A review on the migration and transformation of heavy metals in the process of sludge pyrolysis

With the substantial increase in sludge production, the disposal of sludge and the reduction of secondary pollution by heavy metals have become one of the hottest topics in the field of pollutant control. Pyrolysis technology, an effective means of sludge treatment, facilitates the reduction of sludge volume and effectively reduces the toxicity and bioavailability of heavy metals in sludge, which promotes the reuse of sludge. Therefore, this review focuses on the migration characteristics of heavy metals in biochar during sludge pyrolysis and highlights the effect of reaction parameters such as reaction temperature, additives, and biomass co-pyrolysis on the behavior of heavy metals. Meanwhile, the current advances and the future perspectives of sludge heavy metal behavior will be prospected. It is hoped that this review may shed light on the harmless treatment and resourceful disposal of heavy metal-rich biomass.