Trattamento di polishing dei reflui di conceria (TANNERY WASTEWATER POLISHING))

This paper reports the results of a preliminary investigation aimed to check, at lab scale, the possibility to replace the Fenton's treatment with a simpler (i.e., alkalinisation with or without ozonation) for treating tannery secondary effluents whose residual COD values are still higher than the Italian COD Maximum Allowable Concentration (MAC) value (i.e., 160 mgO2 l-1). The results have demonstrated that when the value of the residual COD lies in the range 200÷250 mgO2 l-1, a simple alkalinisation with NaOH up to pH 12.5 allows to reach the MAC value with an alkali consumption equivalent to the acid consumption necessary for the Fenton treatment but with a sludge production significantly lower [i.e. ? 0.7 kg(dry) m-3 instead of ?1.5 kg(dry) m-3] Conversely, when the value of the residual COD is in a higher range (300÷350 mgO2 l-1), in order to reach the MAC value, an ozonation step must follow the alkalinisation .