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This paper summarizes the results of a year-long piloting program to evaluate threealternative solids separation processes for spent filter backwash water recovery. The primarygoal of this study was to select a process that would meet the dual objectives of reducing oreliminating process wastewater discharges from the 420 ML/d Bearspaw water treatment plant(WTP) in Calgary, Alberta, Canada, while avoiding any undesirable impacts on the main WTPIn Canada, as in the US, regulations and standards for treating and disposing of WTP residualsare still evolving. For this particular project, a range of disposal/reuse strategies wereinvestigated, each requiring differing treatment standards as follows:disposal of treated water to the Bow River at 20 mg/L TSS;recycling of treated water to the head of the WTP at 5 NTU; and,membrane treatment for potable water production at 0.1 NTU.Three processes were pre-selected for the pilot evaluation as follows:enhanced gravity settling using a plate settler clarifier;flotation using a dissolved air flotation (DAF) clarifier; and,filtration using an ultrafiltration (UF) membrane system.The processes evaluated covered the broad range of treatment standards potentially required forthe final end use/disposal route. The achievable effluent quality, design criteria, and operatingperformance of the evaluated processes are presented in this paper, based on extensive pilotingdata collected at the Bearspaw pilot plant facility.All three processes were proven to meet or exceed the acceptance criteria for their intended enduse. There were some unexpected discoveries regarding all three processes. For example, theultrafiltration membrane process exceeded its manufacturer's pre-piloting expectations. Thelength of this piloting program allowed for a considerable amount of operating and maintenancedata to be collected over a very broad range of water quality conditions and temperatures.Chemical dose optimization, membrane chemical cleaning regimes, and water quality data werecollected and evaluated to establish both the design and operational criteria for each process.The results of the pilot evaluation were used to formulate the following general process criteria:plate settlers with an effluent target of 5 NTU at a Hazen loading rate of 0.6 to 0.8 m/h;dissolved air flotation with an effluent target of 2 NTU at a loading rate of 10 m/h; and,ultrafiltration membranes with an effluent target of 0.1 NTU at a design flux of 42 Lmh(25 gfd) and a recovery rate of 99% for potable water production.Finally, considerations for full-scale implementation are discussed, such as source separationof waste streams, equalization, recycle stream process impacts, and residual solids processing. Includes 9 references, tables, figures.

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Edition: Vol. - No. Published: 06/17/2004 Number of Pages: 18File Size: 1 file , 420 KB