Preparation of biochar and its adsorbing performance evaluation in the petroleum hydrocarbon

The biochar pyrolyzed from the sludge is porous and non-polar and can be used as an adsorbent for polycyclic aromatic hydrocarbon (PAH) pollutants. However, the adsorption process and effect of biochar on the widespread mixed petroleum hydrocarbon pollutants (including saturated hydrocarbons, resins, aromatic hydrocarbons and asphaltenes, etc.) are not thoroughly revealed. Among diverse treatment technologies, pyrolysis can effectively achieve the reduction of the excess sludge and obtain biochar. The characteristics of biochar are inseparably bound to the pyrolysis temperature. The physicochemical properties of biochar obtained from excess sludge which was pyrolyzed at different temperatures (300–900 °C) and the performance of it in absorbing actual ground crude oil were investigated in this study. The results showed that as the pyrolysis temperature increased, the polarity of biochar decreased, and the honeycomb or layered structure containing plenty of micropores appeared. The petroleum hydrocarbons’ removal efficiency of biochar with the pyrolysis temperature of 700℃ was up to 96.01%, which was the highest among all biochar. In addition, the leaching test showed that only four metal ions were detected, of which the highest concentration was 4.78 × 10 −2 mg/g of K + . It indicated that the biochar derived from excess sludge was expected to become environment friendly materials to avoid soil pollution during the process of oil extraction and processing. This study provided new sights for the treatment of excess sludge and the application of the produced biochar.