Kinetics Of Organic Matter Degradation Research Articles

Degradation kinetics of organic matter in domestic sewage by sequencing batch reactor

The sequencing batch reactor (SBR) has become a popular sewage treatment process in various industries due to its strong impact load resistance and numerous other advantages. This study examines the variations of chemical oxygen demand chromium (CODcr), ammoniacal nitrogen (NH3-N), total bound nitrogen (TN) and total phosphorus (TP) with aeration time to investigate the degradation patterns of different pollutants during the SBR’s reaction stage. Additionally, an organic matter degradation kinetic model was developed. The experimental results showed that the CODcr and NH3-N in the reactor met the national discharge standards after two hours of influent. Furthermore, the removal rates of CODcr and NH3-N exceeded 85% and 99%, respectively, at the end of the final aeration. At the same time, the TN and TP removal rates remained stable at approximately 45% and 68%. The analysis of the kinetic model showed that the degradation process of organic matter followed a first-order kinetic equation: S=S0e−0.00012Xt. The regression model's fitting value exhibited a high degree of conformity with CODcr removal’s experimental results, with the average relative error of 5.52% falling within an acceptable range. Furthermore, the correlation coefficient (0.9966) indicated high accuracy and effectively represented the changes in organic matter throughout the SBR reaction stage. Consequently, this model can serve as a theoretical foundation for determining CODcr’s maximum treatment capacity in experimental wastewater.

Transit Time index (TTi) as an adaptation of the humification index to illustrate transit time differences in karst hydrosystems: application to the karst springs of the Fontaine de Vaucluse system (southeastern France)

Abstract. Transit time can be estimated thanks to natural tracers, but few of them are usable in the 0–6-month range. The main purpose of this work is to analyze the potential of the ratio of heavy- to light-weight organic compounds (the humification index (HIX); Ohno, 2002; Zsolnay et al., 1999) as a natural tracer of short transit time (Blondel et al., 2012). Critical analysis of former studies shows that although the link between HIX and transit time seems consistent, the whole methodological approach needs to be consolidated. Natural organic matter fluorescence from 289 groundwater samples from four springs and 10 flow points located in the unsaturated zone of the Vaucluse karst system is characterized by parallel factor analysis (PARAFAC) thanks to the excitation–emission matrix (EEM), thus (i) allowing for the identification of main fluorescent compounds of sampled groundwater and (ii) evidencing the inadequacy of HIX 2D emission windows to characterize groundwater organic matter. We then propose a new humification index called the Transit Time index (TTi) based on the Ohno (2002) formula but using PARAFAC components of heavy and light organic matter from our samples instead of 2D windows. Finally, we evaluate TTi relevance as a transit time tracer by (i) performing a detailed analysis of its dynamics on a selected spring (Millet) and (ii) comparing its mean value over karst springs of the Vaucluse karst system. Principal component analysis (PCA) of TTi and other hydrochemical parameters monitored at Millet spring put in relief the different ranges of transit time associated with the different organic matter compounds. PCA results also provide evidence that TTi can detect a small proportion of fast infiltration water within a mix, while other natural tracers of transit time provide no or less sensitive information. TTi distributions at monitored karst springs are consistent with relative transit times expected for the small-scale, short average transit time systems. TTi thus appears as a relevant qualitative tracer of transit time in the 0–6-month range where existing tracers fail and may remain applicable, even in the case of anthropic contamination thanks to PARAFAC modeling. Transforming it into quantitative information is a challenging task which may be possible thanks to intensive studies of organic matter degradation kinetics in natural waters with the help of radiogenic isotope usage or an artificial tracer test.

Composting of swine production chain wastes with addition of crude glycerin: organic matter degradation kinetics, functional groups, and carboxylic acids

Composting of swine production chain wastes with addition of crude glycerin: organic matter degradation kinetics, functional groups, and carboxylic acids

Comparison of first-order kinetic models for sewage treatment in horizontal subsurface-flow constructed wetlands

ABSTRACT There are several techniques for sizing horizontal subsurface-flow constructed wetlands systems (CWs), and mathematical models have been frequently used for this purpose because they more accurately represent the liquid behaviour in these reactors. The P-k-C* model has already been used in the prediction of organic matter removal in CWs, but it has been little explored in the literature. On other hand, the model proposed by Chan and Chu [Modeling the reaction kinetics of Fenton’s process on the removal of atrazine. Chemosphere. 2003;51(4):305–311] was not known for prediction of organic matter removal in CW systems. In the present work, the kinetic data for chemical oxygen demand (COD) removal of 28 horizontal subsurface-flow constructed wetlands were used to compare the performance of two pseudo-first-order kinetic models (P-k-C* model and model from Chan and Chu. The comparisons of nonlinear regressions were performed considering Akaike information criterion (AIC), root-mean-square error (RMSE), and adjusted coefficient of determination (). In general, both models were able to provide good predictions of relative remaining concentration (C/C 0). However, the Chan and Chu model produced higher adjustment coefficients, showing the potential to be used in modelling and simulation of the degradation kinetics of organic matter in wetlands.

Thermogravimetric and Calorimetric Characteristics of Alternative Fuel in Terms of Its Use in Low-Temperature Pyrolysis

One of the refuse derived fuel (RDF) utilization methods is low temperature pyrolysis. However, the high heterogeneity of RDF and the fact that its various components may influence on the degradation of other components causes difficulties with proper energy balance of the process. Determination of the energy balance could be performed with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Those methods allows the identification of kinetics of organic matter degradation in thermal processes, the calculation of activation energy, and energy demand/release during organic matter transformations. TGA and DSC were used to examine the potential of using RDF in low temperature pyrolysis. TGA analysis shows that main organic matter decomposition in RDF occurs at temperature range between 400 and 600 °C. This temperature range is typical for plastics decomposition, as plastics are a main component of alternative fuel derived from municipal solid waste. For the analyzed RDF samples activation energy within the 400–600 °C temperature range was at the level of 25.5 kJ mol−1. The four distinctive specific heat changes in the tested RDF material were observed, which means, four specific materials groups were decomposed. Four of this reaction were endothermal, and one was exothermal. The whole process is endothermic. The energy demand for transformations is − 63.62 J g−1. The results also shown that RDF low temperature pyrolysis product’s lower calorific value was at the level of 7.55 MJ kg−1, thus pyrolysis should not be considered as a pretreatment method for preparing CRDF for energy reuse.

Degradation kinetics of organic matter in dairy industry wastewater by flotation/ozonation processes

This study evaluated the adjustment of four kinetic models and their respective parameters on data of dairy wastewater treatment by the physico-chemical process of flotation and ozonation. The experiment was implemented during the year 2014, with all the tests in triplicate. The treatments were carried out at different pH levels (3.6, 7.0 and 10.4), and flotation/ozonation was catalyzed by manganese (Mn2+) in neutral level (pH 7.0). Best removal efficiencies for chemical oxygen demand (COD) were obtained in acidic medium, with removals greater than 75% after 20 min of treatment. There was no significant difference with regards to addition of Mn2+on COD removal by the physico-chemical process. The kinetic models that best fit to the experimental data, for all treatments, were the asymptotic (residual) model and that of Chan and Chu. Treatment in acidic medium showed the highest values of the kinetic parameters for the adjusted model, obtaining a k coefficient equal to 0.2394 min-1for the asymptotic model and kinetic coefficient 1/ρ of 0.4816 min-1for the Chan and Chu model, both presenting a determination coefficient greater than 99%.

Optimization of organic matter degradation kinetics and nutrient removal on artificial wetlands using Eichhornia crassipes and Typha domingensis

ABSTRACTThis study describes the optimization of the wastewater treatment process through the use of a free water surface flow constructed wetland with floating macrophytes at the laboratory level (20 L). A factorial design 23 was used in order to find the best operation conditions of the wastewater treatment process. The performance of macrophytes Eichhornia crassipes and Typha domingensis was investigated by operating the wetland system at hydraulic retention times of 2 and 4 days. The results showed an optimum operational condition that removed 92.39% of initial organic load (measured as COD). The nutrient removal efficiency of the constructed wetland was 99.28% for total nitrogen and 87.78% for phosphorus. The best operating condition includes the use of E. crassipes, with 4 days of hydraulic retention and the use of gravel as a filter. According to this, organic matter degradation kinetics was studied by the comparison of three kinetic models: first-order model, Stover–Kincannon model and Grau-second-order model. Stover–Kincannon and Grau kinetics models were more appropriate to represent the organic matter degradation kinetics in constructed wetland, with a determination coefficient of 0.9997. Based on the kinetic removal results, the process showed a maximum rate of organic load removal of 2500 mg/L d.

Nutritional and Metabolic Characteristics of Brassica carinata Co-products from Biofuel Processing in Dairy Cows.

The increased utilization of Brassica carinata in the biofuel industry in Canada has resulted in the large-scale production of co-products that can be potentially exploited as alternative protein ingredients in dairy ration. The objectives of this study were to investigate the nutritive value of carinata presscake and meal for dairy cows in terms of (1) nutrient and antinutrient composition, (2) rumen degradation kinetics of organic matter (OM), crude protein (CP), and neutral detergent fiber, (3) hourly effective degradation ratio and potential N to energy synchronization, (4) intestinal digestion of rumen undegraded protein (RUP), and (5) total metabolizable protein (MP) supply to the small intestine. Samples (n = 3) of carinata meal, carinata presscake, and canola meal (as reference feed), collected from three consecutive batches, were evaluated. In comparison to canola meal, carinata presscake and meal had greater (p < 0.05) contents of CP [39.7 versus 48.5 and 53.5% dry matter (DM)], with a high proportion of soluble crude protein (24.0 versus 53.0 and 72.6% CP), resulting in their extensive degradation (59.2 versus 76.3 and 89.3% CP) in the rumen. As a result, carinata presscake and meal supplied smaller (p < 0.05) quantities (92 and 136 g/kg of DM) of MP compared to canola meal (153 g/kg of DM). The contents of glucosinolates were greater (p < 0.05) in carinata presscake (168.5 μmol/g) and meal (115.2 μmol/g) compared to canola meal (3.4 μmol/g), limiting its utilization as a ruminant feed. Carinata co-products can be used as an alternative feed protein source, given their nutrient composition, rumen degradation, and intestinal digestion characteristics, provided that the high glucosinolate content can be reduced.

A model for the evolution in water chemistry of an arsenic contaminated aquifer over the last 6000 years, Red River floodplain, Vietnam

Aquifers on the Red River flood plain with burial ages ranging from 500 to 6000years show, with increasing age, the following changes in solute concentrations; a decrease in arsenic, increase in Fe(II) and decreases in both pH, Ca and bicarbonate. These changes were interpreted in terms of a reaction network comprising the kinetics of organic carbon degradation, the reduction kinetics of As containing Fe-oxides, the sorption of arsenic, the kinetics of siderite precipitation and dissolution, as well as of the dissolution of CaCO3. The arsenic released from the Fe-oxide is preferentially partitioned into the water phase, and partially sorbed, while the released Fe(II) is precipitated as siderite. The reaction network involved in arsenic mobilization was analyzed by 1-D reactive transport modeling. The results reveal complex interactions between the kinetics of organic matter degradation and the kinetics and thermodynamic energy released by Fe-oxide reduction. The energy released by Fe-oxide reduction is strongly pH dependent and both methanogenesis and carbonate precipitation and dissolution have important influences on the pH. Overall it is the rate of organic carbon degradation that determines the total electron flow. However, the kinetics of Fe-oxide reduction determines the distribution of this flow of electrons between methanogenesis, which is by far the main pathway, and Fe-oxide reduction. Modeling the groundwater arsenic content over a 6000year period in a 20m thick aquifer shows an increase in As during the first 1200years where it reaches a maximum of about 600μg/L. During this initial period the release of arsenic from Fe-oxides actually decreases but the adsorption of arsenic onto the sediment delays the build-up in the groundwater arsenic concentration. After 1200years the groundwater arsenic content slowly decreases controlled both by desorption and continued further, but diminishing, release from Fe-oxide being reduced. After 6000years the arsenic content has decreased to 33μg/L. The modeling enables a quantitative description of how the aquifer properties, the reactivity of organic carbon and Fe-oxides, the number of sorption sites and the buffering mechanisms change over a 6000year period and how the combined effect of these interacting processes controls the groundwater arsenic content.

Seasonal Microbial Population Shifts in a Bioremediation System Treating Metal and Sulfate-Rich Seepage

Biochemical reactors (BCRs) using complex organics for bioremediation of mine-influenced water must operate successfully year round. In cold climates, where many mines in Canada are located, survival of the important microorganisms through the winter months is a concern. In this work, broad phylogenetic surveys, using metagenomics, of the microbial populations in pulp mill biosolids used to remediate metal leachate containing As, Zn, Cd and sulfate were performed to see if the types of microorganisms present changed over the seasons of one year (August 2008 to July 2009). Despite temperature variations between 0 and 17 °C the overall structure of the microbial population was fairly consistent. A cyclical pattern in relative abundance was detected in certain taxa. These included fermenter-related groups, which were out of phase with other taxa such as Desulfobulbus that represented potential consumers of fermentation byproducts. Sulfate-reducers in the BCR biosolids were closely related to psychrotolerant species. Temperature was not a factor that shaped the microbial population structure within the BCR biosolids. Kinetics of organic matter degradation by these microbes and the rate of supply of organic carbon to sulfate-reducers would likely affect the metal removal rates at different temperatures.

Mechanism and kinetics of organic matter degradation based on particle structure variation during pig manure aerobic composting

Characterization of the dynamic structure of composting particles may facilitate our understanding of the mechanisms of organic matter degradation during pig manure–wheat straw aerobic composting. In this study, changes in the size, shape, pores, chemical compositions, and crystal structures of pig manure particles during composting were investigated. The results showed that the median diameter (D50) decreased exponentially, while the particle aspect ratio and sphericity were unchanged, suggesting that particles were degraded uniformly along different radial directions. Pores had a mean diameter of 15–30μm and were elliptical. The particle porosity increased linearly mainly because of hemicellulose degradation. Furthermore, the influence of particle structure variation on the first order rate constant (k) of organic matter degradation was corrected, which may facilitate the optimization of operation conditions. The k value was proportional to the reciprocal of D50 according to the specific surface area of particles, and it decreased with increased porosity due to the stabilized chemical compositions and crystal structures of particles. However, the applicability of these data to other composting materials should be verified.

Determination of nutrient content and digestibility characteristics ofPrangos ferulacea (L.) on grazing lands of Eastern Anatolia

The aim of this study was to compare nutrient content, and in situ protein and organic matter degradation kinetics of Prangos ferulacea (L.) (locally called helis), a naturally growing plant on the top of Mount Artos, with those of alfalfa. P. ferulacea plants used in the study were collected from three different parts of Mount Artos in Van Province over two years. While organic matter content and in vitro organic matter digestibility of P. ferulacea were significantly higher, neutral detergent fiber, acid detergent fiber, and acid detergent insoluble nitrogen contents were significantly lower compared with those of alfalfa (P 0.05). It can be concluded that P. ferulacea has a better nutrient quality compared with even high quality alfalfa based on nutrient contents and digestibility values, and therefore substitution of alfalfa by P. ferulacea in the diet of ruminant animals is feasible.

Cinética ruminal de rações com diferentes níveis de glicerina bruta

The current consumption of glycerol is not enough to use all the glycerol that can be generated by high production levels of biodiesel, which could lead to irresponsible disposal of this residue in the environment. An alternative to consuming part of the glycerol produced is its use in animal feeding. An important assessment to be made before adding any ingredient in the diet of ruminants is if the new ingredient causes some change in the kinetics of ruminal organic matter. In this context, increasing levels of crude glycerin (0, 30, 60, 90, 120, 150, 180, 210 and 240 g kg-1 dry matter) were included in isonitrogen and isocaloric diets formulated to meet the nutritional requirements of a 300 kg beef cattle gaining 1.2 kg d -1, in order to evaluate possible effects of glycerol on the in vitro kinetics of organic matter degradation, Ph and ammonia ruminal levels, and microbial protein production. The experimental design was completely randomized with nine treatments and three replications. The maximum volume of gas produced by soluble and insoluble fractions, the rate of gas production by the degradation of the soluble fraction and insoluble fractions, the latency, the ruminal pH, the production of ammonia and of microbial protein did not differ among levels of glycerin. In contrast, the in vitro digestibility of dry matter, the organic matter and the fiber showed a linear increase with the inclusion of glycerin.

Chemical composition and in sacco ruminal degradation of tropical trees rich in condensed tannins

The study was aimed at determining the chemical composition, in sacco ruminal dry matter and organic matter degradability of leaves and fruits of tropical condensed tannin rich multipurpose tree species (MPTS). The MPTS studied were Ekebergia capenesis, Ficus sycomorus, Maesa lanceolata, and Rhus glutinosa. Chemical composition of dry matter (DM), crude protein (CP), crude ash (CA), ether extract (EE), crude fibre (CF), neutral detergent fibre (NDF), non-fibre carbohydrates (NFC), and condensed tannin (CT) was determined. In sacco rumen degradability was measured using three rumen fistulated Holstein Friesian-Boran cross steers at 0, 6, 12, 24, 48, 72, and 96 h. The DM and organic matter (OM) degradability data were fitted to the equation Y = a + b(1 &amp;ndash; e&lt;sup&gt;&amp;ndash;ct&lt;/sup&gt;). The values for each chemical constituent ranged 5.43&amp;ndash;11.49% (CA), 7.97&amp;ndash;17.06% (CP), 1.57&amp;ndash;31% (EE), 12.20&amp;ndash;27.5% (CF), 5.84&amp;ndash;39.30% (NFC), and 7.2&amp;ndash;16.72% (CT). Ekebergia capensis leaves had the greatest values for slowly degradable fraction (b), effective degradability (ED), and rate of degradation (c) in DM (P &amp;lt; 0.001) whereas E. capensis fruit had significantly the greatest soluble fraction (a), potential degradability (b), and effective degradability (ED) values as compared to the a, PD, and ED values in the fruits of other plants(P &amp;lt; 0.001). Yet in OM degradation kinetics, the greatest and least values of potential degradability (PD) were recorded for F. sycomorus (89.89%) and E. capensis (55.90%) leaves (P &amp;lt; 0.001). Similar to the rapidly soluble fraction a, ED was found to be the greatest in fruits as compared to leaves of the plants (P &amp;lt; 0.001). Generally variation of plant parts led to significant differences in chemical composition, DM, and OM degradability and the degradable parameters. The leaves and fruits recorded more than 60% DM and OM degradability at 24 h, which implied that they were all greatly degradable in the rumen.

The impact of intermediate thermal hydrolysis on the degradation kinetics of carbohydrates in sewage sludge

The purpose of this paper is to report the results, from laboratory-scale investigations, on the impact of intermediate thermal hydrolysis process (ITHP) on already digested sludge in general, and sludge carbohydrate content degradation process efficiency in particular. The ITHP performance data were compared with the performance of established conventional thermal hydrolysis process (THP). The degradation of sludge carbohydrates as a result of thermal pre-treatment and anaerobic digestion followed the first order kinetics. The overall sludge organic matter degradation kinetics rate constants indicated that the use of THP as an intermediate digestion step can enhance the already digested sludge organic matter degradation; further reducing the sludge mass and increasing its conversion to biogas.

Control of sulphate and methane distributions in marine sediments by organic matter reactivity

The reactivity of organic matter serving as fuel for microbial activity in buried sedimentary layers imposes a strong control on the subsurface biogeochemical zonation and rates of metabolism. To understand the consequences of different organic matter degradation rates on subsurface microbial activity and sediment pore water chemistry, sulphate and methane concentration profiles were simulated using different organic matter decay models from the literature. Results show how the decay of a more reactive pool of organic matter results in a more curved sulphate profile and deeper sulphate methane transition (SMT) with decreasing apparent initial age of the organic matter. A minimum in SMT is reached if the initial age is intermediate, commonly in the order of 104–105 years. If the initial age is very large the sulphate profile is almost linear and the sulphate methane transition is located deeper with increasing apparent initial age of the organic matter. Curved versus linear shaped sulphate profiles reflect different relative contributions of organoclastic sulphate reduction versus anaerobic methane oxidation to the total consumption of sulphate. Our model results demonstrate that the SMT can move up or down depending on organic matter reactivity and its depth is not necessarily diagnostic of total organic carbon flux. The model provides a mechanistic understanding of how the shape of the sulphate profiles and the relative contributions of organoclastic sulphate reduction versus anaerobic oxidation of methane are controlled by the kinetics of organic matter degradation.

Influence of flow direction in the performance of anaerobic filters

This work aimed to evaluate the performance of similar anaerobic filters operating with opposite wastewater flows, and compare mathematical models that describe the kinetics of organic matter degradation in both. Two pilot-scale filters were fed with domestic effluent – one filter worked as upflow (UAF) and the other as downflow (DAF). Experimental COD data obtained from samples taken along the length of the filters were used to fit the first-order mathematical model, the model proposed by Leduy and Zajic (1973) and the model proposed by Brasil et al. (2007). The first model showed overestimated reaction constant (k) values when compared to those obtained using the other models. The models proposed by Brasil et al. (2007) and Leduy and Zajic (1973) presented the highest coefficients of determination (R2). The average removal efficiencies of total COD were equal to 68 and 79% for UAF and DAF, respectively. The results revealed no significant differences between the two filters with regard to the variables applied.

Kinetics of organic matter degradation in the Murchison meteorite for the evaluation of parent-body temperature history

Abstract– To evaluate kinetic parameters for thermal degradation of organic matter, in situ heating experiments of insoluble organic matter (IOM) and bulk of Murchison (CM2) meteorite were conducted under Fourier transform infrared micro-spectroscopy combined with a heating stage. Decreases of aliphatic C–H band area under Ar flow were well fitted with Ginstling-Brounshtein three-dimensional diffusion model, and the rate constants for decreases of aliphatic C–H were determined. Activation energies Ea and frequency factors A obtained from these rate constants at different temperatures using the Arrhenius equation were Ea = 109 ± 3 kJ mol−1 and A = 8.7 × 104 s−1 for IOM, and Ea = 61 ± 6 kJ mol−1 and A = 3.8 s−1 for bulk, respectively. Activation energy values of aliphatic C–H decrease are larger for IOM than bulk. Hence, the mineral assemblage of the Murchison meteorite might have catalytic effects for the organic matter degradation. Using obtained kinetic expressions, the time scale for metamorphism can be estimated for a given temperature with aliphatic C–H band area, or the temperature of metamorphism can be estimated for a given time scale. For example, using the obtained kinetic parameters of IOM, aliphatic C–H is lost approximately within 200 years at 100 °C and 100 Myr at 0 °C. Assuming alteration period of 7.5 Myr, alteration temperatures could be calculated to be <15 ± 12 °C. Aliphatic C–H decrease profiles in a parent body can be estimated using time–temperature history model. The kinetic expression obtained by the infrared spectral band of aliphatic C–H could be used as an alternative method to evaluate thermal processes of organic matter in carbonaceous chondrites.

Effect of different levels of Quebracho tannin on nitrogen utilization and growth performance of Najdi sheep fed alfalfa (Medicago sativa) hay as a sole diet

A commercial tannin source (Quebracho tannin, QT), containing 75% condensed tannins (CT) in dry matter (DM) was used to evaluate the effects of addition of different levels of QT to alfalfa hay on the in vitro degradation kinetics of organic matter (OM) and nitrogen (N) in experiment 1 (Exp. 1), N utilization and microbial N synthesis (MNS) in experiment 2 (Exp. 2) and growth performance of growing Najdi lambs in experiment 3 (Exp. 3). Alfalfa hay was treated with QT at the levels of 0, 1, 2 and 3% of DM to form four treatments of QT0, QT1, QT2 and QT3 to have actual levels of CT being 0, 0.75, 1.5 and 2.25% of DM, respectively. Degradation rate and the effective degradability of N were significantly decreased (P < 0.05) for QT2 and QT3 as compared with the QT0. In Exp. 2, digestibility coefficients for OM, neutral detergent fiber and acid detergent fiber were significantly decreased (P < 0.05) at QT3, whereas QT1 and QT2 showed no difference to QT0. In the metabolism trial (Exp. 2), digested N (DN) and urinary N (UN) excretion for QT2 and QT3 were significantly decreased (P < 0.05) compared to QT0 and QT1. The DN and UN as percentage of N intake were 79.2, 76.9, 75.5 and 69.8%; and 24.4, 22.6, 19.9 and 19.6% for QT0, QT1, QT2 and QT3, respectively. QT2 had the highest MNS and the lowest value was in QT3, the MNS of the treatments were 18.1, 18.7, 19.2 and 15.8 g/day for QT0, QT1, QT2 and QT3, respectively. In the growth trial of 56 days duration (Exp. 3, n = 24 lambs), the addition of QT at the level of QT2 enhanced (P < 0.05) the average daily gain and feed conversion rate compared with the QT0, while, QT1 and QT3 had intermediate values. It is concluded that alfalfa hay treated with QT at the level of 2% of DM could be used to protect alfalfa N from ruminal degradation that would lead to improve growth performance of lambs.

Kinetics of organic matter degradation, microbial methane generation, and gas hydrate formation in anoxic marine sediments

Seven sediment cores were taken in the Sea of Okhotsk in a south-north transect along the slope of Sakhalin Island. The retrieved anoxic sediments and pore fluids were analyzed for particulate organic carbon (POC), total nitrogen, total sulfur, dissolved sulfate, sulfide, methane, ammonium, iodide, bromide, calcium, and total alkalinity. A novel method was developed to derive sedimentation rates from a steady-state nitrogen mass balance. Rates of organic matter degradation, sulfate reduction, methane turnover, and carbonate precipitation were derived from the data applying a steady-state transport-reaction model. A good fit to the data set was obtained using the following new rate law for organic matter degradation in anoxic sediments: R POC = K C C ( DIC ) + C ( CH 4 ) + K C · k x · POC The rate of particulate organic carbon degradation ( R POC) was found to depend on the POC concentration, an age-dependent kinetic constant ( k x ) and the concentration of dissolved metabolites. Rates are inhibited at high dissolved inorganic carbon (DIC) and dissolved methane (CH 4) concentrations. The best fit to the data was obtained applying an inhibition constant K C of 35 ± 5 mM. The modeling further showed that bromide and iodide are preferentially released during organic matter degradation in anoxic sediments. Carbonate precipitation is driven by the anaerobic oxidation of methane (AOM) and removes one third of the carbonate alkalinity generated via AOM. The new model of organic matter degradation was further tested and extended to simulate the accumulation of gas hydrates at Blake Ridge. A good fit to the available POC, total nitrogen, dissolved ammonium, bromide, iodide and sulfate data was obtained confirming that the new model can be used to simulate organic matter degradation and methane production over the entire hydrate stability zone (HSZ). The modeling revealed that most of the gas hydrates accumulating in Blake Ridge sediments are neither formed by organic matter degradation within the HSZ nor by dissolved methane transported to the surface by upward fluid flow but rather through the ascent of gas bubbles from deeper sediment layers. The model was further applied to predict rates of hydrate accumulation in Sakhalin slope sediments. It showed that only up to 0.3% of the pore space is occupied by gas hydrates formed via organic matter degradation within the HSZ. Gas bubble ascent may, however, significantly increase the total amount of hydrate in these deposits.