Initial Mineralization Rate Research Articles

Effect of Different Bacterial Fertilizers on Soil Carbon Mineralization

In this study, aimed to investigate the effect of bacterial fertilizer: A (Bacillus spp., Trichoderma spp. ), B (Azorhizobium, Azotobacter and Azospirillum) and C (Azotobacter spp., Bacillus spp. and Pseudomonas putida) on soil carbon mineralization. On the application of A, B and C bacterial fertilizers on the sterilized control soil, whose initial carbon mineralization rates is 1.1%, mineralization rates of 5.12%, 3.54%, and 10.78% were respectively recorded. According to these results, it was observed that the application of bacterial fertilizer increased the carbon mineralization rate of the sterilized control soil by 365.45%, 221.82% and 880%, respectively. A carbon mineralization rate of 7.03%, 6.15% and 12.95% was recorded in the non-sterilized soil sample whose initial carbon mineralization rate is 5.1%, thereby increasing the mineralization rate by 25.31%, 9.63% and 130.84%. The application of the bacterial fertilizer to the soil was found to increase the soil carbon mineralization rate. It is recommended to incorporate bacterial fertilizers with CO2- sequestering materials, such as biochar, to mitigate the fluctuations in the natural balance due to carbon release.

Pickering interfacial biocatalysis with enhanced diffusion processes for CO2 mineralization

Utilization of carbon dioxide (CO2) has become a crucial and anticipated solution to address environmental and ecological issues. Enzymes such as carbonic anhydrase (CA) can efficiently convert CO2 into various platform chemicals under ambient conditions, which offers a promising way for CO2 utilization. Herein, we constructed a Pickering interfacial biocatalytic system (PIBS) stabilized by CA-embedded MOFs (ZIF-8 and ZIF-L) for CO2 mineralization. Through structure engineering of MOFs and incorporation of Pickering emulsion, the internal and external diffusion processes of CO2 during the enzymatic mineralization were greatly intensified. When CO2 was ventilated at a flow rate of 50 mL min–1 for 1 h, the pH value of PIBS dropped from ~8.00 to ~6.50, while the average pH value of free system only dropped to ~7.15, indicating that the initial reaction rate of CO2 mineralization of PIBS is nearly twice that of the free system. After the 8th cycle reaction, PIBS can still produce more than 9.8 mg of CaCO3 in 5 min, realizing efficient and continuous mineralization of CO2.

Bimetallic oxides with package structure for enhanced degradation of bisphenol a through peroxymonosulfate activation

Cobalt oxide (CoO) could activate peroxymonosulfate (PMS) to remove pollutants but the catalytic performance was restricted by limited active sites and it was with risk of harmful cobalt ion leaching. In order to solve these problems, bimetallic oxides with package structure were researched by dispersing CoO nanoparticles on a stable support (magnesium oxide, MgO) via simple one-step coprecipitation method. Co-Mg bimetallic oxides with minute quantities of CoO and highly dispersed structure could efficiently activate PMS for degradation of bisphenol A (BPA). The catalytic properties of catalysts with different molar ratios of Co and Mg were evaluated. The optimal molar ratio (0.075:15) of Co and Mg was found in the Co-Mg bimetallic oxides, which could maximize its catalytic performance for PMS in a wide pH range. Influences of different systems, catalyst dosages, PMS concentrations, temperatures, initial pH values and mineralization rates were researched for BPA degradation. And the oxidation capacities to remove BPA in the different aqueous matrices were evaluated for the catalyst/PMS system. The addition of anions and nature organic matter (NOM) showed that there existed positive (Cl- and H2PO4-) and negative (NO3-, HCO3-, HPO42- and NOM) effects for BPA degradation. Additionally, main reactive radicals were certified by quenching experiments. Four successive experiments and evaluation of concentration of cobalt ion leaching illustrated good stability of the catalyst, which was related with its package structure. Finally, activation mechanism of PMS, proposed degradation pathways of BPA and acute toxicity of degradation intermediates of BPA were analyzed.

Kinetics of Soil Carbon Mineralization Under Continuous Site-Specific Nutrient Management in Ultisols Under Cassava

ABSTRACT The present study focused on the effect of 10 years of continuous fertilizer trials on soil organic carbon (SOC) mineralization in cassava grown ultisols. The study determines the carbon (C) mineralization potential, dynamics, and kinetics of C mineralization by fitting five decay models, significance of various long-term fertilizer applications on C mineralization and the relationship between soil physico-chemical properties with carbon mineralization parameters derived from the best model. To determine the potential of the soil to mineralize organic C a short-term aerobic incubation procedure – alkali trap method – was used. The best model fitting first-order E (R2 = 0.994) was used to describe the dynamics and kinetics of C mineralization. Relationships between soil physico-chemical properties and C mineralization parameters of first-order E model were studied by using correlation analysis. The site-specific nutrient management (SSNM) treatment showed the highest carbon dioxide-carbon (CO2-C) evolution value (2049.61 mg of CO2-C kg−1 soil) while NPK omission treatment showed the lowest (1703.37 mg of CO2-C kg−1 soil). The initial potential rate of carbon mineralization (C0k) was highest for SSNM treatment (159.78 mg kg−1) and lowest for K omission treatment (123.25 mg kg−1) indicating that the organic matter quality has increased in continuous SSNM treatment for 10 years compared to all other treatments. Significant positive correlations were shown between cumulative C evolved (Cm) and SOC. Significant negative correlations were observed between size of the mineralization flush (C1) and silt as well as between potentially mineralizable carbon (C0K) and clay.

Treatment of simulated industrial pharmaceutical wastewater containing amoxicillin antibiotic via advanced oxidation processes

ABSTRACT The treatment of pharmaceutical industrial wastewaters, containing the antibiotic amoxicillin (218.29 mg L−1), via some advanced oxidation processes (POA), was studied. The H2O2 photolysis process presented the highest percentage of mineralization (97%), after the total reaction time (180 min). However, the photo-Fenton process showed the highest organic carbon removal rate, mineralizing 65% of the initial concentration, in 30 min. Because of this fact, this process was studied in more detail. The initial concentration of ferrous ions (0.03–1.00 mmol L−1) did not affect the performance of the photo-Fenton process, possibly operating using concentrations of below 15 mg L−1 (0.27 mmol L−1), that is the iron content limit for discharging wastewaters established in the Brazilian environmental legislation. Furthermore, experiments were performed according to the composite experimental design technique (Doehlert matrix), analyzing the following variables: (i) the inlet molar flow rate of H2O2 (FH2O2 ) and (ii) the initial concentration of ferrous ions ([Fe2+]). Besides that, the initial mineralization rate and the total organic carbon removal percentages, measured at 5, 10, 15 and 30 min of reaction, were chosen as the response variables. It was observed that FH2O2 was the most important variable in relation to the initial degradation rate. In the optimal conditions (FH2O2 = 3.27 mmol min−1 and [Fe2 +] = 0.27 mmol L−1), the photo-Fenton process achieved a percentage of organic carbon removal of 84%, in only 30 min of reaction, presenting an interesting potential for real industrial applications, combined, or not, with conventional technologies (as biological treatments, for example).

Impact of Phosphate on Iron Mineralization and Mobilization in Nonheme Bacterioferritin B from Mycobacterium tuberculosis.

Ferritins are supramolecular nanocage proteins, which synthesize hydrated ferric oxyhydroxide mineral via protein mediated rapid Fe2+ sequestration and ferroxidase reactions. Ferritin minerals are also associated with a significant amount of phosphate, which contribute toward their structure and reactivity. Like iron, phosphate also regulates the pathogenesis of Mycobacterium tuberculosis (Mtb), which expresses two types of ferritin: heme binding bacterioferritin A (BfrA) and nonheme binding bacterioferritin B (BfrB). Unlike Mtb BfrA, the rapid kinetics and mechanism of ferroxidase activity, and the mineral core formation/dissolution in Mtb BfrB are not well explored. Moreover, the effect of physiological levels of phosphate (0-10 mM) on the synthesis, structure, and reactivity of ferritin mineral core also require investigation in detail. Therefore, the stopped-flow rapid kinetics of ferroxidase activity (ΔA650/Δt) of Mtb BfrB was carried out, which detected a transient intermediate similar to diferric peroxo species as observed in frog and human ferritins. Increasing phosphate concentration increased the initial rate of iron mineralization (ΔA350/Δt) and dissolved O2 consumption (both ∼1.5-2-fold). Phosphate not only decreased the amount of iron loading and size of the BfrB mineral core (both up to 2-fold) but also decreased its crystallinity, resembling the variations observed in the core morphology of different native ferritins. In addition, phosphate inhibited the kinetics of reductive iron mobilization (∼6-8-fold) indicating its influence on the stability of the iron mineral core. Hence, the current work provides the kinetic/mechanistic insight toward the ferroxidase activity in Mtb BfrB, apart from demonstrating the role of phosphate toward the structure/reactivity of its iron mineral.

Photocatalytic disinfection and purification of water employing reduced graphene oxide/TiO2 composites

AbstractBACKGROUNDRecombination of photogenerated carriers in titanium dioxide (TiO2)‐mediated semiconducting photocatalysis is considered to be the principal obstacle in its unlimited exploitation in practical applications. Hybridization of TiO2 with graphene‐based materials appears to be a highly promising alternative. In this context, reduced graphene oxide (rGO)/TiO2 composites were prepared using a simple ultrasonically assisted route under mild reaction conditions.RESULTSThe as‐prepared composites were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy‐dispersive X‐ray spectrometry (EDS), Fourier‐transform infrared spectroscopy (FTIR) and nitrogen adsorption–desorption isotherms. Photocatalytic efficiencies of the as‐prepared composites were evaluated employing the pesticide clopyralid as a model pollutant. Initial degradation and mineralization rates obtained in the presence of the as‐prepared composites were, in all cases, higher than the one obtained in the presence of the bare TiO2, with 5% rGO/TiO2 achieving the highest r0 and rDOC values. The as‐prepared composites also were evaluated based on their potential to inactivate bacterial endospores of the Bacillus stearothermophilus species, well‐known for their extraordinary resistance to most inactivation processes. Prevalence of 5% rGO/TiO2 in the inactivation of B. stearothermophilus among all as‐prepared materials was evident, accomplished within 120 min of UV‐A illumination. Real‐time PCR experiments enabled the detection of genomic DNA released during photocatalytic oxidation, in the presence of 5% rGO/TiO2 and UV‐A, suggesting lysis of the outer and inner spore coat caused by the generated ROS.CONCLUSIONSThese findings demonstrate the potential of rGO, a low‐cost, nontoxic material to serve as a reliable alternative in the enhancement of TiO2 photocatalytic efficiency in water processing applications. © 2019 Society of Chemical Industry

Photo-electro-Fenton process applied to the degradation of valsartan: Effect of parameters, identification of degradation routes and mineralization in combination with a biological system

In this work, the oxidation of the antihypertensive drug valsartan by the Electro-Fenton (EF) and photo-electro-Fenton (PEF) processes was studied using a Ti/IrO2 doped with SnO2 as anode, and a carbon felt air diffusion electrode as cathode. Initially, the influence of variables such as supporting electrolyte type, current density, and pH on EF and/or PEF processes was evaluated. The processes were carried out in batch mode, in an open and undivided cell of 200 cm3. The efficiency of the systems was evaluated in terms of the removal of the initial contaminant and rate of mineralization. When NaCl was used as a supporting electrolyte at pH 3.0 and current density 3.46 mA/cm2 adding 3.6 × 10−5 mol/L of Fe2+, total valsartan (20 mg/L) degradation was observed after 45 min. After 120 min, even if total removal of valsartan was reached, only 25% of mineralization was obtained. Thus, valsartan degradation tests at near neutral pH in presence of oxalic acid (4.6 × 10−5 mol/L) lead to comparable results with those obtained at pH 3.0. Primary aromatic intermediates were identified by high resolution mass spectrometry (HRMS) using hybrid quadrupole- time-of-flight (QTOF) MS, from which an initial degradation pathway was proposed. At the end of the PEF system, several aliphatic acids were accumulated and observed, which were effectively removed in a subsequent aerobic biological system. The results demonstrate the feasibility of PEF and biological coupling process to completely mineralize emerging pharmaceutical pollutants, such as valsartan, at natural pH.

Mineralization of the antineoplastic drug carboplatin by heterogeneous photocatalysis with simultaneous synthesis of platinum-modified TiO2 catalysts

Photocatalytic oxidation of carboplatin, a platinum antineoplastic drug, has been investigated in aqueous heterogeneous solutions containing TiO2 photocatalysts. The current study, besides the photocatalytic degradation of the drug, examines the utilization of the photo-reduction process occurring on the surface of the catalyst, leading simultaneously to the photo-deposition and recovery of platinum. TiO2 photocatalytic process was evaluated for its ability to degrade the molecule of carboplatin and concurrently result in the synthesis of efficient platinum modified TiO2 catalysts. The degradation kinetic was studied under different operational conditions, such as type of photocatalyst, catalyst loading, initial pH and addition of electron acceptors. Three systems were evaluated namely, TiO2 P25 under UV-A and TiO2 Kronos vlp 7000 under UV-A or visible illumination, with respect to their activity for substrate degradation and mineralization and their ability to bind platinum on their surface during photocatalytic oxidation of the drug. The initial degradation rate (r0) decreased in the order TiO2 P25/UV-A > TiO2 Kronos vlp 7000/UV-A > TiO2 Kronos vlp 7000/visible light. For TiO2 P25/UV-A, the addition of 100 mg L−1 H2O2 increases slightly the initial mineralization rate, while degradation rates gradually decrease as photocatalysis takes place in neutral and alkaline pH. Phytotoxicity measurements, showed that heterogeneous photocatalytic oxidation in the presence of TiO2 P25 is capable of reducing the phytotoxicity of carboplatin. For TiO2 P25 and TiO2 Kronos vlp 7000 under UV-A illumination, photo-reduction and deposition of platinum is fully accomplished within 60 min of oxidation, while for TiO2 Kronos vlp 7000 in the presence of visible light, the percentage of platinum deposited on the surface of the catalyst reaches 40%. Platinum photo-deposition is feasible, employing TiO2 P25, even after the catalyst is reused. The synthesized platinum modified TiO2 P25, demonstrated higher photocatalytic efficiency in comparison to the bare one, leading to 100% degradation of the model pollutant malachite green and 40% DOC reduction, after 30 min of photo-oxidation.

Antibiotics do not affect the degradation of fungicides and enhance the mineralization of chlorpyrifos in biomixtures

The use of antibiotics in agriculture produces residues in wastewaters. The disposal of such wastewaters in biopurification systems (BPS) employed for the treatment of pesticides could result in the inhibition of the degrading capacity of the biomixtures used in the BPS. We assayed the effect of two commercial formulations of antibiotics used in agriculture, one containing kasugamycin (KSG) and the other oxytetracycline plus gentamicin (OTC+GTM), on the biomixture performance. Doses from 0.1mgkg−1 to 1000mgkg−1 of KSG increased the respiration of the biomixture, and low doses enhanced the mineralization rate of the insecticide 14C-chlorpyrifos. On the contrary, OTC+GTM depressed the respiration of the biomixture and the initial mineralization rate of 14C-chlorpyrifos; nonetheless, the antibiotics did not decrease overall mineralization values. The application of both formulations in the biomixture at a relevant concentration did not harm the removal of the fungicides carbendazim and metalaxyl, or their enhanced degradation; on the other hand, the biomixture was unable to dissipate tebuconazol or triadimenol, a result that was unchanged during the addition of the antibiotic formulations. These findings reveal that wastewater containing these antibiotics do not affect the performance of BPS. However, such a response may vary depending on the type of pesticide and microbial consortium in the biomixture.

Substrate quality influences organic matter accumulation in the soil silt and clay fraction

Substrate quality impacts the rate of microbial decomposition of soil organic matter (OM), with higher quality substrates leading to faster rates of decomposition. Since OM decomposition is the opposite of OM stabilization, one might presume higher quality substrates would lead to less OM stabilization. Yet, there is growing evidence that C stabilized in the soil silt and clay fractions is preferentially derived from microbial metabolites. We hypothesized that the decomposition of higher quality substrates would increase silt and clay-sized (S)OM pools despite higher initial mineralization rates. Soils low in initial organic carbon were incubated for 139 d with substrates spanning a range of quality/lability including: (a) bermudagrass forage cut after 14d, 21d, 28d, 35d, and 42d of re-growth, and (b) ruminal digesta produced from these forages. We then monitored the production of CO2 as well as the carbon abundance and isotopic composition in the bulk, silt, and clay fractions. Undigested forage was respired at higher initial rates than ruminal digesta and resulted in more carbon (C) and nitrogen (N) in the clay fraction. Overall, substrate quality—assessed as the ratio of neutral detergent fiber (NDF-cellulose, hemicellulose, and lignin) to crude protein (CP)—was directly related to decomposition kinetics with higher substrate quality resulting in more silt and clay C. These findings provide evidence that substrate quality, as a driver of microbial response, can control the flow of C and N to silt and clay fractions where there is the potential for interactions with mineral surfaces to greatly increase C and N residence times. Incorporating this concept into numerical models of SOM generation and turnover will likely improve projections of carbon dynamics in global change models.

Magnetic lanthanide oxide catalysts: An application and comparison in the heterogeneous catalytic ozonation of diethyl phthalate in aqueous solution

Abstract Catalytic oxidation with nano magnetic catalysts has the advantages of easy recovery, good stability and high activity. In this study, three nano magnetic lanthanide catalysts with a core–shell structure of Ce/SiO 2 @Fe 3 O 4 , La/SiO 2 @Fe 3 O 4 and Pr/SiO 2 @Fe 3 O 4 were prepared and characterized by Brunauer–Emmet–Teller, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectrum and vibrating sample magnetometer analysis. All catalysts have Fe 3 O 4 nanoparticles as cores, SiO 2 as the mid-layer, and CeO 2 , La 2 O 3, or Pr 6 O 11 as the outer layer, and have a good magnetic property. The catalyst activities followed the descending order of Pr/SiO 2 @Fe 3 O 4 > La/SiO 2 @Fe 3 O 4 > Ce/SiO 2 @Fe 3 O 4 upon the degradation of diethyl phthalate (DEP), and the catalytic ozonation process followed an OH reaction mechanism. The removal rate of DEP was small effected because of the presence of Cl − , and addition of sodium carbonate had no obviously influence. The initial mineralization rate had a positive relation with the hydroxyl groups and pH value at the zero charge point (pH pzc ) of the catalysts, but had no significant relation with the surface area of the catalysts. The catalysts were relatively effective and stable after 3 repeated uses, and the leaching out concentrations of Ce, La and Pr were 1.33 mg/L, 0.138 mg/L and 0.115 mg/L after a 90 min reaction.

Decomposition and Carbon Sequestration Potential of Different Rice-Residue-Derived By-products and Farmyard Manure in a Sandy Loam Soil

Large quantities of rice straw are produced annually in India and the majority of it is burnt in the fields, leading to environmental pollution and loss of carbon (C) and essential nutrients. It is imperative to manage rice residues and by-products to derive benefits for soil health and environment conservation. We studied the decomposition of rice straw (RS), rice-straw-derived biochar and compost (RSC), rice husk (RH), rice husk ash (RHA), and farmyard manure (FYM) in laboratory incubation experiments at 30 ºC and field-capacity moisture. The decomposition of organic sources depended on the size of decomposable and recalcitrant C pools. Carbon mineralization was greater from RS and RH compared to FYM, biochar, RSC, and RHA. The initial rate of mineralization was faster for RS and RH, followed by FYM, biochar, and RSC, and the least for RHA. The proportion of antecedent C mineralized from different sources followed the order RS > RH > FYM> RSC = biochar > RHA. The RS and RH showed larger decomposable pools than the other sources. Rice husk ash had decomposable pool and associated rate coefficient similar to the unamended soil. Residence time for recalcitrant pool in FYM, RSC, and biochar applied at 5 g C kg–1 soil ranged between 1020 and 1149 days as opposed to 180 and 254 days for RS and RH, respectively. Increasing the rate of C application (15 g C kg−1) markedly increased the residence time for all the sources, except FYM, and these followed the order RHA (2273 d) > RSC (2000 d) > biochar (1961 d) > RH (529 d) > RS (400 d). It was concluded that RS and RH could result in short-term C accrual in soil, whereas RSC, biochar, and FYM may lead to long-term C sequestration. The disposal of RHA to soil, which is characterized by mainly recalcitrant C, could lead to buildup of soil organic C.

Can Simple Soil Parameters Explain Field-Scale Variations in Glyphosate-, Bromoxyniloctanoate-, Diflufenican-, and Bentazone Mineralization?

The large spatial heterogeneity in soil physico-chemical and microbial parameters challenges our ability to predict and model pesticide leaching from agricultural land. Microbial mineralization of pesticides is an important process with respect to pesticide leaching since mineralization is the major process for the complete degradation of pesticides without generation of metabolites. The aim of our study was to determine field-scale variation in the potential for mineralization of the herbicides glyphosate, bromoxyniloctanoate, diflufenican, and bentazone and to investigate whether this variation can be predicted by variations in basic soil parameters. Sixty-five soil samples were sampled from an agricultural, loamy field in Silstrup, Denmark, from a 60 × 165 m rectangular grid. The mineralization potential of the four pesticides was determined using a 96-well microplate 14C-radiorespirometric method. Initial mineralization rates were determined using first-order kinetics for glyphosate and bromoxyniloctanoate and zero-order kinetics for diflufenican and bentazone. The mineralization rates of the four pesticides varied between the different pesticides and the different soil samples, but we could not establish correlations between the pesticide mineralization rates and the measured soil parameters. Only the glyphosate mineralization rates showed slightly increasing mineralization potentials towards the northern area of the field, with increasing clay and decreasing OC contents. The mineralization potentials for glyphosate and bentazone were compared with 9-years leaching data from two horizontal wells 3.5 m below the field. The field-scale leaching patterns, however, could not be explained by the pesticide mineralization data. Instead, field-scale pesticide leaching may have been governed by soil structure and preferential flow events.

Short-term compost application increases rhizosphere soil carbon mineralization and stimulates root growth in long-term continuously cropped cucumber

Continuous cropping, a common agricultural practice in the world, often results in soil degradation and eventually lead to crop yield decline over time. Composts application has several advantages such as improving soil quality and increasing crop yields. However, little information is available regarding the effect of compost application on crop growth in continuous cropping systems. In this study, we investigated three long-term (>15 years) continuously cropped cucumber soils to examine the effect of compost application on carbon mineralization of rhizosphere soils and plant growth. All three soils were treated with/without compost, Bacillus subtilis and their combination. In general, the amounts of cumulative carbon mineralization in soils treated with compost were larger than those in untreated soils. The initial carbon mineralization rate, m0, was significant higher in soils treated with compost than in untreated soils. Soil microbial biomass carbon (MBC) and root growth was significantly (P<0.05) increased by the compost addition, but was not statistically (P>0.05) affected by the bacterial inoculation in all soils. In compost-treated soils, there was a higher faction of thin roots (<0.5mm diameter) and a smaller fraction of thicker roots (>0.5mm diameter) compared with untreated soils. Cucumber fruit yield was significantly positively correlated with the CCM and MBC values. Our results suggested that short-term compost application increases rhizosphere soil carbon mineralization and stimulates root growth in long-term continuously cropped cucumber.

Life in the ‘charosphere’ – Does biochar in agricultural soil provide a significant habitat for microorganisms?

Biochar application has become a novel and emergent technology for sequestering C, improving soil quality and crop production, and is a potential win–win strategy for ecosystem service delivery. Biochar addition can also stimulate soil microbial activity, and although it is unclear exactly why biochar should benefit soil microorganisms, it is thought that the large surface area and volume of pores provide a significant habitat for microbes. The aim of this study was to determine the level of microbial colonisation of wood-derived biochar that had been buried in an agricultural soil for three years. We have examined the level of colonisation on the internal and external surfaces of field-aged biochar by scanning electron microscopy, and used 14C-labelled glucose to quantify the rates of microbial activity in different spatial niches of the biochar and the surrounding soil. Microbial colonisation of field-aged biochar was very sparse, with no obvious differences between the external and internal surfaces. At the high field application rate of 50 t ha−1, biochar contributed only 6.52 ± 0.11% of the total soil pore space and 7.35 ± 0.81% of the total soil surface area of the topsoil (0–30 cm). Further, 17.46 ± 0.02% of the biochar pores were effectively uninhabitable for most microbes, being <1 μm in diameter. The initial rate of microbial mineralization of 14C-labelled glucose was significantly greater in the control bulk soil and the soil immediately surrounding the biochar than on the biochar external and internal surfaces. However, lower C use efficiency values of microbes on, or within, the biochar also suggested lower available C status or differences in the structure of the microbial community in the biochar relative to the surrounding soil. This study suggests that, at least in the short term (≤3 y), biochar does not provide a significant habitat for soil microbes. While biochar is extremely recalcitrant and largely unavailable to soil microbes, changes in soil physicochemical properties and the introduction of metabolically available labile compounds into the surrounding soil (the ‘charosphere’) may significantly alter soil microbial activity and structure, which could ultimately affect soil–plant–microbe interactions. Therefore, before the wide-scale application of biochar to agricultural land is exploited, it is important that we understand further how the properties of biochar positively or negatively affect soil microbial communities, and in turn, how they interact with, and colonise biochar.

Degradation of acetaminophen in an aerated Fenton reactor

This study investigates the degradation of acetaminophen (ACTP) using a novel Fenton aerated reactor. The aerator was used to agitate and sludge was removed from a sludge outlet. The effects of operating parameters such as pH, Fe2+ and H2O2 concentrations on the initial rate of ACTP degradation (r), removal efficiency and mineralization were studied. The results indicate that a novel Fenton aerated reactor was successfully performed to degrade ACTP. The highest r value was obtained at pH 3. At pH 3, the r value and ACTP removal efficiency were significantly improved as the [Fe2+]:[H2O2] ratio increased. The removal efficiencies of ACTP, COD and TOC were 99%, 34% and 14%, respectively, at 40min, when optimum conditions for 5mM acetaminophen, 25mM H2O2 and 0.1mM Fe2+ were used at pH 3.

The role of biodegradation in limiting the accumulation of petroleum hydrocarbons in raingarden soils

Previous studies have indicated that raingardens are effective at removing petroleum hydrocarbons from stormwater. There are concerns, however, that petroleum hydrocarbons could accumulate in raingarden soil, potentially resulting in liability for the site owner. In this work, 75 soil samples were collected from 58 raingardens and 4 upland (i.e., control) sites in the Minneapolis, Minnesota area, representing a range of raingarden ages and catchment land uses. Total petroleum hydrocarbon (TPH) concentrations in the samples were quantified, as were 16S rRNA genes for Bacteria and two functional genes that encode for enzymes used in the degradation of petroleum hydrocarbons. TPH levels in all of the raingarden soil samples were low (<3 μg/kg) and not significantly different from one another. The TPH concentration in raingarden soil samples was, however, significantly greater (p ≤ 0.002) than TPH levels in upland sites. In addition, the number of copies of Bacteria 16S rRNA genes and functional genes were greater in the raingardens planted with deeply-rooted natives and cultivars than in raingardens containing simply turf grass or mulch (p < 0.036), suggesting that planted raingardens may be better able to assimilate TPH inputs. The ability of microorganisms present in the soil samples to degrade a representative petroleum hydrocarbon (naphthalene) was also investigated in batch experiments. A sub-set of the field sites was selected for re-sampling, and all soil samples tested (n = 8) were able to mineralize naphthalene. In these experiments the initial mineralization rate correlated with the number of copies of Bacteria 16S rRNA genes present.

Modelling of crop yields and N 2O emissions from silty arable soils with differing tillage in two long-term experiments

The choice of tillage system affects crop growth and soil nitrogen dynamics. Models help us to better understand these systems and the interaction of the processes involved. Objectives were to test a calibration and validation scheme for applications of the denitrification–decomposition (DNDC) model to describe a long-term field experiment with conventional tillage (CT) and reduced tillage (RT) at two sites (G and H, silty Haplic Luvisols) near Göttingen, Germany (G-CT, G-RT, H-CT, H-RT). Crop growth of field bean ( Vicia faba L.) and winter wheat ( Triticum aestivum L.) as well as soil water dynamics and nitrous oxide (N 2O) emissions were determined for two subsequent years. A model test was performed based on a model parameterization to best describe the case G-CT. This parameterization was then applied to the other cases as a retrospective simulation. Results of model variant v1 (no parameter optimization) indicated that soil water contents were not accurately simulated using the DNDC default values for a silt loam. After successful calibration of the soil water flow model using modified water-filled pore spaces at field capacity and wilting point and a modified hydro-conductivity that led to a good fit of the measured water content data, grain yields were markedly underestimated and modelled N 2O emissions were too large (v2). An optimization of the crop properties (maximum grain yield, N fixation index, thermal degree days, transpiration coefficient) was essential for a better match of measured yields (v3). Further adjustments in the model (v4) were required to better match cumulative N 2O emissions: reducing the initial soil organic carbon content and mineralization rates. Predictions of crop yields and annual cumulative N 2O emissions using model variant v4 were fairly accurate for the reduced tillage system G-RT and also for the second field experiment H-CT and H-RT, but annual distributions of N 2O emissions were not. Overall our results indicate that site specific calibration was an essential requirement for the silty German sites, and that the pedotransfer functions and denitrification sub-model of DNDC may need further improvement.

Effects on soil organic matter mineralization and microbiological properties of applying compost to burned and unburned soils

This study was undertaken in the context of a project of reclamation of a burned forest area applying municipal waste compost (MWC) and it consisted of an incubation experience carried out under laboratory conditions. The objectives of this research were to asses the effect of three doses of MWC added to burned and unburned calcareous soils on a) SOM mineralization and b) soil microbiological parameters. The laboratory incubation experience was carried out with three compost doses (1, 2 and 4% w/w) on a burned soil and another unburned one from an adjacent plot, besides the corresponding control samples. The mineralization kinetics of the organic matter was studied for 92 days. The kinetics data were adjusted to a double exponential model, showing two C pools of different degrees of resistance to mineralization and concentration, with half-life times of 1.9-4.9 and 34-76 days, respectively. In the unburned soil, the initial potential mineralization rate of the labile and stable C pools showed an opposed behavior, increased and decreased with the MWC dose, respectively. However in the burned soil no significant tendencies were observed. Although applying compost tended to increase the size of more labile pool with respect to total mineralizable C, however most of the soil or compost OM did not result mineralizable in the short and medium term. The compost amendment did not increase soil microbial activity.