Dairy wastewater treatment by chemical coagulation and adsorption on modified dried activated sludge: a pilot-plant study

Abstract

Dairy industries and milk processing plants normally discharge their wastes directly to the close surroundings, generating environmental nuisances. Consequently, dairy wastewater deserves special attention since its levels of potential contaminants typically exceed those levels considered hazardous for domestic wastewater. At present study, performance of conventional chemical coagulation using poly aluminum chloride as an inorganic pre-polymerized coagulant (at various pH and coagulant dosages) and adsorption process by modified dried activated sludge (with ZnCl2) for treatment of real dairy wastewater was investigated. Maximum removal efficiency of pollutants (BOD5 and chemical oxygen demand (COD)) by chemical coagulation process was achieved at initial pH 8 and coagulant dose 100 mg/L in 60 min. In addition, optimum conditions for adsorption process were found to be: initial pH 6, adsorbent dose of 7 g/L, and contact time 90 min. The biosorption equilibrium data were fitted by Freundlich isotherm. Furthermore, according to the thermodynamic properties, ΔG°, ΔH°, and ΔS°, adsorption of COD onto modified dried activated sludge was spontaneous, endothermic, and feasible in the temperature range of 298–318 K.