Department of Chemical Engineering, University of Alicante, P.O. Box 99, E-03080 Alicante, Spain.
Department of Chemical Engineering, University of Alicante, P.O. Box 99, E-03080 Alicante, Spain.
Sci Total Environ. 2018 Mar;616-617:763-773. doi: 10.1016/j.scitotenv.2017.10.249. Epub 2017 Oct 31.
Composting of sewage sludge is a common practice for sludge disposal. Some previous studies found high levels of polychorodibenzo-p-dioxins and polychorodibenzofurans (PCDD/Fs) after composting, especially octachlorodibenzo-p-dioxin (OCDD) but also 1234678-heptachlorodibenzo-p-dioxin (1234678-HpCDD) to a lesser extent. In this work, the concentrations of OCDD, 1234678-HpCDD and the rest of the 17 toxic congeners of PCDD/Fs were determined in compost obtained under different conditions. Although the toxicity of the two compounds mentioned above is small, their generation may reach undesirable levels. The PCDD/F content was analyzed in a composting plant and in a laboratory test. In both cases, the composted material was a mixture of sewage sludge, straw and sawdust. The composting plant was a tunnel with air turbine aeration and with a turner to homogenize and move the mixture upwards. The laboratory tests were carried out with Dewar vessels (with air dispersion at the bottom and controlled temperature) and with small vessels inside a controlled oven with non-forced aeration. The laboratory runs were also carried out with the addition of pentachlorophenol in some runs, as a dioxin precursor. The highest OCDD levels were found in three samples of the composting plant (30000-90000pg/g dry matter or dm), with toxicity values surpassing the limit level for soil amendment (17pgI-TEQ/gdm). Their formation was analyzed considering their concentration vs. that of octachorodibenzofuran (OCDF), which is not formed during composting. In the laboratory, in experiments carried out in a vessel with non-forced aeration conditions and with the addition of pentachlorophenol, the formation of OCDD was significant (e.g. from 80 to 1500pg/gdm). That means that these two factors, non-forced aeration and the presence of pentachlorophenol, can cause the OCDD formation.
污泥堆肥是一种常见的污泥处理方法。一些先前的研究发现，在堆肥后会产生高水平的多氯二苯并对二恶英和多氯二苯并呋喃（PCDD/Fs），尤其是八氯二苯并对二恶英（OCDD），但也有少量的 1234678-七氯二苯并对二恶英（1234678-HpCDD）。在这项工作中，在不同条件下获得的堆肥中测定了 OCDD、1234678-HpCDD 和 PCDD/Fs 其余 17 种有毒同系物的浓度。尽管上述两种化合物的毒性较小，但它们的生成可能达到不理想的水平。在一个堆肥厂和一个实验室试验中分析了 PCDD/F 的含量。在这两种情况下，堆肥的原料都是污水污泥、稻草和木屑的混合物。堆肥厂是一个带有空气涡轮曝气的隧道，并带有一个转台，用于使混合物均匀化并向上移动。实验室试验是在 Dewar 容器（底部空气分散，温度可控）和控制烤箱内的小容器中进行的，没有强制曝气。在一些试验中还添加了五氯苯酚作为二恶英前体进行了实验室运行。在堆肥厂的三个样品中发现了最高的 OCDD 水平（30000-90000pg/g 干物质或 dm），其毒性值超过了土壤改良剂的限值（17pgI-TEQ/gdm）。考虑到 OCDD 与八氯二苯并呋喃（OCDF）的浓度比，分析了它们的形成，OCDF 不会在堆肥过程中形成。在实验室中，在非强制曝气条件下并添加五氯苯酚的容器中进行的实验中，OCDD 的形成非常显著（例如，从 80 到 1500pg/gdm）。这意味着这两个因素，非强制曝气和五氯苯酚的存在，可能导致 OCDD 的形成。
