New measurement techniques for secondary settlers: a review

Abstract

In activated sludge wastewater treatment research, most of the attention has been devoted to the biodegradation process. However, in terms of effluent quality, the final settling and clarification processes are at least as important because any particle carried over the overflow weir brings with it not only COD, but also nitrogen and phosphorus. In recent years we see indeed increased attention on this separation step, and alternatives such as membrane separation are increasingly introduced. Still, a large installed base of settlers exists, whose operation could/should be optimised. The measurement techniques presented in this contribution each focus on one of the key processes in the secondary settler: hydrodynamics, particle aggregation and breakage, hindered settling and compression. For each technique, the measuring principle is explained and a typical data set shown.

Sludge Quality: The Key to Secondary Clarifier Performance

“…The clear supernatant above the visible solids/liquid interface forms at the expense of the solids that come into contact with the bottom of the column or with other solids that are resting on solids that are resting on the bottom of the column. The existence of this second, invisible interface has recently been demonstrated using the radioisotope Tc-99m and a gamma camera by Vanrolleghem et al (2006). It is important to note that the solids concentration between the two interfaces is constant with time and is equal to the initial solids concentration of the sample.…”

Shall we use hardware sensor measurements or soft-sensor estimates? Case study in a full-scale WWTP

“…This leads to considerably time-delayed responses unsuitable for the monitoring and control of the dynamic treatment processes. Fortunately, considerable developments in the on-line instrumentation in municipal wastewater treatment plants (WWTPs) have occurred during the past decades, providing more real-time information on the evolving process conditions (Vanrolleghem and Lee, 2003;Vanrolleghem et al, 2006;Madsen et al, 2011;Sweeney and Kabouris, 2013;Olsson et al, 2014). In spite of these developments, the instruments still tend to get fouled in the biological treatment processes, giving rise to a poor performance of sensors (Olsson, 2012).…”

Integrating Fluorescent Dye Flow‐Curve Testing and Acoustic Doppler Velocimetry Profiling for In Situ Hydraulic Evaluation and Improvement of Clarifier Performance

“…A key factor controlling clarifier solids separation efficiency is its hydraulic performance (Parker et al, 2000;Vanrolleghem et al, 2006). Several analytical and mathematical models have been developed for designing and improving flow-path-current distribution (Armbruster et al, 2001;Ekama et al, 1997;Krebs et al, 1995Krebs et al, , 1996WEF, 2005).…”

“…Hence, new methodologies for in situ measuring are needed. To date, flowcurve testing, dye tracing, and non-invasive current profiling are the best in situ techniques for identifying short-circuiting and characterizing hydraulics flow paths (Boyle et al, 2005;De Clercq et al, 2002;Vanrolleghem et al, 2006;WEF, 2005). The flow-curve test (FCT) is a characterization of the behavior of a tracer passing through a settler (Boyle et al, 2005;Ekama et al, 1997;WEF, 2005), and it is used mainly to identify shortcircuiting problems.…”