Biodegradability of nitrogenous compounds under anaerobic conditions and its estimation

The anaerobic biodegradability of 23 nitrogenous compounds, including nitrogenous heterocyclic compounds and aliphatic amines, was tested and assessed in integration. These nitrogenous compounds were classified into readily, partially, and poorly biodegradable compounds after calculation of their integrated assessment indices (IAIs), Rules for anaerobic biodegradation of these compounds were also drawn. Stepwise regression and backpropagation artificial neural network (BP-ANN) methods were applied to establish quantitative structure–biodegradability relationships (QSBRs) based on the assessment results. In QSBR models, three molecular structure descriptors—second-order molecular connectivity index ( 2χv3χpv), and energy of the highest occupied molecular orbital (EHOMO)—were included. After analysis of the sensitivity of variables in QSBR models, it was found that the key molecular structure descriptor affecting anaerobic biodegradability of nitrogenous compounds is EHOMO, which is directly proportional to the anaerobic biodegradability of nitrogenous compounds.