Atomic Layer Deposition of Zirconia on Titanium Implants Improves Osseointegration in Rabbit Bones.

Purpose: Atomic layer deposition (ALD) is a method that can deposit zirconia uniformly on an atomic basis. The effect of deposited zirconia on titanium implants using ALD was evaluated in vivo. Methods: Machined titanium implants (MTIs) were used as the Control. MTIs treated by sandblasting with large grit and acid etching (SA) and MTIs deposited with zirconia using ALD are referred to as Groups S and Z, respectively. Twelve implants were prepared for each group. Six rabbits were used as experimental animals. To evaluate the osteogenesis and osteocyte aspects around the implants, radiological and histological analyses were performed. The bone-to-implant contact (BIC) ratio was measured and statistically analyzed to evaluate the osseointegration capabilities. Results: In the micro-CT analysis, more radiopaque bone tissues were observed around the implants in Groups S and Z. Histological observation found that Groups S and Z had more and denser mature bone tissues around the implants in the cortical bone area. Many new and mature bone tissues were also observed in the medullary cavity area. For the BIC ratio, Groups S and Z were significantly higher than the Control in the cortical bone area (P < 0.017), but there was no significant difference between Groups S and Z. Conclusion: MTIs deposited with zirconia using ALD (Group Z) radiologically and histologically showed more mature bone formation and activated osteocytes compared with MTIs (Control). Group Z also had a significantly higher BIC ratio than the Control. Within the limitations of this study, depositing zirconia on the surface of MTIs using ALD can improve osseointegration in vivo.

Assessment of Inhibition of Biofilm Formation on Non-Thermal Plasma-Treated TiO2 Nanotubes.

Peri-implantitis is an inflammatory disease similar to periodontitis, caused by biofilms formed on the surface of dental implants. This inflammation can spread to bone tissues and result in bone loss. Therefore, it is essential to inhibit the formation of biofilms on the surface of dental implants. Thus, this study examined the inhibition of biofilm formation by treating TiO2 nanotubes with heat and plasma. Commercially pure titanium specimens were anodized to form TiO2 nanotubes. Heat treatment was performed at 400 and 600 °C, and atmospheric pressure plasma was applied using a plasma generator (PGS-200, Expantech, Suwon, Republic of Korea). Contact angles, surface roughness, surface structure, crystal structure, and chemical compositions were measured to analyze the surface properties of the specimens. The inhibition of biofilm formation was assessed using two methods. The results of this study showed that the heat treatment of TiO2 nanotubes at 400 °C inhibited the adhesion of Streptococcus mutans (S. mutans), associated with initial biofilm formation, and that heat treatment of TiO2 nanotubes at 600 °C inhibited the adhesion of Porphyromonas gingivalis (P. gingivalis), which causes peri-implantitis. Applying plasma to the TiO2 nanotubes heat-treated at 600 °C inhibited the adhesion of S. mutans and P. gingivalis.

Effect of Non-Thermal Plasma Treatment of Contaminated Zirconia Surface on Porphyromonas gingivalis Adhesion and Osteoblast Viability.

Plasma treatment on a zirconia surface prevents bacterial contamination and maintains osteoblast activity. To assess the degree of adhesion of Porphyromonas gingivalis on a zirconia surface after non-thermal plasma (NTP) treatment, specimens were treated with plasma for 60, 300, and 600 s, after which P. gingivalis was inoculated onto the surface and incubated for 48 h. To assess osteoblast activity after NTP treatment, osteoblasts (MC3T3-E1) were dispensed onto the specimens contaminated with P. gingivalis immediately after NTP for 60 and 120 s, followed by incubation for 48, 72, and 96 h. P. gingivalis was cultured after 60 s of NTP treatment of zirconia. The NTP and control groups showed no significant difference (p = 0.91), but adhesion was significantly increased following NTP treatment for 300 s or longer (300, 600 s groups) (p < 0.05). After NTP treatment of P. gingivalis-contaminated zirconia, osteoblast activity significantly increased at 72 and 96 h (I60 and I120 s group) in the groups treated with plasma (p < 0.017). Application of NTP to dental zirconia implants for 60 s not only inhibits the proliferation of P. gingivalis, which causes peri-implantitis but also increases osseointegration on zirconia surfaces contaminated with P. gingivalis.

Biocarriers facilitated gravity-driven membrane filtration of domestic wastewater in cold climate: Combined effect of temperature and periodic cleaning.

In this study, two lava stone biocarrier facilitated gravity-driven membrane (GDM) reactors were operated at ~8 °C and ~22 °C in parallel for treating primary wastewater effluent. Although the biocarrier reactor at 8 °C displayed less efficient removals of biodegradable organics than that at 22 °C, both GDM systems (without cleaning) showed comparable fouling resistance distribution patterns, accompanying with similar cake filtration constants and pore constriction constants by modelling simulation. Compared to the GDM at 8 °C, more foulants were accumulated on the GDM at 22 °C, but they presented similar soluble organics/inorganics contents and specific cake resistances. This indicated the cake layers at 22 °C may contain greater-sized foulants due to proliferation of both prokaryotes and eukaryotes, leading to a relatively less-porous nature. In the presence of periodic cleaning (at 50 °C), the cleaning effectiveness followed a sequence as ultrasonication-enhanced physical cleaning > two-phase flow cleaning > chemical-enhanced physical cleaning > physical cleaning, regardless of GDM operation temperature. However, significantly higher cake resistances were observed in the GDM system at 22 °C than those at 8 °C, because shear force tended to remove loosely-attached foulant layers and may compress the residual dense cake layer. The presence of periodic cleaning led to dissimilar dominant prokaryotic and eukaryotic communities in the cake layers as those without cleaning and in the lava stone biocarriers. Nevertheless, operation temperature did not influence GDM permeate quality, which met EU discharge standards.

Enhancing performance of biocarriers facilitated gravity-driven membrane (GDM) reactor for decentralized wastewater treatment: Effect of internal recirculation and membrane packing density.

This study aims to investigate the effect of internal recirculation and membrane packing density on the performance (water quality, membrane performance, and microbial community) of a biocarriers facilitated gravity-driven membrane (GDM) reactor under intermittent aeration condition. The results revealed that the presence of internal recirculation in the GDM reactors could effectively improve water quality (especially increasing nitrogen removal) and membrane performance (especially reducing cake layer resistance) compared to those without internal recirculation. In addition, compared to a high packing density membrane module (1150 m2/m3), a lower packing density membrane module (290 m2/m3) benefited to improve 15% of nitrogen removal and 44% of permeate flux due to the effective aeration scouring effect and less-limited eukaryotic activity, as well as reduce 20% of total treatment cost. In addition, the presence and absence of internal recirculation could lead to dissimilar microbial community compositions of the biofilms in the GAC layers and on the membrane surfaces. However, the membrane packing density could play an insignificant effect on the microbial community compositions of the biofilms in the GDM reactors with internal recirculation.

Impact of salt accumulation in the bioreactor on the performance of nanofiltration membrane bioreactor (NF-MBR)+Reverse osmosis (RO) process for water reclamation.

The impacts of salt accumulation, through adjusting the solid retention time (SRT), in the bioreactor on the bioprocess as well as membrane performance of a high retention nanofiltration membrane bioreactor (NF-MBR) and subsequent reverse osmosis (RO) process for water reclamation are addressed in this study. The build-up of salts (i.e., Ca, Mg, PO4) is a function of SRT, hydraulic retention time (HRT) and membrane rejection. Despite the accumulation of salts, both NF-MBRs at SRT of 30 and 60 days, achieved (i) similar biodegradation efficiency; (ii) excellent organic removal (> 97%); and (iii) excellent ammonia removal (> 98%). Extending the SRT could improve the microbial bio-flocculation capability, but did not influence the microbial activity, viability, and community structure. However, more severe membrane fouling was observed in the NF-MBR with elevated salt levels, which was attributed to the greater formation of calcium phosphate scale and Ca-polysaccharides complex (i.e., irreversible fouling layer) as well as the cake-enhanced-osmotic-pressure (CEOP) effect. Although both NF-MBRs produced comparable quality of permeate, a higher RO membrane fouling rate was observed when the permeate of NF-MBR with SRT at 60 days was fed to the RO system, implying organic compositions in NF-MBR permeate may influence RO performance.

Biocarriers facilitated gravity-driven membrane (GDM) reactor for wastewater reclamation: Effect of intermittent aeration cycle.

This study investigated the performances of gravity-driven membrane (GDM) reactors integrated with granule activated carbon (GAC) biofilm process for wastewater treatment under different intermittent aeration cycles (intensity and frequency). The results showed the removal efficiencies of dissolved organic carbon, total nitrogen, ammonia were significantly improved under intermittent aeration conditions (~86-87%, ~29-37%, and ~83-99%, respectively) compared to non-aeration condition (~72% and ~18%, and ~17%, respectively). In addition, it was found that the intermittent aeration significantly reduced the cake layer resistance and therefore improved ~130-300% the permeate flux compared to control without aeration. Microbial community analysis indicated that prokaryotic and eukaryotic compositions in the cake layer biofilm were significantly influenced by aeration condition. Lastly, energy consumption analysis revealed that GAC + GDM with shorter aeration period and low aeration intensity could be promising as a decentralized wastewater treatment process in terms of water quality and operating energy.

A comparison of gravity-driven membrane (GDM) reactor and biofiltration + GDM reactor for seawater reverse osmosis desalination pretreatment.

In this study, permeate quality, membrane performance, and microbial community in a gravity-driven microfiltration (GDM) reactor and a biofiltration (BF) + GDM reactor for seawater reverse osmosis (RO) desalination pretreatment were compared at both lab-scale and pilot-scale. The presence of BF column was more efficient in removing soluble organic substances by biosorption/biodegradation, leading to superior permeate quality from BF + GDM and subsequently lower RO fouling than GDM. Compared to the biofilm-saturated anthracite media, the granular activated carbon media in BF improved the assimilable organic substances removal in BF + GDM. Although less organic substances and microbial cells were accumulated on the membrane in BF + GDM, its permeate flux was 10-20% lower than GDM. Furthermore, BF lowered the amounts and diversity of prokaryotes (due to less organic substances) and eukaryotes (due to BF media rejection and lacking of prokaryotic preys) in the membrane biofilm of BF + GDM, but did not cause significant shifts of predominant species. Thus, the lower flux in BF + GDM was attributed to the limited predation and movement of eukaryotes in membrane biofilm, which may result in the formation of less porous and compact biofilm layer. The cost analysis indicated that BF + GDM-RO requires 5.2% less operating cost and 1.5% less water production cost than GDM-RO.

Stopping Autoinducer-2 Chatter by Means of an Indigenous Bacterium ( Acinetobacter sp. DKY-1): A New Antibiofouling Strategy in a Membrane Bioreactor for Wastewater Treatment.

Bacterial quorum quenching (QQ) by means of degrading signaling molecules has been applied to antibiofouling strategies in a membrane bioreactor (MBR) for wastewater treatment. However, the target signaling molecules have been limited to N-acyl homoserine lactones participating in intraspecies quorum sensing. Here, an approach to disrupting autoinducer-2 (AI-2) signaling molecules participating in interspecies quorum sensing was pursued as a next-generation antibiofouling strategy in an MBR for wastewater treatment. We isolated an indigenous QQ bacterium ( Acinetobacter sp. DKY-1) that can attenuate the expression of the quorum-sensing (QS) response through the inactivation of an autoinducer-2 signaling molecule, 4,5-dihydroxy-2,3-pentanedione (DPD), among four kinds of autoinducer-2 QS bacteria. DKY-1 released AI-2 QQ compounds, which were verified to be hydrophilic with a molecular weight of <400 Da. The addition of DKY-1 entrapping beads into an MBR significantly decreased DPD concentration and remarkably reduced membrane biofouling. This new approach, combining molecular biology with wastewater engineering, could enlarge the range of QQ-MBR for antibiofouling and energy savings in the field of wastewater treatment.

Mitigation of Membrane Biofouling in MBR Using a Cellulolytic Bacterium, Undibacterium sp. DM-1, Isolated from Activated Sludge.

Biofilm formation on the membrane surface results in the loss of permeability in membrane bioreactors (MBRs) for wastewater treatment. Studies have revealed that cellulose is not only produced by a number of bacterial species but also plays a key role during formation of their biofilm. Hence, in this study, cellulase was introduced to a MBR as a cellulose-induced biofilm control strategy. For practical application of cellulase to MBR, a cellulolytic (i.e., cellulase-producing) bacterium, Undibacterium sp. DM-1, was isolated from a lab-scale MBR for wastewater treatment. Prior to its application to MBR, it was confirmed that the cell-free supernatant of DM-1 was capable of inhibiting biofilm formation and of detaching the mature biofilm of activated sludge and cellulose-producing bacteria. This suggested that cellulase could be an effective anti-biofouling agent for MBRs used in wastewater treatment. Undibacterium sp. DM-1-entrapping beads (i.e., cellulolytic-beads) were applied to a continuous MBR to mitigate membrane biofouling 2.2-fold, compared with an MBR with vacant-beads as a control. Subsequent analysis of the cellulose content in the biofilm formed on the membrane surface revealed that this mitigation was associated with an approximately 30% reduction in cellulose by cellulolytic-beads in MBR.

Enhancing the Physical Properties and Lifespan of Bacterial Quorum Quenching Media through Combination of Ionic Cross-Linking and Dehydration.

Quorum quenching (QQ) bacteria entrapped in a polymeric composite hydrogel (QQ medium) have been successfully applied in membrane bioreactors (MBRs) for effective biofouling control. However, in order to bring QQ technology closer to practice, the physical strength and lifetime of QQ media should be improved. In this study, enforcement of physical strength, as well as an extension of the lifetime of a previously reported QQ bacteria entrapping hollow cylinder (QQ-HC), was sought by adding a dehydration procedure following the cross-linking of the polymeric hydrogel by inorganic compounds like Ca2+ and boric acid. Such prepared medium demonstrated enhanced physical strength possibly through an increased degree of physical cross-linking. As a result, a longer lifetime of QQ-HCs was confirmed, which led to improved biofouling mitigation performance of QQ-HC in an MBR. Furthermore, QQ-HCs stored under dehydrated condition showed higher QQ activity when the storage time lasted more than 90 days owing to enhanced cell viability. In addition, the dormant QQ activity after the dehydration step could be easily restored through reactivation with real wastewater, and the reduced weight of the dehydrated media is expected to make handling and transportation of QQ media highly convenient and economical in practice.

Fungal Quorum Quenching: A Paradigm Shift for Energy Savings in Membrane Bioreactor (MBR) for Wastewater Treatment.

In the last 30 years, the use of membrane bioreactors (MBRs) for advanced wastewater treatment and reuse have been expanded continuously, but they still suffer from excessive energy consumption resulting from the intrinsic problem of membrane biofouling. One of the major causes of biofouling in MBRs is bacterial quorum sensing (QS) via N-acylhomoserine lactones (AHLs) and/or autoinducer-2 (AI-2), enabling intra- and interspecies communications, respectively. In this study, we demonstrate that farnesol can substantially mitigate membrane biofouling in a MBR due to its quorum quenching (QQ) activity. When Candida albicans (a farnesol producing fungus) entrapping polymer beads (AEBs) were placed in the MBR, the rate of transmembrane pressure (TMP) rise-up was substantially decreased, even for lower aeration intensities. This finding corresponds to a specific aeration energy savings of approximately 40% (25% through the physical washing effect and a further 15% through the biological QQ effect of AEBs) compared to conventional MBRs without AEBs. A real-time RT-qPCR analysis revealed that farnesol secreted from C. albicans mitigated the biofilm formation in MBRs via the suppression of AI-2 QS. Successful control of biofouling and energy savings through fungal-to-bacterial QQ could be expanded to the plant scale for MBRs in wastewater treatment with economic feasibility.

More Efficient Media Design for Enhanced Biofouling Control in a Membrane Bioreactor: Quorum Quenching Bacteria Entrapping Hollow Cylinder.

Recently, membrane bioreactors (MBRs) with quorum quenching (QQ) bacteria entrapping beads have been reported as a new paradigm in biofouling control because, unlike conventional post-biofilm control methods, bacterial QQ can inhibit biofilm formation through its combined effects of physical scouring of the membrane and inhibition of quorum sensing (QS). In this study, using a special reporter strain (Escherichia coli JB525), the interaction between QS signal molecules and quorum quenching bacteria entrapping beads (QQ-beads) was elucidated through visualization of the QS signal molecules within a QQ-bead using a fluorescence microscope. As a result, under the conditions considered in this study, the surface area of QQ-media was likely to be a dominant parameter in enhancing QQ activity over total mass of entrapped QQ bacteria because QQ bacteria located near the core of a QQ-bead were unable to display their QQ activities. On the basis of this information, a more efficient QQ-medium, a QQ hollow cylinder (QQ-HC), was designed and prepared. In batch experiments, QQ-HCs showed greater QQ activity than QQ-beads as a result of their higher surface area and enhanced physical washing effect because of their larger impact area against the membrane surface. Furthermore, it was shown that such advantages of QQ-HCs resulted in more effective mitigation of membrane fouling than from QQ-beads in lab-scale continuous MBRs.

Effect of the Shape and Size of Quorum-Quenching Media on Biofouling Control in Membrane Bioreactors for Wastewater Treatment.

Recently, spherical beads entrapping quorum quenching (QQ) bacteria have been reported as effective moving QQ-media for biofouling control in MBRs for wastewater treatment owing to their combined effects of biological (i.e., quorum quenching) and physical washing. Taking into account both the mass transfer of signal molecules through the QQ-medium and collision efficiencies of the QQ-medium against the filtration membranes in a bioreactor, a cylindrical medium (QQ-cylinder) was developed as a new shape of moving QQ-medium. The QQ-cylinders were compared with previous QQ-beads in terms of the QQ activity and the physical washing effect under identical loading volumes of each medium in batch tests. It was found that the QQ activity of a QQ-medium was highly dependent on its specific surface area, regardless of the shape of the medium. In contrast, the physical washing effect of a QQ-medium was greatly affected by its geometric structure. The enhanced anti-biofouling property of the QQ-cylinders relative to QQ-beads was confirmed in a continuous laboratory-scale MBR with a flat-sheet membrane module.

Crossing the Border between Laboratory and Field: Bacterial Quorum Quenching for Anti-Biofouling Strategy in an MBR.

Quorum quenching (QQ) has recently been acknowledged to be a sustainable antifouling strategy and has been investigated widely using lab-scale membrane bioreactor (MBR) systems. This study attempted to bring this QQ-MBR closer to potential practical application. Two types of pilot-scale QQ-MBRs with QQ bacteria entrapping beads (QQ-beads) were installed and run at a wastewater treatment plant, feeding real municipal wastewater to test the systems' effectiveness for membrane fouling control and thus the amount of energy savings, even under harsh environmental conditions. The rate of transmembrane pressure (TMP) build-up was significantly mitigated in QQ-MBR compared to that in a conventional-MBR. Consequently, QQ-MBR can substantially reduce energy consumption by reducing coarse bubble aeration without compromising the effluent water quality. The addition of QQ-beads to a conventional MBR substantially affected the EPS concentrations, as well as microbial floc size in the mixed liquor. Furthermore, the QQ activity and mechanical stability of QQ-beads were well maintained for at least four months, indicating QQ-MBR has good potential for practical applications.