This study was undertaken to identify the relevant bending points in ORP, pH, and DO profiles in ammonia removal through online monitoring. A novelty BAF system as newl application for drinking water treatment that equipped with ORP, pH, DO and sensors was used. Two types of polluted drinking water strength (low and high strength) with various concentrations and aeration flow were treated at a fixed-time reaction of 24 h. Experiments were conducted at four track studies (TS) of TS1 ( 50？mg/L, aeration 0.3 L/min), TS2 ( = 100？mg/L, aeration 2.0 L/min), TS3 ( 100？mg/L, no aeration) and TS4 ( 10？mg/L, aeration 0.1 L/min). The results showed that the removal of was more than 95% for TS1, TS2, and TS4. From the online monitoring performances, DO elbow and ammonia valley appeared in ORP and pH profiles, respectively. Similarly, new positive plateaus were observed in DO, indicating that the nitrifiers stopped to consume the DO after was completely removed. Hence, based on the bending points, the aeration system is possible to be automatically stopped just after DO elbow and ammonia valley appears in order to save the energy consumption and to shorten the time demands for the drinking water treatment process. 1. Introduction The presence of ammonia in drinking water exceeding the Malaysian regulated limit (<1.5？mg/L) became a major problem to drinking water treatment plants (DWTPs). Recently, there is no specific treatment system that can remove the pollutant efficiently which finally causes plant shutdown for a period of time. Consequently, the populations in the area will face a shortage in water supply and interruption in almost daily activities. Moreover, high ammonia level in drinking water provided a complication on chlorination process due to the yield of chloramines [1], human nervous system damage and created a deteriorating taste and odour of water [2]. Therefore, it is necessary to develop an effective additional water treatment system, typically for ammonia removal in order to prevent the plant shutdown due to the high level of ammonia in water. Based on the literature, biological aerated filter (BAF) is a suitable process as an additional system in DWTPs where the system is well known as one of the biological treatment systems in wastewater treatment but not in drinking water treatment. The BAF system is an attached growth process where consortium microorganisms grow on media which are stationary during normal operation with aeration [3, 4]. Among the outstanding advantages of BAF are that it is a flexible reactor and able to perform solids
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