The Ontario Water Works Association (OWWA) Treatment Committee and Continuing Education Committee sponsored a one day seminar on Particle Counting as an Operational Tool on March 20, 1997 at the Four Points Hotel in Mississauga, Ontario.

One of the novel features of the seminar was that the suppliers of the commercially available particle counters were present on site. Photo - T. Davey

Particle counters provide a rapid means of determining the size and the number of particles in water. Particle counting data offers more detailed information on the quality of water as compared to turbidity measurements and this information can be used to optimize the water treatment process. Application of particle counters in municipal and industrial water treatment plants is gaining momentum because of recent outbreaks of waterborne diseases in North America caused by microorganisms such as Giardia lamblia and Cryptosporidium parvum.

Brian Jobb, Vice-Chair, Treatment Committee, addressed the timeliness of this topic and the need to disseminate this information to the operating level at the water treatment plants. Roland Welker, of Dillon Consulting Limited, talked about the multi-barrier approach for particulate and microbial removal and the monitoring techniques for assessing the removals. He also introduced Microscopic Particulate Analysis as another tool to measure the performance of microbial removals. It was discussed whether an absolute guideline value for particle counts for treatment should be established or not and if so, what should it be. Erika Hargesheimer, of the City of Calgary, examined turbidity versus particle counting measurements.

There is excellent correlation between turbidity and particle counts for water with turbidity greater than 0.1 NTU. However, at very low turbidities (less than 0.1 NTU - operating detection limit for turbidimeters), correlation is poor. It is in this range that particle counting provides improved sensitivity and analytical confidence for monitoring the effectiveness of the treatment process.

Wayne Manley, of the Peterborough Utilities Commission, reflected why the parasitic cysts, which have existed in the past, are currently a drinking water problem. He challenged both regulatory agencies as well as plant operators to set higher operating standards, use additional tools such as particle counters and adopt operating procedures that encourage "filter to waste", a set maximum filter run length, no recycle of the backwash waters, annual filter maintenance and optimization of pre-treatment process.

Erika Hargesheimer then dealt with the criteria for selection of the on-line particle counters, calibration and channel sizes, quality assurance issues and the need to define water quality goals based on particle counting data.

Douglas Stendahl, of the Manheim Water Treatment Plant, Kitchener, described particle counting as "not a silver bullet but another arrow in an operator's quiver". Since particle count data is very much source water and plant specific, he recommended establishing a plant-specific (say less than 50 particles) "total particle count per millilitre greater than 2 m size" as an uncomplicated operational goal.

John Mogavero, of the Erie County Water Authority, Tonawanda, New York, described their experience with the particle counters at the two conventional surface water treatment plants on Lake Erie and the Niagara River. Particle count data was used to optimize the treatment process and was beneficial in detecting filter breakthrough of the particulate matter.

The speakers' presentations were followed by a panel discussion. The question of whether particle counters would replace turbidimeters was discussed. There was a general consensus that the turbidimeters would continue to be used for the foreseeable future while particle counters would be increasingly used for trouble-shooting and process optimization.

It was also recognized that there is a need to develop on-site calibration capabilities, define quality assurance protocols, develop manageable data file structures and integrate data with the existing SCADA systems for real time operation based on particle counts. Regarding particle monitors (as opposed to particle counters), it appeared that they had limited application in the water industry since particle monitors measure a "relative" index of water cleanliness which is not clearly defined.

Three suppliers had their units on display and were available for a technical dialogue and participation in the panel discussion.

The seminar was partially funded by the Ministry of Environment and Energy and Ontario Clean Water Agency.