Summary
Microbial management in anaerobic digestion is mainly focused on physically present and metabolically active species. Because of its complexity and operation near the thermodynamic ...equilibria, it is equally important to address functional regulation, based on spatial organisation and interspecies communication. Further establishment of the knowledge on microbial communication in anaerobic digestion through quorum sensing and nanowires is needed. Methods to detect centres of concentrated activity, related to the presence of highly active and well‐connected species that take a central role in the anaerobic digestion process, have to be optimized. Bioaugmentation could serve as a crucial tool to introduce keystone species that may create or sustain such centres. Functional stability can be maintained by keeping the microbial community active. This results in a clear trade‐off between functionally active and redundant microorganisms as primary basis for microbial community organization. Finally, a microbial community based prediction strategy for advanced process control is formulated.
As the human population continues to grow, food production industries such as aquaculture will need to expand as well. In order to preserve the environment and the natural resources, this expansion ...will need to take place in a sustainable way. Biofloc technology is a technique of enhancing water quality in aquaculture through balancing carbon and nitrogen in the system. The technology has recently gained attention as a sustainable method to control water quality, with the added value of producing proteinaceous feed in situ. In this review, we will discuss the beneficial effects of the technology and identify some challenges for future research.
► Biofloc technology aims at enhancing water quality through balancing C and N. ► Heterotrophic bacteria assimilate inorganic N waste into biomass. ► The bioflocs can be used as proteinaceous feed for the cultured animals. ► We discuss advantages of biofloc technology and challenges for further research.
► The role of Methanosarcina in anaerobic digestion is underestimated. ► Methanosarcina is a very robust methanogen. ► Methanosarcina is crucial for anaerobic digestion at high organic loading rates. ...► Molecular tools, highlighting the archaeal speciation, become valuable for operational control of anaerobic digesters.
Anaerobic digestion is an important technology in the framework of renewable energy production. The anaerobic digestion system is susceptible to perturbations due to the sensitivity of the methanogens towards environmental factors. Currently, technology is evolving from conventional waste treatment, i.e. the removal of pollutants, to very intensive biogas production from concentrated wastes, in the framework of bio-energy production. In the latter configuration Methanosarcina species appear to be of crucial importance. Methanosarcina sp. are, compared to other methanogens, quite robust towards different impairments. They are reported to be tolerant to total ammonium concentrations up to 7000mgL−1, salt concentrations up to 18,000mgNa+L−1, a pH shock of 0.8–1.0 units and acetate concentrations up to 15,000mgCODL−1. The possibilities of Methanosarcina sp. as key organisms in specific types of anaerobic digestion systems are demonstrated in this review.
Domestic used water treatment systems are currently predominantly based on conventional resource inefficient treatment processes. While resource recovery is gaining momentum it lacks high value ...end-products which can be efficiently marketed. Microbial protein production offers a valid and promising alternative by upgrading low value recovered resources into high quality feed and also food. In the present study, we evaluated the potential of hydrogen-oxidizing bacteria to upgrade ammonium and carbon dioxide under autotrophic growth conditions. The enrichment of a generic microbial community and the implementation of different culture conditions (sequenced batch resp. continuous reactor) revealed surprising features. At low selection pressure (i.e. under sequenced batch culture at high solid retention time), a very diverse microbiome with an important presence of predatory Bdellovibrio spp. was observed. The microbial culture which evolved under high rate selection pressure (i.e. dilution rate D = 0.1 h−1) under continuous reactor conditions was dominated by Sulfuricurvum spp. and a highly stable and efficient process in terms of N and C uptake, biomass yield and volumetric productivity was attained. Under continuous culture conditions the maximum yield obtained was 0.29 g cell dry weight per gram chemical oxygen demand equivalent of hydrogen, whereas the maximum volumetric loading rate peaked 0.41 g cell dry weight per litre per hour at a protein content of 71%. Finally, the microbial protein produced was of high nutritive quality in terms of essential amino acids content and can be a suitable substitute for conventional feed sources such as fishmeal or soybean meal.
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•Sequenced batch reactor operations selected a highly diverse culture with low biological performances.•High rate continuous reactor operations attained a culture dominated at 97% by Sulfuricurvum spp.•The Sulfuricurvum spp. dominated culture achieved long term stable biological performances.•Ammonium and carbon dioxide were biologically converted into high-quality microbial protein.
► Silica gel and polyurethane were used to immobilize and protect bacteria. ► Bacteria can precipitate CaCO
3 after being immobilized. ► Bacteria have a higher activity in silica gel than in ...polyurethane. ► Bacteria can precipitate CaCO
3 in a mimic self-healing process. ► More self-healing efficiency were observed in the cracked specimens treated by polyurethane immobilized bacteria.
Cracks in concrete are the main reason for a decreased service life of concrete structures. It is therefore more advisable and economical to restrict the development of early age small cracks the moment they appear, than to repair them after they have developed to large cracks. A promising way is to pre-add healing agents to the concrete to heal early age cracks when they appear, i.e. the so-called self-healing approach. In addition to the more commonly studied polymeric healing materials, bacterial CaCO
3 precipitation also has the potential to be used for self-healing. It is more compatible with the concrete matrix and it is environment friendly. However, bacterial activity decreases a lot in the high pH (>12) environment inside concrete. In this research, the possibility to use silica gel or polyurethane as the carrier for protecting the bacteria was investigated. Experimental results show that silica gel immobilized bacteria exhibited a higher activity than polyurethane immobilized bacteria, and hence, more CaCO
3 precipitated in silica gel (25% by mass) than in polyurethane (11% by mass) based on thermogravimetric analysis. However, cracked mortar specimens healed by polyurethane immobilized bacteria had a higher strength regain (60%) and lower water permeability coefficient (10
−10–10
−11
m/s), compared with specimens healed by silica gel immobilized bacteria which showed a strength regain of only 5% and a water permeability coefficient of 10
−7–10
−9
m/s. The results indicated that polyurethane has more potential to be used as a bacterial carrier for self-healing of concrete cracks.
Propionate is a major microbial fermentation metabolite in the human gut with putative health effects that extend beyond the gut epithelium. Propionate is thought to lower lipogenesis, serum ...cholesterol levels, and carcinogenesis in other tissues. Steering microbial propionate production through diet could therefore be a potent strategy to increase health effects from microbial carbohydrate fermentation. The present review first discusses the two main propionate‐production pathways and provides an extended gene‐based list of microorganisms with the potential to produce propionate. Second, it evaluates the promising potential of arabinoxylan, polydextrose, and L‐rhamnose to act as substrates to increase microbial propionate. Third, given the complexity of the gut microbiota, propionate production is approached from a microbial‐ecological perspective that includes interaction processes such as cross‐feeding mechanisms. Finally, it introduces the development of functional gene‐based analytical tools to detect and characterize propionate‐producing microorganisms in a complex community. The information in this review may be helpful for designing functional food strategies that aim to promote propionate‐associated health benefits.
Phosphorus (P) is an essential element for all life on earth. However, natural P resources (phosphate rock) are depleting. The authors describe the current situation and a forecast for future ...phosphate production and reserves. The current depletion of phosphate reserves and the increasingly stringent discharge regulations have led to the development of various P-recovery techniques from wastewater. Existing full-scale P-recovery techniques from the liquid phase, sludge phase, and sludge ash are reviewed. Although the full-scale P-recovery techniques have been shown to be technologically feasible, the economical feasibility, legislation and national policies are the major reasons why these techniques are not yet operational worldwide.
Resources in used water are at present mainly destroyed rather than reused. Recovered nutrients can serve as raw material for the sustainable production of high value bio-products. The concept of ...using hydrogen and oxygen, produced by green or off-peak energy by electrolysis, as well as the unique capability of autotrophic hydrogen oxidizing bacteria to upgrade nitrogen and minerals into valuable microbial biomass, is proposed. Both axenic and mixed microbial cultures can thus be of value to implement re-synthesis of recovered nutrients in biomolecules. This process can become a major line in the sustainable “water factory” of the future.
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•Mini-review of hydrogen-oxidizing bacteria and their potential applications.•The feasibility of microbial protein and biopolymers production is analysed.•Nitrogen removal and recovery from wastewater is discussed.•A H2-based biorefinery for nutrients upgrade and CO2 capture is proposed.
Use of bacteria to repair cracks in concrete Van Tittelboom, Kim; De Belie, Nele; De Muynck, Willem ...
Cement and concrete research,
2010, 2010-01-00, 20100101, Letnik:
40, Številka:
1
Journal Article
Recenzirano
Odprti dostop
As synthetic polymers, currently used for concrete repair, may be harmful to the environment, the use of a biological repair technique is investigated in this study. Ureolytic bacteria such as
...Bacillus sphaericus are able to precipitate CaCO
3 in their micro-environment by conversion of urea into ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of carbonate as calcium carbonate in a calcium rich environment. These precipitated crystals can thus fill the cracks. The crack healing potential of bacteria and traditional repair techniques are compared in this research by means of water permeability tests, ultrasound transmission measurements and visual examination. Thermogravimetric analysis showed that bacteria were able to precipitate CaCO
3 crystals inside the cracks. It was seen that pure bacteria cultures were not able to bridge the cracks. However, when bacteria were protected in silica gel, cracks were filled completely.
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