Fabrication of poly(vinyl alcohol) hydrogel beads crosslinked using sodium sulfate for microorganism immobilization

Azo dye anaerobic treatment in anaerobic reactors coupled with PVA/Fe/Starch gel bead

A novel bio-carrier, PVA/Fe/starch gel bead, was fabricated and developed to enhance the anaerobic treatment performance of synthetic azo dye-containing wastewater. PVA-gel beads with 5 % magnetite and 0.5 % starch were optimal for physical strength and treatment performance. A pair of 2 L-up-flow anaerobic sludge blankets (UASB), one with the bead (UB) and another without (U) as a controller, operated continuously at 30 °C and an HRT of 11-24 h for 302 days. UB showed better performance than U in most phases, especially with influent dye of 200 mg·L-1, suggesting a greater tolerance to dye toxicity of UB than U. Microbial analysis revealed that the PVA/Fe/starch gel beads successfully captured the dye degrader Clostridium. Diversity indices indicated that PVA/Fe/Starch gel beads effectively support microbial diversity and resilience under varying dye concentrations. Overall, these findings demonstrate the potential of PVA/Fe/Starch gel beads to improve the stability and efficiency of the dye treatment system.

Optimum quorum quenching bacteria concentration in the better-quality cell entrapping beads to control biofouling in membrane bioreactor

Quorum quenching (QQ) by cell entrapping beads (CEBs) is known to inhibit biofouling by its biological and physical cleaning effect. Although there are better QQ media reported, due to the ease of fabrication of QQ-CEBs, this study focused on improving the quality of CEBs by comparing two distinct bead-making methods - polyvinyl alcohol-alginate (PVA-alginate) and phase inversion - and on finding the optimum concentration of QQ bacteria in the CEBs. The evaluation of PVA-alginate bead showed better uniformity, and higher mechanical and chemical strength in comparison with the phase inversion bead. Through the operations of two control membrane bioreactors (MBRs) (no bead, vacant bead) and four QQ-MBRs with different Rhodococcus sp. BH4 concentrations (2.5-15 mg cell ml-1) in PVA-alginate CEBs, the maximum QQ effect was observed by 5 mg ml-1 BH4 concentration beads. This implies that an optimum cell concentration of QQ-CEBs is crucial to economically improve MBR performance using QQ.

Microbe-cellulose hydrogels as a model system for particulate carbon degradation in soil aggregates

Particulate carbon (C) degradation in soils is a critical process in the global C cycle governing greenhouse gas fluxes and C storage. Millimeter-scale soil aggregates impose strong controls on particulate C degradation by inducing chemical gradients of e.g. oxygen, as well as limiting microbial mobility in pore structures. To date, experimental models of soil aggregates have incorporated porosity and chemical gradients but not particulate C. Here, we demonstrate a proof-of-concept encapsulating microbial cells and particulate C substrates in hydrogel matrices as a novel experimental model for soil aggregates. Ruminiclostridium cellulolyticum was co-encapsulated with cellulose in millimeter-scale polyethyleneglycol-dimethacrylate (PEGDMA) hydrogel beads. Microbial activity was delayed in hydrogel-encapsulated conditions, with cellulose degradation and fermentation activity being observed after 13 days of incubation. Unexpectedly, hydrogel encapsulation shifted product formation of R. cellulolyticum from an ethanol-lactate-acetate mixture to an acetate-dominated product profile. Fluorescence microscopy enabled simultaneous visualization of the PEGDMA matrix, cellulose particles, and individual cells in the matrix, demonstrating growth on cellulose particles during incubation. Together, these microbe-cellulose-PEGDMA hydrogels present a novel, reproducible experimental soil surrogate to connect single cells to process outcomes at the scale of soil aggregates and ecosystems.

The Effect of Gelatin Source on the Synthesis of Gelatin-Methacryloyl and the Production of Hydrogel Microparticles

Gelatin methacryloyl (GelMA) is widely used for the formulation of hydrogels in diverse biotechnological applications. After the derivatization of raw gelatin, the degree of functionalization (DoF) is an attribute of particular interest as the functional residues are necessary for crosslinking. Despite progress in the optimization of the process found in the literature, a comparison of the effect of raw gelatin on the functionalization is challenging as various approaches are employed. In this work, the modification of gelatin was performed at room temperature (RT), and eight different gelatin products were employed. The DoF proved to be affected by the bloom strength and by the species of gelatin at an equal reactant ratio. Furthermore, batch-to-batch variability of the same gelatin source had an effect on the produced GelMA. Moreover, the elasticity of GelMA hydrogels depended on the DoF of the protein as well as on bloom strength and source of the raw material. Additionally, GelMA solutions were used for the microfluidic production of droplets and subsequent crosslinking to hydrogel. This process was developed as a single pipeline at RT using protein concentrations up to 20% (w/v). Droplet size was controlled by the ratio of the continuous to dispersed phase. The swelling behavior of hydrogel particles depended on the GelMA concentration.

Denitrification effect and strengthening mechanism of SAD/A system at low temperature by gel-immobilization technology

Sulfur autotrophic denitrification coupled anaerobic ammonia oxidation (SAD/A) has several advantages over other denitrification processes; for example, it does not consume the organic carbon source, has low operation costs, and produces less excess sludge; however, it has certain disadvantages as well, such as a long start-up time, easy loss of bacteria, and low microbial activity at low temperature. The use of microbial immobilization technology to embed functional bacteria provides a feasible method of resolving the above problems. In this study polyvinyl alcohol‑sodium alginate was used to prepare a composite carrier for fixing anaerobic ammonia oxidizing bacteria (AAOB) and sulfur oxidizing bacteria (SOB), and the structure and morphology of the encapsulated bodies were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Subsequently, the nitrogen removal performance of the immobilized microbial carriers in the gradient cooling process (30 °C to 10 °C) was determined, and the corresponding mechanism was discussed. The results showed that the nitrate-removal efficiencies observed with granular sludge and gel embedding were at 10 °C 21.44 % and 14.31 % lower, than those at 30 °C, respectively, whereas the ammonia-removal efficiency decreased by up to approximately three-fold. The main mechanism was the 'insulation' provided by the external gel composed of PVA and SA for the internal sludge and subsequent improvement of its low temperature resistance, while protecting AAOB and SOB from oxygen inhibition, which is conducive to enriching denitrifying bacteria. In addition, the gel does not change the internal sludge species, it can shift the dominance of specific microorganisms and improve the removal efficiency of nitrogen. In summary, the immobilization of AAOB and SOB by the gel can achieve effectively mitigate nitrogen pollution in low temperature environments, thus indicating that the SAD/A process has broad engineering application prospects.

Poly(vinyl alcohol)/modified porous starch gel beads for microbial preservation and reactivation: preparation, characterization and its wastewater treatment performance

Poly(vinyl alcohol) (PVA)/modified porous starch (MPS) gel beads were prepared through in situ chemical cross-linking by incorporating with MPS, which was obtained by modifying porous starch (PS) with polyethyleneimine (PEI) and glutaraldehyde (GA). Addition of MPS could improve the storage modulus and the effective crosslinking density (ve) of the gel beads, and the mechanical properties were enhanced. The PVA-MPS gel beads were preserved as immobilized microbial carriers for 40 d and reactivated in wastewater. Scanning electron microscope (SEM) observations showed that the beads were highly porous and conducive for microorganism adhesion. The PVA-MPS gel beads were able to remove 97% of ammonia nitrogen and 80% of chemical oxygen demand (COD) after reactivation under all four preservation conditions. The abundance of Hydrogenophaga as denitrifying bacteria on PVA-MPS gel beads increased, with abundance of 8.44%, 5.55%, 8.90% and 9.48%, respectively. It proved that the carrier provided a partial hypoxic environment for microorganisms.

Continuous Phosphate Removal and Recovery Using a Calcium Silicate Hydrate Composite Monolithic Cryogel Column

Toward the development of a practical and green approach for removing phosphate from water, a monolithic cryogel based on starch and calcium silicate hydrate (Cry-CSH) was employed as a phosphate adsorbent in a continuous flow system for the first time. The influence of flow rate, initial phosphate concentration, and adsorbent height on the adsorption efficiency was investigated. As the rate of flow and the initial concentration of phosphate increased, the total quantity of adsorbed phosphate dropped; however, the performance of the column was greatly enhanced by an increase in adsorbent height. The experimental data fit the Adams-Bohart model better than the Thomas and Yoon-Nelson models at the beginning of the adsorption process. To evaluate its applicability, the continuous flow system based on the monolithic Cry-CSH column was applied for the removal of phosphate from the discharge effluent of the Patong Municipality Wastewater Treatment Plant (Phuket, Thailand), achieving an excellent total adsorption of 94.61%.

Biocompatible Silica-Polyethylene Glycol-Based Composites for Immobilization of Microbial Cells by Sol-Gel Synthesis

Biocatalysts based on the methylotrophic yeast Ogataea polymorpha VKM Y-2559 immobilized in polymer-based nanocomposites for the treatment of methanol-containing wastewater were developed. The organosilica composites with different matrix-to-filler ratios derived from TEOS/MTES in the presence of PEG (SP_EG-composite) and from silicon-polyethylene glycol (STP_EG-composite) differ in the structure of the silicate phase and its distribution in the composite matrix. Methods of fluorescent and scanning microscopy first confirmed the formation of an organosilica shell around living yeast cells during sol-gel bio-STP_EG-composite synthesis. Biosensors based on the yeast cells immobilized in STP_EG- and SP_EG-composites are characterized by effective operation: the coefficient of sensitivity is 0.85 ± 0.07 mgO₂ × min^-1 × mmol^-1 and 0.87 ± 0.05 mgO₂ × min^-1 × mmol^-1, and the long-term stability is 10 and 15 days, respectively. The encapsulated microbial cells are protected from UV radiation and the toxic action of heavy metal ions. Biofilters based on the developed biocatalysts are characterized by high effectiveness in the utilization of methanol-rich wastewater-their oxidative power reached 900 gO₂/(m³ × cycle), and their purification degree was up to 60%.

Tailoring polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads by controlling crosslinking pH and time

Hydrogel-encapsulated catalysts are an attractive tool for low-cost intensification of (bio)-processes. Polyvinyl alcohol-sodium alginate hydrogels crosslinked with boric acid and post-cured with sulfate (PVA-SA-BS) have been applied in bioproduction and water treatment processes, but the low pH required for crosslinking may negatively affect biocatalyst functionality. Here, we investigate how crosslinking pH (3, 4, and 5) and time (1, 2, and 8 h) affect the physicochemical, elastic, and process properties of PVA-SA-BS beads. Overall, bead properties were most affected by crosslinking pH. Beads produced at pH 3 and 4 were smaller and contained larger internal cavities, while optical coherence tomography suggested polymer cross-linking density was higher. Optical coherence elastography revealed PVA-SA-BS beads produced at pH 3 and 4 were stiffer than pH 5 beads. Dextran Blue release showed that pH 3-produced beads enabled higher diffusion rates and were more porous. Last, over a 28-day incubation, pH 3 and 4 beads lost more microspheres (as cell proxies) than beads produced at pH 5, while the latter released more polymer material. Overall, this study provides a path forward to tailor PVA-SA-BS hydrogel bead properties towards a broad range of applications, such as chemical, enzymatic, and microbially catalyzed (bio)-processes.

Effect of Aeration Intensity on Performance of Lab-Scale Quorum-Quenching Membrane Bioreactor

Biofouling is one of the main drawbacks of membrane bioreactors (MBRs). Among the different methods, the quorum-quenching (QQ) technique is a novel method as it delays biofilm formation on the membrane surface through disruption of bacterial cell-to-cell communication and thus effectively mitigates membrane biofouling. QQ bacteria require a certain concentration of dissolved oxygen to show their best activities. Despite the importance of the amount of aeration, there have not been enough studies on aeration condition utilizing the separate determination of pure QQ effect and physical cleaning effect. This research aimed to find the optimum aeration intensity by separation of the two effects from QQ and physical cleaning. Three bead type conditions (no bead, vacant bead, and QQ beads) at three aeration intensities (1.5, 2.5, and 3.5 L/min representing low, medium, and high aeration intensity) were applied. From the results, no QQ effect and small QQ effect were observed at low and high aeration, while the greatest QQ effect (48.2% of 737 h improvement) was observed at medium aeration. The best performance was observed at high aeration with QQ beads having a 1536 h operational duration (303% improvement compared to the no bead condition); however, this excellent performance was attributed more to the physical cleaning effect than to the QQ effect.

Enhanced nitrate, manganese, and phenol removal by polyvinyl alcohol/sodium alginate with biochar gel beads immobilized bioreactor: Performance, mechanism, and bacterial diversity

Water pollutants, such as nitrate, heavy metals, and organics have attracted attention due to their harms to environmental and biological health. A novel polyvinyl alcohol/sodium alginate with biochar (PVA/SA@biochar) gel beads immobilized bioreactor was established to remove nitrate, manganese, and phenol. The optimum conditions for preparing gel beads were studied by response surface methodology (RSM). Notably, the removal efficiencies of nitrate, Mn(II), and phenol were 94.64, 72.74, and 93.97% at C/N of 2.0; the concentrations of Mn(II) and phenol were 20 and 1 mg L^-1, respectively. Moreover, addition of different concentrations of phenol significantly affected the components of dissolved organic matter, bacterial activity, and bioreactor performance. The biological manganese oxide (BMO) with three-dimensional petal-type structure produced during Mn(II) oxidation showed excellent adsorption capacity. The removal of phenol relied on a combination of biological action and adsorption processes. High-throughput analysis showed that Zoogloea sp. was the predominant bacterial group.

Succinic acid fermentation with immobilized Actinobacillus succinogenes using hydrolysate of carbohydrate-rich microalgal biomass

This work aimed to study the efficiency of polyvinyl-alcohol-immobilized Actinobacillus succinogenes ATCC55618 for succinic acid (SA) production. Batch fermentation (pH 7, 45% CO₂ gas at 0.04 vvm) using glucose (40 g L^-1) resulted in SA titer, 26.7 g L^-1; productivity, 3.33 g L^-1h^-1; yield, 0.621 g g^-1. Fed-batch mode with cyclic extrication of SA from the medium markedly enhanced the yield to 0.699 g g^-1 and concentration to 59.5 g L^-1. Batch fermentation using sugars derived from Chlorella vulgaris ESP-31 without yeast extract gave a SA productivity, concentration, and yield of 1.82 g L^-1h^-1, 36.1 g L^-1, and 0.720 g g^-1, respectively. Furthermore, continuous fermentation (at 6 h HRT) with microalgal sugar improved the productivity and yield to 3.53 g L^-1h^-1 and 0.62 g g^-1, respectively, which is comparable to those obtained by using glucose. This study reports the highest productivity for SA fermentation using microalgae-derived sugars.

Synergic Effect of Adsorption and Biodegradation by Microsphere Immobilizing Bacillus velezensis for Enhanced Removal Organics in Slaughter Wastewater

Bacterial cell immobilization offers considerable advantages over traditional biotreatment methods using free bacteria. Bacillus velezensis was underwented isolation and genetic identification as COD-degrading bacteria in slaughter wastewaterand immobilized on the surface of polyvinyl alcohol (PVA) microsphere with the adhesion to bio-carrier through direct physical adsorption. The removal CODMn rates of microsphere (PVA) immobilized cells were 16.99%, increased 9.38% from a 50% concentration of slaughter wastewater within 24 h at 37 °C, pH 7.0, and 120 rpm, which was about 2.2 times that of the free bacteria. A significant difference was found in two groups (p < 0.01 p value less than 0.01 means statistical significance), and the COD degradation rate of the microsphere immobilized Bacillus velezensis strain was higher than the control group (PVA: control vs 20.08: 10.81), with the processing time reaching 36 h (p < 0.05). Additionally, similar results were obtained from a 20% concentration of slaughter wastewater within 24 h and 36 h. Moreover, the starch and protein digestibility of the immobilized Bacillus velezensis strain was higher than that of the free bacteria (20.1%: 42.2% vs. 17.5%: 37.2%). These findings revealed that the PVA-bacteria system was a simple, green, and inexpensive process, as well as a promising method. The research goal is aimed to synergize the effects of adsorption and biodegradation, as it can enhance organic removal by immobilized Bacillus velezensis in slaughter wastewater. Moreover, it may be possible that more potential materials can be used as biological carriers for the immobilization of bacterial cells later, which is beneficial for the recycling of resources.

Enhanced denitrification of secondary effluent using composite solid carbon source based on agricultural wastes and synthetic polymers

Solid-phase denitrification is a promising approach to enhance nitrate removal. In this work, polybutylene succinate (PBS) and peanut shell (PS) (with crosslinked polyvinyl alcohol-sodium alginate (PVA-SA) as carrier) were used to prepare a composite solid carbon source (3P) to denitrify the secondary effluent. The results showed that for carbon release performance, 3P had not only a large release of organics, like PS, but also the excellent sustainability of PBS. Among the short chain fatty acids released by PBS, PS, PVA-SA and 3P, the percentages of acetic acid were 59.42%, 72.54%, 72.29% and 92.11%, respectively. When 3P was used as external carbon source, denitrification performance could be enhanced with effluent dissolved organic carbon lower than 20 mg/L. The prepared 3P could improve denitrification, from both microbial and kinetic aspects. The relative abundance of Gammaproteobacteria increased from 39.32% to 43.58%, and the half saturation constant of the fitting Monod equation was 21.28 mg/L. The prepared 3P is an ideal carbon source for secondary effluent denitrification. Using multiple crosslinking methods to produce carrier is an effective way to show the properties of each material.

Enhanced stability and nitrogen removal efficiency of Klebsiella sp. entrapped in chitosan beads applied in the domestic sewage system

Although numerous denitrifying bacteria have been isolated and characterized, their capacity is seriously compromised by traditional inoculant addition and environmental stress in open bioreactors for wastewater treatment. In this study, a biocompatible material, chitosan, was used as a carrier to immobilize a simultaneously heterotrophic nitrifying-aerobic denitrifying bacterium Klebsiella sp., KSND, for continuous nitrogen removal from domestic wastewater in an open purification tank. The results showed that immobilization had no significant effect on cell viability and was beneficial for the reproduction and adhesion of cells. The entrapped KSND exhibited a slightly higher nitrogen removal efficiency of 90.09% than that of free KSND (87.69%). Subsequently, repeated batch cultivation experiments and analysis of the effects of organic contaminants and metal ions were performed using artificial wastewater and domestic wastewater. The findings revealed that the immobilized KSND beads presented desirable biophysical properties with good mechanical stability, cell viability, and enrichment, remarkable stability in organic contaminants and metal ions, and high efficiency nitrogen removal capacity. In conclusion, the developed immobilized denitrifying bacteria system has great potential for continuous wastewater treatment in open bioreactors.

Kinetics of a fixed bed reactor with immobilized microorganisms for the removal of organic matter and phosphorous

The biodegradation of domestic wastewater contaminants has been carried out using microorganisms immobilized in sodium alginate gel (Alg-Na). A fixed bed reactor with immobilized microorganisms was used for the treatment of domestic wastewater. A wastewater pretreatment was carried out to remove the larger particulate matter, which consisted of a reactor packed with different materials (anthracite, zeolite, and activated carbon). Later, a second reactor packed with balls with immobilized microorganisms was used to eliminate organic matter and nutrients. 2.5% w/v of Alg-Na was used as a support to immobilize the microorganisms. According to the results, a total phosphorus (TP) and chemical oxygen demand (COD) removal of 94.26% and 78.25% was obtained, respectively. In addition, the degradation rate for both organic matter and phosphorous was studied by using the kinetic model for fix bed reactor. © 2020 Water Environment Federation PRACTITIONER POINTS: Phosphorous and organic matter removal by adsorption and immobilized microorganisms. High removal efficiency of phosphorous and organic matter was found. An innovative wastewater treatment alternative is proposed. Kinetic model for fixed bed reactor is also proposed for scaling-up purposes.

Biosorption of uranium by immobilized Saccharomyces cerevisiae

A novel biosorbent was prepared and applied for the removal of uranium from aqueous solution. A new immobilization method was studied and used to embed living yeast cells of Saccharomyces cerevisiae (2% w/v) by sodium sulfate (0.5 mol/L) based on saturated boric acid-alginate calcium cross-linking method. The swelling ratio, hydraulic and chemical stability and bioactivity of immobilized microbial cells were examined. Their ultra-microstructure and property were observed by SEM, TEM and FTIR techniques. The influencing factors, such as contact time, initial uranium concentration, and initial pH were investigated. The adsorption capacity of biosorbent increased from 0.75 to 113.4 μmol/g when the equilibrium concentration of U was 0.9, and 43.9 μmol/L, respectively. U adsorption followed pseudo first-order kinetic model. SEM-EDS and TEM-EDS observation indicated that uranium was adsorbed both on the surface and the inner parts of the biosorbent. FTIR and the XPS results confirmed the role of oxygen in capturing uranium from aqueous solution. XPS analysis showed that the mixture of U (VI) and U (IV) existed on the surface of biosorbent, which evidenced that uranium was microbiologically reduced.

Application of cell entrapping beads for Quorum Quenching technique in submerged membrane bioreactor

Biofouling is unwanted accumulation of microbial population on the membrane surface which limits the use of membrane bioreactor (MBR) in the market. Disruption of the biofilm formation by Quorum Quenching (QQ) by using cell entrapping beads (CEBs) is an approach with great potential to control membrane biofouling as the beads used provide not only mitigating effect on biofilm formation, by interfering Quorum Sensing, but also physical forces to detach the biofilm from the membrane surface. This research aimed to develop QQ-CEB with locally available chemicals in Pakistan and its application to evaluate the QQ effect together with physical and chemical cleaning. Various CEBs were made of different mixtures of sodium alginate and polyvinyl alcohol (PVA) and their quality was tested considering physical and biological aspects. Rhodococcus sp. BH4 and Pseudomonas putida were entrapped in the CEBs and then introduced in MBR as one of biofouling control methods along with standard backwash and chemical backwash. The CEBs made of specific concentration of PVA were proven to be more durable and helpful in mitigating biofouling as compared to that of sodium alginate. An MBR operated with PVA-alginate QQ CEBs together with chemical backwash showed the best performance without deterioration of effluent quality.

Electrodialytic bioproduction of xylonic acid in a bioreactor of supplied-oxygen intensification by using immobilized whole-cell Gluconobacter oxydans as biocatalyst

Immobilized whole-cell fermentation has been proven to be an effective method to improve the performance and cost-effectiveness of Gluconobacter oxydans ATCC 621. In the bio-oxidation of xylose to xylonic acid, the oxygen supply through the immobilized beads is a well-known factor that limits the biocatalytic performance of Gluconobacter oxydans as obligate aerobic bacteria. The activity of immobilized cells could be efficiently improved by execution of pressurized pure oxygen supply strategy. Subsequently, in order to further enhance the production efficiency of xylonic acid and reduce end-product inhibition, online-electrodialysis was employed. Finally, a design of pressurized oxygen supply bioreactor combining with online-electrodialysis was put forward for implementing successive production of xylonic acid. The central features of this a highly integrated design are feasible and thus might enable cost-competitive bacterial xylonic acid production.

Long-Term Storage and Use of Artificially Immobilized Anaerobic Sludge as a Powerful Biocatalyst for Conversion of Various Wastes Including Those Containing Xenobiotics to Biogas

The aim of this paper is to demonstrate the possibilities of anaerobic sludge cells immobilized into poly(vinyl alcohol) cryogel for the methanogenic conversion of various lignocellulosic waste and other media containing antibiotics (ampicillin, kanamycin, benzylpenicillin) or pesticides (chlorpyrifos or methiocarb and its derivatives). It was established that the immobilized cells of the anaerobic consortium can be stored frozen for at least three years while preserving a high level of metabolic activity. The cells after the long-term storage in an immobilized and frozen state were applied for the methanogenesis of a wide number of wastes, and an increase in both methane yield and methane portion in the produced biogas as compared to the conventionally used suspended anaerobic sludge cells, was ensured. It was shown that the “additional” introduction of bacterial Clostridium acetobutylicum, Pseudomonas sp., Enterococcus faecalis cells (also immobilized using same support) improves characteristics of methanogenesis catalyzed by immobilized anaerobic sludge.

PVA/CS and PVA/CS/Fe gel beads' synthesis mechanism and their performance in cultivating anaerobic granular sludge

Biomass washout from high-speed anaerobic suspended bed bio-reactors is still a challenge to their stable operation. Preserving active biomass to efficiently retain biomass in the reactor is one of the solutions to this problem. Herein, two carriers (polyvinyl alcohol/chitosan (PVA/CS) and PVA/CS/Fe gel beads) were prepared using the cross-linking method. The fourier transform infrared (FTIR) and ¹³C nuclear magnetic resonance (¹³C NMR) analyses showed that PVA/CS gel beads formed mainly through hydrogen-bonds (NH₂OH^-). Furthermore, FTIR, ¹³C NMR, energy dispersive spectrum (EDS), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that PVA/CS/Fe gel beads formed mainly through chelate bond (NH₂-Fe^M+OH^-). The scanning electron microscope (SEM) results affirmed that the gel beads had rough and well-developed porous structure for the attachment of microbes. Furthermore, the abilities of gel beads on the cultivation of granular sludge in an up-flow anaerobic sludge bed (UASB) reactor were effectively demonstrated while treating wastewater polluted with glucose and alkali lignin. The results showed that the gel beads-assisted reactors had a higher performance than those without the gel beads. The cultivation of granules in these reactors was accelerated, while the granules became bigger and exhibited better settling velocities. The reactor with gel beads was easier to withstand a higher organic loading rate due to dense microbial aggregates, which were caused by more humic-like substance. Particularly, the reactor with PVA/CS/Fe gel beads was able to improve the overall robustness of the system due to stronger mechanical properties of gel beads, and also prevented cells detachment.

Selective Synthesis of Furfuryl Alcohol from Biomass-Derived Furfural Using Immobilized Yeast Cells

Furfuryl alcohol (FA) is an important building block in polymer, food, and pharmaceutical industries. In this work, we reported the biocatalytic reduction of furfural, one of the top value-added bio-based platform chemicals, to FA by immobilized Meyerozyma guilliermondii SC1103 cells. The biocatalytic process was optimized, and the tolerance of this yeast strain toward toxic furfural was evaluated. It was found that furfural of 200 mM could be reduced smoothly to the desired product FA with the conversion of 98% and the selectivity of >98%, while the FA yield was only approximately 81%. The gap between the substrate conversion and the product yield might partially be attributed to the substantial adsorption of the immobilization material (calcium alginate) toward the desired product, but microbial metabolism of furans (as carbon sources) made a negligible contribution to it. In addition, FA of approximately 156 mM was produced within 7 h in a scale-up reaction, along with the formation of trace 2-furoic acid (1 mM) as the byproduct. The FA productivity was up to 2.9 g/L/h, the highest value ever reported in the biocatalytic synthesis of FA. The crude FA was simply separated from the reaction mixture by organic solvent extraction, with the recovery of 90% and the purity of 88%. FA as high as 266 mM was produced by using a fed-batch strategy within 15.5 h.

Immobilization of powdery calcium silicate hydrate via PVA covalent cross-linking process for phosphorus removal

Calcium silicate hydrate (CSH) is a popular material used for phosphorus removal in recent years. In this work, a novel immobilized material, polyvinyl alcohol-CSH (PVA-CSH), was prepared using a 1:10 weight ratio of CSH powder to 8% PVA solution and then used for phosphorus removal. Samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The adsorption mechanism and practical application properties of phosphorus wastewater were studied by sequential batch and continuous flow experiment. The results showed PVA-CSH possessed a porous network structure and an average pore diameter of 24.94 ± 0.11 nm. Furthermore, the CSH functional groups were unaffected by PVA immobilization. Compared with CSH, PVA-CSH did not easily lose CSH after being immobilized by PVA, and the duration of efficient phosphorus removal stage was approximately 20 h longer than that of CSH. In addition, the effluent turbidity of PVA-CSH was 0.11 ± 0.03 NTU during the continuous operation period, which was significantly lower than CSH. In summary, this research study demonstrated the significant potential of PVA-CSH for practical phosphorus removal.

Biodegradation and kinetic study of benzene in bioreactor packed with PUF and alginate beads and immobilized with Bacillus sp. M3

Benzene removal in free and immobilized cells on polyurethane foam (PUF) and polyvinyl alcohol (PVA)-alginate beads was studied using an indigenous soil bacterium Bacillus sp. M3 isolated from petroleum-contaminated soil. The important process parameters (pH, temperature and inoculums size) were optimized and found to be 7, 37°C and 6.0×10⁸CFU/mL, respectively. Benzene removals were observed to be 70, 84 and 90% within 9days in a free cell, immobilized PVA-alginate beads and PUF, respectively under optimum operating conditions. FT-IR and GC-MS analysis confirm the presence of phenol, 1,2-benzenediol, hydroquinone and benzoate as metabolites. The important kinetic parameter ratios (µ_max/K_s; L/mg·day₎ calculated using Monod model was found to be 0.00123 for free cell, 0.00159 for immobilized alginate beads and 0.002016 for immobilized PUF. Similarly inhibition constants (K_i; mg/L) calculated using Andrew-Haldane model was found to be 435.84 for free cell, 664.25 for immobilized alginate beads and 724.93 for immobilized PUF.

Synthesis of spherical porous cross-linked glutaraldehyde/poly(vinyl alcohol) hydrogels

Spherical glutaraldehyde cross-linked poly(vinyl alcohol) (PVA) hydrogels (G-PVA) were prepared in three steps: gelatification, cross-linking, and removal of alginate. Gelatification was carried out by dropping a solution of alginate, PVA, and glutaraldehyde into a calcium chloride solution to form calcium alginate. Calcium alginate gels were prepared at 20°C, 40°C, 60°C, and 80°C to study the effect of gelatification temperature on the formation of pores on the surface of G-PVA. The effect of the alginate content was studied. PVA and glutaraldehyde were cross-linked by immersion of the gels in a solution of H2SO4 and Na2SO4. The effect of sodium alginate and inorganic salts, such as MgSO4 and K2SO4, on the formation of pores on the surface of G-PVA was confirmed.

Detection of pathological biomarkers in human clinical samples via amplifying genetic switches and logic gates

Whole-cell biosensors have several advantages for the detection of biological substances and have proven to be useful analytical tools. However, several hurdles have limited whole-cell biosensor application in the clinic, primarily their unreliable operation in complex media and low signal-to-noise ratio. We report that bacterial biosensors with genetically encoded digital amplifying genetic switches can detect clinically relevant biomarkers in human urine and serum. These bactosensors perform signal digitization and amplification, multiplexed signal processing with the use of Boolean logic gates, and data storage. In addition, we provide a framework with which to quantify whole-cell biosensor robustness in clinical samples together with a method for easily reprogramming the sensor module for distinct medical detection agendas. Last, we demonstrate that bactosensors can be used to detect pathological glycosuria in urine from diabetic patients. These next-generation whole-cell biosensors with improved computing and amplification capacity could meet clinical requirements and should enable new approaches for medical diagnosis.

Reactive toughening of polyvinyl alcohol hydrogel and its wastewater treatment performance by immobilization of microorganisms

Toughened PVA hydrogel beads were prepared by co-crosslinking with glycerol, resulting in the formation of a uniform and dense network gel structure, and the tensile property and hydraulic impact resistance were efficiently improved.

Saccharomyces cerevisiae yeast immobilized on marrow stem sunflower and polyacrylamide hydrogels

Biocatalysts with microorganisms immobilized on solid carriers could provide the solution for development of continuous industrial processes for ethanol obtaining by fermentation of sugars. In this study, modified polyacrylamide hydrogels and marrow stem sunflower are used as supports for Saccharomyces cerevisiae yeast immobilization. The obtained structures are used for fermentation of molasses in batch systems. The free yeast cells are used as reference. The modification of polyacrilamide matrix with (2-hydroxyethyl)methacrylate has a positive effect on structure pore uniformity and fermentation performance. The mechanical properties of the obtained biocatalysts are compared. The novel natural matrix has net superior compression strength.

A disposable biofilm-modified amperometric biosensor for the sensitive determination of pesticide biotoxicity in water

A novel, disposable and sensitive whole cells biosensor based on permeabilizedS. cerevisiaehas been fabricated for the biotoxicity assessment of pesticides in wastewater.

Effect of chitosan-gluconic acid conjugate/poly(vinyl alcohol) cryogels as wound dressing on partial-thickness wounds in diabetic rats

We previously developed chitosan cryogels from chitosan-gluconic acid conjugate without using toxic additives for wound care. In this study, we improved physiological characteristics of the previous cryogels by incorporating poly(vinyl alcohol) that also form cryogels. Mechanical strength of the cryogels was more than two times higher than that of the previous cryogels. Furthermore, the incorporation of poly(vinyl alcohol) enhanced water retention and resistance to degradation of the gels by lysozyme. The cryogels retained the favorable biological properties of the previous cryogels that they accelerate infiltration of inflammatory cells into wound sites. Time period for repairing 50 % of initial area of partial-thickness skin wound treated with the cryogels (4.0 ± 1.1 days) was shorter than those with gauze (6.5 ± 0.3 days) or a commercial hydrogel dressing (5.7 ± 0.3 days). Finally, we confirmed that incorporation of basic fibroblast growth factor into the cryogels was effective to further accelerate wound healing (2.7 ± 1.0 days). These results demonstrate that the cryogels in this study are promising for wound care.