Compressibility characteristics of bio-cemented calcareous sand treated through the bio-stimulation approach

Calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength.Microbial-induced calcium carbonate precipitation(MICP)is a promising technique for soil improvement.However,the commonly adopted bio-augmented MICP approach is in general less compatible with the natural soil environment.Thus,this study focuses on the bio-stimulated MICP approach,which is likely to enhance the dominance of ureolytic bacteria for longer period and thus is deemed more efficient.The main objective of this paper is to investigate the compressibility of calcareous sand treated by bio-stimulated MICP approach.In the current study,a series of one-dimension compression tests was conducted on bio-cemented sand pre-pared via bio-stimulation with different initial relative densities(D r).Based on the obtained compression curves and particle size distribution(PSD)curves,the parameters including cementation content,the coefficient of compressibility(a v),PSD,relative breakage(B r),and relative agglomeration(A r)were discussed.The results showed that a v decreased with the increasing cementation content.The bio-cemented sand prepared with higher initial D r had smaller(approximately 20%e70%)a v values than that with lower initial D r.The specimen with higher initial D r and higher cementation content resulted in smaller B r but larger A r.Finally,a conceptual framework featuring multiple contact and damage modes was proposed.

The Effects of Initial Cell Density on the Growth and Proliferation of the Potentially Toxic Cyanobacterium Microcystis aeruginosa

Increasing input of nutrients is leading to significant eutrophication in aquatic systems across the globe. Toxin production in those blooms is correlated with high cell density. A study was done to investigate the effects of initial cell density on the growth rate of the potentially toxic cyanobacterium Microcystis aeruginosa, in unfiltered lake water as well a common algal growth medium under laboratory conditions. Five treatments were established in the laboratory varying the initial cell density of M. aeruginosa and the growth medium. Unfiltered lake water was inoculated with a low, medium, and high initial cell density and Bold’s medium was inoculated with low and high initial cell densities. There was a significant difference in final cell density between the lake water treatments with the high inoculum of cell treatment reaching the highest final cell density. There was also a significant difference in final cell density between the Bold’s medium treatments. These results indicate there is a relationship between initial cell density of M. aeruginosa and final cell density, however, the results are similar when nutrients are available. Diverse algal communities can keep toxin producing algae in low density therefore precluding the need of toxin production.

UCIMS: Advances in geotechnical construction and performance monitoring

The Crossrail project currently under construction in Central London has been described as ＂The Big Digon Steroids＂, obviously referencing the Central Artery/Tunnel project in Boston completed in 2007. Toaddress the multiple demands for timely construction performance monitoring, Crossrail envisioned theunderground construction information management system （UCIMS） to monitor construction progressand structural health along the entire route, with a network of geotechnical instruments （i.e. slope inclinometers,extensometers, piezometers, etc.） and tunnel boring machine （TBM） position information.The UCIMS is a geospatially referenced relational database that was developed using an open sourcegeographic information system （GIS） that allowed all stakeholders near immediate feedback of constructionperformance. The purpose of this article is to provide a brief history of geotechnical andstructural monitoring software, to describe the structure and operation of the UCIMS, and to demonstratehow the functionality afforded by this system provided the requisite feedback to the stakeholders.Examples will be given regarding how the data management and visualization concepts incorporatedinto the UCIMS advanced the geotechnical construction industry. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Determination of growth kinetics of microorganisms linked with 1,4-dioxane degradation in a consortium based on two improved methods

The conventional method for determining growth kinetics of microbial consortia relies on the total biomass concentration.This may be inaccurate for substrates that are uncommon in nature and can only be degraded by a small portion of the microbial community.1,4-dioxane,an emerging contaminant,is an example of such substrates.In this work,we evaluated an improved method for determining the growth kinetics of a 1,4-dioxane-degrading microbial consortium.In the improved method,we considered only bacterial taxa whose concentration increase correlated to 1,4-dioxane concentration decrease in duplicate microcosm tests.Using PEST(Parameter Estimation),a modelindependent parameter estimator,the kinetic constants were estimated by fitting the Monod kineticsbased simulation results to the experimental data that consisted of the concentrations of 1,4-dioxane and the considered bacterial taxa.The estimated kinetic constants were evaluated by comparing the simulation results with experimental results from another set of microcosm tests.The evaluation was quantified by the sum of squared relative residual,which was four orders of magnitude lower for the improved method than the conventional method.By further dividing the considered bacterial taxa into oligotrophs and copiotrophs,the sum of squared relative residual further decreased.