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Due to the demand for a low level of nutrients in watershed discharges, the requirement for wastewater treatment plants to achieve low nutrient levels is growing in Alabama. This paper studies the utilization of Sequencing Batch Reactors (SBR) followed by Cloth Media Filtration for such a purpose, focusing more specifically on phosphorus removal.
The SBR and cloth media filter technologies were chosen for a number of plants in Alabama due to the ability to efficiently achieve high levels of nutrient removal without the need for supplemental carbon addition or separate anoxic mixing tanks. The Buxahatchee Creek and Leesburg plants are among the plants referenced. In operation of the plants, the operators have seen the low effluent values of phosphorus biologically, therefore requiring minimal amounts of metal salts to achieve the low effluent Total Phosphorus requirement.
The basic principle of biological phosphorus removal in the system is to expose bacteria to alternating aerobic and anoxic conditions to anaerobic conditions. Under anoxic to anaerobic conditions such as those found in the Mix Fill phase in the SBR process, some bacteria have the ability to take in organic substrate, such as BOD5. In order to obtain the energy to incorporate BOD5 into the microbial cell under anaerobic conditions, the bacteria release phosphorus into the wastewater. When aerobic conditions are restored at the beginning of the React Fill phase, the organic substrate that has been taken in is converted to energy and cell mass. This allows the bacteria to take in phosphorus, and after being exposed to anaerobic conditions, the bacteria can take in more phosphorus then needed to fulfill its nutrient needs. The biological phosphorus uptake in the SBR system is followed by metal salt and polymer addition prior to the cloth media filtration system in order to achieve low levels of effluent Total Phosphorus.
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