| Water from Canadian prairie reservoirs is a challenge to treat. The water is often high in dissolved organic carbon (DOC) and low in turbidity, and is compounded by low water temperatures that sometimes drop to less than 2°C. Jar tests were used to test the performance of three coagulant chemicals with cold prairie water and to test the benefit of coagulant aids in this water using aluminum sulphate. The jar tests showed that cold water temperature significantly affected turbidity and particle removal for aluminum sulphate coagulation, however, polyaluminum chloride (PACI) was impacted only slightly and ferric chloride was not affected. Cold water temperature did not affect DOC, UV254 absorbance or colour reduction for the three coagulant chemicals tested, but DOC removal efficiencies varied amongst the chemicals used for coagulation. The addition of bentonite to increase turbidity did not improve the treated water turbidity but with the increased particles in the water initially, the overall particle removal increased. The addition of powdered activated carbon (PAC) also did not improve the particle removal but did remove up to 12 percent more DOC. Acidification removed more DOC at a lower coagulant dosage, however, turbidity and particle removal was affected. Settling aid polymers and biocides were found to significantly improve turbidity and suspended solids removal. The study concluded that low turbidity water may not be a factor in cold water coagulation if adequate alkalinity is present, however, DOC concentrations determined coagulant dosages and coagulation efficiency. |
