Developing an operating strategy for the fill period is a complex problem for designers of hazardous wastewater SBR systems. Domestic wastewater treatment systems seldom require laboratory treatability studies, because these systems follow conservative design approaches and municipal wastewater flow rates and characteristic variations are predictable. Laboratory treatability studies are almost always needed to design SBRs and to select the appropriate fill policy for hazardous wastes. The following describes alternative fill policies that must be developed during treatability studies.
SBR influent may require pretreatment. The decision to provide screening and degritting is made on the same basis used by designers of conventional continuous flow plants. Upstream flow equalization allows for rapid fill rates (i.e., higher than influent flow rates). This results in reduced cycle times and reduced reactor size. The use of rapid fill periods also results in the accumulation of high substrate concentrations. Upstream flow equalization is not necessary because idle is a normal SBR function. However, upstream flow equalization may be selected, allowing wastewaters with highly variable characteristics, or from more than one process to be blended for more uniformity. In addition, high concentrations resulting from spill events can be caught and kept from interfering with the biological process. Flow equalization basins are often included in SBR systems because they are inexpensive, provide added system flexibility, and reduce or eliminate idle time.
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