New contributions to the ORP & DO time profile characterization to improve biological nutrient removal

► The classical KPIs have been related to ORP, pH and DO profiles. ► Two new KPIs, named as ORP Arrow and ORAS, have been defined. ► The ASS seasonal variations have been characterized by using K-means clustering. ► The correlation between classical and new KPIs has been studied with PCA. ► The two new KPIs are related to the organic matter and nitrogen removal processes.