Biodegradation of selected organic nitrogen compounds in activated sludge systems

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Activated sludge systems are commonly used to remove organic matter and nutrients from wastewater. They are also used to remove synthetic organic compounds from industrial activities. In this study, two identical activated sludge-based continuous stirred tank reactors (CSTRs) were employed to study the biodegradation of melamine and 4-nitrophenol and their impact on wastewater effluent water quality and microbial structure and functions. Two CSTRs at steady-state conditions were fed with two synthetic organic nitrogen compounds, melamine and p-nitrophenol (PNP) for 12 hours on day 136 and 150, respectively, of an extended test. Melamine, although toxic to human and animals, presented no detrimental effect on bioreactor performance and it appeared to act as an inert soluble substance in the activated sludge system. After the shock loading, melamine was quickly washed out of the continuous flow system. Batch degradation studies confirmed that the activated sludge from the CSTR was not capable of degrading melamine. The other chemical p-nitrophenol (PNP), however, showed significant toxicity towards the activated sludge, although subpeaks of possible PNP degradation metabolites were detected by high performance liquid chromatography indicating that the PNP could be partially degradable by the activated sludge. After 12-h shock loading of PNP, significant inhibition of nitrification and bacterial activity by PNP resulted in a prolonged period (> 22 days) of deterioration of effluent water quality. The results indicate that the fate and toxicity of synthetic organic nitrogen compounds can be quite different in activated sludge systems, although both melamine and PNP increased total nitrogen concentrations in wastewater effluent.