Solids Processing Challenges at WSSC Western Branch — Can an Innovative Technology Offer a Solution?

Abstract

Enhanced nutrient removal upgrades at the Western Branch Facility required improvements to the solids handling system in order to properly process the additional solids. This paper provides an overview of the evaluation of four alternatives for handling these additional solids. The evaluated alternatives include an innovative electrodewatering technology, belt drying technology, lime stabilization to Class A or Class B, and finally centrifuge thickening and dewatering in series followed by lime stabilization for producing Class B biosolids. The performance of the electrodewatering technology was verified in a bench-scale study in terms of required cake solids and potential stabilization, solids throughput, and electricity consumption, which aided in equipment sizing and O&M cost estimation.A life cycle cost analysis, consisting of capital and O&M present worth cost, was performed and compared among the four alternatives. In summary, the cost analysis for both electrodewatering and lime stabilization to Class B were very close, followed by lime stabilization to Class A biosolids, centrifugal thickening/dewatering with Class B lime stabilization, and finally belt drying. Life cycle cost comparison, coupled with the additional benefits from operating the system continuously during incineration, to achieve autogenous burning, and during incineration downtime for maintenance, to achieve higher dry cake solids for disposal or reuse, led to recommending the electrodewatering technology for solids handling at this facility.