Measurement And Reduction Of COD In BOP Alkali Waste Water

The alkali waste water drained from Butanol and Octanol Plant (BOP) contains some polarity organic compounds, such as alcohol, aldehyde and trimer, etc., and has very high COD value up to 30000 mg/1. In order to reduce the error and time of COD measurement, gas chromatography with 530 μm polar FFAP capillary column, flame iron detector and programmed temperature was applied to analyze the composition and to measure COD value of the waste water. The concept of contribution factor was proposed to describe the contribution of individual organic compounds to the COD of alkali waste water and a model was developed to determine the COD of alkali waste water by gas chromatography.The experiments were carried out to optimize the measuring conditions and to confirme the relative factors of all organic compounds respectively. The measurement by gas chromatography has shorter time of about 1.5 hr than the method of potassium dichromate oxidation and the relative error of 3%, lower than the national standard, 4.3%. The gas chromatography could be applied to determine COD value of waste water succeefully and overcome the disadvantages of classical potassium dichromate oxidation method.The alkali waste water from BOP was treated to reduce COD by the liquid to liquid extraction by using column-bottom residuals of BOP as extractant. The extraction experiments show that the phase interface between two liquids is clear and there are no phenomena of emulsification. The COD could be reduced to 3500 ~ 5000 mg/1 and the removal rate of COD was over than 90% at the temperature of 40-60 ℃ and ratio of waste water to extractant of 1:6. The alkali waste water treated by the liquid to liquid extraction meets the emission control standard of waste water. Based on the laboratory test results, an industrial treatment equipment of waste water was designed and built to treat the alkali waste water by the liquid to liquid extraction. COD in treated water is less than 5000 mg/1. Because the extractant agent is the column-bottom residuals from BOP and can be directly used to treat the alkali waste water at the same temperatur, the liquid to liquid extraction process can recover the organic compounds and comsumes less energy, which reduces the contamination pollution on environment and increases the economic benefit profit of BOP.