Procedures in Ready Biodegradability Testing: Effects of the Inoculation and the Monitored Parameter

Ready biodegradability tests are often limited because of a lack of definition in some operating conditions, which can be critical for reproducibility and efficiency. In this paper, the effects of the monitored analytical parameter and the variations in the inoculum quantity on test results are studied. In a Sturm standardized assay, sodium acetate and dodecylbenzene sulfonate (DBS) were tested at several initial substrate to biomass ratios (S0/X0). The analytical parameter did show itself to be determinant in the estimation of the extent of the acetate biodegradation. In DBS assays, imposed S0/X0 ratios did control both lag time and biodegradation level as well as final carbon distribution in cellular, mineralized and residual carbon. Therefore, quantitative measurement of the S0/X0 ratio, or alternatively its setting at a certain value, could enhance the reliability of test results. In order to improve the comparison between different analytical procedures, a low S0/X0 ratio is deemed advantageous. The results of these studies have implications for the methodology used in biodegradation test systems and suggest caution before utilization of a non characterized inoculum possibly leading to erroneous conclusions.