Improving quality of COD analysis using AgNO3 for wastewater samples with high chloride content

Abstract

Chemical oxygen demand, or COD, is one of the important environmental parameters that provides the extent of pollution in the water bodies. Valid analysis of COD is needed as a basis to evaluate the condition of water bodies or a wastewater plant. Therefore, any potential deviations suspected during analysis are required to be thoroughly investigated. The problems generally found for COD analyzes came from interferences and contaminations. One challenge that the Badak LNG’s Laboratory had, was the wastewater interferences from inorganic substance. It was reflected from the results of COD analyses which prevented to deliver accurate and reliable results for high chloride wastewater samples. It is also mentioned on the Standard Method that high chloride ions (> 2000 mg/L) on wastewater can cause problems on COD determination. Further evaluations are conducted to ensure whether pre-treatment with the addition of specific compounds can compensate the interferences. On this opportunity, mercuric sulfate and silver nitrate are evaluated to determine whether they deliver effective measures to remove the chloride interference and provide valid and accurate results. Later, it was silver nitrate that had more capability to remove chloride interference with additional benefits, less cost and less hazardous wastes generated.