Influence of the size and source of the inoculum on biodegradation curves in closed-bottle tests

Test variables influencing the results of the closed-bottle test include size and source of the inoculum. The inoculum originates from activated sludge plants maintained at various sludge retention times. The lag period prior to biodegradation, which is influenced primarily by acclimation, decreased with increasing numbers of competent microorganisms. The rate of biodegradation in the closed-bottle test is influenced by the sludge retention time by which the inocula are maintained. Acclimated sludges maintained at low sludge retention times used as inocula gave biodegradation curves with steep slopes, indicating degradation at high rates. Therefore, unacclimated ready biodegradability tests enable only conservative assessments of the biodegradation potential of wastewater purification plants. The results reported here demonstrate that other tests should be used in risk assessment to estimate the full biodegradation potential in wastewater treatment plants.