Cow urine as a source of nutrients for Microbial-Induced Calcite Precipitation in sandy soil

Microbial Induced Calcite Precipitation (MICP) via biostimulation of urea hydrolysis is a biogeochemical process in which soil indigenous ureolytic microorganisms catalyse the decomposition of urea into ammonium and carbonate ions which, in the presence of calcium, precipitate as calcium carbonate minerals. The environmental conditions created by urine in soil resemble those induced by MICP via urea hydrolysis. Thus, this study assesses the suitability of a waste product, cow urine, as a source of nutrients for MICP. Urea stability in fresh and sterilised urine were monitored for a month to cover the length of a potential MICP intervention. An experimental soil column set up was used to compare the soil response to the repeated application of fresh and sterilised cow urine, within pH of 7 and 9, and the chemical-based solution. Urea hydrolysis and the carbonate content in solution were monitored to assess the suitability of the proposed alternative. In addition, the nitrification process was monitored. Key findings indicated i) urea concentration and stability in fresh and sterilised cow urine are suitable for MICP application; ii) the soil response to treatments of cow urine within pH of 7 and 9 are similar to the chemical-based solution; and iii) increasing solution pH results in a faster activation of ureolytic microorganisms and higher carbonate content in solution. These results demonstrate that cow urine is a suitable substitute of the chemical-based MICP application

Dolerite fines used as a calcium source for microbially induced calcite precipitation reduce the environmental carbon cost in sandy soil

Microbial-Induced Calcite Precipitation (MICP) stimulates soil microbiota to induce a cementation of the soil matrix. Urea, calcium and simple carbon nutrients are supplied to produce carbonates via urea hydrolysis and induce the precipitation of the mineral calcite. Calcium chloride (CaCl2) is typically used as a source for calcium, but silicate rocks and other materials have been investigated as alternatives. Weathering of calcium-rich silicate rocks (e.g. basalt and dolerite) releases calcium, magnesium and iron; this process is associated with sequestration of atmospheric CO2 and formation of pedogenic carbonates. We investigated atmospheric carbon fluxes of a MICP treated sandy soil using CaCl2 and dolerite fines applied on the soil surface as sources for calcium. Soil-atmosphere carbon fluxes were monitored over two months and determined with an infrared gas analyser connected to a soil chamber. Soil inorganic carbon content and isotopic composition were determined with isotope-ratio mass spectrometry. In addition, soil-atmosphere CO2 fluxes during chemical weathering of dolerite fines were investigated in incubation experiments with gas chromatography. Larger CO2 emissions resulted from the application of dolerite fines (116 g CO2-C m-2) compared to CaCl2 (79 g CO2-C m-2) but larger inorganic carbon precipitation also occurred (172.8 g C m-2 and 76.9 g C m-2, respectively). Normalising to the emitted carbon to precipitated carbon, the environmental carbon cost was reduced with dolerite fines (0.67) compared to the traditional MICP treatment (1.01). The carbon isotopic signature indicated pedogenic carbonates (δ13Cav = 8.2±5.0‰) formed when dolerite was applied and carbon originating from urea (δ13Cav = 46.4±1.0‰) precipitated when CaCl2 was used. Dolerite fines had a large but short-lived (<2 d) carbon sequestration potential, and results indicated peak CO2 emissions during MICP could be balanced optimizing the application of dolerite fines

Soil management and engineering for blue-green infrastructure

As urban areas continue to expand, the value of urban blue-green infrastructure (BGI) for increasing the social, environmental and economic sustainability of cities is increasingly recognised. However, there remains an inherent lack of knowledge and awareness around the fundamental contribution that soils make to the functioning of ecosystems within urban BGI. Urban landscapes are a nexus of environmental, engineered and socio-economic factors, which combine to create multifunctional spaces for people to live and work, all underpinned by the soil beneath us. In this chapter, we first outline the characteristics of urban soils and their importance for providing a range of beneficial ecosystem services, such as food production, flood mitigation, carbon storage and opportunities for recreation. We then highlight the key challenges and opportunities around the management and creation of soils within urban BGI. We conclude by emphasising the urgent need for better recognition of urban soils within planning policy and setting out a series of land-use specific management recommendations that will better enable urban soils to support the delivery of ecosystem services and, ultimately, enhance human health and wellbeing

Greenhouse gas fluxes of microbial-induced calcite precipitation at varying urea-to-calcium concentrations

Microbial-induced calcite precipitation (MICP) is regarded as environmentally friendly, partly due to the storage of carbon as carbonates. Although CO2 emissions during MICP have been reported, quantification of its environmental impact regarding total greenhouse gas fluxes has not yet been thoroughly investigated. In particular, N2O fluxes could occur in addition to CO2 since MICP involves the microbially mediated nitrogen cycle. This study investigated the greenhouse gas fluxes during biostimulation of MICP in quartz sand in incubation experiments. Soil samples were treated with MICP cementation solution containing calcium concentrations of 0, 20, 100 and 200 mM at a fixed urea concentration of 100 mM to offer a range of carbonation potential and/or mitigation of CO2 emissions. Greenhouse gas (CO2, CH4 and N2O) measurements were determined by gas chromatography during incubations. Soil total inorganic carbon and the isotopic composition of precipitated and emitted CO2 were determined by isotope ratio mass spectrometry. CO2 emissions (0.52 to 4.08 μg of CO2–C h−1 g−1 soil) resulted from MICP, while N2O and CH4 fluxes were not detected. Increasing Ca2+ with respect to urea resulted in lower CO2 emissions, lower solution pH, similar carbonate precipitation and urea hydrolysis inhibition. The highest urea-to-calcium ratio (1:0.2) emitted roughly two times the amount of CO2 (112 μg of CO2–C g−1 soil) compared to the 1:1 and 1:2 ratios (47 to 58 μg of CO2–C g−1 soil) and five to six times more than samples that did not receive Ca2+ (1:0) (~18 μg of CO2–C g−1 soil). Precipitated CaCO3–C was tenfold higher than cumulative emitted CO2–C, and isotopic analysis indicated both emitted and precipitated carbon were of urea origin. Both emitted and precipitated carbon accounted for a very low percentage of total carbon applied in the system (<0.35 and <4.5%, respectively), presumably due to limited urea hydrolysis which was negatively affected by increasing the Ca2+ concentration

Greenhouse gas fluxes of microbial-induced calcite precipitation at varying urea-to-calcium concentrations

Microbial-induced calcite precipitation (MICP) is regarded as environmentally friendly, partly due to the storage of carbon as carbonates. Although CO2 emissions during MICP have been reported, quantification of its environmental impact regarding total greenhouse gas fluxes has not yet been thoroughly investigated. In particular, N2O fluxes could occur in addition to CO2 since MICP involves the microbially mediated nitrogen cycle. This study investigated the greenhouse gas fluxes during biostimulation of MICP in quartz sand in incubation experiments. Soil samples were treated with MICP cementation solution containing calcium concentrations of 0, 20, 100 and 200 mM at a fixed urea concentration of 100 mM to offer a range of carbonation potential and/or mitigation of CO2 emissions. Greenhouse gas (CO2, CH4 and N2O) measurements were determined by gas chromatography during incubations. Soil total inorganic carbon and the isotopic composition of precipitated and emitted CO2 were determined by isotope ratio mass spectrometry. CO2 emissions (0.52 to 4.08 μg of CO2–C h−1 g−1 soil) resulted from MICP, while N2O and CH4 fluxes were not detected. Increasing Ca2+ with respect to urea resulted in lower CO2 emissions, lower solution pH, similar carbonate precipitation and urea hydrolysis inhibition. The highest urea-to-calcium ratio (1:0.2) emitted roughly two times the amount of CO2 (112 μg of CO2–C g−1 soil) compared to the 1:1 and 1:2 ratios (47 to 58 μg of CO2–C g−1 soil) and five to six times more than samples that did not receive Ca2+ (1:0) (~18 μg of CO2–C g−1 soil). Precipitated CaCO3–C was tenfold higher than cumulative emitted CO2–C, and isotopic analysis indicated both emitted and precipitated carbon were of urea origin. Both emitted and precipitated carbon accounted for a very low percentage of total carbon applied in the system (<0.35 and <4.5%, respectively), presumably due to limited urea hydrolysis which was negatively affected by increasing the Ca2+ concentration

Greenhouse gas fluxes of Microbial-Induced Calcite Precipitation at varying urea-to-calcium concentrations

Microbial-induced calcite precipitation (MICP) is regarded as environmentally friendly, partly due to the storage of carbon as carbonates. Although CO2 emissions during MICP have been reported, quantification of its environmental impact regarding total greenhouse gas fluxes has not yet been thoroughly investigated. In particular, N2O fluxes could occur in addition to CO2 since MICP involves the microbially mediated nitrogen cycle. This study investigated the greenhouse gas fluxes during biostimulation of MICP in quartz sand in incubation experiments. Soil samples were treated with MICP cementation solution containing calcium concentrations of 0, 20, 100 and 200 mM at a fixed urea concentration of 100 mM to offer a range of carbonation potential and/or mitigation of CO2 emissions. Greenhouse gas (CO2, CH4 and N2O) measurements were determined by gas chromatography during incubations. Soil total inorganic carbon and the isotopic composition of precipitated and emitted CO2 were determined by isotope ratio mass spectrometry. CO2 emissions (0.52 to 4.08 μg of CO2–C h−1 g−1 soil) resulted from MICP, while N2O and CH4 fluxes were not detected. Increasing Ca2+ with respect to urea resulted in lower CO2 emissions, lower solution pH, similar carbonate precipitation and urea hydrolysis inhibition. The highest urea-to-calcium ratio (1:0.2) emitted roughly two times the amount of CO2 (112 μg of CO2–C g−1 soil) compared to the 1:1 and 1:2 ratios (47 to 58 μg of CO2–C g−1 soil) and five to six times more than samples that did not receive Ca2+ (1:0) (~18 μg of CO2–C g−1 soil). Precipitated CaCO3–C was tenfold higher than cumulative emitted CO2–C, and isotopic analysis indicated both emitted and precipitated carbon were of urea origin. Both emitted and precipitated carbon accounted for a very low percentage of total carbon applied in the system (<0.35 and <4.5%, respectively), presumably due to limited urea hydrolysis which was negatively affected by increasing the Ca2+ concentration