Norwegian Geotechnical Institute (NGI), Sognsveien 72, 0855 Oslo, Norway.
Norwegian Geotechnical Institute (NGI), Sognsveien 72, 0855 Oslo, Norway.
Sci Total Environ. 2020 May 20;718:137335. doi: 10.1016/j.scitotenv.2020.137335. Epub 2020 Feb 14.
Pyrolysis of organic waste or woody materials yields a stable carbonaceous product that can be mixed into soil and is often termed "biochar". During pyrolysis carbon-containing gases are emitted, mainly volatile organic carbon species, carbon monoxide and aerosols. In modern pyrolysis units, gases are after-combusted, which reduces emissions substantially. However, emission data for medium- to large-scale pyrolysis units are scant, both regarding gases, aerosols, heavy metals and polycyclic aromatic hydrocarbons (PAH). Making biochar from lightly contaminated waste timber (WT) is a promising waste handling option as it results in the potential valorization of such residues into e.g. sorbents for contaminant stabilization. For this process to be environmentally sustainable, emissions during the process need to be low and the resulting biochar of sufficient quality. To investigate both issues, we pyrolyzed three batches of WT and one reference batch of clean wood/leaves in a representative medium-scale pyrolysis unit (Pyreg-500, 750 t/year) with after-combustion of the pyrolysis gases, and measured the gas, aerosol, metal and PAH emissions, as well as the characteristics and contamination levels of the resulting biochar, including contaminant leaching. Mean emission factors for the WT were (g/kg biochar); CO = 7 ± 2, non-methane volatile organic compounds (NMVOC) = 0.86 ± 0.14, CH = 0, aerosols (PM) = 0.6 ± 0.3, total products of incomplete combustion (PIC) = 9 ± 3, PAH-16 = (2.0 ± 0.2) · 10, As (most abundant metal) = (2.3 ± 1.9) · 10 and NO = 0.65 ± 0.10. There were no significant differences in emission factors between the pyrolysis of WT and the reference respectively, except for PM, NMVOC, and PAH-16, which were significantly lower for WT than for the clean wood/leaves. The WT biochar did not satisfy premium or basic European Biochar Certificate criteria due to high levels of zinc and PAH. However, leachable metal contents were <0.1% of total contents. Still, use of the WT-biochar without further improvement or investigation would be limited to ex situ use, not improving soil fertility or in situ remediation.
有机废物或木质材料的热解产生一种稳定的碳素产物，可混入土壤中，通常称为“生物炭”。在热解过程中会排放含碳气体，主要是挥发性有机碳物质、一氧化碳和气溶胶。在现代热解装置中，气体在后续燃烧，这大大减少了排放。然而，中大型热解装置的气体、气溶胶、重金属和多环芳烃 (PAH) 的排放数据很少。用轻度污染的废木材 (WT) 生产生物炭是一种很有前途的废物处理选择，因为它有可能将这些残留物转化为例如污染物稳定的吸附剂。为了使该过程具有环境可持续性，过程中的排放需要低，并且所得生物炭的质量要足够高。为了研究这两个问题，我们在具有后续燃烧的代表性中型规模热解装置 (Pyreg-500，750 t/年) 中对三批 WT 和一批清洁木材/叶片进行了热解，并测量了气体、气溶胶、金属和 PAH 的排放，以及所得生物炭的特性和污染水平，包括污染物浸出。WT 的平均排放因子为 (g/kg 生物炭)；CO=7±2，非甲烷挥发性有机化合物 (NMVOC)=0.86±0.14，CH=0，气溶胶 (PM)=0.6±0.3，不完全燃烧产物 (PIC)=9±3，PAH-16=(2.0±0.2)·10，As（最丰富的金属）=(2.3±1.9)·10 和 NO=0.65±0.10。WT 热解与参考热解之间的排放因子没有显著差异，除了 PM、NMVOC 和 PAH-16，WT 的排放因子明显低于清洁木材/叶片。由于锌和 PAH 的含量较高，WT 生物炭不符合优质或基本的欧洲生物炭证书标准。然而，可浸出金属含量<总含量的 0.1%。尽管如此，如果不进一步改进或研究，WT 生物炭的使用将仅限于异位使用，而不会提高土壤肥力或原位修复。
