Microbial-Induced Calcite Precipitation in soils

: use of alternative raw materials and analysis of environmental implications

Abstract

Microbial-Induced Calcite Precipitation (MICP) is a biogeochemical process that induces the precipitation of calcium carbonate minerals as a result of microbial activity. In MICP via urea hydrolysis, urea, calcium, and simple carbon and nitrogen chemical compounds are supplied to stimulate degradation of urea by ureolytic microorganisms to produce carbonates and induce precipitation of calcium carbonate minerals. In soil, MICP alters soil mechanical properties through filling soil pores and binding soil particles. Therefore, MICP is investigated as a soil stabilisation technique in soil engineering. Compared to traditional soil stabilisation techniques, MICP is regarded as ‘environmentally friendly’ however, environmental impact of MICP is not yet fully assessed and reliance on industry end products (e.g., urea, calcium chloride) increases both the environmental impact and treatment costs of MICP.

This thesis considered, on the basis of a circular economy, use of available ‘waste’ products as alternatives to the chemical-based treatment used for MICP to increase sustainability and potentially reduce treatment costs. Dolerite fines by-product of the quarrying sector and cow urine derived from the farming sector were investigated as sources of calcium and nutrients to induce urea hydrolysis, respectively.

Suitability of the proposed products was investigated, on the one hand, in dissolution experiments on dolerite quarry fines to determine their potential to source calcium-rich solutions through chemical weathering and, on the other hand, characterising urea content and stability in urine. The effectiveness of the proposed products was investigated monitoring reactants and products of MICP in soil column experiments and compared to the chemical-based treatment. Soil carbonation and improvement of mechanical properties via MICP with dolerite fines as a source of calcium was investigated. Environmental aspects of MICP investigated included quantification of ammonium and nitrates in soil leachates and a study on the greenhouse gas fluxes of MICP, where dolerite fines were investigated for their capacity to act as a carbon sink.

Experimental results demonstrated dolerite fines and cow urine, on their own and potentially combined, could be used effectively as alternatives to the chemical-based treatment to stimulate MICP in soil. The environmental impact of MICP with both products through accumulation of ammonia was comparable to the chemical-based treatment. Experimental results on greenhouse gas fluxes revealed MICP results in carbon dioxide emissions due to high microbial activity induced by the treatment. The potential of dolerite fines to enhance soil respiration and increase the overall capacity of the system to store inorganic carbon was evidenced. The findings of this thesis provide the foundations for future experimentation with both products in MICP applications and highlight areas for future work in geotechnical and environmental research.

Date of Award	Oct 2022
Original language	English
Awarding Institution	Abertay University
Sponsors	Norman Fraser Design Trust & Scottish Alliance for Geoscience Environment and Society
Supervisor	Ehsan Jorat (Supervisor) & Joseph Akunna (Supervisor)