Tracking filter performance with particle counting

Abstract

Particle counting can be a sensitive tool for monitoring filter performance and improving the quality of finished water. Minor changes (1–2 mg/L) in the primary coagulant dosage can significantly affect particle counts in filtered water. Jar tests were inconclusive in selecting a coagulant dosage for source water of low turbidity (<5 ntu). Measurements of turbidity in filtered water were also not definitively altered by small changes in coagulant dosage. On‐line particle counting was successfully used in a 0.5 × 106–m3/d (135‐mgd) conventional water treatment plant to distinguish the effects on water quality of small changes in coagulant dosage and filter flow. Measurable changes in particle counts in filtered water were detected when the aluminum sulfate dosage ranged from 5 to 10 mg/L at filter loading rates of 4–9.5 m/h (1.7–4.0 gpm/sq ft). Particle count percentile plots and statistics (10th, 50th, 90th, 95th, and 98th percentiles) were valuable indicators of the performance of both individual filters and the overall plant.

Evaluation of Particle Removal at Water Treatment Plants in Nova Scotia

“…Because turbidity increased by only 0.06 NTU, it would be difficult to reliably discern whether the filter would be vulnerable to particle breakthrough. Similarly, Hargesheimer et al (1998) found that changes in upstream process operation had very little affect on filtered water turbidity. Figure 5 shows the plot of total raw and filtered particles during the stressed filter run.…”

“…The spikes are a result of minor fluctuations in water quality, which are generally of less concern than the overall trend. Based on a study by Hargesheimer et al (1998), changes in water treatment processes had little affect on turbidity. Because turbidity increased by only 0.06 NTU, it would be difficult to reliably discern whether the filter would be vulnerable to particle breakthrough.…”

“…Nevertheless particle counting is becoming increasingly popular for process optimization (Barsotti et al 1998) in conventional plants and for monitoring membrane integrity in new microfiltration and/or ultrafiltration plants (Mourato and Carscadden 1998). Hargesheimer et al (1998) observed that increasing the alum dose from 5 to 10 mg/L had relatively little effect on turbidity, whereas the number of particles ≥2 µm/mL in the filtered water was reduced by at least a factor of 3 under steady-state conditions. In addition the higher coagulant dosages result in a shorter bed life, as detected by an increase in particle counts prior to filter backwashing (Hargesheimer et al 1998).…”

Comparing crushed recycled glass to silica sand for dual media filtration

“…Particle counting has been shown to be a more sensitive tool for quantifying filtration performance, especially for lower turbidity levels typical of filtration effluent (Eisnor et al 2001;Chowdhury et al 1997). Particle counting has been shown to detect particle breakthrough sooner and to be capable of detecting changes in effluent quality due to minor process changes (Hargesheimer et al 1998).…”

Comment

“…Moreover, low level turbidity measurements are routinely presented without qualification in water engineering,5 6epidemiology (for example, Fox and Lytle7(incidentally, an official EPA study)), and microbiology 8. Indeed, many of these studies were published in the same journal that published the Hart article.…”