First-order Decay Research Articles

Study of Flow Field Characteristics During the Impact of a High-pressure Gas Jet on a Bulk-loaded Liquid

A visual experiment platform for high-pressure gas jet impacting the bulk-loaded liquid was designed and built in order to investigate the real law of the interaction between the high-pressure gas jet and the liquid medium during the liquid-balance launch of rocket launcher. The experiments of single-phase gas jet injection and the high-pressure gas jet at different temperatures impacting the bulk-loaded liquid were carried out, and the effects of gas temperature on the characteristics of the gas-liquid flow field have been revealed. The results show that the turbulent mixing between the high-pressure gas jet and the liquid medium leads to the appearance of pressure fluctuations in the gas chamber connected to the nozzle. The higher the gas temperature, the greater the amplitude of the pressure fluctuations. Under the impact of high-pressure gas jet, a gas cavity with an arc-shaped head is formed inside the bulk-loaded liquid. The higher the gas temperature, the faster and more unstable the development of the gas cavity and the flow field. The displacement equation of the gas cavity confirms to the first-order exponential decay function, and the error between the fitting value of the established mathematical model and the measured value is within 2%.

Biotransformation kinetics and pathways of typical synthetic progestins in soil microcosms

Gestodene (GES), altrenogest (ALT), and medroxyprogesterone acetate (MPA) are three potent synthetic progestins detected in agricultural soils; however, their biotransformation outcomes in soils remain unclear. This study explored the biotransformation of these progestins in five agricultural soils with different physicochemical properties. The biotransformation data were well-described by a first-order decay model (R2 = 0.83–0.99), with estimated half-lives ranging between 12.1 and 188 h. Amplicon sequencing indicated that the presence of progestins changed the bacterial richness and community structure in the soils. Linear correlation, canonical correlation, and two-way correlation network analysis revealed that soil properties can affect biotransformation rates by interfering with progestin–soil interactions or with keystone taxa in soils. The clustermap demonstrated the formation of abundant transformation products (TPs). Isomerization and C4(5) hydrogenation were the major transformation pathways for GES (yields of ∼ 13.7 % and ∼ 10.6 %, respectively). Aromatic dehydrogenation was the major transformation pathway for ALT (yield of ∼ 17.4 %). The C17 hydrolysis with subsequent dehydration and hydrogenation was the major transformation pathway for MPA (yield of ∼ 196 %). In particular, some TPs exhibited progestagenic, androgenic, or estrogenic activity. This study highlights the importance of evaluating the ecotoxicity of progestin and TP mixtures for better understanding their risks in the environment.

Lipophilic N-Hydroxyimide Derivatives: Design, Synthesis, and Application to Aerobic Alkane Oxidation Under Neat Conditions.

This work reports the design and synthesis of a series of 5-membered and 6-membered N-hydroxyimides flanked by lipophilic alkyl groups adjacent to carbonyl groups, aiming to endow lipophilicity and tolerance toward ring opening degradation. Their solubility in cyclohexane was 5-20 times higher than those of unsubstituted N-hydroxyphthalimide (NHPI) and even 3-10 times higher than a formerly known lipophilic NHPI analog bearing a long alkyl ester. UV-Vis spectroscopy determined the rate constants of first-order decay of N-oxyls, which revealed enhanced stability of 3,5-di-tert-butyl-NHPI and N-hydroxyglutarimide flanked by spiro-cyclohexanes compared with that of NHPI. Their bond dissociation energies were assessed by EPR spectroscopy and DFT calculation, suggesting these lipophilic N-hydroxyimides catalyzed aerobic cyclohexane oxidation under neat conditions with up to 60 turnovers, which is the highest among hitherto reported reactions under neat conditions.

Coupled effect of UV ageing and temperature on the diffusive transport of aqueous, vapour and gaseous phase organic contaminants through HDPE geomembrane

High-density polyethylene geomembranes (HDPE GMBs) are indispensable in constructing composite barriers of modern engineered landfills. GBMs would be exposed to various weathering conditions apart from the interaction of organic pollutants in landfill gas and leachate. Though many studies have investigated the contaminant's migration, the transport of volatile organic compounds (VOCs) concerning the synergistic effect of thermal and UV exposure has not been thoroughly explored. Given this, the present study investigated the diffusive transport of four VOCs (aqueous and vapour phase) at 10 °C, 25 °C, 40 °C, and methane diffusion through an HDPE GMB subjected to accelerated UV weathering. The results indicated that the contaminant phase (aqueous, vapour, gaseous), its properties (aqueous solubility, molar mass, polarity), temperature, and the extent of ageing significantly influenced the transport behaviour. The standard oxidative induction time decreased appreciably with ageing duration following a first-order exponential decay. The change in tensile properties and melt flow index indicated the dominance of UV degradation by cross-linking, resulting in an increased crystallinity of GMB that was identified using Fourier transforms infrared (FTIR) spectroscopy and Differential scanning calorimeter (DSC). The crystallinity increased with UV ageing and caused the sorption and diffusion coefficients to decrease.

An advection-reaction model of emerging contaminants in ground and surface waterbodies with known topology: a data-based approach

A simple data-based advection-reaction (reactive transport) model applicable to both rivers and aquifers monitoring networks is proposed. It is built on (a) available monitoring data, and (b) graph-theoretical concepts, specifically making use of the Laplacian matrix to capture the network topology and the advection process. The method yields useful information regarding the dynamic spatial behavior of the variables monitored, expressed in terms of quantitative parameters like characteristic length, entropy, first-order decay constants, synchronization between sites, and the external inputs/outputs to the system.The model was tested in an unconfined shallow aquifer located in the lower Besòs River (Spain), in which 37 pharmaceutical compounds were monitored at 7 sites, alongside two campaigns (February and May 2021). Characteristic lengths were, on average, of the same order (24.5 m) as the mean distance between consecutive monitoring sites (33.6 m), thus reflecting an adequate monitoring network design. From an estimated mean advection velocity (0.24 m·h−1), first-order decay constants were calculated for each compound and campaign, with mean values of 0.025 h−1 (February) and 0.005 h−1 (May). Whereas entropy was generally slightly larger values in February than in May (mean values of 1.02 and 0.9 entropy units respectively), synchronization showed the opposite trend (mean values of 62.4% and 68.8% respectively). The input/output profiles were generally site-dependent, regardless of the compound, and campaign considered. • A new advection-reaction modeling approach directly based on experimental data obtained from monitoring campaigns together with the network topology is proposed. • The method yields new quantitative information regarding the dynamic behavior of the variables monitored, useful for both research and management purposes.

One-dimensional numerical model for unsteady solute transport in open channels under multi-point loading

A numerical method for solving the unsteady-one-dimensional advection-dispersion equation for solute transport in streams and channels imposed with multiple point-loading is presented. The numerical technique proposes to solve the equation, which also includes a first-order decay term and a loading term, using techniques similar to those employed by the finite volume method (FVM). The channel length is segmented into cells and the solution aims at evaluating the concentrations at the cell interfaces or the internal nodes, at prescribed time steps for the steady condition of the flow. The results are computed commencing from a specified time level with known spatial concentration within the domain. It is assumed that the boundary nodes at the two ends of the channel, one each at the upstream and the downstream, are specified with solute concentration values or its spatial gradient at all times. Unlike the standard within-the-cell spatial approximations of a variable assumed in the finite volume or finite element schemes, the proposed method models the spatial variation of the solute concentration within a cell by an analytical expression in terms of the concentrations at the two boundary nodes of the cell and the influx rate of point-loading, if any, located within the cell. Using such a closed-form function based upon the true nature of the problem not only helps in capturing the spatial variation of concentration within a cell more precisely but also allows a better approximation of its spatial gradients at the cell interfaces, thus helping to achieve a more accurate computation of the inter-cell dispersive fluxes. The performance of the proposed algorithm is evaluated against analytical benchmarks, a standard finite difference scheme, and one public-domain computational package. Data sets reported from field tests are used for demonstrating the potential of the technique in simulating real situations.

Simulation of reactive transport in porous media using Meshless Local Petrov Galerkin (MLPG) and combination of Meshless Weak and Strong (MWS) form methods

In this paper, two meshless methods, namely, a weak form Meshless Local Petrov Galerkin (MLPG) method, and Meshless Weak Strong (MWS) form method, obtained by combining MLPG with a strong form Radial Point Collocation Method (RPCM), are presented for simulation of advection-dispersion-reaction phenomena of the contaminants in the porous media. The first-order decay and sorption reactions are considered in this study. The Crank Nicolson scheme is applied for the time discretization. The weak form MLPG is a truly meshless and robust numerical technique, that can be applied to complex aquifer systems with derivative boundaries. However, in this method, the computational time is increased due to the integration, which is not essential for simple problems. Thus, the MLPG method is further coupled with a strong form RPCM with an aim of decreasing the background integration, by modelling only the nodes around the derivative boundaries using MLPG method and the other nodes by a direct RPCM which do not require integration. The proposed MWS model automatically converts into a complete RPCM model if there are no derivative boundaries. Thus, this model being both accurate and computationally efficient is suitable for simple and moderately complex aquifer systems and MLPG is the most stable and reliable method for modelling the most complex aquifer problems. Both the developed models are tested with available analytical solutions and applied for hypothetical case studies. The results prove the efficiency of the models and the applicability of each model is described in detail.

Influence of nitrogen species and biomass retention time on nutrient removal and biomass productivity in a microalgae-based bioreactor

This study examined the effects of nitrogen species (NH 4 + N/NO 3 − N ratio) and biomass retention time (BRT) on nutrient uptake and biomass productivity in Chlorella sp . In batch photobioreactors (PBR), microalgae were cultivated with varied nitrogen species ratios (100% NH 4 + N, 50% NH 4 + N:50% NO 3 − N, and 100% NO 3 − N). It was observed that a medium containing 100% NO 3 − N boosted algae growth, with a maximum biomass concentration of 3188 mg/L. However, the lowest nutrient removal rates were obtained under the 100% NO 3 − N condition, according to the reverse logistics model. In contrast, the highest removal rates occurred for substrate containing 100% of NH 4 + N species based on first-order decay models, although yield biomass was lower (2940 mg/L). The presence of the ammonia nitrogen resulted in the flocculation of the microalgae into large flocs, suggesting that ammonia nitrogen was rapidly consumed to produce flocculation-related metabolic products rather than for biomass production. Using the 100% NH 4 + N medium, different BRT values (7, 5, 3, 2 days) were examined under continuous operation using a membrane photobioreactor (MPBR). At 3-day BRT, the maximum biomass productivity, nitrogen, and phosphorous removal rates were 214 ± 4, 63.1 ± 4.1, and 2.1 ± 0.6 mg/L d, respectively. The biomass yield increased as the BRT decreased, leading to an increase in pollutant removal rates. Finally, this study provides some essential information for improving the operating conditions of membrane photobioreactor system under different biomass retention times and various nitrogen sources in the feed. • The highest biomass productivity was achieved in the 100% NO 3 − N medium. • The highest nutrient removal occurred in the 100% NH 4 + N medium. • The highest biomass productivity and nutrient removal was observed at 3-day BRT. • Lower fouling rates were achieved at higher BRTs.

Seasonal methane emission from municipal solid waste disposal sites in Lagos, Nigeria

The Municipal Solid Waste (MSW) Sector is a major source of Methane (CH4) emission, a Greenhouse Gas (GHG) that contributes to Climate Change. However, governments of developing countries have not been able to address the challenges posed by this sector due to inadequate funding and technical requirement. The objective of this study was to determine how seasonal variation influences the CH4 gas emission. The First Order Decay (FOD) Tier 1 Model was used to estimate CH4 emission from four Solid Waste Disposal Sites (SWDS) in Lagos namely: Ewu-Elepe (Ewu), Abule-Egba (A/E), Soluos (Sol), and Olushosun (Olu) covering the dry and wet seasons, respectively for the inventory year 2020. A known weight of the wet waste deposited was characterized. The study revealed that the Degradable Organic Carbon (DOC) for the dry season was 12.897 GgC/kgWaste while that of the wet season was 12.547 GgC/kgWaste. But, the methane gas generated during the wet season was 0.331 Gg higher than that of the dry season which was 0.134 Gg for the study period. This is an appreciable quantity of methane that can contribute to the global Climate Change impact if not addressed. Therefore, these waste types should be segregated from other recyclables and processed into compost or energy resource.

Decolorization and Biodegradability Enhancement of Synthetic Batik Wastewater Containing Reactive Black 5 and Reactive Orange 16 by Ozonation

The batik industry generates large amounts of highly colored wastewater. Azo dyes in batik wastewater can cause environmental pollution. In this study, synthetic batik wastewater containing 32 mg/L Reactive Black 5 (RB5) and 32 mg/L Reactive Orange 16 (RO16) was treated by ozonation in a 2 L batch reactor. The wastewater color unit was reduced from 4240 to 70 after 10 min ozonation and to below 50 after 15 min ozonation (7.3 g O3/m3, 4 L/min). The first-order decay constant for 5 min ozonation was determined to be 1.11 min−1 for RB5 and 0.82 min−1 for RO16. Biodegradation tests using activated-sludge microorganisms showed the toxicity of RB5 and RO16 for microbial respiration and revealed the detoxification of the dyes by ozonation. Three-dimensional fluorescence spectroscopy analysis indicated the temporal accumulation of ozonolysis products of RO16 and RB5. The chemical oxygen demand concentration of the wastewater was reduced from 86 mg/L to 73 mg/L by biodegradation alone, 63 mg/L by ozonation alone, and 54 mg/L by ozonation followed by biodegradation. Existing wastewater treatment plants using conventional bioprocesses can be upgraded to achieve robust dye treatment by installing the ozonation process as a pretreatment.

A new view into three-dimensional excitation-emission matrix fluorescence spectroscopy for dissolved organic matter

Three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs) has been extensively used for dissolved organic matter (DOM) characterization. However, the application of 3D EEMs is constantly limited by issues such as contradictory component identification, confusing interpretation of spectral indicators, and inability to establish biodegradability. In this study, some improvements were proposed by investigating the 3D EEMs, spectral indicators, and degradability of the standard and representative DOM. To overcome the unclear identification of DOM components, it was recommended to partition 3D EEMs into three subareas: aromatic protein (New-I), humic-like (New-II), and soluble microbial by-product-like (New-III). Significant strong positive correlations (ρ = 0.727, P < 0.001) were observed between fluorescence index (FI) and biological index (BIX), and (R = 0.809, P < 0.001) humification index (HIX) and specific ultraviolet absorbance of 254 nm (SUVA254). Except for FI (R = -0.483, P = 0.023), no other spectral indicators (P > 0.05) were found to be significantly correlated with molecular weight. As thence results, the FI and HIX were the most suitable indicators for evaluating DOM. The half-life (20 < 21 < 26 < 29 < 46 days) revealed that the degradability of individual DOM components was in the order of tyrosine > tryptophan > fulvic acid > protein > humic acid. The degradation dynamics were governed by first-order decay kinetics (R2 = 0.91–0.99). This study clarified the fluorescence properties and degradability of DOM, as well as the reliability of spectral indicators. The degradation performance of individual DOM components engaged in the carbon cycling process was revealed, paving the path for further applications of 3D EEMs in DOM research.

Influence of temperature and water quality on the persistence of human mitochondrial DNA, human Hf183 Bacteroidales, fecal coliforms and enterococci in surface water in human fecal source tracking context.

Mitochondrial DNA (mtDNA) is used as a genetic marker to track fecal contamination in surface water. Its potential to effectively discriminate between the nonpoint sources of fecal pollution (e.g. human, livestock) in water environments is relevant for water quality management. However, there is a lack of knowledge about the environmental persistence of mtDNA in relation to those of other microbial parameters, such as fecal indicator bacteria (FIB). In this study, mesocosms composed of water collected from four rivers and tap water were spiked with raw wastewater to mimic human fecal contamination. Mesocosms composed of raw wastewater were also studied. The mesocosms were incubated at 4 °C or at 22 °C for 189 days, from which the levels of human mtDNA (HumtDNA) and human Bacteroidales (Hf183) were measured by qPCR. The levels of FIB (fecal coliforms and enterococci) and heterotrophs were determined by culture methods along with the determination of physicochemical attributes. The decay rates of the genetic markers and FIB were determined with first-order decay rate models. The decay rates of HumtDNA (0.004-0.059 d-1), Hf183 (0.007-0.082 d-1), and the two FIBs (0.005-0.066 d-1) were similar at 4 °C, while the genetic markers both had higher decay rates (0.013-0.919 d-1) at 22 °C. Different HumtDNA decay rates were observed between the river mesocosms (0.043-0.919 d-1) and the wastewater and tap water mesocosms (0.004-0.095 d-1). Covariations of pH and conductivity among the HumtDNA, Hf183 and FIB decay rates were observed. HumtDNA and Hf183 had similar environmental persistence, whereas fecal coliforms and enterococci persisted longer at 22 °C. Finally, HumtDNA had the same trends of persistence in the four river mesocosms, suggesting a relative stability of this marker in different rivers. Our results suggest that HumtDNA could be more suitable for tracking the source of a recent fecal contamination in complement to FIB.

TIPT: The Tracer Injection Planning Tool

Despite their frequent use, there are few simple and readily accessible tools to help guide the logistical planning of tracer injections in streams and rivers. We combined the widely used advection-dispersion-reaction equation, peak concentration estimates based on a meta-analysis of hundreds of tracer injections carried out in streams and rivers, and simple mass balances in a dynamic Excel Workbook to 1) help users decide how much tracer mass should be added to achieve a specific dynamic concentration range that reduces known issues associated with breakthrough curve tail truncation, and 2) generate tables and graphs that can be readily used to plan the deployment of resources. Our Tracer Injection Planning Tool, TIPT, handles instantaneous and continuous tracer injections and assumes steady-state and uniform flow conditions, as well as first-order decay or production. While those assumptions do not strictly apply to natural streams and rivers, they help simplify the planning of tracer injections with a predictive ability that is disproportionally favorable with respect to the few inputs required. TIPT is a versatile, user-friendly, and graphical tool that can help design tracer injections and solute transport experiments that are more easily replicated within and across sites. Thus, TIPT contributes directly to advancing Integrated, Coordinated, Open, and Networked (ICON) principles. Similarly, TIPT can help generate datasets that more closely follow Findable, Accessible, Interoperable, and Reusable (FAIR) principles. We demonstrate the use of TIPT through two case studies featuring 1) a continuous injection in a 2nd order stream and 2) an instantaneous injection in a 7th order stream.

Meta-Analysis Addressing the Implications of Model Uncertainty in Understanding the Persistence of Indicators and Pathogens in Natural Surface Waters.

This study evaluates the impact persistence model selection has on the prediction of persistence values of interest and the identification of influential water quality and environmental factors for microorganisms in natural surface waters. Five persistence models representing first-order decay and nonlinear decay profiles were fit to a comprehensive database of 629 data sets for fecal indicator bacteria (FIB), bacteriophages, bacteria, viruses, and protozoa mined from the literature. Initial periods of minimal decay and decay rates tapering off over time were often observed, and a two-parameter model, based on the logistic probability distribution, provided the best fit to the data most frequently. First-order decay kinetics provided the best fit to less than 20% of the analyzed data. Using the best fitting models in this analysis, T90 and T99 metrics were calculated for each data set and used as the dependent variable in a variety of exploratory factor analyses. Random forest methods identified temperature and predation as some of the most important water quality factors influencing persistence, and the protozoa target type differed the most from FIB. This analysis further confirmed the interactions between temperature and predation and suggests that pH and turbidity be more frequently documented in persistence studies to further elucidate their impact on target persistence. The findings from this analysis and the calculated persistence metrics can be used to better inform quantitative microbial risk assessments and may lead to improved predictions of human health risks and water management decisions.

Dynamic Behaviors of Newly Deposited Atmospheric Heavy Metals in the Soil-Pak Choi System.

Dynamic behaviors of the newly deposited atmospheric heavy metals in the soil-pak choi (Brassica chinensis L.) system are investigated by a fully factorial atmospheric exposure experiment using soils exposed to 0.5-year and 1.5-year atmospheric depositions. The results showed approximately 17-87%, 19-64%, and 43-84% of the Cu, Cd, and Pb in pak choi edible parts were contributed from the new depositions, respectively. For the newly deposited metals, foliar uptake was the key pathway of shoot bioaccumulation rather than from root uptake of the deposited metals in soils, resulting in no significant soil contribution differences between pak chois growing in 0.5-year and 1.5-year exposed soils. Indeed, highly bioavailable metals in atmospheric deposition significantly increased the soil plant-bioavailable Cu, Cd, and Pb fractions; however, soil aging resulted in similar percentages of the plant-bioavailable fractions in 0.5-year and 1.5-year exposed soils, which indicated the bioavailability of metals deposited into soils rapidly decreased with aging. The soil aging process of the deposited metals was well fitted with the first-order exponential decay model, and soil organic matter and clay were the major driving factors. Our findings highlight high plant bioaccumulation rates and the rapid soil aging process of newly deposited metals during the plant growth period.

Microbial cultivation using mathematical representations accounting for the reaction kinetics in two-stage nitritation/ANAMMOX process

Mathematical representations accounting for the reaction kinetics were used to improve the cultivation rate of ANAMMOX microorganisms in the pilot-scale partial nitritation (PN)/anaerobic ammonium oxidation (ANAMMOX) reactor. In line with the fluctuations in the properties of raw reject water, control strategies of the hydraulic retention time (HRT) and the mixed liquid suspended solid (MLSS) concentration calculated by the mass balance-based model were proposed to improve PN performance. As a result, control of the MLSS concentration to cope with the fluctuation of C/N ratio resulted in a higher nitrite production rate (NPR) that was suitable for enhancing the cultivation rate of the ANAMMOX microorganisms. Based on the performance in the optimized PN, the observed yield of ANAMMOX microorganisms was calculated to be 0.091 gVSS/gNH4+−N. The biomass as volatile suspended solids (VSS) wasted was 309.8–554.3 gVSS/d. Based on the reaction kinetics of ANAMMOX, the quantity of stored microorganisms over time was simulated using a modified first-order exponential decay model; the calculated value was 6.3–11.2 kg/m3/year. These results can be used for the scale-up or design of the ANAMMOX process.

Denitrification kinetics during aquifer storage and recovery of drainage water from agricultural land

An aquifer storage transfer and recovery (ASTR) system was studied in which tile drainage water (TDW) was injected with relatively high NO3 (about 14 mg/L) concentrations originating from fertilizers. Here we present the evolution of denitrification kinetics at 6 different depths in the aquifer before, and during ASTR operation. First-order denitrification rate constants increased over time before and during the first days of ASTR operation, likely due to microbial adaptation of the native bacterial community and/or bioaugmentation of the aquifer by denitrifying bacteria present in injected TDW. Push-pull tests were performed in the native aquifer before ASTR operation. Obtained first-order denitrification rate constants were negligible (0.00–0.03 d−1) at the start, but increased to 0.17–0.83 d−1 after a lag-phase of about 6 days. During the first days of ASTR operation in autumn 2019, the arrival of injected TDW was studied at 2.5 m distance from the injection well. First-order denitrification rate constants increased again over time (maximum >1 d−1). Three storage periods without injection were monitored in winter 2019, fall 2020, and spring 2021 during ASTR operation. First-order rate constants ranged between 0.12 and 0.61 d−1. Denitrification coupled to pyrite oxidation occurred at all depths, but other oxidation processes were indicated as well. NO3 concentration trends resembled Monod kinetics but were fitted also to a first-order decay rate model to facilitate comparison. Rate constants during the storage periods were substantially lower than during injection, probably due to a reduction in the exchange rate between aquifer solid phases and injected water during the stagnant conditions. Denitrification rate constants deviated maximally a factor 5 over time and depth for all in-situ measurement approaches after the lag-phase. The combination of these in-situ approaches enabled to obtain more detailed insights in the evolution of denitrification kinetics during AS(T)R.

A new analytical model for transport of multiple contaminants considering remediation of both NAPL source and downgradient contaminant plume in groundwater

The contamination of groundwater aquifers by chlorinated solvents is a water-resource issue of great importance worldwide. Such contaminants are difficult to treat because they are often released as dense non-aqueous phase liquids (DNAPLs). Research shows that the application of remediation technologies to both the NAPL source and dissolved plume can lead to more efficient remediation, rather than to either alone. In these remediation efforts, analytical models that evaluate behavior and fate of contaminants do provide a better understanding of the performance of these remedial technologies. To the best of our knowledge, there exist no analytical model of simulating the plume migration of multiple contaminants with capabilities of accounting for both NAPL source and plume remediation simultaneously and different retardation for original chlorinated solvent contaminant and its degradation byproducts. In this study, we present a new analytical model for remediating both NAPL source and downgradient contaminant plume in groundwater at sites contaminated with chlorinated solvents and their degradation products with different retardation factors as well as considering both NAPL source and plume remediation simultaneously. A source model that accounts for the depletion of mass by the processes of dissolution or first-order decay reactions, corresponding with the removal or destruction of the source mass, is coupled to a plume reactive transport model. The source model is accounted for by relating source mass to the flux-averaged source discharge concentration through a power function. The developed analytical model considers 1-D advection, 3-D dispersion, first-order decay reactions and ingrowth as well as linear isothermal equilibrium sorption. The proposed analytical solution was derived through successive application of the Laplace transform in time and the double finite Fourier cosine transform regarding y and z. The correctness of the analytical model and its auxiliary FORTRAN computer program code are proved by showing excellent agreements between the simulated plume concentrations of all contaminants obtained from the derived analytical model and from a semi-analytical model available in the literature. Application of the proposed analytical solutions illustrates that the use of identical retardation factors for all contaminants may lead to underestimation or overestimation of the mobility of the contaminants, in cases when the retardation factors of the individual contaminants are greatly different from the identical retardation factor value adopted in all contaminants. From the experiments on six scenarios corresponding six remedial treatments, we found out that both the enhanced source decay and partial removal of source mass are main controlling factors at reducing the concentrations of all the contaminants, whereas plume decay leads to effective reduction in the concentrations of PCE, however, rather it causes unfavorable increases of the concentrations of the degradation byproducts.Ultimately, the developed model is used to better understand the impacts of various possible combinations of remedial efforts and management decisions on remediation of the subsurface contamination and quantify the benefit of a certain remediation decision.

Investigation of provincial capacity to produce biogas from waste disposal sites in Turkey

The main aim of this study is to determine the theoretical capacities of waste disposal sites to produce biogas and electricity in Turkey in 81 provinces by using the First Order Decay (FOD) methodology. The population data of each province starting from 1950 to 2020 was used as time series to estimate the best fit model. The same model was also used for the future population estimations until the year 2080. The provinces have different characteristics. The big provinces in Turkey are best fitted with polynomial models. For 38 provinces the best fit models are “third order polynomials”, and for 10 provinces the “second order polynomials” are best fitted. The exponential and linear models are good for 15 and 13 provinces, respectively.Many statistical and “model performance studies” are done for increasing the accuracy level of this study. The results of this study have shown that the best fitted model is acceptable at province level although there are small differences between observed and fitted values.The CH4 emission potential of disposal sites are calculated as 273 thousand tonnes in 1950. This has increased and reached 1.2 million tonnes in 2020. It is projected that it will reach 3.1 million tonnes in 2080. The methane production capacity in Marmara and Central Anatolia regions is calculated as 46% of total capacity. In 2020 these two regions have 1.7 and 0.9 million kW-hr/year electricity production capacity, respectively. The highest provincial capacity of electricity production is observed in İstanbul, Ankara, İzmir, Bursa and Antalya with respective values of 1.02, 0.37, 0.29, 0.20 and 0.16 million kW-hr/year. These top five provinces constitute 37% of Turkey's total capacity.The results of this study have shown that approximately 4.8–7.4% of GHG emissions can be stopped by using CH4 produced in waste disposal sites in energy production. Further usage of methane instead of solid fuels or other non-renewable fuels will decrease the total GHG emissions an extra 2–3.5%. In 2020, 35 million tonnes of CO2 eq. emissions can be reduced in Turkey due to biogas production in waste disposal sites. This is very important from the Climate Change point of view.

Flow distribution and mass removal in floating treatment wetlands arranged in series and spanning the channel width

Floating treatment wetlands (FTWs) use plants’ roots for water quality improvement. The plants are supported by a buoyant structure deployed at the water surface. The roots form a porous zone beneath the structure and remove pollutants carried in suspension through filtering, absorption and uptake. This paper used CFD simulation to model FTWs arranged in series and spanning the channel width and to study the effects of root length and spacing between FTWs on flow distribution and mass removal. The root zone was modelled as a porous media, and removal was computed using first-order decay, for which a range of removal constants was tested. Longer roots increased the reactive volume of the root zone, which increased the fraction of pollutant inflow entering the FTWs. Increasing the distance between FTWs allowed greater mixing between water that went through and beneath the upstream FTW. This increased the concentration entering each FTW, which enhanced mass removal per FTW. However, a larger distance between FTWs reduced the number of FTWs in the channel, reducing the reactive volume. In the tradeoff between mixing and reactive volume, the reactive volume was more important, such that total removal in the channel increased with longer roots and more units of FTW (shorter gap distance). However, removing the gap entirely was detrimental, as FTWs in series removed more mass than a continuous FTW of same volume. This study points to two design recommendations for FTWs in series. First, if resources for building FTWs are not limiting, but the channel length is, it is preferable to prioritize higher reactive volume (shorter gap distance) to achieve maximum removal per channel length. Second, if resources for FTWs are limiting, but channel length is not, it is better to place the FTWs with a longer gap distance, preferably along enough to allow mixing over the full depth between FTWs, as this will achieve maximum removal per FTW.