CO2 Consumption Research Articles

Carbonate Mineral Dissolution and Its Carbon Sink Effect in Chinese Loess

The relationship between the source and sink of atmospheric CO2 has always been a widely discussed issue in global climate change research. Recent studies revealed that the chemical weathering of carbonate rocks contributed to 1/3 (~0.5 Pg C/yr) of the missing carbon sinks (MCS) globally, and there are still 2/3 of MCS (~0.5 Pg C/yr) that need to be explored. As one of the main overburdened parts of the earth, loess is one of the important driving factors for atmospheric CO2 consumption. Here, we elaborated on the dissolution process and the carbon sink effect from carbonate and silicate minerals in loess. The relationship between carbonate dissolution and carbon source/sink is elucidated, and the mechanism of carbon sink formation from secondary carbonates in loess is clarified. Additionally, the commonly used methods for the identification of primary and secondary carbonates are summarized, and the methods for the study of loess carbon sinks and the influencing factors of loess carbon sinks are also revealed. Based on the research results and progress interpretations, the prospects of loess carbon sinks are discussed to provide a scientific basis for further research on loess carbon sinks.

Comparison of fuel consumption and recoverable energy according to NEDC and WLTP cycles of a vehicle

Since 1997, the NEDC (New European Driving Cycle) has been used to measure CO2 emissions. However, because this cycle is unable to accurately replicate real-world driving conditions, a new procedure has been developed. The WLTP (Worldwide Harmonised Light Vehicles Test Procedure), which is 10 minutes longer and more dynamic than NEDC, has been used since late 2017. In this paper, fuel consumption, CO2 emissions, and energy demand of these two cycles are compared. The vehicle mathematical model was created in a MATLAB program using vehicle longitudinal motion equations for a light commercial vehicle with a diesel engine. The speed profiles of the commonly used NEDC and WLTP cycles were defined in the model, and the fuel consumption, CO2 emission values, and the total energy values required for each cycle were calculated. Furthermore, the recoverable energy potential of the cycle has been revealed. According to the WLTP cycle, the vehicle's fuel consumption and CO2 emission values were calculated at approximately 11% more than the NEDC cycle. The recoverable energy potential is 2.64 times higher in the WLTP cycle compared to the NEDC cycle. Thus, for vehicle designers, it is a very useful tool that can calculate the fuel and CO2 consumption of a vehicle in 100 km according to certain cycles, based on vehicle parameters.

Dynamic life cycle assessment of the recurring embodied emissions from interior walls: Cradle to grave assessment

The construction sector is recognized as being one of the main generators of CO₂ emissions and consumption of resources. Lately, special attention has been directed to the search for strategies that optimize and mitigate the embodied impact of constructive systems. In this research, the widely used life cycle assessment is applied to analyze the embodied emissions of several constructive systems used as interior partition walls (IPW), from a “cradle to grave” perspective. The study includes dynamic parameters in the design of scenarios for calculating the recurrent embodied emissions. The aim of the research is to assess the influence of these parameters on the variability of the accumulated results and to identify the constructive systems with optimal environmental performance. The results show the importance of maximizing the service life of systems and buildings in order to reduce the associated emissions, since the impact can be reduced by up to 60% over a 120-year perspective for the same system. This parameter's direct influence on the accumulated environmental performance was observed when an IPW with high initial impact but with longer service life consideration (IPW 26 – scenario 28 with 506 kg CO2 eq) could be just as suitable as an IPW with lower impact but shorter service life (IPW 27 – scenario 22 with 500 kg CO2 eq). It is also concluded that the initial embodied emissions of the construction systems are determinant in the cumulative impact, therefore highlighting the importance of material selection and optimization and the need for improvement in production processes.

Thermodynamic and Kinetic Effects of Quaternary Ammonium and Phosphonium Ionic Liquids on CO2 Hydrate Formation.

The paper elaborates the effects of ionic liquids (ILs) on the phase equilibrium temperature, induction time, gas consumption, gas consumption rate, and water to hydrate conversion in the presence of 0.25, 0.63, 0.95, 1.25, 3.75, 6.25, and 10.00 wt % ethyltributylphosphonium hexafluorophosphate ([P2444][PF6]), tributylhexylphosphonium hexafluorophosphate ([P6444][PF6]), tetraethylammonium bromide ([N2222]Br), tetraethylammonium bistrifluoromethanesulfonimide ([N2222][NTf2]), and tetraethylammonium hexafluorophosphate ([N2222][PF6]) under a pressure of 2 MPa. The results indicate that all five ILs could increase CO2 consumption and enhance the water to hydrate conversion. Compared with the pure water system, [P2444][PF6] and [P6444][PF6] shifted the phase equilibrium temperature of CO2 hydrates to a slightly higher temperature with reduced induction times by boosting CO2 hydrate nucleation, showing the dual function promotion effects. In contrast, [N2222]Br, [N2222][NTf2], and [N2222][PF6] shifted the phase equilibrium temperature of CO2 hydrates to a lower temperature and prolonged the induction time by slowing down CO2 hydrate nucleation. The inhibition effects of anions on CO2 hydrates follow an order of Br- > [NTf2]- > [PF6]-. Besides, the density functional theory and molecular dynamic calculations were conducted to explain the inconsistent influences of [N2222]Br and [N4444]Br on CO2 hydrate formation. It was found that the anion-cation interaction of [N2222]Br was stronger than that of [N4444]Br, and Br- in [N2222]Br is less likely to participate in the formation of hydrate cages in the [N2222]Br + H2O + CO2 system according to the intermolecular anion-water, anion-CO2, and water-water radial distribution function in [N2222]Br + H2O + CO2 and [N4444]Br + H2O + CO2 systems.

CO2 capture enhancement by forming tetra‐n‐butyl ammonium bromide semiclathrate in graphite nanofluids

AbstractIn this work, CO2 capture was experimentally investigated by forming tetra‐n‐butyl ammonium bromide (TBAB) semiclathrate in a new system of TBAB + graphite nanofluids. The experiments were carried out at 3.5 MPa and 277.15 K. Compared to the TBAB solution and the TBAB + sodium dodecyl sulphate (SDS) solution, it was found that the system of TBAB + graphite nanofluids was preferable for CO2 capture, and 0.2 wt.% graphite nanoparticles (GNP) was an optimal concentration for the enhancement of hydrate growth in TBAB + graphite nanofluids. At this GNP concentration, CO2 consumption gained at 0.29 mol% TBAB is greater than that acquired at 0.62 and 2.57 mol% TBAB. CO2 consumption obtained in TBAB + graphite nanofluids is larger than other systems containing GNP. Moreover, the morphologies of TBAB + CO2 semiclathrate formed in TBAB solution, TBAB + SDS solution, and TBAB + graphite nanofluids were presented, and the mechanism of CO2 capture using TBAB semiclathrate formation in graphite nanofluids was presented. Therefore, it is an efficient way to capture CO2 by forming TBAB semiclathrate in graphite nanofluids.

Experimental study on the gasification characteristics of polyethylene terephthalate (PET) microplastics in supercritical H2O/CO2 environment

Plastic waste can be seen everywhere in our life, while the increasing emission of CO2 is causing concern. The use of supercritical fluids to treat plastic waste is highly efficient and provides a new idea for the green treatment of plastic waste. Green treatment of plastics can be achieved, and the possibility of CO2 consumption can be explored in supercritical fluids. Still, its mechanism has not been clearly explained yet, so it is essential to study its laws carefully. This paper carried out the gasification experiment of polyethylene terephthalate (PET) in supercritical H2O/CO2. The effects of temperature, residence time, initial CO2 volume and seawater on the gasification reaction are discussed. The results showed that: increasing the gasification temperature, extending the reaction residence time, and increasing the amount of carbon dioxide can improve the gasification efficiency, and the metal salts contained in seawater can promote the pyrolytic gasification of plastics. And the temperature change significantly influences the interface of PET plastics. The carbon conversion efficiency of PET plastics reached 40.5% with a certain amount of raw material and water for 20 min at 700 °C in supercritical carbon dioxide and water. At 500 °C, PET plastic has the best thermochemical reduction of CO2. This work provides new ideas for future green treatment of plastic waste and contributes to carbon reduction efforts.

Heterogeneous and Combined Heterogeneous/Homogeneous Combustion Modeling of SOFC Off-Gases.

The heterogeneous (catalytic) and the hetero-/homogeneous (catalytic and gas-phase) combustion processes of solid oxide fuel cell (SOFC) off-gases with compositions typical of a high cell utilization rate are investigated with high-fidelity 2D simulations in a platinum-coated planar channel using detailed hetero-/homogeneous chemistry. The pressures are 1-8 bar; the reactant streams have volumetric H2 and CO contents 0.7-1.5 and 5.3-9.7%, respectively; H2O and CO2 dilutions are ∼40 and ∼50%, respectively; and the global fuel/air equivalence ratio is 0.90. Water inhibits chemically the catalytic oxidation of H2, as it leads to high H(s) surface coverage that favors the recombinative desorption of H(s) to H2. On the other hand, H2O promotes chemically the catalytic oxidation of CO by creating high OH(s) coverage that in turn accelerates the CO consumption. Strong flames are established at the highest H2 content cases and for pressures p ≥ 3 bar. For all cases with vigorous homogeneous combustion, the catalytic and gas-phase reaction pathways coexist and compete with each other for the consumption of H2 and CO. The large H2O content leads to gas-phase production of H2 via the reaction H2O + H = H2 + OH. However, the gas-phase produced H2 is subsequently consumed by the catalytic pathway, such that nearly complete H2 conversion is attained at the reactor outlet. Gaseous chemistry does not affect the reactor lengths required for complete H2 conversion but substantially reduces the corresponding lengths for CO conversion. The H2 emissions decrease with increasing pressure and are in the range 8-110 ppmv, while the CO emissions increase with rising pressure and span the range 0.3-52 ppmv, thus leading to corrected CO emissions (at 15% O2) of less than 15 ppmv. Finally, the peak wall temperatures are largely acceptable in terms of catalyst thermal stability.

Chemical weathering and CO2 consumption rate of montane silicate in South China: a case study of the Xizhijiang River Basin

Chemical weathering and CO2 consumption rate of montane silicate in South China: a case study of the Xizhijiang River Basin

Geological carbon cycle in a sandstone aquifer: Evidence from hydrochemistry and Sr isotopes

Sr isotopes have been widely used to quantify silicate versus carbonate weathering reflected in rivers, but there is no such study in groundwater, which is restricted by the difficulty of accurately determining the Sr contents and isotopic ratios of the two endmembers in silicate-dominated aquifers. In a sandstone catchment, we find rainwater, modern groundwater in the recharge area, and old groundwater in the discharge area have contrast 87Sr/86Sr ratios, with mean values of 0.710784, 0.711448, and 0.710269, respectively. If we follow previous studies and use the acetic acid leachate of sandstone to represent the calcite fraction, the resulting 87Sr/86Sr ratio cannot explain most groundwater samples. By considering the simultaneous dissolution of calcite and silicates in the acetic acid leachate, we find the typical 87Sr/86Sr ratio of calcite equals 0.709113, which well explains the 87Sr/86Sr ratios of all groundwater samples. The 87Sr/86Sr ratios of groundwater in the recharge area with abundant dissolved CO2 are contributed by three endmembers (rainwater, silicate and calcite), whereas those of old groundwater in the discharge area with low dissolved CO2 as well as low Cl− and SO42− can be explained by two endmembers (calcite and groundwater in the recharge area). Based on strontium isotopic budget, we find the equivalent concentrations of CO2 consumption by silicates and calcite in groundwater are both larger than those in river waters studied in previous studies, and the majority of dissolved CO2 in groundwater can be fixed by carbonate weathering as long as the residence time is long enough. This study enhances understanding of the roles of silicate and carbonate weathering during long-time groundwater circulation.

Enrichment of homoacetogens converting H2/CO2 into acids and ethanol and simultaneous methane production.

An anaerobic granular sludge was enriched to utilize H2/CO2 in a continuous gas-fed up-flow anaerobic sludge reactor by applying operating conditions expected to produce acetic acid, butyric acid, and ethanol. Three stages of fermentation were found: Stage I with acetic acid accumulation with the highest concentration of 35mM along with a pH decrease from initial 6 to 4.5. In Stage II, H2/CO2 was replaced by 100% H2 to induce solventogenesis, whereas butyric acid was produced with the highest concentration of 2.5mM. At stage III with 10 µM tungsten (W) addition, iso-valeric acid, valeric acid, and caproic acid were produced at pH 4.5-5.0. In the batch tests inoculated with the enriched sludge taken from the bioreactor (day 70), however, methane production occurred at pH 6. Exogenous 15mM acetate addition enhanced both the H2 and CO2 consumption rate compared to exogenous 10, 30, and 45mM acetate by the enriched sludge. Exogenous acetate was failed to be converted to ethanol using H2 as electron donor by the enriched acetogens.

Estimation of pH on total scale in coastal environments for the understanding of the variability of the carbonate system in the context of ocean acidification

Most of the theoretical and practical development of the ocean acidification (OA) phenomenon involves the open ocean, and not much is known of the significance of variation in pH and carbonate system in coastal environments and the effect, if any, of OA. Traditional potentiometric pH measurements are carried out on the NBS scale (pHNBS), developed for freshwaters, but for OA it is necessary to use the total scale (pHT), which includes the additional ions of seawater. Using a series of in-situ measurements of potential, carried out with a pHNBS electrode in the artificial coastal lagoon La Escollera in Santa Marta (Colombia), a methodology to calculate pHT was tested. For this, the equation pHT(X) = pHT(TRIS) - EX-ETRISR*T*ln10/F was used, which calculates pHT(X) of the sample from the pHT(TRIS) of the TRIS standard solution, the potentials E measured at temperature T, and the constants R and F. ETRIS was determined experimentally for the lagoon temperature range, and the linear regression showed a coefficient of determination (R2) of 0.9977. In a first qualitative analysis, it was verified that pH variations during the day-night cycle are closely associated with those of oxygen, from the production and consumption of CO2 by photosynthesis and respiration. These high-frequency variations are of greater magnitude than those of the open ocean, raising questions about the real effect of OA on coastal ecosystems.

Geochemical Trends and Rare Earth Elements’ Behaviour in the Recently Exposed Weathering Profiles of the Deccan Basalts from Central India

Abstract The Deccan basalts have been undergoing intense weathering in the tropical conditions since the passage of India through the equator. This study is on the basalts’ weathering from central India’s present present-day semiarid climate. Two weathering profiles from the districts of Indore and Dhar, Madhya Pradesh, have been studied using mineralogy and geochemistry. The profiles show incipient weathering with low to medium Chemical Index of Alteration (CIA) and Mafic Index of Alteration-oxidising (MIA(O)) values. The presence of smectite in weathered zones, mineralogically attests to incipient weathering. The pyroxene and plagioclase-rich zones have produced smectite clays in the basalts. The rare earth elements (REE) and, to a greater extent, the heavy (H) REE show mobility during incipient weathering, which appears to be due to differential retention of REE in the clay minerals. The smectites seem to retain light (L) REE more significantly than HREE. The ancient terrain showing currently incipient weathering indicates recent exposure of the profiles by the erosion under neotectonic activity. In this fashion, the frequent exposures of new weathering surfaces on the basalts may have played a significant role in the uninterrupted consumption of CO2 by silicate weathering since around 50 Ma.

Geochemical reaction of compressed CO2 energy storage using saline aquifer

During the use of compressed CO2 storage in saline aquifers, complex geochemical reactions may occur, affecting the petrophysical properties of the reservoir rocks and leading to CO2 depletion. In this paper, the geochemical reaction mechanism of CCES-SA was studied numerically with the Yingcheng Group in the southeast uplift area of the Songliao Basin as the study area. The hydrogeological parameters of the target study area were used as the initial parameters for the numerical simulation study, and the CO2-brine-rock geochemical reaction simulation was carried out using the reaction transport model to study the effects of the 20-year geochemical reaction on the physical properties of reservoir rocks and CO2 consumption through numerical simulation. The following results were obtained by analyzing the numerical simulation results. The long-term geochemical reactions dissolved chlorite and feldspar minerals, etc., and also precipitated carbonates and clay minerals, etc., which were consistent with the actual results. Besides, the dissolution and precipitation of the above minerals did not affect the porosity and permeability of underground aquifers and did not have adverse consequences for extraction. At the end of 20 years of inter-seasonal energy storage, the percentages of CO2 captured in gas, aqueous phase and minerals were 27%, 65% and 8%, respectively. During storage, it was recommended to inject CO2 appropriately during closure to maintain gas phase CO2 content and pressure. During the production process, the acidified formation fluid came into contact with the inner pipe, increased the risk of wellbore corrosion. When selected materials for wellbore materials, it was recommended to choose corrosion-resistant pipes. What was studied in this paper could provide a theoretical reference for underground energy storage projects involving fluid-rock interactions.

The Hydrochemistry, Ionic Source, and Chemical Weathering of a Tributary in the Three Gorges Reservoir

Riverine dissolved matter reflects geochemical genesis information, which is vital to understand and manage the water environment in a basin. The Ganjing River located in the hinterland of the Three Gorges Reservoir was systematically investigated to analyze the composition and spatial variation of riverine ions, probe the source and influencing factors, and assess the chemical weathering rates and CO2 consumption. The results showed that the total dissolved solid value (473.31 ± 154.87 mg/L) with the type of “HCO3−–Ca2+” was higher than that of the global rivers’ average. The hydrochemical parameters were relatively stable in the lower reservoir area of the Ganjing River, which was largely influenced by the backwater of Three Gorges Reservoir. The carbonate weathering source contributed 69.63% of TDS (Total dissolved solids), which generally dominated the hydrochemical characteristics. The contribution rates of atmospheric rainfall were relatively low and stable in the basin, with an average of 4.01 ± 1.28%. The average contribution rate of anthropogenic activities was 12.05% in the basin and even up to 27.80% in the lower reservoir area of the Ganjing River, which illustrated that the impoundment of Three Gorges Reservoir had brought great challenges to the water environment in the reservoir bay. The empirical power functions were tentatively proposed to eliminate the dilution effect caused by runoff discharge on the basis of previous studies. Accordingly, the rock weathering rate was calculated as 23.54 t/km2 in the Ganjing River Basin, which consumed atmospheric CO2 with a flux of 6.88 × 105 mol/y/km2. These results highlight the geochemical information of tributaries in the hinterland of the Three Gorges Reservoir, have significant implications for understanding the impact of impoundment, and provide data support for the integrated management of water resources in the Ganjing River Basin.

Hafnium isotope evidence for enhanced weatherability at high southern latitudes during Oceanic Anoxic Event 2

The Oceanic Anoxic Event 2 (OAE 2; ca. ∼94 Ma) represents one of the most extreme carbon cycle perturbations of the Phanerozoic, which coincided with major environmental and climate reorganization in both terrestrial and marine realms. Chemical weathering of continental silicate rocks is thought to have played a crucial role during OAE 2, through enhanced release of bio-essential nutrients to the ocean, promoting high rates of marine primary production and organic carbon burial, but also due to its effect on atmospheric CO2 drawdown, which altogether possibly drove the OAE 2 termination. Yet, the evolution of continental chemical weathering during OAE 2 remains poorly defined, especially in high-latitude regions. In this study, we present a combined hafnium-neodymium isotope investigation of the clay-size detrital fraction (△εHfclay) of late Cenomanian to early Turonian sediments from the southwest Australian margin, at a site (International Ocean Discovery Program U1516) located in the southern high latitudes (∼62°S) during the late Cretaceous. The reliability of △εHfclay as a proxy for continental chemical weathering in ancient anoxic marine sediments was assessed by analyzing a suite of samples retrieved from methanogenic sediments experiencing marine silicate weathering at ocean margins, suggesting negligible effect of reverse weathering on hafnium-neodymium isotope compositions. At Site U1516, the early stage of OAE 2 was characterized by relatively low △εHfclay values (−5.9 ± 2), typical of reduced chemical weathering in nearby continental regions. At the onset of the most prominent carbon isotope excursion, an abrupt decrease in △εHfclay points towards accelerated export of poorly weathered sediments resulting from the abrupt reactivation of river systems in southwest Australia. This period was followed by a pronounced △εHfclay shift towards positive values, indicative of intensifying chemical weathering conditions during the OAE 2 interval showing the highest δ13C anomaly. Based on these results, we posit that enhanced hydrological cycle, most likely caused by a southward shift of the westerlies, led to a large increase in weatherability at southern high latitudes during peak OAE 2 warmth. This finding provides empirical support for the potential role played by high-latitude weathering systems in driving the termination of OAE 2, via weathering-driven consumption of atmospheric CO2 and accelerated riverine fluxes of nutrients leading to enhanced organic carbon burial in marine sediments.

Late Permian ∼ 6 My cooling induced by basaltic weathering of the Emeishan large igneous province: Evidence from interbasaltic paleosols

Land surface temperature variations during the Emeishan large igneous province volcanism helps to reveal the effect on the climate in the late phase of the late Paleozoic Ice Age. Paleosols preserved between the Emeishan basalts record hiatuses in basalt eruptions and provide detailed information on the Earth's surface environment. Forty-seven paleosol profiles in eleven locations were identified, described, and assigned to four pedotypes: I, II, III, and IV. The majority of pedotypes I, II, and III had a dominant mineral assemblage of kaolinites, hematite, and anatase, high chemical index of alteration values of 90–99 and Al2O3 and Fe2O3 enrichments, and were classified as Oxisols or Ultisols (alternatively, laterite). Pedotype IV contained large amounts of primary minerals from basalts, yielded low chemical index of alteration values of 35–65, and were classified as Entisols or Inceptisols. The eastern Emeishan large igneous province was dominated by highly weathered pedotypes I and II, with small amounts of pedotype III, while the western Emeishan large igneous province was dominated by pedotype III and weakly weathered pedotype IV. We interpreted this spatial distribution pattern of pedotypes as a result of the paleotopographic difference formed by the subaerial mafic lava accumulation, with steep highlands in the western Emeishan large igneous province and lowlands in the eastern areas. Based on the silica-alumina‑iron ratio climofunction, a land surface temperature cooling trend of ∼2–4 °C was recognized in the upper part of the Emeishan basalt succession (i.e., the waning phase) in three sections and was constrained to ∼260 to ∼253 Ma by new high-precision zircon UPb dates. This land surface temperature cooling trend was temporally coupled with the sea surface temperature cooling trend and the alpine P4 glaciation in eastern Australia. We propose that the intense weathering of extensive Emeishan basalts in the tropical humid belt, directly evidenced by the numerous thick laterites in the upper part of the basalt succession across the broad regions of the Emeishan large igneous province, elevated atmospheric CO2 consumption flux, leading to global cooling and further triggering the P4 glaciation.

Microbial electrosynthesis of acetate from CO2 under hypersaline conditions

Microbial electrosynthesis (MES) enables the bioproduction of multicarbon compounds from CO2 using electricity as the driver. Although high salinity can improve the energetic performance of bioelectrochemical systems, acetogenic processes under elevated salinity are poorly known. Here MES under 35–60 g L−1 salinity was evaluated. Acetate production in two-chamber MES systems at 35 g L−1 salinity (seawater composition) gradually decreased within 60 days, both under −1.2 V cathode potential (vs. Ag/AgCl) and −1.56 A m−2 reductive current. Carbonate precipitation on cathodes (mostly CaCO3) likely declined the production through inhibiting CO2 supply, the direct electrode contact for acetogens and H2 production. Upon decreasing Ca2+ and Mg2+ levels in three-chamber reactors, acetate was stably produced over 137 days along with a low cathode apparent resistance at 1.9 ± 0.6 mΩ m2 and an average production rate at 3.80 ± 0.21 g m−2 d−1. Increasing the salinity step-wise from 35 to 60 g L−1 gave the most efficient acetate production at 40 g L−1 salinity with average rates of acetate production and CO2 consumption at 4.56 ± 3.09 and 7.02 ± 4.75 g m−2 d−1, respectively. The instantaneous coulombic efficiency for VFA averaged 55.1 ± 31.4%. Acetate production dropped at higher salinity likely due to the inhibited CO2 dissolution and acetogenic metabolism. Acetobacterium up to 78% was enriched on cathodes as the main acetogen at 35 g L−1. Under high-salinity selection, 96.5% Acetobacterium dominated on the cathode along with 34.0% Sphaerochaeta in catholyte. This research provides a first proof of concept that MES starting from CO2 reduction can be achieved at elevated salinity.

Study on the real-world emission characteristics of gaseous and particulate pollutants from an inland ship using a portable emission measurement system.

The emissions of pollutants from inland ships endanger the urban environment and human health, deserving quantitative study to make reduction measurements to achieve clean emissions. In this study, the real-world gaseous emissions (CO, THC, SO2, NOx) and particulate emissions including particle mass (PM) and particle number (PN) as well as the particle size distribution and particle compositions from an inland ship were investigated using a portable emission measurement system (PEMS) method. The results showed that the emission concentrations of CO, THC, PM and PN at departure and idling conditions were significantly higher than those at other conditions, while the emission concentrations of NOx and SO2 at cruising condition were the highest. The particle size distribution always presented a bimodal distribution ranged at 40nm and 200nm respectively at different conditions and engine loads. The proportion of nucleation mode particles was the highest at departure condition, and a larger engine load resulted in a declined proportion of nucleation mode particles. The anions of the emitted particles mainly included nitrite ion (NO2-), nitrate ion (NO3-), sulfate ion (SO42-), and cations mainly included ammonium ion (NH4+), sodium ion (Na+) and potassium ion (K+). The main components of organic carbon (OC) in soot were OC1 and OC2, accounting for more than 80%, while the main component of elemental carbon (EC) was EC2, accounting for 83.9%. The emission factors based on fuel consumption of CO and THC were significantly higher at idling conditions than other conditions, and the emission factor of NOx was higher at cruising conditions, while the emission factors of PM and PN were higher at departure and idling conditions than other conditions.

Elucidating the role of nanoparticles on photosynthetic biogas upgrading: Influence of biogas type, nanoparticle concentration and light source

Three different nanoparticles, namely Fe2O3, carbon coated zero valent iron (CACOI) and SiO2, were added to a mixed microalgae culture in order to improve photosynthetic biogas upgrading. Fe2O3 and CACOI nanoparticles at 10 mg/L supported higher CO2 consumptions compared to their respective controls. The addition of Fe2O3 nanoparticles at 70 mg/L resulted in a 38 % enhanced biomass productivity, and 20 % higher CO2 consumption but delayed exponential growth. The CACOI nanoparticles at 70 mg/L resulted in a shorter lag phase, enhanced CO2 consumption by 13 %, and carbohydrate content enhancement by 64 %, while the addition of SiO2 nanoparticles at this concentration induced an enhanced lipid and carbohydrates production by 47 % and 68 %, respectively. Interestingly, UV light exposure reduced the beneficial effects of nanoparticles, although CACOI nanoparticles still supported a shorter lag phase and higher carbohydrates production at 70 mg/L. In brief, CACOI nanoparticles hold an untapped potential to promote the metabolism of microalgae during photosynthetic biogas upgrading.

Insight into the comprehensive effect of carbon dioxide, light intensity and glucose on heterotrophic-assisted phototrophic microalgae biofilm growth: A multifactorial kinetic model

Heterotrophic-assisted photoautotrophic microalgae biofilm cultivation was an alternative way to realize CO2 reduction and wastewater treatment. Growth kinetics supplied a channel to better understand how the cultivation conditions affect microalgal growth and CO2 reduction. However, the two growth modes (heterotroph and photoautotroph) have different needs for organic and inorganic nutrients. Thus, combining the threshold theory and multiplication theory, an integral multifactorial kinetic model that looking insight into the comprehensive effect of glucose, CO2, light intensity, and nitrate was developed for heterotrophic-assisted photoautotrophic microalgae biofilm growth in this study. R2 between model and experiment was 0.99. It predicted the maximum specific growth rate and maximum CO2 consumption rate of heterotrophic-assisted photoautotrophic microalgae biofilm was 1.868 h−1 and 1.02 h−1, respectively. This model fully explained the influence of the main factors on microalgae biofilm growth and reasonably predicted the growth rate of microalgae biofilm under different growth conditions.