Evaluation Of T&O Treatment Alternatives And Pilot Testing Ozone For Control
- Aaron Duke, Erik Rosenfeldt, Meric Selbes
Like most reservoir supplies, the surface waters in Virginia provides good, stable water quality, but can experience periods of high algae in summer and high iron and manganese levels during reservoir turnover, with accompanying taste and odor (T&O) changes. While the existing treatment process at the selected surface water treatment plant in Virginia is capable of lowering odor in the finished water under normal to low raw water odor conditions, these events (turnover or algae blooms) could potentially lead to T&O events in the finished water. The objectives of the study were (i) to identify the nature and intensity of T&O in the surface water (depth profile, seasonal variation, etc.), (ii) to identify appropriate treatment options for reducing the odor(s) at the reservoir, and (iii) to pilot test the selected treatment option and assess its effectiveness for removing T&O.
Objective (i): Four sampling events were conducted between April 2013 and April 2014 and the samples were analyzed for inorganic sulfur compounds, flavor profile analysis and MIB/geosmin. Sampling results suggested that the observed tastes and odors were Earthy/Musty associated with MIB and/or geosmin from Bluegreen algae (cyanobacteria), and Swampy/Marshy/Sulfur associated with the low dissolved oxygen conditions in the reservoir.
Objective (ii): To mitigate the T&O episodes, several treatment alternatives were examined via desktop-evaluation. The alternatives evaluated included reservoir aeration/mixing, activated carbon, ozone and UV-AOP. While reservoir aeration/mixing methods can alleviate some T&O concerns, this strategy alone may not address T&O episodes. Preliminary analysis has indicated that oxidation with ozone will likely be more effective than implementation of activated carbon or UV-AOP. Therefore, ozone treatment approach will be coupled with reservoir mixing/aeration to provide a multi-barrier approach to T&O episodes, while also achieving improvement with additional water quality concerns, including manganese, iron, turbidity, and organics.
Objective (iii): A pilot testing, which will include pilot-scale ozonation, coagulation/flocculation/sedimentation, and filtration, will be conducted at the treatment plant to assess the removal of T&O during ozonation. This pilot testing efforts will examine the effect of pre-ozonation on downstream treatment processes (i.e., operational needs) and changes in effluent water quality. Samples will be collected weekly at each pilot-scale processes and analyzed for iron, manganese, color,MIB & Geosmin, DOC, UV254, AOC, BDOC, bromide and bromate.
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