Treatment of cheese whey wastewater: combined coagulation-flocculation and aerobic biodegradation.

Cheese wastewater has been treated by means of a coagulation-flocculation process. Three different coagulants have been used, namely, FeSO(4), Al(2)(SO(4))(3), and FeCl(3). When FeSO(4) was used, the optimum conditions were obtained using 250 ppm of the salt at pH 8.5. At these conditions, 50 and 60% of chemical oxygen demand (COD) and biological oxygen demand (BOD) were reduced, respectively. Al(2)(SO(4))(3) achieved slightly lower reductions of COD and BOD; however, the amount needed was significantly higher (1000 ppm). When FeCl(3) was added, similar results to those obtained with FeSO(4) were experienced; again, 250 ppm was enough to eliminate COD and BOD contents in the range of 40-60%, depending upon operating conditions. The sludge formed in the coagulation-flocculation process did show acceptable settling properties, which is crucial in settling tank design. A first approach to sedimentation tank design is also conducted on the basis of experimental results. The aerobic biodegradation of cheese whey wastewater achieves the reduction of the main contaminant indicators (COD and BOD) to values close to 100%; however, effluents coming from the coagulation-flocculation pre-stage necessitate half of the time required by the non-pretreated raw wastewater.