Sensors for waste water: Many needs but financial and technical limitations

Abstract

A wastewater system can be divided into three steps from upstream to downstream according to their different responsibilities of operation: (1) discharge of waste water in the sewer, (2) collecting network (combined or separate) and combined sewer overflows, (3) and wastewater treatment plant and discharge of epurated water in receiving water. This chapter examines separately the needs at the three levels as well as the current practice, because they are very different when considered technically, financially, or legally. Most of the online measurements are performed after treatment or pretreatment in order to check compliance with a predefined consent level. Recent environmental directives in EEC are pushing in parallel the various ways of measuring water quality: laboratory analysis, field instruments, and online monitors, especially at discharge level. However, online monitoring is also expanding in control system for the automatic or man assisted operation of the water work. Technically, the need of online monitoring is strong in order to operate and to follow up the wastewater systems, but more than technical aspects, the lack of standards and the high cost are the main reasons why online monitoring is not yet developed in wastewater. A clear methodology must be followed before obtaining online measurements: user's needs definition, supplier consulting, choice based on financial and technical evaluation, well defined ordering, installation according to standard guidelines, commissioning, adequate maintenance, and operation.