First-order Decay Model Research Articles

Biodegradation of phthalic acid esters by a novel marine bacterial strain RL-BY03: Characterization, metabolic pathway, bioaugmentation and genome analysis

Biodegradation is recognized as the main route for the decomposition of phthalic acid esters (PAEs) in nature, but the fate of PAEs in marine ecosystems is not well understood. Herein, a novel marine bacterium, Gordonia sihwaniensis RL-BY03, was identified and analyzed for its ability to degrade PAEs. Furthermore, the metabolic mechanism of di-(2-ethylhexyl) phthalate (DEHP) was examined through UPLC-MS/MS and genomic analysis. RL-BY03 could rely solely on several types of PAEs as its sole carbon source. Initial pH and temperature for DEHP degradation were optimized as 8.0 and 30°C, respectively. Surprisingly, RL-BY03 could simultaneously degrade ethyl acetate and DEHP and they could increase the cell surface hydrophobicity. DEHP degradation kinetics fitted well with the first-order decay model. The metabolic pathway of DEHP was deduced following the detection of five metabolic intermediates. Further, genes that are related to DEHP degradation were identified through genomic analysis and their expression levels were validated through RT-qPCR. A co-related metabolic pathway at biochemical and molecular level indicated that DEHP was turned into DBP and DEP by β-oxidation, which was further hydrolyzed into phthalic acid. Phthalic acid was utilized through catechol branch of β-ketoadipate pathway. Additionally, RL-BY03 exhibited excellent bioremediation potential for DEHP-contaminated marine samples. In general, these findings have the potential to enhance our understanding of the fate of PAEs in marine ecosystems.

Isotope Evidence for Rice Accumulation of Newly Deposited and Soil Legacy Cadmium: A Three-Year Field Study.

Biogeochemical processes of atmospherically deposited cadmium (Cd) in soils and accumulation in rice were investigated through a three-year fully factorial atmospheric exposure experiment using Cd stable isotopes and diffusive gradients in thin films (DGT). Our results showed that approximately 37-79% of Cd in rice grains was contributed by atmospheric deposition through root and foliar uptake during the rice growing season, while the deposited Cd accounted for a small proportion of the soil pools. The highly bioavailable metals in atmospheric deposition significantly increased the soil DGT-measured bioavailable fraction; yet, this fraction rapidly aged following a first-order exponential decay model, leading to similar percentages of the bioavailable fraction in soils exposed for 1-3 years. The enrichment of light Cd isotopes in the atmospheric deposition resulted in a significant shift toward lighter Cd isotopes in rice plants. Using a modified isotopic mass balance model, foliar and root uptake of deposited Cd accounted for 47-51% and 28-36% in leaves, 41-45% and 22-30% in stems, and 45-49% and 26-30% in grains, respectively. The implications of this study are that new atmospheric deposition disproportionately contributes to the uptake of Cd in rice, and managing emissions thus becomes very important versus remediation of impacted soils.

Efficient PFAS removal from contaminated soils through combined washing and adsorption in soil effluents

This study investigates soil washing as a viable strategy to remove poly- and perfluoroalkyl substances (PFAS) from contaminated soils using various washing agents including water, methanol, ethanol, and cyclodextrin ((2-Hydroxypropyl)-β-cyclodextrin HPCD)). Water was less effective (removing only 30 % of PFAS), especially for long-chain hydrophobic PFAS. Methanol (50 % v/v) or HPCD (10 mg g–1 soil) achieved > 95 % PFAS removal regardless of PFAS type, soil size fraction (0–400 µm or 400–800 µm), or experimental setups (batch or column, at liquid/solid (L/S) = 1). Column optimization studies revealed improved efficiency at L/S = 10 with diluted washing solutions, where HPCD exhibited rapid PFAS mobilization even at lower concentrations (1 mg mL–1). We then applied a first-order decay model to effectively predict PFAS breakthrough curves and mobilization within soil columns. Subsequent treatment of wash effluents by activated carbon and biochar effectively reduced PFAS concentrations below detection limits. The performance of both soil washing and subsequent adsorption was found to depend strongly on the specific characteristics of PFAS compounds. These findings highlight the significant potential of methanol and HPCD in soil washing and the effectiveness of integrated soil washing and adsorption for optimizing PFAS removal.

Chlorpyrifos degradation and its impacts on phosphorus bioavailability in microplastic-contaminated soil

Pesticide residues and microplastics (MPs) in agricultural soils are two major concerns for soil health and food safety. The degradation of chlorpyrifos (CPF), an organophosphorus pesticide, releases phosphates. This process may be affected by the presence of MPs in the soil. The combination of CPF and MPs presence in the soil may thus produce interaction effects that alter the soil phosphorus (P) balance. This study explores the degradation pathways of CPF (6 mg kg−1, 12 mg kg−1 of CPF addition) in soils with different levels of polylactic acid MPs (PLA-MPs) (0.0 %, 0.1 %, 0.5 %, 1.0 % w/w), and analyzes soil P fractions and phosphatase enzyme activities to investigate soil P bioavailability under different treatments. Results show that the degradation of CPF fits to a first-order decay model, with half-lives (DT50) ranging from 11.0 to 14.8 d depending on PLA-MPs treatment. The concentration of its metabolite 3, 5, 6-trichloropyridine 2-phenol (TCP) reached a peak of 0.93–1.67 mg kg−1 within 7–14 days. Similarly, the degradation of CPF led to a significant transient increase in P bioavailability within 3–7 days (p < 0.05), with a peak range of 22.55–26.01 mg kg−1 for Olsen-P content and a peak range of 4.63–6.76 % for the proportions of available P fractions (H2O-P+NaHCO3-P+NaOH-P), before returning to prior levels (Olsen-P: 11.28–19.52 mg kg−1; available soil P fractions: 4.15–5.61 %). CPF degradation (6 mg kg−1) was significantly inhibited in soil with 1.0 % PLA-MPs addition. The effects of MPs and CPF on soil P fractions occur at different time frames, implying that their modes of action and interactions with soil microbes differ.

Decay pattern of SARS-CoV-2 RNA surface contamination in real residences

The COVID-19 pandemic has provided valuable lessons that deserve deep thought to prepare for the future. The decay pattern of surface contamination by SARS-CoV-2 RNA in the residences of COVID-19 patients is important but still unknown. We collected 2,233 surface samples from 21 categories of objects in 141 residences of COVID-19 patients in Shanghai when attacked by the omicron variant in spring 2022. Several characteristics of the patients and their residences were investigated to identify relevant associations. The decay of contamination was explored to determine the persistence. Approximately 8.7% of the surface samples were tested positive for SARS-CoV-2 RNA. The basin, water tap, and sewer inlet had the highest positive rates, all exceeding 20%. Only time was significantly associated with the level of surface contamination with SARS-CoV-2, showing a negative association. The decrease fit a first-order decay model with a decay rate of 0.77 ± 0.07 day−1, suggesting a 90% reduction in three days. Positive associations between the cumulative number of newly diagnosed patients in the same building and the positive rate of SARS-CoV-2 RNA in the public corridor were significant during the three days. Our results, in conjunction with the likely lower infectivity or viability, demonstrate that fomite transmission played a limited role in COVID-19 spread. The time determined SARS-CoV-2 RNA contamination, which was reduced by three days. This study is the first to show the decay patterns of SARS-CoV-2 contamination in real residential environments, providing insight into the patterns of transmission, as well as community-based prevention and control of similar threats.

Landfill gas collection efficiency: Categorization of data from existing in-situ measurements

Landfill methane emissions are commonly estimated using cover-type dependent default collection efficiency values, with a first-order decay model or measured gas collection. Current default collection efficiencies used in the United States were predominately derived from 4 studies conducted during or prior to 2007 that relied on flux chambers. Flux chambers are limited by small sample sizes, placement restrictions, and the inability to measure emissions from gas or leachate collection systems. Since 2007, over 14 new studies have been completed using more advanced technologies that allow for direct measurement of methane plumes from most or all of a landfill’s surface. On average, these measurements are 2–3 times greater than emissions predicted by current models and collection efficiency defaults. In lieu of measuring emissions from all landfills, updating collection efficiency defaults can bring modeled emissions into better alignment with measurements. To this end, collection efficiency estimates derived from measured data were categorized into cover types and then adjusted to account for cases where whole plume measurement was an amalgamation of multiple cover types. The resultant adjusted default values were 41% for daily cover, 69% for intermediate cover, and 71% for final cover. Direct measurement of landfill methane emissions is preferrable to account for the full range of variables driving landfill emissions, including collection system design and operation. However, applying these updated defaults back into the landfill emission models eliminates underprediction of landfill emissions for the dataset reviewed, and would provide a more accurate estimate of landfill gas emissions where measurements are unavailable.

Dynamic changes in carbohydrate components and the bacterial community during the ensiling of wilted and unwilted sweet sorghum.

Sweet sorghum can be used to produce a substantial quantity of biofuel due to its high biological yield and high carbohydrate content. In this study, we investigated the dynamic changes in fermentation characteristics, carbohydrate components, and the bacterial community during the ensiling of wilted and unwilted sweet sorghum. The results revealed a rapid fermentation pattern and high-quality fermentation quality in wilted and unwilted sweet sorghum, wherein lactic acid, and acetic acid accumulated and stabilized during the initial 9 days of ensiling, with the pH values less than 4.2, until 60 days of ensiling. We found that the ensiling of sweet sorghum involved the degradation (5% ~ 10%) of neutral detergent fiber (NDF) and hemicellulose and that the degradation of NDF fit a first-order exponential decay model. A shift in dominance from Lactococcus to Lactobacillus occurred before the first 9 days of ensiling, and the abundance of Lactobacillus (r = -0.68, p < 0.001) was negatively correlated with the NDF content. The relative abundances of Lactobacillus in wilted and unwilted sweet sorghum after ensiling for 60 days were 76.30 and 93.49%, respectively, and relatively high fermentation quality was obtained. In summary, ensiling is proposed as a biological pretreatment for sweet sorghum for subsequent biofuel production, and unlike other materials, sweet sorghum quickly achieves good fermentation quality and has great potential for bioresource production.

Estimation of Landfill Gas and Its Renewable Energy Potential from the Polesgo Controlled Landfill Using First-Order Decay (FOD) Models

Estimation of Landfill Gas and Its Renewable Energy Potential from the Polesgo Controlled Landfill Using First-Order Decay (FOD) Models

Anaerobic digestion of the organic fraction of municipal solid waste in a simulated bioreactor to improve predictive modeling of landfill systems

Municipal solid waste (MSW) generation is increasing globally, containing up to 57 % organic matter. Trapping and extraction of methane (CH4) produced via anaerobic digestion (AD) of the organic fraction of MSW (OFMSW) reduces CH4 released from landfills into the atmosphere. To estimate CH4 production from OFMSW, mathematical models are frequently used, but their accuracy varies under the non-ideal conditions that are inevitable in real landfilling scenarios. This work calibrates first-order decay (FOD) and Gompertz models for predicting CH4 production from the OFMSW based on experimental results from a pilot-scale landfill bioreactor operating under non-ideal conditions, namely under dry and mesophilic conditions with low leachate recirculation inteded to represent landfills in developing countries. This study achieved a 73 % and 66 % reduction in volatile solids (VS) and total solids (TS), respectively, demonstrating successful organic degradation. Models were calibrated using laboratory data, showing high correlation and accuracy >80 % in a Chemical Oxygen Demand (COD) mass balance. The experiment produced 104.3 mL CH4 g−1 VS with accurate predictions from calibrated models Non-calibrated models, however, overestimated methane production by 75 %. Work highlights the importance of modifying models for non-ideal conditions, and results provide useful information for landfills in developing countries.

Respiration and carbon use efficiency characteristics of soluble protein-derived carbon by soil microorganisms: A case study at afforested sites

Soluble protein plays a significant role in the release of carbon dioxide (CO2) in soils. However, our understanding of the respiration and C use efficiency (CUE) characteristics of soluble protein-derived C by soil microorganisms is limited. To address this issue, we sampled surface soils (0−10 cm) from seven tree monocultures and examined the temporal dynamics of turnover of 14C-labelled soluble protein-derived C by soil microorganisms. Two double first-order exponential kinetic decay models were applied to analyze the mineralization data (i.e., with and without abiotic protein-surface interactions). The model incorporating the immobilization of protein on the non-living solid phase exhibited the best fit to the experimental data (R2 > 99.6%). Our results suggest that 66.1−73.9% of the soluble protein-derived C was immobilized by the non-living solid phase in soils. After uptake by the soil microbial community, 8.0−13.8% of the C was rapidly respired as CO2, while 15.0−20.8% was used in anabolic processes, resulting in a CUE of 55.1–70.2%. However, there was little effect of forest type on protein turnover rate in the soil. The C:N ratio of soil microbial biomass (C/Nmic) was positively related to the CUE of protein and exhibited less variation within a forest type. Compared with soil microbial biomass C and N, C/Nmic could serve as a better indicator of the CUE of protein by soil microorganisms. This study sheds light on the respiration and CUE characteristics of soluble protein-derived C by soil microorganisms at afforested sites and enhances our understanding of the trade-off between the metabolism of protein-derived C by soil microorganisms and its immobilization by the non-living solid phase in soils.

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 &gt; plastic/polythene &gt; yard waste &gt; miscellaneous &gt; papers/carboard &gt; wood &gt; glass/ceramic &gt; textiles &gt; 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.

Outflow risks of antibiotic-resistant bacteria in stormwater bioretention cells: understanding roles of adsorption and transmission.

In this study, lab-scale bioretention cells were designed for the investigation of antibiotic-resistant bacteria (ARB) outflow profiles at different depths, effects of adsorption and transmission, as well as modelling evaluation of ARB outflow risks using the common decay models (e.g., first-order decay models). ARB outflow was first found in the upper layers (after 100 days of the operation) with the lowest transmission frequencies of antibiotic resistance. Although the adsorption of ARB onto the substrate and its surface biofilms was effective with the maximum amount of ARB adsorbed (Qmax) reaching 108 CFU/g of the substrate and 107 CFU/g of biofilms, ARB outflow was detected in the bottom outlets after over 4 months of operation, reflecting that there was still a risk of antibiotic resistance through the treatment of bioretention cells. ARB outflow for both upper and middle outlets could be well described by third-order polynomial equations with correlation coefficients 0.9067 (p = 0.0002) and 0.9780 (p < 0.0001), respectively, where there were both positive and negative relationships between outflow ARB and inflow ARB, confirming the combined action of mechanisms blocking ARB outflow (e.g., substrate adsorption) and promoting ARB outflow (like transmission). These suggested two potential controlling approaches for ARB outflow from stormwater bioretention cells.

Biotransformation of cyproterone acetate, drospirenone, and megestrol acetate in agricultural soils: Kinetics, microbial community dynamics, transformation products, and mechanisms

The occurrence of biologically active synthetic progestins in agricultural soils is of growing concern due to their potential to disrupt the endocrine function of aquatic fish in nearby surface waters. This study investigated the biotransformation outcomes of cyproterone acetate (CPA), drospirenone (DRO), and megestrol acetate (MGA) in four agricultural soils. The biotransformation data were fitted to a first-order decay model (R2 = 0.93–0.99), with half-lives and first-order decay coefficients ranging from 76.2–217 h and 9.10 × 10−3–3.20 × 10−3 (h−1), respectively. Abundant biotransformation products (TPs) were generated during incubation, with the number and yields varying across the four soils. 1,2-Dehydrogenation was the main transformation pathway of DRO in the four soils (yields of 32.3–214 %). Similarly, 1,2-dehydrogenation was the most relevant transformation pathway of MGA in the four soils (yields of 21.8–417 %). C3 reduction was the major transformation pathway of CPA in soils B, C, and D (yields of 114–245 %). Hydrogenation (yield of 133 %) and hydroxylation (yield of 21.0 %) were the second major transformation pathway of CPA in soil B and C, respectively. In particular, several TPs exhibited progestogenic and antimineralocorticoid activity, as well as genotoxicity. The high-throughput sequencing indicated that interactions between microorganisms and soil properties may affect biotransformation. Spearman correlation and bidirectional network correlation analysis further revealed that soil properties can directly interfere with the soil sorption capacity for the progestins, thus affecting biotransformation. In particular, soil properties can also limit or promote biotransformation and the formation of TPs (i.e., biotransformation pathways) by affecting the relative abundances of relevant microorganisms. The results of this study indicate that the ecotoxicity of synthetic progestins and related TPs can vary across soils and that the assessment of environmental risks associated with these compounds requires special consideration of both soil properties and microbial communities.

Techno-economic and environmental assessment of the landfill gas to energy potential of major Colombian cities

Landfills account for significant methane emissions worldwide. However, municipal solid wastes can be energetically revalorized using landfill gas-to-energy (LFGtE) systems. This study assesses from a technical, economic, and environmental point of view the potential to implement LFGtE in major Colombian cities, including Bogota, Medellin, Cali, Barranquilla, Cartagena, and Bucaramanga, and the smaller capital city of Sincelejo. Municipal solid waste disposal rates in these cities are forecasted using the exponential smoothing (ETS) method. Additionally, methane emissions are forecasted using the first-order decay model, in line with the U.S. EPA methodology. Moreover, the methane generation capacity of the decomposable organic fractions of MSW is calculated following guidelines from IPCC. The assessment includes four scenarios with electricity and heat generation for each city. These scenarios consider using gas turbines, reciprocating internal combustion engines, and cogenerating electricity and heat. The economic performance is assessed with the net present value (NPV), the internal rate of return (IRR), the profitability index, the benefits-costs ratio, and the economic sensitivity analysis. Finally, the environmental performance is assessed by calculating the GHG emissions reduction potential and avoidance potential. The results show an electric power generation potential of 1.6 MWe to 47.5 MWe, a heat potential of 9.6 MW to 54.8 MW to produce steam, and 1.7 MW to 49.2 MW to produce hot water. The scenarios show economic profitability with NPV values of 5.3 million USD to 201.9 million USD.11M$: Millions of USD. At the same time, IRR varies from 14.9 % to 31.1%, a profitability index of 2.4 to 7.0 million USD, and a benefits-costs ratio of 1.3 to 1.6 million USD. Overall, scenarios consider using combustion engines to show the best economic performance. The potential to reduce greenhouse gas emissions was quantified in 1.2 MtCO2e to 40.0 MtCO2e, while the avoidance potential of greenhouse gas emissions varies between 0.1 and 4.3 MtCO2e depending on the scenario and the city.

Considerations on the methane correction factor and fraction of methane parameters in the IPCC first-order decay model for active aeration landfills

Understanding the behavior of organic carbon in municipal solid waste landfills is a major challenge for estimating methane (CH4) emissions using the Intergovernmental Panel on Climate Change (IPCC) first-order decay (FOD) model. According to the IPCC guidelines, the default values of CH4 correction factor (MCF) and fraction of CH4 (F) for active aeration landfills are set as 0.4 and 0.5, respectively. However, whether it is reasonable to apply the default values of MCF and F to active aeration landfills is questionable. This study aims to estimate the MCF and develop a method to determine the F value for active aeration landfills. In this investigation, three landfill sites were operated as active aeration landfills to estimate the MCF and the F. The study results indicate that MCF values were lower than the default value of 0.4 provided in the IPCC guidelines under aerobic conditions with a CH4 concentration of less than 5%. According to the carbon balance analyses, there was a mismatch between the theoretical CH4/CO2 ratio based on the F default value of 0.5 and the measured CH4/CO2 ratio. Using the F calculation method proposed in this study, the theoretical CH4/CO2 ratio and the measured CH4/CO2 ratio was calculated equally. The F values during air injection ranged from 0.25 to 0.93 at three landfill sites, suggesting that adapting the F default value of 0.5 for active aeration landfills may lead to significant errors in the estimation of CH4 emissions using the IPCC FOD model.

Evaluation of stabilization status of the landfill layers by comparing long-term monitoring data of methane emission with FOD model estimate

ABSTRACT Long-term monitoring and treatment of landfill leachate (LFL) and landfill gas (LFG) is required until landfilled municipal solid waste (MSW) is sufficiently stabilized and post-closure care can be terminated. Monitoring data of methane (CH4) emissions in LFG from a marine landfill over 30 years were compared with the IPCC first order decay (FOD) model estimates. The observed changes in CH4 showed a similar attenuation trend to the estimates, but the observed CH4 emissions were only about 30% of the estimate over 30 years; LFL is considered to be another pathway for organic carbon to be released to the environment, but the total organic carbon in discharged LFL was only about 0.2% of CH4 carbon in LFG emission over the same period. The increase in the CO2/CH4 ratio in LFG over time suggests that the discrepancy between estimated and observed emissions is due to methane oxidation in the overlying soil, in addition to the high coefficient values used in the FOD model. Total organic carbon (TOC) in LFL discharged as effluent reached a maximum value in the early stages of the landfill and gradually decreased, but only to about one-third of the maximum value after more than 30 years and a decrease in the amount of effluent. As incineration of MSW is expected to reduce organic carbon and nitrogen, the CH4 reduction effect of incineration of business and household waste and sewage sludge was investigated using FOD model estimates.

Bioremediation of PAEs-contaminated saline soil: The application of a marine bacterial strain isolated from mangrove sediment

Phthalic acid esters (PAEs) are known as the most widely used plasticizer as well as one of the ubiquitously distributed emerging pollutants. Biodegradation and bioremediation via application of PAEs-degrading microbes is promising. In this study, a novel marine microbe, Gordonia hongkongensis RL-LY01, was isolated from mangrove sediment showing high di-(2-ethylhexyl) phthalate (DEHP) degradation capacity. Strain RL-LY01 could degrade a wide range of PAEs and the degradation kinetics of DEHP followed the first-order decay model. Meanwhile, good environmental adaptability, preference to alkaline conditions and good tolerance to salinity and metal ions was shown. Further, metabolic pathway of DEHP in strain RL-LY01 was proposed, with di-ethyl phthalate, phthalic acid, benzoic acid and catechol as intermediates. Additionally, one known mono-alkyl phthalate hydrolase gene (mehpH) was identified. Finally, the excellent performance during bioremediation of artificial DEHP-contaminated saline soil and sediment indicated strain RL-LY01 employs great application potential for the bioremediation of PAE-contaminated environments.

Optimization of landfill gas generation based on a modified first-order decay model: a case study in the province of Quebec, Canada

Landfills will likely remain an essential part of integrated solid waste management systems in many developed and developing countries for the foreseeable future. Further improvements are required to model the generated gas from landfills. The literature has not addressed detailed waste characterization in landfill gas (LFG) modeling by a first-order decay model such as LandGEM while using a genetic algorithm. Additionally, little has been done in the literature regarding H2S generation modeling. This paper uses a genetic algorithm to independently fit parameters to a CH4 and H2S generation model based on a modified first-order decay model. In the case of CH4 generation modeling, biodegradable organic waste (OW) was segregated into food waste, yard waste, paper, and wood. In addition to optimizing the OW fractions, key modeling parameters of OW, such as CH4 generation potential ({L}_{0}) and CH4 decay rate ({k}_{C{H}_{4}}), were determined independently for different periods in the landfill’s life. Similarly, in the case of H2S generation modeling, the construction and demolition waste (CD) was classified into fines (FCD) and bulky materials (BCD), and H2S generation potential ({S}_{0}) and H2S decay rate ({k}_{{H}_{2}S}) of FCD and BCD were determined. LFG collection data from a landfill site in the province of Quebec, Canada, was used to validate the LFG generation model. A range of scenarios was analyzed using the validated model, including fourteen scenarios (two benchmark and twelve optimizing) for CH4 and two for H2S modeling. The results showed that the differentiation of more waste types improves the modeling accuracy for CH4. Moreover, within the decade-long lifetime of a landfill, the waste management strategies change, requiring different assumptions for the modeling. Also, the work showed the importance of considering how different landfill sectors are filled over time. Finally, scenario twelve of optimizing scenarios, which assumed four waste types, constant three periodic waste fractions, and six sectors, had the lowest residual sum of squares (RSS) value. For H2S generation modeling, both scenarios, with or without separate fits of {S}_{0} and {k}_{{H}_{2}S} for FCD and BCD, predicted the generated H2S well and had a very similar RSS value. Further data could improve H2S generation modeling.

Experimental research on formaldehyde emission characteristics from glubam by climate chamber test

Glued laminated bamboo (glubam) is a type of bamboo-based lamina, and manufactured by pressure lamination of phenol-formaldehyde saturated bamboo strips under elevated temperature. Estimating, controlling, and limiting the formaldehyde release from glubam are important issues in indoor air quality of building with glubam. This study investigates formaldehyde emission characteristics from two types of glubam under different conditions including temperature, relative humidity, edge treatment, and surface covering material. A series of formaldehyde concentration tests were performed using 1 m3 climate chamber. The results indicate that the peak values of the formaldehyde concentration of glubam specimens under all testing conditions are lower than 0.124 mg/m3, and thus can be classified as Class E1 according to EN 13986. An analysis model was provided to estimate formaldehyde release based on the test data and a first-order decay model. Initial formaldehyde emission rate E0 and decay rate constant k in the proposed model was utilized for comparison and analysis of the experimental parameters. This investigation reveals that the temperature and relative humidity have significant influence on the formaldehyde emission characteristics of glubam boards. Sealing cutting edges and covering surface layer of the samples can significantly reduce the releasing rate and amount of formaldehyde from glubam.

Enhancement of Biomass Conservation and Bioethanol Production of Sweet Sorghum Silage by Constructing Synergistic Microbial Consortia.

The efficient storage of materials before bioethanol production could be key to improving pretreatment protocol and facilitating biodegradation, in turn improving the cost-effectiveness of biomass utilization. Biological inoculants were investigated for their effects on ensiling performance, biodegradability of silage materials, and final bioethanol yield from sweet sorghum. Two cellulolytic microbial consortia (CF and PY) were used to inoculate silages of sweet sorghum, with and without combined lactic acid bacteria (Xa), for up to 60 days of ensiling. We found that the consortia notably decreased pH and ammonia nitrogen content while increasing lactic acid/acetic acid ratios. The microbes also functioned in synergy with Xa, significantly reducing lignocellulose content and improving biomass preservation. First-order exponential decay models captured the kinetics of nonstructural carbohydrates and suggested high water-soluble carbohydrate (grams per kilogram dry matter [DM]) preservation potential in PY-Xa (33.48), followed by CF-Xa (30.51). Combined addition efficiently improved enzymatic hydrolysis and enhanced bioethanol yield, and sweet sorghum treated with PY-Xa had the highest ethanol yield (28.42 g L-1). Thus, combined bioaugmentation of synergistic microbes provides an effective method of improving biomass preservation and bioethanol production from sweet sorghum silages. IMPORTANCE Ensiling is an effective storage approach to ensure stable year-round supply for downstream biofuel production; it offers combined facilities of storage and pretreatment. There are challenges in ensiling sweet sorghum due to its coarse structure and high fiber content. This study provides a meaningful evaluation of the effects of adding microbial consortia, with and without lactic acid bacteria, on changes in key properties of sweet sorghum. This study highlighted the bioaugmented ensiling using cellulolytic synergistic microbes to outline a cost-effective strategy to store and pretreat sweet sorghum for bioethanol production.