Mass balance for on-line alpha k(L)a estimation in activated sludge oxidation ditch

The capacity of an aeration system to transfer oxygen to a given activated sludge oxidation ditch is characterised by the alphak(L)a parameter. This p arameter is difficult to measure under normal plant working conditions. Usu ally this measurement involves off-gas techniques or static mass balance. T herefore an on-line technique has been developed and tested in order to eva luate akLa. This technique deduces akLa from a data analysis of low cost se nsor measurement: two flow meters and one oxygen probe. It involves a dynam ic mass balance applied to aeration cycles selected according to given crit eria. This technique has been applied to a wastewater treatment plant durin g four years. Significant variations of the alphak(L)a values have been det ected while the number of blowers changes. This technique has been applied to another plant during two months.