Lane Daniel J, Sippula Olli, Jokiniemi Jorma, Heimonen Mikko, Kinnunen Niko M, Virkajärvi Perttu, Shurpali Narasinha
Commonwealth Scientific and Industrial Research Organization (CSIRO), Queensland Centre for Advanced Technologies (QCAT), 1 Technology Court, PO Box 883, Pullenvale, Kenmore, QLD, 4069, Australia.
Department of Chemistry, University of Eastern Finland, Joensuu, FI-80130, Finland.
Bioresour Bioprocess. 2024 Dec 30;11(1):115. doi: 10.1186/s40643-024-00828-7.
Thermal processes are emerging as promising solutions to recovering phosphorus and other nutrient elements from anaerobic digestates. The feasibility of nutrient element recovery depends largely on the fates of nutrient elements and heavy metals during thermal processing. This study assesses the partitioning of macronutrients (N, P, K, Na, Ca and Mg) and heavy metals (Zn, Cu, and Mn) between condensed and gaseous phases during thermal conversion of cattle slurry digestates in gas atmospheres of pyrolysis, combustion, and gasification processes. This study also assesses the chemical forms of macronutrients retained in combustion ashes. The partitioning of elements between condensed and gaseous phases was quantified by mass balances based on elemental analyses of char and ash residues. The char and ash residues were prepared in a fixed-bed, batch reactor at temperatures within the range 800-1000 °C. Powder X-ray diffraction was used to identify the chemical forms of macronutrient elements in combustion ashes. Volatilisation of P was low (< 20%) when the digestates were heated in inert and oxidising atmospheres, whereas a reducing atmosphere volatilized P to a major extent (~ 60% at 1000 °C). Oxidising atmospheres increased volatilisation of N but suppressed volatilisation of K, Na, and Zn. Volatilisation of the following elements was low (< 30%) in all investigated operating conditions: Ca, Mg, Mn, and Cu. The combustion ashes contained both high concentrations of P (around 7 w/w%) and acceptable concentrations of regulated heavy metals (Cu, and Zn) for application on agricultural and forest soils in Finland. Phosphorous was retained in the combustion ashes in the form of whitlockite. This form of P is expected to be available to plants when the ashes are added to soil.
热法正成为从厌氧消化物中回收磷和其他营养元素的有前景的解决方案。营养元素回收的可行性在很大程度上取决于热加工过程中营养元素和重金属的去向。本研究评估了在热解、燃烧和气化过程的气体氛围中，牛粪消化物热转化过程中常量营养素（氮、磷、钾、钠、钙和镁）和重金属（锌、铜和锰）在冷凝相和气态相之间的分配情况。本研究还评估了燃烧灰分中保留的常量营养素的化学形态。基于焦炭和灰渣残留物的元素分析，通过质量平衡对冷凝相和气态相之间的元素分配进行了量化。焦炭和灰渣残留物是在固定床间歇式反应器中于800 - 1000°C的温度范围内制备的。采用粉末X射线衍射法鉴定燃烧灰分中常量营养元素的化学形态。当消化物在惰性和氧化气氛中加热时，磷的挥发率较低（<20%），而在还原气氛中磷会大量挥发（1000°C时约为60%）。氧化气氛增加了氮的挥发，但抑制了钾、钠和锌的挥发。在所有研究的操作条件下，以下元素的挥发率较低（<30%）：钙、镁、锰和铜。燃烧灰分中含有高浓度的磷（约7 w/w%）以及芬兰农业和森林土壤施用时可接受浓度的受监管重金属（铜和锌）。磷以白磷钙矿的形式保留在燃烧灰分中。当将这些灰分添加到土壤中时，这种形式的磷预计对植物有效。
