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Development of carbon-rich biochar-mineral complexes for soil amendment, carbon sequestration and beyond (CarboPlex)

Periodic Reporting for period 1 - CarboPlex (Development of carbon-rich biochar-mineral complexes for soil amendment, carbon sequestration and beyond (CarboPlex))

Reporting period: 2015-04-01 to 2017-03-31

The overall aim of this project is to investigate and exploit the potentials of a new category of materials termed biochar-mineral complexes (BMCs). The simple yet ground-breaking idea is to use common organic and mineral waste streams to produce BMCs with distinct properties for sophisticated applications.
Primary target is the use of BMCs as soil amender, especially in soils, where the delicate but crucial structure of organo-mineral complexes is threatened or already destroyed by unsustainable soil use or climate change. Where pure biochar is known to face its limits, BMCs because of their mineral part are assumed to allow much higher functionality (e.g. water and nutrient storage), increased stability and faster integration in the soil matrix. In the long term, developing soil-specific BMCs could improve the soil effects even further. It is only recently that the potential of BMCs started to be recognized, and only preliminary research on BMCs has been conducted. To provide evidence base on production, properties and soil effects, this project will carry out the first comprehensive and systematic study of BMCs.
Biochar-mineral composites (BMC)have been produced from organic wastes (i.e. sewer sludge, compost-like output) and mineral substances (wood ash, lignite coal ash, natural zeolite) by means of pyrolysis and hydrothermal carbonization (HTC). Chemical characterisation revealed the pH, the electric conductivity (EC), the elemental composition (C, H, N, S) the content of trace elements and heavy metals. SEM and EDS were conducted to reveal the morphology of the materials. In addition, germination trials were conducted to reveal the phytotoxic potential of the novel materials.

The results show that the two types of feedstock (organic and mineral) form a novel and amorphous type of BMCs. Interestingly, HTC derived BMC have a much lower EC because of salt losses to the liquid phase of the HTC process. However, germination tests showed better plant response and less inhibition for pyrolysis-derived BMCs. Plant response to BMC appears highly diverse. However, some BMCs clearly showed a better plant response compared to their feedstocks. The underlying mechanisms that causes or prevent plant growth inhibition seem to concentrate on availability of organic and mineral toxicants. Further work is necessary to get a deeper understanding on individual mechanisms.
The work expended the current state of knowledge on co-carbonization of organic and mineral materials into biochar-mineral composites (BMC). The findings have an economic potential as they show the possibility to produce carbon materials from wastes that are considerable less phytotoxic than their precursors. Further work will be done to show if the BMCs have a fertilizer effect.
Structure of biochar-mineral composites