Improvement of Methane Production and Sludge Dewaterability by FeCl3-Assisted Anaerobic Digestion of Aluminum Waste-Activated Sludge

In this study, FeCl3 was added to improve methane production from aluminum waste-activated sludge (Al-WAS) during anaerobic digestion. The results showed that the addition of 160 mg/L FeCl3 resulted in the maximum methane yield of 169 mL/g volatile solids (VS), exceeding the methane yield of the control group by 31.33%. The fractal dimension (D-j) decreased after adding FeCl3, suggesting an alteration of the sludge's physical structure. The Lewis acid-base interaction free energy (Delta G(SL)(AB)) was significantly affected by the FeCl3 addition, and the maximum absolute value was obtained at the dosage of 160 mg/L (10.7 mJ/m(2)). Delta G(SL)(AB) contributed the most to the interfacial free energy, suggesting the dominant force between the digested sludge and water was an AB interaction. Further, the value of Delta G(SL)(AB) changed from positive to negative after the FeCl3 addition, suggesting the interfacial interaction of the digested sludge changed from hydrophilic to hydrophobic. The hydrophobic surface of the digested sludge improved the contact with enzymes via hydrophobic attraction, thus improving sludge biodegradability. The sludge hydrophobicity enhanced floc aggregation through hydrophobic interactions, improving the dewatering ability. This work provides a new method for the large-scale utilization of Al-WAS via anaerobic digestion.