Improving nitrogen removal using on-line sensors in the A/O process

A bench-scale anoxic-oxic (A/O) system was used to treat a synthetic starch wastewater for 1 year. The objectives were to improve nitrogen removal and reduce operating costs by using on-line sensors DO, pH and ORP. It is found that the DO in the first aerobic zone could be used to estimate influent ammonia load under constant aeration. The pH profiles and DO profiles along the length of aerobic zones give good indication of the nitrification, and the pH profiles in the aerobic zones and anoxic zones could be classified into two types: descending and rising type. Further, ORP value at the end of aerobic zone showed a good correlation with the effluent ammonia and nitrate nitrogen concentration, good effluent quality corresponded with the range of 40-60 mV of ORP in this study. ORP was also correlated well with nitrate concentration at the end of anoxic zone, and the maximum denitrification capacity could be achieved when ORP was maintained at about -90 mV. A fuzzy inference system for on-line aeration, nitrate recirculation flow and external carbon dosage control is developed on the basis of these observations and is implemented on the bench-scale system. Promising control performance is achieved. (c) 2006 Elsevier B.V. All rights reserved.