Pulka Jakub, Manczarski Piotr, Stępień Paweł, Styczyńska Marzena, Koziel Jacek A, Białowiec Andrzej
Faculty of Agronomy and Bioengineering, Poznan University of Life Sciences, 28 Wojska Polskiego Str., 60-637 Poznań, Poland.
Department of Environmental Engineering, Faculty of Building Services, Hydro and Environmental Engineering, Warsaw University of Technology, 20 Nowowiejska Str., 00-653 Warszawa, Poland.
Materials (Basel). 2020 Feb 20;13(4):954. doi: 10.3390/ma13040954.
Sewage sludge (SS) recycling is an important part of the proposed 'circular economy' concept. SS can be valorized via torrefaction (also known as 'low-temperature pyrolysis' or 'roasting'). SS can, therefore, be considered a low-quality fuel or a source of nutrients essential for plant growth. Biochar produced by torrefaction of SS is a form of carbonized fuel or fertilizer. In this research, for the first time, we tested the feasibility of torrefaction of SS with high ash content for either fuel or organic fertilizer production. The research was conducted in 18 variants (six torrefaction temperatures between 200~300 °C, and three process residence times of 20, 40, 60 min) in 5 repetitions. Fuel and fertilizer properties and multiple regression analysis of produced biochar were conducted. The higher heating value (HHV) of raw SS was 21.2 MJ·kg. Produced biochar was characterized by HHV up to 12.85 MJ·kg and lower H/C and O/C molar ratio. Therefore, torrefaction of SS with high ash content should not be considered as a method for improving the fuel properties. Instead, the production of fertilizer appears to be favorable. The torrefaction increased C, N, Mg, Ca, K, Na concentration in relation to raw SS. No significant ( < 0.05) influence of the increase of temperature and residence time on the increase of biogenic elements in biochar was found, however the highest biogenic element content, were found in biochar produced for 60 min, under the temperature ranging from 200 to 240 °C. Obtained biochars met the Polish regulatory criteria for mineral-organic fertilizer. Therefore SS torrefaction may be considered a feasible waste recycling technology. The calculation of torrefaction energy and the mass balance shows energy demand <2.5 GJ∙Mg w.m., and the expected mass yield of the product, organic fertilizer, is ~178 kg∙Mg w.m of SS. Further investigation should consider the scaling-up of the SS torrefaction process, with the application of other types of SSs.
污水污泥（SS）回收利用是“循环经济”理念的重要组成部分。污水污泥可通过烘焙（也称为“低温热解”或“烘烤”）实现增值。因此，污水污泥可被视为一种劣质燃料或植物生长所需养分的来源。通过污水污泥烘焙产生的生物炭是一种碳化燃料或肥料形式。在本研究中，我们首次测试了高灰分含量的污水污泥用于燃料或有机肥料生产的烘焙可行性。该研究在18个变体（200~300°C之间的六个烘焙温度，以及20、40、60分钟的三个工艺停留时间）下进行了5次重复实验。对生产的生物炭进行了燃料和肥料特性以及多元回归分析。原生污水污泥的高位发热量（HHV）为21.2 MJ·kg。生产的生物炭的特征是HHV高达12.85 MJ·kg，且H/C和O/C摩尔比更低。因此，高灰分含量的污水污泥烘焙不应被视为改善燃料特性的方法。相反，肥料生产似乎更有利。烘焙使生物炭中C、N、Mg、Ca、K、Na的浓度相对于原生污水污泥有所增加。然而，未发现温度和停留时间的增加对生物炭中生物成因元素增加有显著（<0.05）影响，但在200至240°C温度下60分钟生产的生物炭中发现了最高的生物成因元素含量。所获得的生物炭符合波兰矿物有机肥料的监管标准。因此，污水污泥烘焙可被视为一种可行的废物回收技术。烘焙能量和质量平衡的计算表明能量需求<2.5 GJ∙Mg w.m.，产品有机肥料的预期质量产量约为每Mg w.m.污水污泥178 kg∙Mg w.m.。进一步的研究应考虑扩大污水污泥烘焙工艺的规模，并应用其他类型的污水污泥。
