Carbon Limitation in Periphytic Algal Wastewater Treatment Systems

As global eutrophication poses an ever increasing threat to water quality new techniques must be implemented to improve the sustainability of natural resource consumption. Wastewater treatment facilities (WWTF) are designed to destroy pathogens, remove particulates, lower oxygen demanding substances, and reduce nutrients from influent waste water to avoid the degradation of receiving waters. WWTF are generally effective, however they are mostly inadequate at removing nutrients. When wastewater derived nutrients such as nitrate and phosphate are discharged to receiving waters, they stimulate algal blooms. Algal blooms can reduce dissolved oxygen, block sunlight for submerged aquatic plants, and render state waters unusable for recreational activities; these issues can negatively impact ecological systems and local economies. One experimental approach to reducing nitrogen and phosphorus in wastewater effluent uses algae as a tertiary treatment system. Algae are photosynthetic organisms that not only remove nutrients from wastewater, but they produce biomass for biofuels. Research is needed to increase the productivity of algae in tertiary treatment systems to make WWTF more ecologically sustainable and economically viable. Because algae in tertiary wastewater treatment systems are typically not limited by nutrients, the algae may become limited by dissolved inorganic carbon. To test this hypothesis, this study characterized the effects of adding carbon dioxide to lab scale, recirculating wastewater algal treatment floways. Eight 61 cm x 121 cm x 5.1 cm (height x length x diameter) recirculating floways, lined with unglazed clay tiles were administered gaseous carbon dioxide for 18 days while eight more were left untreated as controls. The floways, which were administered carbon dioxide, had a 41% greater algal dry mass, and 43% greater ash free dry mass compared to controls. By day 18 phosphate and total phosphorus concentrations in treated floways averaged 67% and 39% iower than controls respectively. Nitrate and total nitrogen concentrations in treated floways averaged 37% and 10% lower than controls respectively. The results demonstrated that carbon dioxide stimulates algae in tertiary wastewater treatment floways. Because floways administered carbon dioxide had a magnitude lower pH than control floways, a secondary experiment was designed to determine if lower pH stimulated algal production. Replicating the previous experiment, recirculating (8L, n=8) floways were treated with 2N hydrochloric acid daily to lower their target pH to 6.48. A pH 7 solution of HCI and sodium hydroxide (n=8) was administered to floways (n=8) and others were left unmanipulated (n=8). After 18 days the acidified floways had 51% less dry algal mass compared to controls. The only nutrient concentration to differ significantly was nitrate which was 17% higher in acidified floways compared to controls. A final experiment was conducted to determine if another carbon source could stimulate algal production. For the third experiment, floways (n=8) were spiked with 8 g/L of sodium bicarbonate (NaHC03l a carbon source) or left untreated for controls (n=8). After 18 days the floways administered NaHC03 showed no difference in nutrient removal compared to control floways. However, these floways did have a 50% increase in volatile solids, a measure of algal biomass, and 39% greater dry algal mass. The first experiment supported the hypothesis that algae may become carbon limited but confounding variables left assigning causality impossible. The second experiment directly assessed the pH effect on algae while the third experiment confirmed the carbon limitation hypothesis by manipulating dissolved inorganic carbon. By assessing each variable a stronger case can be made for the benefits of algal wastewater treatment flow ways such as reducing global eutrophication and improving water quality with a sustainable system

Shockwaves in converging geometries

Plate impact experiments are a powerful tool in equation of state (EOS) development, but are inherently limited by the range of impact velocities accessible to the gun. In an effort to dramatically increase the range of pressures which can be studied with available impact velocities, a new experimental technique is being developed. The possibility of using a confined converging target to focus Shockwaves and produce a large amplitude pressure pulse is examined. When the planar shock resulting from impact enters the converging target the impedance mismatch at the boundary of the confinement produces reflected Mach waves and the subsequent wave interactions produce a diffraction cycle resulting in increases in the shock strength with each cycle. Since this configuration is limited to relatively low impedance targets, a second technique is proposed in which the target is two concentric cylinders designed such that the inner cylinder will have a lower shock velocity than the much larger shock velocity in the outer cylinder. The resulting dispersion in the wave front creates converging shocks, which will interact and eventually result in a steady Mach configuration with an increase in pressure in the Mach disk. Numerical simulations indicate a significant increase in pressure for both methods and show promise for the proposed concepts

Advances in Shock Compression of Mantle Materials and Implications

Hugoniots of lower mantle mineral compositions are sensitive to the conditions where they cross phase boundaries including both polymorphic phase transitions and partial to complete melting. For SiO_2, the Hugoniot of fused silica passes from stishovite to partial melt (73 GPa, 4600 K) whereas the Hugoniot of crystal quartz passes from CaCi_2 structure to partial melt (116 GPa, 4900 K). For Mg_2SiO_4, the forsterite Hugoniot passes from the periclase +MgSiO_3 (perovskite) assemblage to melt before 152 GPa and 4300 K, whereas the wadsleyite Hugoniot transforms first to periclase +MgSiO_3 (post-perovskite) and then melts at 151 GPa and 4160 K. Shock states achieved from crystal enstatite are molten above 160 GPa. High-pressure Grüneisen parameters for molten states of MgSiO_3 and Mg_2SiO_4 increase markedly with compression, going from 0.5 to 1.6 over the 0 to 135 GPa range. This gives rise to a very large (>2000 K) isentropic rise in temperature with depth in thermal models of a primordial deep magma ocean within the Earth. These magma ocean isentropes lead to models that have crystallization initiating at mid-lower mantle depths. Such models are consistent with the suggestion that the present ultra-low velocity zones, at the base of the lowermost mantle, represent a dynamically stable, partially molten remnant of the primordial magma ocean. The new shock melting data for silicates support a model of the primordial magma ocean that is concordant with the Berkeley-Caltech iron core model [1] for the temperature at the center of the Earth

Shock temperatures of preheated MgO

Shock temperature measurements via optical pyrometry are being conducted on single-crystal MgO preheated before compression to 1905–1924 K. Planar shocks were generated by impacting hot Mo(driver plate)-MgO targets with Mo or Ta flyers launched by the Caltech two-stage light-gas gun up to 6.6 km/s. Quasi-brightness temperature was measured with 2–3% uncertainty by a 6-channel optical pyrometer with 3 ns time resolution, over 500–900 nm spectral range. A high-power, coiled irradiance standard lamp was adopted for spectral radiance calibration accurate to 5%. In our experiments, shock pressure in MgO ranged from 102 to 203 GPa and the corresponding temperature varied from 3.78 to 6.53 kK. For the same particle velocity, preheated MgO Hugoniot has about 3% lower shock velocity than the room temperature Hugoniot. Although model shock temperatures calculated for the solid phase exceeded our measurements by ~5 times the uncertainty, there was no clear evidence of MgO melting, up to the highest compression achieved

A Laboratory Investigation of Supersonic Clumpy Flows: Experimental Design and Theoretical Analysis

We present a design for high energy density laboratory experiments studying the interaction of hypersonic shocks with a large number of inhomogeneities. These ``clumpy'' flows are relevant to a wide variety of astrophysical environments including the evolution of molecular clouds, outflows from young stars, Planetary Nebulae and Active Galactic Nuclei. The experiment consists of a strong shock (driven by a pulsed power machine or a high intensity laser) impinging on a region of randomly placed plastic rods. We discuss the goals of the specific design and how they are met by specific choices of target components. An adaptive mesh refinement hydrodynamic code is used to analyze the design and establish a predictive baseline for the experiments. The simulations confirm the effectiveness of the design in terms of articulating the differences between shocks propagating through smooth and clumpy environments. In particular, we find significant differences between the shock propagation speeds in a clumpy medium compared to a smooth one with the same average density. The simulation results are of general interest for foams in both inertial confinement fusion and laboratory astrophysics studies. Our results highlight the danger of using average properties of inhomogeneous astrophysical environments when comparing timescales for critical processes such as shock crossing and gravitational collapse times.Comment: 7 pages, 6 figures. Submitted to the Astrophysical Journal. For additional information, including simulation animations and the pdf and ps files of the paper with embedded high-quality images, see http://pas.rochester.edu/~wm

Simulation of Particle Size Effect on Dynamic Properties and Fracture of PTFE-W-Al Composites

Recent investigations of the dynamic compressive strength of cold isostatically pressed composites of polytetrafluoroethylene (PTFE), tungsten (W) and aluminum (Al) powders show significant differences depending on the size of metallic particles. The addition of W increases the density and overall strength of the sample. To investigate relatively large deformations multi-material Eulerian and arbitrary Lagrangian-Eulerian methods, which have the ability to efficiently handle the formation of free surfaces, were used. The calculations indicate that the increased strength of the sample with fine metallic particles is due to the formation of force chains under dynamic loading. This phenomenon occurs even at larger porosity of the PTFE matrix in comparison with samples with larger particle size of W and higher density of the PTFE matrix.Comment: 5 pages, 6 figure