Accuracy of COD Test for Landfill Leachates

COD (chemical oxygen demand) has historically been considered to be an estimate of organic matter, and though this is no longer the case, for most kinds of water it is still a fair approximation. Landfill leachates may, however, be one of the exceptions. Landfill leachate contains many inorganic substances and, in certain circumstances, high concentrations of volatile organic compounds like acetic acid; the COD value may be affected by these conditions. Designed experiments were performed to determine how COD could be affected by the composition of landfill leachates. The factors studied include the content of iron(II), manganese(II), sulphide, ethanol, acetic acid, ammonia, and chloride as well as different aspects of the COD analysis design. The results show that up to about one-third of COD may be due to the inorganic components of leachates. The main conclusion from the experiments is that COD cannot be used solely as a measure of the organic matter of landfill leachate since inorganic substances as well as interactions between substances may interfere with the COD results.