Observing the Effects of Temperature and Surface Roughness on Cetyltrimethylammonium Bromide Adsorption Using a Quartz-Crystal Microbalance with Dissipation Monitoring

The effects of temperature and surface roughness on the mass and viscoelasticity of an adsorbed surfactant layer were monitored using a quartz crystal microbalance with dissipation monitoring (QCM-D). Adsorption isotherms at 30, 40, 50, and 60 °C and at two different roughnesses on gold were measured for cetyltrimethylammonium bromide (CTAB). All isotherms displayed an increase in mass and dissipation as surfactant concentration was increased to its critical micelle concentration (CMC). Above the CMC, adsorption reached a peak followed by a slight decrease to a plateau at the equilibrium adsorption value. As the temperature was increased, the adsorbed mass above the CMC decreased. The adsorbed mass decreased further by increasing substrate roughness, while the dissipation remained unchanged within experimental uncertainty. Dynamic adsorption experiments were also conducted at various temperatures for select concentrations above and below the CMC, providing evidence for the importance of different adsorption mechanisms as a function of both surfactant concentration and surface roughness.     

Individual and competitive adsorption of arsenate and phosphate to a high-surface-area iron oxide-based sorbent

Individual and competitive adsorption of arsenate and phosphate were studied on a high-surface-area Fe/Mn-(hydr)oxide sorbent with surface and bulk properties similar to those of two-line ferrihydrite. It has maximum adsorption densities of 0.42 micromol As m(-2) at neutral pH and 1.24 micromol As m(-2) at pH 3. A surface complexation model (SCM) that used the diffuse double layer model was developed that could simulate single and binary sorbate adsorption over pH 4-9. The predominant adsorbed arsenate and phosphate species were modeled as bidentate binuclear surface complexes at low pH and as monodentate complexes at high pH. The model initially overpredicted the inhibition of arsenate adsorption by the presence of phosphate. The overprediction was resolved by separating surface sites into two types: ones to which both arsenate and phosphate bind and a smaller number to which only phosphate binds. The modified model predicted the competitive adsorption of arsenate and phosphate over pH 4-9 at total As concentrations of 6.67 and 80.1 microM and a total P concentration of 129 and 323 microM. The model may be used to predict arsenic adsorption to the sorbent for a given water source based on solution chemistry.     

Reverse osmosis desalting of inland brackish water of high gypsum scaling propensity: kinetics and mitigation of membrane mineral scaling

The potential for mineral scaling that may limit the generation of new potable water resources by reverse osmosis (RO), from inland brackish water of high gypsum scaling propensity, was experimentally explored via flux decline measurements and real-time RO membrane surface imaging. Antagonistic gypsum and calcium carbonate scaling kinetics were demonstrated for high-sulfate brackish water desalting. RO scaling studies with brackish water from the California San Joaquin Valley (approximately 10 000 mg/L total dissolved solids) revealed that membrane gypsum scaling was increasingly retarded with rising bicarbonate concentrations. Crystal growth rate, fractional membrane scale coverage, and flux decline decreased by up to about 63, 78, and 73%, respectively, as the bicarbonate concentration increased, at the membrane surface, from < 0.01 to 7.81 mM, for a gypsum saturation index of 2. Inhibition of gypsum crystal growth was attributed to bicarbonate adsorption onto the crystal surfaces, and CaCO3 scaling was undetected even up to a calcite saturation index of approximately 16. Given the suppression of gypsum scaling by bicarbonate, it is essential to considerthis effect in the conventional practice of pH adjustment to suppress CaCO3 scaling. The present results suggest that antagonistic and synergistic mineral crystallization kinetics effects are important for optimizing scale-control strategies (e.g., acid and antiscalants addition to the RO feed).     

Coadsorption of arsenic(III) and arsenic(V) onto hydrous ferric oxide: effects on abiotic oxidation of arsenic(III), extraction efficiency, and model accuracy

Single solute adsorption and coadsorption of As(III) and As(V) onto hydrous ferric oxide (HFO), oxidation of As(III), and extraction efficiencies were measured in 0.2 atm O2. Oxidation was negligible for single-adsorbate experiments, but significant oxidation was observed in the presence of As(V) and HFO. Single-adsorbate As(III) or As(V) were incompletely extracted (0.5 M NaOH for 20 min), but all As was recovered in coadsorbate experiments. Single-adsorbate data were well-simulated using published surface complexation models, but those models (calibrated for single-adsorbate results) provided poor fits for coadsorbate experiments. An amended model accurately simulated single- and coadsorbate results. Model predictions of significant change in As(III) surface complex speciation in coadsorbate experiments was confirmed using zeta potential measurements. Our results demonstrate that mobility of arsenic in groundwater and removal in engineered treatment systems are more complicated when both As(III) and As(V) are present than anticipated based on single-adsorbate experimental results.     

Minimization of artifacts in sulfuric acid mist measurement using NIOSH Method 7903

NIOSH Method 7903 employs a silica gel tube for sulfuric acid mist measurement in workplaces. However, SO2 gas present in the sample volume can be transformed into sulfate in the sampling process causing an artifact that is reported as sulfuric acid. A sampling train incorporating a honeycomb denuder system was applied for field sampling at seven phosphate fertilizer plants to evaluate its use for reducing the artifact sulfate concentration while preserving the actual sulfuric acid mist concentration. The denuder system was designed to remove SO2 gas before the air entered the silica gel tube and to monitor SO2 concentration at the same time. A deactivation model was also applied to correct for the presence of the artifact. The denuder system had 95.7 +/- 6.8% collection efficiency for SO2 gas, and the impact of sulfate aerosol on SO2 collection was negligible. SO2 concentrations at the seven plants ranged from 34 ppb to 5.6 ppm. The honeycomb denuder system and the deactivation model were shown to reduce the artifact sulfate concentration by 70% and 39%, respectively. However, they were still higher than the sulfate aerosol concentration measured by a cascade impactor. One possible reason is the residual sulfate in the glass fiber filter and the silica gel.     

Green roof valuation: a probabilistic economic analysis of environmental benefits

Green (vegetated) roofs have gained global acceptance as a technologythat has the potential to help mitigate the multifaceted, complex environmental problems of urban centers. While policies that encourage green roofs exist atthe local and regional level, installation costs remain at a premium and deter investment in this technology. The objective of this paper is to quantitatively integrate the range of stormwater, energy, and air pollution benefits of green roofs into an economic model that captures the building-specific scale. Currently, green roofs are primarily valued on increased roof longevity, reduced stormwater runoff, and decreased building energy consumption. Proper valuation of these benefits can reduce the present value of a green roof if investors look beyond the upfront capital costs. Net present value (NPV) analysis comparing a conventional roof system to an extensive green roof system demonstrates that at the end of the green roof lifetime the NPV for the green roof is between 20.3 and 25.2% less than the NPV for the conventional roof over 40 years. The additional upfront investment is recovered at the time when a conventional roof would be replaced. Increasing evidence suggests that green roofs may play a significant role in urban air quality improvement For example, uptake of N0x is estimated to range from $1683 to $6383 per metric ton of NOx reduction. These benefits were included in this study, and results translate to an annual benefit of $895-3392 for a 2000 square meter vegetated roof. Improved air quality leads to a mean NPV for the green roof that is 24.5-40.2% less than the mean conventional roof NPV. Through innovative policies, the inclusion of air pollution mitigation and the reduction of municipal stormwater infrastructure costs in economic valuation of environmental benefits of green roofs can reduce the cost gap that currently hinders U.S. investment in green roof technology.     

Colour improvement of common carp (Cyprinus carpio) fillets by hydrogen peroxide for surimi production

The preferred colour for surimi is white, but surimi prepared from light fillets of common carp (Cyprinus carpio) is slightly pink. Hydrogen peroxide (H₂O₂; 1–3% v/v) with and without sodium tri‐polyphosphate (STP; 1–2% w/v) was added to a sodium carbonate bath (pH 7.0–11.5) resulting in a final pH range of 4.4–10.1 which was injected into carp fillets. After soaking and tumbling for 30 min at 4–10 °C, the fillets were evaluated for colour and water holding capacity (WHC). Fillets tumbled with treatment solution with different pH levels (7.0–11.5), but with no H₂O₂ or STP added, had improved colour with significantly (P < 0.05) higher L* compared with untreated fillets as the control. However, the colour improvement [(L* and colour deviation (ΔE)] was not significantly different (P > 0.05) within the pH levels (7.0–11.5) trialled. With increasing H₂O₂ levels (1–3%), fillets became lighter and ΔE increased significantly (P < 0.05), especially with a 3% H₂O₂ treatment at pH of 10.5 (adjusted pH before H₂O₂ addition, actual pH after H₂O₂ addition was 8.2). The whiteness (L*?3b*) of kamaboko produced from treated (3% H₂O₂, pH 10.5) common carp light fillets was not significantly different to that of kamaboko from Alaska pollock and threadfin bream. Treatments combining H₂O₂ (3%) with STP (1–2%) significantly reduced the L* value obtained in comparison with fillets treated with only H₂O₂ (3%). Similarly, fillets treated with STP (1%) alone, resulting in lower L* values, irrespective of treatment pH (7.0–11.5). WHC, an indicator of the quality of the fillet texture, increased from 816 g/kg at pH 7.0 without STP to 841 g/kg at pH 11.5 with 1% STP. Treatment with H₂O₂ (without STP) decreased the WHC of the fillets.