Continuous, On-line Monitoring of Polymer Dose for Dewatering Using Liquid Stream Viscosity
Abstract:This paper describes research conducted to test the use of continuous centrate viscosity measurements for polymer dose monitoring in the biosolids dewatering process. The researchers have previously documented that minimum centrate or filtrate viscosity indicated the optimum polymer dose as determined by capillary suction time (CST) and solids recovery. To date, however, no on-line viscosity measurements have been conducted to test the feasibility of this parameter in continuously monitoring polymer feed.
Initial results indicate that liquid stream viscosity must be measured on-site since filtrate samples in the overdosing range decrease in viscosity over several hours following sampling. A sensitive viscometer is required for continuous monitoring since the observed viscosity range is from 1–3 mPa-sec. An international search for viscometer vendors showed that two types of viscometers could be used for this purpose: rotational and vibrational. Only data from rotational type viscometers was obtained for this paper. The viscometer was installed to continuously sample centrate from the centrifugation of anaerobic digested biosolids. Full-scale dose response experiment showed that minimum viscosity correlates with solids measurements, and thus such viscometers can be used in monitoring and controlling polymer dose during dewatering. However, several modifications are required for such viscometers to withstand the demanding conditions in wastewater treatment plants. Use of viscosity for control of polymer dose requires use of a minimum value, necessitating a complex vontrol algorithm.
Document Type: Research Article
Publication date: January 1, 2002
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