The biological self-purification capacity of natural and waste waters by assessing the ratio between biodegradable and toxic pollutants

The study emphasizes the significant impact of chemical pollution in the aquatic environment, originating from various sources - continuous, intermittent, and accidental - with particular focus on small rivers in the Republic of Moldova. The article applies the methodology for evaluating the self-purification capacity of natural and waste waters using parameters as biochemical oxygen demand (BOD5) and chemical oxygen demand (CODCr). These parameters are essential for assessing the contribution of pollutant biodegradation processes in natural and waste waters. The classification of waters into five levels of self-purification, from efficient to impossible, is based on the ratio BOD5/CODCr. This paper emphasizes the need to comply with the normative requirements for the treatment of wastewater from different economic sectors. Monitoring compliance with these requirements can be achieved by calculating the self-purification capacity using the BOD5/CODCr ratio.