Achieving BPR Without Nitrification - A Low SRT Dilemma

摘要

Clean Water Services has historically operated the Forest Grove Wastewater Treatment Facility (WWTF) to achieve secondary treatment goals during the winter (between November and April), and transfers raw wastewater to the Rock Creek Advanced Wastewater Treatment Facility (AWWTF) to meet the stringent nutrient limits imposed on the discharge to the Tualatin River during the summer (May through October). To avoid consuming treatment capacity at Rock Creek AWWTF and to assist in meeting thermal load limits, the Forest Grove WWTF has transitioned to year-round treatment with the construction of the Fernhill Natural Treatment System (NTS) downstream of the Forest Grove facility. The Forest Grove WWTF is operated to meet suspended solids, oxygen demand, and phosphorus limit, but not to nitrify to allow this process to be achieved in the downstream natural treatment system. While part of a beneficial holistic treatment strategy, this goal requires that the facility be operated with an aggressively-low SRT that has proved to present additional operational difficulties. From 2016 through 2018, testing has been conducted at the facility to determine how to consistently operate under these conditions. The resulting experience has helped to provide adequate evidence that the nutrient goals for phosphorus and non-nitrifying conditions can be met, but the volatility in the process under these conditions has presented challenges to meet the effluent suspended solids limits for the process.