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•Membrane bioreactors for chemical production is of growing interest.•Integrating membranes with bioprocesses can enhance overall productivity.•Membranes are promising for cell ...recycling, substrate delivery and product removal.•Further studies into membrane-bioreactoer challenges such as scale-up are required.
The potential of membrane bioreactors to produce value-added products such as biofuels, biopolymers, proteins, organic acids and lipids at high productivities is emerging. Despite the promising results at laboratory scale, industrial deployment of this technology is hindered due to challenges associated with scale-up. This review aims to address these challenges and create a framework to encourage further research directed towards industrial application of membrane bioreactors to produce value-added products. This review describes the current state-of-the art in such bioreactor systems by exploiting membranes to increase the mass transfer rate of the limiting substrates, reach high cell concentrations and separate the inhibitory substances that may inhibit the bioconversion reaction. It also covers the current trends in commercialization, challenges linked with membrane usage, such as high costs and membrane fouling, and proposes possible future directions for the wider application of membrane bioreactors.
Comparisons between the physiological properties of Pseudomonas fluorescens biofilm cells grown in a tubular biofilm reactor and planktonic cells grown in a chemostat were performed. Fluoroacetate ...was the sole carbon source for all experiments. The performance of cells was assessed using cell cycle kinetics and by determining specific fluoroacetate utilization rates. Cell cycle kinetics were studied by flow cytometry in conjunction with the fluorescent stain propidium iodide. Determination of the DNA content of planktonic and biofilm cultures showed little difference between the two modes of growth. Cultures with comparable specific glycolate utilization rates had similar percentages of cells in the B phase of the cell cycle, indicating similar growth rates. Specific fluoroacetate utilization rates showed the performance of planktonic cells to be superior to that of biofilm cells, with more fluoroacetate utilized per cell at similar specific fluoroacetate loading rates. A consequence of this decreased biofilm performance was the accumulation of glycolate in the effluent of biofilm cultures. This accumulation of glycolate was not observed in the effluent of planktonic cultures. Spatial stratification of oxygen within the biofilm was identified as a possible explanation for the overflow metabolism of glycolate and the decreased performance of the biofilm cells.
Solid waste management has become a global problem as the rate at which waste is generated exceeds population growth. Although it is not the most environment friendly option due to the inevitable ...generation of greenhouse gases and leachate, landfilling is globally still the most commonly applied waste disposal method. Leachate, an extremely polluted wastewater, threatens ground and surface waters and requires adequate treatment before discharge. Co-treatment of leachate in municipal wastewater treatment plants (WWTPs) is a commonly practiced method for leachate management. However, changing characteristics of leachate and more stringent discharge limits in WWTPs have led to questions about sustainability of co-treatment. On the other hand, several new technologies and processes, which can be adopted in conventional WWTPs, are now being deployed. For instance, floccular activated sludge has evolved to granule processes, shortcut denitrification processes can potentially lower the oxygen and carbon requirement for nitrogen removal, membrane processes can provide higher effluent quality, more advanced aeration methods enhance energy efficiency, instrumentation, and control and automation capabilities have increased. This is the first dedicated review that compiles and critically evaluates studies concerning co-treatment of leachate and municipal wastewater. Moreover, potential concerns, challenges and opportunities for co-treatment are discussed in the context of new developments in wastewater treatment technology.
Particle-tracking microrheology is an
technique that allows quantification of biofilm material properties. It overcomes the limitations of alternative techniques such as bulk rheology or force ...spectroscopy by providing data on region specific material properties at any required biofilm location and can be combined with confocal microscopy and associated structural analysis. This article describes single particle tracking microrheology combined with confocal laser scanning microscopy to resolve the biofilm structure in 3 dimensions and calculate the creep compliances locally. Samples were analysed from
biofilms that were cultivated over two timescales (24 h and 48 h) and alternate ionic conditions (with and without calcium chloride supplementation). The region-based creep compliance analysis showed that the creep compliance of biofilm void zones is the primary contributor to biofilm mechanical properties, contributing to the overall viscoelastic character.
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•A facile anti-biofouling technology for membranes was developed based on an anti-biofouling layer that can be regenerated.•Anti-biofouling nanomaterials were combined with a biofilm ...degrading enzyme with excellent & durable anti-fouling capacity.•The anti-fouling membranes retain the same permeance as the pristine membranes.
Biofouling of membranes is an unresolved problem in the water industry. Numerous anti-biofouling membrane technologies have been proposed but the duration of their anti-fouling properties is short relative to the required lifetime of the membrane.
The present work investigated a facile renewable anti-biofouling layer strategy whereby smart enzymatic nanomaterials are self-assembled onto a commercial membrane surface, creating a pH-triggered releasable and regenerable anti-biofouling system. The Proteinase-K-functionalized-PEGylated-silica (SPK) nanoparticles were characterized both chemically and biologically. These smart enzymatic particles demonstrated an excellent capability of against Pseudomonas fluorescens biofilms, and their activity persisted for at least 45 days in synthetic wastewater. Surface morphology and analysis of chemical compositions showed that these smart nanoparticles generated an anti-biofouling layer on the cellulose-based membrane surface through a submersion method, attributed to the strong noncovalent affinity-interactions between the particles and membrane. The SPK anti-biofouling layer stably attached to the membrane surfaces in synthetic wastewater (pH 7.4), whilst having the capacity to be released for regeneration in a pH 10 solution. Regeneration was accomplished by simple reloading of fresh particles on the membrane. Filtration tests revealed that the SPK anti-biofouling layer negligibly affected on membrane permeance while effectively mitigated membrane biofouling. Besides significant improvement in filtration fluxes, the SPK assembled membrane efficiently reduced the irreversible fouling and bacterial coverages on the membrane surface.
Enhancement of fluorescence through the application of plasmonic metal nanostructures has gained substantial research attention due to the widespread use of fluorescence-based measurements and ...devices. Using a microfabricated plasmonic silver nanoparticle–organic semiconductor platform, we show experimentally the enhancement of fluorescence intensity achieved through electro-optical synergy. Fluorophores located sufficiently near silver nanoparticles are combined with diphenylalanine nanotubes (FFNTs) and subjected to a DC electric field. It is proposed that the enhancement of the fluorescence signal arises from the application of the electric field along the length of the FFNTs, which stimulates the pairing of low-energy electrons in the FFNTs with the silver nanoparticles, enabling charge transport across the metal–semiconductor template that enhances the electromagnetic field of the plasmonic nanoparticles. Many-body perturbation theory calculations indicate that, furthermore, the charging of silver may enhance its plasmonic performance intrinsically at particular wavelengths, through band-structure effects. These studies demonstrate for the first time that field-activated plasmonic hybrid platforms can improve fluorescence-based detection beyond using plasmonic nanoparticles alone. In order to widen the use of this hybrid platform, we have applied it to enhance fluorescence from bovine serum albumin and Pseudomonas fluorescens. Significant enhancement in fluorescence intensity was observed from both. The results obtained can provide a reference to be used in the development of biochemical sensors based on surface-enhanced fluorescence.
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•Industrial scale PHB production model using various carbon sources was developed.•Techno-economic analysis was used to assess the effect of raw materials on cost.•Cheapest PHB unit ...production cost was 3.63 $/kg when fructose was consumed.•Sensitivity analysis show that the price of H2 effects PHB price the most.•Using CO2 and formate for producing PHB can be feasible in the bioplastic market.
Polyhydroxybutyrate (PHB) is a biodegradable polymer that has potential to replace petroleum-derived plastics. However, the commercialisation of PHB is hindered by high production costs. In this study, the material flow and economics of an industrial scale PHB production process using fructose, formic acid and carbon dioxide (CO2) as carbon sources were simulated and analysed. The lowest breakeven price of 3.64 $/kg PHB was obtained when fructose was utilized as carbon source. When formic acid and CO2 were used, the breakeven price was 10.30 and 10.24 $/kg PHB due to raw material cost, respectively. Although using formic acid and CO2 is more expensive, they meet the emerging sustainable needs for plastic production and contribute to the circular economy via CO2 fixation. This study suggests that the use of formic acid and CO2 as feedstock for PHB production has potential to become competitive in the bioplastic market with further research.
Gas-transfer membranes have been successfully deployed as efficient aeration devices in wastewater treatment. There is an increasing interest in using such membrane technology in industrial ...biotechnology. This study proposes membrane bioreactors as a novel bioreactor setup for polyhydroxybutyrate (PHB) production using Cupriavidus necator, whereby gas-transfer membranes are used for aeration. A proof-of-concept membrane bioreactor was built by combining a 50 ml centrifuge tube with hollow fiber membrane bundles. Different numbers and length of polydimethylsiloxane (PDMS) hollow fiber membranes were used to create membrane bundles with varying specific surface areas for oxygen transfer. In batch mode, a maximum biomass concentration of 10.3 g/L, which corresponds to a yield of 0.67 g biomass/g substrate, was achieved with 250 m2/m3 as the specific surface area of the membranes and 40 rpm as the liquid recirculation rate. Two different fed-batch modes were investigated to induce PHB production by applying nitrogen source limitation via fill-and-draw and two-step feeding strategies. A PHB level of 22% was obtained with fill-and-draw feeding by supplying 0.25 g/L NH4Cl after initial cultivation. Results indicate that membrane bioreactors are promising for C. necator cultivation, but further research is needed to enhance the PHB productivity.
•A novel gas-transfer membrane bioreactor was developed for microbial fermentation.•Various operating parameters were tested in batch for maximizing microbial growth.•Two different fed-batch operation modes were investigated for PHB production.•Membrane bioreactors has shown promising results to cultivate Cupriavidus necator.
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