Abstract: The present invention relates to a process for production of pure terephthalic acid comprising: a) removing a mother liquor from a terephthalic acid through a filter with a gas, wherein the gas comprises steam at a concentration of least about 50% by volume; b) purifying the gas; and c) recycling the gas purified in step (b) back to step (a).

Abstract: An acidic organics-containing waste water stream (12) derived from for example plant for the production of an aromatic carboxylic acid such as terephthalic acid is treated to allow recovery of alkali and water for recycle to the production process. The treatment comprises adjusting the pH of the waste water stream using an alakaline medium, oxidising (10) the organics content of the stream to convert the same to water, carbon dioxide and (bi)carbonate ions, and supplying the treated stream to a reverse osmosis membrane (28, 30) to produce a retentate containing (bi)carbonate ions and cations derived from the alkaline medium and a permeate which is substantially free of those components. The retentate (46) is recycled for use in adjustment of the pH of the waste water stream and, if desired, water-consuming facilities which can tolerate less pure water.