On-line determination of pollution loads (Suspended Solids, Volatile Suspended Solids, Biological Oxygen Demand and Chemical Oxygen Demand) on biological waste-water treatment plant is the prevalent practice for process control. Both measurement of turbidity and others on - line parameters allows to approach plant loads. It is possible to estimate Suspended Solids of inlet by turbidity measurement at 550nm and 850nm. COD could be approached by turbidity and conductivity measurement. The conception of a dynamic probe in activated sludge allows us to determine suspended solids (with turbidity and settleability of sludge) and its volatile part (turbidity with settleability and oxygen decrease rate). By the way it can be possible to predict sludge bulking. All these parameters are obtained with a less than 15% average error (8% for sludge). We have to compare these results with the important error induced by sample conservation before analysis in the case of classic self-control.