Biofilm Thickness Research Articles

Effects of Different Polymeric Materials on the Bacterial Attachment and Biofilm Formation in Anoxic Fixed-Bed Biofilm Reactors

Six biofilm carriers with different polymer were studied in fixed-film systems under anoxic conditions. Different media of polymers influence wastewater treatment performance. The aim of this study was to investigate different polymeric materials, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), high-density polyethylene (HDPE), and polymethyl methacrylate (acrylic), that affect bacterial attachment and biofilm formation in biofilm-based wastewater treatment technologies. Water contact angle (WCA) measurement was employed to analyze the role of wetting (hydrophilic/hydrophobic) of polymeric material surfaces in the initial phase of bacterial attachment. The increase of biofilm formation during the observation was determined by gravimetric (total attached solid) and microscopic (SEM and CLSM) analysis. The results showed the value for WCA of PET < HDPE < PVC < PP < acrylic, which indicated that a higher hydrophilicity surface leads to a higher total attached solid (TAS), biofilm formation rate, and biofilm thickness on the surface of media. The hydrophilic material (i.e., PET and HDPE) demonstrated wastewater treatment performance better than slightly hydrophilic material (i.e., PVC, PP, and acrylic) under a steady-state period (over an 80-day operation). The data showed a positive correlation between hydrophilic material and COD, NH4+-N, and TP removal. Hydrophilic material was beneficial for a fast start-up and stable biofilm formation of a fixed-bed biofilm reactor. PET media showed feasible polymer types compared to HDPE, PVC, and PP; thus, it can be used as an alternative biofilm carrier media in a larger-scale application. The findings of this study highlighted the polymeric material type has a significant effect on the performance of fixed-bed wastewater treatment.

Biofilm thickness controls the relative importance of stochastic and deterministic processes in microbial community assembly in moving bed biofilm reactors.

Deterministic and stochastic processes are believed to play a combined role in microbial community assembly, though little is known about the factors determining their relative importance. We investigated the effect of biofilm thickness on community assembly in nitrifying moving bed biofilm reactors using biofilm carriers where maximum biofilm thickness is controlled. We examined the contribution of stochastic and deterministic processes to biofilm assembly in a steady state system using neutral community modelling and community diversity analysis with a null-modelling approach. Our results indicate that the formation of biofilms results in habitat filtration, causing selection for phylogenetically closely related community members, resulting in a substantial enrichment of Nitrospira spp. in the biofilm communities. Stochastic assembly processes were more prevalent in biofilms of 200 µm and thicker, while stronger selection in thinner (50 µm) biofilms could be driven by hydrodynamic and shear forces at the biofilm surface. Thicker biofilms exhibited greater phylogenetic beta-diversity, which may be driven by a variable selection regime caused by variation in environmental conditions between replicate carrier communities, or by drift combined with low migration rates resulting in stochastic historical contingency during community establishment. Our results indicate that assembly processes vary with biofilm thickness, contributing to our understanding of biofilm ecology and potentially paving the way towards strategies for microbial community management in biofilm systems.

Biofilm formation by sulphate-reducing bacteria on different metals and their prospective role in titanium corrosion

ABSTRACT This study describes the biofilm formation by sulphate-reducing bacteria (SRB) on different materials, which has implications for the biomedical, pharmaceutical, food and chemical process industries. SRB was chosen as a model organism being an anaerobic bacterium. Biofilm formation on different materials and corrosion of titanium by SRB were monitored with time using confocal laser scanning microscopy and fluorescent FISH probes were used to authenticate the SRB strain. The thickness of the mono-culture SRB biofilm has ranged from 4 to 24 µm during thed 12–84 hr; however, the maximum biofilm thickness (24 µm) was recorded after 60 hr of growth. Planktonic growth of the SRB strain showed a log phase up to 48 hr and the sulphide production ranged from 2 to 14 mg l−1. For a comparative account, the SRB biofilm formation on copper was chosen as a positive control. Finally, the putative role of extracellular electron transfer by SRB in the biocorrosion process and the plausible mechanism of pitting corrosion of titanium is described in detail.

Plant-Pathogenic Ralstonia Phylotypes Evolved Divergent Respiratory Strategies and Behaviors To Thrive in Xylem.

Bacterial pathogens in the Ralstonia solanacearum species complex (RSSC) infect the water-transporting xylem vessels of plants, causing bacterial wilt disease. Strains in RSSC phylotypes I and III can reduce nitrate to dinitrogen via complete denitrification. The four-step denitrification pathway enables bacteria to use inorganic nitrogen species as terminal electron acceptors, supporting their growth in oxygen-limited environments such as biofilms or plant xylem. Reduction of nitrate, nitrite, and nitric oxide all contribute to the virulence of a model phylotype I strain. However, little is known about the physiological role of the last denitrification step, the reduction of nitrous oxide to dinitrogen by NosZ. We found that phylotypes I and III need NosZ for full virulence. However, strains in phylotypes II and IV are highly virulent despite lacking NosZ. The ability to respire by reducing nitrate to nitrous oxide does not greatly enhance the growth of phylotype II and IV strains. These partial denitrifying strains reach high cell densities during plant infection and cause typical wilt disease. However, unlike phylotype I and III strains, partial denitrifiers cannot grow well under anaerobic conditions or form thick biofilms in culture or in tomato xylem vessels. Furthermore, aerotaxis assays show that strains from different phylotypes have different oxygen and nitrate preferences. Together, these results indicate that the RSSC contains two subgroups that occupy the same habitat but have evolved divergent energy metabolism strategies to exploit distinct metabolic niches in the xylem. IMPORTANCE Plant-pathogenic Ralstonia spp. are a heterogeneous globally distributed group of bacteria that colonize plant xylem vessels. Ralstonia cells multiply rapidly in plants and obstruct water transport, causing fatal wilting and serious economic losses of many key food security crops. The virulence of these pathogens depends on their ability to grow to high cell densities in the low-oxygen xylem environment. Plant-pathogenic Ralstonia can use denitrifying respiration to generate ATP. The last denitrification step, nitrous oxide reduction by NosZ, contributes to energy production and virulence for only one of the three phytopathogenic Ralstonia species. These complete denitrifiers form thicker biofilms in culture and in tomato xylem, suggesting they are better adapted to hypoxic niches. Strains with partial denitrification physiology form less biofilm and are more often planktonic. They are nonetheless highly virulent. Thus, these closely related bacteria have adapted their core metabolic functions to exploit distinct microniches in the same habitat.

Performance of Copolymerized Organo-Selenium RO Feed Spacers during Fouling

Fouling of reverse osmosis (RO) systems to produce clean drinking water is a major problem. Organo-selenium inhibition is an attractive solution for this application because biofilm prevention has been shown in medical devices, water filtration systems, and plastics. This study examined whether selenium-coated polymers would have positive effects in controlling RO fouling. This study included an analysis of modified feed spacers’ performance on reduction of total biomass concentration, average biofilm thickness on the surface of RO membranes versus real wastewater sources, the impact of selenium catalytic activity on the reduction of RO membrane chemical scaling, and the performance of fouling and biofilm formation. A 1.5% organo-selenium was copolymerized into spacer elements used in an RO system. These systems were then tested with both city and industrial wastewater with different total dissolved solids (TDS) concentrations for effects on (1) flux, (2) biofilm formation, and (3) inorganic binding. The comparison of an organo-selenium spacer with a control spacer yielded the following for RO membranes: (1) lower calcium and magnesium binding; (2) better flux at high TDS concentrations in both city and industrial water; (3) lower biofilm thickness and volume; and (4) a decrease in both dead and viable bacteria. Testing of varying solids concentrations resulted in greater log inhibition of fouling as a result of operating the RO system with selenium copolymerized feed spacer. The impact of selenium catalytic activity versus divalent foulants (magnesium and calcium) is important because of their ability to create bridges between biological cells and membrane surface, leading to increased possibility of biofouling.

Microbial community stratification in scale-up Anaerobic Fluidized Bed Reactor applied for 4-Nonylphenol degradation

This is the first report of the microbial community stratification in a scale-up (20 L) Anaerobic Fluidized Bed Reactor (AFBR) during the degradation of the endocrine disruptor 4-Nonylphenol (4-NP). Bed stratification occurred after 100 running days. The bed visually characterized as granules were, actually, thick biofilm covering the entire surface of the sand particle, acting as a protection strategy of microbial populations against 4-NP addition. The community differentiation may have occurred to the Quorum-Sensing (QS) system due to the greater abundance of biofilm-forming genera in the granule. Furthermore, the syntrophic relation between electrogenic bacteria and methanogenic archaea via Direct Interspecies Electron Transfer (DIET) may also explain the bed stratification, due to the higher abundance of Geothrix (8.3 %), Enterococcus (4.8 %), Lactobacillus (3.9 %), Bacillus (2.0 %) and Methanosaeta (15.6 %) in the granular bed. Bed stratification is an extremely complex issue and can influence the AFBR operation, modeling and scaling up.

Comparison and Evaluation of Fermentation Results of Probiotic Products by Acenobacter xylinum

products with Acetobacter xylinum starter included Nata and Kombucha. The large number of studies on probiotic product innovation should be followed by a survey on public acceptance of the products. This research aim to compare of the yield of probiotic products after fermentation process which was evaluated from a physical perspective, pH and public acceptance. This research is an experimental study to compared the fermented results of two types of probiotic products, nata and kombucha which are differentiated based on their raw ingredients. The nata products sample which had the largest thickness and weight of cellulose biofilm was NDC, while the kombucha products sample which had the largest thickness and weight of cellulose biofilm was KGF. pH of all samples, both nata and kombucha, decreased during the fermentation process. The samples of nata products that were most accepted by the panelists were NDC and NDM in terms of color, smell and taste. The samples of kombucha products that were most accepted by the panelists were KAF and KMF in terms of color, smell and taste.

Elongated Riboflavin-Producing Shewanella oneidensis in a Hybrid Biofilm Boosts Extracellular Electron Transfer.

Shewanella oneidensis is able to carry out extracellular electron transfer (EET), although its EET efficiency is largely limited by low flavin concentrations, poor biofilm forming-ability, and weak biofilm conductivity. After identifying an important role for riboflavin (RF) in EET via in vitro experiments, the synthesis of RF is directed to 837.74 ± 11.42µm in S. oneidensis. Molecular dynamics simulation reveals RF as a cofactor that binds strongly to the outer membrane cytochrome MtrC, which is correspondingly further overexpressed to enhance EET. Then the cell division inhibitor sulA, which dramatically enhanced the thickness and biomass of biofilm increased by 155% and 77%, respectively, is overexpressed. To reduce reaction overpotential due to biofilm thickness, a spider-web-like hybrid biofilm comprising RF, multiwalled carbon nanotubes (MWCNTs), and graphene oxide (GO) with adsorption-optimized elongated S. oneidensis, achieve a 77.83-fold increase in power (3736mW m-2 ) relative to MR-1 and dramatically reduce the charge-transfer resistance and boosted biofilm electroactivity. This work provides an elegant paradigm to boost EET based on a synthetic biology strategy and materials science strategy, opens up further opportunities for other electrogenic bacteria.

A strategy for fast anammox biofilm formation under mainstream conditions

One of the bottlenecks to applying anaerobic ammonium oxidation (Anammox) is the long start-up time, especially under mainstream conditions. This study proposed a strategy for fast anammox biofilm formation under mainstream conditions. By first cultivating an aerobic heterotrophic biofilm, and then transferring to anoxic conditions, a pre-cultivated heterotrophic biofilm can be formed in 12 days. The pre-cultivated heterotrophic biofilm then functions as a “glue” to accelerate anammox bacteria adhesion and biofilm formation. Secondary settled effluent with externally added 15–30 mg-N·L−1 ammonium and nitrite was applied as reactor influent. With a single inoculation of suspended growth anammox-laden biomass and no bioaugmentation, an anammox-enriched biofilm formed after 5 months of operation under uncontrolled temperature of 15–20 °C. Both the nitrogen removal rate and specific anammox activity exponentially increased over the course of study, corresponding to an estimated anammox doubling time of 10.8 days. The biofilm thickness on primed carriers was 2–3 times higher than on the non-primed carriers over the first 5 months of operation, and the hszA gene copy number in primed biofilms revealed was consistently 1 to 2 times higher than the non-primed carrier biofilm, indicating that biofil m carrier priming via selection for a pre-cultivated heterotrophic biofilm base can effectively improve the anammox enrichment rate at early stages of reactor operation. Time, rather than the type of biofilm (primed versus non-primed), had a stronger influence on microbial community structure over the full 230 days of reactor operation. Candidatus Brocadia was the only detected anammox bacteria genus. Overall, pre-cultivation of heterotrophs on biofilm carriers provides a simple route to accelerate anammox-enriched biofilm formation under mainstream conditions.

Characterization of selected species of Pichia and Candida for their growth capacity in apple and grape must and their biofilm parameters.

Pichia and Candida species include biofilm-forming yeasts able to spoil foods and beverages. Strains belonging to 10 Pichia and Candida species isolated from apples, grape musts, and wines were analysed. They were subjected to molecular typing and characterized for their ability to grow and ferment must for cider and wine production, and for their biofilm properties. All strains grew similarly in apple and grape must. Glucose-fermenting strains displayed differentiated fermentation performances. Great variation in SO2 and ethanol sensitivity was observed among the strains. Pichia manshurica strains showed high tolerance to both molecules. Eleven and five surface-spreading biofilm (MAT) phenotypes were identified in solid and liquid media, respectively. Strains produced biofilms with variable thicknesses and widths in culture tubes. Cell adherence and aqueous-hydrocarbon biphasic hydrophobicity assays were carried out. Some Pichia manshurica and P. membranifaciens strains exhibited a high capacity to form a thick biofilm and had high cell adherence and hydrophobicity values. These strains could be more likely to colonize the internal surfaces of tanks. This study evidenced that some Pichia and Candida strains can proliferate during apple and grape must fermentation and may be detrimental the beverage quality, due to their specific biofilm properties.

Development and Application of Membrane Aerated Biofilm Reactor (MABR)—A Review

As a new type of biological treatment process, membrane aerated biofilm reactors (MABRs), which have received extensive attention and research in recent years, could reduce energy consumption by 70% compared to the traditional activated sludge process. The MABR system uses bubble-free aeration membrane material as the carrier, the counter-diffusion mechanism of oxygen and pollutants enables ammonium oxidizing bacteria (AOB) and nitrate oxidizing bacteria (NOB) to adhere to the membrane surface so that simultaneous nitrification and denitrification (SND) can occur to achieve simultaneous nitrogen and carbon removal. Currently, MABR technology has been successfully applied to the treatment of municipal sewage, various industrial wastewater, pharmaceutical, high salinity, high ammonia, aquaculture wastewater, landfill leachate and black and odorous water bodies in rivers. Many laboratory experiments and pilot-scale MABR reactors have been used to study the performance of membrane materials, the mechanism of pollutant removal and the effects of different factors on the system. However, the performance of MABR is affected by factors such as dissolved oxygen (DO), pH, C/N, biofilm thickness, hydraulic retention time (HRT), temperature, etc., which limits large-scale promotion. Therefore, membrane materials, membrane modules, biofilm, application of MABR technology, influencing factors of MABR system performance, and limitations and perspectives of MABR are reviewed in this paper, and we expect to provide valuable information.

Biofilm characteristics for providing resilient denitrification in a hydrogen-based membrane biofilm reactor

In a hydrogen-based membrane biofilm reactor (H2-MBfR), the biofilm thickness is considered to be one of the most important factors for denitrification. Thick biofilms in MBfRs are known for low removal fluxes owing to their resistance to substrate transport. In this study, the H2-MBfR was operated under various loading rates of oxyanions, such as NO3-N, SO4-S, and ClO4− at an H2 flux of 1.06 e− eq/m2-d. The experiment was initiated with NO3-N, SO4-S, and ClO4− loadings of 0.464, 0.026, and 0.211 e− eq/m2-d, respectively, at 20 °C. Under the most stressful conditions, the loading rates increased simultaneously to 1.911, 0.869, and 0.108 e− eq/m2-d, respectively, at 10 °C. We observed improved performance in significantly thicker biofilms (approximately 2.7 cm) compared to previous studies using a denitrifying H2-MBfR for 120 days. Shock oxyanion loadings led to a decrease in total nitrogen (TN) removal by 20 to 30%, but TN removal returned to 100% within a few days. Similarly, complete denitrification was observed, even at 10 °C. The protective function and microbial diversity of the thick biofilm may allow stable denitrification despite stress-imposing conditions. In the microbial community analysis, heterotrophs were dominant and acetogens accounted for 11% of the biofilm. Metagenomic results showed a high abundance of functional genes involved in organic carbon metabolism and homoacetogenesis. Owing to the presence of organic compounds produced by acetogens and autotrophs, heterotrophic denitrification may occur simultaneously with autotrophic denitrification. As a result, the total removal flux of oxyanions (1.84 e− eq/m2-d) far exceeded the H2 flux (1.06 e− eq/m2-d). Thus, the large accumulation of biofilms could contribute to good resilience and enhanced removal fluxes.

Preparations of antibacterial yellow-green-fluorescent carbon dots and carbon dots-lysozyme complex and their applications in bacterial imaging and bacteria/biofilm inhibition/clearance

The preparation of functional long-wavelength-emitting nanomaterials and the researches on their applications in antibacterial and antibiofilm fields have important significance. This paper reports the preparation of yellow-green-fluorescent and high- quantum yield carbon dots (4-ACDs) with 4-aminosalicylic acid and polyethylene imine as raw materials through one-step route, and the impacts of raw material structure and the reaction conditions upon the optical properties of the products have been investigated. 4-ACDs exhibit excellent broad-spectrum antibacterial activity, and their good biocompatibility ensures them as ideal fluorescent nano-probe for cell imaging. However, 4-ACDs could not effectively eliminate the biofilm of Staphylococcus aureus (S. aureus). CDs-LZM complex was prepared through the coupling between 4-ACDs and lysozyme (LZM) and the complex showed strong antibacterial activity against Gram-positive bacteria, particularly with MIC against S. aureus at 5 μg mL−1. Besides, CDs-LZM showed excellent ability against the biofilm of S. aureus. At the concentration of 60 μg mL−1, its inhibition rate against the growth of biofilm was 86 %, and elimination rate against biofilm reached 76 %. CDs-LZM exhibited obvious antibiofilm ability through removing extracellular matrix of biofilm, greatly reducing the thickness of biofilm under confocal microscopy. The application of novel long-wavelength-emitting nanomaterial in eliminating pathogenic bacteria is of great significance.

Model-based evaluation of simultaneous nitrification and denitrification in aerobic granular sludge systems.

A lab-scale granular sludge sequencing batch reactor (G-SBR) system was operated using synthetic wastewater. The total nitrogen removal efficiency of 85% was obtained together with the achievement of complete total phosphorus removal with average granule diameter of 400µm. Dual-step nitrification and denitrification model with fixed biofilm thickness was used for performance analysis. The denitrification mode only contributed to TN removal with 25% which can be calculated with process stoichiometry. The remaining nitrogen removal could be explained by simulating simultaneous nitrification and denitrification which was responsible for 75% denitrification during aerobic period. In addition, low NO3- concentration at the beginning of the fill period provided advantage for securing a prolonged anaerobic period for enhanced biological phosphorus removal (EBPR). The model parameters of boundary layer thickness (zBL = 50µm) and half-saturation of O2 for nitrite-oxidizing bacteria (KO2,NOB = 0.5 gO2/m3) were tuned to fit NO2 and NO3 profiles in SBR cycle.

Characterization and biofouling potential analysis of two cyanobacterial strains isolated from Cape Verde and Morocco.

Cyanobacteria are new sources of value-added compounds but also ubiquitous and harmful microfoulers on marine biofouling. In this work, the isolation and identification of two cyanobacterial strains isolated from Cape Verde and Morocco, as well as their biofilm-forming ability on glass and Perspex under controlled hydrodynamic conditions, were performed. Phylogenetic analysis revealed that cyanobacterial strains isolated belong to Leptothoe and Jaaginema genera (Leptothoe sp. LEGE 181153 and Jaaginema sp. LEGE 191154). From quantitative and qualitative data of wet weight, chlorophyll a content and biofilm thickness obtained by optical coherence tomography, no significant differences were found in biofilms developed by the same cyanobacterial strain on different surfaces (glass and Perspex). However, the biofilm-forming potential of Leptothoe sp. LEGE 181153 proved to be higher compared with Jaaginema sp. LEGE 191154, particularly at the maturation stage of biofilm development. Three-dimensional biofilm images obtained from confocal laser scanning microscopy showed different patterns between both cyanobacterial strains and also among the two surfaces. Because standard methodologies to evaluate cyanobacterial biofilm formation, as well as two different optical imaging techniques, were used, this work also highlights the possibility of integrating different techniques to evaluate a complex phenomenon like cyanobacterial biofilm development.

Microbe-induced pitting of Fe-based amorphous coating

It is well known that Fe-based amorphous coatings demonstrate excellent performance against marine corrosion, but the corrosion resistance is significantly reduced in the presence of ocean-microbes. However, the mechanism of microbe-induced corrosion, named as microbiologically influenced corrosion (MIC), has yet to be understood. In this paper, the MIC mechanism of an Fe-based amorphous coating (with the composition of Fe43.7Co7.3Cr14.7Mo12.6C15.5B4.3Y1.9) in the presence of Pseudomonas aeruginosa (one of the typical ocean-microbes) was elaborately investigated by electrochemical impedance spectroscopy (EIS), electrochemical noise analysis (EN), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The electrochemical results show that P. aeruginosa reduced the corrosion resistance of the amorphous coating, manifested by the lower impedance values and higher metastable pitting initiation rate compared to those in a sterile medium. XPS analysis indicates the enrichment of soluble high-valent metal oxides in the passive film formed in the P. aeruginosa medium. In addition, TEM observation reveals pitting initiated exactly beneath P. aeruginosa cells, rather than defect regions (i.e., intersplat) as expected. In the pitting region, a thick biofilm was formed, which resulted in thinning of the underlying passive film. Based on these results, an MIC mechanism based on the inward extracellular electron transfer (EET) effect was proposed, and a potential strategy to relieve MIC was examined.

Chapter 6: Diagnostic Considerations regarding Coronal Caries.

This chapter considers the main principles guiding diagnosis of the disease dental caries in clinical practice by means of clinical examination and radiographs as adjunct method. Dental professionals have been trained to diagnose caries disease by assessing clinical symptoms and signs of caries lesions complemented by radiographic examination as an adjunct method. Clinical examination is the foundation of the diagnosis and should be performed after removal of dental biofilm of tooth surfaces, air-drying, and under good illumination. Clinical diagnostic methods categorize caries lesions according to their severity and in some methods according to their activity. Caries lesion activity has been determined by surface reflection and texture. The detection of thick or heavy biofilm on tooth surfaces is an additional diagnostic clinical tool to estimate caries lesion activity. Patients with no caries experience, that is, without clinical and/or radiographic signs of caries lesions in the dentition, are considered caries inactive. Other caries-inactive patients may present inactive caries lesions/restorations in their dentition. In contrast, patients are considered caries active when presenting any active caries lesion at clinical level and/or any progressing lesion as demonstrated by at least two bitewing radiographs taken at different points in time. The main concern about caries-active patients is that caries lesions are likely to progress unless effective measures are implemented to interfere with its progression. Prescribed according to individual needs, bitewing radiographs provide additional information for clinical examination in the detection of approximal enamel and outer third dentine lesions that can be inactivated by nonoperative treatment.

Comparative Genomic Analysis of Bacterial Strain PL and Detection of Sustainable Bio-Electricity Producing Features

This study aimed to analyze the whole genome of the bacterial strain PL, isolated from pond sediment, to evaluate its genetic characteristics in the degradation of waste and toxic substrates and the generation of bioelectricity. This was compared to the type strain of the bacterial species Geobacter sulfurreducens (G. sulfurreducens) (PCA) and the strain KN400. Genomic taxonomy on the TYGS platform established the affiliation of strain PL with the bacterial species G. sulfurreducens. Subsequently, a genomic study of strains PL, PCA, and KN400 was performed using various bioinformatics tools. These included the study of genes associated with functional categories (COG) through genome annotation using the RAST server, followed by gene identification using the Prokka program to discover and identify genes related to electricity production. The results of the genomic analysis of the PL strain showed that it possesses many genes necessary for generating electric current. These included genes related to the formation of thick biofilms, adhesion to the anode of microbial fuel cells (MFCs), oxidation of various substrates and environmental pollutants, and extracellular electron transfer. Overall, the obtained results indicate that the PL strain is a promising candidate for sustainable bioenergy generation. KEYWORDS bioinformatics tools, genomic analysis, geobacter sulfurreducens, MFCs, sustainable bioenergy, whole genome

Evaluation of the effect of biofilm formation on the reductive transformation of triclosan in cathode-modified electrolytic systems

The performance of electrochemical reduction is often enhanced by electrode modification techniques. However, there is a risk of microbial colonization on the electrode surface to form biofilms in the treatment of actual wastewater with modified electrodes. In this work, the effects of biofilm formation on modified electrodes with reduced graphene oxide (rGO), platinum/carbon (Pt/C), and carbon nanotube (CNT) were investigated in triclosan (TCS) degradation. With biofilm formation, the TCS degradation efficiencies of carbon cloth (CC), rGO@CC, Pt/C@CC, and CNT@CC decayed to 54.53 %, 59.77 %, 69.19 %, and 53.97 %, respectively, compared to the raw electrodes. Confocal laser scanning microscopy and microbial community analysis revealed that the difference in biofilm thickness and activity were the major influencing factors on the discrepant TCS degradation rather than the microbial community structure. The electrochemical performance tests showed that the biofilm formation increased the ohmic resistance by an order of magnitude in rGO@CC, Pt/C@CC, and CNT@CC, and the charge transfer resistance was increased by 2.45, 3.78, and 7.75 times, respectively. The dechlorination and hydrolysis governed the TCS degradation pathway in all electrolysis systems, and the toxicity of electrochemical reductive products was significantly decreased according to the Toxicity Estimation Software Tool analysis. This study presented a systematic assessment of the biofilm formation on modified electrodes in TCS reduction, and the undisputed experimental outcomes were obtained to enrich the knowledge of implementing modified electrodes for practical applications.

Potential negative effects of illumination on gravity-driven membrane system in treating sulfamethoxazole-containing water

Sunlight illumination could affect the stability and sustainability of the gravity-driven membrane (GDM) system. In this study, sunlight-based GDM and GDM were compared to treat sulfamethoxazole (SMX)-contained water. Results indicated that the removal of DOC, SMX and fluorescent pollutants became worse due to the bacteria activity limited by algae proliferation in sunlight-based GDM. But the total phosphorus (TP) removal rate increased by 74.72% due to algal assimilation. Algae promoted a thick and sticky biofilm with enrichment of extracellular polymeric substances (EPS), and the biofouling layer possessed the highest fluorescence intensity of pollutants. Long-term illumination reduced the biodiversity and richness in the biofouling layer. Pseudomonas was dominant in the sunlight-based GDM (71.3%), while Acinetobacter and Saccharimonadales were more prevalent in the GDM blank, which were related to SMX degradation. Besides, algae reduced the degradation pathways of SMX. Considering the application of GDM in rural areas, long-term illumination should be avoided.