AWWA WQTC57192

This paper discusses how, in January, 2000, the City of Wilsonville, Oregon authorized the design and construction of the Willamette River Water Treatment Plant (WRWTP) to treat Willamette River water for delivery of potable water to approximately 14,000 people in the Wilsonville area. Tualatin Valley Water District (TVWD) is also a project participant and has purchased 5 mgd of the total 15 mgd capacity. The WRWTP is a 15 mgd conventional treatment plant with an ultimate capacity of 120 mgd at build-out. Selection of water treatment processes for the WRWTP was based on providing multiple barriers for all major water quality concerns and to minimize the overall plant footprint. The plant includes flash mixing, a ballasted coagulation/clarification (Actiflo) system, ozonation, filtration, disinfection, waste washwater recovery and sludge dewatering facilities. The greatest space savings at the plant were gained by selecting the ACTIFLO process for combined flocculation/sedimentation. The raw water can be characterized as having low mineralization, low to moderate organic content, and seasonal taste and odors resulting from algae and algal decay. Turbidity levels average below 20 NTU throughout most of the year. Higher turbidity spikes (e.g. >50 NTU) typically occur in the fall, or following unusually intense rainstorms in the winter. Trace levels of synthetic organic compounds are occasionally detected in the river but only following a storm event. The paper gives a description of the Actiflo process and details its performance as far as turbidity removal, treatment capacity, and sand loss. Includes tables.