Examining Energy Consumption and Carbon Emissions of Microbial Induced Carbonate Precipitation Using the Life Cycle Assessment Method

Fruit and vegetable waste used as bacterial growth media for the biocementation of two geomaterials

This paper investigates the feasibility of using randomly collected fruit and vegetable (FV) waste as a cheap growing medium of bacteria for biocementation applications. Biocementation has been proposed in the literature as an environmentally-friendly ground improvement method to increase the stability of geomaterials, prevent erosion and encapsulate waste, but currently suffers from the high costs involved, such as bacteria cultivation costs. After analysis of FV waste of varied composition in terms of sugar and protein content, diluted FV waste was used to grow ureolytic (S. pasteurii, and B.licheniformis) and also an autochthonous heterotrophic carbonic anhydase (CA)-producing B.licheniformis strain, whose growth in FV media had not been attempted before. Bacterial growth and enzymatic activity in FV were of appropriate levels, although reduced compared to commercial media. Namely, the CA-producing B.licheniformis had a maximum OD600 of 1.799 and a CA activity of 0.817 U/mL in FV media. For the ureolytic pathway, B. licheniformis reached a maximum OD600 of 0.986 and a maximum urease activity of 0.675 mM urea/min, and S. pasteurii a maximum OD600 = 0.999 and a maximum urease activity of 0.756 mM urea/min. Biocementation of a clay and locomotive ash, a geomaterial specific to UK railway embankments, using precultured bacteria in FV was then proven, based on recorded unconfined compressive strengths of 1-3 MPa and calcite content increases of up to 4.02 and 8.62 % for the clay and ash respectively. Scanning Electron Microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), attested the formation of bioprecipitates with characteristic morphologies and elementary composition of calcite crystals. These findings suggest the potential of employing FV to biocement these problematic geomaterials and are of wider relevance for environmental and geoenvironmental applications involving bioaugmentation. Such applications that require substrates in very large quantities can help tackle the management of the very voluminous fruit and vegetable waste produced worldwide.

State-of-the-art review of soil erosion control by MICP and EICP techniques: Problems, applications, and prospects

In recent years, the application of microbially induced calcite precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) techniques have been extensively studied to mitigate soil erosion, yielding substantial achievements in this regard. This paper presents a comprehensive review of the recent progress in erosion control by MICP and EICP techniques. To further discuss the effectiveness of erosion mitigation in-depth, the estimation methods and characterization of erosion resistance were initially compiled. Moreover, factors affecting the erosion resistance of MICP/EICP-treated soil were expounded, spanning from soil properties to treatment protocols and environmental conditions. The development of optimization and upscaling in erosion mitigation via MICP/EICP was also included in this review. In addition, this review discussed the limitations and correspondingly proposed prospective applications of erosion control via the MICP/EICP approach. The current review presents up-to-date information on the research activities for improving erosion resistance by MICP/EICP, aiming at providing insights for interdisciplinary researchers and guidance for promoting this method to further applications in erosion mitigation.

Simultaneous removal of fluoride and phosphate from semiconductor wastewater via chemical precipitation of calcium fluoride and hydroxyapatite using byproduct of recycled aggregate

Semiconductor wastewater with high concentrations of fluoride and phosphate is an environmental issue that cannot be ignored. Moreover, the byproduct of recycled aggregates, concrete fines, cannot be reused in concrete manufacturing, which is a key issue to address for the sustainable development of the concrete industry. The objective of this study was to tackle the crucial environmental issues of these two industries by developing concrete fines as an alternative material to treat semiconductor wastewater. The chemical precipitation of calcium fluoride and hydroxyapatite in the presence of concrete fines was determined as the mechanism underpinning the removal of fluoride and phosphate in wastewater. Owing to the wide range of contaminant concentration and solution pH and the possibility of multi-stage treatment, the effects of the initial contaminant concentration (F: 100-1000 mg/L; P: 20-200 mg/L) and solution pH (pH: 2-7) on the removal reactions were determined. The highest F and P removal percentages were more than 99%, and the final F and P concentrations met the effluent standard (F: 15 mg/L, P: 1.3 mg/L). The removal reactions of F and P are generally in competition, and the removal of F has priority over the removal of P. The pseudo-second-order model can describe the kinetics of the removal reactions well. The formation of fluorapatite can reduce the F concentration below the concentration achievable by CaF2 precipitation alone. Furthermore, using the byproduct of recycled aggregates instead of conventional chemicals to treat semiconductor wastewater is promising in terms of reducing CO2 emissions, and prospective applications are discussed. This study can lead to the development of a sustainable and clean process for semiconductor wastewater treatment using byproducts from the concrete industry.

Assessment of the Composition Effect of a Bio-Cementation Solution on the Efficiency of Microbially Induced Calcite Precipitation Processes in Loose Sandy Soil

Soil properties are the most important factors determining the safety of civil engineering structures. One of the soil improvement methods studied, mainly under laboratory conditions, is the use of microbially induced calcite precipitation (MICP). Many factors influencing the successful application of the MICP method can be distinguished; however, one of the most important factors is the composition of the bio-cementation solution. This study aimed to propose an optimal combination of a bio-cementation solution based on carbonate precipitation, crystal types, and the comprehensive strength of fine sand after treatment. A series of laboratory tests were conducted with the urease-producing environmental strain of bacteria B. subtilis, using various combinations of cementation solutions containing precipitation precursors (H2NCONH2, C6H10CaO6, CaCl2, MgCl2). To decrease the environmental impact and increase the efficiency of MICP processed, the addition of calcium lactate (CaL) and Mg ions was evaluated. This study was conducted in Petri dishes, assuming a 14-day soil treatment period. The content of water-soluble carbonate precipitates and their mineralogical characterization, as well as their mechanical properties, were determined using a pocket penetrometer test. The studies revealed that a higher concentration of CaL and Mg in the cementation solution led to the formation of a higher amount of precipitates during the cementation process. However, the crystal forms were not limited to stable forms, such as calcite, aragonite, (Ca, Mg)-calcite, and dolomite, but also included water-soluble components such as nitrocalcite, chloro-magnesite, and nitromagnesite. The presence of bacteria allowed for the increasing of the carbonate content by values ranging from 15% to 42%. The highest comprehensive strength was achieved for the bio-cementation solution containing urea (0.25 M), CaL (0.1 M), and an Mg/Ca molar ratio of 0.4. In the end, this research helped to achieve higher amounts of precipitates with the optimum combination of bio-cementation solutions for the soil improvement process. However, the numerical analysis of the precipitation processes and the methods reducing the environmental impact of the technology should be further investigated.

Self-Healing of Cementitious Materials via Bacteria: A Theoretical Study

Cracks on the surface of cementitious composites represent an entrance gate for harmful substances—particularly water—to devastate the bulk of material, which results in lower durability. Autogenous crack-sealing is a significantly limited mechanism due to a combination of the hydration process and calcite nucleation, and self-healing cementitious composites are a research area that require a great deal of scientific effort. In contrast to time-consuming experiments (e.g., only the preparation of an applicable bare concrete sample itself requires more than 28 days), appropriately selected mathematical models may assist in the deeper understanding of self-healing processes via bacteria. This paper presents theoretically oriented research dealing with the application of specific bacteria (B. pseudofirmus) capable of transforming available nutrients into calcite, allowing for the cracks on the surfaces of cementitious materials to be repaired. One of the principal objectives of this study is to analyze the sensitivity of the bacterial growth curves to the system parameters within the context of the logistic model in the Monod approach. Analytically calculated growth curves for various parameters (initial inoculation concentration, initial nutrition content, and metabolic activity of bacteria) are compared with experimental data. The proposed methodology may also be applied to analyze the growth of microorganisms of nonbacterial origin (e.g., molds, yeasts).

Life cycle assessment of biocemented sands using enzyme induced carbonate precipitation (EICP) for soil stabilization applications

Integrating sustainability goals into the selection of suitable soil stabilization techniques is a global trend. Several bio-inspired and bio-mediated soil stabilization techniques have been recently investigated as sustainable alternatives for traditional techniques known for their high carbon footprint. Enzyme Induced Carbonate Precipitation (EICP) is an emerging bio-inspired soil stabilization technology that is based on the hydrolysis of urea to precipitate carbonates that cement sand particles. A life cycle assessment (LCA) study was conducted to compare the use of traditional soil stabilization using Portland cement (PC) with bio-cementation via EICP over a range of environmental impacts. The LCA results revealed that EICP soil treatment has nearly 90% less abiotic depletion potential and 3% less global warming potential compared to PC in soil stabilization. In contrast, EICP in soil stabilization has higher acidification and eutrophication potentials compared to PC due to byproducts during the hydrolysis process. The sensitivity analysis of EICP emissions showed that reducing and controlling the EICP process emissions and using waste non-fate milk has resulted in significantly fewer impacts compared to the EICP baseline scenario. Moreover, a comparative analysis was conducted between EICP, PC, and Microbial Induced Carbonate Precipitation (MICP) to study the effect of treated soil compressive strength on the LCA findings. The analysis suggested that EICP is potentially a better environmental option, in terms of its carbon footprint, at lower compressive strength of the treated soils.

Experimental Study on Optimization of Cementation Solution for Wind-Erosion Resistance Using the MICP Method

In the present study, an environmentally friendly microbial-induced calcium carbonate precipitation (MICP) technique was explored to reinforce the desert sand using the stopped-flow pouring method. A detailed experimental study has been conducted with Sporosarcina (S.) pasteurii urease-producing bacteria with a 0.5 M cementation solution. To optimize the cementation solution, three different pore volumes (PV), i.e., 0.4, 0.6, and 0.8, were considered. The cementation solution was provided every 24 h and considered as one treatment cycle. The cylindrical specimen in three replicas was biotreated for 7, 14, and 21 days in 1:1 and 1:2 (diameter: height) ratios for determina-tion of split-tensile strength (STS) and unconfined compressive strength (UCS), respectively. Micro-structure characterization of untreated and biotreated sand was also examined using a scanning electron microscope (SEM) and energy-dispersive X-ray analysis (EDX). Rocklike behavior was ob-served for biotreated-sand samples using the UPV test. Test results for 21 days with 0.8 PV were 1340 kPa, 241 kPa, and 1762 m/s for UCS, STS, and UPV, respectively, with an average calcite content of 16.2%. Overall, the 0.5 M cementation solution with a 24 h treatment cycle, 0.8 PV with 7 days, and 0.4 PV with 14 days gave optimum treatment solution, and showed heavily cemented and rock-type behavior of the biotreated-sand sample.

Sustainability in Geotechnics through the Use of Environmentally Friendly Materials

The reduction in the exploitation of non-renewable natural resources is nowadays widely recognized as a pressing need for a more sustainable society. Moreover, the increase in waste valorization and reuse of waste materials are undoubtedly important steps forward for environmental sustainability. Geotechnical design being part of typical civil engineering projects can play a major role in the sustainability of the built environment. Thus, a Special Issue was proposed focused on the use of environmentally friendly materials in geotechnical solutions, highlighting the relevance of geotechnics to reduce our carbon footprint. Their main purpose to collect and publish original research papers pointing out the use of sustainable materials in geotechnics has been achieved, through the great interest of the research community and a high number of submissions. This editorial summarizes the papers published during the 2020–2021 biennium, highlighting their main conclusions.

Construction of Biophysical Indicators for the Catalan Economy: Building a New Conceptual Framework

The main objective of this work is to create an environmental vision of the Catalan economy based on various indicators. To do this, we started from the fundamental idea of obtaining new metrics to measure impacts on the economy. The methodology used is focused on the systematization of descriptive statistics and econometric review. In this sense, GDP and GDP per capita are valued as chrematistic units, and biophysical variables are incorporated. For the period 2000–2016, the figures for energy consumption, CO2 emissions, energy intensity of the economy and water consumption were collected. In addition, demographic evolution and the Gini index were also ordered as factors that contribute to explaining not only population trajectory but also some of the social factors. Greater technological efficiency in regard to environmental aspects is intuited as sensitive to the economic cycle. The study is novel in the panorama of the regional economy of Spain, by incorporating biophysical variables to the applied economic analysis.