Aeration Improvements Yield Improved Settleability and Nutrient Optimization at the East End WWTF

摘要

The East End Wastewater Treatment Facility (WWTF), located in the Presumpscot watershed of Casco Bay, is owned and operated by the Portland (Maine) Water District (PWD). The activated sludge process previously used mechanical surface aerators that were original to the plant and could no longer effectively deliver oxygen. Due to the low dissolved oxygen concentrations, the facility experienced sludge settleability issues and filamentous organism growth. An in-depth evaluation of several aeration technologies included fine bubble diffused aeration, INVENT® mixer/aerators, and a hybrid of the two technologies. Fine bubble diffusers were ultimately selected because of the lower capital and operational costs (Rohrbacher, 2016). In addition, an evaluation of blower technologies was performed. PWD selected single-stage integrally geared blowers because of lower long-term operating costs. Construction of the aeration system upgrades were completed in October 2017. Since the upgrades have been put online, average sludge volume index (SVI) values have dropped from 250 mL/g to 120 mL/g. As a secondary benefit, effluent nitrogen loads have significantly decreased during the warmer months.