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In order to solve the cost and environmental pollution problems caused by the transportation and stacking of shield tunneling muck, and to achieve the goal of resource reutilization of solid waste, a study was conducted based on a section of the Zhengzhou Metro Line 10 shield tunneling project. Excavated muck was used to replace sand, fly ash, and bentonite, while rice husk ash (RHA) was used to partially replace cement in the preparation of micro expansion synchronous grouting material. The effects of RHA content, muck particle size, water-binder ratio, and the type and content of expansion agents on the working and mechanical properties of synchronous grouting material were investigated. The results indicate that RHA significantly affects the slurry consistency and setting time, and higher RHA content leads to lower slurry consistency and shorter setting time. When RHA content is 25% (based on mass ratio of cement), the slurry consistency decreases by 27. 5% and the setting time shortens by 39. 9%. As RHA content increases, the compressive strength of slurry decreases first and then increases. As the particle size of muck increases, the slurry consistency and setting time decrease. Quicklime powder and high soundless static cracking agent (HSCA) as expansion agents reduce slurry consistency but effectively improve setting time and compressive strength. When HSCA mass fraction exceeds 3%, the expansion effect of HSCA is superior to that of quicklime powder. The tests determine that a water-binder ratio of 2.6, RHA content of 25%, adding larger particle size of muck, and the appropriate addition of expansion agents collectively meet all engineering requirements for slurry indicators, thereby providing a novel approach for the reutilization of shield tunneling muck and rice husk ash. [ABSTRACT FROM AUTHOR]

Aspartate ammonia-lyase gene of Bacillus sp.YM55-1 was cloned into the expression vector pET-28a(+). By site-directed mutagenesis of aspartate ammonia-lyase gene, the heterologous expression was obtained in E. coli BL21 (DE3) cells. Conversion of crotonic acid to (R)-3-aminobutyric acid was performed by the recombinant aspartate ammonia-lyase in the presence of ammonia and ammonium sulfate. The aspartate ammonia-lyase engineering bacteria were prepared into immobilized cells, and then enzymatic reaction conditions were optimized to achieve higher production of (R)-3-aminobutyric acid. The optimum pH and reaction temperature was 9.0 and 40 °C, respectively. Under these conditions, immobilized cells of 30 g/L were added and incubated for 22 h. Finally, the production of (R)-3-aminobutyric acid was 220 g/L, enantiomeric excess was more than 99.95%, conversion up to 98% and immobilized cells could be reused no less than 24 times. [ABSTRACT FROM AUTHOR]