TWIRL and RSA Key Size

The present invention relates to a process for the purification of effluent which results in the textile, paper and leather industries and in the manufacture of dyestuffs, and which contains water-soluble, anionic dyestuffs or optical brighteners, the said process comprising the addition of a water-soluble formaldehyde condensation product to the said effluent and the subsequent removal of the occurring flocculate from the effluent.