• Energy Research

This study evaluated the efficacy of enzyme induced calcite precipitation (EICP) in restricting the mobility of heavy metals in soils. EICP is an environmentally friendly method that has wide ranging applications in the sustainable development of civil infrastructure. The study examined the desorption of three heavy metals from treated and untreated soils using ethylene diamine tetra-acetic acid (EDTA) and citric acid (C6H8O7) extractants under harsh conditions. Two natural soils spiked with cadmium (Cd), nickel (Ni), and lead (Pb) were studied in this research. The soils were treated with three types of enzyme solutions (ESs) to achieve EICP. A combination of urea of one molarity (M), 0.67 M calcium chloride, and urease enzyme (3 g/L) was mixed in deionized (DI) water to prepare enzyme solution 1 (ES1); non-fat milk powder (4 g/L) was added to ES1 to prepare enzyme solution 2 (ES2); and 0.37 M urea, 0.25 M calcium chloride, 0.85 g/L urease enzyme, and 4 g/L non-fat milk powder were mixed in DI water to prepare enzyme solution 3 (ES3). Ni, Cd, and Pb were added with load ratios of 50 and 100 mg/kg to both untreated and treated soils to study the effect of EICP on desorption rates of the heavy metals from soil. Desorption studies were performed after a curing period of 40 days. The curing period started after the soil samples were spiked with heavy metals. Soils treated with ESs were spiked with heavy metals after a curing period of 21 days and then further cured for 40 days. The amount of CaCO3 precipitated in the soil by the ESs was quantified using a gravimetric acid digestion test, which related the desorption of heavy metals to the amount of precipitated CaCO3. The order of desorption was as follows: Cd > Ni > Pb. It was observed that the average maximum removal efficiency of the untreated soil samples (irrespective of the load ratio and contaminants) was approximately 48% when extracted by EDTA and 46% when extracted by citric acid. The soil samples treated with ES2 exhibited average maximum removal efficiencies of 19% and 10% when extracted by EDTA and citric acid, respectively. It was observed that ES2 precipitated a maximum amount of calcium carbonate (CaCO3) when compared to ES1 and ES3 and retained the maximum amount of heavy metals in the soil by forming a CaCO3 shield on the heavy metals, thus decreasing their mobility. An approximate improvement of 30% in the retention of heavy metal ions was observed in soils treated with ESs when compared to untreated soil samples. Therefore, the study suggests that ESs can be an effective alternative in the remediation of soils contaminated with heavy metal ions.

AbstractAdaptation is key to minimizing heatwaves' societal burden; however, our understanding of adaptation capacity across the socioeconomic spectrum is incomplete. We demonstrate that observed heatwave trends in the past four decades were most pronounced in the lowest‐quartile income region of the world resulting in >40% higher exposure from 2010 to 2019 compared to the highest‐quartile income region. Lower‐income regions have reduced adaptative capacity to warming, which compounds the impacts of higher heatwave exposure. We also show that individual contiguous heatwaves engulfed up to 2.5‐fold larger areas in the recent decade (2010–2019) as compared to the 1980s. Widespread heatwaves can overwhelm the power grid and nullify the electricity dependent adaptation efforts, with significant implications even in regions with higher adaption capacity. Furthermore, we compare projected global heatwave exposure using per‐capita gross domestic product as an indicator of adaptation capacity. Hypothesized rapid adaptation in high‐income regions yields limited changes in heatwave exposure through the 21st century. By contrast, lagged adaptation in the lower‐income region translates to escalating heatwave exposure and increased heat‐stress inequality. The lowest‐quartile income region is expected to experience 1.8‐ to 5‐fold higher heatwave exposure than each higher income region from 2060 to 2069. This inequality escalates by the end of the century, with the lowest‐quartile income region experiencing almost as much heatwave exposure as the three higher income regions combined from 2090 to 2099. Our results highlight the need for global investments in adaptation capabilities of low‐income countries to avoid major climate‐driven human disasters in the 21st century.

Soil is a composite material of great interest to civil engineers. When the quality of such composite soils is poor, ground improvement techniques must be adopted to withstand the design load of superstructure. Existing soil stabilizers include lime and cement; however, their environmental safety and sustainable use during stabilization have been receiving increasing attention in recent years. This study investigated the use of granite sand (GS) and calcium lignosulphonate (CLS) as sustainable stabilizers that could be blended with clayey soils. The considered dosages of GS were 30%, 40% and 50%, and those of the CLS were 0.25%, 0.5%, 1% and 1.5%. Direct shear and consolidation tests were performed on the GS–CLS blended soil samples that were cured for 7 and 14 days. The amended stabilizers improved the shear parameters and consolidation characteristics at an optimum dosage of 30% GS and 0.5% CLS. Maximum improvements of 84% and 163% were observed in the cohesion and angles of internal friction, respectively. A significant change was also observed in the consolidation characteristics, making them practically applicable. The soil hydraulic conductivity was reduced by 14%, and the coefficient of consolidation increased by 203% for 30% GS and 05% CLS. Carbon footprint analyses were performed on the soil composition that would be best-suited for a typical homogenous earthen dam section. The results showed that the use of GS and CLS together reduced the carbon emissions by 6.57 and 7.7 times, compared to traditional stabilizers, such as cement and lime.

Research within civil engineering is focusing on newer ideas and philosophies such as sustainability and resiliency (S&R). This is evident in the development of frameworks for assessing the sustainability or the resiliency of civil infrastructures. Several frameworks have been developed by researchers to quantify the S&R of civil infrastructures. It is evident that the S&R are not mutually exclusive, and it is important to assess these aspects at the same time and that frameworks are able to accommodate simultaneous assessments. While there are other frameworks that follow a unified approach to S&R assessments, they do not account for the risk of the hazard as part of the framework. In the proposed framework, an attempt was made to include the risk of the hazard as part of the assessment to gain a realistic perspective of the hazard impact. This paper presents explicit steps to use the framework, along with an example of using the framework in assessing an earthen dam subjected to two types of hazards, earthquakes and floods. The novel aspects of this framework revolve around the simplicity and flexibility of the framework. Major input parameters are user-defined, which allows for a wide range of variables to be considered when determining the overall quality of the infrastructure.

Generally, researchers consider sustainability and resiliency aspects of infrastructure projects independently, without considering the relationship that exists between them. Unified approaches that combine sustainability, resiliency, and analyze risk are very minimal. This paper proposes a unified approach to assessing sustainability, resiliency, and risk for infrastructure via evaluating the performance of a tailings dam under various earthquake magnitudes. A tailings dam is typically in operation for many years, which means they may have a direct impact on the local environment, society, and economy. Due to the extended life of the dam, the probability of a major event occurring that could negatively impact the durability of the dam increases. Hence, it is important to study impacts on the environment and economy under regular (sustainability analysis) and extreme (resiliency analysis) conditions in conjunction with their probabilities of occurrence. This paper studies the interrelationships between sustainability, resiliency and the potential risks of a negative impact upon infrastructure. Results provided show that a unified approach with emphasis on risk offers a more holistic, and accurate depiction of a system‟s overall quality.