Consideration of DAF retrofit to a large conventional water treatment plant

• Published in: Water science and technology 1995-02, Vol.31 (3-4), p.93-101
• Main Authors: Vallance, B. C., Pritchard, R. G., Hargesheimer, E. E., Seidner, R. T.
• Format: Article
• Language: English
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.1995.0520

Recent historical trends have shown a deterioration of raw water quality feeding the 60 year old Glenmore WTP. This deterioration has manifested itself in a chronic increase in nutrient loads and consequent chlorine demand. The plant's existing pre-treatment and sedimentation facilities have had difficulty in handling flash turbidity spikes. Lack of contact time for post chlorination has created a reliance on high pre-chlorination practice to ensure a safe distribution system disinfectant residual. These trends, together with the regulatory authority's tightening of compliance standards and enforcement policies, plus growing public expectations for consistently high quality drinking water, pointed towards a need for a comprehensive assessment of the plant. The City of Calgary, with its Engineering Consultant, embarked on a programme to review the existing plant facilities; identify alternatives with potential for addressing known concerns; and pilot both conventional and advanced treatment processes side by side, to establish relative and definitive performance data. This paper addresses the piloting aspect of the study programme, and in particular, the rationale for piloting dissolved air flotation (DAF). Conceptual development, design and construction of the pilot plant are all discussed. The conceptual development was based on the needs and design constraints imposed by the existing plant, such as hydraulic profile. The approach to design was predicated by a desire for a pilot plant that would provide not only guidance for the plant upgrade, but also a working tool for future studies, process monitoring and optimization. The construction and commissioning was planned with a view to having the pilot plant operational in time for spring run-off. Some of the operational experiences with the pilot plant are discussed. These included modifications to the DAF baffle weir; the collection, display, manipulation and graphing of data from online monitors; filter performance following DAF pre-treatment, and the establishment of a successful set of operating conditions.