Assessment of Capillary Suction Time (CST) Test Methodologies

Abstract

The capillary suction time (CST) test is a commonly used method to measure the filterability and the easiness of removing moisture from slurry and sludge in numerous environmental and industrial applications. This study assessed several novel alterations of both the test methodology and the current standard capillary suction time (CST) apparatus. Twelve different papers including the standard Whatman No. 17 chromatographic paper were tested. The tests were run using four different types of sludge including a synthetic sludge, which was specifically developed for benchmarking purposes. The standard apparatus was altered by the introduction of a novel rectangular funnel instead of a standard circular one. A stirrer was also introduced to solve the problem of test inconsistency (e.g. high CST variability) particularly for heavy types of sludge. Results showed that several alternative papers, which are cheaper than the standard paper, can be used to estimate CST values accurately, and that the test repeatability can be improved in many cases and for different types of sludge. The introduction of the rectangular funnel demonstrated an obvious enhancement of test repeatability. The use of a stirrer to avoid sedimentation of heavy sludge did not have statistically significant impact on the CST values or the corresponding data variability. The application of synthetic sludge can support the testing of experimental methodologies and should be used for subsequent benchmarking purposes.

Specific Conductance Reduction in Valley Fill Runoff Using the Cost-Effective Sulfate Removal Process

“…Capillary Suction Time (CST) values for the sludge, as determined using Standard Methods, were 34 seconds for OF and 20.6 seconds for BH. A commonly used CST value for wastewater sludge is 20 seconds (Vesilind, 1988), with CST values above 50 seconds also being acceptable for heavier sludge (Sawalha and Scholz, 2007). When compared to these values, the CESR sludge is reasonably near an acceptable dewatering time for most wastewater residuals even before any further polymer addition or modification.…”

“…The average CST for OF sludge was 34 seconds, while the average for BH was 20.6 seconds. A CST of 20 seconds is often the goal for wastewater sludge (Vesilind, 1988), though times of 50 seconds or higher have been used as acceptable dewatering times for heavy wastewater sludge (Sawalha and Scholz, 2007). The CST of the CESR sludge is well within this range and can be dewatered without further modification.…”

Waste activated sludge dewaterability: comparative evaluation of sludge derived from CAS and MBR systems

“…After one minute of mixing phase (200 rpm) and 20 min of flocculation phase (30 rpm), samples of conditioned sludge were collected and investigated for CST. The optimal flocculants dosage was the one corresponding to the minimum value of the achieved CST [34].…”

Assessment of pressure-driven electro-dewatering as a single-stage treatment for stabilized sewage sludge

“…However, sample 3-D gives better dewatering performance, suggesting the effect of sludge variations on the EDW process. On the other hand, this result can be predicted from the dewaterability indicators: sample 3-D gives lower CST value and weaker negative zeta potential as seen in the sludge characterization test (see Table 1) [33,40]. Fig.…”