Development of a respirometric assay to measure the transient load response of activated sludge to individual organic chemicals

This study described a new respirometric technique to monitor the transient response of activated sludge systems to individual synthetic organic compounds (SCOs). The assay used a fed-batch reactor system which contained mixed liquor from the parent reactor and received a biogenic feed and the target SOC at the same F/M ratio as was applied to the parent reactor. The fed-batch reactor was oxygenated using a hollow-fiber reaeration module to meet the steady-state oxygen demand. The reaeration module was characterized by means of K_L a studies. The assay monitored the dissolved oxygen concentration profile after application of a shock load achieved by switching to a fed-batch feed with the target SOC at an elevated concentration. Mathematical descriptions of the transient profiles were derived and the experimentally observed dissolved oxygen profiles were subsequently compared to profiles predicted using extant kinetic parameters for SOC removal measured using an earlier developed assay. The use of the assay were complicated by the difficulty in maintaining a reaeration capacity at constant and low capacity. As a result, the adequacy of the measured extant kinetic parameters as predictors of the transient response could not be confirmed.