The pyrolytic conversion of domestic sewage sludge (SS) into biochar is a promising method to reduce its large volume and recycle its high-value fuel gas as renewable energy and the use of its chemicals as soil fertilizers. Even though the effects of pyrolysis temperature on energy recovery have been extensively studied, little information has been found on nutrient recovery and biochar’s phytotoxicity before its reuse as a soil amendment. This study aims to investigate the ideal pyrolysis temperature that guarantees higher fertility levels as well as meeting quality standards for land disposal. Accordingly, air-dried domestic sewage sludge has been pyrolyzed at 260°C (PSS1), at 420°C (PSS2), and at 610°C (PSS3) with a residence time of 20, 40, and 60 minutes, respectively. The raw sewage sludge and the produced biochars have been analyzed to determine their volatile organic matter (VOM), mineral content (MC), nutrients’ level (total nitrogen TN, available phosphorus P, and potassium K), alkalinity (pH), and salinity (electrical conductivity EC and Na). The toxic effect of biochars derived from SS has been evaluated through the analysis of trace metals (Pb, Cr, Cd, Cu, and Zn) and their toxicity by measuring root elongation inhibition (REI). As expected, pyrolysis temperature has a significant impact on the biochars’ characteristics. This has been justified by higher VOM, TN, and P in the sewage sludge (SS) and the biochar (PSS1) produced at low temperature (260°C). However, higher pH, EC, Na, and K have been found in the biochars (PSS2 and PSS3) produced at higher temperature (420 and 610°C). The effect of pyrolysis temperature on trace metals concentrations has shown different patterns from one element to another, which indicates lower levels in the biochar (PSS2) produced at 420°C. As a result, the lowest REI has been observed in PSS2 compared to that in SS, PSS1, and PSS3, which highlights that 420°C is the ideal pyrolysis temperature for the safe reuse of SS as a soil amendment.

中文翻译：

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生活污水污泥衍生生物炭：温度热解对生物炭化学性质和植物毒性的影响

生活污水污泥（SS）热解转化为生物炭是一种有前景的方法，可以减少其大体积并将其高价值燃气作为可再生能源进行回收，并将其化学品用作土壤肥料。尽管已经广泛研究了热解温度对能量回收的影响，但在将其作为土壤改良剂再利用之前，关于养分回收和生物炭的植物毒性的信息很少。本研究旨在调查理想的热解温度，以保证更高的肥力水平并满足土地处置的质量标准。因此，风干生活污水污泥已在 260°C (PSS1)、420°C (PSS2) 和 610°C (PSS3) 下热解，停留时间分别为 20、40 和 60 分钟。对未经处理的污水污泥和产生的生物炭进行了分析，以确定它们的挥发性有机物 (VOM)、矿物质含量 (MC)、营养物质水平（总氮 TN、有效磷 P 和钾 K）、碱度 (pH) 和盐度（电导率 EC 和 Na）。通过分析痕量金属（Pb、Cr、Cd、Cu 和 Zn）及其毒性，通过测量根伸长抑制 (REI) 来评估源自 SS 的生物炭的毒性作用。正如预期的那样，热解温度对生物炭的特性有显着影响。低温 (260°C) 下产生的污水污泥 (SS) 和生物炭 (PSS1) 中较高的 VOM、TN 和 P 证明了这一点。然而，在较高温度（420 和 610°C）下生产的生物炭（PSS2 和 PSS3）中发现了较高的 pH、EC、Na 和 K。热解温度对痕量金属浓度的影响显示出从一种元素到另一种元素的不同模式，这表明在 420°C 下产生的生物炭 (PSS2) 中的含量较低。因此，与 SS、PSS1 和 PSS3 相比，在 PSS2 中观察到的 REI 最低，这突出表明 420°C 是 SS 作为土壤改良剂安全再利用的理想热解温度。