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We aimed to verify whether (i) biochar-compost application improves plant growth when compared with compost application alone and (ii) a diversity of biochar caused by feedstock type and carbonization temperature affects the extent of plant growth. We prepared six types of biochar from larch (Larix kaempferi Sarg.) and dairy manure at 300 °C, 450 °C, and 600 °C for 1 h. Compost was applied as control, and each biochar was co-applied with compost to oat plants (Avena sativa L.). The total nitrogen input of all the seven treatments was adjusted to the same level to assess their effects on plant nitrogen uptake and nitrogen content. Compared with the control, biomass production increased from 13.1 to 34.0% with the wood biochar application and from 39.7 to 64.2% with manure biochar application because of more mineralization of compost and nitrogen fixation through rhizobacteria and/or diazotrophic endophytes. The diversity of biochar caused a difference in the extent of oat growth, and feedstock type of biochar was a more dominant factor than carbonization temperature. Due to the favorable chemical properties of manure biochar like high pH and more labile-C and -N content, the manure biochar application increased average biomass production by 26.0% compared with the wood biochar application. The carbonization temperature had no significant impact on oat growth, but the optimal temperature was indicated as approximately 450 °C. Biochar diversity causes a difference in plant growth in biochar-compost application, and the selection of appropriate biochar, such as manure biochar at 450 °C, would be a guideline for achieving a robust crop production system.

This paper describes the role of ambient pressure in self-heating torrefaction of livestock manure. We explored the initiating temperatures required to cause self-heating of wet dairy cattle manure at different ambient pressures (0.1, 0.4, 0.7, and 1.0 MPa). Then, we conducted proximate, elemental, and calorific analyses of biochar torrefied at 210, 250, and 290 degrees C. The results showed that self-heating was induced at 155 degrees C or higher for 0.1 MPa and at 115 degrees C or lower for 0.4 MPa or higher. The decrease of the initiating temperature at elevated pressure was due not only to more oxygen, but also to the retention of moisture that can promote chemical oxidation of manure. Biochar yields decreased with increasing torrefaction temperature and pressure, and the yield difference at 0.1 and 1.0 MPa was more substantial at lower temperatures: a 29.8, 16.4, and 9.4% difference at 210, 250, and 290 degrees C, respectively. Proximate and elemental analyses showed that elevated pressure promotes devolatilization, deoxygenation, and coalification compared to atmospheric pressure; its impact, however, was less at higher temperatures as the torrefaction temperature became more dominant. Calorific analysis revealed that elevated pressure can increase the higher heating value (HHV) on a dry and ash-free basis at 210 degrees C because of the increase in carbon content, but its impact is limited at 250 and 290 degrees C. Meanwhile, the HHV on a dry basis exhibited the opposite trend due primarily to an enlargement of ash content. The present study revealed that ambient pressure considerably affects the initiating temperature of self-heating and the chemical properties of biochar at a low torrefaction temperature.

This report describes a new oxidative torrefaction method employing spontaneous self-heating of feed-stock as a means of overcoming practical difficulties in converting livestock manure to biochar. We examined the initiating temperature required to induce self-heating of wet dairy cattle manure under 1.0 MPa pressure and conducted elemental and calorific analyses of the solid products prepared at 200, 250, and 300C°. Self-heating was initiated with oxidation below 100C°, and the lower limit of the initiation temperature was between 85 and 90C°. Comparing processes performed at 0.1 and 1.0 MPa, the higher pressure promoted self-heating by both preventing heat loss due to moisture evaporation occurring at approximately 100C° and supplying oxygen to the high-moisture feedstock. In addition, as drying occurred at 160-170C° during the process, the system did not require pre- or post-drying. Although the heating values of the solid products decreased due to high ash content, the elemental composition of the products was altered to that of peat-like (200C°) and lignite-like (250 and 300C°) materials. Cessation of self-heating of the manure is recommended at approximately 250C° to avoid severe decomposition at higher temperatures. Overall, these results demonstrated the utility of the proposed method for converting wet manure into dried biochar through self-heating as well as potential applications in manure management systems. © 2019 The Authors. Published by Elsevier Ltd.