Kyle Guembel, Undergraduate Research Associate (kwguembe@engmail.uwaterloo.ca)

and

Dr. M. B. Emelko, Assistant Professor (mbemelko@uwaterloo.ca)

Department of Civil Engineering, Water Resources Group

University of Waterloo

Waterloo ON, N2L 3G1

The importance of physico-chemical processes such as granular media filtration is emphasized by the limited efficacy of traditional chemical disinfection. The inactivation of pathogens such as Cryptosporidium parvum is a difficult task due to their resistance to chemical disinfectants traditionally used in drinking water treatment. The removal of such pathogens is of increasing interest and importance to utilities. In the shadow of more stringent regulations such as USEPA’s anticipated Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), a variety of treatment processes may be necessary for compliance. The LT2ESWTR will require additional treatment processes or a demonstration of performance equivalence for specific pathogen removal.

Applicable to large systems, several studies have suggested that granular media filtration can remove between 4.0 and 6.0 log of C. parvum. Of these studies, some have demonstrated that polystyrene microspheres are reasonable surrogates for C. parvum removal by filtration. For small systems, diatomaceous earth (DE) filtration can similarly supplement disinfection as an additional barrier for pathogen removal. DE filtration experiments utilizing a fine grade of DE have yielded C. parvum removals in excess of 6.0 log. The majority of these filtration data (granular media and DE) have been generated from experiments during which high concentrations of oocysts were seeded into the treatment processes (e.g., 10⁶-10⁷ oocysts/L). Such high concentrations are not indicative of naturally occurring C. parvum concentrations. In addition, the introduction of such an abundance of particles to the filter influents my have an affect on filter operation.

The present research is aimed at demonstrating the impact of seeded concentrations on observed C. parvum and polystyrene microsphere removals by both granular media and DE filtration processes. Traditional seeding experiments typically involve seeding of high concentrations of pathogens or their respective surrogates. This research compares C. parvum and polystyrene microsphere removals as they are related to seeded concentrations. In the context of the LT2ESWTR, this understanding is critical to demonstrating treatment performance and assigning log removal credits for filtration technologies.

The performance of DE and traditional granular media filtration will soon be subject to new regulations (LT2ESWTR). Knowledge of oocyst and microsphere removal by different filtration systems will be critical in prescribing log removal credits for C. parvum in the context of these regulations. Municipalities operating small systems for water treatment are equally sensitive to new regulations and public pressure for reliable drinking water. Confirmation of DE filtration performance abilities will help to determine the range of uses for DE filtration. DE may be an equally effective polishing step (as compared to UV, bag filters, etc.) for current water treatment processes as well as an effective primary treatment process for small systems.