ABSTRACT
The stripper is similar in configuration to a gravity thickener and maintains the MLSS in the RAS under anaerobic conditions in a sludge blanket, with a residence time of 8 to 12 hr. The stripper is the anaerobic zone where phosphorus release occurs, while the aerobic zone is provided by the main bioreactor where phosphorus uptake occurs. Since the anaerobic zone is provided in a sidestream bioreactor, the Phostrip® process is referred to as a side-stream process. In addition to a portion of the RAS, an external elutriant stream, such as a small portion of the influent wastewater or treated effluent, is added to the stripper to remove the released phosphorus. The loading of biodegradable organic matter on the stripper is relatively low. One source is particulate organic matter entrapped in the MLSS added to the stripper. The particulate matter can be solubilized and then fermented into VFAs in the stripper, thereby providing a VFA source for the PAOs. Another source is the organic matter contained in the elutriation stream. Indeed, experience indicates that process performance is enhanced when wastewater is used as the elutriant rather than treated effluent. The stripper overflow, which is enriched in phosphorus, is typically treated with lime to precipitate the phosphorus. Consequently, two phosphorus removal mechanisms operate in the Phostrip® process: through the WAS, due to the enriched phosphorus content of the MLSS, and in the stripper overflow.
