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

Eighteen polycyclic aromatic hydrocarbons (PAT-Is) 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 AFIP and EHP, following: EHP (213.7 ng/g) < AHP (451.9 ng/g) < BHP (860.1 ng/g). The total carcinogenic PAHs (Sigma PAH(care)) were found to be 34.6, 65.2, and 127.0 ng/g for EHP, AHP and BHP, respectively. The concentration of metals was found to be in the order of Fe > 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 acute toxicity tests using Brocarded carp did not show any significant effects on the mortality, incidence of clinical signs, and body weight loss. During the 14 day experiment, the total concentrations of PAHs were in the range from 1.0 to 69.0 ng/g, whereas the carcinogenic PAHs in the carp fresh were found very low in the EHP recovered proteins. Based on these results, the EHP is an efficient and environmental friendly method to remove the PAHs as compared to BHP, for the production of animal feeds.