Wastewater purification process

Wastewater from various sources may be purified by contacting it with sludge derived from an oxidative biological water purification process and subsequently subjected to a complete anaerobic fermentation step followed by a dying-off step. A variety of contaminants such as metals, colorants, detergents, phenols and the like may be adsorbed by the sludge in this way and removed from the wastewater by separating the sludge and wastewater after contact. The process may serve as an introductory step to a normal oxidative biological water purification process. In a special embodiment, cationic contaminants are removed from the wastewater, with the aid of a sludge of the aforesaid type, whilst anionic contaminents are removed with the aid of a sludge of the same type that has been pretreated with a cationic detergent.