A process for removing urea from water

Abstract

A process for removing urea from water, the concentration of urea in the feed water being less than 1 ppm, the process comprising the steps of adding a nitrite ion to the water and of then passing the water through a strong cation exchange resin in an ion exchange column is provided. The molar ratio of nitrite to urea is preferably between 50 and 1500. The urea reacts with the nitrite to form dissolved nitrogen and carbon dioxide gases, and ammonium. The ammonium is removed in the ion exchange column. There may be two columns in series. The nitrite may be added in the form of a sodium nitrite salt, nitrous acid, or nitrogen dioxide gas. The excess of nitrite present in the treated water may be removed with an anion exchange resin, by reaction with an oxidant, or with a reverse osmosis treatment step. Regeneration of the column is triggered by a measurement of the pH or of the conductivity and is conducted with an acidic solution.

Description

Background technique [0001] Urea (CO(NH 2 ) 2 ) are very small molecules, very polar and highly soluble in water. This makes it difficult to remove at low concentrations (up to 1000 ppb, where ppb means parts per billion). In most natural waters (well water, drinking water and surface water) and recycled wastewater (urban industrial and agricultural water), urea can be present in the range of 1-100ppb, especially depending on the seasonal agricultural run-off ). [0002] For the production of ultrapure water (UPW), especially for the preparation of semiconductor wafers, urea is a very critical pollutant, because urea is hydrolyzed on the surface during the production of semiconductor equipment, mainly producing prohibited ammonia, a ionic compound. [0003] The reduction in urea during conventional UPW is very low and not sufficient to reduce urea to acceptable levels. Biofilters can handle urea to some extent, but it is very difficult to control how to make the biofilte...

AI Technical Summary

Problems solved by technology

Biofilters can handle urea to some extent, but it is very difficult to control how to make the biofilter work at these low urea concentration levels

Chemical processes are known to be used to reduce urea like oxidation with chlorine, bromine followed by absorption, reverse osmosis etc but expensive in capital and operating costs

[0004] It is also known to use nitrite ion (NO 2 -) (as NaNO 2 (sodium nitrite) salt, nitrous acid (HNO 2 ) or NO 2 gas) to reduce urea levels, but at these low concentrations, the urea is too dispersed to generate sufficient reactions to convert the urea into elements or compounds that can be more easily removed

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