A contour plot technique for depicting wastewater lagoon parameters and analysing their interrelatedness

Most wastewater treatment plants regularly monitor plant performance. Analysis of the resulting data can provide valuable insights into plant behaviour. A useful first step in the systematic analysis of such data is to depict them graphically. The resulting plots help identify the more obvious relationships between measured wastewater characteristics. They also help in locating anomalous data points. In the case of multi-pond wastewater treatment lagoons, finding an informative way of depicting the monitoring data is difficult. This is because the required data plots need to show not only how measured characteristics vary with time but also how they vary along the pond chain. Conventional 2-D “time-series” plots are inadequate for this task if the lagoon comprises more than a few ponds, or if the amount of accumulated data is large. An alternative, contour plot based approach was developed that overcomes the problems with conventional 2-D plots. The procedure for producing such plots is described and factors affecting their accuracy discussed. A major advantage of the contour plot approach is that contour plots for different parameters can be superimposed. By examining these superimposed plots, one can learn much about the way different parameters are related. A procedure is described that enables the interrelatedness of any given pair of parameters to be systematically characterised. The effectiveness of the contour plot approach is illustrated using data obtained over a 9-year period for an 11 (later 10) pond lagoon at the Western Treatment Plant in Melbourne, Australia.