How to mitigate rising CO2 levels? The answer says Ehsan Jorat is right under our feet. Here he tells us about the EPSRC-funded project called SUCCESS and why soil could be designed to permanently sequester atmospheric CO2
The COP21 Paris Agreement has given renewed impetus to tackle the effects of climate change by focusing on reduction of CO2 emissions while embracing nature-based solutions for sequestering existing atmospheric CO2.
Several European governments have committed to raise national soil carbon stock by 0.4% per year by focusing on expansion of agricultural soils to remove CO2 organically. Although photosynthesis removes a significant amount of CO2 from the atmosphere annually, plant and soil respiration return most of the photosynthesised CO2 into the atmosphere, marking organic CO2 removal as an unstable sink. In contrast, SUCCESS (Sustainable Urban Carbon Capture through Engineering the Soil System) has shown that photosynthesised carbon can be fixed in soils as natural carbonate minerals.
Demolition wastes present an abundant source of calcium which is a key requirement for inorganic carbon sequestration which makes these brownfield sites ideal
Restoration of urban brownfield sites – those that have been previously used for building – could offer huge capacity to sequester CO2 in inorganic form as calcium carbonate. Demolition wastes present an abundant source of calcium which is a key requirement for inorganic carbon sequestration which makes these brownfield sites ideal. Dissolution of photosynthesised CO2 into ground water results in carbonate or bicarbonate – depending on soil’s pH – and where a source of calcium is present in soil, calcium carbonate is precipitated. Using this method, CO2 is sequestrated and precipitated in soil as a solid matter and yes, on a human timescale this is a permanent sink for the atmospheric CO2.
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Newcastle brown tale
Recent research on an urban brownfield site containing demolition waste at Newcastle University led by Professor David Manning has shown that the site has the capacity of sequestering 85 tonnes of CO2 per hectare annually. The UK has 1.7 million hectares of urban land and if proactively managed, just 10% of urban land has the potential to meet 2.5% of the UK’s annual CO2 reduction target. Although much of the urban land is occupied by infrastructures at any one time, future demolition and construction activities provide a unique opportunity to recycle the demolition waste as a source of calcium and implement the inorganic carbon capture into design of future structures.
Multifunctionality is a focus of SUCCESS, meaning that design of permanent CO2 removal could be introduced into soil while providing other engineering and ecosystem services. In one of our recent papers we concluded that designing roadside verges and central reservations associated with construction of new roads to capture CO2 inorganically while providing other designed services, has the theoretical capacity to store 11 million tonnes of CO2 in the UK over the next ten years. This equates to economic benefit of £61,930,000 in terms of mitigation of CO2 emission.
The key is to sustainably source the calcium required to introduce inorganic CO2 removal – demolition waste remaining from recycling demolition material is one option, closing part of the carbon cycle for cement manufacture. In addition, fine-grained products of quarries extracting and crushing igneous rocks (such as basalt) provide an ideal source of calcium which could be used for the inorganic CO2 removal.
To work more closely with a large cross-section of scientists in Scotland working on carbon cycle I have recently taken up a role as a co-leader for the theme, ‘Carbon & Biogeochemical Cycles: Sustaining Life’ at the Scottish Alliance for Geoscience, Environment & Society (SAGES).