Sea water reverse osmosis (SWRO) would face some problems like energy saving and management of concentrated brine. To solve these problems at the same time, the energy recovery by Pressure Retarded ...Osmosis (PRO) was proposed in the Mega-ton Water System project. Prototype plant test was conducted using concentrated brine from SWRO plant and fresh water from regional waste water treatment facility. Hollow-fiber membrane module were examined in the prototype plant and the test operation was carried out for more than one year. We have reached the maximum membrane power density, 13.5W/m2, using 10-in. module. Followings were still existing obstacles for further effective PRO. It was also challenging how to get clean fresh water from waste or river water without additional cost. Innovative new technologies were also required to address these concerns. We have also estimated plant cost and surveyed financial impacts on the energy saving of SWRO operation, based on the situation of currently operated SWRO plants worldwide, especially about the Mega-ton scale ones. Those studies indicated that potential market of PRO was 1–2GW, and 10% energy saving was possible on the Megaton scale SWRO plants. Those results indicate that the commercialization plant would be available very near future.
•Our PRO system was used concentrated brine and treated wastewater.•Hollow fiber membrane module examined in our PRO prototype plant.•UF membrane treatment and the chemical dosing made the operation available.•Energy reduction for sea water reverse osmosis is possible by our PRO system.
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.
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.
Pre-concentration is essential for energy and resource recovery from municipal wastewater. The potential of forward osmosis (FO) membranes to pre-concentrate wastewater for subsequent biogas ...production has been demonstrated, although biofouling has also emerged as a prominent challenge. This study, using a cellulose triacetate FO membrane, shows that chloramination of wastewater in the feed solution at 3⁻8 mg/L residual monochloramine significantly reduces membrane biofouling. During a 96-h pre-concentration, flux in the chloraminated FO system decreased by only 6% and this flux decline is mostly attributed to the increase in salinity (or osmotic pressure) of the feed due to pre-concentration. In contrast, flux in the non-chloraminated FO system dropped by 35% under the same experimental conditions. When the feed was chloraminated, the number of bacterial particles deposited on the membrane surface was significantly lower compared to a non-chloraminated wastewater feed. This study demonstrated, for the first time, the potential of chloramination to inhibit bacteria growth and consequently biofouling during pre-concentration of wastewater using a FO membrane.
The new sustainable power generation technique which can convert the salinity gradient energy to the hydroelectric energy is expected. This technique is called Pressure Retarded Osmosis (PRO). ...Clarification of the relationship between the performance of the PRO module and permeation characteristics is important. It’s already known that increase of salt concentration can increase the permeation flux through the membrane. As the conventional researches, the effects of increase of fresh water concentration and concentration polarization have evaluated. In this research, relationship between the salt concentration and membrane module is focused. The effects of fresh water dissipation and flow state of salt water in hollow fiber membrane module as new factors are researched with experiment and numerical simulation. As result, in the case of low salt concentration, permeation is not caused sufficiently in module. On the other hand, in the case of high salt concentration, very low permeation flux area exists extensively, and the effects of concentration polarization and fresh water dissipation are relatively large. Therefore salt water flow rate and module shape should be changed for each salt concentration.
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•Ppy grafted CMC carbon aerogels are applied in CDI for the first time.•Ppy/CA-2 shows excellent electrochemical and electrosorption performance.•The salt adsorption capacity of ...Ppy/CA-2 reaches 34.03 mg g−1.•Ppy could capture Cl− via surface redox reaction during CDI.
Capacitive deionization (CDI) has been identified as a prospective desalination technology. There has been increasing interest in the exploration of electrodes with high electrochemical properties and salt adsorption capacity. Here, polypyrrole (Ppy)/CA electrodes were prepared by grafting Ppy on carbon aerogel (CA) via in-situ polymerization and applied in CDI desalination. Compared with CA, the Ppy/CA samples display higher specific capacitance, lower charge transfer resistance as well as enhanced ion diffusion rate. Particularly, Ppy/CA shows enhanced pseudocapacitance generation and the synergistic effect of the diffusion-controlled dominating process and capacitive process by Ppy introduction, conducive to the desalination performance. The optimal Ppy/CA-2 CDI system exhibits high adsorption capacity (34.03 mg g−1 with 500 mg L−1 solution), fast salt adsorption rate (0.053 mg g−1 s−1 with 500 mg L−1 solution) together with reasonable long-term stability. The outstanding desalination performance is principally on account of the positively charged nitrogen atoms of Ppy could capture Cl− well through the surface redox reaction in CDI and the most positively charged nitrogen in Ppy/CA-2 contribute its best adsorption capacity. The simple preparation method, excellent electrochemical properties, outstanding adsorption performance, and good cycling stability render Ppy/CA-2 a potential CDI electrode material.
Pressure Retarded Osmosis (PRO) is expected to the new power generation system. The performance of the PRO module is closely relating to the permeation characteristics. In this paper, when fresh ...water flow rate is changed, 4 factors related to the reduction of permeation flow rate are researched with experiment. These 4 factors are concentration of solute in fresh water, salt leakage, concentration polarization, and dissipation of fresh water. The characteristics of the fresh water flow and permeation are studied for the hollow fiber membrane module used in PRO system. It is cleared that the dissipation of fresh water and the concentration polarization in hollow fiber largely influence to the reduction of permeation flow rate in the case of the low fresh water flow rate. Concentration of solute in fresh water, salt leakage influence to the reduction of permeation flow rate in the case of high fresh water flow rate.
Microbiological risks associated with drinking water can be minimized by providing enhanced integrity monitoring of bacterial removal by water treatment processes. This study aimed to evaluate the ...efficacy of real-time bacteriological counters for continuously assessing the performance of a full-scale sand filter to remove bacteria. Over the course of an 8-day evaluation, online counting of bacteria was successfully performed, providing continuous bacterial counts in the sand filter influent and effluent over approximate ranges from 17 × 104 to 94 × 104 and from 0.2 × 104 to 1.3 × 104 counts/mL, respectively. Periodic variations were observed with online bacterial counts in the sand filter influent because of the changes in the performance of flocculation and sedimentation processes. Overall, online removal rates of bacteria determined during the full-scale test were 95.2–99.3% (i.e., 1.3–2.2-log), indicating that online bacterial counting can continuously demonstrate over 1.3-log removal in the sand filter. Real-time bacteriological counting technology can be a useful tool for assessing variability and detecting bacterial breakthrough. It can be integrated with other online water quality measurements to evaluate underlying trends and the performance of sand filters for bacterial removal, which can enhance the safety of drinking water.
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•Performance of a full-scale sand filter for bacterial removal was evaluated.•Online counting of bacteria in the filter influent and effluent was performed.•Periodic variations were observed with online bacterial counts.•Online removal rates of bacteria determined during the evaluation were over 1.3-log.
A promising electrode material, manganese dioxide (MnO2), has been widely studied for capacitive deionization (CDI) desalination and recently researched for heavy metal removal. However, there are ...significant differences in the performance of MnO2 in applications for heavy metal removal and desalination. In this paper, the mechanism for different electrochemical processes of Cd2+/Na+ ions on MnO2 electrodes was comprehensively studied. MD simulations show that the diffusion performance of Cd2+ is much slower than that of Na+ in the presence of CdCl−, leading to a lower adsorption rate of Cd2+. Of the two ion storage mechanisms (capacitive and diffusion-controlled progress), capacitance contributions provided 65.6% of the total in the Na+ electrolyte, while diffusion-controlled progress contributed 55.2% in the Cd2+ electrolyte. For diffusion, tunnelling is the main storage mechanism for Na+; instead, Cd2+ undergoes a sequential surface redox process: (1) the combination of Cd2+ and O atoms from Mn-O-Mn results in the transition from Mn4+ to Mn3+, and (2) the H substitution reaction on Mn-O-H is generated from (1). Therefore, the adsorption capacity of Cd2+ is closely related to the chemical state of MnO2 on the surface, which results in worse cycling stability than Na+.
•The presence of CdCl+ reduces the migration of Cd2+ on the electrode surface.•Different faradaic processes are responsible for differences in the adsorption of Cd2+ and Na+.•The surface redox mechanism for Cd2+ in MnO2 involves two processes.•The results of this study provide significant insights into the cation storage mechanism of MnO2.
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.
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