Two Chemical Engineers Look at the COVID-19 Pandemic.

Chemical engineering involves a skill set that is transferrable to a broad range of other areas. A case in point is the work that is being done by chemical engineers to better understand and fight the COVID-19 epidemic. In this study, we consider a problem that has eluded the COVID-19 research community, which is nevertheless very tractable with a chemical engineering mindset: the true or intrinsic mortality rate of COVID-19, i.e., the fraction or percentage of COVID-19 infected people that die of the disease. We solve this problem in two locations (Spain and the state of New York) for the epidemic's first wave with a combination of daily death data, a fit of a computer simulation of an epidemiological model with adjustable parameters, and independent results of immunological blood testing on a random sample of the population. Parallels are drawn with the problem of determining the turnover frequency of a catalyst based on a similar combination of data and approaches. It is concluded from the study that the intrinsic mortality rate of COVID-19 was 1.45 ± 0.45 % during the first wave, a number that reflects OECD countries. By incorporating data on the age dependence of the mortality rate, a relationship f mort = (3.0 ± 0.7)×10-5 exp(0.1a), where a is the age in years, is tentatively put forward for the mortality rate as a fraction. This article is protected by copyright. All rights reserved.

Experimental and numerical study of steady state stability in a toluene biodegrading biofilter.

Different steady states in a toluene biodegrading biofilter were explored experimentally and numerically. Experimental results showed that a gradual increase of the toluene inlet concentration over several weeks leads to a consistently low exit concentration, with a drastic increase at an inlet concentration change from 7.7 to 8.5 g m-3, indicating an alteration in steady state. A significant and sudden drop in the removal efficiency from 88 to 46% was observed. A model that includes nitrogen and biomass dynamics predicted results matching the experimental biofilter performance well, but the timing of the concentration jump was not reproduced exactly. A model that assumes a gradual increase of toluene inlet concentration of 0.272 g m-3 per day, accurately reproduced the experimental relationship between inlet and outlet concentration. Although there was variation between experimental and simulated results, a clear confirmation of the jump from one steady state to another was found.

The effect of biogas ebullition on ammonia emissions from animal manure-processing lagoons.

Various models have been developed to determine ammonia (NH3 ) emissions from animal manure-processing lagoons to enable relatively simple estimations of emissions. These models allow estimation of actual emissions without intensive field measurements or "one-size-fits-all" emission factors. Two mechanisms for lagoon NH3 emissions exist: (a) diffusive gas exchange from the water surface and (b) mass-flow (bubble transport) from NH3 contained within the ebullition gas bubble (as it rises to the surface) produced from anaerobic decomposition of organic matter. The purpose of this research is to determine whether gas ebullition appreciably affects NH3 emissions and therefore should be considered in emissions models. Specifically, NH3 mass-flow emissions were calculated and compared with calculated diffusive NH3 emissions. Mass-flow NH3 emissions were evaluated based on a two-film model, in connection with the acid dissociation constant of ammonium, to predict the degree of NH3 gas saturation within the bubbles. Average daily ammoniacal nitrogen concentration, pH, and measured biological gas production (ebullition) in conjunction with literature values for Henry's law constant were used to calculate emissions from NH3 saturation of ebullition gases. Ebullition enhancement of NH3 surface emissions due to increased turbulence was estimated from average lagoon ebullition rates and literature values of turbulence enhancement. Ebullition enhancement of NH3 surface emissions and ebullition mass-flow NH3 emissions was determined to be <10% and <0.052%, respectively, of total NH3 emissions. Therefore, because ebullition effects are small, they may be neglected when developing process models to estimate NH3 emissions from water surfaces of swine manure processing lagoons.

The COVID-19 pandemic: model-based evaluation of non-pharmaceutical interventions and prognoses.

An epidemiological model for COVID-19 was developed and implemented in MATLAB/GNU Octave for use by public health practitioners, policy makers, and the general public. The model distinguishes four stages in the disease: infected, sick, seriously sick, and better. The model was preliminarily parameterized based on observations of the spread of the disease. The model assumes a case mortality rate of 1.5%. Preliminary simulations with the model indicate that concepts such as "herd immunity" and containment ("flattening the curve") are highly misleading in the context of this virus. Public policies based on these concepts are inadequate to protect the population. Only reducing the R 0 of the virus below 1 is an effective strategy for maintaining the death burden of COVID-19 within the normal range of seasonal flu. The model is illustrated with the cases of Italy, France, and Iran and is able to describe the number of deaths as a function of time in all these cases although future projections tend to slightly overestimate the number of deaths when the analysis is made early on. The model can also be used to describe reopenings of the economy after a lockdown. The case mortality rate is still prone to large uncertainty, but modeling combined with an investigation of blood donations in The Netherlands imposes a lower limit of 1%.

Effect of diffusion limitation and substrate inhibition on steady states of a biofilm reactor treating a single pollutant.

The occurrence of multiple steady states in a toluene biodegrading, diffusion-limited biofilm under aerobic conditions was investigated by computer models: one steady-state, and one nonsteady-state. Two stable and one unstable intermediate steady-state were identified in a narrow set of combinations of parameters values. The nonsteady-state model predicts conditions that evolve to a steady state that is within 0.02-1% of the solution of the steady-state model, depending on the number of grid points used, confirming the algorithms are valid. Multiple steady states occur if, (1) a biofilm is exposed to a constant gas-phase pollution concentration, which exceeds or undershoots a certain threshold, (2) in a narrow range of parameter values and (3) provided that the pollutant degradation follows Haldane kinetics. Such a biofilm displays half-saturation (i.e., Michaelis-Menten)-like apparent ("falsified") kinetics from a concentration range starting at zero up to the occurrence of a second steady state. Multiple steady states and falsified kinetics can negatively affect a biofilter and the experimental determination of kinetic parameters, respectively. Implications: The occurrence of multiple steady states in a VOC treating biofilm, shows the significant impact of degradation kinetics and diffusion limitation on the biofilm behavior. Moreover, the implied possible sudden drop of removal efficiency of a biofilter, based on the occurrence of multiple steady states lead to possible bottle-necks in biofilter application and operation.

Comparison of Electronic and Physicochemical Properties between Imidazolium-Based and Pyridinium-Based Ionic Liquids.

To compare 1-butyl-3-methylimidazolium ([BMIM]+)- and 1-butyl-3-methylpyridinium ([BMPy]+)-based ionic liquids (ILs) and investigate the influence of intramolecular and intermolecular interactions on physicochemical properties, a systematic study was performed on the electronic structures and physicochemical properties of [BMIM]+ tetrafluoroborate ([BMIM][BF4]), [BMIM]+ hexafluorophosphate ([BMIM][PF6]), [BMIM]+ hydrogen sulfate ([BMIM][HSO4]), [BMIM]+ methylsulfate ([BMIM][MSO4]), [BMIM]+ ethylsulfate ([BMIM][ESO4]), [BMPy]+ tetrafluoroborate ([BMPy][BF4]), [BMPy]+ hexafluorophosphate ([BMPy][PF6]), [BMPy]+ hydrogen sulfate ([BMPy][HSO4]), [BMPy]+ methylsulfate ([BMPy][MSO4]), and [BMPy]+ ethylsulfate ([BMPy][ESO4]) using density functional theory and molecular dynamics simulation. The results reveal that aggregation behavior exists in [HSO4]-- and [ESO4]--based ILs, and the differences between their densities and self-diffusion coefficients are smaller when there is an aggregation effect in ILs. A dimer is formed by two strong hydrogen bonds between two [HSO4]- anions in [HSO4]-based ILs, and the existence of hydrogen bonds in ILs increases density and decreases the self-diffusion coefficient. The intermolecular interaction strength of [BMIM]+-based ILs is stronger than that of [BMPy]+-based ILs.

Interactions of Biodegradable Ionic Liquids with a Model Naphthenic Acid.

Density functional theory models are used to examine five biodegradable ionic liquids (ILs) each one consisting of a substitutional group (-OH, -NH2, -COOH, -COOCH3, and -OCH3) incorporated into the cation of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). The results reveal that hydrogen atoms in -NH2, -COOH, and -COOCH3 form intramolecular hydrogen bonds with fluorine atoms in [BF4]-, whereas hydrogen atoms in -OH and -OCH3 do not form hydrogen bonds with [BF4]-. Further analysis of electron density at bond critical points and noncovalent interactions suggest that [BMIM][BF4] with -COOH has stronger intramolecular hydrogen bonds than other ILs. The extraction mechanism for a model naphthenic acid is hydrogen bonding, with F···H being the strongest hydrogen bond and O···H ranking second. More intermolecular hydrogen bonds occur when model naphthenic acid is adsorbed by [BMIM][BF4] with -COOH and -COOCH3. The interaction energy between model naphthenic acid and ILs with -COOH and -COOCH3 is higher than that with -OH, -NH2, and -OCH3.

Microbial methane oxidation processes and technologies for mitigation of landfill gas emissions.

Landfill gas containing methane is produced by anaerobic degradation of organic waste. Methane is a strong greenhouse gas and landfills are one of the major anthropogenic sources of atmospheric methane. Landfill methane may be oxidized by methanotrophic microorganisms in soils or waste materials utilizing oxygen that diffuses into the cover layer from the atmosphere. The methane oxidation process, which is governed by several environmental factors, can be exploited in engineered systems developed for methane emission mitigation. Mathematical models that account for methane oxidation can be used to predict methane emissions from landfills. Additional research and technology development is needed before methane mitigation technologies utilizing microbial methane oxidation processes can become commercially viable and widely deployed.

Toluene removal biofilter modeling.

On the basis of the model proposed by De Visscher and Van Cleemput for methane oxidation in landfill cover soils, simulation models for biofiltration of toluene-contaminated air were performed for biofilters with or without substrate inhibition and operated at constant or varying airflow rates. The toluene oxidizing activity (V(max)) expressions of the derived models clearly indicate that V(max) is not a constant along a biofilter height. The equations derived when V(max) is set to zero can be used to predict the minimum concentration requirement for a viable biofiltration process. The simulation results show that the model of De Visscher and Van Cleemput, modified to incorporate Haldane kinetics, provides a good description of the biofiltration performance for toluene removal biofilters. Predictions of the minimum concentration that can be treated indicate that conventional biofilters are not suitable for indoor air pollutant removal.

Modelling of stable isotope fractionation by methane oxidation and diffusion in landfill cover soils.

A technique to measure biological methane oxidation in landfill cover soils that is gaining increased interest is the measurement of stable isotope fractionation in the methane. Usually to quantify methane oxidation, only fractionation by oxidation is taken into account. Recently it was shown that neglecting the isotope fractionation by diffusion results in underestimation of the methane oxidation. In this study a simulation model was developed that describes gas transport and methane oxidation in landfill cover soils. The model distinguishes between 12CH4, 13CH4, and 12CH3D explicitly, and includes isotope fractionation by diffusion and oxidation. To evaluate the model, the simulations were compared with column experiments from previous studies. The predicted concentration profiles and isotopic profiles match the measured ones very well, with a root mean square deviation (RMSD) of 1.7 vol% in the concentration and a RMSD of 0.8 per thousand in the delta13C value, with delta13C the relative 13C abundance as compared to an international standard. Overall, the comparison shows that a model-based isotope approach for the determination of methane oxidation efficiencies is feasible and superior to existing isotope methods.

Municipal solid waste characterization and its assessment for potential methane generation: a case study.

There has been a significant increase in municipal solid waste (MSW) generation in India during the last few decades and its management has become a major issue because the poor waste management practices affect the health and amenity of the cities. In the present study, various physico-chemical parameters of the MSW were analyzed to characterize the waste dumped at Gazipur landfill site in Delhi, India, which shows that it contains a high fraction of degradable organic components. The decomposition of organic components produces methane, a significant contributor to global warming. Based on the waste composition, waste age and the total amount dumped, a first-order decay model (FOD) was applied to estimate the methane generation potential of the Gazipur landfill site, which yields an estimate of 15.3 Gg/year. This value accounts to about 1-3% of existing Indian landfill methane emission estimates. Based on the investigation of Gazipur landfill, we estimate Indian landfill methane emissions at 1.25 Tg/year or 1.68 Tg/year of methane generation potential. These values are within the range of existing estimates. A comparison of FOD with a recently proposed triangular model was also performed and it shows that both models can be used for the estimation of methane generation. However, the decrease of the emission after closure is more gradual in the case of the first-order model, leading to larger gas production predictions after more than 10 years of closure. The regional and global implications of national landfill methane emission are also discussed.

Induction of enhanced methane oxidation in compost: temperature and moisture response.

Landfilling is one of the most common ways of municipal solid waste disposal. Degradation of organic waste produces CH(4) and other landfill gases that significantly contribute to global warming. However, before entering the atmosphere, part of the produced CH(4) can be oxidised while passing through the landfill cover. In the present study, the oxidation rate of CH(4) was studied with various types of compost as possible landfill cover. The influence of incubation time, moisture content and temperature on the CH(4) oxidation capacity of different types of compost was examined. It was observed that the influence of moisture content and temperature on methane oxidation is time-dependent. Maximum oxidation rates were observed at moisture contents ranging from 45% to 110% (dry weight basis), while the optimum temperature ranged from 15 to 30 degrees C.

Nitrogen cycling through swine production systems: ammonia, dinitrogen, and nitrous oxide emissions.

Ammonia (NH(3)) emissions from animal systems have become a primary concern for all of livestock production. The purpose of this research was to establish the relationship of nitrogen (N) emissions to specific components of swine production systems and to determine accurate NH(3) emission factors appropriate for the regional climate, geography, and production systems. Micrometeorological instrumentation and gas sensors were placed over two lagoons in North Carolina during 1997-1999 to obtain information for determining ammonia emissions over extended periods and without interfering with the surrounding climate. Ammonia emissions varied diurnally and seasonally and were related to lagoon ammonium concentration, acidity, temperature, and wind turbulence. Conversion of significant quantities of ammonium NH(4)(+) to dinitrogen gas (N(2)) were measured in all lagoons with the emission rate largely dependent on NH(4)(+) concentration. Lagoon NH(4)(+) conversion to N(2) accounted for the largest loss component of the N entering the farm (43% as N(2)); however, small amounts of N(2)O were emitted from the lagoon (0.1%) and from field applications (0.05%) when effluent was applied nearby. In disagreement with previous and current estimates of NH(3) emissions from confined animal feeding operation (CAFO) systems, and invalidating current assumptions that most or all emissions are in the form of NH(3), we found much smaller NH(3) emissions from animal housing (7%), lagoons (8%), and fields (2%) using independent measurements of N transformation and transport. Nitrogen input and output in the production system were evaluated, and 95% of input N was accounted for as output N from the system.

Simulation model for gas diffusion and methane oxidation in landfill cover soils.

Landfill cover soils oxidize a considerable fraction of the methane produced by landfilled waste. Despite many efforts this oxidation is still poorly quantified. In order to reduce the uncertainties associated with methane oxidation in landfill cover soils, a simulation model was developed that incorporates Stefan-Maxwell diffusion, methane oxidation, and methanotrophic growth. The growth model was calibrated to laboratory data from an earlier study. There was an excellent agreement between the model and the experimental data. Therefore, the model is highly applicable to laboratory column studies, but it has not been validated with field data. A sensitivity analysis showed that the model is most sensitive to the parameter expressing the maximum attainable methanotrophic activity of the soil. Temperature and soil moisture are predicted to be the environmental factors affecting the methane oxidizing capacity of a landfill cover soil the most. Once validated with field data, the model will enable a year-round estimate of the methane oxidizing capacity of a landfill cover soil.

Kinetic model for the sonochemical degradation of monocyclic aromatic compounds in aqueous solution: new insights.

The kinetic model of De Visscher et al. [J. Phys. Chem. 100 (1996) 11636] for the sonochemical degradation of apolar monocyclic aromatic compounds in aqueous solution is based on a large number of assumptions, some of which have never been stated explicitly. An example is a homogeneous temperature of cavitation. The present study focuses on those "hidden assumptions", and reveals that some of them are not realistic. It is shown that an entirely different set of assumptions leads to essentially the same mathematical formulation of the kinetics. The old and new version of the model can be considered as limiting cases which envelope the real conditions of ultrasonic cavitation chemistry. However, the new model does not lead to the inconsistencies experienced with the old model.