Treatment methods for firefighter training area effluent
Most airports in Canada set aside small areas for firefighter training purposes. The fire drills consist of saturating with water a hum area, sprinkling a mock-up aircraft with gasoline, igniting and finally extinguishing it with water and chemical agents, such as Aqueous Film Forming Foam (AFFF) and Purple-K. Surface water and groundwater quality can be affected by this activity since it generates an effluent which is highly contaminated by soluble AFFF and residual gasoline. Aéroports de Montréal (ADM) plans to build a new firefighter training area at Mirabel airport to accommodate firefighters from both Dorval and Mirabel airports. With this perspective, ADM launched a characterization campaign for such wastewaters. The following parameters did not meet Mirabel's discharge criteria: Sanitary sewer: Total oil and grease, gasoline Storm water sewer: Total oil and grease, 5-day biochemical oxygen demand (BOD?) total suspended solids, phenol, and gasoline. The mean annual volume of effluent to be treated at the future Mirabel firefighter training area is estimated at 3 711 m³. Over 75% of this volume is due to rainfall. Concentrated AFFF volumes, dilution water and volumes involved in target practices accounts for the other 25%. The monthly maximum volume of effluent is estimated at 407 m³, and the daily maximum at 114 m³. A comparative study was conducted at Mirabel airport to determine the most suitable treatment process for firefighter training area effluent. Three different treatment methods based either on membrane or biological process were investigated. They are: a) ultrafiltration/ reverse osmosis; b) aerated lagoons with discharge either to the sanitary or storm water sewer system depending on the treatment efficiency; and c) biological batch pre-treatment with controlled discharge to the sanitary sewer. Virtually 100% removal of the total suspended solids (TSS) and close to 100% removal of total oil and grease (TOG) were achieved with the ultrafiltration/ reverse osmosis (UF/RO) process. A biochemical oxygen demand (BOD?) removal rate as high as 99.7% and a total organic carbon (TOC) removal as high as 99.3% were noted. Ultrafiltration/ reverse osmosis (UF/RO) operated as a single-pass sea water RO membranes proved to be a very efficient treatment process, with a permeate that can be discharged directly in the storm water sewer. Removal rates of up to 85% for BOD?, 79% for chemical oxygen demand (COD), 97% for TOG, and 94% for gasoline concentrations were achieved in the aerated lagoons. Although such high removal rates were achieved, the effluent's BOD?, TSS and gasoline concentrations did not comply with Mirabel's storm water discharge criteria. However, the effluent meets all sanitary sewer discharge criteria excluding gasoline, which could be eliminated by activated carbon. The biological batch pre-treatment process was examined under two operating conditions: with or without activated carbon. The effluent's TOG concentrations and the residual gasoline concentrations of the biological batch pre-treatment process without activated carbon are found to be high, and the BOD? removal is generally found to be low. Residual gasoline concentrations being still considerably high (up to 40 mg/L), a simple biological batch pre-treatment process without activated carbon is not recommended as it deemed inefficient for treating effluent from fire training area. Results from the biological batch pre-treatment process with activated carbon showed this method to be far more efficient than one without any additives. The TOG concentration of the biological batch pre-treatment effluent was found to be below.
- CUFE – Essais