Low-biofouling membrane bioreactor: Effects of cis-2-Decenoic acid addition on EPS and biofouling mitigation.

Biofouling is inevitable in the membrane process, particularly in membrane bioreactors (MBR) combined with activated sludge processes. Regulating microbial signaling systems with diffusible signal factors such as cis-2-Decenoic acid (CDA) can control biofilm formation without microbial death or growth inhibition. This study assessed the effectiveness of CDA in controlling biofouling in membrane bioreactors (MBRs), essential for wastewater treatment. By modulating microbial signaling, CDA mitigated biofilm formation without hindering microbial growth. Analysis using Confocal Laser Scanning Microscopy (CLSM) revealed structural alterations in the biofilm, reducing biomass and thickness upon CDA application. Moreover, examination of extracellular polymeric substances (EPS) highlighted a decrease in total EPS, particularly effective polysaccharides. In addition, the possibility of shifting from high molecular weight EPS to low molecular weight EPS was revealed through the change in dispersion activity. The 56% extension of MBR operational lifespan resulting from the reduction in EPS is anticipated to offer potential cost savings and improved performance. Despite these results, further investigation is crucial to validate any potential environmental risks associated with CDA and to comprehend its long-term effects at various conditions.

Dispersive biofilm from membrane bioreactor strains: effects of diffusible signal factor addition and characterization by dispersion index.

Introduction: Biofilm occurs ubiquitously in water system. Excessive biofilm formation deteriorates severely system performance in several water and wastewater treatment processes. Quorum sensing systems were controlled in this study with a signal compound cis-2-Decenoic acid (CDA) to regulate various functions of microbial communities, including motility, enzyme production, and extracellular polymeric substance (EPS) production in biofilm. Methods: The addition of CDA to six strains extracted from membrane bioreactor sludge and the Pseudomonas aeruginosa PAO1 strain was examined for modulating biofilm development by regulating DSF expression. Results and discussion: As the CDA doses increased, optical density of the biofilm dispersion assay increased, and the decrease in EPS of the biofilm was obvious on membrane surfaces. The three-dimensional visual images and quantitative analyses of biofilm formation with CDA proved thinner, less massive, and more dispersive than those without; to evaluate its dispersive intensity, a dispersion index was proposed. This could compare the dispersive effects of CDA dosing to other biofilms or efficiencies of biofouling control practices such as backwashing or new cleaning methods.

Adsorption mechanisms on perfluorooctanoic acid by FeCl3 modified granular activated carbon in aqueous solutions.

Perfluorooctanoic acid (PFOA) is an emerging organic pollutant that is persistent in the environmental, and has been detected in humans, and wildlife. Several technologies, such as activated carbon (AC) adsorption have been used to remove PFOA from water. In this study, Fe-impregnation with/without post-thermal treatment of AC was applied to improve the adsorption of PFOA. The adsorption mechanisms were evaluated using three kinetic models: pseudo-first-order model, pseudo-second-order model, and intra-particle diffusion models. Interpretation of experimental results with the kinetic models revealed that chemical interactions, such as electrostatic attraction or complexation were suggested as the adsorption mechanisms along with physical adsorption. Two isotherm models demonstrated that the modified ACs (171.0-189.9 mg g-1) had increases in adsorption capacities than the unmodified AC (164.9 mg g-1), which indicated that modification improved the maximum achievable surface concentrations and adsorption affinity to some extent. The evenly distributed iron content on the modified ACs was visualized using an energy dispersive X-ray spectroscopy. The Fe-impregnated AC showed a reduction in the specific surface area and total pore volume; however, post-thermal treatment largely recovered the pore structures. The isotherms normalized by the accessible surface area revealed the importance of the Fe-impregnated surfaces on PFOA adsorption. Comparable pH values of the point of zero charge and chemical compositions of the ACs implied that an increase in Fe-impregnated surface was crucial to improve PFOA adsorption. Thus, substantial enhancement of PFOA removal can be achieved by implementing a proper strategy for AC modification, especially using Fe-impregnation.

Fabrication of Zwitterion TiO2 Nanomaterial-Based Nanocomposite Membranes for Improved Antifouling and Antibacterial Properties and Hemocompatibility and Reduced Cytotoxicity.

Although zwitterion nanomaterials exhibit outstanding antifouling property, hemocompatibility, and antibacterial activity, their poor solubility in organic solvents limits their practical applications. In the present study, natural lysine (amino acids) was surface-grafted onto one-dimensional (1D) TiO2 nanofibers (NFs) through an epoxy ring opening in which the 3-glycidyloxypropyl (dimethoxy) methyl silane was used as a coupling agent. Chemical binding and morphological studies, such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, were conducted to confirm the successful grafting of lysine onto the TiO2 NFs. The lysine-grafted TiO2 NF-polyethersulfone (PES) membrane induced electrostatic interactions and increased the surface charges from -28 to 16 mV in ζ-potential analysis. The lysine exhibited zwitterion characteristics owing to the presence of amino (cations) and carboxyl (anions) functional groups. Moreover, the modified TiO2-PES zwitterion membranes exhibited good water flux performances compared to the pristine membrane. ZT-4 membrane displayed the highest water fluxand bovine serum albumin (BSA) rejection of 137 ± 1.8 L m-2 h-1 and 94 ± 1%, respectively. The cell viability results revealed that the zwitterion PES membrane had excellent biocompatibility with peripheral blood mononuclear cells. The present work offers a convenient strategy to improve the hydrophilicity, antifouling property, and hemocompatibility of modified TiO2-PES zwitterion membranes for their biomedical and blood-contacting applications such as hemodialysis.

Humic acid removal and microbial community function in membrane bioreactor.

A membrane bioreactor with humic acid substrate (MBR-H) was operated to investigate organic removal and membrane performance. Approximately, 60% of chemical oxygen demand removal was observed in MBR-H. The biosorption capacity reached to the maximum value of 29.2 mg g-1 in the experiments with various activated sludge concentrations and the amount adsorbed on the newly produced microbes was limited. To understand key functions of microorganisms in the biodegradation of humic acid, the microbial community was examined. The dominant phylum was changed from Actinobacteria at the raw sludge to Proteobacteria at the MBR-H. Especially, great increases of ß-, γ-, and δ-Proteobacteria in the MBR-H indicated that those class of Proteobacteria played a vital role in humic acid removal. Investigation at the genus level showed enrichment of Stenotrophobacter in the MBR-H, which indicated the presence of metabolites in the proposed humic substance degradation pathway. In addition, the bacteria producing extracellular polymeric substances were increased in the MBR-H. Substantial variation of microbial community function was occurred in the MBR to degrade humic acid. Operational parameters in MBRs might be sought to maintain water permeability and to obtain preferable condition to evolution of microbial consortia for degradation of the refractory organic matter.

Recent development of photocatalytic nanomaterials in mixed matrix membrane for emerging pollutants and fouling control, membrane cleaning process.

Membrane-based separation is an area of extensive research in wastewater treatment, which includes the control of pollution and reuse of water. The fabrication and modification membranes for prevention and reduction of pollution to provide quality water with fouling-free membranes through the wastewater treatment are the progressive approaches in the industries. Several research works have been extensively working on modification and fabrication polymer membranes with integration of advanced oxidation process (AOP) to overcome the membrane fouling. This review describes the modification of membranes with various nanomaterials such as inorganic and modified carbon which can be used for pollution control and enhance the anti-fouling properties of ultrafiltration membranes. The effects on nanomaterials loading percentage, nanomaterials interaction with the polymers and rejection performances of the surface tuned membrane are elaborated. Secondly, the fouled membrane chemical cleaning process and NaOCl adverse effect on polymer structure are critically investigated. Moreover, state-of-art in the photocatalytic self-cleaning process are reviewed in this manuscript, and future perspectives on fouling mitigation based on AOP integrated membrane technology have also discussed.

Disinfection by-product formation potential of algogenic organic matter from Microcystis aeruginosa: Effects of growth phases and powdered activated carbon adsorption.

Algae can exhibit different disinfection by-product formation potential (DBPFP) depending on the characteristics of the algogenic organic matter (AOM) released during growth. In this study, the amount of AOM released by Microcystis aeruginosa and its DBPFP were compared between the exponential growth phase and the death phase. Moreover, the efficiency of DBPFP removal through powdered activated carbon (PAC) adsorption was evaluated. The correlations between DBPFPs and dissolved organic carbon concentration or ultraviolet absorbance at 254 nm (UV254) were also investigated to predict DBPFPs. Among DBPFPs, which were higher at the death phase, the formation potential (FP) of haloacetic acid was the highest. In addition, the high relative haloacetonitrile FP at the death phase indicated that a relevant portion of the intracellular organic matter derived from cell autolysis was converted into a large amount of haloacetonitriles. Furthermore, PAC addition reduced all DBPFPs at both growth phases. PAC was found to selectively adsorb dichloroacetic acid precursors at the death phase and dichloroacetonitrile precursors at both growth phases. Finally, UV254 showed greater correlations with the three DBPFPs at all growth phases. These results highlight the possible use of UV254 as an alternative analytical tool for fast determination of M. aeruginosa DBPFPs.

Characteristics of organic fouling, reversibility by physical cleaning and concentrates in forward osmosis membrane processes for wastewater reclamation.

Numerous advantages of forward osmosis (FO) include operation at low or no hydraulic pressure, high rejection of a wide range of contaminants, and low irreversible fouling. The FO has been investigated to reduce effluent discharge in wastewater reclamation. The application of wastewater effluent as a feed stream to FO yields fouling on the active layer of the FO membrane. Fouling was examined using two compounds (i.e., alginate and humic acid) with distinguished hydrophobic properties. The repeated filtration and surface wash were applied and flux decline and reversibility of physical cleaning were evaluated. In addition, the characteristics of fouling cakes and concentrates were also analyzed. The foulants showed different behaviors in flux decline. The thick cake layer of alginate was obvious and the cake enhanced concentration polarization was also observed. The recovery results along with the FTIR spectra and FE-SEM images proved that the surface cleaning was not effective to detach foulants, especially for alginate fouling. The osmotic backwash showed greater flux recovery for alginate fouling than humic acid fouling, which indicated that restoring membrane pores or disturbing cake layers by osmotic backwash might be successful for the foulants for strong interactions between foulants and foulants. The concentrates were mostly composed of humic substances and low-molecular weight neutrals. The differences in the relative portions of the major components were occurred in the concentrates implying that the organic properties of the feed water and also interactions of foulants and membranes should be evaluated prior to determination of disposal options for concentrates.

Natural organic matter removal from algal-rich water and disinfection by-products formation potential reduction by powdered activated carbon adsorption.

Algal blooms intensified operational problems in water treatment due to the increases of taste- and odor-causing compounds and natural organic matter (NOM). Effects of powdered activated carbon (PAC) addition during algal blooms on NOM removal was investigated in this study using an algal-rich water. Water quality analyses including dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254) and specific UV absorbance (SUVA) were performed to elucidate characteristics of NOM removal by PAC adsorption. Variations of MW distributions and emission/excitation matrix (EEM) spectra with increasing PAC dosages were also measured. In addition, formation potential (FP) of trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs) was evaluated with increasing PAC dosage. The correlations between disinfection by-products formation potential (DBPFP) and water qualities such as DOC, UV254, SUVA, and EEM spectra were also investigated to identify factors associated with DBPFP. The PAC addition was effective to remove NOM, especially low molecular weights NOM and proteinaceous substances with weak aromatics. The PAC addition showed the consistent reduction of THMFPs, HAAFPs, and HANFPs with increasing PAC dosage while the greater reduction of HAN precursors was eminent compared to the other two FPs. The close correlations between UV254 and the three DBPFPs were obtained. The low molecular weight (i.e., 1-700 Da) NOM and three fluorescence spectra peaks, i.e., T1, A and C peaks, also showed high correlation factors with the three DBPFPs. Those analyses with high correlations with DBPFPs would provide useful information to reduce DBPs during algal blooms.

Monitoring biofouling based on aerobic respiration in reverse osmosis system.

A monitoring method of biofouling in reverse osmosis (RO) system was proposed based on the fluorescent signal of resorufin, which is reduced by nicotinamide adenine dinucleotide released from viable cells during aerobic respiration. The fluorescent signal of resorufin reduced by planktonic cells and microorganisms of biofilm showed linearity, indicating its feasibility to monitor biofouling in a RO system. For the application of the method to the lab-scale RO system, the injection concentration of resazurin and the injection flow rate were optimized. Biofilm on RO membranes continuously operated in a lab-scale RO system was estimated by resorufin fluorescence under optimized detection condition. As a result, resorufin fluorescence on RO membrane showed a significant increase in which the permeability of RO system decreased by 30.48%. Moreover, it represented the development of biofilm as much as conventional biofilm parameters such as adenosine triphosphate, extracellular polymeric substances, and biofilm thickness. The proposed method could be used as a sensitive and low-cost technology to monitor biofouling without autopsy of membranes.

Comparison of formation of disinfection by-products by chlorination and ozonation of wastewater effluents and their toxicity to Daphnia magna.

This study compared the two most frequently used disinfectants (i.e., chlorine and ozone) to understand their efficiency in wastewater effluents and the ecotoxicity of disinfection by-products created during chlorination and ozonation. Four trihalomethanes (THMs) and nine haloacetic acids (HAAs) were measured from a chlorine-disinfected sample and two aldehydes (i.e., formaldehydes and acetaldehydes) were analyzed after ozonation. Chlorination was effective for total coliform removal with Ct value in the range of 30-60 mg-min/L. Over 1.6 mg/L of ozone dose and 0.5 min of the contact time presented sufficient disinfection efficiency. The concentration of THMs increased with longer contact time (24 h), but that of HAAs showed little change with contact time. The measured concentration of formaldehyde at the ozone dose of 1.6 mg/L and the contact time of 9 min showed the greatest value in this study, approximately 330 µg L(-1), from which the corresponding ecotoxicity was determined using an indicator species, Daphnia magna. The ecotoxicity results were consistent with the toxicological features judged by occurrence, genotoxicity, and carcinogenicity. Both the disinfection efficiency as well as the DBP formation potential should therefore be considered to avoid harmful impacts on aquatic environments when a disinfection method is used for wastewater effluents.

Oxidant production from corrosion of nano- and microparticulate zero-valent iron in the presence of oxygen: a comparative study.

In aqueous solution, zero-valent iron (ZVI, Fe(0)) is known to activate oxygen (O2) into reactive oxidants such as hydroxyl radical and ferryl ion capable of oxidizing contaminants. However, little is known about the effect of the particle size of ZVI on the yield of reactive oxidants. In this study, the production of reactive oxidants from nanoparticulate and microparticulate ZVIs (denoted as nZVI and mZVI, respectively) was comparatively investigated in the presence of O2 and EDTA. To quantify the oxidant yield, excess amount of methanol was employed, and the formation of its oxidation product, formaldehyde (HCHO), was monitored. The concentration of HCHO in the nZVI/O2 system rapidly reached the saturation value, whereas that in the mZVI/O2 system gradually increased throughout the entire reaction time. The mZVI/O2 system exhibited higher yields of HCHO than the nZVI/O2 system under both acidic and neutral pH conditions. The higher oxidant yields in the mZVI/O2 system are mainly attributed to the less reactivity of the mZVI surface with hydrogen peroxide (H2O2) relative to the surface of nZVI, which minimize the loss of H2O2 by ZVI (i.e., the two-electron reduction of H2O2 into water). In addition, the slow dissolution of Fe(II) from mZVI was found to be partially responsible for the higher oxidant yields at neutral pH.