Straw Carbon Research Articles

Suitability of various chemically prepared activated carbons for the removal of copper(II) ions

Studies on the suitability of various chemically prepared activated carbons (CPACs) like straw carbon (SC), sawdust carbon (SDC), dates nut carbon (DNC) and commercial activated carbon (CAC) for the removal of copper(II) ions by adsorption from simulated wastewater have been carried out under batch mode at 30 ± 1°C and the results are compared. The percentage removal of Cu(II) ions increased with a decrease in initial concentration, particle size and added electrolytes (ionic strength) and increased with an increase in contact time, dose of adsorbent and initial pH of the solution. The adsorption data were fitted with the Langmuir isotherm. The applicability of the first order kinetic equation viz. Lagergren equation was tested by correlation analysis. The adsorption process is concluded to be a spontaneous, first order reaction, occurring with increased randomness at the solid–liquid interface. Studies on the desorption of Cu2+-loaded activated carbons (ACs) were carried out with nitric acid (0.2–1 N). The possibility of reuse of the regenerated ACs in cycle (in cue-one after another) was tested. SC was found to be a suitable adsorbent alternative to CAC among CPACs for the removal of metal ions, in general, and Cu2+ ions, in particular.

Optimisation of Process Parameters for Adsorption of Metal Ions on Straw Carbon by using Response Surface Methodology

Optimisation of process parameters for adsorption of metal ions viz., Cu2+, Cd2+ and Ni2+ ions on Straw Carbon (SC) was carried out by using Box-Behnken statistics and analysis of variance methods. Response surface methodology with three levels of initial pH (4, 5, 6), dose (8, 10, 12 gl-1) and particle size (0.075, 0.090, 0.106m micron) were used in the identification of significance of the effects and interactions in adsorption studies. Response surface methodology requires no assumption and identifies the principal experimental variables and their interactions which have the greatest effect on adsorption. The optimum process parameters for maximum adsorption of Ni2+, Cu2+ and Cd2+ were obtained by this procedure.

Effects of shifting growth stage and regulating temperature on seasonal variation of CH4 emission from rice

Seasonal variations in CH4 emission rates from rice paddies have been reported to have one or more maxima during the middle and late periods of rice growth. The factor affecting an appearance of CH4 emission maxima was examined in three types of pot experiments. In the experiment 1, four rice cultivars with difference in length of the period from transplanting to heading were transplanted on the same days. For the experiment 2, a cultivar was transplanted 4 times with interval of two weeks. In these experiments, the heading differed about a month between the earliest and latest treatments, respectively. However, shifting growth stage of rice plants did not shift the CH4 emission maxima, and the CH4 emission maxima often matched the maxima of daily mean air temperature. The effect of variation in temperature on CH4 emission rate was further investigated in the experiment 3 by placing the rice‐planted pots under regulated temperature. Besides the first emission peak of CH4 attributable to rice straw (RS) carbon, three emission peaks corresponding to the peaks of air temperature were detected for the RS‐applied pots placed outdoors. These three peaks were not observed or much less conspicuous for the RS‐applied pots in a phytotron at 30°C. Temporal decreases in CH4 emission were detected both for the pots placed in the phytotron and outdoors just after the topdressing of (NH4)2SO4, which was considered to be a major cause of irregular disagreement between the variations in CH4 emission rates and in air temperature during the middle period of rice growth.

Temperature responses of carbon mineralization in conifer forest soils from different regional climates incubated under standard laboratory conditions

Summary 14C‐labelled straw was mixed with soils collected from seven coniferous forests located on a climatic gradient in Western Europe ranging from boreal to Mediterranean conditions. The soils were incubated in the laboratory at 4°, 10°, 16°, 23° and 30 °C with constant moisture over 550 days. The temperature coefficient (Q10) for straw carbon mineralization decreased with increasing incubation temperatures. This was a characteristic of all the soils with a difference of two Q10 units between the 4–10° and the 23− 30 °C temperature ranges. It was also found that the magnitude of the temperature response function was related to the period of soil incubation. Initial temperature responses of microbial communities were different to those shown after a long period of laboratory incubation and may have reflected shifts in microbial species composition in response to changes in the temperature regime. The rapid exhaustion of the labile fractions of the decomposing material at higher temperatures could also lead to underestimation of the temperature sensitivity of soils unless estimated for carbon pools of similar qualities. Finally, the thermal optima for the organic soil horizons (Of and Oh) were lower than 30 °C even after 550 days of incubation. It was concluded that these responses could not be attributed to microbial physiological adaptations, but rather to the rates at which recalcitrant microbial secondary products were formed at higher temperatures. The implication of these variable temperature responses of soil materials is discussed in relation to modelling potential effects of global warming.

Nitrogen availability to Pseudomonas fluorescens DF57 is limited during decomposition of barley straw in bulk soil and in the barley rhizosphere.

The availability of nitrogen to Pseudomonas fluorescens DF57 during straw degradation in bulk soil and in barley rhizosphere was studied by introducing a bioluminescent reporter strain (DF57-N3), responding to nitrogen limitation, to model systems of varying complexity. DF57-N3 was apparently not nitrogen limited in the natural and sterilized bulk soil used for these experiments. The soil was subsequently amended with barley straw, representing a plant residue with a high carbon-to-nitrogen ratio (between 60 and 100). In these systems the DF57-N3 population gradually developed a nitrogen limitation response during the first week of straw decomposition, but exclusively in the presence of the indigenous microbial population. This probably reflects the restricted ability of DF57 to degrade plant polymers by hydrolytic enzymes. The impact of the indigenous population on nitrogen availability to DF57-N3 was mimicked by the cellulolytic organism Trichoderma harzianum Rifai strain T3 when coinoculated with DF57-N3 in sterilized, straw-amended soil. Limitation occurred concomitantly with fungal cellulase production, pointing to the significance of hydrolytic activity for the mobilization of straw carbon sources, thereby increasing the nitrogen demand. Enhanced survival of DF57-N3 in natural soil after straw amendment further indicated that DF57 was cross-fed with carbon/energy sources. The natural barley rhizosphere was experienced by DF57-N3 as an environment with restricted nitrogen availability regardless of straw amendment. In the rhizosphere of plants grown in sterilized soil, nitrogen limitation was less severe, pointing to competition with indigenous microorganisms as an important determinant of the nitrogen status for DF57-N3 in this environment. Hence, these studies have demonstrated that nitrogen availability and gene expression in Pseudomonas is intimately linked to the structure and function of the microbial community. Further, it was demonstrated that the activities of cellulolytic microorganisms may affect the availability of energy and specific nutrients to a group of organisms deficient in hydrolytic enzyme activities.

Effect of wheat straw carbon:Sulfur ratio on mineralization of sulfur in soils under simulated laboratory aerobic‐flooding cycles1

This study was undertaken to assess the effect of residue carbon:sulfur (C:S) ratio on the mineralization of S in rice soils under aerobic‐flooding cycles. A lab incubation study with a 3x2x2 factorial design (two replications) was carried out for 12 weeks. The treatments were two rice soils, Faridpur and Joydebpur; three levels of wheat straw (Triticum aestivum L.) added to soils as 1) control, 2) straw C:S ratio (400:1), or 3) straw C:S ratio (100:1); and two moisture levels of 1) two weeks aerobic‐flooding cycles or 2) four weeks aerobic‐flooding cycles. The organic residues (25 mg straw g‐1 soil) were mixed with 30 g soil and an equal amount of glass bead mixtures (1:1) and transferred into a leaching tube. Soils in leaching tubes were leached with deionized water and analyzed for sulfate‐sulfur (SO4‐S) and other chemical properties at two week intervals up to 12 weeks. Cumulative SO4‐S in all soils amended with a narrow C:S ratio (100:1) of the straw had a significantly higher accumulation of SO4‐S over the control or the wider C:S ratio (400:1). The first‐order rate constants (Ks) in soils amended with wheat straw under aerobic‐flooding cycles ranged from 0.112 to 0.160 mg S kg‐1 wk‐1 and the Kg values ranged from 0.030 to 0.149 mg S kg‐1 wk‐1 for unamended and straw amended soils, respectively. Among the two straw C:S ratio treatments, the narrow C:S ratio residue treatment had the highest Ks values, indicating greater rates of microbial S mineralization and potential to provide more plant‐available S. The cumulative amount of C mineralized was linearly related to time of incubation and corresponded to S mineralization.

Contribution of rice straw carbon to CH4 emission from rice paddies using 13C‐enriched rice straw

It is generally recognized that the application of rice straw (RS) increases CH4 emission from rice paddies. To estimate the contribution of RS carbon to CH4 emission, a pot experiment was conducted using 13C‐enriched RS. The percentage contributions of RS carbon to CH4 emission throughout the rice growth period were 10±1, 32±3, and 43±3% for the treatments with RS applied at the rates of 2, 4, and 6 g kg−1 soil, respectively. The increase in the rate of application of RS increased CH4 emission derived from both RS carbon and other carbon sources. The percentage contribution of RS carbon to CH4 emission was larger in the earlier period (maximum 96%) when the decomposition rate of RS was larger. After RS decomposition had slowed, CH4 emission derived from RS carbon decreased. However, the δ13C values of CH4 emitted from the pots with 13C‐enriched RS applied at rates of 4 and 6 g kg−1 soil were significantly higher than those from the pots with natural RS until the harvesting stage. An increased atom‐13C% of roots of rice plants growing in the pots with 6 g kg−1 of 13C‐enriched RS at around the maximum tiller number stage and a decrease during the following 2 months suggested that rice plants assimilated RS carbon once and then released a portion of it. This supply of RS carbon from roots may be one of the sources of CH4 in the late period of rice growth.

Methane formation and emission from flooded rice soil incorporated with 13C-labeled rice straw

Pot experiments with or without 13C-labeled rice straw and rice plants were made to investigate the contribution of organic sources to the formation and emission of CH 4 from flooded rice soil. The 13C abundance in emitted CH 4 and contained in soil bubbles peaked at 20–40 d after flooding (DAF). After 40 DAF, 13C abundance was higher in unplanted pots than in planted pots. A similar pattern was found in the abundance of 13CCO 2 in the soil bubbles. Using the δ 13C values in the soil bubbles of the pots without straw application as the background values, the percentages of the CH 4 emitted from soil to the atmosphere or contained in the soil bubbles originating from straw were calculated. These percentages were multiplied by the CH 4 flux to estimate the quantities of the emitted CH 4 from rice straw. The most active CH 4 emission from the straw was found during 40–80 DAF, when the first peak of CH 4 emission was observed. The contribution of sources other than added straw to the formation and emission of CH 4 increased sharply only in the planted pots after 80 DAF (heading stage), suggesting this increase was due to the release of organic materials from rice plants. The relative contribution of 13C derived from straw in CH 4 and CO 2 was not significantly different, indicating that methanogens did not have any preference for the straw-derived substrates. After the cropping season, ca. 5% of the rice straw carbon remained in the soil and 1% was incorporated into the rice plants.

The use of 13C-NMR for studies of wheat straw decomposition

13C-NMR was used to study the field decomposition of surface retained and incorporated wheat straw. Results showed decreasing proportions of straw carbon as carbohydrate and increasing proportions of aromatic compounds during straw decomposition. These changes were greater for the surface retained straw, however greater relative microbial contamination of incorporated straw may have affected results. The cost of 13C-NMR may lessen its role in studies of this nature.

Carbon transfer in a winter wheat (Triticum aestivum) ecosystem

In a field experiment with 14C-labeled winter wheat conducted in the north-central region of the United States, crop-accumulated carbon (grain excluded) returned to the soil was found to be 542 g m−2 year−1. Almost half of the carbon from the underground compartment was released in the form of CO2 during the first 3 months after harvest due to very favorable conditions for biological activity. After 18 months, no less than 80% of the carbon from the plant residues was mineralized. About 16% of straw carbon and 24% of root carbon was transferred into soil organic matter. The annual rate of soil organic matter decomposition was approximated as 1.7%.

Litter Placement Effects on Microbial and Organic Matter Dynamics in an Agroecosystem

Two different agricultural tillage practices were used to study how changes in the structure of the soil—litter system affected litter decomposition rates, microbial community composition, and soil organic matter dynamics. Surface straw placement results in spatial separation of carbon—rich litter (C:N ratio 80:1) and mineralized soil nitrogen. In contrast, when the litter is plowed into the soil, straw carbon and soil nitrogen are in intimate contact. Our field studies in Colorado showed that fungal biomass in surface—straw treatments was 144% of that in the incorporated—straw treatments, probably because fungi, with their extensive hyphal networks, are able to utilize both the surface straw carbon and the available soil nitrogen. Field studies using 14C—labeled wheat straw showed that a greater proportion of added 14C was retained in the surface—straw treatment than in the incorporated—straw treatment. Maximum net N immobilization was higher and litter decomposition was slower in the surface straw than in the incorporated straw placements both with and without experimental nitrogen addition. Slower litter decomposition of the surface litter may contribute to reduced soil organic matter losses. Soil organic matter losses may also be reduced in no—till systems as a result of the increase in the ratio of fungal to bacterial activity because of the greater growth efficiency of fungi and the accumulation of carbon in the less decomposable fungal biomass. The surface placement of straw in no—till agriculture allowed management of microclimate and microbial populations so that losses of soil organic matter and nutrients were minimized.

Wheat straw decomposition in subtropical Australia .II. Effect of straw placement on decomposition and recovery of added 15N urea

Decomposition of 14C-labelled wheat straw and its effect on fertilizer 15N transformations was studied in a subtropical environment over a 2 year period. The effect of straw management was also studied. Wheat straw incorporated in topsoil initially decomposed at a faster rate than wheat straw placed on the soil surface. This was due to the greater positional availability of straw carbon to soil organisms in incorporated straw. Later decomposition rates were similar. After 1.5 months, 44% of applied 15N-urea was recovered from incorporated straw treatments and 55% from surface-retained straw treatments. Losses were attributed to biological denitrification. The greater loss in incorporated straw treatments was suggested to be due to a greater availability of carbon to the denitrifying population compared with treatments where straw was retained on the surface. After 2 years, the recovery of 15N decreased to between 12 and 15% of that applied.

Effect of Moisture and Nitrogen Levels on the Decomposition of Wheat Straw in Soil

Two per cent of wheat straw was mixed with samples of a slightly degraded chernozem soil, and its decomposition was studied at 10, 20, and 30 per cent moisture content of the soil with the addition of 160, 240, and 400 ppm of NH4 + -N. The overall decomposition, measured as CO2 production, and total carbon loss from the soil at 28 degrees C was enhanced by the added nitrogen at all levels of moisture in proportion to the quantity added. Maximum mineralization of the straw carbon was observed at 30 per cent moisture content but there was no significant difference between the amount of carbon mineralized at 20 and 30 per cent moisture levels. No stabilization of the substrate took place in the soil except at 240 and 400 ppm of applied nitrogen at 30 per cent moisture level towards the end of the incubation period. More straw carbon was mineralized when the soil samples were subjected to daily measurements of CO2 evolved than when CO2 measurements were made at intervals over the same period of incubation.

Organic Matter Decomposition as Influenced by Oxygen Level and Flow Rate of Gases in the Constant Aeration Method

AbstractLaboratory experiments were conducted to determine the rate of decomposition of wheat straw added to soil when continuous aeration was conducted with N2‐O2 gas mixtures containing 0, 0.5, 1.0, 2.5, 5.0, and 21% oxygen at flow rates of ⅛, ¼, ½, 1, and 2 liters per hour. Rates of decomposition and total decomposition were followed by determination of wheat straw carbon evolved as CO2.Total decomposition at all oxygen levels varied directly with aeration flow rate, except for the 0% level where an inverse relationship was observed.Microbial activity at the 21% oxygen level was greatly stimulated as flow rate increased from ⅛ through 2 liters per hour.A rapid increase in microbial activity occurred for the 0.5, 1.0, 2.5, and 5.0% oxygen levels as flow rate increased from ⅛ through ½ liters per hour, however, little increase in CO2 production was observed at higher flow rates.