PLATE SETTLERS DOUBLE TERTIARY CAPACITY TO 127 MGD WITHIN SAME FOOTPRINT

The Alexandria Sanitation Authority's Advanced Wastewater Treatment Facility needed to have its capacity increased from 66 MGD to 127 MGD in order to meet the increasingly stringent standards adopted by the Commonwealth of Virginia for discharge into Chesapeake Bay. Eight of the existing 12 settling tanks were upgraded with an additional stage of flocculation and inclined plate settlers. Preliminary operational data indicate the upgraded tanks are capable of equaling the effluent quality of the unmodified tanks at flows up to three times higher. The remaining four settling tanks were demolished and a new granular media filter facility was constructed in its footprint. A detailed construction sequence was developed to maintain the plant's advanced wastewater treatment capabilities during the upgrade of the facility. Three-dimensional modeling was used extensively during the design to improve product quality and constructability. To the best of the authors' knowledge, the Alexandria Advanced Wastewater Treatment Facility will be the largest wastewater inclined plate installation in the world.