  The introduction of the Water Framework directive sets stringent limits on
phosphorous discharge from wastewater treatment plants to maintain the complex
interdependent relationship between water tributaries and the ecosystem. This
paper studies a cobalt based electrochemical sensor for phosphate detection in
wastewater. An evaluation of the sensors operational envelope, impact of pH,
detection limits, linearity of response, accuracy and reproducibility in a
single ion solution was conducted. An indirect method was employed to assess
the effect of all of these parameters; the parameter was kept constant, while
the phosphate concertation was varied. Tests on real wastewater samples
verified the effect of the interfering factors, as phosphate measurements from
three different sampling points (influent, activated sludge mixed liquors and
effluent) did not correlate favourably with measurements acquired from a
specialised laboratory. The success of this sensor is probably dependent on the
simultaneous measurement of, or the calibration for, interfering parameters.
However, the former approach would most likely require additional probes to
measure these interfering parameters and the latter would probably require a
complex calibrating matrix to account for all the interfering parameters.
Nonetheless, variations of such sensors reviewed in this paper and their
encouraging results offer an optimistic field of improvement on the design of
the sensor studied in this paper for it to be employed on real wastewater
systems.
