Methane Concentration Research Articles

Methane and sulfide sulfur in water and bottom sediments of streams of the steppe zone of the European part of Russia

The results of long-term studies of the conjugate distribution of concentrations of methane (CH 4 ) and sulfide sulfur (S sulfide ) in bottom sediments of streams of the steppe zone of the European part of Russia are analyzed. In addition to CH 4 and S sulfide , Eh and pH values, humidity and density were determined in various sediment horizons; CH 4 , dry residue and pH values were determined in water. Concentrations of CH 4 in the water of watercourses vary from 0.1 to 2007.0 µl/l (median 24.3 µl/l), with the largest number of values (72 %) in the range 10.1–100.0 µl/l. The concentrations of CH 4 and Ssulfide in the bottom sediments of watercourses are quite high and vary, respectively, from 0.01 to 51.0 µg/g of wet sediment (median 1.35 µg/g) and from 0.001 to 4.50 mg/g of wet sediment (median 0.813 mg/g). Usually, there is an increase in CH 4 and S sulfide from the surface layer to the subsurface horizons, after which their concentrations decrease. The difference between the distribution of sulfides and the distribution of CH 4 is the more frequent occurrence of maximum concentrations of sulfides in less deep sediment horizons. Seasonal changes in the distribution of CH 4 and S sulfide along the vertical of sediments were recorded not only in terms of their concentrations, but also in the location of maximum and minimum values. There is a weak direct relationship between the concentrations of CH 4 and S sulfide , which indicates synchronous processes of formation of these gases in separate layers of sediments of the studied watercourses. The direct relationship established between the concentrations of CH 4 in water and the 0–2 cm layer of bottom sediments indicates sediments as an important source of CH 4 entering water and its emission into the atmosphere.

Evaluation of additive effecton anaerobic sewage sludge digestion

An additive based on iron oxides was applied to reduce the amount of produced sludge and to increase the production and quality of biogas. The C/N ratio was 11.0–11.3 and the pH of the sludge mixture was 7.3 before the anaerobic digestion. The determined optimal dose of the additive was 0.35 g/g of sludge dry matter over 20 days. This allowed a reduction in the sludge retention time up to 6–11 days. Consequently, maximum biogas production was reached on average 1.6 times faster, volatile solids degradation increased by 56.7%, biogas production increased by 75%, specific biogas production increased by 11.5%, and methane concentration in the biogas increased by 8.4%–18.2%. When the additive was applied, the quantity of phosphate phosphorus in the supernatant was reduced by up to 19%, and hydrogen sulfide reduction efficiency in the biogas ranged between 55% and 62%. In sludge treatment facilities, using an iron oxide-based additive could reduce the dewatering and drying costs for digested sludge by up to 35% .

Operation of solid municipal waste landfills in northern climates

The author considers specific features of operation of solid municipal waste landfills at the post-operation stage in northern climate conditions. It is emphasized that safe operation of landfills requires efficient management of landfill gas and leachate formation. Increased precipitation leads to increased waste moisture content and, as a consequence, to methane generation during different seasons. The author presents the results of measuring methane concentrations and calculating leachate volumes at a landfill located in the north-west of Russia. The conclusion is made about the need to control and manage leachate formation, as well as to take measures for its treatment to prevent environmental and sanitary-hygienic problems associated with evaporation and accumulation of leachate.

Study on the Lower Explosion Limit of Ventilation Air Methane at 700–1200℃

ABSTRACT Regenerative thermal oxidation (RTO) of Ventilation Air Methane (VAM) is an environmentally friendly technology for harnessing heat energy. Higher concentrations of methane can improve utilization efficiency, but it suffers from a high risk of explosion. The lower explosive limit (LEL) of methane at temperatures of 700–1200°C is determined using a self-designed experimental apparatus, and the mechanism at the LEL is analyzed using the GRTO (Gas regenerative thermal oxidation) model constructed by our research group. Results reveal that a linear correlation between the LEL and temperature within 700–1200°C. As the temperature rises, the LEL exhibits a consistent decline. Furthermore, the maximum concentration of VAM in RTO process is elucidated, with an average of 95.3% of LEL. The concentration of ·OH determines the explosive severity at the LEL, and methane explosions are dominated by H+O2⇔O+OH and H2+ OH⇔OH+H2O. 2CH3(+M)⇔C2H6(+M) plays a vital role in inhibiting methane explosion, and its inhibitory effect decreases by 59.5% at 1200°C compared to 700°C.

Investigation of the Products and the Migration of Sodium and Chlorine During Pyrolysis of High‐Sodium Coal Mixed With Phosphorite

ABSTRACTThe impact of adding phosphorite during the pyrolysis of high‐sodium Shaerhu coal to address severe deposition and corrosion issues caused by the release of volatile sodium and chlorine compounds was explored. During pyrolysis, sodium compounds volatilize and condense on cooler surfaces, leading to deposits that corrode metal and reduce boiler efficiency. By copyrolyzing phosphorite with coal, the study finds that tar yield decreases, whereas char yield increases, with slightly improved char reactivity. The pyrolysis gas yield also increases, with higher concentrations of methane and hydrogen, enhancing energy utilization. Calcium compounds in phosphorite react with sodium chloride and sodium sulfate, forming high‐melting‐point, insoluble sodium compounds and water‐soluble chlorides, thereby reducing the release of sodium and chlorine. This reduces fouling and corrosion, improving equipment efficiency. Additionally, recycling copyrolyzed phosphorite for yellow phosphorus production can enhance conversion ratios, supporting the production of higher‐value phosphorus chemicals.

Visualization Study of Methane Deflagration Characteristics in Variable Diameter Pipelines Based on Schlieren Technique

ABSTRACT The phenomenon of pipe diameter change often exists in urban natural gas pipelines. To study the impact of pipe diameter variation on the propagation characteristics of combustible gas deflagration and provide theoretical basis for the prevention and emergency treatment of gas pipeline explosion accidents, this work uses a self-developed circular explosion pipe test bench with a length of 12 m and an inner diameter of 90 mm to study the methane deflagration characteristics in variable diameter pipelines. Under four experimental conditions of variable cross-sectional area ratio (VR) of 1.0, 0.6, 0.4, and 0.2, the schlieren images of the deflagration process of methane/air premixed gas with a methane concentration of 9.5% were captured by a high-speed camera. Combined with the traditional pressure and flame signal point source information, the research results show that the existence of variable diameter pipelines can change the flame structure and shape, causing the flame front to transform into a tulip flame in advance. The flame propagation speed under different experimental conditions is: VR = 0.4 > VR = 0.2 > VR = 0.6. The influence of the variable diameter pipeline on flame velocity depends on the suppression effect of the reflected wave generated by the cross-section area of the variable diameter pipe and the coupling effect of the reduced aperture area of the variable diameter section on the flame acceleration effect. When the reflected wave acts on the flame front, the flame propagation speed decreases, and in severe cases, it will cause flame stagnation and backfire.

Chemical composition, rumen fermentation kinetics, and degradability of cassava stem hay ammoniated with urea using the in vitro gas production technique

ABSTRACT A completely randomised design was adopted with five treatments urea levels of 0, 2, 4, 6, and 8% of dry matter and five replicates per treatment. The fermentation products were analysed using an in vitro semiautomatic gas production technique. Ammoniation had a significant linear effect on DM, NDF, hemicellulose, acid detergent fiber, and neutral detergent insoluble nitrogen. Ammoniation had a positive linear effect on crude protein (CP) content; increasing urea by 1% caused an increase in CP by 5.19 g kg−1 DM. The gas production based on DM, OM, and NDF decreased linearly with increasing urea for every 1% urea added to the hay, there was a reduction in gas production of 1.40, 3.27, and 4.21 ml/g DM, OM, and NDF, respectively. The concentration of methane decreased linearly with urea dose; for each 1% reduction in urea, there was a 0.15, 0.34, and 0.41 ml/g reduction in methane concentration during the degradation of DM, OM, and NDF, respectively. Ammoniation with 8% urea improved the chemical composition of cassava stem hay and decreased methane production.

Effect of Codigestion of Rice Straw, Fish Meal, and Cow Manure on Biogas Production and Quality of Solid Bioslurry Fertilizer

The solid phase bioslurry (sludge) had the potential to be used as organic fertilizer. However, the NPK content in it did not meet SNI standards. This research aimed to study the effect of adding rice straw and fish meal to cow dung substrate for anaerobic processing, on the NPK content of the sludge produced and biogas production. Two digesters were used, which functioned as a control and a codigestion digester. Initially, in both digesters, starter breeding was carried out in batches. After the starter had grew well, then the substrate along with water was fed continuously at 88 mL/day in each digester, and an output of 88 mL/day was also produced. Analysis of COD, sCOD, VFA concentrations, and measurements of the pH values of feed and output were carried out every 3 days. Biogas volume measurements were carried out every day. The process was stopped when conditions were steady. At the end of the process, an analysis of the NPK content in the sludge and the methane content in the biogas were carried out. The results showed that biogas from codigestion content almost no methane. However, the sludge contained NPK within the range of SNI standard. Keywords: Biogas, Cow dung, Fish meal, Rice straw, Solid bioslurry fertilizer.

Effects of Climate Change and Greenhouse Gas Emission Relevance to Environmental Stress on Horticultural Crops

Global climate change significantly impacts the yield and quality of sustainable horticulture crops. Rising global temperatures have forced the agricultural community to modify planting and harvesting timetables, frequently calling for earlier crop production. Notably, several concerning elements are brought about by climate change, including greenhouse gas emissions (GHGs), higher temperatures, higher concentrations of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4), ozone depletion (O3), and deforestation. All of these factors exacerbate environmental stresses on crops. Climate change is, therefore, likely to have a negative impact on livestock production and crop yields. Thus, the main goal of the review paper is to provide a thorough summary of the various aspects that affect the production of fruits, vegetables, and plantation crops in horticulture, with a focus on greenhouse gas emissions and environmental stressors like high temperatures, droughts, salinity, and CO2 emissions. This assessment will also look at how new greenhouse technologies and horticultural crop varieties can be used to lessen the adverse effects of climate change on crops.

Potential of Biogas Production from Wastewater of Shredded Pork Processing with Cow Manure

Small and Medium Enterprises (SMEs) play a crucial role in driving the economy, especially in developing countries. Since they are essential employment resources and support local development, in SMEs relate to processed meat production, large amounts of wastewater containing blood, fat, and protein require high-efficiency treatment methods to prevent environmental pollution. If the wastewater is not treated appropriately, the impact will cause environmental pollution. Therefore, this research aims to study the potential of biogas production from wastewater of shredded pork processing (WSPP) to find the optimal substrate-to-inoculum ratio and evaluate its industrial application potential. The research also experimented following the biochemical methane potential method, where the total volume was 1000 mL, and the working volume was 400 mL. The experiment used the substrate-to-inoculum ratio (SIR) ratios, which were 1:2, 1:1, and 2:1 VS-based. The operating temperatures were 35 ± 2 °C in the mesophilic period. The study results showed that the most appropriate ratio for biogas production was 2:1 VS-based. During the 33 days of the experiment, it was found that the potential of the highest cumulative biogas and methane yield was 1640.19 ± 97.46 and 650.59 ± 48.04 N mL/g VS added, respectively, which contained a maximum methane content of 68.60%. Moreover, COD, TS, and VS removal efficiency were 57.57 ± 2.28, 57.30 ± 2.19, and 1.49 ± 0.16, respectively. The research results demonstrated that the wastewater from the WSPP was a high-potential substrate for biogas production and would continuously be developed at the industrial level.

The suppression and CO elimination performance of Co3O4 dust cloud for methane-air mixture explosion

This paper experimentally studied the effect of Co3O4 dust clouds on the methane-air mixture explosion characteristics and post-explosion CO concentration, aiming to propose a novel method for simultaneously suppressing explosion and eliminating CO product. The Co3O4 catalyst was synthesized utilizing the co-precipitation method. We varied the methane concentration and Co3O4 dust cloud concentration to investigate their effects on the flame propagation behavior, maximum explosion overpressure (Pm), flame combustion time (tc), and the gaseous product concentration. The hazard of the gaseous product was evaluated by the effective escape time (te) based on the Fraction Effective Dose (FED) mathematical model. The results demonstrated that the Co3O4 dust cloud could significantly reduce the explosion severity and CO concentration. Furthermore, the higher the concentration of Co3O4 dust clouds, the more significant the explosion suppression and CO elimination performance, which was as a result of the significant increase in the contact area and collision probability between the Co3O4 particles and the reaction components increased. Compared to traditional inhibitors that only reduce the severity of an explosion, Co₃O₄ could not only significantly reduce the explosion severity, but also quickly eliminate post-detonation CO. The method proposed in this paper could effectively reduce the hazard of methane-air mixture explosion, which was of great practical significance for ensuring the safety of personnel involved in the risk.

Непараметрическая оценка прогностической точности моделей на примере временны́х рядов концентраций метана в атмосферном воздухе арк­тического острова Белый

Over the past few decades, the number, variety, and complexity of time series forecasting models have grown. There has also been an increased interest among researchers in comparing and assessing the predictive accuracy and performance of models, and in determining which models are more accurate. The researchers propose using the hypothesis testing approach to assess the performance of a time series forecast model. They obtained data for the study while monitoring the dynamics of ground-level concentrations of the main greenhouse gases on the Arctic Island of Bely, Yamalo-Nenets Autonomous Area, Russia. A total of three models based on autoregressive neural networks with exogenous input (NARX) were considered to predict changes in methane concentration in the surface layer of atmospheric air. The performance of the models was assessed using 8 “traditional” indices (correlation and determination coefficients, Wilmott goodness-of-fit indices, mean absolute error, relative mean square error, etc.) and the proposed permutational approach using the hypothesis testing method. In general, based on the data under study, the estimates of the permutation approach and other indicators of accuracy and error coincide, but there are discrepancies. Effect sizes do not always determine the statistical significance of differences.

Data-Science-Informed Operation, Maintenance Practices Reduce Emissions

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 3866061, “Reducing Methane Emissions: Implementing Data-Science-Informed Operation and Maintenance Work Practices Using Continuous Monitoring Technology,” by Kathleen Jenkins, Carol A. Brereton, and Alex MacGregor, Qube Technologies, et al. The paper has not been peer reviewed. _ Diverse methods are used by oil and gas operators for methane leak detection and repair (LDAR). Deploying continuous monitoring (CM) point-sensor technologies to an oil and gas facility allows operators to implement novel operation and maintenance work practices to respond efficiently to methane emissions. The authors examine how data-science-driven work practices can result in substantial reduction in methane emissions compared with other LDAR methods. CM Technology CM point sensors track changes in parts per million of methane in the air. When several fixed sensors are deployed at a site, a large area can be surveilled. Using proprietary algorithms based on a plume-dispersion model, the volume and site rate of the methane emission are calculated. The probable location of the emission is estimated and, together with the volume, is shown on a Web-based dashboard that displays the changes in site rate through time. Alerts generated by the CM system allow the operator to respond to leaks more quickly than when waiting for data from an intermittent inspection to provide emission data. CM was deployed by a Permian Basin operator with a desire to operate cleanly, with transparency. The devices were installed with the operator beginning in March 2022 and continue to be active at the time of writing. Alerts generated by the system are delivered to operations personnel, including control-room operators, and investigated by field operators. When the source is identified, repairs are scheduled or completed on the spot and recorded for review. The operator has expanded the deployments throughout the field and uses the data to identify and repair leaks. Theory and Methods The CM devices were deployed around the fence line at several production facilities in the Permian Basin. The optimal number and placement of sensors was determined by analyzing publicly available wind data and sources of emissions at the facility. The CM devices have an inlet port that allows the ambient air to enter the device and flow across a metal oxide sensor. Metal oxide sensors measure the change in conductivity as the air flows across them as a result of the methane adhering to the metal. The change in conductivity, directly correlated with the parts per million of methane in the air, is recorded. Also measured are temperature and wind data, read by temperature sensors and anemometers on each device. This data is sent through a mobile telecommunications network to cloud-based servers that apply an emission-estimation model based on a plume dispersion and a localization algorithm to the data. Cloud services facilitate the transfer of information from devices to Web-based software. Each methane sensor is calibrated in the laboratory before installation by exposing it to known levels of methane. In this process, the temperature and humidity are systematically varied while the methane concentrations are changed and the reported conductivity is recorded. The resulting coefficients of conductivity are stored with the serial number of the device and sent to the device through the mobile network when it is deployed in the field.

Direct synthesis of liquid hydrocarbons from CO2 and H2 over bifunctional ZnCrOx-НZSM-5 combined and composite catalysts in a single reactor

A one-stage synthesis of gasoline fraction from CO2 and H2 was carried out on Zn-Cr–oxide-zeolite combined and composite catalysts. It was found that after oxidative and reduction treatment the catalysts contain ZnO and ZnCr2O4 phases. The one-step coprecipitation of zinc and chromium salts in the presence of zeolite allows obtaining an active bifunctional composite catalyst, each particle of which contains Zn-Cr oxide and zeolite components. A synergistic catalysis due to a closer distance of metal and acid sites increased the efficiency of such a catalyst in CO2 hydrogenation. It was found that the optimal temperature of oxidative activation of the composite catalyst is 400 ° C. With an increase in the temperature of oxidative treatment of the composite catalyst from 400 to 500°C, part of the zinc leaves the structure of the non-stoichiometric spinel and leads to a decrease in the basicity of the catalyst, which is responsible for the activation of CO2 on surface oxygen vacancies. Agglomerated ZnO particles blocked the pores and reduced their volume, as well as the specific surface of the catalyst. At the same time, the total acidity of the catalyst decreased. ZnO-species, which have hydrogenating activity, under the reaction conditions removed alkenes from the reaction cycle and thereby reduced the C5+–selectivity of the composite catalyst. Among the studied catalysts, the ZnCrOx-НZSM-5/Al2O3(400) composite catalyst in the tail-gas recirculation mode at 380°C and 10 MPa demonstrated high CO2 conversion of 25% and high selectivity for C5+–HCs of 53 wt% with a high content of isoalkanes 71 wt% for 60 hours. The methane content in the tail-gas did not exceed 3 vol%. The results obtained will be used to develop approaches to creating effective catalysts for the one-stage CO2 hydrogenation into valuable petrochemical products.

Biomethane Production Through Performance Enhancement of Anaerobic Digestion and Sludge Dewatering Processes in a Wastewater Treatment Plant

Sewage sludge management poses a persistent challenge due to increasing volumes and stringent environmental regulations. Current municipal wastewater treatment technologies are energy intensive, produce large quantities of residuals and fail to recover the potential resources available in wastewater. Anaerobic digestion (AD) is widely recognized for its cost-effective stabilization, high organic matter removal, and biogas production potential. However, the hydrolysis phase remains a bottleneck in AD, limiting methane yield. Furthermore, its application for low strength municipal wastewater is limited. To address such challenges, the effects of combined microwave-ultrasonic and combined microwaveoxidative pre-treatment of thickened excess activated sludge and mixed sludge on the performance enhancement of conventional mesophilic digester and on two-stage digesters are presented in this study. Microwave-ultrasonic pretreatment was optimized for enhanced cell disruption, while microwave oxidation pretreatment incorporated hydrogen peroxide to generate reactive oxygen species for accelerated organic solubilization. Experimental setups included single- and two-stage anaerobic digesters operated under mesophilic and thermophilic conditions. Results demonstrated that combined microwave-ultrasonic pretreatment improved cumulative methane production by 18% and total solids reduction by 31%, compared to microwave-only pretreatment. Microwave oxidation pretreatment with 1% H₂O₂ achieved 40% volatile solids solubilization, significantly enhancing methane yield and sludge dewaterability. The two-stage AD process further improved performance, achieving 76.4 mL/g TCOD methane yield and 58% methane content in biogas, outperforming single-stage systems. Findings indicate that hybrid pretreatments synergistically enhance hydrolys

From thaw till fall: Interacting hydrology, carbon cycle, and greenhouse gas dynamics in a subarctic stream-lake continuum.

Carbon-water interaction studies between aquatic and terrestrial ecosystems are especially needed today in Arctic and Boreal regions, as they are facing drastic warming and precipitation shifts. Despite the importance of streams in the carbon cycle, northern stream-based studies are scarce, owing to a lack of measurements throughout the north, and possibly skewing global greenhouse gas estimates. We used a combination of multiscale measurements to quantify water sources (H2O isotope proxies), carbon availability (dissolved in/organic carbon concentrations) and quality (water absorbance, SUVA254 -index), microbial community structure (16S rRNA sequencing), and carbon dioxide (CO2) and methane (CH4) fluxes and concentrations. Our study site comprises a groundwater-influenced and peatland-dominated second-order stream, along with its adjacent lake inlet located in Northern Finland. Sampling was conducted three times during the summer of 2019 at 21 locations along the stream-lake continuum. Temporal and spatial shifts in water sources altered carbon characteristics, with CH4 concentrations being the key environmental factor shaping the microbial communities, overriding the influence of dissolved organic carbon amount and quality. The prevalence of methanotrophic bacteria highlighted the importance of CH4 as a carbon source and the methanotrophic groups as drivers of the CH4/CO2 source-sink attributes of subarctic stream systems. Our results highlight the value of integrated hydrological, biogeochemical, and microbiological measures to resolve the biocomplexity of carbon-water interactions in northern headwater catchments.

Anaerobic Co-digestion of Palm Oil Sludge, Cassava Peels, Cow Dung and Ground Eggshells: Process Optimization and Biogas Generation

Indiscriminate disposal of crop and animal wastes has grown in acceptance across the globe as an environmentally hazardous practice. This study used a 225L polyethylene digester that was specially made to produce biogas from anaerobic co-digestion of palm oil sludge, cassava peels, and cow dung using ground eggshells for pH stabilization and a greenhouse for temperature control. Cassava peels, palm oil sludge, cow dung, and water were combined in a ratio of 1:1:2:5.3, respectively, and 1.3 kilograms of crushed eggshells were added. The bio-digestion system generated 650.60 L of cumulative biogas throughout the 30-day sludge retention period. The pH averaged 6.0, and the slurry temperature averaged 34.76oC during digestion, which is favorable for the production of biogas since microbial populations thrive under hospitable conditions. The biogas produced after a hydraulic retention time (HRT) of over 20 days had the highest methane concentration of 60%, while days under 10 HRT had the lowest methane content of 45.5%. On the 13th day of anaerobic digestion, biogas output peaked at 34.90L, and pH and temperature were maintained at 6.5 and 35.0°C, respectively, the ideal ranges for a healthy process. An efficient technique for producing energy in the form of biogas was shown by optimized anaerobic co-digestion of animal and crop waste utilizing ground eggshells and a greenhouse for pH and temperature control. Future research should focus on developing more efficient, cheaper microbial agents, such as enzymes for biological pre-treatment of palm oil sludge to reduce lignin, which negatively impacts biogas generation.

Controls on spatial variation in porewater methane concentrations across United States tidal wetlands

Tidal wetlands can be a substantial sink of greenhouse gases, which can be offset by variable methane (CH4) emissions under certain environmental conditions and anthropogenic interventions. Land managers and policymakers need maps of tidal wetland CH4 properties to make restoration decisions and inventory greenhouse gases. However, there is a mismatch in spatial scale between point-based sampling of porewater CH4 concentration and its predictors, and the coarser resolution mapping products used to upscale these data. We sampled porewater CH4 concentrations, salinity, sulfate (SO42−), ammonium (NH4+), and total Fe using a spatially stratified sampling at 27 tidal wetlands in the United States. We measured porewater CH4 concentrations across four orders of magnitude (0.05 to 852.9 μM). The relative contribution of spatial scale to variance in CH4 was highest between- and within-sites. Porewater CH4 concentration was best explained by SO42− concentration with segmented linear regression (p < 0.01, R2 = 0.54) indicating lesser sensitivity of CH4 to SO42− below 0.62 mM SO42−. Salinity was a significant proxy for CH4 concentration, because it was highly correlated with SO42− (p < 0.01, R2 = 0.909). However, salinity was less predictive of CH4 with segmented linear regression (p < 0.01, R2 = 0.319) relative to SO42−. Neither NH4+, total Fe, nor relative tidal elevation correlated significantly with porewater CH4; however, NH4+ was positively and significantly correlated with SO42− after detrending CH4 for its relationship with SO42− (p < 0.01, R2 = 0.194). Future sampling should focus on within- and between-site environmental gradients to accurately map CH4 variation. Mapping salinity at sub-watershed scales has some potential for mapping SO42−, and by proxy, constraining spatial variation in porewater CH4 concentrations. Additional work is needed to explain site-level deviations from the salinity-sulfate relationship and elucidate other predictors of methanogenesis. This work demonstrates a unique approach to remote team science and the potential to strengthen collaborative research networks.

Nano zerovalent iron boosts methane content in biogas and reshapes microbial communities in long-term anaerobic digestion of pig slurry

Nano zerovalent iron boosts methane content in biogas and reshapes microbial communities in long-term anaerobic digestion of pig slurry

Assessing data variability in groundwater quality monitoring of contaminated sites through factor analysis and multiple linear regression models

Monitoring of long-term contaminant concentrations trends is essential to verify that attenuation processes are effectively occurring at a site. However, monitoring data are often affected by extreme variability which prevents the identification of clear concentration trends. The variability is higher in long-screened monitoring wells, which are currently used at many contaminated sites, although it has been known since the 1980s that monitoring data from long-screened wells can be biased. Understanding the factors that may influence the variability of monitoring data is pivotal. To this end, following hydrochemical conceptual modelling using a multi-method approach, the variability of hydrocarbon concentrations from fully screened monitoring wells was assessed over eleven years at a former oil refinery located in Northern Italy. The proposed methodology combined factor analysis with multiple linear regression models.Results pointed out a higher variability in hydrocarbon concentrations at the plume fringe and a lower variability at the plume source and core. 44–46 % of the total variability in measured hydrocarbon concentrations is due to “intrinsic plume heterogeneity”, related to the three-dimensional structure of a contaminant plume, which becomes thinner at the edge, creating a vertical heterogeneity of redox conditions at the plume fringe. This variability, expressed as increasing concentrations of sulfate and decreasing concentrations of methane, represents a background variability that cannot be reduced by improving sampling procedures. The remaining 56–54 % of the total variability may be due to the non-standardization of some purging and sampling operations, such as pump intake position, purging and sampling time/flow rates and variations in the analytical methods. This finding suggests that monitoring improvements in fully screened wells by standardizing all purging/sampling operations or using sampling techniques that can reduce the actual screen length (e.g., packers or separation/dual pumping techniques) would reduce data variability by more than half.