Comparison of two online flocculation monitoring techniques for predicting turbidity removal by granular media filtration

Abstract

Particulate matter removal in drinking water treatment via direct granular filtration requires specific flocculation conditions (a process typically termed 'high energy flocculation'). Predicting filtered water turbidity based on flocculated water characteristics remains difficult. This study has sought to establish a relationship between filtered water turbidity and the flocculated water characteristics. Flocculation oflow-turbidity raw water was evaluated online using a Photometric Dispersion Analyser (PDA) and a Dynamic Particle Analyser in a modified jar test followed by a bench-scale anthracite filter. Coagulants used were alum, PASS100 and ferric sulphate, in addition to a polydiallyldimethylammonium chloride (polyDADMAC) cationic polymer. They were dosed in warm and cold waters, and flocculated with intensities (G) from 0 to 100 s(-1). Of the two instruments selected to analyse flocculation performance, the Dynamic Particle Analyser was shown to be the most sensitive, detecting small changes in floc growth kinetics and even floc growth under low flocculation conditions which remained undetected by the PDA. Floc size was shown to be insufficient in predicting particulate matter removal by direct granular filtration as measured by turbidity, although a threshold d(v) value (50 microm) could be identified for the test conditions evaluated in this project, above which turbidity was systematically lower than 0.2 NTU.

Continuous floc image analyser (C-FIA) for tracking floc particle dynamics during coagulation–flocculation–settling processes

“…An exact number and actual sizes of particles, can only be provided through a visual based systems such as photography followed by an image analysis approach. 22 In this context, Ball, et al (2011) 23 compared the photo dispersive analyser (PDA) with a dynamic particle analyser, [DPA], (Model DPA4100 Brightwell Technologies Inc., Canada) that used the Micro-Flow Imaging™ Technique. They reported that the DPA was more sensitive than the PDA in detecting small changes in floc growth kinetics and even floc growth under low flocculation conditions, which remained undetected by the PDA.…”

Micro-flow imaging for in-situ and real-time enumeration and identification of microplastics in water

“…A digital camera with an extended depth field and ample magnification is utilized for this purpose (Sharma et al, 2010;Ripple and DeRose, 2018). Coagulation-flocculation studies (Ball et al, 2011) and differentiating silicone oil droplets from protein particles (Sharma et al, 2009) are a few of the common applications of this technology. With no sample preparation, MFI directly analyses the liquid and categorizes the particles based on their morphological features along with the data on particle distribution.…”

Optimization of coagulation-flocculation parameters using a photometric dispersion analyser

“…These techniques are advantageous as they offer an estimation of a wide range of particle sizes in a rapid and non-destructive manner (Selomulya et al, 2001). A photometric dispersion analyser (PDA) has become an important instrument that has been widely used in monitoring coagulation-flocculation kinetics (Mixon et al, 2013;Ball et al, 2011;Staaks et al, 2011;Tzoupanos, 2009, 2010;Xiao et al, 2009;Huang and Liu, 1996). A PDA is a fibre-optical monitor which measures the fluctuation in the intensity of light transmitted through a flowing suspension (Huang and Liu;.…”