3rd Year PhD Student , Engineering Department, Cambridge University
Soil stabilisation by bacterial induced calcite crystals for bonding soil particles
Soil stabilisation by bacterial induced calcite crystals for bonding soil particles and changing soil into rock
Abstract: Authors: Donovan Mujah ; Mohamed A. Shahin ; Liang Cheng Article URL: http://www.tandfonline.com/doi/full/10.1080/01490451.2016.1225866?ai=z4&mi=3fqos0&af=R Citation: Geomicrobiology Journal Publication Date: 2016-08-26T01:28:29Z Journal: Geomicrobiology Journal
Pub.: 26 Aug '16, Pinned: 25 Aug '17
Abstract: This study explored the biomimetic regulation of microbially induced calcium carbonate precipitation via employing immobilization technology. Calcium alginate gel was used to immobilize urea-positive Sporosarcina pasteurii. CO32− was generated by ureolysis and reacted directly with Ca2+, and amorphous calcium carbonate, vaterite, and calcite appeared in order. The discussed techniques are applicable to other polysaccarides on CaCO3.Many researchers in the past decade have explored the controlled synthesis of calcium carbonate with specific size, morphology, and polymorphism. This study explored the biomimetic regulation of microbially induced calcium carbonate precipitation (MICP) via employing immobilization technology. Calcium alginate gel was used to immobilize Sporosarcina pasteurii, a urea-positive microorganism. CO32– was generated driven by ureolysis and reacted directly with Ca2+ that was cross-linked in sodium alginate to produce CaCO3 precipitation. Based on SEM, TEM, XRD, HRTEM, and SAED results, amorphous calcium carbonate, vaterite, and calcite appeared in order. This evolution of CaCO3 morphology and polymorphism apparently conforms to Ostwald’s rule. Various concentrations (1–3%) of sodium alginate caused different alginate molecules to form due to the collapse of calcium alginate gel carrying negative charges and exerting a significant influence on the morphology of CaCO3 from hexagonal vaterite to capsule-shaped vaterite. The techniques discussed here can also be applied to other polysaccharides on CaCO3, which implies that they are valuable with regard to polymorphic regulation because abundant polysaccharide apparently favors the vaterite polymorph.
Pub.: 07 Feb '17, Pinned: 25 Aug '17
Abstract: Limestone from aggregate quarries and acetic acid from pyrolysis of lignocellulosic biomass was used to produce biocement.Biocement production from microbially induced calcium carbonate precipitation (MICP) is an environmentally friendly approach for construction works, but the use of calcium chloride (CaCl2) in the conventional MICP process is a cost-limiting factor. The aim of this work is to develop a method for producing soluble calcium ions through two waste sources, limestone powder derived from aggregate quarries and acetic acid derived from fast pyrolysis of lignocellulosic biomass, as a replacement for the reagent grade CaCl2 in the MICP process. The ratio of limestone powder to acetic acid solution was optimized for a desirable calcium concentration with an appropriate pH. Procedures for applying the urease-producing bacteria, urea, and calcium solutions were developed for a successful MICP process and were treated for sand column test. The engineering properties of the biocemented sand, including water permeability, unconfined compressive strength, and tensile strength, were evaluated as a function of the calcium carbonate content of the product. It was found that the properties of the sand treated using the limestone/acetic acid derived calcium solution were comparable to those of sand treated using reagent grade CaCl2. Collectively, the results indicate that the new MICP process is effective, more sustainable, and cheaper compared with the conventional MICP method.
Pub.: 16 May '17, Pinned: 25 Aug '17
Abstract: Microbially-induced CaCO3 precipitation (MICP) is a naturally occurring process wherein durable carbonates are formed as a result of microbial metabolic activities. In recent years, MICP technology has been widely harnessed for applications in civil engineering wherein synthesis of calcium carbonate crystals occurs at ambient temperature paving way for low energy biocement. MICP using pure urease (UA) and carbonic anhydrase (CA) producing bacteria has been promising in laboratory conditions. In the current study we enriched ureolytic and carbonic anhydrase communities in calcareous soil under biostimulation and bioaugmentation conditions and investigated the effect of microbial dynamics on carbonate precipitation, calcium carbonate polymorph selection and consolidation of biological sand column under nutrient limited and rich conditions. All treatments for stimulation and augmentation led to significant changes in the composition of indigenous bacterial population. Biostimulation as well as augmentation through the UA route was found to be faster and more effective compared to the CA route in terms of extracellular enzyme production and carbonate precipitation. Synergistic role of augmented cultures along with indigenous communities was recorded via both the routes of UA and CA as more effective calcification was seen in case of augmentation compared to stimulation. The survival of supplemented isolates in presence of indigenous bacterial communities was confirmed through sequencing of total diversity and it was seen that both UA and CA isolate had the potential to survive along with native communities under high nutrient conditions. Nutrient conditions played significant role in determining calcium carbonate polymorph fate as calcitic crystals dominated under high carbon supplementation. Finally, the consolidation of sand columns via stimulation and augmentation was successfully achieved through both UA and CA route under high nutrient conditions but higher consolidation in short time period was noticed in UA route. The study reports that based upon the organic carbon content in native soils, stimulation can be favored at sites with high organic carbon content while augmentation with repeated injections of nutrients can be applied on poor nutrient soils via different enrichment routes of microbial metabolism.
Pub.: 27 Jul '17, Pinned: 25 Aug '17