WET WEATHER IMPACTS ON INFLUENT FINE SCREENING SYSTEM DESIGN AND OPERATION

The implementation of increasingly finer influent screening technology applied to raw municipal wastewater has been a trend in the past 5 to 10 years. As screen opening size decreases, more screenings are removed at the headworks and the ability to estimate the quantity of screenings under varying raw wastewater flow conditions becomes an important parameter in the design and selection of equipment for capturing, washing, compacting, and conveying the screenings.Peak flow variations during wet weather and spring break-up can cause serious issues for wastewater treatment facilities, particularly in the Pacific Northwest and Alaska. There is currently little information available to accurately predict screenings quantities for these fine screens during these peak flow events. WEF's Manual of Practice No. 8 (MOP 8) includes screenings quantity curves based on screening technology using bar screens, with extrapolated quantities for the smaller opening sizes. This paper provides information gathered over the past two years in Alaska, Idaho, and Oregon municipal wastewater treatment facilities and relates this data to design considerations for sizing and comparing screenings washing, compacting, and conveyance equipment at the J.M Asplund Wastewater Treatment Facility in Anchorage, Alaska.