Application of the Streaming Current Detector in Sludge Conditioner Selection and Control

Abstract

The streaming current detector (SCD) can be utilized to measure charge characteristics of a suspension or sludge which can be related to zeta potential. In this study, the SCD was used as a tool for polymer selection and dose control toward improved sludge conditioning prior to centrifugation. In laboratory studies, polymer addition to sludges was followed by controlled mixing then measurement of streaming current (SC) and capillary suction time (CST). Plant studies employed facilities at an 18.8 MGD wastewater treatment facility in Warminster, PA, USA. Anaerobically digested sludge was conditioned with varying doses of cationic polymer and dewatered using two parallel solid-bowl centrifuges. The polymer caused a transition from negative to positive charge in both conditioned sludge and centrate. The polymer dose range for optimum dewaterability, as indicated by CST and solids recovery, corresponded to near-zero SC in all cases. Even when greater mixing intensities or times increased the polymer demand, the charge transition was similarly related. This correspondence was used to successfully confirm a calculation method establishing velocity gradient and mixing time similitude between jar tests and in-line mixing prior to the centrifuge.

Dual‐chemical conditioning and dewatering of anaerobically digested biosolids: laboratory evaluations

“…Comparison with Figures I and 2 shows that optimal CST values were invariably attained at an SC between -15 and -20. This may be the level at which sufficient charge neutralization occurs to produce flocculation: because a negative offset is sometimes observed in SC readings relative to measured~potentials (Dentel, 1995), it is also possible that these values indicate true charge neutralization (0 zeta potential). Comparison of SC read-ings with colloid titrations in a previous report to EBMUD supported this hypothesis (Dentel et al, 1994).…”

“…A SCD (Model SC4200, Milton Roy [Ivyland, Pennsylvania]) was used for determination of relative colloidal charge. This device and the method of measuring SC are described elsewhere (Dentel, 1995). The pH meter used in this work was an Accumer@Model 830 (Fisher Scientific) using a standard combination electrode.…”

“…This work (Chitikela, 1996, andDentel andChitikela, 1995) investigated the combined use of an inorganic conditioner (ferric chloride) or a cationic surfactant, hexadecyltrimethyl ammonium bromide (HDTMA), combined with a cationic polymer (Percol 757) for the conditioning and dewatering of municipal ADBS. In the past, ferric chloride (FeCI 3) was commonly used in conjunction with lime for solids conditioning, but the current 1062 practice is generally to use cationic polymers (polyelectrolytes) alone.…”

Automation in sludge dewatering by novel on-line characterisation of flocculation

“…the capillary suction time (CST, see Vesilind, 1988), the particle size distribution (Karr and Keinath, 1978;Kayser and Nellenschulte, 1991;Olboeter and Vogelpohl, 1993), the mean particle diameter (Hemme et al, 1994), and the zeta potential (Igarashi and Nishizawa, 1992). Other methods provide a closed loop feedback control for sludge conditioning by the streaming current detection of filtrate (Dentel and Kingery, 1989;Dentel and Abu-Orf, 1993), the mean particle diameter (Peters, 1992) and the rheological parameters, especially the torque of conditioned sludge (Campbell and Crescuolo 1982;Campbell and Crescuolo, 1989). The conditioning control systems would lead to a higher level of dewatering efficiency as well as lower polymer addition compared to dewatering without automatic control (Crawford, 1990).…”