Correlation between BOD5 and COD – biodegradability indicator of wastewater

Abstract

Biochemical Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD) are the most commonly parameters for characterization of organic matter content of water. Correlation between BOD5 and COD for different types of water can provide relevant information about the nature of pollution, the content of organic matter and its level of biodegradability. This correlation could also be used to assess the quality of effluent after the treatment processes, to improve the performance of wastewater treatment plants (WWTPs) and/or to monitor the quality of river water into which wastewater are discharged. The objective of this study was to assess the degree of biodegradability of different types of water (influents and effluents of 3 important municipal WWTPs of Romania, untreated wastewater discharged by different economic units from Bucharest; effluents of 5 different hospitals and surface water - natural receptors of the effluents discharged by the municipal treatment plants), based on the ratios of BOD5/COD. BOD5/COD ratio (also called Biodegradability Index) varied depending on the type of water investigated and should be periodically rechecked due to variations in climatic conditions, untreated industrial wastewater discharged into natural receptors, water supply characteristics, water availability. Biodegradability Index enable the evaluation of the organic pollution of wastewater, providing the possibility of estimation regarding the biological treatability of influent of WWTP.