The aim of this study was to understand the limiting flux in cross-flow microfiltration of a colloidal suspension in terms of the balance of hydrodynamic forces on a particle. Numerical simulations ...were carried out to estimate the lift force resulting from the cross-flow, drag force resulting from the convective flux, and net force. Assuming that the limiting flux is the flux when the net force on a particle is zero, we analyzed the simulation data to determine the correlation of two particle Reynolds numbers: Rep_Jlimit, calculated from the limiting flux, and Rep_uδ, calculated from the cross-flow rate. The results indicate that Rep_Jlimit is proportional to the square of Rep_uδ when a particle is at a dimensionless distance (distance divided by diameter) of less than 6.7 from the cake layer, in spite of the experimental fact that Rep_Jlimit is proportional to the 1.5th power of Rep_uδ. In contrast, Rep_Jlimit is proportional to the 1.5th power of Rep_uδ when a particle is at a dimensionless distance of 48–60. This means that the force balance of a particle at such a position, not at the membrane surface, determines the limiting flux in cross-flow microfiltration of a colloidal suspension.
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•Hydrodynamic force on a particle in cross-flow microfiltration is simulated.•We focus on drag force induced by flux and lift force induced by cross-flow.•The balance of forces on a particle in a viscous sublayer is discussed.•The relationship between the force balance and limiting flux is discussed.
The development of renewable energy technologies is of global importance. To realize a sustainable society, fossil-resource-independent technologies, such as solar- and wind-power generation, should ...be widely adopted. Pressure retarded osmosis (PRO) is one such potential renewable energy technology. PRO requires salt water and fresh water, both of which can be found at seawater desalination plants. The total power generation capacity of PRO, using concentrated seawater and fresh water, is 3 GW. A large amount of energy is required for seawater desalination; therefore, the introduction of renewable energy should be prioritized. Kyowakiden Industry Co., Ltd., has been working on introducing PRO to seawater desalination plants since 2001 and is attracting attention for its ongoing PRO pilot plant with a scale of 460 m
/d, using concentrated seawater and treated sewage water. In this study, we evaluated the feasibility of introducing PRO in existing desalination plants. The feasibility was examined based on technology, operation, and economy. Based on the number of seawater desalination plants in each country and the electricity charges, it was determined whether the introduction of PRO would be viable.
•Permeation of submicron particles through microfiltration membranes was tested.•The electrolyte and its concentration in feed dispersion affected the permeation.•The zeta potential of the particles ...should be the most negative for the permeation.•For the permeation of silica particles, the addition of 0.1 mM NaOH was the best.
The permeation behaviors of submicron silica particles that were smaller than the pore size of microfiltration membranes were studied in the presence of various electrolytes with changing the concentrations. Stable permeations that maintained the initial fluxes and high permeation ratios were demonstrated when the monodisperse submicron silica particles containing 0.1 mM sodium hydroxide (NaOH) as electrolytes were used as the feed. Under these conditions, the zeta potentials of the silica particles were the most negative, and, accordingly, the electro-repulsive effect was strengthened to avoid deposition onto the surface as well as clogging inside the pores of the membranes. A stable permeation in the presence of 0.1 mM NaOH was also demonstrated for polydisperse submicron silica particles. These results are helpful to develop a novel particle classification technique using the microfiltration membranes that we have been studying.
•Microfiltration of particles under high cross-flow rate was studied.•Complete prevention of fouling by particles was demonstrated in microfiltration.•Classification of bi-dispersed particles using ...membranes was demonstrated.
We investigated the effects of flow rate, particle diameter and initial flux on fouling mitigation in cross-flow microfiltration of suspensions containing silica and PMMA particles. Regardless of the difference in PMMA and silica, the fouling mitigation was more effective at a larger flow rate and larger particle diameter, due to sufficient hydrodynamic lift force. Lower initial flux was also shown to be better for the mitigation of fouling. Fouling was completely prevented when cross-flow filtration of particles with 1.5μm of diameter was carried out under a flow rate of 30Lmin−1 and 4.0×10−5m3m−2s−1 of initial flux. We also demonstrated that classification of bi-dispersed particles using membranes could be achieved by the cross-flow microfiltration, where fouling by larger particles than the pore size was completely prevented because of the sufficient hydrodynamic lift force and only the smaller particles permeated through the membrane. This classification remained stable for 3h while maintaining the flux and permeation of the smaller particles.
Pressure retarded osmosis （PRO） is an alternative source of renewable energy. PRO is a powerful generating technology that uses salinity differential as a driving force. The completed PRO system, ...uses brine and treated sewage water to reduce the power consumed by the seawater desalination plant by 10 ％ on a Mega-ton scale. The power generation cost is estimated to be 10.6 JPY / kWh because general-purpose parts and equipment can be obtained at low cost.In order to achieve a PRO system that uses seawater and treated waste water, it is necessary to develop a novel PRO membrane module. The PRO membrane module parameters to be developed are A value: 2.05×10－6 m/s/MPa and B value: 5.5×10－9 m/s. The power generation cost of a PRO system using seawater and treated sewage water is estimated to be 22 JPY / kWh using the developed novel PRO membrane module. The development of superior PRO membrane modules will revolutionize the worldʼs energy supply.
This study evaluates the feasibility of a power generation system adopting pressure retarded osmosis (PRO) using seawater and fresh water. The authors measured the membrane power density of a ...commercially available hollow fiber membrane module. The power density of the current membrane module is 3.1 W/m2, but 6.5 W/m2 is required to realize a commercially feasible power plant adopting PRO. In this case of the net output power is 2.8 W/m2 when the DS pressure was 1.5 MPa and the FS pressure was 0.1 MPa, respectively. The cost of power generation is 0.20 $/kWh assuming a commercial plant that uses 1 million m3 of seawater per day and has the calculated membrane power density. It is necessary to improve the A and B values per membrane module to realize this system. Here, the A and B values are coefficients representing water permeability and salt permeability, respectively. The target membrane power density can be achieved using A and B values per membrane module of 2.05 × 10−6 m/s/MPa and 5.5 × 10−9 m/s, respectively. This evaluation is based on theoretical calculations using the solution-diffusion model of membrane permeation in PRO.
•A PRO hollow fiber membrane module was considered for analysis.•Power generation cost was calculated by adopting the Loeb model.•The required performance of the membrane module was proposed.•A commercially feasible PRO power generation system can be realized.
Safety of potable reuse can be enhanced by improved water quality monitoring techniques for assessing water treatment processes. This study evaluated the efficacy of online bacterial counting for ...continuous monitoring of reverse osmosis (RO) membranes to remove bacteria using real-time bacteriological commercial counters and an on-site pilot-scale RO system. Prior to on-site assessments, the online bacterial counting was verified by comparing the measurement of fluorescent particles in water with flow cytometry. During a seven day pilot test of RO treatment at a water reclamation plant, online bacterial counts in RO permeate were monitored below 15 counts/mL; whereas the bacterial counts in RO feed water were approximately 2500 to 10,000 counts/mL. Removal rates of bacterial counts ranged from 2.6 to 3.1-log (average = 2.9-log) by continuously monitoring bacterial removal. This is greater than a 2-log reduction frequently determined using other water quality surrogates (i.e., electrical conductivity). Overall, the continuous monitoring of bacteria in RO feed and permeate can be implemented without the addition of chemicals to provide near real-time bacterial counts to measure their reduction after RO treatment. This can be developed for continuous performance monitoring of the RO process, providing greater assurance of microbial water quality after RO treatment.
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•Efficacy of online bacterial counting for monitoring RO system integrity was assessed.•Real-time bacteriological commercial counters were used for this study's assessment.•Online bacterial counting was verified by measuring surrogates.•Bacterial counts in RO feed and permeate were monitored online at the pilot scale.•A range of 2.6 to 3.1-log reduction in bacteria was determined by online monitoring.
Membrane fouling is a major challenge toward achieving direct nanofiltration (NF) treatment of surface water. This study aimed to evaluate the potential of the novel submerged flat-sheet NF membrane ...module to achieve low fouling propensity and high separation performance during the direct filtration of surface water. Laboratory-scale NF tests showed that the transmembrane pressure (TMP) increased only by 10 kPa over 24 d during the direct treatment of river and dam water. The NF system showed high (>80%) and stable rejection of color and organics, as well as low and variable conductivity rejection (28–47%). The rejection of negatively charged trace organic chemicals (TOrCs) was >50%, while that of uncharged or positively charged TOrCs was <50%. Another NF test that was conducted at a drinking water treatment plant showed negligible membrane fouling with a TMP increase of 3 kPa over 35 d. Separation performance of the NF system remained high: total organic carbon (TOC) removal was >70%, which was greater than the conventional rapid sand filtration system with powdered activated carbon and intermediate chlorine doses (TOC removal = 20–60%). Overall, this study demonstrated high water quality and stable system operation of the submerged flat-sheet NF system during direct treatment of surface water.
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•Efficacy of a novel submerged NF membrane in direct water treatment was evaluated.•Low permeate flux of 4 L/m2h led to a low level membrane fouling.•NF system showed high and stable rejection of color and organics at >80%.•Rejection of ions and many TOrCs was below 50%.
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