ADSORPTION CHARACTERISTICS OF A BIOTREATED PULP-MILL EFFLUENT

Spent bleaching effluents from the chlorination and extraction steps of a sulfate pulp mill were subjected to activated carbon treatment to investigate the elimination of nonbiodegradable matter. For this purpose the biotreated wastewater containing mainly nonbiodegradable matter was treated with different activated carbon types. The elimination degree of nonbiodegradable matter was determined and adsorption isotherms were generated in terms of the parameters COD, DOC, Color436 and UV254. The removal level was over 90% when the carbon dosage exceeded 10 000 mg/l. AOX compounds could be eliminated over 90%. The isotherms could be expressed by the Freundlich equation. It was shown that the shape of the isotherms was strongly dependent on the carbon dosage employed. According to carbon dosage three different adsorption regions were distinguished and for each region the corresponding Freundlich constants K and n were determined. Carbon addition led to a change in the composition of wastewater as shown by decreasing COD/DOC, UV254/DOC and Color436/DOC ratios. Further it was shown that the relatively fast color and UV analyses were accurate enough to characterize the adsorptivity.