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Concept: Settling


Laboratory experiments were carried out to study the effects of slow mixing conditions on magnesium hydroxide floc size and strength and to determine the turbidity and total suspended solid (TSS) removal efficiencies during coagulation of highly turbid suspensions. A highly turbid kaolin clay suspension (1,213 ± 36 nephelometric turbidity units (NTU)) was alkalized to pH 10.5 using a 5 M NaOH solution; liquid bittern (LB) equivalent to 536 mg/L of Mg(2+) was added as a coagulant, and the suspension was then subjected to previously optimized fast mixing conditions of 100 rpm and 60 s. Slow mixing speed (20, 30, 40, and 50 rpm) and time (10, 20, and 30 min) were then varied, while the temperature was maintained at 20.7 ± 1 °C. The standard practice for coagulation-flocculation jar test ASTM D2035-13 (2013) was followed in all experiments. Relative floc size was monitored using an optical measuring device, photometric dispersion analyzer (PDA 2000). Larger and more shear resistant flocs were obtained at 20 rpm for both 20- and 30-min slow mixing times; however, given the shorter duration for the former, the 20-min slow mixing time was considered to be more energy efficient. For slow mixing camp number (Gt) values in the range of 8,400-90,000, it was found that the mixing speed affected floc size and strength more than the time. Higher-turbidity removal efficiencies were achieved at 20 and 30 rpm, while TSS removal efficiency was higher for the 50-rpm slow mixing speed. Extended slow mixing time of 30 min yielded better turbidity and TSS removal efficiencies at the slower speeds.

Concepts: Colloid, Physical quantities, Calcium hydroxide, Suspension, Total suspended solids, Flocculation, Turbidity, Settling


Successful recruitment in corals is important for the sustenance of coral reefs, and is considered a demographic bottleneck in the recovery of reef populations following disturbance events. Yet several factors influence larval settlement behaviour, and here we quantified thresholds associated with light attenuation and accumulated sediments on settlement substrates. Sediments deposited on calcareous red algae (CRA) directly and indirectly impacted coral settlement patterns. Although not avoiding direct contact, Acropora millepora larvae were very reluctant to settle on surfaces layered with sediments, progressively shifting their settlement preference from upward to downward facing (sediment-free) surfaces under increasing levels of deposited sediment. When only upward-facing surfaces were presented, 10% of settlement was inhibited at thresholds from 0.9 to 16mgcm(-2) (EC10), regardless of sediment type (carbonate and siliciclastic) or particle size (fine and coarse silt). These levels equate to a very thin (<150μm) veneer of sediment that occurs within background levels on reefs. Grooves within settlement surfaces slightly improved options for settlement on sediment-coated surfaces (EC10: 29mgcm(-2)), but were quickly infilled at higher deposited sediment levels. CRA that was temporarily smothered by sediment for 6d became bleached (53% surface area), and inhibited settlement at ~7mgcm(-2) (EC10). A minor decrease in settlement was observed at high and very low light intensities when using suboptimal concentrations of a settlement inducer (CRA extract); however, no inhibition was observed when natural CRA surfaces along with more realistic diel-light patterns were applied. The low deposited sediment thresholds indicate that even a thin veneer of sediment can have consequences for larval settlement due to a reduction of optimal substrate. And while grooves and overhangs provide more settlement options in high deposition areas, recruits settling at these locations may be subject to ongoing stress from shading, competition, and sediment infilling.

Concepts: Algae, Sediment, Coral, Coral reef, Scleractinia, Sedimentary rock, Silt, Settling


Typicalin vitroassays used for high throughput toxicological screening and measuring nano-bio interactions are conducted by pipetting suspensions of engineered nanomaterials (ENMs) dispersed in nutrient-rich culture media directly onto cells. In order to achieve fairly monodisperse and stable suspensions of small agglomerates, ultrasonic energy is usually applied to break apart large agglomerates that can form upon suspension in liquid. Lack of standardized protocols and methods for delivering sonication energy can introduce variability in the ENM suspension properties (e.g. agglomerate size, polydispersity, suspension stability over time), and holds significant implications forin vitrodosimetry, toxicity, and other nano-bio interactions. Careful assessment of particle transformations during dispersion preparation and sonication is therefore critical for accurate interpretation ofin vitrotoxicity studies. In this short communication, the difficulties of preparing stable suspensions of rapidly settling ENMs are presented. Furthermore, methods to optimize the delivery of the critical sonication energy required to break large agglomerates and prepare stable, fairly monodispersed suspensions of fast settling ENMs are presented. A methodology for the efficient delivery of sonication energy in a discrete manner is presented and validated using various rapidly agglomerating and settling ENMs. The implications of continuousvs.discrete sonication on average hydrodynamic diameter, and polydispersity was also assessed for both fast and slow settling ENMs. For the rapidly agglomerating and settling ENMs (Ag15%/SiO2, Ag and CeO2), the proposed discrete sonication achieved a significant reduction in the agglomerate diameter and polydispersity. In contrast, the relatively slow agglomerating and settling Fe2O3suspension did not exhibit statistically significant differences in average hydrodynamic diameter or polydispersity between the continuous and discrete sonication approaches. Our results highlight the importance of using the proposed material-specific discrete sonication method to effectively deliver the critical sonication energy necessary to reproducibly achieve stable and fairly monodispersed suspensions that are suitable forin vitrotoxicity testing.

Concepts: Statistics, Fluid dynamics, Statistical significance, Ronald Fisher, Statistical hypothesis testing, P-value, Suspension, Settling


It remains unclear how the primary particle concentration and salinity conditions influence the flocculation and settling characteristics of water-sediment suspensions. In this study, two sets of experiments were performed to examine the flocculation and settling properties of low- and high-concentration sediment suspensions. In low-concentration suspensions, the sediment concentration undergoes a rapid initial decrease followed by a slow decrease until it approaches zero with increasing flocculation time. Increases in salinity or the valence of cations from the saline solution added to the suspension lead to a more rapidly decreasing sediment concentration with flocculation time. The valence of cations from the saline solution has a larger influence on the flocculation-settling behaviours of the suspension than the salinity. In high-concentration sediment suspensions, the height of the clear water-turbid water interface in the water-sediment suspension experiences an initial, rapidly decreasing phase followed by a slowly decreasing phase with increasing flocculation time. Increasing the primary particle concentration, salinity or valence of cations from the saline solution added to the suspension causes the height reduction of the clear water-turbid water interface to become gentler. Finally, the valence of cations from the saline solution has a greater influence on the settling characteristics of the high-concentration water-sediment suspension than the salinity.

Concepts: Chemistry, Colloid, Solution, Colloidal chemistry, Suspension, Flocculation, Sedimentation, Settling


An experimental study dedicated to the characterization of the settleability of solids produced in immersed fixed media biofilm reactors has been carried out. The influence of operating temperature (0.1 to 16 °C) and surface organic loading rate (OLR) (0.4 to 10 g of soluble carbonaceous BOD5 per m2 of media per day) on settleable solids quantities, particle size distributions (PSD) as well as flocs morphology was evaluated. Results have shown that the OLR has no statistically significant influence on the settleability of the suspended solids. However, the operating temperature was identified as a factor that significantly influences the settling potential. The highest operating temperatures (14-16 °C) were related to the worst settling performances. On the other hand, the best settling performances were observed at intermediate operating temperatures (around 10 °C). The latter conditions were also associated with the largest fractions of large particles (>100 μm) in the effluent. Differences in PSD were found to be well correlated with settling performances. Part of the performance results variability which cannot be explained by differences in PSD can potentially be attributed to differences in flocs morphology (compactness).

Concepts: Statistics, Temperature, Solubility, Solid, Liquid, Gas, Operating temperature, Settling


The purpose of this study is to describe the methods used to capture flow-weighted water and suspended particulates from farm canals during drainage discharge events. Farm canals can be enriched by nutrients such as phosphorus (P) that are susceptible to transport. Phosphorus in the form of suspended particulates can significantly contribute to the overall P loads in drainage water. A settling tank experiment was conducted to capture suspended particulates during discrete drainage events. Farm canal discharge water was collected in a series of two 200 L settling tanks over the entire duration of the drainage event, so as to represent a composite subsample of the water being discharged. Imhoff settling cones are ultimately used to settle out the suspended particulates. This is achieved by siphoning water from the settling tanks via the cones. The particulates are then collected for physico-chemical analyses.

Concepts: Agriculture, Transport, Irrigation, Aqueduct, Canal, Drainage, Imhoff tank, Settling


Sewer sediments and their associated contaminant released along with wet-weather discharges pose potential pollution risks to environment. This paper presents total characteristics of sediments collected from Jiaxing, China. Size distribution and concentrations of volatile solids (VS) and four metals (Pb, Cu, Zn, Cr) of sediment samples from seven land use categories were analyzed. Then, the sediment samples were graded five fractions according to its settling velocity through the custom-built settling velocity-grading device. Sediment mass and pollution load distribution based on settling velocity were also assessed. The results show that there are relatively high level of heavy metal load in the sediment of separated storm drainage systems in Jiaxing, especially for the catchment of residential area (RA), road of developed area (RDA), and industrial area (IA). Although grain size follows a trend of increasing along with settling velocity, the methods of settling velocity grading are meaningful for stormwater treatment facilities with precipitation. For all land use categories, the pollution concentrations of the three lower settling velocity-fractionated sediment are relatively consistent and higher than others. Combined with mass distribution, the pollution percentage of fraction with different velocities for seven land use categories were also evaluated. Based on it, the statistical conclusion of design target settling velocity to different pollution load removal rates are drawn, which is helpful to guide design of on-site precipitation separation facilities.

Concepts: Sediment, Water pollution, Mass, Kinetic energy, Storm, Heavy metal music, Silt, Settling


Ex-situ and in-situ techniques were used to characterize the suspended phase over time for a vaccine drug product supplied in syringes. Micro-CT was used to characterize the suspended sediment in-situ in the syringe, while traditional techniques such as particle size distribution, charge (zeta potential), settling rate and front-faced-fluorescence were used to characterize the suspension ex-situ. In addition, analytical chemical measurements were conducted in parallel during the course of the study. The ex-situ and in-situ techniques together with the chemical analyses provided different sets of data, but all leading to the same conclusion that the older hard to re-disperse vaccine product syringes were similar in product quality attributes (both physical and chemical) to the freshly made easy to re-disperse syringes. Longer re-dispersion time with age was not a result of any altered physical or chemical attributes of the product but simply because of the distance travelled by the sediment from the neck of the syringe barrel deeper into the bore of the syringe over time under the influence of gravity in the tip down orientation; making it harder for the continuous external phase to access the sediment in the bore and enable easy re-dispersion.

Concepts: Sediment, Colloid, Particle size distribution, Colloidal chemistry, Chemical engineering, Syringe, Suspension, Settling


The impact of anthropogenic activities on coastal waters is a cause of concern because such activities add to the total suspended sediment (TSS) budget of the coastal waters, which have negative impacts on the coastal ecosystem. Satellite remote sensing provides a powerful tool in monitoring TSS concentration at high spatiotemporal resolution, but coastal managers should be mindful that the satellite-derived TSS concentrations are dependent on the satellite sensor’s radiometric properties, atmospheric correction approaches, the spatial resolution and the limitations of specific TSS algorithms. In this study, we investigated the impact of different spatial resolutions of satellite sensor on the quantification of TSS concentration in coastal waters of northern Western Australia. We quantified the TSS product derived from MODerate resolution Imaging Spectroradiometer (MODIS)-Aqua, Landsat-8 Operational Land Image (OLI), and WorldView-2 (WV2) at native spatial resolutions of 250 m, 30 m and 2 m respectively and coarser spatial resolution (resampled up to 5 km) to quantify the impact of spatial resolution on the derived TSS product in different turbidity conditions. The results from the study show that in the waters of high turbidity and high spatial variability, the high spatial resolution WV2 sensor reported TSS concentration as high as 160 mg L-1 while the low spatial resolution MODIS-Aqua reported a maximum TSS concentration of 23.6 mg L-1. Degrading the spatial resolution of each satellite sensor for highly spatially variable turbid waters led to variability in the TSS concentrations of 114.46%, 304.68% and 38.2% for WV2, Landsat-8 OLI and MODIS-Aqua respectively. The implications of this work are particularly relevant in the situation of compliance monitoring where operations may be required to restrict TSS concentrations to a pre-defined limit.

Concepts: Optics, Water pollution, Water quality, Remote sensing, Total dissolved solids, Total suspended solids, Turbidity, Settling


Fast and reliable methods to determine biomass concentration are necessary to facilitate the large scale production of microalgae. A method for the rapid estimation of Chlorella sorokiniana biomass concentration was developed. The method translates the suspension particle size spectrum gathered though laser reflectance into biomass concentration by means of two machine learning modelling techniques. In each case, the model hyper-parameters were selected applying a simulated annealing algorithm. The results show that dry biomass concentration can be estimated with a very good accuracy (R(2=)0.87). The presented method seems to be suited to perform fast estimations of biomass concentration in suspensions of microalgae cultivated in moderately turbid media with tendency to aggregate.

Concepts: Model, Monte Carlo method, Estimation, Solution, Colloidal chemistry, Suspension, Tabu search, Settling