Abstract
The present study is an attempt to anaerobically co-digest excess sludge from aerobic facility of dairy wastewater treatment plant in a hybrid upflow anaerobic sludge blanket reactor. The sludge was made amenable for anaerobic degradation using ozone and chemical pretreatment. The efficiency of the treatment at optimized condition (pH 11 and ozone dosage 0.06 gO(3)/g suspended solids) showed 68 and 61% of chemical oxygen demand solubilization and suspended solids reduction, respectively. Further, anaerobic co-digestion of pretreated sludge was evaluated in two lab-scale hybrid upflow anaerobic sludge blanket reactors, namely experimental (ER) and control reactors (CR), with 5.6 L working volume for a period of 310 d. Treatment of dairy wastewater at the highest applied organic loading rate of 16.78 kg chemical oxygen demand/m(3) d, the biogas production increased in ER reactor (18.8 L/d) with the introduction of pretreated sludge than in CR reactor (17.9 L/d). The performance of ER reactor is not influenced by anaerobic co digestion of pretreated sludge, because no statistical difference between soluble chemical oxygen demand removal efficiencies of ER and CR reactors.