Background

A history of high particulate in the water at University Hospital Southampton (UHS) prompted research into the benefits of prefiltration. A series of silt density index (SDI) tests were run on the water at UHS, indicating significant particulate contamination in the water and suggesting that prefiltration on the main incoming water could provide benefits.

It was decided that prefiltration would be installed on a new building on the UHS campus. Once the building was commissioned, a study would commence to collect qualitative and quantitative data on the prefiltration performance.

Fig 1. Raw and soft water filtration housings.

UHS installed four Pall Coreless filter housings with Profile™ Coreless 10 µm filter elements: two housings on raw water and two on soft water. SDI measurements would be taken on the water monthly, before and after the filter housings and at distal points. The goal was to determine:

• Could prefilters help reduce overall maintenance of the water system? (such as reducing required cleaning of storage tanks).
• Would reducing particulate correlate with decreased microbial growth? (by reducing the nutrient source, as studies have suggested) ¹.

Data collected

In addition to monthly SDI measurements, UHS sampled the water for Legionella pneumophila and Pseudomonas aeruginosa per national guidance. Temperature and water usage data were also monitored over the course of the study to confirm the plumbing system was working as intended.

Outcomes

SDI results during the study showed a significant decrease in particulate contamination when comparing upstream versus downstream samples on both raw and softened water. Distal samples tended to show an increase versus samples downstream of the filter, which is often the case as the water travels through the pipes and collects debris from the system. When evaluating the condition of the strainers and water storage tank, a clear improvement was seen during the study and neither required the typical extensive cleaning. This resulted in a cost savings for the hospital.

Fig 2. Two samples from the study are shown: raw water “upstream” of SDI membrane (left) and raw water “downstream” of SDI membrane (right).

During the entirety of the study, one positive sample for Pseudomonas was recovered from sink in a staff toilet, which was one of the most used in the unit. The sample cleared as expected after cleaning, flushing, and fitting a Point-of-Use water filter. There was one positive Legionella sample on the filtered water which coincided with low occupancy/low water use and the issue was quickly resolved. Compared to other buildings, it was simpler to take corrective action, which included increasing flow and making sure filters were regularly changed. This data is promising, but additional investigation would provide more confidence in the correlation.

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References

1. Liu G, Ling F, van der Mark EJ, Zhang XD, Knezev A, Verberk JQJC, et al. Comparison of Particle-Associated Bacteria from a Drinking Water Treatment Plant and Distribution Reservoirs with Different Water Sources. Sci Rep. 2016 Feb;6:20367. doi.org/10.1038/srep20367.
    

Author bio

Marissa Khoukaz, Former Business Development Manager — Hospital Water

Marissa was a Business Development Manager for Hospital Water and managed the prefiltration portfolio globally. She worked with high-risk units to reduce waterborne pathogen risk to patients.