AUTOMATIC MONITORING OF ACTIVATED-SLUDGE SETTLING CHARACTERISTICS AND PLANT CONTROL APPLICATIONS

A fully automatic instrument has been developed to allow the on-line measurement of activated sludge settling characteristics. The monitor uses the derived data to calculate final sedimentation tank solids loadings and the required rates of returned activated sludge pumping. The instrument has been developed by Thames Water Utilities Limited and is now manufactured under licence by Phox Systems Ltd. It samples mixed liquor and returned sludge alternately and measures solids concentration, the initial settling rate (or rate of hindered settlement) and the stirred specific volume index. The stirred specific volume index at a standard solids concentration of 3.5 g/l is derived from the data. Actual and maximum final sedimentation tank loadings (kg/m(2)h) are calculated, and the required returned sludge pumping rate is predicted and may be controlled by the monitor. Tests have been carried out on a number of sewage-treatment works during several years of development, and some of the results are presented and discussed.