Research progress on enhancing the performance of autotrophic nitrogen removal systems using microbial immobilization technology

The autotrophic nitrogen removal process has great potential to be applied to the biological removal of nitrogen from wastewater, but its application is hindered by its unstable operation under adverse environmental conditions, such as those presented by low temperatures, high organic matter concentrations, or the presence of toxic substances. Granules and microbial entrapment technology can effectively retain and enrich microbial assemblages in reactors to improve operating efficiency and reactor stability. The carriers can also protect the reactor's internal microorganisms from interference from the external environment. This article critically reviews the existing literature on autotrophic nitrogen removal systems using immobilization technology. We focus our discussion on the natural aggregation process (granulation) and entrapment technology. The selection of carrier materials and entrapment methods are identified and described in detail and the mechanisms through which entrapment technology protects microorganisms are analyzed. This review will provide a better understanding of the mechanisms through which immobilization operates and the prospects for immobilization technology to be applied in autotrophic nitrogen removal systems.

Biohythane production via single-stage anaerobic fermentation using entrapped hydrogenic and methanogenic bacteria

This study demonstrates the continuous biohythane production in a single-stage anaerobic digester using a biomass mixture of separately entrapped hydrogenic and methanogenic bacteria (H₂- and CH₄-producing bacteria, respectively). The entrapped hydrogenic/methanogenic bacteria biomass ratios of 1/4, 2/3, 3/2 and 4/1 were tested and shown to have a great effect on the single-stage biohythane production performance. At steady-states, the cultivations had biohythane production rates in the range of 381-480 mL/L-d, with H₂ content in biohythane (HCH) varying from 1% to 75% (v/v) and chemical oxygen demand removal efficiencies (TCOD_re) of 57.6-81.9%. Biomass ratio 2/3 (weight ratio 1/1.5) resulted in peak biohythane production with H₂ and CH₄ production rates being 64.6 and 395 mL/L-d, respectively, HCH 15% and TCOD_re 74.4%. The novelty of this work is to show the potential of producing biohythane from an innovative single-stage dark fermentation system using entrapped hydrogenic and methanogenic bacteria.

Bottom-up engineering of cell-laden hydrogel microfibrous patch for guided tissue regeneration

The development of three-dimensional (3D) fibrous networks as platforms for tissue engineering applications has been attracting considerable attention. Opportunely arranged microscaled fibers offer an appealing biomimetic 3D architecture, with an open porous structure and a high surface-to-volume ratio. The present work describes the development of modified-alginate hydrogel microfibers for cell entrapment, using a purpose-designed flow circuit. For microfibers biofabrication, cells were suspended in gel-precursor alginate solution and injected in a closed-loop circuit with circulating cross-linking solution. The flow promoted stretching and solidification of continuous cell-loaded micro-scaled fibers that were collected in a strainer, assembling into a microfibrous patch. The process was optimized to allow obtaining a self-standing cohesive structure. After characterization of the microfibrous patch, the behavior of embedded human mesenchymal stem cells (hMSCs) was evaluated. Microfibers of oxidized alginate modified with integrin-binding ligands provided a suitable 3D cellular microenvironment, supporting hMSCs survival and stimulating the production of endogenous extracellular matrix proteins, such as fibronectin and collagen Type I. Collectively, these features make the proposed microfibrous structures stand out as promising 3D scaffolds for regenerative medicine.

Mitigation of bactericidal effect of carbon nanotubes by cell entrapment

This study investigated the effects of the alginate and polyvinyl alcohol (PVA) entrapment on the viability of Escherichia coli cells exposed to single wall carbon nanotubes (SWCNTs) with a diameter of 1-2nm. Viability was examined using a galactosidase enzyme assay, LIVE/DEAD BacLight assay, and total ribonucleic acid quantity. Variables studied included SWCNT concentration (5, 10, 20, 50, 100, 200, 500, and 1000μg/ml), SWCNT length (0.5-2μm for short SWCNTs and 5-30μm for long SWCNTs), and initial bacterial concentration (6.5 log10 CFU and 9 log10 CFU per test). Results showed that both alginate and PVA entrapments mitigate the bactericidal effect of SWCNTs. At the highest SWCNT concentration tested (1000μg/ml), the viability of the cells relative to controls (systems with only E. coli, no SWCNTs), was 0-60% for free cells and 60-90% for alginate and PVA entrapped cells. The bactericidal effect depended on SWCNT type and concentration, and bacterial concentration. In general, long SWCNTs (5-30μm) caused significantly greater reductions in the viability of entrapped cells than the short SWCNTs except for the two highest SWCNT concentrations studied, 500 and 1000μg/ml. Microscopy showed that the entrapment matrices prevented SWCNTs from entering the beads. This study shows that bacterial entrapment is effective at limiting the bactericidal effect of SWCNTs.

Characterization of a bioactive fiber scaffold with entrapped HUVECs in coaxial electrospun core-shell fiber

Human umbilical vein endothelial cells (HUVECs) were successfully entrapped in polyethylene oxide (PEO) core /polycaprolactone (PCL) shell electrospun fibers thus creating a "bioactive fiber." The viability and release of biomolecules from the entrapped cells in the bioactive fibers were characterized. A key modification to the core solution was the inclusion of 50% fetal bovine serum (FBS), which improved cell viability substantially. The fluorescein diacetate (FDA) staining revealed that the entrapped cells were intact and viable immediately after the electrospinning process. A long-term cell viability assay using AlamarBlue® showed that cells were viable for over two weeks. Secreted Interleukin-8 (IL-8) was monitored as a candidate released protein, which can also act as an indicator of HUVEC stress. These results demonstrated that HUVECs could be entrapped within the electrospun scaffold with the potential of controllable cell deposition and the creation of a bioactive fibrous scaffold with extended functionality.