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Bioactive cement plaster: Bioengineering in action
Electron micrographs of the cross-section of magnesium phosphate cement-cylinders. (a) MPC-cylinder without bacteria. (b) Macroporous structure within the inner section of freshly prepared MPC with embedded R. ruber bacteria. (c) Macroporous structure within the inner section of MPC with embedded R. ruber after 19 batch cycles. The arrows mark assemblies of R. ruber bacteria. Credit: Soltmann et al; Adv. Eng. Mat.
For some time, it has been common to use enzymes as a biocatalyst. When the enzymes required are difficult or expensive to extract, the utilization of microorganisms such as bacteria, yeast, or fungi is an alternative.
For many applications, the living cells are immobilized within a stable matrix system. This prevents the embedded cells against culture washout and protects them from external impact like shear forces, pH, or solvents. Besides commonly used natural polymers some porous inorganic matrices have become increasingly important for immobilizing living cells.
Results of former studies have shown that bacteria can be successfully embedded within a very hard concrete matrix and remained viable for a period of four months. This encouraged the R&D organization GMBU and the company InnoTERE (both Dresden, Germany) to investigate the immobilization of microorganisms in cements. The researchers examined the viability and biocatalytic applicability of the bacteria Rhodococcus ruber and the yeast Saccharomyces cerevisiae, in particular their dependence on preparation conditions.
For their investigations, they used magnesium phosphate cement, which can be easily prepared by mixing hard-burned tribasic magnesium phosphate powder and ammonium phosphate solution. Due to the stiffness of the cement matrix bioactive MPC could be very interesting for applications in bioremediation, in biotechnology as bulk material in large columns or reactive walls, or as bioactive cement plaster within sewers.
To evaluate the applicability of MPC for the immobilization of living microorganisms the researchers determined the glucose conversion using immobilized S. cerevisiae and the phenol degradation using immobilized R. ruber.
The results of the study, “Cements with embedded living microorganisms — a new class of biocatalytic composite materials for application in bioremediation, biotechnology” (doe:10.1002/adem.201080040) revealed that the bioactive composite material exhibits good mechanical and chemical stability. The embedded cells survived the embedding within the cement matrix even though the cements showed much slower glucose and phenol consumption in comparison to non-immobilized cells.
Limitations in mass-transfer probably cause the reduced activity of the embedded cells. To overcome such limitations further examinations especially to the size and pore structure are necessary. Nevertheless, combining a cement matrix with living microorganisms very promising biocomposite materials for application in biotechnology can be fabricated.
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Video of the Week: ‘Green concrete’ composed of 70% fly ash
Researchers at Missouri University of Science and Technology believe that increasing the amount of fly ash in concrete up to 70 percent can result in excellent concrete in terms of both strength and durability. And it could prevent millions of tons of the waste product from ending up in landfills.
“Traditional specifications limit the amount of fly ash to 35 or 40 percent cement replacement,” says Jeffery Volz, assistant professor of civil, architectural and environmental engineering at Missouri S&T in a university press release. “Recent studies have shown that higher cement replacement percentages - even up to 70 percent - can result in excellent concrete in terms of both strength and durability.”
Fly ash is commonly used as a concrete additive, but increasing the amount used will cut CO2 emissions, but it also brings its own set of challenges.
“Construction workers might refuse to work with it,” Volz says. “And there’s also the issue of at what point is it not a hazardous material when used for beneficial reuse. Is it once it is added to the ready mix truck, which means it is a hazardous waste in the silo at the ready mix plant? Or is it once the concrete hardens, which means it’s a hazardous waste up to that point?”
The EPA supports adding fly ash to concrete, however the agency is considering designating fly ash as a hazardous waste. And although it has been proven that adding fly ash to concrete renders is chemically altered and unable to leach toxic material, a hazardous waste label would make it more difficult to garner wide acceptance.
Volz is working with the Missouri Department of Transportation to develop guidelines for the proper application of high-volume fly ash concrete in infrastructure components.
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Ceramic science stories we missed the first time around
Weddings, vacation, illness, travel days . . . Looking back, sometimes there have been events that caused us to miss a few good ceramic- and glass-related developments and press releases. The stories in this grab bag have only a few cobwebs on them, so check ‘em out:
Closing in on a carbon-based solar cell
Better boron nitride nanotubes may be on the way
Lasers at the cutting edge of science
Japanese company develops world’s first ultra-thin piezoelectric waterproof speaker
Murata Supplying World’s Smallest 0402*-Size 10μF 6.3V-Rated Monolithic Ceramic Capacitor
Nanospheres stretch limits of hard disk storage
and, a video from Onyx Solar: Paving the way for building integrated photovoltaics:
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Cement failures, lack of regulations coming under scrutiny in Gulf oil spill
Credit: Boston.com
The AP is reporting that there have been numerous problems and failures related to the use of cement in sealing oil wells in the Gulf of Mexico. One current theory is the the Deepwater Horizon spill also may have been caused by problems with cement.
And, apparently federal regulators never set standards about what type of cement(s) should be used:
The drillers are urged to simply follow guidelines of the American Petroleum Institute, an industry trade group.
Far more stringent federal and state standards and controls exist on cement work for roads, bridges and buildings.
[. . . ]
An AP review of federal accident and incident reports on offshore wells shows that the cementing process has been implicated at least 34 times since 1978. Many of the reports, available from the U.S. Minerals Management Service that regulates offshore wells, identify the cause simply as “poor cement job.”
[ . . . ]
Reports by MMS, a branch of the Interior Department, also provide evidence of the role bad cement work has played in accidents. One study named cementing as a factor in 18 of 39 well blowouts at Gulf rigs from 1992 to 2006. Another attributed five of nine out-of-control wells in the year 2000 to cementing problems.
[ . . . ]
Halliburton, which had the Deepwater Horizon job, mixes in nitrogen to make its slurry more elastic. The nitrogen also helps create a lightweight cement that resembles a gray foamy mousse and bonds better to the casing.
But the recipe also depends on the job, because cement must respond to varying pressures and temperatures. Cement contractors work closely with oil and gas companies on the formulas for individual wells. The oil and gas companies have the final say on what is used.
ACerS Cements Division is partnering for an upcoming meeting July 11-13 with the Center for Advanced Cement-Based Materials. As one of the big cements research centers in the U.S., it’s good to see ACBM and other colleagues weigh in on this:
In the wake of the accident, some experts support mandatory uniform cement standards for underwater wells. “When you change the composition, it should meet a certain standard. Such standards exist for the building construction industry,” said Surendra Shah, Northwestern University engineering professor and director of the Center for Advanced Cement-Based Materials at Evanston, Ill.
[ . . . ]
Many construction projects use concrete hardened with sand and gravel aggregate, but cement is the glue that holds it together. On federal projects, “just about everything is regulated, from the thickness of the concrete, to the strength of the concrete, to the type of aggregate that’s used,” said Brian Turmail, spokesman for the Associated General Contractors of America.
I suspect this topic may be hashed over at the ACerS Cements Division/ACBM meeting.
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