A review of the principles of turbidity measurement

Abstract

Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Turbidity of water due to the presence suspended sediment is measured and interpreted in a variety of ways, which can lead to the misinterpretation of data. This paper re-examines the physics of lightscattering in water, and exposes the extent to which the reporting of turbidity data is inconsistent. It is proposed that the cause of this inconsistency is the fact that the accepted turbidity standards USEPA Method 180.1, ISO 7027 and GLI Method 2 are mutually inconsistent, as these standards give rise to a large number of measurement units that are not based on the optical properties of light absorption and scattering by suspensions in water, but by the arbitrary definition of the degree of turbidity being due to a concentration of formazin or other similar polymerbased calibration standard. It is then proposed that all turbidity-measuring devices should be calibrated with precise optical attenuators such as ND filters. Such calibration would allow for the definition of a beam attenuation coefficient (BAC) for every turbidity measuring instrument which would be cross-comparable with any other instrument calibrated in the same way.The units for turbidity measurements should be based on attenuation and reported as dB m-1. It is also proposed that a new standard should be drafted according to this attenuation-based method, and this new standard should also define the nomenclature for reporting data collected at any specific scattering angle in terms of an attenuation in dB m-1. The importance of multi-parameter turbidity measurements for the improvement of the quality of turbidity data, and the application of parameter-rich data sets to new methods of sediment characterization are discussed. It is suggested that more research into multi-parameter turbidity measurements is needed, as these new methods will facilitate an increase in parity between turbidity and suspended sediment concentration (SSC), a relationship that is subjective.http://mc.manuscriptcentral.com/PiPG Progress in Physical Geography 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Turbidity of water due to the presence suspended sediment is measured and interpreted in a variety of 2 ways, which can lead to the misinterpretation of data. This paper re-examines the physics of light-3 sc...

Thermostabilization of viruses via complex coacervation

“…Briefly, turbidity was measured by placing 100 µL of the sample into a clear, flatbottom, 96-well plate and measuring the absorbance at 562 nm using a Synergy Mx monochromator-based multimode microplate reader (Winooski, VT). 42,48 The measured signal was referenced against a control well containing only Nanopure water and HEPES buffer. Samples were then examined using an Olympus IX51 microscope with a DP72 camera (Center Valley, PA) to confirm the presence or absence of coacervation, and the 100 µL aliquot was recovered for subsequent use in the infectivity assay.…”

Predicting suspended sediment concentration from nephelometric turbidity in organic‐rich waters

“…Turbidity, quantified in nephelometric units, is a widely used surrogate indicator of suspended particles in water bodies employed by researchers and environmental monitoring agencies (Kitchener, Wainwright, & Parsons, ). In the broadest sense, water turbidity is inversely related to water clarity, in terms of light penetration and visual clarity, because the presence of suspended particles within a water column acts to decrease light penetration and visual clarity and causes light scattering, of which turbidity is a relative index of the side scattering of light (Davies‐Colley & Smith, ).…”

“…From an environmental monitoring perspective, turbidity is an inexpensive and convenient proxy measure of the “cloudiness” of water and provides an inexpensive relative index of the amount of particulate contaminants from land use disturbance, principally as suspended sediment concentration (SSC; Ankcorn, ; Gray & Gartner, ). However, turbidity is not a physical quantity; rather, it is a convenient relative index, used to predict the quantity of suspended particulates in a water column (Davies‐Colley & Smith, ; Kitchener et al, ). Its use is problematic, however, because particles have different light scattering properties; and these particulate properties (e.g., size, shape, and composition) contribute different amounts of light scatter that result in noisy or poor relationships between the physical quantity of suspended sediment and observed turbidity.…”

“…These models of optical theory assume a spherical particle, where Rayleigh scattering is limited to small nonabsorbing spherical particles (usually in the range of 2–75 nm). More typical of the refraction that occurs in suspension in water is Mie scattering, where light is absorbed or scattered from nonabsorbing spherical particles of unlimited sizes but is usually in the size range of 20 nm to 765 μm (Kitchener et al, ). For particles >200 μm, light refraction, reflection, and absorption are explained through geometric optics theories, which are most applicable when the wave length of the light source is less than the particle size of the incipient surface (Kitchener et al, ).…”

“…More typical of the refraction that occurs in suspension in water is Mie scattering, where light is absorbed or scattered from nonabsorbing spherical particles of unlimited sizes but is usually in the size range of 20 nm to 765 μm (Kitchener et al, ). For particles >200 μm, light refraction, reflection, and absorption are explained through geometric optics theories, which are most applicable when the wave length of the light source is less than the particle size of the incipient surface (Kitchener et al, ). When translated to measurements of turbidity, these optical properties strongly influence the type and direction of light scattering and are contingent on the light wavelength and detectors used in turbidimeters to measure the light scattering.…”