Comparison of Time Resolved Optical Turbidity Measurements for Water Monitoring to Standard Real-Time Techniques

Abstract

Environmental water monitoring requires the estimation of the suspended solids load. In this paper, we compare the concentration range accessible through three different techniques: optical turbidity, acoustic backscattering and the newly in-lab developed time resolved optical turbidity. We focus on their comparison on measurements made in the laboratory on water suspensions of known particles and concentrations. We used laboratory grade kieselguhr, wheat starch and kaolin as suspended solid surrogates. The explored concentration domains are the ones, for the total suspended solid load, commonly encountered in wastewater and rivers in standard (less than 1 g/L to a few g/L) or extreme conditions such as floods or storm events (up to several dozen g/L). Regarding the operable concentration domain, the time resolved optical turbidity shows a clear advantage upon the other methods, whatever the kind of particle is.

Development of a Frugal, In Situ Sensor Implementing a Ratiometric Method for Continuous Monitoring of Turbidity in Natural Waters

“…While complementary methods such as acoustic [ 8 ] or time-resolved [ 9 ] ones are also used for specific cases, turbidity is mostly measured optically by a combination of a light source and one or more photodetectors that measure the scattering and/or absorption properties of particles suspended in the water sample. While absorption is a directional measurement, scattering occurs in all directions, with a diffraction pattern dependent on the particle size [ 2 ]; hence, different optical configurations can be implemented.…”

Practical Assessment of Real‐Time Suspended Sediment Load Monitoring Using Time Domain Reflectometry

“…Therefore, field automated surrogates for SSC measurement are required to overcome these limitations. Among these automated surrogates are optical turbidity meter–based methods (Campbell et al., 2005; Downing, 1996; Gentile et al., 2010; Gillett & Marchiori, 2019; Khairi et al., 2015; Matos et al., 2019; Navratil et al., 2011; Omar & MatJafri, 2009; Pallarès et al., 2021), acoustic transmission or backscattering methods (Huang et al., 2018; Li et al., 2018; Moore et al., 2013; Thorne & Hanes, 2002; Thorne & Meral, 2008; Thorne et al., 1991; Topping et al., 2007; Wenjie et al., 2019), focused beam reflectance measurement methods (which involve the use of a laser focused on a focal plane and retrieval of the backscattering data of a sediment particle) (Heath et al., 2002; Jeldres et al., 2020; Law & Bale, 1998), laser diffraction methods (Agrawal & Pottsmith, 1994; Blott et al., 2004; Czuba et al., 2015), nuclear methods (which involve the use of a gamma radioactive source to measure the density of turbid water) (Berke & Rakoczi, 1981; McHenry et al., 1968), spectral reflectance methods (which involve the use of a remote sensing technique to capture the increased volume reflectance of water areas) (Choubey, 1994; Han, 1997; Qu, 2014; Sváb et al., 2005), and differential pressure methods (which involve the measurement of differential pressure from two transmitters at different water depths) (Hsu & Cai, 2010; Lewis & Rasmussen, 1996; Petrovic et al., 2016; Sumi et al., 2002; Tollner et al., 2005).…”