Biotreatment of incinerated bottom ash and biocementation of sand blocks using soybean urease

Because of the high cost of cultivating urease-producing bacteria(UPB),this paper proposes soybean-urease-induced carbonate precipitation(SUICP)as a novel biocement for treatment of nickel contaminants and cementation of sandy soil.We found the optimal soaking time and soybean-powder content to be 30 min and 130 g/L,respectively,based on a standard of 5 U of urease activity.The most efficient removal of nickel ions is obtained with an ideal mass ratio of urea to nickel ions to soybean-powder filtrate(SPF)of 1:2.4:20.The removal efficiency of nickel ions can reach 89.42%when treating 1 L of nickel-ion solution(1200 mg/L with the optimal mass ratio).In incinerated bottom ash(IBA),the removal efficiency of nickel ions is 99.33%with the optimal mass ratio.In biocemented sandy soil,the average unconfined compressive strength(UCS)of sand blocks cemented with soybean urease-based biocement can reach 118.89 kPa when the cementation level is 3.Currently,the average content of CaCO_(3)in sand blocks is 2.52%.As a result,the SUICP process can be applied to remove heavy metal ions in wastewater or solid waste and improve the mechanical properties of soft soil foundations.

Biomineralization and mineralization using microfluidics:A comparison study

Biomineralization through microbial process has attracted great attention in the field of geotechnical engineering due to its ability to bind granular materials,clog pores,and seal fractures.Although minerals formed by biomineralization are generally the same as that by mineralization,their mechanical behaviors show a significant discrepancy.This study aims to figure out the differences between biomineralization and mineralization processes by visualizing and tracking the formation of minerals using microfluidics.Both biomineralization and mineralization processes occurred in the Y-shaped sandcontaining microchip that mimics the underground sand layers.Images from different areas in the reaction microchannel of microchips were captured to directly compare the distribution of minerals.Crystal size and numbers from different reaction times were measured to quantify the differences between biomineralization and mineralization processes in terms of crystal kinetics.Results showed that the crystals were precipitated in a faster and more uncontrollable manner in the mineralization process than that in the biomineralization process,given that those two processes presented similar precipitation stages.In addition,a more heterogeneous distribution of crystals was observed during the biomineralization process.The precipitation behaviors were further explained by the classical nucleation crystal growth theory.The present microfluidic tests could advance the understanding of biomineralization and provide new insight into the optimization of biocementation technology.

Application of microbially induced carbonate precipitation to form biocemented artificial sandstone

It is difficult to collect and characterise well-preserved samples of weakly-cemented granular rocks as conventional sampling techniques often result in destruction of the cementation.An alternative approach is to prepare synthetic geomaterials to match required specifications.This paper introduces microbially induced carbonate precipitation(MICP)as a method to reliably deliver artificiallycemented specimens with customised properties,closely resembling those of soft carbonate sandstones.The specimens are generated from materials with two highly different particle size distributions(PSDs)to access a range of achievable combinations of strengths and porosities.The MICP parameters are kept constant across all samples to obtain similar calcium carbonate characteristics(size of individual crystals,type,etc.),while injected volume is varied to achieve different cementation levels.Although uniform cementation of very coarse sands has been considered very difficult to achieve,the results show that both the fine and coarse sand specimens present high degrees of uniformity and a good degree of repeatability.The unconfined compressive strengths(UCSs)(less than 3000 kPa)and porosities(0.25e0.4)of the artificial specimens fall in the same range of values reported for natural rocks.The strength gainwas greater in the fine sand than that in the coarse sand,as the void size in the latter was significantly larger compared to the calcium carbonate crystals’size,resulting in precipitation on less effective locations,away from contacts between particles.The strengths and porosities obtained for the two sands in this work fall within ranges reported in the literature for natural soft rocks,demonstrating theMICP technique is able to achieve realistic properties and may be used to produce a full range of properties by varying the grain sizes,and possibly the width of PSD.

A critical review of microbially induced carbonate precipitation for soil stabilization:The global experiences and future prospective

Microbially induced carbonate precipitation(MICP)is a new technology having the potential to induce soil stabilization and provide a green and sustainable comprehensive solution to some geotechnical engineering problems in the environment.The present article is dedicated to present a critical review of this technology and discuss its mechanisms of action and the key factors influencing its performance.The global experiences and national participation from Egypt are demonstrated,in addition to attempts for real life applications.This review provides an insight into the practical steps taken to mitigate some of the current limitations of MICP application and the identified gaps in analogous studies.It was concluded that integrating MICP with existing technologies would favor both engineering needs and market requirements.In addition,providing effective solutions to MICP limitations would highlight this technology as an eco-friendly and cost-effective option to several engineering obstacles.Finally,recommendations focused on encouraging global collaboration for knowledge transfer about this technology among different countries,as well as positive financial support from industrial entities to aid in the progress of scientific research and achieving large-scale applications in the near future,are provided.

Recent development in biogeotechnology and its engineering applications

Microbial geotechnology or biogeotechnology is a new branch of geotechnical engineering.It involves the use of microbiology for traditional geotechnical applications.Many new innovative soil improvement methods have been developed in recent years based on this approach.A proper understanding of the various approaches and the performances of different methods can help researchers and engineers to develop the most appropriate geotechnical solutions.At present,most of the methods can be categorized into three major types,biocementation,bioclogging,and biogas desaturation.Similarities and differences of different approaches and their potential applications are reviewed.Factors affecting the different processes are also discussed.Examples of up-scaled model tests and pilot trials are presented to show the emerging applications.The challenges and problems of biogeotechnology are also discussed.