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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 × 10 4 to 94 × 10 4 and from 0.2 × 10 4 to 1.3 × 10 4 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., Chemosphere, 229, pp.509-514; 2019

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 m3/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.

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) was50%, while that of uncharged or positively charged TOrCs was50%. 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 was70%, 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.

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+.

We developed a novel fiber filtration system, which allows the filter bed packing density to be adjusted, to treat raw water of differing turbidities without coagulants. A bench-scale fiber filter is used to remove 5–20 μm poly(methyl methacrylate) particles with high efficiency, without the use of coagulants. The obtained data are analyzed using Yao’s model and regression models. The first filtration cycle achieved a benchmark removal efficiency of 90 % of 5 μm particles for 71 min with a Darcy velocity of 38.2 m/h. Each cycle included a backwash process, but the filtration time gradually decreased to about 46 min by the 5th cycle. However, pressure loss did not increase significantly during the filtration cycles. The shortening duration of filtration over operating successive cycles was postulated as residual particles remaining in the bed after backwash and rinsing. We measured pressure loss at various Darcy velocities for fiber filters with different packing densities and found that the square term of Darcy velocity in Ergun’s model was significant by the regression analysis. Based on the experimental results of the novel fiber filtration system, we compare the performance and running cost of a conventional fiber filtration system and a rapid sand filtration system. The novel fiber filtration system comprising 940 mm fiber filter elements at a packing density of 110 g/L removed 96 % of 5 μm particles at a Darcy velocity about four times greater than that of the rapid sand filter. The running cost of the novel fiber filter was estimated to be approximately one-sixth that of the conventional fiber filter using poly aluminum chloride and less than approximately 30 % of the sand filter.

Direct nanofiltration (NF) of secondary treated effluent can significantly simplify water recycling, especially for small scale operations. This study evaluated the performance of a novel flat-sheet submerged NF membrane module at low water flux to minimize membrane fouling. The separation performance of the NF system was assessed by periodically measuring the color, turbidity, pH, UV light absorbance at the wavelength of 254 nm, and total organic carbon concentrations of the NF feed water and permeate. During the 48-d test, negligible membrane fouling was found when direct NF treatment of secondary wastewater effluent was conducted at a water flux of 3 L/m2h. The trans-membrane pressure increased by less than 0.072 kPa/d. The foulant layer on the membrane surface was readily removed by simple physical cleaning, which suggests that the reversible fouling was the major fouling mechanism. Direct NF treatment achieved high and stable removal of organics (total organic carbon removal of >80 %) during the operation period. This study demonstrated the efficacy of the direct NF treatment using a submerged NF module for achieving stable operations and producing high-quality recycled water.

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.

Water quality and reliability during potable reuse can often depend on the performance of the reverse osmosis (RO) membrane treatment for the attenuation of microbial contaminants. This pilot-scale study aimed to assess the passage of bacteria through the intact RO membrane element and O-ring seal using stable fluorescent (FL) microspheres as surrogates for bacteria and fluorescently stained bacteria. The removal of FL microspheres by three low pressure RO membrane elements varied considerably from 3.1 to 5.0log (99.92% to 99.999%). O-Ring seal bonding at the interface between RO feed and permeate streams increased the removal of FL microspheres by 0.2 to 0.4log and the removal of actual bacteria in reclaimed water by 0.5log.The results also show that conductivity is not a suitable surrogate parameter to monitor bacterial removal by these RO membranes.Overall, this study identified that even the intact O-ring seal can allow for some bacterial passage and the O-ring seal can be a source of low RO performance for bacterial removal. This study suggested the potential that the improvement of O-ring sealing performance can increase bacterial removal by 0.5log., Environmental Science: Water Research and Technology, 5(2), pp.239-245; 2019

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.

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, 13.5 W/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 1–2 GW, 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.

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., International Journal of Environmental Research and Public Health, 15(10), art.no.2124; 2018

Forward Osmosis (FO) is recently paied attention to preprocessing of the Reverse Osmosis (RO). It can reduce the input power of RO plant. It is required to reduce the salt concentration at outlet and increase the permeation flow rate. In this paper, the characteristics of the fresh water flow and permeation are studied for the hollow fiber membrane module used in FO system. It is cleared that the disappearance 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 fresh water and the leakage of salt influence to the reduction of permeation flow rate in the case of high fresh water flow rate.Copyright © 2015 by JSME