Development of a New Additive Based on Textile Fibers of End-of-Life Tires (ELT) for Sustainable Asphalt Mixtures with Improved Mechanical Properties

End-of-life tires (ELT) are a worldwide problem. Rubber, steel, and different textile fibers are the by-products of ELT. Unlike rubber and steel, waste tire textile fibers (WTTF) are disposed of in landfills or burned. This study developed an additive made with WTTF to be incorporated into conventional hot mix asphalt (HMA), and its performance properties were evaluated. First, a characterization of the WTTF used was made and a manufacture protocol was established. Then, a reference HMA was designed and mixtures with different addition percentages (2%, 5% and 8%) of the WTTF-based additive were evaluated. The mechanical properties studied were stiffness modulus, moisture susceptibility, rutting resistance, stripping, and cracking resistance. The results indicated that the addition of the 2% and 5% WTTF-based additive improved these performance properties. Moreover, all addition percentages of the WTTF-based additive evaluated demonstrated a decrease of over 29% in permanent deformation according to the Hamburg Wheel Tracking Test. Thus, the use of the WTTF would not only be valuing a waste, but an asphalt mixture with improved properties would be obtained, contributing to the circular economy by reusing a material and prolonging the useful life of the asphalt mixture

Can Microbially Induced Calcite Precipitation (MICP) through a Ureolytic Pathway Be Successfully Applied for Removing Heavy Metals from Wastewaters?

Microbially induced calcite precipitation (MICP) through a ureolytic pathway is a process that promotes calcite precipitation as a result of the urease enzymatic activity of several microorganisms. It has been studied for different technological applications, such as soil bio-consolidation, bio-cementation, CO2 sequestration, among others. Recently, this process has been proposed as a possible process for removing heavy metals from contaminated soils. However, no research has been reported dealing with the MICP process for heavy metal removal from wastewater/waters. This (re)view proposes to consider to such possibility. The main characteristics of MICP are presented and discussed. The precipitation of heavy metals contained in wastewaters/waters via MICP is exanimated based on process characteristics. Moreover, challenges for its successful implementation are discussed, such as the heavy metal tolerance of inoculum, ammonium release as product of urea hydrolysis, and so on. A semi-continuous operation in two steps (cell growth and bio-precipitation) is proposed. Finally, the wastewater from some typical industries releasing heavy metals are examined, discussing the technical barriers and feasibility

Application of microbe-induced carbonate precipitation for copper removal from copper-enriched waters: Challenges to future industrial application

Copper contamination in watercourses is a recent issue in countries where mining operations are prevalent. In this study, the application of copper precipitation through microbe-induced carbonate precipitation (MICP) was analyzed using urea hydrolysis by bacteria to evaluate precipitated copper carbonates. This article demonstrates the application of a copper precipitation assay involving Sporosarcina pasteurii (in 0.5 mM Cu2+ and 333 mM urea) and analyzes the resultant low removal (10%). The analysis indicates that the low removal was a consequence of Cu2+ complexation with the ammonia resulting from the hydrolysis of urea. However, the results indicate that there should be a positive correlation between the initial urea concentration and the bacterial tolerance to copper. This identifies a challenge in the industrial application of the process, wherein a minimum consumption of urea represents an economic advantage. Therefore, it is necessary to design a sequential process that decouples bacterial growth and copper precipitation, thereby decreasing the urea requirement

Testing the Capacity of Staphylococcus equorum for Calcium and Copper Removal through MICP Process

This research focused on the evaluation of the potential use of a soil-isolated bacteria, identified as Staphylococcus equorum, for microbial-induced calcite precipitation (MICP) and copper removal. Isolated bacteria were characterized considering growth rate, urease activity, calcium carbonate precipitation, copper tolerance as minimum inhibitory concentration (MIC) and copper precipitation. Results were compared with Sporosarcina pasteurii, which is considered a model bacteria strain for MICP processes. The results indicated that the S. equorum strain had lower urease activity, calcium removal capacity and copper tolerance than the S. pasteurii strain. However, the culture conditions tested in this study did not consider the halophilic feature of the S. equorum, which could make it a promising bacterial strain to be applied in process water from mining operations when seawater is used as process water. On the other hand, copper removal was insufficient when applying any of the bacteria strains evaluated, most likely due to the formation of a copper–ammonia complex. Thus, the implementation of S. equorum for copper removal needs to be further studied, considering the optimization of culture conditions, which may promote better performance when considering calcium, copper or other metals precipitation