Combined Biological Treatment/Ozonation of Wastewaters for the Mineralisation of Non‐Biodegradable Naphthalene‐1,5‐Disulphonic Acid

This paper deals with the ozonation and biological treatment for achieving the mineralisation of the non‐biodegradable compound naphthalene‐1,5‐disulphonic acid (NADSA; C₁₀H₈O₆S₂), a basic chemical for dyes and building materials. This combination of ozonation and biological treatment is expected to minimise the ozone consumption compared to ozonation alone. To examine the influence of ozone on the biodegradability of NADSA, a lab‐scale plant was run semi‐continuously and batch tests were conducted for comparison. For total ozonation, 1.8 mol O₃/mol DOC have to be used. For optimum biodegradation, only 0.8 mol O₃/mol DOC are needed. The results show that by using a combination of ozonation and biological treatment the ozone consumption can be reduced by more than 50% compared to ozonation alone. Some of the intermediate products are isolated and suggestions for their chemical structures are made. A proposal for the first steps of ozonation is also presented to illustrate a possible pathway of ozonation. All the major identifiable compounds are non‐biodegradable. From these results, it is quite clear that further intermediate products are formed, which are biodegradable.     

Rapid Removal of Tetrabromobisphenol A by Ozonation in Water: Oxidation Products,Reaction Pathways and Toxicity Assessment

Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardants and has attracted more and more attention. In this work, the parent TBBPA with an initial concentration of 100 mg/L was completely removed after 6 min of ozonation at pH 8.0, and alkaline conditions favored a more rapid removal than acidic and neutral conditions. The presence of typical anions and humic acid did not significantly affect the degradation of TBBPA. The quenching test using isopropanol indicated that direct ozone oxidation played a dominant role during this process. Seventeen reaction intermediates and products were identified using an electrospray time-of-flight mass spectrometer. Notably, the generation of 2,4,6-tribromophenol was first observed in the degradation process of TBBPA. The evolution of reaction products showed that ozonation is an efficient treatment for removal of both TBBPA and intermediates. Sequential transformation of organic bromine to bromide and bromate was confirmed by ion chromatography analysis. Two primary reaction pathways that involve cleavage of central carbon atom and benzene ring cleavage concomitant with debromination were thus proposed and further justified by calculations of frontier electron densities. Furthermore, the total organic carbon data suggested a low mineralization rate, even after the complete removal of TBBPA. Meanwhile, the acute aqueous toxicity of reaction solutions to Photobacterium Phosphoreum and Daphnia magna was rapidly decreased during ozonation. In addition, no obvious difference in the attenuation of TBBPA was found by ozone oxidation using different water matrices, and the effectiveness in natural waters further demonstrates that ozonation can be adopted as a promising technique to treat TBBPA-contaminated waters.     

Correlation of Biological Activity and Reactor Performance in Biofiltration of Toluene with the Fungus Paecilomyces variotii CBS115145

A biofiltration system inoculated with the mold Paecilomyces variotii CBS115145 showed a toluene elimination capacity (EC) of around 250 g/m³ of biofilter/h, which was higher than the values usually reported for bacteria. P. variotii assimilated m- and p-cresols but not the o isomer. Initial toluene hydroxylation occurred both on the methyl group and through the p-cresol pathway. These results were corroborated by detecting benzyl alcohol, benzaldehyde, and p-cresol as volatile intermediates. In liquid cultures with toluene as a substrate, the activity of toluene oxygenase (TO) was 5.6 nmol of O₂/min/mg of biomass, and that of benzyl alcohol dehydrogenase was 16.2 nmol of NADH/min/mg of protein. Toluene biodegradation determined from the TO activity in the biofilter depended on the biomass distribution and the substrate concentration. The specific enzymatic activity decreased from 6.3 to 1.9 nmol of O₂/min/mg of biomass along the reactor. Good agreement was found between the EC calculated from the TO activity and the EC measured on the biofilter. The results were confirmed by short-time biofiltration experiments. Average EC measured in different biofiltration experiments and EC calculated from the TO activity showed a linear relation, suggesting that in the biofilters, EC was limited by biological reaction. As the enzymatic activities of P. variotii were similar to those reported for bacteria, the high performance of the fungal biofilters can possibly be explained by the increased transfer of the hydrophobic compounds, including oxygen, from the gas phase to the mycelia, overcoming the transfer problems associated with the flat bacterial biofilms.     

Decomposition of toluene in a steady-state atmospheric-pressure glow discharge

Results are presented from experimental studies of decomposition of toluene (C₆H₅CH₃) in a polluted air flow by means of a steady-state atmospheric pressure glow discharge at different water vapor contents in the working gas. The experimental results on the degree of C₆H₅CH₃ removal are compared with the results of computer simulations conducted in the framework of the developed kinetic model of plasma chemical decomposition of toluene in the N₂: O₂: H₂O gas mixture. A substantial influence of the gas flow humidity on toluene decomposition in the atmospheric pressure glow discharge is demonstrated. The main mechanisms of the influence of humidity on C₆H₅CH₃ decomposition are determined. The existence of two stages in the process of toluene removal, which differ in their duration and the intensity of plasma chemical decomposition of C₆H₅CH₃ is established. Based on the results of computer simulations, the composition of the products of plasma chemical reactions at the output of the reactor is analyzed as a function of the specific energy deposition and gas flow humidity. The existence of a catalytic cycle in which hydroxyl radical OH acts a catalyst and which substantially accelerates the recombination of oxygen atoms and suppression of ozone generation when the plasma-forming gas contains water vapor is established.     

The effect of ozone on the biodegradation of 17α-ethinylestradiol and sulfamethoxazole by mixed bacterial cultures

The potential development of antibacterial resistance and endocrine disruption has led to increased research investigating the removal of contaminants from wastewater (WW) such as sulfamethoxazole (SMX) and 17α-ethinylestradiol (EE2). These compounds react quickly with ozone (O₃), thus ozonation during WW treatment may result in their complete removal. Also, O₃ has demonstrated the ability to increase the biodegradability of WW and certain pharmaceuticals, suggesting its potential as a pretreatment to activated sludge (AS, biological treatment). The objective of this study was to determine whether ozonation, conducted at doses lower than commonly applied to treated WW, would lead to an increased biodegradability of SMX and EE2. The results show that after ozonation performed at lab-scale the bacterial mixtures removed 5 % to 40 % more SMX; however, 2 % to 23 % less EE2 was removed, which was attributed to the observed preferential degradation of a by-product of EE2 ozonation. These results suggest that although ozonation, used as a pretreatment, was shown in literature to increase the overall biodegradability of AS as well as some specific antibiotic compounds and a blood lipid regulator, the potential for increased removal of pharmaceuticals seems to be compound-dependent and cannot yet be extrapolated to this entire class of compounds.     

Enhancement of the ozonation of wine distillery wastewaters by an aerobic pretreatment

The decomposition of the organic substrate present in wine distillery wastewaters (WDW) is studied in batch reactors, by an ozonation process, by an aerobic degradation and by another ozonation of the aerobically pretreated wastewaters. In the ozonation process, the effects on the substrate removal obtained of the temperature, pH and the presence of H₂O₂ and UV radiation are established, and an approximate kinetic study is conducted which leads to the evaluation of the apparent kinetic constants for the substrate reduction. In the aerobic degradation treatment, the evolution of the substrate, biomass and total phenolic compounds are followed during the process, and a kinetic study is performed by using the Contois model, which applied to the experimental data provides the specific kinetic parameters q_max and K₁. Finally, in the ozonation of the pretreated wastewaters, the?influence of the operating variables is established, and the effect of this aerobic pretreatment on the substrate removal and kinetic constants obtained in the ozonation stage is also discussed.     

Simulation of toluene decomposition in a pulse-periodic discharge operating in a mixture of molecular nitrogen and oxygen

The kinetic model of toluene decomposition in nonequilibrium low-temperature plasma generated by a pulse-periodic discharge operating in a mixture of nitrogen and oxygen is developed. The results of numerical simulation of plasma-chemical conversion of toluene are presented; the main processes responsible for C₆H₅CH₃ decomposition are identified; the contribution of each process to total removal of toluene is determined; and the intermediate and final products of C₆H₅CH₃ decomposition are identified. It was shown that toluene in pure nitrogen is mostly decomposed in its reactions with metastable N₂(A₃?? _u ⁺ ) and N₂(a??¹?? _u ^? ) molecules. In the presence of oxygen, in the N₂ : O₂ gas mixture, the largest contribution to C₆H₅CH₃ removal is made by the hydroxyl radical OH which is generated in this mixture exclusively due to plasma-chemical reactions between toluene and oxygen decomposition products. Numerical simulation showed the existence of an optimum oxygen concentration in the mixture, at which toluene removal is maximum at a fixed energy deposition.     

The effects of ozone on growth and stomatal response in the F<Subscript>2</Subscript> generation of hybrid poplar (<Emphasis Type="Italic">Populus trichocarpa × Populus deltoides</Emphasis>)

Thirty-six F₂ hybrid poplar (Populus trichocarpa × P. deltoides) clones were fumigated with ozone to record its effects on growth, correlate them with stomatal response and screen for ozone sensitivity. Fumigation was applied for 6 to 9 h each day for approximately 3 months at ozone concentrations of 85 to 128 μg g⁻¹ using open-top chambers. Height, diameter, number of leaves, stomatal conductance, transpiration rate, total biomass, biomass components and root/shoot ratios were reduced by ozone stress. Percent of leaf fall in ozone-treated plants was nearly three times higher than in control plants exposed to charcoal-filtered air. Leaf senescence, because of ozone exposure, did not appear to be associated with reduced biomass production. Some clones had a high percentage of leaf-fall with ozone exposure, but were able to maintain total biomass production near that of the control. Their response may be an example of an ability to adjust or compensate for ozone damage. There was no significant or consistent relationship between stomatal conductance and total biomass or the change in stomatal conductance as a result of ozone exposure and the change in total biomass. Taken together, these results suggest that effects of ozone on poplar growth cannot be solely correlated to changes in stomatal conductance, more physiological and biochemical parameters should be examined.     

臭氧胁迫对水稻生长以及C、N、S元素分配的影响

采用开顶式气室(Open-top Chamber, OTC),对水稻"3694繁"(Oryza sativa L., 3694 Fan)在浙江嘉兴进行田间原位臭氧(O₃)熏气实验,研究不同臭氧浓度熏气对水稻生长以及C、N,S元素分配的影响。实验设置分4个水平:过滤大气组(CF,10 nL/L)、自然大气组(NF,40 nL/L)和两个不同浓度的臭氧处理组(O₃-1:100 nL/L; O₃-2:150 nL/L)。主要结果表明:(1)开始臭氧熏气时,各个处理组单茎水稻各组分生物量没有差异. 在熏气后期(水稻成熟期),臭氧处理使单茎水稻根、茎和穗生物量显著下降,根冠比降低,株高显著降低,表明臭氧胁迫增加水稻地上部分的干物质分配,且对株高的影响可能大于对地上生物量的影响;(2)臭氧处理使水稻根和茎C元素含量下降,叶C元素含量上升,表明臭氧胁迫提高了叶片中碳分配,而降低了根和茎的碳分配;(3)各个组分N元素含量上升和碳氮比下降;(4)茎、叶和穗S元素含量上升,可能会增强水稻抗氧化系统的作用,从而抵抗臭氧胁迫。所有实验结果表明臭氧浓度升高会对水稻生长产生严重不利影响,从而导致水稻各个组分的C、N、S元素分配格局发生改变。     

Effects of elevated ozone concentration on CH4 and N2O emission from paddy soil under fully open‐air field conditions

We investigated the effects of elevated ozone concentration (E‐O₃) on CH₄ and N₂O emission from paddies with two rice cultivars: an inbred Indica cultivar Yangdao 6 (YD6) and a hybrid one II‐you 084 (IIY084), under fully open‐air field conditions in China. A mean 26.7% enhancement of ozone concentration above the ambient level (A‐O₃) significantly reduced CH₄ emission at tillering and flowering stages leading to a reduction of seasonal integral CH₄ emission by 29.6% on average across the two cultivars. The reduced CH₄ emission is associated with O₃‐induced reduction in the whole‐plant biomass (?13.2%), root biomass (?34.7%), and maximum tiller number (?10.3%), all of which curbed the carbon supply for belowground CH₄ production and its release from submerged soil to atmosphere. Although no significant difference was detected between the cultivars in the CH₄ emission response to E‐O₃, a larger decrease in CH₄ emission with IIY084 (?33.2%) than that with YD6 (?7.0%) was observed at tillering stage, which may be due to the larger reduction in tiller number in IIY084 by E‐O₃. Additionally, E‐O₃ reduced seasonal mean NO_x flux by 5.7% and 11.8% with IIY084 and YD6, respectively, but the effects were not significant statistically. We found that the relative response of CH₄ emission to E‐O₃ was not significantly different from those reported in open‐top chamber experiments. This study has thus confirmed that increasing ozone concentration would mitigate the global warming potential of CH₄ and suggested consideration of the feedback mechanism between ozone and its precursor emission into the projection of future ozone effects on terrestrial ecosystem.     

Harvesting of Scenedesmus obliquus FSP-3 using dispersed ozone flotation

The Scenedesmus obliquus FSP-3, a species with excellent potential for CO₂ capture and lipid production, was harvested using dispersed ozone flotation. While air aeration does not, ozone produces effective solid-liquid separation through flotation. Ozone dose applied for sufficient algal flotation is similar to those used in practical drinking waterworks. The algae removal rate, surface charge, and hydrophobicity of algal cells, and fluorescence characteristics and proteins and polysaccharides contents of algogenic organic matter (AOM) were determined during ozonation. Proteins released from tightly bound AOM are essential to modifying the hydrophobicity of bubble surfaces for easy cell attachment and to forming a top froth layer for collecting floating cells. Humic substances in the suspension scavenge dosed ozone that adversely affects ozone flotation efficiency of algal cells.     

Metabolism of Benzene, Toluene, and Xylene Hydrocarbons in Soil

Enrichment cultures obtained from soil exposed to benzene, toluene, and xylene (BTX) mineralized benzene and toluene but cometabolized only xylene isomers, forming polymeric residues. This observation prompted us to investigate the metabolism of ¹⁴C-labeled BTX hydrocarbons in soil, either individually or as mixtures. BTX-supplemented soil was incubated aerobically for up to 4 weeks in a sealed system that automatically replenished any O₂ consumed. The decrease in solvent vapors and the production of ¹⁴CO₂ were monitored. At the conclusion of each experiment, ¹⁴C distribution in solvent-extractable polymers, biomass, and humic material was determined, obtaining ¹⁴C mass balances of 85 to 98%. BTX compounds were extensively mineralized in soil, regardless of whether they were presented singly or in combinations. No evidence was obtained for the formation of solvent-extractable polymers from xylenes in soil, but ¹⁴C distribution in biomass (5 to 10%) and humus (12 to 32%) was unusual for all BTX compounds and especially for toluene and the xylenes. The results suggest that catechol intermediates of BTX degradation are preferentially polymerized into the soil humus and that the methyl substituents of the catechols derived from toluene and especially from xylenes enhance this incorporation. In contrast to inhibitory residues formed from xylene cometabolism in culture, the humus-incorporated xylene residues showed no significant toxicity in the Microtox assay.     

Do chronic aboveground O3 exposure and belowground pathogen stress affect growth and belowground biomass partitioning of juvenile beech trees (Fagus sylvatica L.)?

The impact of chronic free air ozone (O₃) exposure and belowground pathogen stress on growth and total biomass development of young beech trees (Fagus sylvatica L.) was investigated in a lysimeter study. Plants were growing during four years under ambient or elevated atmospheric O₃ concentrations. Additionally, in the last vegetation period the root rot pathogen Phytophthora citricola was introduced to study the interaction of ozone exposure and pathogen stress in the soil-plant system. A complete harvest at the end of the experiment enabled for the first time the assessment of fine and coarse root biomass of individual trees with a high vertical resolution down to two meter depth. Plant growth was significantly reduced by elevated ozone but not affected by P. citricola. Biomass partitioning between fine and coarse roots as well as vertical root distribution were significantly affected by both factors, whereas changes in root/shoot biomass ratio were not observed.     

Influence of synthetic packing materials on the gas dispersion and biodegradation kinetics in fungal air biofilters

The biodegradation of toluene was studied in two lab-scale air biofilters operated in parallel, packed respectively with perlite granules (PEG) and polyurethane foam cubes (PUC) and inoculated with the same toluene-degrading fungus. Differences on the material pore size, from micrometres in PEG to millimetres in PUC, were responsible for distinct biomass growth patterns. A compact biofilm was formed around PEG, being the interstitial spaces progressively filled with biomass. Microbial growth concentrated at the core of PUC and the excess of biomass was washed-off, remaining the gas pressure drop comparatively low. Air dispersion in the bed was characterised by tracer studies and modelled as a series of completely stirred tanks (CSTR). The obtained number of CSTR (n) in the PEG packing increased from 33 to 86 along with the applied gas flow (equivalent to empty bed retention times from 48 to 12 s) and with operation time (up to 6 months). In the PUC bed, n varied between 9 and 13, indicating that a stronger and steadier gas dispersion was achieved. Michaelis–Menten half saturation constant (k _m) estimates ranged 71–113 mg m⁻³, depending on the experimental conditions, but such differences were not significant at a 95% confidence interval. The maximum volumetric elimination rate (r _m) varied from 23 to 50 g m⁻³ h⁻¹. Comparison between volumetric and biomass specific biodegradation activities indicated that toluene mass transfer was slower with PEG than with PUC as a consequence of a smaller biofilm surface and to the presence of larger zones of stagnant air.     

Reduction of bromate by biogenic sulfide produced during microbial sulfur disproportionation

Bromate (BrO₃ ⁻) is a carcinogenic contaminant formed during ozonation of waters that contain trace amounts of bromide. Previous research shows that bromate can be microbially reduced to bromide using organic (i.e. acetate, glucose, ethanol) and inorganic (H₂) electron-donating substrates. In this study, the reduction of bromate by a mixed microbial culture was investigated using elemental sulfur (S⁰) as an electron donor. In batch bioassays performed at 30°C, bromate (0.30 mM) was completely converted to bromide after 10 days and no accumulation of intermediates occurred. Bromate was also reduced in cultures supplemented with thiosulfate and hydrogen sulfide as electron donor. Our results demonstrated that S⁰-disproportionating microorganisms were responsible for the reduction of bromate in cultures spiked with S⁰ through an indirect mechanism involving microbial formation of sulfide and subsequent abiotic reduction of bromate by the biogenic sulfide. Confirmation of this mechanism is the fact that bromate was shown to undergo rapid chemical reduction by sulfide (but not S⁰ or thiosulfate) in abiotic experiments. Bromate concentrations above 0.30 mM inhibited sulfide formation by S⁰-disproportionating bacteria, leading to a decrease in the rate of bromate reduction. The results suggest that biological formation of sulfide from by S⁰ disproportionation could support the chemical removal of bromate without having to directly use sulfide as a reagent.     

Characterization of the ozone effect over an α-amylase from Bacillus licheniformis

Starch usually soils industrial process equipment, hence demanding specific washing procedures to ensure optimal products and reliable process performance. α-Amylases have been included in detergent formulations to hydrolyse starch making easier its elimination. Ozone is frequently used as disinfectant but could also help to remove the starchy soils improving the cleaning process. To study the effect of ozone on the enzyme, the ozonation of an α-amylase from Bacillus licheniformis at pH 7.5 and 25 °C was carried out. Enzyme activity assays showed that the relative α-amylase activity after ozonation decreased with increasing ozone/enzyme molar ratio exponentially. On the other hand, the ozone concentration after the reaction was negligible as some enzymatic activity remained, being the ozone consumption fast due to the high reaction kinetics of aromatic and sulfur-containing amino acids residues of the enzyme. The UV and MALDI-TOF mass spectra confirmed the oxidation of these amino acids, while the peptide bonds were unaffected. Therefore the loss of the α-amylase activity observed would be caused by the oxidation of amino acids residues directly involved in the hydrolysis mechanism such as tyrosine and histidine and/or by denaturation of the enzyme upon amino acid residues oxidation.     

Wine vinasses treatments by ozone and an activated sludge system in continuous reactors

In this work wine vinasses have been treated separately by means of a chemical ozonation and a biological aerobic degradation in an activated sludge system, and later by means of a combined process which consisted of an aerobic pretreatment followed by an ozonation treatment, in continuous reactors in all cases. In the ozonation experiments, the hydraulic retention time and the ozone partial pressure were varied leading to substrate removals in the range 4.4-16%, with increases in this removal when both operating variables were increased. A kinetic study, which combines mixed flow reactor model for the liquid phase and plug flow reactor model for the gas phase, allows to determine the rate constant for the ozone reaction and the consumption ratio, which are k_O3 = 3.6 l/(g COD · h) and b = 22.5 g COD degraded/mol O₃ consumed. The aerobic degradation experiments were conducted in the activated sludge system with variations in the retention time and influent organic substrate concentration in the wastewater. A modified Contois model applied to the experimental results leads to the determination of the kinetic parameters of that model: K₁ = 5.43 l/g VSS and q_max = 6.29 g COD/(g VSS · h). Finally, the combined process reveals an improvement in the efficiency of the ozonation stage due to the previous aerobic treatment with increases in the substrate removal reached and in the rate constant obtained, the last one being k_O3 = 5.6 l/(g COD · h).     

Estimation of biological kinetic parameters from an analysis of the BOD curve of waste waters–effects of a chemical preoxidation

Urban waste waters were treated with pure ozone or combinations of ozone, hydrogen peroxide and/or UV radiation to study the course of resulting BOD (biological oxygen demand)-time profiles and to propose a kinetic model. BOD-time profiles of chemically treated waste waters show an initial lag period that first order kinetic models cannot describe. A second order kinetic model is then proposed that satisfactorily fits experimental BOD-time profiles, except when hydrogen peroxide has been used. In these cases, BOD-time profiles present the highest lag periods observed. By applying this model, three parameters are determined: the biokinetic constant (k) which is an index of the biological removal rate; the potential amount of biodegradable matter (BOD_T), and the measure of the size of inocula and microbial activities of microoganisms (λ). The model was checked with experimental results of BOD-time profiles corresponding to both untreated and chemically ozonated urban waste waters. Ozonated waste waters showed the highest values of k and BOD_T, which implies an improvement of waste water biodegradability after ozonation. However, values of λ corresponding to ozonated waste waters presented lower values than those of untreated waste waters. This was due to the lag period observed in the BOD-time profile, which was a consequence of a lack of microorganism acclimation to ozonated waste waters. The effect of the ozone does, pH and carbonates during ozonation on COD (chemical oxygen demand) and the above indicated parameters was also studied. There was an optimum ozone dose which was 138 mg/l for this specific system. This led to the highest biodegradable fraction (φ) and the highest biokinetic constant (39% increase in φ and 4.7- fold increase in the value of k, respectively, compared to untreated waste waters.). Another significant fact was that a higher COD reduction was observed in the absence of carbonate during ozonation at basic pH values. In addition, the percentage of variation in the biodegradable fraction (Δφ) of ozonated waste water increased compared to the untreated waste water at acid pH. The results suggest that ozonolysis, the direct molecular ozone way of reaction, due to its selective character, increases the biodegradability of waste water more than other chemically advanced oxidation processes based on hydroxyl radical reactions.     

Implications of cholesterol autoxidation products in the pathogenesis of inflammatory diseases

There is rising interest in non-enzymatic cholesterol oxidation because the resulting oxysterols have biological activity and can be used as non-invasive markers of oxidative stress in vivo. The preferential site of oxidation of cholesterol by highly reactive species is at C₇ having a relatively weak carbon–hydrogen bond. Cholesterol autoxidation is known to proceed via two distinct pathways, a free radical pathway driven by a chain reaction mechanism (type I autoxidation) and a non-free radical pathway (type II autoxidation). Oxysterols arising from type II autoxidation of cholesterol have no enzymatic correlates, and singlet oxygen (¹ΔgO₂) and ozone (O₃) are the non-radical molecules involved in the mechanism. Four primary derivatives are possible in the reaction of cholesterol with singlet oxygen via ene addition and the formation of 5α-, 5β-, 6α- and 6β-hydroxycholesterol preceded by their respective hydroperoxyde intermediates. The reaction of ozone with cholesterol is very fast and gives rise to a complex array of oxysterols. The site of the initial ozone reaction is at the Δ_5,6 –double bond and yields 1,2,3-trioxolane, a compound that rapidly decomposes into a series of unstable intermediates and end products. The downstream product 3β-hydroxy-5-oxo-5,6-secocholestan-6-al (sec-A, also called 5,6-secosterol), resulting from cleavage of the B ring, and its aldolization product (sec-B) have been proposed as a specific marker of ozone-associated tissue damage and ozone production in vivo. The relevance of specific ozone-modified cholesterol products is, however, hampered by the fact sec-A and sec-B can also arise from singlet oxygen via Hock cleavage of 5α-hydroperoxycholesterol or via a dioxietane intermediate. Whatever the mechanism may be, sec-A and sec-B have no enzymatic route of production in vivo and are reportedly bioactive, rendering them attractive biomarkers to elucidate oxidative stress-associated pathophysiological pathways and to develop pharmacological agents.     

CO2 emissions from biomass combustion for bioenergy: atmospheric decay and contribution to global warming

Carbon dioxide (CO₂) emissions from biomass combustion are traditionally assumed climate neutral if the bioenergy system is carbon (C) flux neutral, i.e. the CO₂ released from biofuel combustion approximately equals the amount of CO₂ sequestered in biomass. This convention, widely adopted in life cycle assessment (LCA) studies of bioenergy systems, underestimates the climate impact of bioenergy. Besides CO₂ emissions from permanent C losses, CO₂ emissions from C flux neutral systems (that is from temporary C losses) also contribute to climate change: before being captured by biomass regrowth, CO₂ molecules spend time in the atmosphere and contribute to global warming. In this paper, a method to estimate the climate impact of CO₂ emissions from biomass combustion is proposed. Our method uses CO₂ impulse response functions (IRF) from C cycle models in the elaboration of atmospheric decay functions for biomass‐derived CO₂ emissions. Their contributions to global warming are then quantified with a unit‐based index, the GWP_bio. Since this index is expressed as a function of the rotation period of the biomass, our results can be applied to CO₂ emissions from combustion of all the different biomass species, from annual row crops to slower growing boreal forest.