Gross nitrogen mineralization in pulse-crop rotations on the Northern Great Plains

Pulse crops represent an ever-increasing proportion of cropping systems in the Northern Great Plains. Previous studies have noted apparent benefits associated with pulse crop production that extend beyond the reduced need for N fertilizer in the year of production; these benefits have been attributed to the quality of pulse residues and their effects on N dynamics in subsequent years. This study used isotope dilution techniques to quantify the N-cycling effects of pulse crops in the rotation. Gross N mineralization was measured over three growing seasons at two Agriculture and Agri-Food Canada research sites in Saskatchewan, Canada: Scott (four rotations; one with pulse crop) and Swift Current (three rotations; one with pulse crop). Gross nitrification and the relative contribution of nitrification vs. denitrification to N₂O emissions were also measured. Across all dates and rotations, the average gross mineralization rate at Scott was 2.0 ± 4.0 mg NH₄ ⁺-N kg^?1 soil d^?1 and at Swift Current was 1.4 ± 3.9 mg NH₄ ⁺-N kg^?1 soil d^?1. At both sites, rates were highly variable across the growing season, but tended to be higher at anthesis than either pre-seeding or post-harvest. The only significant difference among rotations was at Swift Current, where the fertilized continuous wheat rotation had the highest gross mineralization rates (rotation average: 2.3 mg NH₄ ⁺-N kg^?1 soil d^?1). The lack of difference among most rotations was particularly notable given the differences in residue quantity among the crops. Ultimately, the lower quantity of residues produced by pulse crops appears to be offset by their higher quality.     

Modelling Effects of Remedial Programs to Aid Great Lakes Environmental Management

Computer simulation of remedial programs was carried out employing a large and diverse information base on both point and nonpoint pollutant sources in the Great Lakes basin to provide a more holistic environmental management perspective. The process utilizes a cascading system of sub-basin unit area pollutant loads (classified by land use and land form), per capita municipal pollutant inputs, river transmission factors, and remedial program effectiveness, in terms of reduced loadings to the lakes and costs. It was employed by PLUARG (Pollution from Land Use Activities Reference Group) to determine scenarios of remedial programs which apparently were practicable and would achieve target lake loads of phosphorus most cost-effectively. The analysis, presented here for Lake Erie, Lake Ontario, and southern Lake Huron, provides a means of evaluating the effectiveness of various remedial program options to fulfill commitments by Canada and the United States to load reductions for these lakes. The methodology can be extended to other pollutants as sufficient data become available to permit a suitable degree of resolution for management decisions.     

Operating conditions for the determination of the biochemical acidogenic potential of wastewater

The aim of this work was to study the test conditions for the determination of the biochemical acidogenic potential (BAP) of wastewater, which should be useful to predict the performance of enhanced biological phosphorus removal (EBPR). Proposed operating conditions for a simple and reproducible BAP test in 250 ml serum bottles (equipped with black butyl stoppers and magnetic bars) are: use of either frozen or fresh water, no inoculum addition, fermentation carried out in the dark during 15 days, addition of 1 mM bromo-ethane sulfonate (BES) and 2 mM barium chloride (BaCl2), stirring speed strong enough to maintain vortex conditions, no pH control and controlled temperature of 20 degrees C.     

Phosphorus removal by electric arc furnace steel slag and serpentinite

Electric arc furnace (EAF) steel slag and serpentinite were tested in columns either alone or mixed with limestone to determine their capacity to remove phosphorus (P) from a solution containing initially 20mg P/L (for 114 days) than 400mg P/L (for 21 days). EAF steel slag was nearly 100% efficient due to specific P adsorption onto metal hydroxides and precipitation of hydroxyapatite. Serpentinite also showed a good performance that decreased with time, adsorption appearing to be the dominant mechanism for P removal. Mixing limestone with these two materials did not improve their performance and in the case of serpentinite, it actually even decreased it. In 114 days of experimentation, serpentinite alone and the mixture of serpentinite and limestone removed 1.0mg P/g while in 180 days of experimentation, EAF steel slag and the mixture of slag and limestone removed an average of 2.2mg P/g, without attaining their maximum P removal potential. The void hydraulic retention time (HRTv) was a key factor for growing hydroxyapatite crystals and had a significant effect on P removal efficiency by EAF steel slag. A temporary increase in HRTv caused by clogging resulted in an increase in EAF steel slag efficiency (from 80% to almost 100%) towards the end of investigation. Results from this study indicate that the use of EAF steel slag in constructed wetlands or filter beds is a promising solution for P removal via adsorption and precipitation mechanisms.     

A kinetic model for the decrease in lipase activity of rhizopus arrhizus and penicillium cyclopium mycelia in organic media

The decrease in Lipase activity of Rhizopus arrhizus and Penicillium cyclopium mycelia (RAM and PCM) were studied in alkanes, ethers and chloroalkanes. The two biocatalysts showed similar behaviour in organic media, although RAM was slightly more stable. The kinetic model obtained indicated that the decrease in activity followed a succession of two first-order reactions. Both RAM and PCM were more stable in hydrophobic solvents. These two mycelia were used to synthesize N-octyl-myristylamide; yield of the amide was linked in a linear relationship to the average activity of biocatalyst in the solvent employed.     

How to extract defect densities from distribution

A technique is presented for representing a defect density, such as might be found on an integrated circuit. Distributions are a powerful tool for presenting defect distributions for test structures and are convenient for yield analysis and modeling. How the concept of distribution can be extended to give more information on the defects is shown. The power of this approach derives from its invariability to test stricture geometry, which enables direct comparison of data from different structures. It is explained how and why defect distributions measured on test structures can be related to those of other structures, i.e. integrated circuits. The mathematics are simple and lead to a defect density which can be expressed in units of defects per geometric factor per independent variable     

Biodegradation of the endogenous residue of activated sludge in a membrane bioreactor with continuous or on-off aeration

The goal of this study was to determine the effect of a long sludge retention time on the biodegradation of the endogenous residue in membrane digestion units receiving a daily feed of sludge and operated under either aerobic or intermittently aerated (22 h off-2 h on) conditions. The mixed liquor for these experiments was generated in a 10.4 day sludge retention time membrane bioreactor fed with a synthetic and completely biodegradable influent with acetate as the sole carbon source. It had uniform characteristics and consisted of only two components, heterotrophic biomass X_H and endogenous residue X_E. Membrane digestion unit experiments were conducted for 80 days without any sludge wastage except for some sampling. The dynamic behaviour of generation and consumption of filtered organic digestion products was characterized in the membrane digestion unit systems using three pore filter sizes. Results from this investigation indicated that the colloidal matter with size between 0.04 μm and 0.45 μm was shown to contain a recalcitrant fraction possibly composed of polysaccharides bound to proteins which accumulated in the membrane digestion unit under both conditions. Modelling the membrane digestion unit results by considering a first-order decay of the endogenous residue allowed to determine values of the endogenous residue decay rate of 0.0065 and 0.0072 d⁻¹ under fully aerobic and intermittently aerated conditions, respectively. The effect of temperature on the endogenous decay rate was assessed for the intermittently aerated conditions in batch tests using thickened sludge from tests gave an endogenous decay rate constant of 0.0075 d⁻¹ at 20 °C and an Arrhenius temperature correction factor of 1.033.     

Model of phosphorus precipitation and crystal formation in electric arc furnace steel slag filters

The objective of this study was to develop a phosphorus retention mechanisms model based on precipitation and crystallization in electric arc furnace slag filters. Three slag columns were fed during 30 to 630 days with a reconstituted mining effluent at different void hydraulic retention times. Precipitates formed in columns were characterized by X-ray diffraction and transmission electronic microscopy. The proposed model is expressed in the following steps: (1) the rate limiting dissolution of slag is represented by the dissolution of CaO, (2) a high pH in the slag filter results in phosphorus precipitation and crystal growth, (3) crystal retention takes place by filtration, settling and growth densification, (4) the decrease in available reaction volume is caused by crystal and other particulate matter accumulation (and decrease in available reaction time), and (5) the pH decreases in the filter over time if the reaction time is too low (which results in a reduced removal efficiency). Crystal organization in a slag filter determines its phosphorus retention capacity. Supersaturation and water velocity affect crystal organization. A compact crystal organization enhances the phosphorus retention capacity of the filter. A new approach to define filter performance is proposed: saturation retention capacity is expressed in units of mg P/mL voids.     

Printability of Methacrylated Gelatin upon Inclusion of a Chloride Salt and Hydroxyapatite Nano‐Particles

3D biomaterial printing requires an ink to have suitable printability characteristics, as well as creating a final construct of controllable swelling and stiffness. To tune such properties, the impact of adding different levels of chloride salts (NaCl and CaCl₂) and hydroxyapatite nano‐particles (nHA) to a highly concentrated and photo‐crosslinkable methacrylated gelatin (GelMA) is investigated. By adding up to 100 mm CaCl₂ or 1.11 m NaCl, the GelMA viscosity decreases from that of control GelMA (no salt). Interestingly, a 25G needle and strong photo‐polymerization kinetics are able to overcome the low viscosity of the 50CaG ink during printing. Adding further CaCl₂ increases GelMA viscosity, while decreasing both the swelling and dynamic modulus of the UV‐cured construct observed in water. As all UV‐cured constructs have a dynamic modulus greater than 1 MPa, this novel system is able to match the dynamic modulus of articular cartilage—a feat not previously reported for a GelMA‐based system. Lastly, nHA inclusion improves ink printability, as well as decreases swelling and increases dynamic modulus of the final construct. Overall, this study leads to the successful development of a new advanced functional ink which will be beneficial in the 3D printing of biomaterials toward tissue engineering applications.