Biocementation through Microbial Calcium Carbonate Precipitation

AbstractBiocementation through microbial carbonate precipitation is a new branch of microbial geotechnology that deals with the applications of microbiological methods to produce cemented materials used in engineering. The primary consideration of these applications is to improve the geophysical properties of soil so that it will be suitable for construction and environmental purposes. The applications of biocementation would require an interdisciplinary research at the confluence of microbiology, ecology, geochemistry, civil and environmental engineering. This new field has the potential to meet society’s expanding needs for innovative treatment processes that improve soil engineering properties. This paper presents an overview of biocementation, particularly through microbial calcium carbonate (CaCO3) precipitation, and non-destructive geophysical techniques for real-time monitoring of soil engineering properties. Focus is then narrowed to an example of laboratory-scale test of biocementation of sandy soil and measurement of strength development by shear wave velocity (Vs). Other analytical results included microscopic imaging by scanning electron microscope (SEM) and identification of CaCO3 precipitation presented in biocemented sand by X-ray diffactometer (XRD) were discussed. Potential advantages and envisioned applications of biocemented soil improvement are identified

Use of a Piezoelectric Bender Element for the Determination of Initial and Final Setting Times of Metakaolin Geopolymer Pastes, with Applications to Laterite Soils

This study proposes the use of a non-destructive testing technique, based on piezoelectric bender element tests, to determine the initial and final setting times of metakaolin geopolymer pastes. (1) Background: Metakaolin geopolymer is a new eco-friendly building material that develops strength rapidly and is high in compressive strength. (2) Methods: The initial and the final setting times were investigated via bender element and Vicat needle tests. Metakaolin powder was prepared by treating kaolin at 0, 200, 800, 1000, and 1200 °C. All metakaolin powder samples were then mixed with geopolymer solution at different mixing ratios of 0.8:1.0, 1.0:1.0, 1.2:1.0, and 1.5:1.0. The geopolymer solution was prepared by adding 10 normal concentrations of sodium hydroxide (10 N NaOH) to sodium silicate (Na2SiO3) at various solution ratios of 1.0:1.0, 1.0:1.2, 1.0:1.5, 1.0:2.0, 1.2:1.0, 1.5:1.0 and 2.0:1.0. (3) Results: The optimum temperature for treating metakaolin is established at 1000 °C, with a mixing ratio between the metakaolin powder and the geopolymer solution of 1.0:1.0, as well as a solution ratio between NaOH and Na2SiO3 of 2.0:1.0. (4) Conclusions: The use of piezoelectric bender elements to determine the initial and final setting times of metakaolin geopolymer pastes is a useful method by which to detect geopolymerization by shear wave velocity in a real-time manner. Moreover, the penetration of the Vicat apparatus can confirm the setting times at specific intervals. The relationships between the shear wave velocity and the Vicat penetration appear to be linear, with an initial setting time of 168 m/s and a final setting time of 187 m/s. Finally, the optimum metakaolin geopolymer pastes are applied to improve laterite soils, as measured by CBR tests

การบำบัดน้ำเสียด้วยระบบเอสบีอาร์ร่วมกับซีโอไลต์-ไคโตซานWastewater Treatment by SBR Zeolite-Chitosan

บทคัดย่องานวิจัยนี้ศึกษาปริมาณตัวดูดซับซีโอไลต์-ไคโตซานที่เหมาะสมสำหรับการบำบัดแอมโมเนียมและซีโอดีในระบบเอสบีอาร์และระบบเอสบีอาร์ร่วมกับซีโอไลต์-ไคโตซาน โดยควบคุมอัตราส่วนการเติมอากาศต่อไม่เติมอากาศ 6:2 อายุตะกอนที่ 10 วันใช้น้ำเสียสังเคราะห์ที่มีค่าซีโอดี เท่ากับ 500-1300 มก./ล. จากการทดลองพบว่าวัสดุดูดซับ    ซีโอไลต์-ไคโตซานมีความสามารถในการดูดซับแอมโมเนียมสูงสุด (qm) เท่ากับ 13.15 มก./ก. ประสิทธิภาพของระบบเอสบีอาร์ร่วมกับซีโอไลต์-ไคโตซานในการบำบัดแอมโมเนียม ที่ซีโอดีในน้ำเข้ามีค่าเฉลี่ยเท่ากับ 510, 1010 และ 1280 มก./ล. มีค่าร้อยละ76, 73 และ 71 ตามลำดับ ระบบเอสบีอาร์มีค่าร้อยละ 65, 65 และ 60 ตามลำดับ สำหรับการบำบัดซีโอดีที่ความเข้มข้นซีโอดี เฉลี่ยเท่ากับ 510, 1010 และ1280 มก./ล. ระบบเอสบีอาร์ร่วมกับซีโอไลต์-ไคโตซานมีประสิทธิภาพการบำบัดคิดเป็นร้อยละ 83, 94 และ 94 ตามลำดับ ในขณะที่ระบบเอสบีอาร์มีประสิทธิภาพการบำบัดคิดเป็นร้อยละ 78, 91 และ 91 ตามลำดับ จะเห็นได้ว่าระบบเอสบีอาร์ร่วมกับซีโอไลต์-ไคโตซานสามารถบำบัดแอมโมเนียมและซีโอดีได้ดีกว่ารวมทั้งการบำบัดมีความคงที่กว่าระบบเอสบีอาร์ที่ทุกความเข้มข้นของซีโอดีAbstractThis research aims to determine the amount of zeolite-chitosan adsorbent and comparatively study efficiencies of SBR and SBR zeolite-chitosan systems for removals of ammonium (NH4-N) and chemical oxygen demand (COD). The ratio between aerated and unaerated period was 6:2 and the sludge retention time (SRT) was controlled at 10 days. Synthetic wastewater having COD values between 500 and 1300 mg/L was used. Results found that the maximum adsorption capacity (qm) of NH4-N was 13.15 mg/g for zeolite-chitosan adsorbent. The NH4-N removal efficiencies at different the average initial COD concentration of 510, 1010 and 1280 mg/L were 76, 73 and 71% respectively in the SBR zeolite-chitosan system and 65, 65 and 60% respectively in the SBR system. As well, efficiencies for COD removal of SBR-zeolite-chitosan system were 83, 94 and 94% at average initial COD concentration of 510, 1010 and 1280 mg/L, respectively. The COD removal efficiency of SBR system was 78, 91 and 91% at average initial COD concentration of 510, 1010 and 1280 mg/L, respectively. It was clear that the SBR zeolite-chitosan system yielded better and stable treatment efficiency than conventional SBR system

Sandy soil improvement using MICP-based urease enzymatic acceleration method monitored by real-time system

This paper aims at monitoring the improvement of sandy soil properties with biocementation through the microbially induced calcite precipitation (MICP) method with reaction accelerations by self-developed soybean urease enzymes. In this study, the concentration of calcium ions (Ca2+ ions as CaCl2) is varied at 50, 100, 250, and 500 mM to determine an optimum shear strength. The self-developed soybean urease enzymes of 20% by volume (v/v) are used to accelerate the MICP reaction to finish within 7 days. Based on real-time monitoring bender element system and direct shear tests, the optimum Ca2+ concentration is found as 250 mM. However, a detrimental effect occurs in case of high concentration of Ca2+ as CaCl2 (500 mM) because of solution acidification from high Cl− concentration. This condition lowers CaCO3 precipitation causing the reduction of biocementation process. At equivalent shear modulus, the biocementation time of MICP-based sand with acceleration by urease enzymes is about 10 times faster than that without. Using spectrophotometer and pH meter, the ammonification rate and the solution pH of biocemented sand with acceleration by urease enzymes for 3 days are found relatively higher than those without urease enzymes for 40 days. The analyses by scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirm not only the occurrence of CaCO3 binding sand particles together but also the improvement of physical strengths of sandy soil samples with the MICP-based urease enzymatic acceleration method. These results introduce an option to accelerate biocemented sandy soil improvement