BIOSORPTION OF HIGH-MOLECULAR-WEIGHT ORGANOCHLORINES IN PULP-MILL EFFLUENT

Since biosorption is considered an important step in the removal of organochlorines in secondary treatment systems from pulp and paper mill effluent, the role of biosorption in the removal of high molecular weight organochlorine (HMW AOX) was studied. UItrafiltered (> 1000 Da) total mill effluent was used as the sorbate and municipal sewage sludge as the sorbent. Eight different parameters were tested: contact time, cell viability, cell concentration, sorbate concentration, desorption, cell type, sorbate type and temperature. Biosorption equilibrium was reached in the first 30 min of an experiment and the removal of the high molecular weight organochlorine was independent of cell viability. The biosorption was characterized by the Freundlich isotherm [Q(mg/g VSS) = KC1/n, C = AOX concentration (mg/l)]; the observed values for the Freundlich coefficients K and 1/n were 1.83 and 0.53, respectively. The Langmuir isotherm [Q = 7.5 C/(3.2 + C)] provided a better characterization for biosorption of HMW AOX since it predicted a saturation biomass phase concentration of 7.5 mg Cl/g VSS at high AOX concentrations. The maximum percentage removal of HMW AOX was 70% at a biomass concentration of 2.0 g VSS/1 or higher. About 8% of the organochlorines desorbed from live biomass after 24 h indicating that the process is not readily reversible. Based on the experiments at various temperatures, the enthalpy of sorption was found to be -4 kJ/mol Cl.