Lower chemical use in wastewater treatment

Model-based development of a control strategy for chemically enhanced primary treatment (CEPT).

Québec City in Canada invested in chemical enhancement of its wastewater treatment plant (WWTP) by installing alum addition in its existing primary clarification process. Despite promising results in preliminary tests, the designed chemical dosage seemed to over-perform, causing chemical supply costs to be unsustainably high. In order to reduce chemical use while keeping good effluent quality, the city set up a project to gain a better understanding of the dynamic effects of alum addition in primary treatment. The aim was to design an appropriate automatic controller able to maintain performance at reduced resources. The city chose a model-based approach using WEST, which allowed it to test different control strategies and settings in a cost-effective way without jeopardising operational stability and performance.