A reservoir in Bend, Oregon functions as a clearwell. In summer conditions, the maximum inflow from surface water sources is about 7,000 gallons per minute (gpm). Water is chlorinated just prior to inflow to the clearwell. At this flow rate, the water in the tank would optimally turn over more than four times per day. However, disinfection efficiency was unacceptably low. Thermal stratification and high flow rates were causing short-circuiting of the flow directly from inlet across the tank to the outlet. Contact times were about 30 minutes. To address these concerns, the Water Division installed a SolarBee mixer and tested the effects of mixing (via a tracer study and computational fluid dynamics). The field tests verified that contact times increased from 30 minutes to 80 minutes, exceeding the regulatory requirement of 30 minutes by over 150 percent.

Long-distance circulators (or mixers) have emerged as an economical, effective solution for controlling odors in many wastewater ponds. Long distance circulators are different from any other reservoir equipment: The adjustable intake takes advantage of the manner in which water forms thin horizontal layers in ponds, and allows a precise horizontal cross-section of water to be circulated throughout the entire pond footprint. This white paper discusses odor control solutions for equalization ponds, anaerobic ponds and deep-storage industrial ponds.

Electrical aeration is used intensively in reactor basins at activated-sludge wastewater treatment plants to supply the mixing and oxygenation needed for digestion. Officials at Eden, North Carolina, investigated the ability of solar-powered circulation technology (SPC) to reduce their operational expense.

The goal was to meet National Pollution Discharge Elimination System (NPDES) standards while reducing grid-powered aeration and operating a single SPC unit in one basin. Study objectives were to compare effluent water quality parameters and grid-power usage and cost during one year of SPC treatment with comparable data from the immediately preceding year when only aeration was used.