Suspended Particle Size Distribution Research Articles

Developing a customized laboratory setup to assess sensors for real-time suspended sediment monitoring

Abstract Sedimentation challenges water reservoir operations globally, particularly for storage hydropower plants (HPPs), necessitating effective management strategies. One such strategy, fine sediment venting through turbines, though effective in managing sediment continuity, increases hydro-abrasive erosion on turbines due to the additional sediment load. Hence, there is a need for precise real-time monitoring of suspended sediments. Existing systems, however, often lack the capability to measure suspended sediment mass concentration (SSC) and particle size distribution (PSD) with low uncertainty, particularly for coarser particles, such as sand. To maintain particles with sizes up to 2 mm in suspension, which is the size of particles vented through the power waterways of the turbines, this study developed a customized laboratory setup with an upward flow column and a closed pump circuit. To foster a homogeneous SSC distribution, the setup was hydraulically optimized by different diffusor designs at the inlet of the upward flow column. We tested particles ranging from 1500 - 2000 μm at SSCs up to 20 gl−1 with optical and acoustic sensors to prove our concept. First results yielded as expected mostly linear relationships between instrument outputs and nominal SSC, particularly for larger particles. This indicates that the setup allows keeping particles up to 2 mm in suspension, enabling further measurement series to better understand the impacts of sand particles in combination with silt on sensor performance. This is crucial for enhancing suspended sediment monitoring capabilities for fine sediment venting at HPPs.

Hydro-sedimentological drivers of fine sediment ingress in a gravel-bed river

Most studies investigating fine sediment ingress in gravel-bed rivers have been conducted at the laboratory scale, and even fewer have explored the ingress processes of flocculated particles. Here, an extensive in-situ sampling programme was undertaken to investigate hydro-sedimentological drivers of interstitial fine sediment accumulation and to evaluate fine sediment ingress directional mechanisms in a gravel-bed river located on the eastern slopes of the Rocky Mountains in southern Alberta. Three sediment trap designs were installed across seven deployment cycles at four sites along the river. Instantaneous discharge, suspended solids concentration, and particle size distributions (of suspended and ingressed particles) were measured, while relevant hydraulic parameters were modelled with a flow model (MOBED). Distinct patterns of ingress dynamics between non-cohesive and cohesive fractions of fine sediment were observed. While the assessed hydro-sedimentological parameters did not statistically explain the ingress rates of non-cohesive 0.5 – 2 mm particles, the opposite was observed for < 0.5 mm particles, which were mostly transported in flocculated form. For flocculated sediment, horizontal ingress accounted for ∼ 60 % of interstitial accumulation. Directional ingress mechanisms, however, were dependent on flow conditions for both particle size fractions, with vertical and horizontal accumulations becoming more important during higher and lower energy flows, respectively. Our observations demonstrate the importance of ingress for the interstitial accumulation of fine sediment, even during events with flow above the critical threshold conditions for fine sediment gravitational deposition. Despite the comparable ingress rates to other studies, no interstitial clogging was observed in this study, demonstrating the channel potential storage capacity, which has implications for legacy impacts from landscape disturbances in the Crowsnest River catchment.

Monitoring the impacts of rainfall characteristics on sediment loss from road construction sites

Exposed soils associated with active construction sites provide opportunities for erosion and sediment transport during storm events, introducing risks associated with excess sediment to downstream infrastructure and aquatic biota. A better understanding of the drivers of sediment transport in construction site runoff is needed to improve the design and performance of erosion and sediment control measures (ESCMs). Eleven monitoring locations on 3 active road construction sites in central Ohio were established to characterize runoff quality from points of concentrated flow during storm events. Grab samples were analyzed for total suspended solids (TSS), turbidity, and particle size distribution (PSD). Median TSS concentrations and turbidity levels across all samples were 626 mg/L (range 25–28,600 mg/L) and 759 NTU (range 22–33,000 NTU), respectively. The median PSD corresponded to a silty clay loam, mirroring the soil texture of much of Ohio’s subsoils. TSS concentrations and turbidity were significantly positively correlated with the rainfall intensity 10 min prior to sample collection, suggesting that higher flow rates created greater shear stress on bare soil which resulted in more erosion. Conversely, rainfall duration was negatively correlated with particle size, indicating that prolonged moisture from rainfall promoted the dispersion of soil aggregates which mobilized smaller particles. Multivariable linear regression models revealed that higher rainfall intensities corresponded to higher turbidity values, while higher TSS concentrations were associated with higher rainfall intensities, depths, and durations. Results from this study highlight the importance of reducing raindrop impact and subsequent shear stress applied by concentrated flows through the use of ESCMs to limit sediment export from construction sites.

Ocean color algorithm for the retrieval of the particle size distribution and carbon-based phytoplankton size classes using a two-component coated-sphere backscattering model

Abstract. The particle size distribution (PSD) of suspended particles in near-surface seawater is a key property linking biogeochemical and ecosystem characteristics with optical properties that affect ocean color remote sensing. Phytoplankton size affects their physiological characteristics and ecosystem and biogeochemical roles, e.g., in the biological carbon pump, which has an important role in the global carbon cycle and thus climate. It is thus important to develop capabilities for measurement and predictive understanding of the structure and function of oceanic ecosystems, including the PSD, phytoplankton size classes (PSCs), and phytoplankton functional types (PFTs). Here, we present an ocean color satellite algorithm for the retrieval of the parameters of an assumed power-law PSD. The forward optical model considers two distinct particle populations: phytoplankton and non-algal particles (NAPs). Phytoplankton are modeled as coated spheres following the Equivalent Algal Populations (EAP) framework, and NAPs are modeled as homogeneous spheres. The forward model uses Mie and Aden–Kerker scattering computations, for homogeneous and coated spheres, respectively, to model the total particulate spectral backscattering coefficient as the sum of phytoplankton and NAP backscattering. The PSD retrieval is achieved via spectral angle mapping (SAM), which uses backscattering end-members created by the forward model. The PSD is used to retrieve size-partitioned absolute and fractional phytoplankton carbon concentrations (i.e., carbon-based PSCs), as well as particulate organic carbon (POC), using allometric coefficients. This model formulation also allows the estimation of chlorophyll a concentration via the retrieved PSD, as well as percent of backscattering due to NAPs vs. phytoplankton. The PSD algorithm is operationally applied to the merged Ocean Colour Climate Change Initiative (OC-CCI) v5.0 ocean color data set. Results of an initial validation effort are also presented using PSD, POC, and picophytoplankton carbon in situ measurements. Validation results indicate the need for an empirical tuning for the absolute phytoplankton carbon concentrations; however these results and comparison with other phytoplankton carbon algorithms are ambiguous as to the need for the tuning. The latter finding illustrates the continued need for high-quality, consistent, large global data sets of PSD, phytoplankton carbon, and related variables to facilitate future algorithm improvements.

Dual wavelength laser Doppler anemometer for simultaneous velocity and particulate size distribution measurements in submarine environments.

An in-situ laser Doppler current probe (LDCP) for the simultaneous measurements of the micro-scale subsurface current speed and the characterizations of micron particles is dedicated in this paper. The LDCP performs as an extension sensor for the state-of-the-art laser Doppler anemometry (LDA). The all-fiber LDCP utilized a compact dual wavelength (491 nm and 532 nm) diode pumped solid state laser as the light source to achieve the simultaneous measurements of the two components of the current speed. Besides its ability for the measurements of the current speed, the LDCP is also capable of obtaining the equivalent spherical size distribution of the suspended particles within small size range. The micro-scale measurement volume formed by two intersecting coherent laser beams makes it possible to accurately estimate the size distribution of the micron suspended particles with high temporal and spatial resolution. With its deployment during the field campaign at Yellow Sea, the LDCP has been experimentally demonstrated as an effective instrument to capture the micro-scale subsurface ocean current speed. The algorithm for retrieving the size distribution of the small suspended particles (2∼7.5µm) has been developed and validated. The combined LDCP system could be applied to the continuous long-term observations of plankton community structure, ocean water optical parameter over a wide range, and useful to elucidate the processes and interactions of the carbon cycles in the upper ocean.

In-Stream Laser Diffraction for Measuring Suspended Sediment Concentration and Particle Size Distribution in Rivers: Insights from Field Campaigns

This study evaluates the laser in situ scattering and transmissometry (LISST) instrument LISST-SL2, a laser diffraction instrument for suspended sediment sampling in rivers, with concurrent physical measurements of suspended sediment concentration (SSC) and particle size distribution (PSD) as well as velocity measurements by an acoustic Doppler current profiler (ADCP). We collected 136 LISST-SL2 samples along with 61 physical samples for SSC measurement, of which 24 physical samples included PSD measurement during 2018–2020 from 11 sites in Washington state and Virginia. An effective density is required to convert the measured volumetric SSC by the LISST-SL2 into a reported mass SSC, and by default the LISST-SL2 assumes a value of 2.65 g/mL. From our data set, we computed effective densities (mass SSC/volumetric SSC) that ranged from 0.5 to 5.4 g/mL, with a best-fit value of 2.05 g/mL. Additionally, the LISST-SL2 was not able to measure the finest sediment sizes in suspension, which affects the resulting PSD. Therefore, we propose some adjustments of the LISST-SL2 data with a supporting physical sample to account for these effective density and PSD issues. When doing so, we were able to reduce the root-mean square relative error (RMSRE) to 18% from 117% for SSC, and to 26% from 78% for PSD. LISST-SL2 velocities were generally higher than ADCP velocities with a 21% RMSRE. Our results and guidance will allow for more accurate sampling by the LISST-SL2, which has potential for studying spatial and temporal variation of suspended sediment characteristics in rivers.

Effect of mixed magnetic field on physical properties of atmospheric suspended fine particles

In recent years, the fine particles suspended in the atmosphere, especially the particle size less than 10 μm, have caused very adverse effects on the climate environment and human health. However, the current research on the causes of air pollution mainly focuses on human activities and weather conditions. Considering the weak magnetism and chargeability of atmospheric fine particles, this study proposed a new view that space electromagnetic radiation may affect the physical properties of fine particles. We first analyzed the dynamic characteristics of magnetic micro-particle in the electromagnetic environment, and built a simulation model in the COMSOL simulation software. Finally, based on the theoretical analysis and simulation results, we built an experimental verification system to evaluate the effects of electromagnetic radiation on the physical properties of micro-particle, and carried out a 30-day control experiment. The experimental results showed that the physical properties such as particle size distribution, mass concentration, and morphology of suspended fine particles in the atmosphere under electromagnetic radiation are significantly different from those under non-electromagnetic radiation environment. It can be inferred that the aggregation, fusion, and deposition of suspended particles in the atmosphere are closely related to the complex electromagnetic environment in space.

Observations of Suspended Particulate Matter Concentrations and Particle Size Distributions within a Macrotidal Estuary (Port Curtis Estuary, Australia)

An understanding of suspended particulate matter (SPM) dynamics is of great importance to design awareness and management strategies of estuaries. Using a Laser In Situ Scattering and Transmissiometry (LISST) instrument, variations in suspended particle size volumetric concentrations (VC) and particle size distributions (PSD) were measured at six sites within Port Curtis estuary (Australia). The port is a macrotidal estuary with significant economic and environmental importance. Observed VC and SPM sizes demonstrated spatial and temporal trends strongly controlled by the variable energy conditions operating on the neap and spring cycle timescale, with a clear trend towards increasing concentrations and decreasing SPM sizes with increasing tidal ranges. Mid-estuary sites were characterized by the greatest depth-averaged VC under transitional and spring conditions. Estuary-wide mean spring tide total water profile concentrations revealed a near 300% increase in comparison to neap tide condition concentrations. In the upper-estuary sites the mean contribution of the combined 2.5–35 µm size classes to the total profile PSDs was greatest during all tidal conditions, whilst within the lower-estuary site the combined 35–130 µm size classes were greatest. Mean contributions of the largest size class (300–500 µm) dominated surface-waters throughout the estuary during the neap tide period, which when compared with the transitional and spring tide conditions, demonstrated changes of −82% to −48% and −82% to −40%, respectively. Overall, the results from this case study provides further evidence of the important influence of neap and spring tidal regimes on SPM dynamics within estuarine settings and the need to observe parameter dynamics on such timescales.

FlocARAZI: An In‐Situ, Image‐Based Profiling Instrument for Sizing Solid and Flocculated Suspended Sediment

AbstractAn inexpensive and compact underwater digital camera imaging system was developed to collect in situ high resolution images of flocculated suspended sediment at depths of up to 60 meters. The camera has a field of view of 3.7 × 2.8 mm and can resolve particles down to 5 . Depending on the degree of flocculation, the system is capable of accurately sizing particles to concentrations up to 500 mg/L. The system is fast enough to allow for profiling whereby size distributions of suspended particles and flocs can be provided at multiple verticals within the water column over a relatively short amount of time (approximately 15 min for a profile of 15 m). Using output from image processing routines, methods are introduced to estimate the mass suspended sediment concentration (SSC) from the images and to separate identified particles into sand and mud floc populations. The combination of these two methods allows for the size and concentration estimates of each fraction independently. The camera and image analysis methods are used in both the laboratory and the Mississippi River for development and testing. Output from both settings are presented in this study.

A comparison study on the sediment flocculation process between a bare tidal flat and a clam aquaculture mudflat: The important role of sediment concentration and biological processes

The flocculation process of cohesive sediment impacts upon estuaries and tidal flats by affecting the sediment dynamics, modifying the biogeochemical exchanges, and playing an essential role in coastal ecosystems and geomorphologic evolution. To understand the roles of biological activity on flocculation processes in aquaculture areas, here we undertook in situ measurements over a bare tidal flat and a nearby clam aquaculture mudflat on the Jiangsu coast, China. Near-bed in situ floc size, the grain size distribution of suspended particles in seawater, suspended sediment concentration (SSC), and currents were obtained for nine consecutive semidiurnal tidal cycles simultaneously at the two sites. Correlation analysis indicated that the flocculation and its break-up process in this study appeared to be controlled by the variations in SSC and bottom shear stress due to combined wave and current. The floc sizes showed less difference between the two sites under calm conditions. However, the near-bed in situ floc size in the aquaculture mudflat was 23% larger than that in the bare tidal flat in the severe erosion events, suggesting modulation of the flocculation process due to the extracellular polymeric substances (EPS) eroded from the seabed sediments at the aquaculture site, as the hydrodynamics were very similar between the two sites. A higher EPS content was observed in the sediment layer below the surface seabed at the aquaculture site. We conclude that abundant filter feeders alter floc properties and enhance flocculation by excretion of exopolymer particles.

Sinking Versus Suspended Particle Size Distributions in the North Pacific Subtropical Gyre

AbstractThe particle size distribution (PSD) is a fundamental property that influences all aspects of phytoplankton ecology. In particular, the size (e.g., diameter d [μm]) and sinking speed w (m/day) of individual particles are inextricable, but much remains unknown about how d and w are related quantitatively for bulk particulate matter. There is significant interest in inferring sinking mass fluxes from PSDs, but doing so requires knowing how both mass and w scale with d. To this end, using both laser diffraction and imaging, we characterized for the first time both sinking and suspended PSDs in the oligotrophic North Pacific subtropical gyre. Comparing these PSDs via a power law parameterization indicates an approximately linear w‐to‐d scaling, suggesting particles are more fractal‐like than sphere‐like in this respect. This result is robust across multiple instruments, depths, and sediment trap deployments and is made comparatively precise by a high degree of replication.

A national‐scale study of spatial variability in the relationship between turbidity and suspended sediment concentration and sediment properties

AbstractTurbidity, an index of light side‐scattering, depends on the mass concentration of suspended sediment (SS) within water. Turbidity of river water is regulated by the presence of suspended particulate matter and is used to identify visual changes in response to SS. We used data from the New Zealand National River Water Quality Network, to calculate “specific turbidity” (K; turbidity normalised to mass concentration of suspended particulates). Specific turbidity is shown here to be an effective metric to assess the effect of suspended material composition and particle size distribution of suspended particulate matter over different landscape characteristics, and the effect on SS‐turbidity relationships. Of the catchment characteristics considered in our study, specific turbidity was most responsive to lithological factors, and relatively insensitive to land use and soil parameters. Decreasing particle size has a positive linear response to K, attributed to the higher proportion of ultra‐fine particulate material that is generated by certain lithologies, underscoring the lithological influence on K. SS‐turbidity relationships, therefore, vary spatially across New Zealand's national record of water clarity, and K is considered a useful index for inter‐catchment comparison of SS than turbidity alone.

Seasonal and tidal variability of the hydrology and suspended particulate matter in the Van Uc estuary, Red River, Vietnam

Abstract This study explores the seasonal and tidal changes in flow and suspended matter dynamics in the tropical and macrotidal Van Uc River estuary (North Vietnam) and aims at understanding, among others, the sediment delivery to the ocean and the processes behind the estuarine siltation. Four campaigns took place during the contrasting high flow and low flow seasons, for each during neap and spring tides. Water and suspended matter fluxes, salinity, turbidity and particle size distribution (PSD) were measured for 24 h at three cross sections along the estuary. During the high-flow season, the estuary was mixed, with seaward sediment flux during neap tide and ephemeral up-estuary sediment flux at spring tides due to tidal distortion. During the low-flow season, the system transitioned from partially mixed to highly stratified with salty waters intrusions, salt wedge presence and up-estuary sediment flux varying with the tidal regime. The highest up-estuary sediment flow occurred during low-flow at spring tides and represented ⅔ of the outflow. The lower river discharge, the higher PSD variation. The increasing proportion of microflocs with increasing salinity as compared to primary particles and flocculi was observed at both seasons. Higher tidal variations of PSD at spring tides indicate the strong effect of turbulent shear. These findings also provide a new benchmark for hydro-sedimentary model calibration/validation.

Evaluation of Particle Size Distribution Metrics to Estimate the Relative Contributions of Different Size Fractions Based on Measurements in Arctic Waters.

The size distribution of suspended particles influences several processes in aquatic ecosystems, including light propagation, trophic interactions, and biogeochemical cycling. The shape of the particle size distribution (PSD) is commonly modeled as a single‐slope power law in oceanographic studies, which can be used to further estimate the relative contributions of different particle size classes to particle number, area, and volume concentration. We use a data set of 168 high size‐resolution PSD measurements in Arctic oceanic waters to examine variability in the shape of the PSD over the particle diameter range 0.8 to 120 μm. An average value of −3.6 ± 0.33 was obtained for the slope of a power law fitted over this size range, consistent with other studies. Our analysis indicates, however, that this model has significant limitations in adequately parameterizing the complexity of the PSD, and thus performs poorly in predicting the relative contributions of different size intervals such as those based on picoplankton, nanoplankton, and microplankton size classes. Similarly, median particle size was also generally a poor indicator of these size class contributions. Our results suggest that alternative percentile diameters derived from the cumulative distribution functions of particle number, cross‐sectional area, and volume concentration may provide better metrics to capture the overall shape of the PSD and to quantify the contributions of different particle size classes.

Method for the determination of preferential orientation of marine particles from laser diffraction measurements.

In situ laser diffractometry (LD) is increasingly used in oceanographic studies to estimate sediment transport, particle fluxes and to assess the concentration of marine phytoplankton. It enables an accurate characterization of the size distribution of suspended particles from the scattering signal produced by their interaction with a collimated laser beam. LD reliably reflects the sizes of suspensions dominated by nearly spherical particles; however, when complex particle morphologies dominate the suspension (e.g. phytoplankton) the resulting particle size distribution (PSD) may present significant variations attributed to different factors. In particular, the orientation of non-spherical particles - which abound in the sea - modifies LD measurements of PSDs. While this may be interpreted as a drawback for some studies (i.e. when precise measurement of the volume concentration is required), we propose that detailed analysis of this signal provides information on particle orientation. We use PDMS micropillars with prescribed elliptical cross-sections to experimentally determine the dependence between the spatial orientation of elongated particles and changes in the PSD measured with a LISST laser diffractometer. We show that LD can be used to adequately characterize the different dimensions of the non-spherical particles at specific orientations. Using this property, we describe and validate a method to infer the preferential orientation of particles in the sea. Our study opens new perspectives in the use of in-situ LD in ocean research.

A novel low-cost turbidity sensor for in-situ extraction in TCM using spectral components of transmitted and scattered light

Abstract Compared with light intensity measurements of turbid liquids based on direct or lock-in amplification methods, the square excitation method (SEM) can be used to obtained abundant information from both the time- and frequency-domains. Voltage-based turbidimetry in the time domain (The voltage readout here refers to the signal obtained directly by the photodetector followed by an amplifier and is a function of the light intensity attenuated by scattering and absorption effects) is subject to measurement error because of the heterogeneous size distribution of suspended particles, fluctuations of the light source, and measurement noise. In this work, a novel low-cost turbidity sensor was proposed by combining spectral component extraction (SCE) with the transmitted (It) and scattered (Is) light signals and their ratio (It/Is). A near-infrared Light Emitting Diode (NIR-LED) at 860 nm was employed as the light source to reduce the system cost. Two independent preprocessing channels composed of a photodiode, a transimpedance amplifier, and a band-pass filter converted the modulated light to signals of a suitable scale. For conversion of the conditioned analog signals, a 16-bit analog-to-digital converter was used and the signal was further processed using a high-performance microcontroller (STM32F405). The SCE algorithm and turbidity correlation were implemented via the integrated digital-signal-processer combined with Fast Fourier Transform digital algorithm. Averaging of multiple measurements further improved the measurement precision when using the first, third, and fifth spectral components that were related to a known turbidity. The calibration measurements for the sensor revealed that the correlation coefficients from the linear fitting were reliable and satisfactory when using It, Is, and (It/Is). Additionally, validation measurements further demonstrated that the proposed sensor had low measurement error. The maximum measured error was 6% for a turbidity of 10 NTU while the lowest relative error was 0.4% for the 280 NTU solution. The results demonstrate that the sensor has potential for automatic in-situ turbidity measurement applications, particularly for in-situ extraction processes used in Traditional Chinese Medicine.

Hydraulic, wash-off and sediment transport experiments in a full-scale urban drainage physical model

This paper presents a dataset obtained from hydraulic and sediment transport experiments performed in a full-scale urban drainage physical model of 36 m2. The study seeks to accurately measure sediment mobilization through the different parts of the model (surface, gully pots and pipe system), also obtaining a precise characterization of water flow and using realistic rainfall simulator to ensure the transferability of the results. Three different rain intensities and five sediment granulometries were tested in 6 hydraulic and 23 wash-off and sediment transport experiments. The following experimental data were produced: surface elevations and 2D runoff velocities measured by visualization techniques; surface and in-pipe water depths; flow discharges, total suspended solids concentrations and particle size distribution at the entrance of the gully pots and at the pipe system outlet; and sediment mass balances. This data is optimal for developing and validating wash-off and sediment transport formulations in urban drainage models, towards better treatment and management techniques for minimizing the impact of urban surface pollutants on the environments of towns and cities.

Characterization of Suspended Particle Size Distribution in Global Highly Turbid Waters From VIIRS Measurements

AbstractNormalized water‐leaving radiance spectra nLw(λ) at the near‐infrared (NIR) bands from six years of observations (2012–2017) with the Visible Infrared Imaging Radiometer Suite (VIIRS) on‐board the Suomi National Polar‐orbiting Partnership are used to derive both the power law slope η of the particle backscattering coefficient spectra bbp(λ) and the particle size power law slope ξ for turbid coastal and inland waters. Based on the fact that the absorption coefficient of sea water aw(λ) is generally much larger than those of the other constituents aiop(λ) at the NIR wavelengths in coastal and inland waters, a NIR‐based bbp(λ) algorithm for turbid waters has been used to derive the power law slope η. A three‐order polynomial function between η and ξ in Kostadinov et al. (2009, https://doi.org/10.1029/2009JC005303) is applied to calculate the particle size slope ξ. Seasonal and interannual variations of η and ξ in China's east coastal region, the Amazon River Estuary, the La Plata River Estuary, the Meghna River Estuary, and the Atchafalaya River Estuary are characterized and quantified. Except for the Amazon River Estuary, η and ξ have significant seasonal dependence in these highly turbid regions. Among the global highly turbid waters, the Meghna River Estuary shows the most significant seasonal variations in η and ξ with the largest particle size in the surface layer. The peaks of the climatology η and ξ are at ~ −1.2 and 3.2 in the Meghna River Estuary, respectively. Particle size parameters η and ξ are also shown to be related to the magnitude of nLw(λ) (or bbp(λ)) at the NIR bands with strong regional dependence. This study demonstrates that η and ξ increase from the inshore to offshore regions in these highly turbid waters, illustrating the more large particles in the inshore waters than the offshore ocean regions. In addition, wind and precipitation data in the Amazon River Estuary and Meghna River Estuary show that wind forcing is the major driver for the particle size distribution dynamics in these highly turbid water regions.

Faecal coliforms, faecal enterococci, &lt;i&gt;Salmonella&lt;/i&gt; Typhi and &lt;i&gt;Acanthamoeba&lt;/i&gt; spp. UV inactivation in three different biological effluents

Efficiency of UV-light to inactivate microbial indicators, Salmonella Typhi and Acanthamoeba spp. was studied in three different biological secondary effluents. Even though effluents differed in terms of their total suspended solids content, transmittance and particle size distribution, the UV-light dose required to fulfil WHO agricultural water reuse criteria was the same (30 mW·s/cm2), because the particle content with sizes > 40 µm was similar and very small. Using this dosage, 3 log of Salmonella Typhi and faecal enterococci were also inactivated. To avoid faecal coliform and Salmonella Typhi photoreactivation, the UV dose had to be doubled and in the process 2.5 log of Acanthamoeba spp. were also inactivated. This is interesting because its presence in wastewater, pathogenicity and resistance to conventional disinfection processes has been reported in the literature. Additionally, it was found that the faecal coliforms' inactivation rate constant was the lowest one of all the bacteria studied (Salmonella Typhi and faecal enterococci), suggesting the limitation of this indicator when several kinds of pathogens are present, as is the case in developing countries.

Evaluation of a simple, inexpensive, in situ sampler for measuring time‐weighted average concentrations of suspended sediment in rivers and streams

AbstractThe accurate measurement of suspended sediment (&lt;200 μm) in aquatic environments is essential to understand and effectively manage changes to sediment, nutrient, and contaminant concentrations on both temporal and spatial scales. Commonly used sampling techniques for suspended sediment either lack the ability to accurately measure sediment concentration (e.g., passive sediment samplers) or are too expensive to deploy in sufficient number to provide landscape‐scale information (e.g., automated discrete samplers). Here, we evaluate a time‐integrated suspended sediment sampling technique, the pumped active suspended sediment (PASS) sampler, which collects a sample that can be used for the accurate measurement of time‐weighted average (TWA) suspended sediment concentration and sediment particle size distribution. The sampler was evaluated against an established passive time‐integrated suspended sediment sampling technique (i.e., Phillips sampler) and the standard discrete sampling method (i.e., manual discrete sampling). The PASS sampler collected a sample representative of TWA suspended sediment concentration and particle size distribution of a control sediment under laboratory conditions. Field application of the PASS sampler showed that it collected a representative TWA suspended sediment concentration and particle size distribution during high flow events in an urban stream. The particle size distribution of sediment collected by the PASS and Phillips samplers were comparable and the TWA suspended sediment concentration of the samples collected using the PASS and discrete sampling techniques agreed well, differing by only 4% and 6% for two different high flow events. We should note that the current configuration of the PASS sampler does not provide a flow‐weighted measurement and, therefore, is not suitable for the determination of sediment loads. The PASS sampler is a simple, inexpensive, and robust in situ sampling technique for the accurate measurement of TWA suspended sediment concentration and particle size distribution.