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Application Three Approaches To Controlling Odor In Wastewater Treatment Ponds Due to their ability to circulate a precise horizontal cross-section of water, long-distance circulators can solve odor problems in equalization ponds, anaerobic ponds, and deep-water industrial ponds. By Joel Bleth S olving odor problems in wastewater treatment ponds should begin with a few investigative questions: How was the pond designed? Has the operation of the pond changed over the years? What is the purpose and operational theory of each pond, and have ponds been added or closed? Why are odors apparent on some days and not others? Understanding these "hows" and "whys" will provide clues to successfully solving odor problems in a variety of wastewater treatment plants. All organic material contains sulfur, a chemical element that is necessary to sustain life. Sulfur in the aerobic digestion process is converted to odorless sulfate in the presence of oxygen. Sulfur in anaerobic digestion becomes sulfide and exists in several forms, from hydrogen sulfide to mercaptins, or thiols. The odors associated with sulfides are equally as diverse, ranging from the smell of garlic to rotten eggs and worse. Wastewater treatment plant operators may rate the odors coming from their plants from mild to offensive, depending on the number of complaints received from nearby residents. Operators have several options for trying to deal with pond odors, from increasing the aeration to applying chemicals to the water or perfume to the air. But often these solutions are expensive and not totally effective. Another alternative — long-distance circulators or mixers — has emerged as an economical, effective solution for controlling odors in many wastewater ponds. These mixers are installed on the pond's surface 14 wateronline.com ■ and consist of a solar-powered or grid-powered motor, an axial flow impeller that pulls water up from the intake to the surface where it is spread out at 360 degrees, an adjustabledepth intake hose, and a power-control system. L o n g - d i s t a n c e circulators are different from any other reservoir equipment in that the adjustable intake takes advantage of the manner in which water forms thin horizontal layers in ponds and allows a precise, horizontal crosssection of water to be circulated throughout the entire pond footprint. This circulated zone can be indexed to the top of the pond, such as a setting to circulate just the top X feet of the pond, or the intake hose can be set to circulate the entire depth of the pond regardless of how full the pond is. This article discusses how this unique characteristic allows long-distance mixers to control odors in three types of wastewater treatment ponds: 1) Equalization ponds 2) Anaerobic ponds 3) Deep storage industrial ponds Equalization Ponds: Keep The Pond Well-Mixed And Aerobic An equalization pond in front of a wastewater treatment plant acts as a shock absorber by temporarily holding excess inflow during rain events until the water can go through the treatment plant. For example, an equalization basin may be designed Water Online The Magazine