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Bacterial aerosols resulting from membrane bioreactor (MBR) processes, which require excessive aeration in a confined space, are important to investigate because of their possible adverse effects on human health. This study investigated the influence of solid retention time (SRT) on bacterial aerosols from MBRs. Moreover, powdered activated carbon (PAC) and calcium were used to attenuate bacterial aerosol emissions from MBRs. The particulate matter (PM) emitted from the MBRs was reduced by 30.5 and 25.2% at SRTs of 20 and 80 d, respectively, compared to the level emitted at an SRT of 10 d. Total cell counts were similarly reduced at SRTs of 20 and 80 d. Longer SRTs also led to greater reductions in the particle size distribution of the sludge within 10 μm. Several factors in the MBR influenced the behavior of the bacterial aerosol emissions from the MBRs. This study showed that changes in viscosity and particle size induced by the SRT influenced the bacterial aerosol emissions in MBRs. Therefore, SRT was identified as an important design parameter affecting bacterial aerosol emissions in MBR processes. The amounts of particulate matter and bacterial aerosols were reduced in MBRs using PAC and calcium, both of which exerted an immediate effect on the bacterial aerosol emissions in MBRs by increasing the aerosol-particle size.

The present research attempted to assess the seasonal variation of engineered nanoparticles (ENPs) in a major municipal wastewater treatment system. A monthly survey over a 12-month period was conducted to monitor the concentration of TiO2 and ZnO nanoparticles throughout the treatment process. Results showed inflow concentrations in the range of 21.6 ± 5.0–391.0 ± 43.0 μg/L and 20.0 ± 12.0–212.0 ± 53.0 μg/L for TiO2 and ZnO, respectively. Seasonal pattern of the inflow ENPs concentration showed elevated value in the summer and winter periods for both TiO2 and ZnO. Based on the concentration profile, the hydraulic flow rate, and the concentration of mixed liquid suspended solid (MLSS), the daily mass loading (DML) or mass flow rate of nanoparticles and the mass ratio of engineered nanoparticle to MLSS were calculated. DML provided a real-time estimate of temporal distribution of ENPs in the treatment processes. Results indicated a daily mass loading of 50.1 ± 12.7 and 44.7 ± 14.1 kg/day (yearly average) for TiO2 and ZnO, respectively. The amount of ENPs captured by sludge particulates were, yearly average, of 7.1 kg-ZnO/d and 39.8 kg-TiO2/d, and 8.9 kg-ZnO/d and 25.1 kg-TiO2/d, by the primary and the secondary sludge particulates, respectively. ENPs to MLSS mass ratio also showed a seasonal patter similar to the inflow ENPs concentration, where summer and winter periods showed elevated values. Additionally, loss of ENPs throughout the treatment plant that was not accounted for, also can be estimated from the daily mass loading rate and the mass ratio of ENPs to MLSS. Based on the seasonal distribution of ENPs in wastewater treatment systems, especially the daily mass loading rate, it is possible to estimate the uses of nanoparticle-related commercial and personal care products in the urban areas and enable decision-making on the strategy of sludge disposal management.

The current study developed a rationalized method for the quantification and identification of engineered nanoparticles (ENPs) in wastewaters. A review of current literature revealed that overall, presently available methods focused on single ENP mostly and were applicable mainly to samples of low organic loadings or under well-controlled laboratory conditions. In the present research, procedures including dialysis for desalting and low-temperature oxidation for organic removal were used to pretreat samples of high organic loadings, specifically, municipal wastewater and sludge. SEM mapping technique identified the presence of nanoparticles, which was followed by ICP-OES quantification of different engineering nanoparticles in wastewater and sludge samples collected from two major regional municipal wastewater treatment plants. Results showed successful identification and quantification of nano-size titanium and zinc oxides from wastewater treatment plants studied. Concentration profile was mapped out for the wastewater treatment plants (WWTPs) using the method developed in this research. Results also showed an overall 80% and 68% removal of titanium and zinc by primary and secondary sludge particulates, respectively. Mass flux of engineered nanoparticles (ENPs) was also calculated to estimate the daily flow of engineered nanoparticles in the system.

This study investigated the effect of powdered activated carbon and calcium on trihalomethane toxicity in zebrafish embryos and larvae in hybrid membrane bioreactors. Two hybrid membrane bioreactors were configured with the addition of powdered activated carbon or calcium to reduce the trihalomethane formation potential. Trihalomethane formation decreased by approximately 37.2% and 30.3% in membrane bioreactor-powdered activated carbon and membrane bioreactor-calcium, respectively. Additionally, the toxic effect of trihalomethane formation was examined on zebrafish embryos and larvae. About 35% of the embryos exposed to trihalomethanes (800 ppb) showed signs of deformation, with the majority displaying coagulation within 24 h after exposure. Color preference tests, which were conducted to identify any abnormal activities of the embryos, showed an increase in preference from short to longer wavelengths upon exposure to high levels of trihalomethanes. This may indicate damage to the optical organs in zebrafish when exposed to trihalomethanes. Behavioral analysis showed reduced mobility of zebrafish larvae under different trihalomethane concentrations, indicating a decrease in the average activity time with an increasing trihalomethane concentration. The membrane bioreactor effluents were toxic to zebrafish embryos and larvae in the presence of high trihalomethane concentrations. To understand the mechanism behind trihalomethane toxicity, further studies are needed.

A new meshed tube filtration (MTF) process was developed and assessed as a low energy-consuming pretreatment process that withstands algal blooms (i.e., red tide). This process can potentially replace the dissolved air flotation (DAF) process in typical seawater reverse osmosis (SWRO) desalination plants. Two marine microalgae species, namely C. polykrikoides and T. suecica, were first cultivated and then utilized to simulate algal bloom conditions in the lab-scale filtration experiments. The algal matter was coagulated and circulated by aeration in the MTF system that was filled with cylindrical polypropylene meshed tubes with ciliary ends and had the ability to capture coagulated algae in an effective manner. The efficiency of the MTF process to remove algal cells was significantly enhanced by optimizing the coagulant dose and the aeration rate. In order to further verify the MTF performance, DAF experiments were conducted, under similar conditions, for the comparison of algal removal effectiveness and energy consumption rates. The results showed high removal rates of algal cells as well as turbidity for MTF, although only a limited reduction of algal organic matter (AOM) was observed. When DAF was operated at energy consumption levels equivalent to MTF, its algae removal rate was lower than that of MTF. Furthermore, under optimal operating conditions, MTF consumed approximately one-third of the energy needed for DAF operation, mainly due to the fact that MTF requires less aeration. For future improvements in the AOM removal process, an energy-efficient pretreatment process could be realized for SWRO desalination facilities facing potential algal blooms.

Hollow microspheres should be characterized in terms of physicochemical aspects to understand the flotation effect principle. There have been insufficient studies on the effect of hollow microspheres in water treatment in terms of flotation. In this study, various analytical and experimental approaches were utilized to identify the flotation characteristics and understand the effect of hollow microspheres on flotation. These approaches included analytical methods such as particle count and zeta potential measurements, scanning electron microscopy-energy dispersive X-ray spectroscopy analysis, X-ray photoelectron spectroscopy, a floc breakage experiment, and a collision efficiency model. The hollow microspheres were spherical shape with an average size of 50 μm. The microspheres were identified to have a higher negative charge (−69.1 mV) than microbubbles (−51.1 and −30.5 mV). The binding energy of Si–O from the hollow microspheres showed the highest peak at 103.18 eV and 61,503.7 counts/s. Si–O binding structure and the molecular structure of the SixOx series were considered to be a structure in which Si 3 2 − is bonded to oxygen ion. The optimum floc breakage condition was determined to be 15 min. The number of particles increased because the average particle size is increased with the concentration of hollow microspheres injection. The turbulent flocculation (TF) model was confirmed to be consentient to the experimental data in comparison with the white-water bubble blanket (WWBB) model. As a result, the hollow microspheres had the characteristic of increasing floc size so that flocs can be floated easily.

The diversity of organic micropollutants (OMPs) in aquatic environments has been increasing rapidly during the last decade. Therefore, it is important to monitor and attenuate emerging contaminants before they can negatively affect the aquatic environment. However, due to the diversity and complexity of OMPs, there are limitations to using a single method for treating a combination of these pollutants. To address this issue, a mobile water treatment system (MWTS) equipped with different treatment units was designed to remove OMPs under field conditions. The MWTS was configured with various modular units including coagulation, flocculation, dissolved air flotation, membrane filtration, ozone oxidation, granular activated carbon, and UV disinfection. Each treatment unit could be operated either individually or in different combinations to identify the optimal configuration of treatment units for the removal of OMPs. To investigate the effectiveness of the MWTS, twelve OMPs were selected and introduced simultaneously into the feed water samples collected from different rivers throughout Korea. The current study proved that the MTWS is an effective solution to treat OMPs and is a time saving treatment system. The combined effects of the different treatment units removed over 99% of the selected OMPs, regardless of their physicochemical properties. Moreover, since the system is mobile, on-site analyses can be conducted to identify the most effective treatment method and configuration for each OMP.

The present research attempted to assess the seasonal variation of engineered nanoparticles (ENPs) in a major municipal wastewater treatment system. A monthly survey over a 12-month period was conducted to monitor the concentration of TiO

In this research, silica-based fluorescent particles were synthesized and used as a surrogate detector to evaluate the integrity of a compromised flat sheet membrane. Three different sizes of particles were synthesized and dyed with a fluorescent dye to make a fluorescence image under a UV light. Experiments were designed to test the sensitivity of the detection limit, stability of particles, and reliability of the proposed method. UV spectrometer and image analysis were used to evaluate the detection limits and measure the concentration and mass of the particles in the feed and permeate. For the stability of the particles, dye-leakage tests were conducted to estimate the amount of fluorescent decay when fluorescent particles were dissolved in an aqueous solvent. The effect of the particles on the membrane fouling was also investigated by conducting a batch filtration test of undamaged membranes. To examine the reliability of the proposed method, a series of filtration tests were performed with t...

In this study, a new approach utilizing silica-based fluorescent particles as a surrogate for checking the integrity of microfiltration membranes was systematically investigated. The fluorescent particles were synthesized as spheres with diameters of 0.5–0.7 μm and used to test the integrity of microfiltration membranes with nominal pore sizes of 0.25 μm. The fluorescent particles only flowed through the damaged parts of membranes. The permeates were then collected and filtered through a GF/C filter to collect the outflow particles. The collected particles were placed under a UV lamp, and the fluorescence was photographed with a digital camera. The mass of the outflow particles was estimated by analyzing the images of the fluorescence pictures. To estimate the size of damage on the membrane surface, the functional relationship between the damaged area of the membrane and the mass of fluorescent outflow particles was established using a dimensional analysis. In addition, the dead-end filtration results show that at particle concentrations >10 mg/L, the flux decline was approximately 10% even then the particle concentration was increased to 100 mg/L. The cake resistance caused by particle deposition increased the total membrane resistance only by 10% in long-term filtration. Therefore, the synthesized fluorescent silica particles are a suitable surrogate for membrane integrity tests.

The adhesion property of Pseudomonas putida on reverse osmosis (RO) membranes was systematically investigated using the asymmetrical flow field-flow fractionation (AsFl-FFF). The adhesion of P. putida on two different RO membranes was investigated by varying the salt concentration of carrier solution to evaluate the effect of ionic strengths and membrane characteristics on the biofouling potential of RO membranes. The elution peak in terms of peak retention time and area obtained from AsFl-FFF analysis was used to evaluate the adhesion tendency of P. putida under different solution ionic conditions. Results showed that P. putida was favorably attached to RO membranes at higher ionic strengths. Hydrophobic RO membrane exhibited more adhesive property to P. putida compared to the tested hydrophilic membrane under the lower ionic strength condition. The effect of solution ionic strength on the adhesion tendency was more influential than membrane characteristics. In addition, the influence of ionic strength variation on adhesion tendency was more sensitive to hydrophilic membranes than hydrophobic membranes.

In this study, various foulants are tested with the conventional fouling indexes such as silt density index (SDI) and modifi ed fouling index (MFI) under high TDS conditions to evaluate the practical appliance of these indexes for RO desalination. A new approach for developing a more realistic fouling index is investigated based on fl ow fi eld-fl ow fraction (Fl-FFF) analysis. The results showed that the SDI and MFI for the feed waters containing the particulate foulants larger than the pore size of the membranes used in SDI and MFI measurements were not signifi cantly aff ected by the feed water salinity. This is due to the fact that the main fouling mechanism is the deposition of particles on the membrane surface and, hence, the cake fi ltration controls the permeate fl ux. In case of the particles as well as organics smaller than the pore size of the membranes, the SDI and MFI failed to accurately predict the fouling potential of feed waters with high salinity. In addition, the characteristics of membrane (i.e., hydrophobicity) also played an important role in determining membrane performance. Based on the results from Fl-FFF analyses, it was demonstrated that both qualitative and quantitative assessments of fouling potential of feed waters with diff erent foulants and TDS conditions were possible.

The amount of water extracted for municipal, agricultural and industrial purpose has been about 36.6% of total run-off in Korea. The long-term water resources plan by the Ministry of Construction and Transport predicted approximately 340 million tons of water shortage in 2011. Based on the prediction, construction of a new dam was necessary. The Ministry of the Environment (MOE) launched the Water Demand Control Plan in the year 2000 to save 790 million tons of water to avoid construction of new dams. In 2003, the MOE evaluated the achievement of the Control Plan and declared the Plan successfully saved about 450 million tons of water per year using several means. The declared achievement has been examined using the water statistics between 1999 and 2004. The analysis has revealed that the conservation has not been as successful as declared. Actual reduction in water production between in 1999 and in 2004 was only about 116 million tons instead of 450 million tons that the MOE announced. Probably the MOE ...

a Department of Civil, Environmental & Architectural Engineering, Korea University, 1, 5-Ga, Anam-Dong, Sungbuk-Gu, Seoul, 136-713, Republic of Korea b Environmental Research Team, R&D Institute, Kolon E&C, 199-5, Jeondae-Ri, Pogok-Eup, Cheoin-Gu, Yongin-Si, Gyeonggi, 449-815, Republic of Korea c School of Civil & Environmental Engineering, Kookmin University, 861-1, Jeongneung-Dong, Seongbuk-Gu, Seoul, 136-702, Republic of Korea