Oral
Abstract
Research summary supplied by the authors
Chrome tanning is the most common type of tanning in the world. Residual Chrome in the effluent and the high chrome sludge disposal costs however poses a significant discharge and disposal problem. The legislative limits on chrome in effluents remain strictly regulated throughout the world with discharge limits of < 1mg/l in most countries. Common practice is to remove chrome in a batch process by precipitation of chrome effluents at pH < 9 and settlement of the chrome containing sludge. Using chrome precipitation is difficult to consistently reach the chrome discharge limit as fats and small fibre tend to float and not to settle. A new promising approach for tanyard effluents is a continues chrome effluent treatment with DAF (Dissolved Air Flotation) treatment. A Dissolved Air Flotation installed at a wet-blue tannery, has shown to efficiently remove chrome from tanyard wastewater, achieving a clear effluent with <0,25 mg/l chrome. The chrome treatment is completely automated, reducing chemical usage and chrome sludge generation and is operated at ideal pH and adjusted coagulant and flocculant addition to allow for complete chrome precipitation. The highly concentrated chrome sludge has a high degree of dryness of 8-10 g/l, which reduces sludge volumes for chrome sludge de -watering. The implementation of continues chrome effluent treatment using Dissolved Air Flotation, removes efficiently chrome and keeps the biological sludge chrome free, opening new disposal routes and allowing to use the biological sludge for biogas generation.