Animal Feeds Extracted from Excess Sludge by Enzyme, Acid and Base Hydrolysis Processes

Eighteen polycyclic aromatic hydrocarbons (PAHs) and crude proteins were recovered by the disintegration of excess sludge (ES) through enzyme hydrolyzed process (EHP), acid hydrolyzed process (AHP) and base hydrolyzed process (BHP) followed by isoelectric precipitation, centrifugation and freeze-drying. The BHP was observed to have the highest total concentrations of PAHs in the crude proteins as compared to AHP and EHP, following: EHP (213.7 ng/g) Zn > Mn > Cu > Pb > Ni > Cr > As > Hg > Cd in the ES samples before treatment. Except Zn, all the metals were in good agreement with the prescribed limits as defined by legal standard. Moreover, the concentration of all metal ions was found to be less or negligible in the EHP recovered proteins as compared to that in the BHP and AHP. The acu...