热解时间对污泥基生物炭中多环芳烃含量及毒性的影响

污泥基生物炭作为土壤改良剂，为污泥提供了一种可持续的资源化利用技术。但由于其中可能含有多环芳烃（PAHs）、重金属等污染物，具有潜在的环境风险，如何制备环境友好的生物炭成为后续利用的先决条件。设置热解温度为500℃，升温速率为10℃/min时，采用4种不同热解时间（1~4 h）制备污泥基生物炭，通过提取测试发现热解后PAHs均明显小于原污泥中的含量；各组分含量及PAHs总量均随着热解时间的增加先增大后减小。2 h的热解时间利于原污泥中有机质充分反应生成新的PAHs，因此PAHs总量达到最大值，超过农用限制；但由于未检出毒性最强的BaP及DahA，其毒性当量（TEQs）反而最低。1 h热解时间虽PAHs总量未超过农用标准，但TEQs最大，超过国际生物炭协会规定的阈值。综合PAHs含量和TEQs的限值，热解时间3，4 h制备的污泥基生物炭更具安全性。从节约能源的角度出发，建议选用3 h作为污泥基生物炭的热解时间。

EFFECT OF PYROLYSIS TIME ON PAHS CONTENT AND TOXICITY IN SLUDGE-BASED BIOCHAR

Sludge-based biochar obtained from pyrolyzing sludge under anaerobic conditions can be used as soil amendment to improve contaminated soil. However, the possible pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals have potential environmental risks. The preparing of the environment-friendly biochar has become a prerequisite for subsequent utilization. In this research, four kinds of sludge-based biochar samples were respectively prepared at the different pyrolysis time (1~4 hours) under 500℃. It was found that the PAHs content in sludge-based biochar was significantly less than that in the raw sludge. The concentration of 4 kinds of PAHs (2~5 rings of PAHs) in the 4 kinds of sludge-based biochar increased firstly and then decreased with the pyrolysis duration increasing and reached the maximum in 2 hours, however the concentration of Σ₁₆PAHs exceeded the agricultural limit. It showed that the duration of 2 hours was conducive to the full reaction of the organic matters in the original sludge to form new PAHs, and it also provided sufficient reaction time for the condensation of low-ring aromatic hydrocarbons to high-ring aromatic hydrocarbons. Since the most toxic BaP and DahA were not detected in the biochar during 2 hours, its corresponding toxic equivalents (TEQs) were also the lowest. Although the concentration in 1 hour did not exceed the agricultural standard in China, the TEQs was the highest, exceeding the threshold specified by the International Biochar Association. Considering the PAHs content and TEQs limit, the sludge based biochar prepared by pyrolysis time of 3 hours and 4 hours was much safer. From the perspective of energy conservation, 3 hours pyrolysis time were recommended.