Initial Mineralization Rate Research Articles

Physicochemical Dynamics of Composting Screw Pressed Cattle Slurry Amended with Italian Ryegrass Straw or Gorse Bulking Agents

Cattle slurry solid fraction (SF) was composted with increasing rates (0, 25, 33 and 50% v/v) of either Italian ryegrass (Lolium multiflorum L.) straw or gorse (Ulex europaes) to determine the effects of these bulking agents on the physicochemical properties during the composting process and to identify approaches to improve final compost quality. Composting temperatures increased to a maximum of 65°C after 42 days for unamended SF. In contrast, temperatures increased more rapidly in piles mixed with straw (68°C at day 7) or with gorse (74°C at day 3). Gorse or straw addition to SF, therefore, also increased the initial rates of organic matter mineralization. However, potential organic matter (OM) mineralization and compost N concentration decreased with the addition of the bulking agents. C/N ratios declined from 32-38 to a value of 13-17 towards the end of composting and followed a similar trend for all compost treatments. Low compost temperature, low C/N ratio and the small content of NH4+ combined with increased concentrations of NO3− indicated SF composts were stabilized and suitable for use in agriculture. High concentrations of OM (780-840 g kg−1 dry matter (DM)) and total N (28-35 g kg−1 DM), and low electrical conductivity (0.7-1.2 dS m−1) suggested that SF composts would be effective soil amendments with agronomic and environmental advantages. The addition of straw or gorse also enhanced compost sanitation.

Investigation of dye functional group on the photocatalytic degradation of dyes by nano-TiO 2

The photocatalytic degradation of five anionic, eight cationic and three solvent dyes using combustion-synthesized nano-TiO 2 (CS TiO 2) and commercial Degussa P-25 TiO 2 (DP-25) were evaluated to determine the effect of the functional group in the dye. The degradation of the dyes was quantified using the initial rate of decolorization and mineralization. The decolorization of the anionic dyes with CS TiO 2 followed the order: indigo carmine > eosin Y > amido black 10B > alizarin cyanine green > orange G. The decolorization of the cationic dyes with DP-25 followed the order: malachite green > pyronin Y > rhodamine 6G > azure B > nile blue sulfate > auramine O ≈ acriflavine ≈ safranin O. CS TiO 2 showed higher rates of decolorization and mineralization for all the anionic dyes compared to DP-25, while DP-25 was better in terms of decolorization for most of the cationic dyes. The solvent dyes exhibited adsorption dependent decolorization. The order of decolorization and mineralization of the anionic and cationic dyes (a) with CS TiO 2 and DP-25 was different and correlated with the surface properties of these catalysts (b) were rationalized with the molecular structure of the dye and the degradation pathway of the dye.

Solar photocatalytic degradation of commercial textile azo dyes: Performance of pilot plant scale thin film fixed-bed reactor

Performances of solar photocatalytic pilot plant using TiO2-P25 (Degussa) were investigated for removal of commercial azo dye chosen as model compound. Experiments were carried out to optimize various parameters, influencing the performance of the operated thin-film fixed-bed reactor (TFFBR) with an area of 25 m2. The results showed kinetic dependency on flow rate, catalyst loading, and initial dye concentration. The best discoloration rate was obtained at the optimum flow rate of 3 m3/h. Increasing catalyst loading density up to 10 g/m2, does not lead to high improvement of the discoloration rate. The photocatalytic degradation kinetic of TOC is discussed in terms of Langmuir–Hinshelwood model. Initial mineralization rate expressed by mg kJ−1 reach a maximum value at initial TOC closed to 30 mg/L.

Short-term effects of crop rotation, residue management, and soil water on carbon mineralization in a tropical cropping system

The purpose of this study was to investigate the short-term effects of maize (Zea mays)-fallow rotation, residue management, and soil water on carbon mineralization in a tropical cropping system in Ghana. After 15 months of the trial, maize–legume rotation treatments had significantly (P < 0.001) higher levels of potentially mineralizable carbon, C0 (μg CO2–C g−1) than maize–elephant grass (Pennisetum purpureum) rotations. The C0 for maize–grass rotation treatments was significantly related to the biomass input (r = 0.95; P = 0.05), but that for the maize–legume rotation was not. The soil carbon mineralization rate constant, k (per day), was also significantly related to the rotation treatments (P < 0.001). The k values for maize–grass and maize–legume rotation treatments were 0.025 and 0.036 day−1 respectively. The initial carbon mineralization rate, m0 (μg CO2–C g−1 day −1), was significantly (P < 0.001) related to the soil water content, θ. The m0 ranged from 3.88 to 18.67 and from 2.30 to 15.35 μg CO2–C g−1 day−1 for maize–legume and maize–grass rotation treatments, respectively, when the soil water varied from 28% to 95% field capacity (FC). A simple soil water content (θ)-based factor, fw, formulated as: \(f_{\text{w}} = \left[ {\frac{{\theta - \theta _{\text{d}} }}{{\theta _{{\text{FC}}} - \theta _{\text{d}} }}} \right]\), where θd and θFC were the air-dry and field capacity soil water content, respectively, adequately described the variation of the m0 with respect to soil water (R2 = 0.91; RMSE = 1.6). Such a simple relationship could be useful for SOC modeling under variable soil water conditions.

Effects of Enrichment with Salicylate on Bacterial Selection and PAH Mineralization in a Microbial Community from a Bioreactor Treating Contaminated Soil

We investigated enrichment with salicylate as a method to stimulate the degradation of polycyclic aromatic hydrocarbons (PAHs) by a microbial communityfrom a bioreactortreating PAH-contaminated soil. DNA-based stable isotope probing (SIP) was used to compare the effect of alternate methods of salicylate addition (spike vs slow, continuous addition) on the diversity of the enriched microbial community. After identification of salicylate degraders by SIP, real-time quantitative PCR (qPCR) primers were developed to quantify the abundances of three groups containing salicylate-utilizing organisms in the bioreactor community before and after enrichment. The different methods of salicylate addition were found to select for different microbial communities. Two groups containing salicylate-degrading bacteria increased in abundance substantially after enrichment by continuous addition of salicylate but did not increase in abundance in response to the spike addition, whereas a third group increased in abundance in response to both methods of salicylate addition. The initial rate of naphthalene mineralization increased significantly after enrichment by spike addition of salicylate, but neither phenanthrene nor benzo[a] pyrene mineralization rates were enhanced. Continuous addition of salicylate did not enhance the mineralization rate for any of the PAHs. These results suggest that enrichment with salicylate can select for naphthalene-degrading bacteria, but does not select for organisms responsible for degrading PAHs of higher molecular weight. Differences in microbial selection observed in this study that resulted from different rates of carbon source addition also have implications for the design of SIP experiments with water-soluble carbon sources.

Effect of sorption and desorption-resistance on biodegradation of chlorobenzene in two wetland soils

Bioavailability of chlorobenzenes (CBs) in soils to microbial populations has implications for remediation of waste sites with long histories of contamination. Bioavailability of CB was assessed using mineralization assays for two types of wetland soils with contrasting properties. The rate and extent of CB mineralization were greater than predicted by mathematical models which assume instantaneous desorption followed by biodegradation. The freshly added CB was degraded with initial mineralization rates (IMRs) of 0.14 μg L −1 h −1 and 1.92 μg L −1 h −1 for marsh soil and wetland soil respectively. These values indicate that CB-degrading bacteria had an access to the sorbed CB. Mineralization assays were also performed for wetland soils after the CB was aged for 1, 7 and 31 days. The results revealed that even a desorption-resistant part of the sorbed CB was degraded although the degradation occurred at lower rates and to a lesser extent.

Development of Engineered Natural Organic Sorbents for Environmental Applications. 4. Effects on Biodegradation and Distribution of Pyrene in Soils

The effects of engineered natural organic amendments on the biodegradation and distribution of pyrene in soils were assessed. Pyrene was aged for 105 days in soils amended with either raw or superheated water (SHW)-processed MI peat or soybean stalks, and then subjected to biodegradation with specifically selected microorganisms for 130 days. Initial rates of pyrene mineralization in the soils were increased by addition of raw MI peat, but markedly decreased by additions of SHW-processed MI peat and both processed and raw soybean stalks. Pyrene sorbed by the processed organic sorbents was, however, slowly but steadily degraded by microorganisms over a greater than 4-month test period. Pyrene distributions in the soils were examined by sequential extractions of samples before and after biodegradation. Fractions of pyrene extracted readilywith water or water/methanol mixtures were decreased substantially in both soils bythe addition of processed amendments, while the nonextractable fractions associated with humic and fulvic acids and humin were increased markedly. The results demonstrate that SHW-processed amendments effectively reduce the ecological and human availability and aqueous phase extractability of organic contaminants while facilitating their steady microbial degradation and eventually complete remediation.

Mineralization of paracetamol by ozonation catalyzed with Fe2+, Cu2+ and UVA light

Acid solutions containing up to 1gl−1 of the drug paracetamol have been treated with ozone alone and ozonation catalyzed with Fe2+, Cu2+ and/or UVA light at 25.0°C. Direct ozonation yields poor degradation due to the high stability of final carboxylic acids formed, whereas more than 83% of mineralization is attained with the catalyzed methods. Under UVA irradiation, organics can be efficiently destroyed by the combined action of generated H2O2 and UVA light. In the presence of Fe2+ and UVA light, the process is accelerated due to the production of oxidant hydroxyl radical (OH) and the photodecomposition of Fe3+ complexes. The highest oxidizing power is achieved by combining Fe2+, Cu2+ and UVA light, because complexes of final acids with Cu2+ are more quickly degraded than those competitively formed with Fe3+. For all catalyzed methods, the initial mineralization rate is enhanced and the percent of degradation generally drops with increasing drug concentration. The paracetamol decay always follows a pseudo-first-order reaction with slightly higher rate constant for catalyzed systems than direct ozonation. Aromatic products such as hydroquinone, p-benzoquinone and 2-hydroxy-4-(N-acetyl)aminophenol are identified by gas chromatography–mass spectrometry (GC–MS) and reversed-phase chromatography. Acetamide is generated when hydroquinone is produced. These products are degraded to oxalic and oxamic acids as ultimate carboxylic acids, as detected by GC–MS and ion-exclusion chromatography. Oxalic acid is generated via glycolic, glyoxylic, tartronic, ketomalonic and maleic acids. While Fe3+-oxalato complexes are photolyzed by UVA light, Cu2+-oxalato, Fe3+-oxamato and Cu2+-oxamato complexes are oxidized with OH. NH4+ and NO3− ions are produced during mineralization.

Optimizing the solar photo-Fenton process in the treatment of contaminated water. Determination of intrinsic kinetic constants for scale-up

The elimination of aromatic compounds present in surface water by photo-Fenton with sunlight as the source of radiation was studied. The concentrations of Fe 3+ and H 2O 2 are key factors for this process. A solar simulator and a prototype parabolic collector were used as laboratory-scale reactors to find the parameters of those key factors to be used in the CPC (compound parabolic collector) pilot plant reactor. The initial mineralization rate constant ( k obs) was determined and evaluated at different Fe 3+ and H 2O 2 concentrations to find the best values for maximum efficiency. In all the experiments the mineralization of an aqueous phenol solution was described by assuming a pseudo-first-order reaction. The intrinsic kinetic constants not dependent on the lighting conditions were also estimated for scale-up.

Relative importance of substrate type and previous soil management in synthesis of microbial biomass and substrate mineralization

SummaryOur aim was to determine whether the soil microbial biomass, which has developed naturally over many years in a given ecosystem, is specially adapted to metabolize the plant‐derived substrate C of the ecosystem within which it developed or whether the nature of recently added substrate is the more important factor. To examine this, soils from three sites in close proximity (woodland, grassland and arable from the Broadbalk Experiment at Rothamsted Research, Harpenden, UK) were each amended with air‐dried wheat straw (Triticum aestivum), ryegrass leaves (Lolium perenne) or woodland leaf litter (mainly Quercus robur and Fagus sylvatica) in a fully replicated 3 × 3 factorial laboratory experiment. The initial mineralization rates (evolved CO2‐C) were determined during the first 6.5 hours and again, together with the amount of microbial biomass synthesized (microbial biomass C), at 7, 14, 21, 30 and 49 days of incubation. The hourly rate of CO2‐C production during the first 6.5 hours was slowest following leaf litter addition, while the added grass gave the fastest rates of CO2‐C evolution both within and between soils. Ryegrass addition to the arable soil led to approximately four times more CO2‐C being evolved than when it was added to the woodland soil, at an overall rate in the arable soils of 41 μg C g−1 soil hour−1. In each soil, the net amounts of CO2‐C produced were in the order grass &gt; straw &gt; leaf litter. In each case, the amount produced by the added leaf litter was significantly less (P &lt; 0.05) than either the added grass or straw. Overall, the trend was for much slower rates of mineralization of all substrates in the woodland soil than in either the arable or grassland soils. During 49 days of incubation in the woodland and grassland soils, the net total amounts of CO2‐C evolved differed significantly (P &lt; 0.01), with grass &gt; straw &gt; leaf litter, respectively. In the arable soil, the amounts of CO2‐C evolved from added grass and straw were significantly larger (P &lt; 0.01) than from the leaf litter treatment. Our findings indicated that the amounts of CO2‐C evolved were not related to soil management or to the size of the original biomass but to the substrate type. The amount of biomass C synthesized was also in the order grass &gt; straw &gt; leaf litter, at all stages of incubation in the woodland and grassland soil. In the arable soil, the same effect was observed up to 14 days, and for the rest of the incubation the biomass C synthesized was in the order grass &gt; straw &gt; leaf litter. Up to three times more biomass C was synthesized from the added grass than from the other substrates in all soils throughout the incubation. The maximum biomass synthesis efficiency was obtained with grass (7% of added C). Overall, the woodland soil was most efficient at synthesizing biomass C and the arable soil the least. We conclude that substrate type was the overriding factor that determined the amount of new soil microbial biomass synthesized. Mineralization of substrate C by soil microorganisms was also influenced mainly by substrate type and less by soil management or size of original biomass.

Enhancement of PAH biomineralization rates by cyclodextrins under Fe(III)-reducing conditions

Amendment of a soil slurry with low concentrations of a cyclodextrin, hydroxypropyl-β-cyclodextrin (HPCD), (0.05–0.5 g l −1) increased the phenanthrene mineralization rate of a microbial consortium by 25% under Fe(III)-reducing conditions. Although a higher concentration (5.0 g l −1) resulted in a faster initial rate of mineralization, mineralization ceased after 25 days with maximum mineralization 17% lower than the control (no HPCD). At lower HPCD concentrations, mineralization was still taking place at day 76. Although pH should affect Fe(III) solubility, mineralization rates at pH 6.0 and 8.0 were comparable. Decreasing the temperature reduced the extent and rate of mineralization, but mineralization rates at 10 °C were still 60% of that obtained at 30 °C.

Degradation of the herbicide 2,4-DP by catalyzed ozonation using the O3/Fe2+/UVA system

Acid solutions of the herbicide 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP) of pH 3.0 at 25.0°C have been treated with ozone and ozonation catalyzed with Fe2+, Cu2+ and/or UVA light. This herbicide is slowly degraded by ozonation alone, while its destruction is enhanced under UVA irradiation. In the presence of Fe2+, the initial mineralization rate is accelerated due to the generation of oxidizing hydroxyl radical (OH), but a large proportion of stable products are formed. These species are partially removed when Fe2+ and UVA light are combined, since greater amounts of OH are produced and Fe3+ complexes are photodecomposed. Addition of Cu2+ to this system does not significantly improve its oxidizing ability, since the Cu2+/Cu+ pair gives a low additional OH concentration. The herbicide decay always follows a pseudo first-order reaction. 2,4-Dichlorophenol, chlorohydroquinone and chloro-p-benzoquinone are detected as aromatic intermediates by reversed-phase chromatography. The initial chlorine is always transformed into chloride ion. Ion-exclusion chromatography allows the quantification of generated carboxylic acids such as lactic, pyruvic, maleic, fumaric, oxalic and acetic. These acids are completely removed, except the two latter ones. Acetic acid remains stable in all cases. Oxalic acid is stable in the O3 system, being partially mineralized to CO2 by the O3/UVA one. It also yields stable Fe3+-oxalato complexes in the O3/Fe2+ system, which are rapidly photodecarboxylated in the O3/Fe2+/UVA and O3/Fe2+ + Cu2+/UVA methods. Cu2+-oxalato complexes also formed in the latter procedure are slowly mineralized with OH. A possible reaction sequence for 2,4-DP degradation involving all intermediates detected is proposed.

Mineralization of erythromycin A in aquaculture sediments

Mineralization of erythromycin A was studied using two differently 14C-labeled erythromycins A, which were added to aquaculture sediment samples obtained from the two salmon hatchery sites in Washington state. The added erythromycin A did not significantly alter the numbers of the total viable colonies and erythromycin-resistant bacteria. Erythromycin-resistant Pseudomonas species contained a constitutive erythromycin esterase activity contributing to the inactivation of biologically active erythromycin A in aquatic and sediment environments. The initial rate of mineralization of erythromycin A appeared to be governed by the rate of release of soil-sorbed erythromycin A. After a prolonged lag time, the S-curves of erythromycin A mineralization were observed probably because of the increase in the population density metabolizing it. This study suggests that erythromycin A is partially or completely mineralized by the sediment microbial populations.

Degradation of the herbicide 2,4-dichlorophenoxyacetic acid by ozonation catalyzed with Fe2+ and UVA light

Solutions of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) with concentrations up to near saturation at pH 3.0 and at 25°C have been treated with ozone and ozonation catalyzed with Fe2+ and/or UVA light. Direct ozonation yields a slow depollution, while all contaminants are completely removed under UVA irradiation. The highest oxidizing power is achieved when Fe2+ and UVA light are combined, since greater amounts of oxidizing hydroxyl radical are generated and Fe3+ complexes are photodecomposed. The initial mineralization rate is enhanced when herbicide concentration increases and more hydroxyl radicals are produced by the catalyzed ozonation processes. The herbicide decay always follows a pseudo first-order reaction. Reverse-phase chromatography allows the detection and quantification of aromatic intermediates such as 2,4-dichlorophenol, 4,6-dichlororesorcinol and chlorohydroquinone. In all treatments, fast dechlorination reactions take place leading to chloride ion accumulation in the medium. The evolution of generated carboxylic acids such as glycolic, glyoxylic, maleic, fumaric and oxalic has been followed by ion-exclusion chromatography. Only oxalic acid remains stable in the O3 system, being quickly mineralized to CO2 by hydroxyl radicals formed in the O3/UVA one. A high stability of oxalic acid in the O3/Fe2+ system has also been found, since it yields Fe3+-oxalato complexes. These species are photodecarboxylated under UVA irradiation in the O3/Fe2+/UVA system. A possible reaction pathway for 2,4-D mineralization involving all intermediates detected is proposed.

Mineralization of aged atrazine, terbuthylazine, 2,4‐D, and mecoprop in soil and aquifer sediment

The effect of aging of the herbicides atrazine, terbuthylazine, 2,4-D, and mecoprop on their bioavailability to degrading microorganisms was studied in soil and aquifer sediment. 14C-ring-labeled herbicide (2.5 mg/kg) was added to sterilized soil or aquifer sediment and stored at 10 degrees C for up to 103 d before inoculation with either the atrazine and terbuthylazine-degrading Pseudomonas sp. strain ADP (atrazine-degrading Pseudomonas) or an enriched culture able to mineralize 2,4-D and mecoprop. The initial mineralization rate and recovery of 14CO2 after 62 to 113 d of incubation were used as measures of the availability of the compounds to the microorganisms. Aging in soil reduced the initial mineralization of atrazine. Thus, only 17% of the added 14C-atrazine had been mineralized after 21 h of incubation when aged for 88 d as compared with 33% when the atrazine had been aged for 1 d. 14CO2 recovery was only 58% after 88 d of aging as compared with 81% when aged for 1 d. A similar effect of aging was seen with terbuthylazine. With 2,4-D, the effect of aging in soil on mineralization by the enriched culture was much smaller. Aging had no effect on mineralization of mecoprop in soil or on mineralization of any of the herbicides in aquifer sediment.

Kinetics of microbial Fe(III) oxide reduction in freshwater wetland sediments

The kinetics of microbial amorphous Fe(III) oxide reduction was investigated in sediments from a freshwater wetland in north central Alabama, USA. Fe(III) oxide concentrations decreased exponentially with time during anaerobic incubation of sediment slurries and homogenized surface sediments. Rates of organic carbon mineralization (ΣCO2 + CH4 accumulation) did not change markedly during the course of Fe(III) oxide reduction, which indicated that the exponential decline in Fe(III) oxide concentration over time resulted primarily from Fe(III) limitation rather than a decrease in organic matter decay rate. Initial rates of Fe(III) oxide reduction were linearly correlated with initial Fe(III) oxide concentrations in experiments with mixtures of Fe(III)‐rich and Fe(III)‐depleted sediment slurries. Similar results were obtained in experiments with sediment from various depth intervals in the upper 3 cm of freshly collected cores. These findings provide explicit evidence that microbial Fe(III) oxide reduction rates are first order with respect to amorphous Fe(III) oxide concentration in the wetland sediment. The observed first‐order relationship between Fe(III) oxide concentration and reduction rate is consistent with established models of surface area‐controlled mineral transformation. An experiment in which Fe(III) oxide‐rich sediment slurries were amended with different amounts of labile organic matter demonstrated a direct correlation between first‐order Fe(III) reduction rate constants and initial rates of organic carbon mineralization. These results provide empirical support for existing approaches to modeling organic matter decay‐dependent Fe(III) oxide reduction kinetics in sediments.

Correlation of foliage and litter chemistry of sugar maple, Acer saccharum, as affected by elevated CO2 and varying N availability, and effects on decomposition

Rising atmospheric carbon dioxide has the potential to alter leaf litter chemistry, potentially affecting decomposition and rates of carbon and nitrogen cycling in forest ecosystems. This study was conducted to determine whether growth under elevated atmospheric CO2 altered the quality and microbial decomposition of leaf litter of a widely distributed northern hardwood species at sites of low and high soil nitrogen availability. In addition, we assessed whether the carbon–nutrient balance (CNB) and growth differentiation balance (GDB) hypotheses could be extended to predict changes in litter quality in response to resource availability. Sugar maple (Acer saccharum) was grown in the field in open‐top chambers at 36 and 55 Pa partial pressure CO2, and initial soil mineralization rates of 45 and 348 μg N g−1 d−1. Naturally senesced leaf litter was assessed for chemical composition and incubated in the laboratory for 111 d. Microbial respiration and the production of dissolved organic carbon (DOC) were quantified as estimates of decomposition. Elevated CO2 and low soil nitrogen resulted in higher litter concentrations of nonstructural carbohydrates and condensed tannins, higher C/N ratios and lower N concentrations. Soil N availability appears to have had a greater effect on litter quality than did atmospheric CO2, although the treatments were additive, with highest concentrations of nonstructural carbohydrates and condensed tannins occurring under elevated CO2–low soil N. Rates of microbial respiration and the production of DOC were insensitive to differences in litter quality. In general, concentrations of litter constituents, except for starch, were highly correlated to those in live foliage, and the CNB/GDB hypotheses proved useful in predicting changes in litter quality. We conclude the chemical composition of sugar maple litter will change in the future in response to rising atmospheric CO2, and that soil N availability will exert a major control. It appears that microbial metabolism will not be directly affected by changes in litter quality, although conclusions regarding decomposition as a whole must consider the entire soil food web.

Repeated inoculation as a strategy for the remediation of low concentrations of phenanthrene in soil.

Phenanthrene, a polycyclic aromatic hydrocarbon, becomes increasingly unavailable to microorganisms for degradation as it ages in soil. Consequently, many bioaugmentation efforts to remediate polycyclic aromatic hydrocarbons in soil have failed. We studied the effect of repeatedly inoculating a soil with a phenanthrene-degrading Arthrobacter sp. on the mineralization kinetics of low concentrations of phenanthrene. After the first inoculation, the initial mineralization rate of 50 ng/g phenanthrene declined in a biphasic exponential pattern. By three hundred hours after inoculation, there was no difference in mineralization rates between the inoculated and uninoculated treatments even though a large fraction of the phenanthrene had not yet been mineralized. A second and third inoculation significantly increased the mineralization rate, suggesting that, though the mineralization rate declined, phenanthrene remained bioavailable. Restirring the soil, without inoculation, did not produce similar increases in mineralization rates, suggesting absence of contact between cells and phenanthrene on a larger spatial scale (>mm) is not the cause of the mineralization decline. Bacteria inoculated into soil 280 hours before the phenanthrene was added could not maintain phenanthrene degradation activity. We suggest sorption lowered bioavailability of phenanthrene below an induction threshold concentration for metabolic activity of phenanthrene-degrading bacteria.

Mineralization of aniline and 4-chlorophenol in acidic solution by ozonation catalyzed with Fe2+ and UVA light

Solutions with 1.07mmoldm−3 aniline or with 1.38mmoldm−3 4-chlorophenol at pH ca. 3 have been treated with ozone and ozonation catalyzed with Fe2+ and/or UVA. The initial mineralization rate increases as more oxidizing hydroxyl radical is produced in the medium by the catalyzed ozonations. Direct ozone treatment leads to stable oxidation products, which are quickly destroyed under UVA illumination. In the presence of Fe2+ as catalyst, the degradation process is inhibited by the formation of Fe3+ complexes with short organic diacids, being photodecomposed by UVA light. Each initial pollutant is destroyed at similar rate in all processes. p-Benzoquinone and nitrobenzene are identified as intermediates of aniline oxidation. The former product is only detected when high amounts of hydroxyl radical are produced by the action of Fe2+. Ammonium ion released during p-benzoquinone formation is also generated in larger extension under the same conditions. Nitrate ion reaches maximum production under UVA irradiation, indicating that generation of nitrobenzene from selective attack of O3 on the amino group of aniline is photocatalyzed. Reaction of 4-chlorophenol with ozone leads to 4-chloro-1,3-dihydroxybenzene and 4-chloro-1,2-dihydroxybenzene. The last product is produced in larger extension when high amounts of hydroxyl radical can selectively attack the initial pollutant. Chloride ion is completely lost during the further degradation of both dihydroxylated derivatives. Oxidation of all aromatic intermediates detected during aniline and 4-chlorophenol degradation gives maleic acid, which is further mineralized via oxalic acid. A general reaction pathway for the degradation of each pollutant is proposed.

Elevated atmospheric [CO 2] from a natural soda spring affects the initial mineralization rates of naturally senesced C3 and C4 leaf litter

Naturally senesced leaves from the grasses Holcus lanatus (Yorkshire fog; C3 photosynthetic pathway) and Pennisetum clandestirum (Kikuyu; C4 photosynthetic pathway), grown in elevated atmospheric [CO 2] surrounding a natural soda spring, were decomposed within respiratory chambers and the initial mineralization (0–30 days) of the litter measured. Significantly greater rates of initial mineralization of the C3 litters previously grown in elevated atmospheric [CO 2] were detected compared to the C3 litters grown in ambient [CO 2]. For example, within the first 15 days the rate of CO 2 production from the litters grown in the elevated atmospheric [CO 2] was two to five times greater than that seen from the litters grown in the ambient concentrations of CO 2. The effect of elevated atmospheric [CO 2] on the mineralization of the C4 litter was less pronounced, however rates of mineralization were still significantly greater from litters grown originally in elevated [CO 2]. A significant decline in the C:N ratios and nitrogen content of the leaves of both the C3 and C4 grasses was observed, although analysing the relationship between the carbon and nitrogen content, or the C:N ratio, with the initial mineralization rate indicated that these litter quality parameters were not good indicators of the rate of mineralization of the litter from these grasses.