The Plant, rated for 200,000 m3/d (90,000 m3/d average dry weather flow), is configured with PSTs, a 6-lane 3-stage Bardenpho activated sludge process, and anaerobic digestion. By 2020, the plant is required to meet a new effluent ammonia permit of 1 mgNH3-N/L. The basis of the permit is a 95-percentile limit on grab samples, which must be met regardless of temperature and peak/storm flows. The Plant, currently permitted for 3 mg NH3-N/L, experiences ammonia breakthrough related to seasonal low temperatures, low alkalinity, oxygen limitations and storm-flow events. Through a model-based assessment of The Plant at future (i.e. 2026) flow and loading, ammonia breakthrough events were found to result from either insufficient HRT or oxygen supply. An aeration control strategy was developed to help mitigate ammonia breakthrough during peak/storm events. The aeration control strategy provided significant cost savings as it optimized the capacity of the existing treatment infrastructure helping decision makers rule out the need to provide an additional activated sludge train and additional aeration capacity. The model-based assessment provides an understanding of the importance of historical flow analysis for model application and control, and the relevance of modelling and control as a means for improving plant management.
Innovation, Optimisation and Process Modelling