The Journal of

  Background: Precise determination of organic load is one of the major and important parameters in selecting appropriate treatment process for industrial and domestic wastewaters . Performing chemical oxygen demand (COD) test in real samples is always subject to interferences, insufficient sample digestion and consuming high levels of chemical pollutants. The main aim of this scientific and applied research is modification of digesting system in COD test with silver nano particles for determination of organic load in effluent of pharmaceutical industries

  Method: In this research silver nano-particles with 20nm in average size was used instead of silver sulfate in COD test. Optimizing some parameters such as digestion time, digestion temperature and catalyst dose was considered and the entire figure of merits was calculated for theproposed method. Then in optimized condition, the COD of pharmaceutical wastewater including domestic, industrial and mixed wastewaters were determined and their results were compared with the reference method.

  Results: The results reveal that with only 16 percent of silver mass in reference method, high efficient and throughput results can be obtained for digestion of pharmaceutical wastewater and some slow-digesting chemicals. Minimum level investigations for digestion time and temperature reveal that in optimized condition and in presence of silver nano particles, the digestion process can be completed in 120 min and 150 ^◦ C respectively. The proposed method enjoyed a 4.03 in mean of RSD% and 5.06 in relative error (n=12) which were better than the reference method. The limit of detection (LOD) and limit of quantification (LOQ) was 5.0 and 15.0 mg/l respectively with a 15-300 mg/l dynamic linear range.

  Conclusion: Considering the efficiency of deterministic COD system based on digesting of organic compounds in the presence of silver nano particles for determination of organic load in pharmaceutical wastewater samples, as well as having high repeatability, compatibility with reference method, high dynamic range, consuming very low levels of silver mass and more environmental compatibility, it can be concluded that this test method can be used for determination of organic load in pharmaceutical wastewater and similar industries.