Optimizing Gravity Thickeners Performance at the World's Largest Advanced WWTP

DC Water operates the Blue Plains Advanced Wastewater Treatment Plant (AWTP), a 370 MGD facility that serves the Nation's capital, along with portions of the metropolitan area in Virginia and Maryland. This facility is undergoing numerous upgrades including installation of biosolids treatment improvements. The biosolids will be treated with new anaerobic digesters and Cambi® thermal hydrolysis to produce Class A biosolids. The digester gas will be utilized by a combined heat and power system. As part of these overall programs, improvements to the gravity thickeners are being implemented.The focus of this paper will be to present evaluations and recommendations for improvements to the gravity thickener system that will greatly facilitate improved performance, make the facilities more operator friendly, increase reliability, and enhance automation and process control. Significant among the identified improvements were items related to air entrainment in the gravity thickeners, the impact and disposal options for primary scum, and the options for control of the sludge blanket and overflow of the thickeners. With a great number of gravity thickener systems throughout the industry, and increasing focus on solids handling systems to provide energy recovery and efficiency, the approaches for improving DC Water's system may be applied to improvements at other systems as well.