Standing on SUCCESS

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.

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).

Dr Jorat is currently working as a lecturer in geotechnical engineering in the Division of Natural and Built Environment in the School of Science, Engineering and Technology, having formerly served as a geotechnical engineering coordinator for the SUCCESS project at Newcastle University.