Abstract: A survey regarding online instrumentation and control was conducted among 90 companies managing their own biological wastewater treatment plant in Flanders, Belgium. In this study, all types of online instrumentation have been found suitable for automatic process control. However, its integration in general process control as well as in nitrogen removal and chemical dosing control appeared to be rather limited. Only dissolved oxygen and pH sensors were widely applied, being present in 96% and 69% of the plants, respectively. Widespread process integration is mainly obstructed by the fact that companies, especially small and medium-sized, still do not regard wastewater treatment as a full-fledged part of the production process. Operators often lack technical expertise in this domain and tend to be skeptical towards automated control mechanisms. In addition, the price of online instrumentation is still perceived as too high, in particular at smaller companies. Lastly, the design of the existing wastewater treatment plant does not always allow for real-time control. Certain measures such as operator training, monitoring of energy and chemical consumption and reduction of instrumentation costs are essential for widespread application of online process control in future years. Additionally, water reuse can create an important incentive.