Toxicity reduction in leather tanning wastewater by improved coagulation flocculation process

The wastewater of leather industry which is one of the most widespread industries having
large amount of water consumption and very high pollution loads, may be characterized by
several key parameters including toxic pollutants exhibiting toxicity. Therefore the effluent of
leather tanning industry must be handled carefully during both treatment plant design and
operation.
The aim of this study was to improve the coagulation process for toxicity reduction of raw
wastewater taken from a leather tanning district central treatment plant (Solofra, (Avellino,
Southern Italy). A series of jar test experiments on three samples taken between February and
July 2005, were performed using ferric chloride, ferrous chloride, aluminium sulphate and polyaluminium
ferric chloride (PAFC).
The optimum coagulation conditions for the first sample were determined as 8.5 pH and 900
mg l-1 dose of PAFC with the addition of Ca(OH)2 which resulted in a 76% COD and 98% TSS
removal and more than 50% of D. magna immobilization (at 50% dilution) reduction.
Coagulation experiments performed on second and third samples showed that PAFC resulted
in the highest COD removal among the coagulants tested The results that PAFC, recently
developed coagulant, is the most promising one for leather tanning wastewater, thus,
improved coagulation followed by biological treatment can result in safe effluent to aquatic
environment.