Estimation of available biodegradable substrate (ABS): Alternative method

The five days Biological Oxygen Demand (BOD5), when related to its COD concentration, is usually used to express the wastewater biodegradability. However, it does not allow to estimate the time required for its degradation and it does not distinguish between rapidly or slowly biodegradable substrates. The reference time for biodegradability assessment is also related to the retention time (hours) of the substrates within the biological reactor, which is very different from the BOD test duration (five days). Innovative methods were developed to improve the determination of the biodegradable and/or readily biodegradable wastewater fraction by comparison of the test response with known substrates. The present study provides an alternative and complementary method to the traditional BOD. The proposed method is based on the evaluation of the biomass oxygen consumption by degradation of the available biological substrate (ABS) into a wastewater, through respirometric tests simulating the biological reactor of the treatment plant at laboratory scale. This method also allows to obtain the actual oxygen consumption for the biodegradation of organic substrate and to evaluate the toxic effect of aqueous waste to biomass. The results obtained show an inverse relationship between the COD fraction that is biodegraded by the hydraulic retention time (HRT) that characterises the oxidative reactor and the organic load fed to biomass. Starting from oxygen uptake/COD ratio of 0.40, obtained with a low organic substrate concentration, 0.05 with high concentration is achieved.