Managing Ponds for BOD Reduction and Odor Control

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Courtesy of Integrated Engineers Inc.

A large number of food processors utilize ponds to treat their wastewater. Most of the time these ponds are aerobic in which they use oxygen to degrade the wastewater biological oxygen demand (BOD). Fruit and vegetables contain a high amount of simple sugars and other organic compounds that when exposed to water are released into the water stream. These organic compounds require oxygen to degrade them to carbon dioxide and water. This sounds very simple yet many ponds have difficulty in achieving a sufficient level of BOD reduction and therefore generate offensive odors. This article helps to define the proper method of pond management to reduce the odors from pond systems.
Treating wastewater is an expense to all food processors. The local regulatory agencies require the level of treatment required for each facility. These regulators are usually the Regional Water Control Board as well as the Air Quality Districts. For ponding systems, the Water Board requires a permit to operate the ponds. The permit defines the level of
‘treatment’ required prior to final discharge whether for percolation (direct seepage into the ground), evaporation, or irrigation (indirect seepage into the ground). The limits on Percolation ponds are governed by the risk of infiltration and possible effects to ground water quality. In addition, if a percolation pond does not have a sufficient amount of BOD reduction of the insoluble BOD, then the percolation rate of the ponds can be decreased (pond plugging). Evaporative ponds are usually lined and require a larger surface area than percolation ponds. Ponds that have a final discharge to land such as an irrigation system are usually permitted based on a fixed quantity of BOD/Day/acre irrigated. Similar to percolation ponds, the limit is due to the risk of too much BOD applied to the soil which creates a slime layer just under the soil and subsequently decreases the percolation rate of the land. Regardless of the pond design, they are biological systems that need to be operated properly. If they are not, odors will increase and the regulatory agencies as well as local neighbors will require proper pond operations.

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