• Canada
• Natural Sciences and Engineering Research Council of Canada close
• 6. Clean water close

The physical properties of confined water can differ dramatically from those of bulk water. Hydration water associated with polysaccharides provides a particularly interesting example of confined water, because differences in polysaccharide structure provide different spatially confined environments for water sorption. We have used attenuated total reflection infrared (ATR-IR) spectroscopy to investigate the structure of hydration water in films of three different polysaccharides under controlled relative humidity (RH) conditions. We compare the results obtained for films of highly branched, dendrimer-like phytoglycogen nanoparticles to those obtained for two unbranched polysaccharides, hyaluronic acid (HA), and chitosan. We find similarities between the water structuring in the two linear polysaccharides and significant differences for phytoglycogen. In particular, the results suggest that the high degree of branching in phytoglycogen leads to a much more well-ordered water structure (low density, high connectivity network water), indicating the strong influence of chain architecture on the structuring of water. These measurements provide unique insight into the relationship between the structure and hydration of polysaccharides, which is important for understanding and exploiting these sustainable nanomaterials in a wide range of applications.

The presence of micropollutants in the environment has triggered research on quantifying and predicting their fate in wastewater treatment plants (WWTPs). Since the removal of micropollutants is highly related to conventional pollutant removal and affected by hydraulics, aeration, biomass composition and solids concentration, the fate of these conventional pollutants and characteristics must be well predicted before tackling models to predict the fate of micropollutants. In light of this, the current paper presents the dynamic modelling of conventional pollutants undergoing activated sludge treatment using a limited set of additional daily composite data besides the routine data collected at a WWTP over one year. Results showed that as a basis for modelling, the removal of micropollutants, the Bürger-Diehl settler model was found to capture the actual effluent total suspended solids (TSS) concentrations more efficiently than the Takács model by explicitly modelling the overflow boundary. Results also demonstrated that particular attention must be given to characterizing incoming TSS to obtain a representative solids balance in the presence of a chemically enhanced primary treatment, which is key to predict the fate of micropollutants.

Abstract The performance of a grooved copper-water thermosyphon with a modest bend between a vertical evaporator section and inclined condenser section was characterized for a moderate fluid loading. The time-averaged temperature varied significantly along the evaporator for heat fluxes up to 10 W/cm2 before becoming more uniform at higher heat fluxes. Transients of the measured temperatures show evidence of different flow regimes that were compared to existing flow pattern maps. The evaporator performance for both the pool region, which had the highest temperature, and the film region were not well predicted for heat fluxes up to 10 W/cm2. The local evaporator performance changed with the change in flow regime, suggesting the need for a flow regime-based performance model. The performance of the condenser appeared to depend on the reduced pressure and was significantly overpredicted by the standard condensation models. A modified model for the condenser was proposed.

In temperate lakes, early springs typically lead to a weak thermal stratification involving water both above and below the temperature at which the density maximum occurs. This implies that mixing of two parcels with the same density, but different temperature, can lead to the creation of denser fluid: a phenomenon known as cabbeling. Here we document the nature of the three-dimensionalization of shear instability at moderate Reynolds number in the cabbeling regime of freshwater.

Experimental investigations were carried out to investigate the effect of thermo-chemical exposures on the hydraulic performance of Compacted Clay Liners (CCLs) in landfills. Hydraulic conductivity of most CCL specimens was increased by two to three times their initial values when exposed to 55 °C for 75 days. CCL specimens also experienced increases in their hydraulic conductivities when exposed to leachate at room temperature. This behaviour could be due to the decrease in viscosity when the permeant was changed from tap water to leachate. However, as the leachate exposure time exceeded the first 15 days, hydraulic conductivity readings decreased to as much as one order of magnitude after 75 days of leachate permeation at room temperature. The gradual decrease in the CCLs hydraulic conductivities was most likely due to chemical precipitation and clogging of pore voids within the soils which seemed to reduce the effective pore volume. The rate of hydraulic conductivity reduction due to leachate permeation was slower at higher temperatures, which was attributed to the lower permeant viscosity and lower clogging occurrence. The observed hydraulic behaviours were correlated to the physical, mineral, and chemical properties of the CCLs and described below.

Summary In this study, a new integrated solar-energy based system for fresh water and electricity production is proposed and thermodynamically analyzed. The proposed system consists of a solar tower with a volumetric solar receiver, a Rankine cycle driven by solar power, molten salt storage subsystem and a multi-stage flash distillation (MFD) subsystem. In the present system, solar tower charges the molten salt, which flows through a heat exchanger to produce steam for the Rankine cycle. A part of the molten salt directly goes to hot storage tank after they are heated up by the solar tower. In order to keep the generated energy at the same level, molten salt in the hot storage tank compensates the deficient energy when direct normal irradiance (DNI) level is not sufficient. After the sunset, only the molten salt from the storage supplies energy to the cycle. The MFD produces the desired amount of fresh water from seawater. The seawater used for the distillation is heated by the saturated steam-water mixture coming from the steam turbine. Utilizing the output fluid as a heat source for the MFD also eliminates the external device for condensation. All system components of the integrated system are analyzed in the Engineering Equation Solver (EES). The overall energy and exergy efficiencies are calculated for each system component. The capacity of the power generation and fresh water production of the proposed system is also calculated. Moreover, a parametric study is undertaken to investigate the effects of varying ambient conditions on the system performance.

Aqueous phase diffusion-related isotope fractionation (DRIF) for carbon isotopes was investigated for common groundwater contaminants in systems in which transport could be considered to be one-dimensional. This paper focuses not only on theoretically observable DRIF effects in these systems but introduces the important concept of constraining "observable" DRIF based on constraints imposed by the scale of measurements in the field, and on standard limits of detection and analytical uncertainty. Specifically, constraints for the detection of DRIF were determined in terms of the diffusive fractionation factor, the initial concentration of contaminants (C0), the method detection limit (MDL) for isotopic analysis, the transport time, and the ratio of the longitudinal mechanical dispersion coefficient to effective molecular diffusion coefficient (Dmech/Deff). The results allow a determination of field conditions under which DRIF may be an important factor in the use of stable carbon isotope measurements for evaluation of contaminant transport and transformation for one-dimensional advective-dispersive transport. This study demonstrates that for diffusion-dominated transport of BTEX, MTBE, and chlorinated ethenes, DRIF effects are only detectable for the smaller molar mass compounds such as vinyl chloride for C0/MDL ratios of 50 or higher. Much larger C0/MDL ratios, corresponding to higher source concentrations or lower detection limits, are necessary for DRIF to be detectable for the higher molar mass compounds. The distance over which DRIF is observable for VC is small (less than 1m) for a relatively young diffusive plume (<100years), and DRIF will not easily be detected by using the conventional sampling approach with "typical" well spacing (at least several meters). With contaminant transport by advection, mechanical dispersion, and molecular diffusion this study suggests that in field sites where Dmech/Deff is larger than 10, DRIF effects will likely not be observable for common groundwater contaminants. Importantly, under most field conditions, Dmech/Deff≥10 is usually satisfied in the longitudinal direction, suggesting that DRIF is not likely to be observable in most groundwater systems in which contaminant transport is predominantly one-dimensional. Given the importance in the MDL it is recommended that MDL should always be explicitly reported in both modeling and field studies.

Abstract The confined impeller stirred tank (CIST) is a test cell designed to scale down elevated local mixing conditions to the bench scale in a more uniform mixing field than the conventional stirred tank. In this study a zone flow model was developed to describe the flow in the vessel, based on mean and fluctuating velocities measured using a laser Doppler velocimeter (LDV). A set of 5 Rushton turbines were used for this first model with water as the test fluid. The impeller rotational speed was kept high enough to ensure fully turbulent flow in the entire vessel (Re ≥ 20 000). It is shown that all five impeller discharge streams have similar behaviours and that the jet leaving the impeller blades does not expand axially as much as the discharge flow in a single impeller stirred tank because the confined return flow reduces the jet width. The radial decay of mean velocity close to the centerline of the blades is proportional to 1/r, and the radial decay of energy dissipation is proportional to 1/r2. A single impeller stirred tank presents a much faster decay of dissipation proportional to 1/r4. Based on these results, and a number of other experimental measurements, the tank was divided into 5 volumes or zones. A zone flow model was developed to describe the flowrate and dissipation rate in each zone, giving the mean residence time and mixing energy for each zone as outputs. It is shown that the CIST has a more uniformly distributed energy dissipation (emax/eave = 8.3) than a single impeller stirred tank (emax/eave > 20).

Naphthalene sulfonic acids (NSAs) are used extensively in industrial applications as dispersants in dyes, rubbers, and pesticides, and as anti-corrosive agents in coatings, gels, and sealants. This study examined the toxicity of three NSA congeners, barium dinonylnaphthalene sulfonate (BaDNS), calcium dinonylnaphthalene sulfonate (CaDNS), and dinonylnaphthalene disulfonic acid (DNDS), to two benthic species, Tubifex tubifex and Hyalella azteca. Two substrates with different levels of organic carbon (sediment [2%] and sand [0%]) were used in toxicity tests. Juvenile production was the most sensitive endpoint for T. tubifex: the 28-d EC50s were18.2, 22.2, and 64.0 μg/g dw in sand and 281.3, 361.6, and 218.9 μg/g dw in sediment for BaDNS, CaDNS, and DNDS, respectively. The 28-d LC50s for H. azteca were similar among compounds: 115.3, 82.1, and 49.0 μg/g dry weight (dw) in sand, and 627.3, 757.9, and188.5 μg/g dw in sediment, for BaDNS, CaDNS, and DNDS, respectively. However, when LC50s were estimated based on concentrations of NSAs measured in overlying water (which can be an important route of exposure for H. azteca), BaDNS and CaDNS were 3-4 orders of magnitude more toxic than DNDS. The NSAs examined were3-fold more toxic when present in substrates with no organic carbon (e.g., sand) for all H. azteca endpoints where LC/EC50s could be calculated and for sublethal endpoints for T. tubifex. The organic carbon content of the sediment appears to have acted as a sink and reduced NSA toxicity by decreasing bioavailability. Environmental sediment samples were collected from 12 river sites across southern Ontario. The maximum concentration of CaDNS observed in sediment collected from this region was 2.8 μg/g dw in sediment with 2% organic carbon; 100-fold lower than the lowest EC10 in the current study.