/ceramic and miscellaneous components, %), the determination of bulk density (kg/L), and measuring moisture content (%). The k values were evaluated from the percentages of different components in MSW based on first-order decay models. Mogadishu city generated 1671.03 kg MSW per week (maximum on Friday: 348.72 kg, and minimum on Monday: 152.04 kg). The total mean MSW generation rate observed in this study was 0.2 kg/person/day. The solid waste generation found was in the decreasing order of food waste > plastic/polythene > yard waste > miscellaneous > papers/carboard > wood > glass/ceramic > textiles > metals by weight. The average bulk density was found to be 0.269 kg/L. The average moisture content was ranged from 61.6 to 73%. The total k values were categorized as fast (Zone 1: 0.216053 yr−1, Zone 2: 0.228739 yr−1, and Zone 3: 0.244595 yr−1) and moderate (Zone 3: 0.244595 yr−1) degradation. This research serves as Somalian MSW baseline data and projected the methane generation rate from the MSW production in the country. The MSW sorting may reduce the impact of global warming and is highly recommended for better SWM in the future.

Employing controlled periodic illumination in identifying limiting factors of heterogeneous catalytic processes: A case study of photocatalytic generation of H2O2 and H2

Semiconductor photocatalysis is a versatile process that has been utilised in a wide range of applications from water treatment to sustainable energy generation and storage. In a heterogeneous photocatalytic reaction, identifying the limiting factor in a reaction is crucial in optimising operating parameters such as catalyst loading or irradiation intensity. With the application of Controlled Periodic Illumination (CPI), it is possible to control the intensity of photons entering the system. In this paper, two processes were evaluated and monitored by employing CPI to identify limiting factors: photocatalytic generation of H2O2 and H2. The relationship between catalyst loading and light intensity on H2/H2O2 generation constant rate was explored using CPI. In photocatalytic generation of H2O2, two commercial catalysts, TiO2 and ZnO were used under identical experimental conditions and the limiting factors on them differed. The effect of CPI varied greatly between both catalysts with TiO2 demonstrating that up to 50% less light is required to achieve comparable H2O2 formation rates at lower catalyst loadings (0.1 g L−1). In contrast, for ZnO photocatalysis, the CPI experiments highlighted the impact of adsorbed O2 levels, catalyst loading, and light intensity on H2O2 yields. The H2O2 formation rate constant plateaued beyond a duty cycle of 0.6 regardless of the tested catalyst loading. For photocatalytic generation of H2 on Pt/TiO2 from glucose, the generation rate constant increased linearly at low duty cycles and plateaued with different catalyst loading, which helped to identify different limiting factors for each condition. Therefore, exploring H2O2 and H2 generation via CPI is reported for the first time and the results show the importance of monitoring the interdependency of photocatalytic parameters and prove the validity of CPI on determining the limiting factor.

Fe2O3/coal fly ash Fenton-like catalyst for the elimination of organic pollutants in wastewater: Kinetic, mechanism, and application feasibility

Fe2O3/CFA was prepared by loading Fe2O3 on the surface of raw coal fly ash (RCFA), and then used as a Fenton-like catalyst to treat refractory organic wastewater. The characterization results of SEM-EDX, XRD, XPS, XRF, and BET test indicate that Fe2O3 is successfully loaded on the surface of RCFA, while the adsorption performance is not significantly affected. Under optimal treatment conditions of p-nitrophenol (PNP) simulated wastewater (H2O2 dosage = 8 mmol/L, Fe2O3/CFA loading = 6 g/L, pH = 3, and T = 303 K), the removal rate of PNP reaches 97.7 % at 50 min. There exist hydroxyl radicals (·OH), superoxide radicals (∙O2−) and singlet oxygen (1O2) in the Fenton-like system, and ·OH is the primary reactive oxygen species in the removal of PNP·H2O2 dosage, Fe2O3/CFA loading, and pH (i.e., [H+]) show different effects on the generation rate constant of hydroxyl radicals (k·OH), and the corresponding mathematic equation is k∙OH=6.51∙e−640.0T∙[H2O2]1.313∙[Fe2O3/CFA]1.093∙[H+]0.815. The Fenton-like process includes heterogeneous and homogeneous catalytic processes, and it is driven by the synergistic catalysis of multiple metallic elements; Fe and other metallic elements play major and auxiliary roles, respectively. In the advanced treatment of real coking wastewater, the catalytic capacity of Fe2O3/CFA can maintain 91.7 % in its 4th use, and the treatment cost is ¥4.15/ton, which can be decreased by further optimizing the preparation process of Fe2O3/CFA.

Nitrate Reduction through Al-Fe Alloy Catalyst: Effects of Activation Pre-Treatment Method and Alloy Type

This study explored the nitrate reduction by Al-Fe alloy. The nitrate conversions of fresh, 30-day and 90-day alloys were 78.1%, 42.8% and 9.5%, respectively. Water activation promoted the reducing ability of the alloy (98% nitrate removal), which was higher than that of copper deposited alloy (66%) and H2-reducing/acid/alkali/Cl− activated alloy (no enhancement). The effects of pre-treatments on the surface O fraction changes confirmed the activation results. With increased Fe:Al mass ratio in the alloy, nitrate conversion initially decreased and then increased again, verifying the proposed electron-donator activity of Al or Fe in alloys. Al-Fe30 had the highest NO3− conversion and Al13Fe4 content, so Al-Fe30 was selected. Significant differences in conversion were observed in alloy usages of 5–10 and 15–30 g/L. High reduction performance (nitrate below the detection limit and 19.1% N2 selectivity) was achieved under the optimal conditions: 15 g/L Al-Fe30, 150 min reaction and without pH adjustment. The rate constants of nitrate removal, nitrogen generation and ammonia generation were k1 = 1.43 × 10−2, k2 = 3.41 × 10−2 and k3 = 10.58 × 10−2 min−1, respectively. The value of (k2 + k3)/k1 was 10, indicating that the conversion of nitrate into nitrite was the rate-determining step. The repetition reaction was performed, and the rate constant decreased as the reaction step was repeated.

Improvement and optimization for the first order decay model parameters at typical municipal solid waste landfills in China

Landfill gas (LFG) generation is commonly modeled by using a first-order model. Methane generation potential (L0) and methane generation rate constant (k) are two key parameters in the first-order model. Coal-ash based default values or roughly analyzed values often used in China may not be appropriate for accurately estimating of LFG generation. In this study, seven groups of parameters were evaluated by comparing the theoretical predictions with real measurements from five Chinese landfills. The optimal approach for calculating L0 is the use of site-specific waste composition and the default values of degradable organic carbon (DOC) reported by the Chinese industry standard (CJJ133-2009), and the matching k can be adjusted by fitting and regression. The optimized average values were L0 = 67 m3 Mg−1, k = 0.06 per year for landfills in Beijing and Zhengzhou in cold–dry regions, L0 = 69 m3 Mg−1, k = 0.16 per year for landfill in Shanghai in cold–wet region, and L0 = 64 m3 Mg−1, k = 0.21 per year for landfills in Guangzhou and Shenzhen in hot–wet regions. Monte Carlo analysis showed that the uncertainty of LFG generation at closure year varied in −22.5% to 20.5%, −17.1% to 17.1% and −28.2% to 34.7% for three climatic regions, respectively. The k value is the key influencing factor, with a 95.6% contribution ratio in the hot–wet region landfill. The results provide references for future better waste management.

An optimal frequency regulation in interconnected power system through differential evolution and firefly algorithm

Automatic generation control is extensively used to regulate power plants in a modern area of the power system network. In this paper, automatic generation and frequency control in interconnected power system is presented. A multisource such as thermal, hydro, and gas-based power plant is considered in this study, which is carried out by incorporating nonlinearity like generation rate constants, HVDC link, and the conventional PID controller design. Further, an optimal setting of the PID controller is performed by employing evolutionary, and metaheuristic algorithm-based approaches such as differential evolution and firefly algorithm, respectively. With these algorithms, the proposed model has been tested with their performance evaluation and comparison characteristics are discoursed. The robustness of the proposed controllers is assessed based on comparative analyses to regulate the interconnected power network’s frequency profile under different loading conditions. The stability analysis is performed using the Eigen and Nyquist plots to assess the proposed controllers’ efficacy. Besides, the frequency control study is summarized with comparative assessment through various performance indices such as settling time, peak overshoot and undershoots under different operating conditions. Finally, the proposed control scheme, in the interconnected power system, is validated through a real-time digital simulation platform, i.e., OPAL-RT 5142. The comparison of simulation and real-time results demonstrates the effectiveness of the FA-optimized PID controller in comparison with that of the DE-optimized PID controller.

Sensitivity Analysis of Thermal Degradation of Plastic Waste Using Statistically Assumed Exponential Factors and Activation Energies.

The rise in the production of plastic waste has prompted the exploration of various recovery options instead of landfilling, burning, and other unethical ways of decomposing. The experimentally generated rate constants for the thermal processing of plastic waste do not yield enough liquid fuels and gases for commercial-scale usage. It is imperative to predict kinetic rate constants statistically using an appropriate combination of activation energies (E a) and frequency factors (A o) for the optimized thermal valorization of plastic waste. This approach also assists in controlling the selectivity and quantity of the pyrolysis products. A statistical kinetic model was tested to find the best combination of rate constants from different combinations of E a and A o to pyrolyze the high-density polyethylene. Two series of E a and A o were first assumed using R software. These series were then used to predict kinetic rate constants and analyze their sensitivity independently using MATLAB. The rate constants were varied from their originally predicted values during the sensitivity analysis. It was found that the rate constant k(7) dominated the other predicted rate constants where high oil and gas yields were concerned. The gas yield increased from lower to higher extreme positions in the range of 60%-74% with the first series and from 65% to 81% with the second series. The maximum oil content was found around 74% and 65% with the first series and second series, respectively.

Biomass derived bifunctional catalyst for the conversion of cassava dreg into sorbitol

A biomass derived bifunctional catalyst (Ru/CCD-SO3H) was used for one-pot conversion of cassava dreg and cassava starch into sorbitol. The cassava dreg is mainly composed of residual cassava starch and holocellulose. The highest sorbitol yield of 11.43 % was achieved using cassava dreg as reactant. A synergistic catalytic effect of acid and metal sites of Ru/CCD-SO3H on cassava starch conversion to sorbitol was observed. The maximum sorbitol yield reached 82.51 % using cassava starch as reactant. A kinetic model of cassava starch degradation was performed. The reaction rate constants of cassava starch degradation, glucose conversion and sorbitol generation improved with enhancing temperature. The activation energy of cassava starch hydrolysis is larger than that of glucose hydrogenation, indicating the cassava starch hydrolysis is rate-determining step of cassava starch conversion into sorbitol. This work not only realizes the comprehensive utilization of cassava dreg, but also provides useful guidance for developing kinetic model of polysaccharide conversion.

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.

The importance of particularising the model to estimate landfill GHG emissions

Methane generation in landfills can be estimated using mathematical models. One of the most widespread estimation models is that developed by the Intergovernmental Panel on Climate Change (IPCC). Despite its popularity, the simplicity that characterises this model markedly limits the possibility of representing operation alternatives, which can strongly impact surface emissions and hinder the introduction of local data that are sometimes available. In this study, the IPCC model was applied to a case study from which field data on gas emissions were available. To fit the model to the studied landfill conditions, a series of modifications were made, including changes in Degradable Organic Carbon (DOC) and methane generation rate constant (k) values, and degradation times for some waste fractions, and by considering leachate carbon and the inclusion of gas lateral migration phenomena or changes in the methane oxidation factor. The model's Final Version improved the fit of its Initial Version to the experimentally estimated values in the case study by more than 65%. Some modifications, such as considering the carbon dragged by leachate or the contour migration of gas, have a minor impact on the model's fit. However, changes in the degradation time of some fractions according to their particular pretreatment or the modification of parameter k in accordance with the moisture conditions in each landfill phase, strongly influence the model's results. This highlights the importance of particularising estimation models to achieve more accurate results, which allow better estimates of the efficiency of mitigation measures for landfill gas emissions in each facility.

A Theoretical Investigation into pH of Neat Water at the Nanoscopic Scale Via Rexpon Force Field and Stochastic Simulations

Design of durable solar CO2 conversion devices requires a mechanistic understanding of molecular-level reactions at the electrode-electrolyte interface that lead to interfacial degradation.[1] This interface often incorporates such features as a porous and rough surface to maximize active area and enhance catalytic performance. However, this roughness may introduce local water pool inclusions, whose size may have an unforeseen, detrimental impact on device durability due to their local pH being very different from the bulk pH. It is well-recognized that for water pools containing less than molecules, the solution pH cannot be defined in the conventional sense because the pools are too small to support stable water ion concentrations near neutral pH. Rather, the water ion concentrations fluctuate to very high values for short periods of time. To better understand pH in small pools, we combine theoretical calculations using QM/MD and stochastic simulations [3]. We combined Ab initio MD and the accurate RexPoN force field [2] simulation to quantify the thermodynamic free energy to create water ion pairs through the reaction as a function of the water pool size. The free energies are used to calculate the equilibrium constants for this reaction and the ion pair generation and recombination rate constants. The rate constants are then used as inputs to the stochastic simulations to gain insights into ion pair generation frequency and lifetime statistics over extended periods of time (hours). Proton and hydroxide diffusion are also incorporated in the stochastic simulation to understand how far water ions may travel from where they are generated. The results show that the combination of Grotthuss and vehicular diffusion mechanisms for H3O+ and OH- can lead to unequal distributions at an adjacent interface. We will discuss how the stochastic generation and recombination of water ions influences buffer chemistry and dissolved CO2 chemistry.Reference[1] S. Nitopi, E. Bertheussen, S.B. Scott, X. Liu, A.K. Engstfeld, S. Horch, B. Seger, I.E.L. Stephens, K. Chan, C. Hahn, J.K. Nørskov, T.F. Jaramillo, I. Chorkendorff, Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte, Chem. Rev. 119 (2019) 7610–7672. https://doi.org/10.1021/acs.chemrev.8b00705.[2] S. Naserifar, W.A. Goddard, The quantum mechanics-based polarizable force field for water simulations, J. Chem. Phys. 149 (2018). https://doi.org/10.1063/1.5042658.[3] W.D. Hinsberg, F.A. Houle, Kinetiscope, (n.d.). http://www.hinsberg.net/kinetiscope.

Quantification of Temperature‐Dependent Charge Separation and Recombination Dynamics in Non‐Fullerene Organic Photovoltaics

AbstractTransient optical spectroscopy is used to quantify the temperature‐dependence of charge separation and recombination dynamics in P3TEA:SF‐PDI2 and PM6:Y6, two non‐fullerene organic photovoltaic (OPV) systems with a negligible driving force and high photocurrent quantum yields. By tracking the intensity of the transient electroabsorption response that arises upon interfacial charge separation in P3TEA:SF‐PDI2, a free charge generation rate constant of ≈2.4 × 1010 s−1 is observed at room temperature, with an average energy of ≈230 meV stored between the interfacial charge pairs. Thermally activated charge separation is also observed in PM6:Y6, and a faster charge separation rate of ≈5.5 × 1010 s−1 is estimated at room temperature, which is consistent with the higher device efficiency. When both blends are cooled down to cryogenic temperature, the reduced charge separation rate leads to increasing charge recombination either directly at the donor‐acceptor interface or via the emissive singlet exciton state. A kinetic model is used to rationalize the results, showing that although photogenerated charges have to overcome a significant Coulomb potential to generate free carriers, OPV blends can achieve high photocurrent generation yields given that the thermal dissociation rate of charges outcompetes the recombination rate.

Chemical insights into the atmospheric oxidation of thiophene by hydroperoxyl radical

The reaction mechanisms and kinetics of thiophene oxidation reactions initiated by hydroperoxyl radical, and decomposition of the related intermediates and complexes, have been considered herein by using high-level DFT and ab initio calculations. The main energetic parameters of all stationary points of the suggested potential energy surfaces have been computed at the BD(T) and CCSD(T) methods, based on the geometries optimized at the B3LYP/6-311 + g(d,p) level of theory. Rate constants of bimolecular reactions (high-pressure limit rate constants) at temperatures from 300 to 3000 K for the first steps of the title reaction have been obtained through the conventional transition state theory (TST), while the pressure dependent rate constants and the rate constants of the second and other steps have been calculated employing the Rice–Ramsperger–Kassel–Marcus/Master equation (RRKM/ME). The results show that the rate constants of addition to α and β carbons have positive temperature dependence and negative pressure dependence. It is found that the additions of HO2 to the α and β carbons of thiophene in the initial steps of the title reaction are the most favored pathways. Also, the addition to the sulfur atom has a minor contribution. But, all efforts for simulating hydrogen abstraction reactions have been unsuccessful. In this complex oxidation reaction, about 12 different products are obtained, including important isomers such as thiophene-epoxide, thiophene-ol, thiophene-oxide, oxathiane, and thiophenone. The calculated total rate constants for generation of all minimum stationary points show that the addition reactions to the α and β carbons are the fastest among all at temperatures below 1000 K, while the proposed multi-step parallel reactions are more competitive at temperatures above 1200 K. Furthermore, important inter-and intra-molecular interactions for some species have been investigated by two well-known quantum chemistry method, the NBO and AIM analyses. Thermochemical properties such as free energy, enthalpy, internal energy, and entropy for thiophene and hydroperoxyl radical and related species in the simulated reactions have been predicted using a combination of the B3LYP and BD(T) methods.

Methane and nitrous oxide emissions from shallow windrow piles for biostabilisation of municipal solid waste

ABSTRACT Shallow windrow piles were applied as a low-cost option for biostabilisation of municipal solid wastes (MSW) prior to their utilization as refuse-derived fuel (RDF). A considerable amount of greenhouse gas (GHG) emissions can be emitted during the biostabilisation of MSW, especially when in operation under high moisture conditions such as there are in tropical Asia. This study investigated the emission of methane (CH4) and nitrous oxide (N2O) from shallow windrow piles – with heights of 0.5–1.0 m – for the stabilization of MSW at a full-scale facility in Thailand. Measurements of CH4, CO2, and N2O emissions using the static-chamber method revealed high spatial heterogeneity characteristics in all zones with different waste ages. Peak methane emissions were observed after four months of biostabilisation. The average spatial methane emissions from the waste piles ranged from 7.33 to 26.88 g m−2 d−1 (14.86 g m−2 d−1, on average). The CH4 generation-rate constant was within the range of 3.3 to 4.0 yr−1, which is higher than that reported – about 2.20–3.50 yr−1 – from a deep windrow pile (3.5–4.0 m height). The spatial distribution of N2O emissions was in the range of 4.51–199.14 mg N2O t−1dry wt.d−1 (6.6–111.7 mg N2O m−2 d−1), similar to those previously studied from landfill operations. This shallow windrow pile technique can be applied as low-cost technology for biostabilisation of MSW in developing countries, where land area is available. Implications: Shallow windrow pile was applied as a low-cost option for biological treatment of municipal solid waste in developing countries where land area is available. This study evaluated the greenhouse gas emission characteristics during the operation of windrow pile. The findings suggest that the emission rates were varied spatially with waste ages in different zones. Higher methane generation rate constant was derived from shallow window pile as compared to deep windrow pile. The methane and nitrous oxide emission factors were derived.

Modeling landfill gas potential and potential energy recovery from Thohoyandou landfill site, South Africa

ABSTRACT The increase in solid waste generation has been a major contributor to the amount of Greenhouse gases (GHGs) present in the atmosphere. To some extent, a great chunk of these GHGs in the atmosphere is from landfill. This study assesses two theoretical models (LandGEM and Afvalzorg models) to estimate the amount of landfill gas (LFG) emitted from Thohoyandou landfill site. Also, the LFGcost Web model was used to estimate the cost and benefits of the implementation of an LFG utilization technology. The Thohoyandou landfill started operations in the year 2005 and it is proposed to reach its peak at approximately in the year 2026. The LandGEM calculates the mass of landfill gas emission using methane generation capacity, mass of deposited waste, methane generation constant and methane generation rate. Meanwhile, the Afvalzorg model determines the LFG emissions using the Methane correction factor, yearly waste mass disposal, waste composition, Degradation Organic Carbon, methane generation rate constant, LFG recovery efficiency. The study findings indicate that the methane (CH4) and carbon dioxide (CO2) emitted from the landfill estimated from LandGEM will peak in the year 2026 with values of 3517 Mg/year and 9649 Mg/year, respectively. Results from the Afvalzorg model show that CH4 emission will peak in the year 2026 (3336 Mg/year). The LandGEM model showed that the total LFG, CH4 and CO2 emitted from the landfill between 2005 and 2040 are 293239.3 Mg/year, 78325.7 Mg/year and 214908.6 Mg/year, respectively. The simulation from the Afvalzorg model found that the CH4 emitted from the years 2005– 2040 is 74302 Mg/year. The implementation of an LFG utilization technology was economically feasible from consideration of the sales of electricity generated and Certified Emission Reductions (CER) (carbon credits). Implications The methane (CH4) and carbon dioxide (CO2) emitted from the Thohoyandou landfill estimated from LandGEM will peak in the year 2026 at 3517 Mg/year and 9649 Mg/year, respectively. The Afvalzorg model shows that CH4 emission will peak in the year 2026 (3336 Mg/year). The LandGEM model showed that total LFG, CH4 and CO2 emitted from the landfill between 2005 and 2040 (Mg/year) are 293,239, 78,325 and 214,908, respectively. The simulation from the Afvalzorg model found that CH4 emitted from years 2005– 2040 is 74,302 Mg/year. Therefore, implementation of LFG utilization is economically feasible from sales of electricity generated and Certified Emission Reductions.

Triclosan photolysis: operating condition study and photo-oxidation pathway

In this paper, Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol; TCS) photodegradation is studied by using a lab-scale experimental apparatus with a parametric variation study. Experiments were performed by using a lab view experimental set-up, consisting in a batch reactor (Petri dish) irradiated by UV-light at a wavelength of 254 nm and an UV dose of 400 mJ m−2. The effect of Triclosan initial concentration (TCS0), irradiated solution volume (V), solution initial pH (pH), nitrate anions (NO3−) and humic acids (HA) as a function of the irradiation time (0–60 min) is investigated, in order to study both direct photolysis and the combination of direct and indirect photolysis. Furthermore, TCS heterogeneous catalytic photolysis is studied when titanium dioxide (TiO2) is added to the experimental solution. The main obtained results have shown that TCS removal seems not to be significantly affected by TCS0 and V, while pH, NO3−, HA and TiO2 appear to be effective for TCS degradation; in particular, TCS photodegradation is enhanced by titanium dioxide. Finally, photo-oxidation by-product identification was performed, by determining 2,8-DCDD and 2,4-DCP as TCS photolysis reaction products, and a photoreaction pathway has been proposed, which allowed to assess TCS photolysis degradation rate constants, 2,8-DCDD and 2,4-DCP generation rate constants.

Intergovernmental panel on climate change's landfill methane protocol: Reviewing 20 years of application.

The Intergovernmental Panel on Climate Change (IPCC) protocol for predicting national methane emission inventories from landfills was published 22 years ago in the 1996 Revised Guidelines. There currently exists a broad dataset to review landfill parameters and reported values and their appropriateness in use and application in a range of site-specific, regional, and national estimates. Degradable organic carbon (DOC) content was found to range from 0.0105 to 0.65 g C/g waste, with an average of 0.166 g C/g waste. The fraction of DOC that would anaerobically degrade (DOC f) was reported to range from 50-83%, whereas higher and lower values have been experimentally determined for a variety of waste components, such as wood (0-50%) and food waste (50-75%). Where field validation occurred for the methane correction factor, values were substantially lower than defaults. The fraction of methane in anaerobic landfill gas ( F) default of 50% is almost universally applied and is appropriate for cellulosic wastes. The methane generation rate constant ( k) varied widely from 0.01 to 0.51 y-1, representing half-lives from 1 to 69 years. Methane oxidation (OX) default values of 0 and 10% may be valid, but values greater than 30% have been reported for porous covers at managed sites. The IPCC protocol is a practical tool with uncertainties and limitations that must be addressed when used for purposes other than developing inventories.