Degradation Rate Coefficients Research Articles

Complete biodegradation of glyphosate with microbial consortium YS622: Structural analysis, biochemical pathways, and environmental bioremediation

The large-scale use of glyphosate has led to the continuous accumulation of residues in the environment, disrupting ecological balance and posing a threat to human health. The main objective of this study was to investigate the potential role of microbial consortium YS622 for the bioremediation of glyphosate-contaminated water/soil environments. YS622 could degrade 100 % of 50 mg/L glyphosate within 36 h, an efficiency higher than that of any other consortia or pure microorganisms reported so far. The kinetic parameters of maximum specific degradation rate, half-rate constant, and inhibition coefficient were determined to be 0.2 h−1, 139.0 mg/L, and 25.1 mg/L, respectively. YS622 metabolized glyphosate via the aminomethylphosphonic acid pathway via breaking the C–N bond. In addition, the sequencing analysis revealed that Azospirillum, Cloacibacterium, and Ochrobactrum were the dominant genera of YS622 in the degradation process, indicating that these genera might play pivotal roles in glyphosate biodegradation. Furthermore, the inoculation of YS622 in both sterilized and unsterilized water–sediment systems significantly promoted the degradation of glyphosate, with over 97 % degradation of 60 mg/L glyphosate within 36 h. The discovery of YS622 fills a gap in the synergistic metabolism of glyphosate at the community level and provides a potential candidate for bioremediation applications.

Quantifying remediation of chlorinated volatile compounds by sulfidated nano zerovalent iron treatment using numerical modeling and CSIA

Sulfidated nanoscale zerovalent iron (S-nZVI) has demonstrated promising reactivity and longevity for remediating chlorinated volatile compounds (cVOC) contaminants in laboratory tests. However, its effectiveness in field applications remains inadequately evaluated. This study provides the first quantitative evaluation of the long-term effectiveness of carboxymethyl cellulose-stabilized S-nZVI (CMC-S-nZVI) at a cVOC-contaminated field site. A reactive transport model-based numerical approach delineates the change in cVOC concentrations and carbon isotope values (i.e., δ13C from compound-specific stable isotope analysis (CSIA)) caused by dissolution of dense non-aqueous phase liquid, sorption, and pathway-specific degradation and production, respectively. This delineation reveals quantitative insights into remediation effectiveness typically difficult to obtain, including extent of degradation, contributions of different degradation pathways, and degradation rate coefficients. Significantly, even a year after CMC-S-nZVI application, degradation remains an important process effectively removing various cVOC contaminants (i.e., chlorinated ethenes, 1,2-dichloroethanes, and chlorinated methanes) at an extent varying from 5 %-62 %. Although the impacts of CMC-S-nZVI abundance on degradation vary for different cVOC and for different sampling locations at the site, for the primary site contaminants of tetrachloroethene and trichloroethene, their predominance of dichloroelimination pathway (≥ 88 %), high degradation rate coefficient (0.4–1.7 d-1), and occurrence at locations with relatively high CMC-S-nZVI abundance strongly indicate the effectiveness of abiotic remediation. These quantitative assessments support that CMC-S-nZVI supports sustainable ZVI-based remediation. Further, the novel numerical approach presented in this study provides a powerful tool for quantitative cVOC remediation assessments at complex field sites where multiple processes co-occur to control both concentration and CSIA data.

Prediction Model of the Remaining Useful Life of the Drill Bit during Micro-Drilling of the Packaging Substrate

The packaging substrate plays a significant role in electrical connection, heat dissipation, and protection for the chips. With the characteristics of high hardness and the complex material composition of packaging substrates, drill bit failure is an austere challenge in micro-drilling procedures. In order to monitor the health state of the drill bit and predict its remaining useful life (RUL) in micro-drilling of packaging substrate, an improved RUL prediction model is established based on the similarity principle, degradation rate, and offset coefficient. And then, a micro-drilling experiment on packaging substrate is carried out to collect the axial drilling force through the precision drilling force measurement platform. Axial drilling force signals, which are processed via the Wiener filtering method, are used to analyze the effectiveness of the improved RUL prediction model. The experiment results indicate that, compared to the curves of the traditional RUL prediction model, the curves of the improved RUL prediction model present a higher fitting degree with the actual RUL curves. The average relative errors of the improved RUL prediction model are small and stable in all groups; all of the values are less than 15%, while the fluctuation of the average relative errors of the traditional model is greatly large, and the maximum value even reaches 74.43%. Therefore, taking the degradation rate and offset coefficient into account is a proper method to enhance the accuracy of the RUL prediction model. Furthermore, the improved RUL prediction model is a reliable theoretical support for the health state monitoring of drill bits during the micro-drilling of packaging substrates, which also acts as a potential method to improve micro hole processing efficiency for packaging substrates.

Synthesis, Characterization and Photocatalytic Activity of Spherulite-like r-TiO2 in Hydrogen Evolution Reaction and Methyl Violet Photodegradation

Synthesis and characterization of spherulite-like nanocrystalline titania with rutile structure (r-TiO2) are described herein. The r-TiO2 particles were synthesized via the convenient and low-cost hydrothermal treatment of TiO(C6H6O7) titanyl citrate. The r-TiO2 spherulites are micron-sized agglomerates of rod-shaped nanocrystals with characteristic sizes of 7(±2) × 43(±10) nm, oriented along (101) crystallographic direction, and separated by micropores, as revealed by SEM and TEM. PXRD and Raman spectroscopy confirmed the nanocrystalline nature of r-TiO2 crystallites. BET analysis showed a high specific surface area of 102.6 m2/g and a pore volume of 6.22 mm3/g. Photocatalytic performances of the r-TiO2 spherulites were investigated for the processes of methyl violet (MV) degradation in water and hydrogen evolution reaction (HER) in aqueous solutions of ethanol. The (MV) degradation kinetics was found to be first-order and the degradation rate coefficient is 2.38 × 10−2 min−1. The HER was performed using pure r-TiO2 spherulites and nanocomposite r-TiO2 spherulites with platinum deposited on the surface (r-TiO2/Pt). It was discovered that the r-TiO2/Pt nanocomposite has a 15-fold higher hydrogen evolution rate than pure r-TiO2; their rates are 161 and 11 nmol/min, respectively. Thus, the facile synthesis route and the high photocatalytic performances of the obtained nanomaterials make them promising for commercial use in such photocatalytic processes as organic contamination degradation and hydrogen evolution.

Drastically enhanced tetracycline degradation performance of a porous 2D g-C3N4 nanosheet photocatalyst in real water matrix: Influencing factors and mechanism insight

Porous 2D nanosheets are an emerging class of materials with exciting physical, chemical, optical, and electronic characteristics. This study reported the facile synthesis of a porous 2D g-C3N4 nanosheet photocatalyst through a simple chemical exfoliation route. The morphological characterization of the samples confirmed its porous 2D nanosheet structure with an approximate thickness of 2.5 nm. The as-prepared photocatalyst displayed a 4.2-fold enhanced tetracycline (TC) degradation rate coefficient compared to the pristine g-C3N4 under LED illumination. Further, the porous 2D g-C3N4 nanosheet photocatalyst exhibited superior TC degradation efficacy in a real water matrix. The synergistic effect of higher pH, presence of carbonate and bicarbonate anions, and the existence of humic substances could have elevated the degradation performance in the real water matrix. Moreover, the as-synthesized catalyst demonstrated remarkable stability and recyclability even after the four-cycle recycling experiment. A possible photocatalytic mechanism has been proposed following the findings of the radical trapping experiment. It is believed that this study would inspire further fabrication of other porous 2D nanosheet photocatalysts.

Novel mechanism and degradation kinetics of allethrin using Bacillus megaterium strain HLJ7 in contaminated soil/water environments

As a common pyrethroid insecticide, allethrin is widely used for various purposes in agriculture and home applications. At present, allethrin residues have been frequently detected worldwide, yet little is known about the kinetics and degradation mechanisms of this insecticide. In this study, a highly efficient allethrin-degrading bacterium, Bacillus megaterium strain HLJ7, was obtained through enrichment culture technology. Strain HLJ7 can remove 96.5% of 50 mg L−1 allethrin in minimal medium within 11 days. The first-order kinetic analysis of degradation demonstrated that the half-life of allethrin degradation by strain HLJ7 was 3.56 days, which was significantly shorter than the 55.89 days of the control. The Box–Behnken design of the response surface method optimized the degradation conditions for strain HLJ7: temperature 32.18 °C, pH value 7.52, and inoculation amount 1.31 × 107 CFU mL−1. Using Andrews equation, the optimal concentration of strain HLJ7 to metabolize allethrin was determined to be 21.15 mg L−1, and the maximum specific degradation rate (qmax), half-rate constant (Ks) and inhibition coefficient (Ki) were calculated to be 1.80 d−1, 1.85 mg L−1 and 68.13 mg L−1, respectively. Gas chromatography-mass spectrometry identified five intermediate metabolites, suggesting that allethrin could be degraded firstly by cleavage of its carboxylester bond, followed by degradation of the five-carbon ring and subsequent metabolism. The results of soil remediation experiments showed that strain HLJ7 has excellent bioremediation potential in the soils. After 15 days of treatment, about 70.8% of the initial allethrin (50 mg kg−1) was removed and converted into nontoxic intermediate metabolites, and its half-life was significantly reduced in the soils. Taken together, these findings shed light on the degradation mechanisms of allethrin and also highlight the promising potentials of B. megaterium HLJ7 in bioremediation of allethrin-comtaminated environment.

Assessment of PV technologies outdoor performance and commercial software estimation in hot and dry climates

Photovoltaic (PV) technologies have become an essential part of the global effort to compact climate change. While the MENA region, and in particular Egypt, has been one of the main target locations for PV system installations; because of the region's tremendous potential for solar energy and its location on the sunbelt. Yet, a gap in both literature and long-term industrial experience of PV technologies' installation in this particular region calls for investigation. Therefore, this work focuses on two main objectives: first, conducting an evaluation of long-term outdoor performance of three grid-connected photovoltaic systems (i.e. poly-crystalline, mono-crystalline, and thin-film Cadmium Telluride) installed on the same rooftop in Cairo, Egypt, since October 2013. In which, the three systems will be compared in terms of yield, degradation rate, modules efficiency, and temperature power coefficient. The second objective is to compare the performance of commonly-used commercial software packages (i.e. PVSyst, PVSol, and SMA Sunny Design Web) to the output of the three PV systems mentioned above.In terms of degradation, the average yield degradation value was 1.19%/year, 1.17%/year, and 1.67%/year for poly-crystalline, mono-crystallin, and thin-film Cadmium Telluride respectively. For degradation against temperature, the rates were −1.53%/°C/kWp, −1.22%/°C/kWp, and −1.06%/°C/kWp for the three systems respectively. As for software packages estimation, all three software tend to produce a reasonably accurate annual estimation but they become significantly less accurate with the monthly estimation. The annual errors of the three software ranged from −6.99% to +4.65% which is consistent with the literature. However, the monthly error introduced in this study of the three software ranged from −23.71% to +22.22%.The current work lays down the foundation to enhance PV systems’ performance in hot and dry climates, as well as, calls for more accurate models for different PV technologies, especially for hot and dry climates.

Comparative Study of the Biological Degradation of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate) Microbeads in Municipal Wastewater in Environmental and Controlled Laboratory Conditions.

From April to June 2019, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3(HA)) microbead samples were exposed to an operational wastewater reclamation facility (WWRF) in an aerobic aeration basin in Athens, Georgia. Samples were withdrawn from the facility over a 13-week timeframe, and the particles were examined by Raman microscopy and thermogravimetric analysis/mass spectroscopy (TGA/MS) coupled with differential scanning calorimetry (DSC). The activated sludge from this facility was also used as an inoculum to examine carbon mineralization under controlled respirometry experiments to corroborate biological degradation rates determined from both the environmental and laboratory approach. Respirometry, Raman microscopy, and TGA/MS-DSC methods all measured similar biodegradation timelines for microbeads bound to an epoxy substrate, indicating that the three methods are temporally comparable and may be used to measure material biological degradation. Samples of epoxy-bound P3(HA) microbeads, free microbeads, the P3(HA) film, and poly(lactic acid) (PLA) film demonstrated carbon mineralization of 90.0, 89.4, 95.0, and 8.15%, respectively, relative to the cellulose positive control. Using a modified Gompertz growth model, the biological degradation rate coefficients (Rm) were determined for cellulose, P3(HA) film, epoxy-bound P3(HA) microbeads, and free P3(HA) microbeads and found to be 31.6, 30.2, 17.5, and 18.7 mL CO2·g-1·day-1, respectively. Moreover, P3(HA) microbeads can efficiently mineralize in WWRF infrastructure at a rate comparable to cellulose.

Persistence and photochemical transformation of water soluble constituents from industrial crude oil and natural seep oil in seawater

The persistence and transformation of water soluble chemical constituents derived from surface oil from the 2015 Refugio Oil Spill and from a nearby natural seep were evaluated under simulated sunlight conditions. Photoirradiation resulted in enhanced oil slick dissolution, which was more pronounced in spill oil compared to seep oil. Nontargeted analysis based on GC × GC/TOF-MS revealed that photoirradiation promoted oil slick dissolution, and more water soluble compounds were released from spill oil (500 compounds) than from seep oil (180 compounds), most of them (488 in spill oil and 150 in seep oil) still persisting in solution after 67 days of photoirradiation. First-order degradation rate coefficients of humic-like water soluble constituents were found to be 0.26 day−1 and 0.29 day−1 for irradiated spill and seep samples, respectively. The decreases in humic-like fluorescence, specific UV absorbance, and aromatic compounds without corresponding decreases in DOC concentration support indirect photochemical transformation in addition to complete photomineralization.

Active food packaging of cellulose acetate: Storage stability, protective effect on oxidation of riboflavin and release in food simulants

In this work, cellulose acetate films were prepared with the incorporation of different carotenoids (lycopene, norbixin, and zeaxanthin). The effect of adding these natural antioxidants was evaluated through stability during storage under controlled conditions (temperature and light), degradation rate coefficient, release in food simulants and protective effect on oxidation of vitamin B2. During storage at 25 °C or 40 °C the light showed a greater effect on the stability of the carotenoids, with significant increase in reaction constants (k) and decrease in half-life (t1/2). The degradation of the carotenoids was followed by a variation in the color parameters and mechanical properties. The films with norbixin showed the highest barrier to the transmission of UV–Vis light, consequently preserving 72% of a vitamin B2 stored under a photooxidative environment. Lycopene presented a higher release rate than norbixin and zeaxanthin to a fatty food simulant.

Decolourization of rhodamine B and methylene blue dyes in the presence of bismuth tungstates: a detailed investigation on the effect of grain size

Solid-state reaction method was opted for the preparation of bismuth tungstates (Bi2WO6) in the stoichiometric ratio. The structural characterization related that the material has got orthorhombic symmetry. The high-energy ball milling did not show any structural change, but a reduction in grain size was observed from 100 to 34 nm after 5 h. The higher activity for the decolourization of rhodamine B (RHB) and methylene blue (MB) in the presence of UV light has been studied by employing Bi2WO6 as a catalyst. The dye degradation was observed by a decrease in the absorption spectrum and decolourization in the presence of UV irradiation. The degradation efficiency was found to be dependent on the size of the catalyst added in the dye solution, which may be due to increased surface area that increased the number of active sites for the reaction. The degradation efficiency of the unmilled and 5-h ball milled (Bi2WO6) catalyst was observed to be 32 and 90% in RHB, respectively. While in MB, 24 and 49% degradation efficiency was achieved by unmilled and 5-h ball milled (Bi2WO6) catalyst. The degradation rate coefficient was found to be in the decreasing order of RHB > MB, which pursued the first-order kinetic mechanism. Therefore, Bi2WO6 can act as a catalyst for the treatment of noxious and imperishable organic pollutants in water.

Chlorinated Ethene Degradation Rate Coefficients Simulated with Intact Sandstone Core Microcosms.

Abiotic transformation of trichloroethene (TCE) in fractured porous rock such as sandstone is challenging to characterize and quantify. The objective of this study was to estimate the pseudo first-order abiotic reaction rate coefficients in diffusion-dominated intact core microcosms. The microcosms imitated clean flow through a fracture next to a contaminated rock matrix by exchanging uncontaminated groundwater, unamended or lactate-amended, in a chamber above a TCE-infused sandstone core. Rate coefficients were assessed using a numerical model of the microcosms that were calibrated to monitoring data. Average initial rate coefficients for complete dechlorination of TCE to acetylene, ethene, and ethane were estimated as 0.019 y-1 in unamended microcosms and 0.024 y-1 in lactate-amended microcosms. Moderately higher values (0.026 y-1 for unamended and 0.035 y-1 for lactate-amended) were obtained based on 13C enrichment data. Abiotic transformation rate coefficients based on gas formation were decreased in unamended microcosms after ∼25 days, to an average of 0.0008 y-1. This was presumably due to depletion of reductive capacity (average values of 0.12 ± 0.10 μeeq/g iron and 18 ± 15 μeeq/g extractable iron). Model-derived rate coefficients and reductive capacities for the intact core microcosms aligned well with results from a previous microcosm study using crushed sandstone from the same site.

3D macroporous architecture of self-assembled defect-engineered ultrathin g-C3N4 nanosheets for tetracycline degradation under LED light irradiation

Herein, the facile fabrication of a novel 3D macroporous structure of graphitic carbon nitride composed of self-assembled 2D nitrogen vacancy engineered nanosheets have been reported. The synthesis of the defect-engineered structure was achieved upon the addition of ethylene glycol during the solid-state synthesis process. The photocatalyst was characterized through a wide range of characterization techniques. The macroporous structure exhibited superior photocatalytic efficiency towards tetracycline antibiotic degradation under LED light illumination. The defect-engineered material (4EGCN) exhibited a 3.3-fold superior degradation rate coefficient of 0.010 min−1, compared to the degradation rate coefficient (0.003 min−1) of the bulk counterpart. This superior photocatalytic performance could be accredited to the extended visible light extraction efficiency, increased suppression efficacy of charge carriers, and porous structure. Moreover, the photocatalyst showed excellent stability even after five cycles of photocatalytic tetracycline degradation. Further, a probable degradation mechanism has been proposed according to the observations of the radical scavenging experiments.

Hybrid Perovskites with Larger Organic Cations Reveal Autocatalytic Degradation Kinetics and Increased Stability under Light

Hybrid organic-inorganic perovskites have shown incredible promise as active materials for photovoltaic devices, but their instability to light remains a significant roadblock in realizing these applications. Changing the organic cation has been shown to affect light-induced degradation. As a strategy for increasing the stability of these materials, we replaced varying percentages of methylammonium ion in the archetypical methylammonium lead iodide (MAPbI3) hybrid organic-inorganic perovskite with three significantly larger organic ammonium cations: imidazolium, dimethylammonium, and guanidinium. We were able to synthesize hybrid organic-inorganic perovskites with the same 3D perovskite structure as MAPbI3 with substitution of the larger ions as high as 20-30%. These substituted hybrid organic-inorganic perovskites retained similar optoelectronic properties. We discovered that the light-induced degradation in MAPbI3 and its substituted derivatives is autocatalytic, and we calculated rate coefficients for the degradation. All of the substituted hybrid organic-inorganic perovskites showed light-induced degradation slower than that of MAPbI3, up to a 62% decrease in degradation rate coefficient, at all substitution percentages up to 20%. This work provides evidence that a high percentage of a variety of large ammonium cations can be substituted into the hybrid organic-inorganic perovskite lattice without compromising its desirable optoelectronic properties. Insight into the autocatalytic mechanism of light-induced degradation will be valuable for designing additional strategies to improve the stability of hybrid organic-inorganic perovskites. We also offer insights into how factors other than size, such as hydrogen bonding, influence the stability of the materials. Overall, we have shown that substitution of methylammonium ion for the much larger imidazolium, dimethylammonium, and guanidinium cations in MAPbI3 is a valid strategy for creating stable hybrid organic-inorganic perovskite derivatives by slowing the rate of light-induced degradation.

A study of external mass transfer effect on biodegradation of phenol using low‐density polyethylene immobilized Bacillus flexus GS1 IIT (BHU) in a packed bed bioreactor

AbstractThe impact of external mass transport on the biodegradation rate of phenol in a packed bed bioreactor (PBBR) was studied. A potential bacterial species, Bacillus flexus GS1 IIT (BHU), was isolated from the petroleum‐contaminated soil. Low‐density polyethylene (LDPE) immobilized with the B. flexus GS1 IIT (BHU) was used as packing material in the PBBR. The PBBR was operated by varying the inlet feed flow rate from 4 to 10 mL/min, and the corresponding degradation rate coefficients were found to be in the range of 0.119–0.157 L/g h. In addition, the highest removal rate of phenol was obtained to be 1.305 mg/g h at an inlet feed rate of 10 mL/min. The external mass transfer was studied using the model . A new empirical correlation for the biodegradation of phenol in the PBBR was developed after the evaluation at various values of K and n.

Bioremediation of diesel and gasoline-contaminated soil by co-vermicomposting amended with activated sludge: Diesel and gasoline degradation and kinetics

Present study aims to examine the efficiency of co-vermicomposting amended with activated sludge and E. fetida earthworm for bioremediation of diesel and gasoline from contaminated soil. The diesel and gasoline removal efficiency and degradation rates coefficients were estimated with gas chromatography (GC) analysis and first-order kinetics. The removal of gasoline and diesel in different co-vermicomposting processes with and without E. fetida ranged between 65-100% and 24.94–63.93%, respectively within 90- day experiment. Removal of gasoline and diesel increased in soil with addition of earthworm (E. fetida); higher degradation rate coefficients (k) were observed for co-vermicomposting with earthworm compared with co-vermicomposting processes. The highest k (0.014) for diesel degradation was estimated for microcosm reactor 4 (R4), where high numbers of E. fetida accelerate the less biodegradable organic contaminant from the soil matrices. The reasonable survival rates of earthworms in exposure to high concentration of petroleum-derivatives contaminated soils indicated increased activity of ligninolytic diesel–degrading earthworms and microorganisms. Therefore, co-vermicomposting amended with activated sludge is suggested as feasible and promising technologies for bioremediation of high content of organic contaminants from the soil matrices.

Relationship between the molecular structure of duckweed starch and its in vitro enzymatic degradation kinetics

Starch molecular structural effects in duckweed (Lemna minor and Landoltia punctata) controlling in vitro enzymatic degradation kinetics was studied. The molecular size distributions of fully-branched starches and the chain length distributions (CLDs) of enzymatically debranched duckweed starches were obtained using size-exclusion-chromatography (SEC). The CLDs of both debranched amylose and amylopectin were fitted with models using biologically-meaningful parameters. While there were no significant correlations between amylose content and starch degradation rate, the total amounts of amylose with shorter chain length negatively correlated with undigested starch content, and the amount of amylopectin long chains negatively correlated with the degradation rate coefficient. This provides new knowledge for the utilization of duckweed starches in bioethanol production.

Factors affecting coupled degradation and time-dependent sorption processes of tebuconazole in mineral soil profiles

This laboratory degradation and adsorption study aimed to determine the tebuconazole degradation parameters for 6 profiles of Polish mineral soils and to find links between the tebuconazole degradation rate, its adsorption, soil microbial activity and other significant soil properties. The values of the adsorption distribution coefficient Kd, obtained in batch experiments after 96 h of shaking were in the range of 6.2–34.6 mL g−1. In both batch experiments and incubation experiments at 20 °C, the typical course of adsorption processes was observed, an initial rapid stage followed by a slow stage. In 3 of the 18 soils examined, adsorption was not reached within 51 days. The range of the half-life values was 201–433 days for the Ap horizon and up to 3904 days for subsoils, which were estimated using the two-site nonequilibrium adsorption model coupled with first-order degradation for dissolved and adsorbed pesticide. It was found that modeling the degradation of tebuconazole on the basis of the coefficients of microbial biomass activity for topsoil and two subsoils explained almost 96% of the variance of the estimated pore water degradation rate coefficients in examined soils. The degradation rate was also negatively correlated with the amount adsorbed in the time dependent adsorption sites. This fraction was the least available for soil microorganisms because it was strongly adsorbed in soil pores with a radius <2.5 nm, determined from the H2O desorption isotherm. The degradation rate was also affected by the ratio of the water content in soil during degradation experiments to the water content at field capacity. The results indicated that degradation occurred in the soil liquid phase only.

Photochemical degradation of acrolein using VUV excimer lamp in air at atmospheric pressure

The photochemical degradation of acrolein (C2H3CHO) was investigated in air at atmospheric pressure using a 172-nm Xe2 excimer lamp. When C2H3CHO was decomposed using the side-on type of lamp, HCOOH, CO, CO2, and O3 peaks were observed in FTIR absorption spectra. The dependence of product concentrations on the irradiation time indicated that HCOOH and CO intermediates are finally converted to CO2 via consecutive reactions. The degradation rate coefficient of C2H3CHO in the batch system increased from 8.4 to 19.3 min−1, as the O2 concentration was decreased from 20 to 1%. It increased also from 8.4 to 40.1 min−1 at 20% O2, as the chamber depth was decreased from 3.0 to 0.5 cm. The best energy efficiency of the C2H3CHO degradation was 3.4 g kW−1 h−1 at 1–20% O2 in a flow system. Besides direct VUV photodissociation of C2H3CHO, reactions of O(3P,1D) and O3, produced from photolysis of O2, can contribute to C2H3CHO degradation in the initial stage. Among them, the contribution of O(1D) and O3 was found to be insignificant on the basis of the total pressure dependence of removal amount of C2H3CHO and results obtained from the O3 + C2H3CHO reaction. It was concluded that at first C2H3CHO is decomposed by direct VUV photodissociation of C2H3CHO and the O(3P) + C2H3CHO reaction. It was further decomposed by secondary reactions of O(3P), OH, and O3 with such intermediates as HCOOH and CO and finally oxidized to CO2.

Influence of molecular structure on the susceptibility of starch to α-amylase

The effect of the molecular structure of sweet potato (SPS), cassava (CAS) and high amylose maize (HAS) starches on the susceptibility to fungal and maltogenic α-amylases was investigated. The logarithm of the slope (LOS) and non-linear least-squares (NLLS) methods were used for fitting hydrolysis kinetics data. The malto-oligosaccharides released during hydrolysis were quantified and the hydrolysis residues were analyzed. The hydrolysis kinetic curves were well fitted to the LOS and NLLS models. SPS, CAS and HAS were hydrolyzed in one single phase by fungal α-amylase while two hydrolysis phases were identified for the root starches and a single phase for HAS, when maltogenic α-amylase was used. The lowest percentage of residual starch was found for CAS, independent of enzyme source, due to the high proportion of amylopectin short chains in this starch. On the other hand, the high proportion of HAS long chains contributed to its increased starch degradation rate coefficient during fungal α-amylase hydrolysis, while the high amylose content favored the endo-action pattern of maltognic α-amylase. Independent of starch source, malto-oligosaccharides of different sizes, especially G2-G5, were released after the fungal α-amylase action which hydrolyzes mainly inner and long amylopectin chains. Mainly maltose was produced in the maltogenic α-amylase hydrolysis which breaks the outer amylopectin chains by exo-action and amylose chains by endo-action. The starch molecular structure strongly interferes in both enzyme susceptibility and the action mechanism, as well as in the distribution and amount of products released.