Biomass waste can be processed to Char and Wood vinegar by pyrolysis, and so delivers valuable products such as pesticide replacements, and soil enhancers []. Within the Circular B-I/O project, which is kindly funded by the Volkswagenfoundation, several biomasses are researched systematically and with the support of Artificial Intelligence in the coming years, in order to replace some of the clinker by biomass ashes in the cement production. Hereby the intention of reducing the cement production’s CO2 emissions is the driving motivation, which is all the more urgent, given the rising CO2 footprint, especially from the energy production (Laura Cozzi, Thomas Spencer, 01 March 2024). In the process of ashing, char should be produced in part, as a means to sequestrate the CO2 in the form of carbon, that in turn was metabolized by growing biomass. Hereby healthy growing trees are excluded as a target, but the millions of tons of waste from agriculture plus the invasive species and cultivations that are infested and need to be removed before pests are spreading to healthy plants. Therefore, as co-lateral research this one aims at estimating what the potential savings by replacing pure combustion with a process that pyrolyzes dominating the combustion. Previous experiments, published on DGMs EUROMAT23 with charring of Beech and Birchwood has shown that the climate relieving pyrolysis preponders the climate burdening combustion. Per kilogram of 24% moist birchwood, and with a 29% char yield, 0,210 kg CO2eq were emitted, while 0,77kg CO2eq were sequestrated. Thus, the conclusion seems justified that carbonizing this way unloads the atmosphere from CO2, which is a growing worry (Nimisha Tripathi1*, 2019). Carbonizing in tropical countries seems even more worth, with much faster growing biomass, and given these encouraging results, the carbonization of other biomass waste is worth studying. Given that this is observed for Birchwood material, the question arises, what tropical materials’s behavior is whether it is worth studying further.

Specifically, this research is aiming at agricultural waste from Kenya generally and as a first value chain the Macadamia shells especially. The Macadamia nut is not a subject of this research, only to the degree that the reference in the value chain is the dried nut’s weight. Instead, Macadamia’s outer soft and inner hard shell are studied in order to estimate the climate effects by pyrolyzing these waste materials. On the other hand, these shells are now either dumped to the ground, as the author observed personally during a field visit in Kenya or utilized as a fuel or production additive. In competition to pyrolyzing, the Macadamia’s hard shell is utilized for the carbonization of steel, given its low ash content and high carbon content, as Mansuri et all are reporting (Irshad Mansuri, Rifat Farzana, Ravindra Rajarao, & Veena Sahajwalla, 2018). Another competing utilization is the one of Macadamia nut shell’s char being an adsorbent for CO2 from combustion plants (Jun-Seok Bae, Shi Su, 2013), where it was found that the porous structure is a good adsorbent.

Here in this study Macadamia Nut’s soft 52,0% and hard shell 33,5%is studied in order to estimate the effect of pyrolyzing that as a means to sequestrate Carbon Dioxide, while adding value chains for income generation to smallholders. The Nut itself amounts to only 14,5% (in terms of the moist macadamia which is dried from about 25% to less than 2%), meaning that the soft-shell amounts to 3,59 times more than the charted trade volumes of macadamia nuts, thus abundance of material for charring. By burning this biomass waste and by starving the combustion, and with predominant pyrolysis it is hoped that over 55% of the equivalent CO2 will be sequestered. Given pyrolysis under atmospheric conditions also generates Wood vinegar that can be utilized as pesticide replacement, the amount is determined. The Char- and Wood vinegar yield over selected temperatures is going to be discussed.

Since the pyrolysis and combustion process will also generate ashes, their mineral content is going to be measured by means of X-Ray Fluorescence (XRF). Initial measurements show Calcium contents of 4.552%, Silicon 2.779 % and Potassium over 66,52% in the inner macadamia hard shell and respectively 4.491% Ca, Silicon 11.12 % and Potassium over 57,83% in the outer macadamia soft shell. This allows estimating the minerals relevant to clinker replacement during the cement production process, allowing to estimate the climate effects. The samples for these experiments are collected off Kenya in the first semester of 2023, but the results of the common agricultural products can be easily transferred to other locations.

The conclusion of this research might be supporting the hypothesis that “biomass waste pyrolysis can relief the climate by means of carbon sequestration, while diversifying and intensifying income generation in countries of the global South.”