Innovative hyper-thermophilic aerobic submerged membrane distillation bioreactor for wastewater reclamation.

For the first time, a hyper-thermophilic aerobic (>60 °C) bioreactor has been integrated with direct submerged membrane distillation (MD), highlighting its potential as an advanced wastewater treatment solution. The hyper-thermophilic aerobic bioreactor, operating up to 65 °C, is tailored for high organic removal, while MD efficiently produces clean water. Throughout the study, high removal rates of 99.5% for organic matter, 96.4% for ammonia, and 100% for phosphorus underscored the impressive adaptability of microorganisms to challenging hyper-thermophilic conditions and a successful combination with the MD process. Despite the extreme temperatures and substantial salinity accumulation reaching up to 12,532 µS/cm, the biomass of microorganisms increased by 1.6 times over a 92-day period, representing their remarkable resilience. The distillation flux ranged from 6.15 LMH to 8.25 LMH, benefiting from the temperature gradient in the hyper-thermophilic setting and the design of the tubular submerged MD membrane module. The system also excels in pH control, utilizing fewer alkali and nutritional resources than conventional systems. Meiothermus, Firmicutes, and Bacteroidetes, the three dominant species, played a crucial role, showcasing their significance in adapting to high salinity and decomposing organic matter.

Implications of climate change and drought on water requirements in a semi-mountainous region of the Vietnamese Mekong Delta.

As the backbone of Vietnam's economy, the country has recently established a number of policies for promoting and investing in smart agriculture in the Mekong Delta, the country's largest agricultural hub, to foster overall socio-economic development. However, water remains a critical constraint for crop production, with progress being hindered by water scarcity and quality issues, and compounded by socio-economic transformation and climate change. Considering these challenges, this study used the CROPWAT model and a wide spectrum of climate change scenarios to investigate future total water demands in the 2030s and 2050s as well as drought levels in two underdeveloped semi-mountainous reservoir catchments, i.e., O Ta Soc and O Tuk Sa in An Giang province. The results suggest that the usable storage capacity of the O Ta Soc reservoir will increase to 650,000 m3 to meet water supply demands under all climate change scenarios and the medium-term, moderate drought conditions. The useable storage capacity of the O Tuk Sa reservoir will also be increased to 880,000 m3 and the irrigation area would see a marked 70% reduction compared to its design irrigation. Under these circumstances, the O Tuk Sa reservoir will continue to supply water under all climate change scenarios and medium-term droughts. As a core element for strategic planning and to ensure efficient management of water resources, the results highlight the importance of estimating potential runoff and rainfall in semi-mountainous reservoir catchments under various drought conditions in order to propose the suitable expansion of the useable water storage capacities.

Recovery of iodide as triiodide from thin-film transistor liquid crystal display wastewater by forward osmosis.

Triiodide, a larger charged molecule compared to iodide, is thermodynamically favored with the presence of both iodide and iodine, and is easier to be retained by membrane processes. For the first time, iodide was recovered in the form of triiodide by forward osmosis (FO) for thin-film transistor liquid crystal display industries by preoxidation of iodide to triiodide. Partial oxidation by NaOCl was used to convert the iodide to iodine and then to form triiodide. Ethylenediaminetetraacetic acid disodium salt (EDTA-2Na), a commonly used chelating agent in the industry, was used as the draw solute because of its low reverse salt flux. The results revealed that the ideal efficiency of iodide recovery was at pH 3 with a preoxidation (adding 0.0150 M NaClO) for the 0.048 M iodide wastewater with a recovery of 98.5%. Additionally, the Pourbaix diagram and starch indicator were used to verify the formation of triiodide. Membrane distillation was demonstrated to recover the EDTA-2Na draw solute, and more than 99% of recoveries for the draw solutes with initial water flux of 12.0 L/m2 h were achieved, indicating that simultaneous recovery of the EDTA-2Na draw solute and water is feasible.

A novel thermophilic anaerobic granular sludge membrane distillation bioreactor for wastewater reclamation.

Membrane distillation (MD) has a high heat requirement. Integrating MD with thermophilic bioreactors could remedy this problem. A laboratory-scale thermophilic anaerobic granular sludge membrane distillation bioreactor (ThAGS-MDBR) was used to treat wastewater with a high organic loading rate (OLR). Waste heat from ThAGS was used directly for the MD process to reduce energy consumption. The result demonstrated that the ThAGS-MDBR system achieved a high-efficiency removal of chemical oxygen demand (more 99.5%) and NH4+-N (96.4%). Furthermore, the highest methane production from the proposed system was 332 mL/g CODremoved at OLR of 16 kg COD/m3/day. Specifically, an aggregate of densely packed diverse microbial communities in anaerobic granular sludge was the main mechanism for the enhancement of bioreactor tolerance with environmental changes. High-quality distillate water from ThAGS-MDBR was reclaimed in one step with total organic carbon less than 1.7 mg/L and electrical conductivity less than 120 µS/cm. Furthermore, the result of the DNA extraction kit recorded that Methanosaeta thermophila was a critical archaea for high COD removal and bioreactor stability.

Application of progressive freezing on forward osmosis draw solute recovery.

Progressive freezing is a solvent purification technology with low energy requirements and high concentration efficiency. Although these advantages make it a promising technology, the technique has never been explored for draw solution recovery for forward osmosis (FO). Hence, in this study, the progressive freezing process was used to concentrate three common diluted draw solutions: NaCl, MgCl2, and EDTA-2Na with different ice front speeds, stirring rates, and initial draw solution concentrations. Effective partition and intrinsic partition constants were also evaluated. The results reveal that the freezing process can achieve a draw solution recovery rate of 99.73%, 99.06%, and 98.65% with NaCl, MgCl2, and EDTA-2Na, respectively, using an ice front speed of 0.5 cm/h, a stirring rate of 2.62 m/s, and 30% of percentage of ice phase. Higher concentration efficiency for NaCl and MgCl2 was achieved due to the high solubility of NaCl and MgCl2 increased solute diffusion into the liquid phase solutions. The concentration factors for all three draw solutions exceeded 1.9, indicating that the draw solutes could be reused for the FO process. In addition, the two mass transfer coefficients depended on the ice front speed and the stirring rates were also obtained for scaling up the experiment in the future.

Exploring Nanosilver-Coated Hollow Fiber Microfiltration to Mitigate Biofouling for High Loading Membrane Bioreactor.

For the first time, a nanosilver-coated hollow fiber microfiltration (MF) was fabricated by a simple chemical reduction method, then tested for membrane biofouling mitigation study under extreme high mixed liquor suspended solid (MLSS) concentration for long term. This study presents a simple and novel technique to modify a commercially available MF membrane using silver nanoparticles (AgNPs) followed by an investigation of mitigating membrane biofouling potentials using this modified membrane to compare with an unmodified membrane for 60-day operation period. The modified membranes showed that AgNPs was attached to the MF-membrane successfully with a high density of 119.85 ± 5.42 mg/m2. After long-term testing of 60 days in membrane bioreactor with a MLSS concentration of 11,000 mg/L, specific flux of the AgNPs coated MF (AgNPs-MF) decreased 59.7%, while the specific flux of the unmodified membrane dropped 81.8%, resulted from the increase of transmembrane vacuum pressure for the AgNPs-MF was lower than that of the unmodified one. The resistance-in-series model was used to calculate the resistance coefficients of membrane modules, and the result showed that the cake layer resistance coefficient of the unmodified membrane was 2.7 times higher than that of the AgNPs-MF after the 60-day operation, confirming that AgNPs displayed great antimicrobial properties to mitigate membrane biofouling under such high MLSS.

Preparation of Zn-Doped Amino Functionalized Biochar from Hazardous Waste for Arsenic Removal.

The utilization of sludge from Far Eastern Memorial hospital (New Taipei city, Taiwan) wastewater treatment plants as biochar adsorbent was investigated. The sludge was carbonized using microwave carbonization and then chemically activated at high temperatures by using ZnCl2 to enhance porosity and surface area. A newly designed Zndoped amino-functionalized sludge biochar (Zn-SBC-DETA) presents effective As adsorption in water. The adsorbent was characterized by nitrogen adsorption-desorption, scanning electron microscopy (SEM) and thermogravimetric analysis. Results show that the surface area and average pore volume of Zn-SBC-DETA are 525 m² g-1 and 0.35 cm³ g-1, respectively. SEM results reveal that Zn-SBC-DETA has uniform pore size. The highest adsorption efficiency of As(III) is 79% at pH 3 with an adsorption capacity of 0.84 mg g-1. In addition, the adsorption efficiency of As(V) is 98% at pH 3 with an adsorption capacity of 1.43 mg g-1. The adsorption data can be described well by the Langmuir model rather than by the Freundlich model The data show good compliance with the pseudo second-order equation, and the correlation coefficient for the linear plots is higher than 0.97. Combined with the As species after reacting with Zn-SBC-DETA, the As transformation and adsorption mechanism are also discussed.

Effects of Different Sacrificial Agents and Hydrogen Production from Wastewater by Pt-Graphene/TiO2.

The Pt and graphene (GN) were used to modify TiO2 nanoparticles. GN/TiO2, Pt-TiO2, Pt-GN/TiO2 were successfully synthesized by modified Hummers' method, alcohol thermal and photodeposition method, respectively. The characterizations of the synthesized catalysts by different characterization techniques, including N2 adsorption-desorption isotherm, fourier transform infrared spectroscopy (FTIR), inductively coupled plasma (ICP) technique and element analyzer (EA), respectively. In addition, different sacrificial agents (methanol, ethanol, n-propanol, i-propanol, n-butanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol and glycerol) have been investigated. There is clearly a linear relationship between hydrogen production rate and the polarity of monohydric alcohols. According to the Langmuir-Hinshelwood results, the surface pseudo-first order rate constant k = 15.06 mmol h-1 g-1 and the adsorption coefficient k = 0.50 mol L-1 were obtained. The feasibility of hydrogen production from wastewater obtained from terephthalic acid industry was studied. After reusing the catalyst under the same experimental conditions, the hydrogen production rate has only slightly decreased for 3 more cycles, which indicated the stability of the synthesized catalysts.

Preparation of Zn-Doped Biochar from Sewage Sludge for Chromium Ion Removal.

Recycling and reuse waste can result in significant savings in materials and energy. In this study, the adsorption of Cr(VI) was analyzed using activated carbon (AC) and biochar (BSC) made from sewage sludge. BSC materials were synthesized using zinc chloride as an activator coupled with carbonized sewage sludge. Specific surface area, pore size distribution, and pore volume were determined by measuring nitrogen adsorption-desorption (BET). BSC morphology was measured using field-emission scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). Results showed that the surface area and average pore volume of the BSC were 490 m2 g-1 and 0.8 cm3 g-1, respectively. SEM results revealed that BSC had uniform pore size. Effects of varying the initial Cr(VI) concentrations, pH values, and dosages of BSC on adsorption performance were also determined. Results showed that the maximum removal efficiency of Cr(VI) was above 99%, and adsorption capacity of 50% ZnCl2-BSC was 677 mg g-1.

Exploration of polyelectrolyte incorporated with Triton-X 114 surfactant based osmotic agent for forward osmosis desalination.

Selection of a proper osmotic agent is important to make the forward osmosis (FO) feasible. The objective of this study was to enhance FO by lowering reverse solute flux and maintaining high water flux. Poly(propylene glycol) with molecular weight of 725 Da (PPG-725) was found to possess high osmolality, making it a strong candidate for using as a draw agent. In addition, to reduce the partial leakage of draw solute, a non-ionic surfactant (Triton X-114) has been incorporated. Typically, when the hydrophobic tails of Triton X-114 interacted with the membrane surface, a layer on the surface of membrane is produced to constrict the pores and thus minimize the reverse solute flux. In this study, different concentrations of PPG-725 incorporated with different concentrations of Triton X-114 (0.2-0.8 mM) were used to evaluate their osmotic potentials as draw solute. The specific reverse solute flux (Js/Jw) of 40% PPG-725 doped with Triton X-114 was found to be 0.01 g/L, considerably much lesser than the conventional inorganic draw agents. Finally, membrane distillation operation was utilized as the recovery system in which solute rejection of 97% was achieved for 40% PPG-725/Triton X-114. Therefore, the overall performance supported PPG-725/Triton X-114 as being an efficient draw agent for forward osmosis-membrane distillation hybrid process.

Enhanced desalination using a three-layer OTMS based superhydrophobic membrane for a membrane distillation process.

Superhydrophobic membranes are essential for improved seawater desalination. This study presents the successful casting of a three-layered membrane composed of a top superhydrophobic coating onto a polypropylene (PP) mat through simple sol-gel processing of octadecyltrimethoxysilane (OTMS), and the bottom layer was casted with hydrophilic poly(vinyl alcohol) (PVA) by using a knife casting technique; this membrane represents a novel class of improved-performance membranes consisting of a top superhydrophobic coating onto a hydrophobic PP mat and a hydrophilic layer (PVA) at the bottom. OTMSs are well known low-surface-energy materials that enhance superhydrophobicity, and they were observed to be the ideal chemical group for increasing the hydrophobicity of the PP mat. The PVA layer acted as base layer absorbing the condensed vapor and thus enhancing the vapor flux across the membrane. The hybrid three-layered membrane exhibited superhydrophobicity, with an average contact angle of more than 160°, and demonstrated high performance in terms of rejection and water flux. This study also examined the pore size distribution, surface roughness, surface area, tensile strength, water flux, and salt rejection of the fabricated membrane. The salt rejection level was calculated to be 99.7%, and a high permeate flux of approximately 6.7 LMH was maintained for 16 h.

Exploration of an innovative draw solution for a forward osmosis-membrane distillation desalination process.

Forward osmosis (FO) has emerged as a viable technology to alleviate the global water crisis. The greatest challenge facing the application of FO technology is the lack of an ideal draw solution with high water flux and low reverse salt flux. Hence, the objective of this study was to enhance FO by lowering reverse salt flux and maintaining high water flux; the method involved adding small concentrations of Al2(SO4)3 to a MgCl2 draw solution. Results showed that 0.5 M MgCl2 mixed with 0.05 M of Al2(SO4)3 at pH 6.5 achieved a lower reverse salt flux (0.53 gMH) than that of pure MgCl2 (1.55 gMH) using an FO cellulose triacetate nonwoven (CTA-NW) membrane. This was due possibly to the flocculation of aluminum hydroxide in the mixed draw solution that constricted membrane pores, resulting in reduced salt diffusion. Moreover, average water fluxes of 4.09 and 1.74 L/m2-h (LMH) were achieved over 180 min, respectively, when brackish water (5 g/L) and sea water (35 g/L) were used as feed solutions. Furthermore, three types of membrane distillation (MD) membranes were selected for draw solution recovery; of these, a polytetrafluoroethylene membrane with a pore size of 0.45 µm proved to be the most effective in achieving a high salt rejection (99.90%) and high water flux (5.41 LMH) in a diluted draw solution.

Casting of a superhydrophobic membrane composed of polysulfone/Cera flava for improved desalination using a membrane distillation process.

Superhydrophobic membranes are necessary for effective membrane-based seawater desalination. This paper presents the successful fabrication of a novel electrospun nanofibrous membrane composed of polysulfone and Cera flava, which represents a novel class of enhanced performance membranes consisting of a superhydrophobic nanofibrous layer and hydrophobic polypropylene (PP). Cera flava, which helps lower the surface energy, was found to be the ideal additive for increasing the hydrophobicity of the polysulfone (PSF) polymeric solution because of its components such as long-chain hydrocarbons, free acids, esters, and internal chain methylene carbons. In the fabricated membrane, consisting of 10 v/v% Cera flava, the top PSF-CF nanofibrous layer is active and the lower PP layer is supportive. The hybrid membrane possesses superhydrophobicity, with an average contact angle of approximately 162°, and showed high performance in terms of rejection and water flux. This work also examined the surface area, pore size distribution, fiber diameter, surface roughness, mechanical strength, water flux, and rejection percentage of the membrane. The salt rejection was above 99.8%, and a high permeate flux of approximately 6.4 LMH was maintained for 16 h of operation.

Adsorption of Methyl Blue on Mesoporous Materials Using Rice Husk Ash as Silica Source.

It is recognized that recycling and reuse of waste can result in significant savings in materials and energy. In this research, the adsorption of methyl blue (MB) using waste rice husk ash (Rha) and mesoporous silica materials made from Rha (R-MCM) were analyzed. Mesoporous silica materials were synthesized using cetyltrimethyl ammonium bromide (CTAB) as a cationic surfactant and Rha as the silica source. The prepared samples were characterized by Brunnaur-Emmet-Teller (BET) adsorption isotherm analyzer and transmission electron microscope (TEM) analysis. The results showed the surface area of R-MCM materials was 1347 m2g-1 and the pore volume was 0.906 cm3g-1. TEM analysis showed that the mesoporous materials generally exhibited ordered hexagonal arrays of mesopores with a uniform pore size. The effects on adsorption performance under different initial dye concentrations, different pH values and different dosages of adsorbent were also studied. Both Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The results show that the maximum removal efficiency of MB more than 99%.

Exploring high charge of phosphate as new draw solute in a forward osmosis-membrane distillation hybrid system for concentrating high-nutrient sludge.

For the first time, a high charge of phosphate was used as the draw solute in a forward osmosis-membrane distillation (FO-MD) hybrid system for concentrating high-nutrient sludge. A high water flux (12.5L/m(2)h) and a low reverse salt flux (0.84g/m(2)) were simultaneously achieved at pH9 by using 0.1M Na3PO4 as the draw solute and deionized water as the feed solution in the FO process. The specific reverse salt flux of 0.1M Na3PO4 (Js/Jw=0.07g/L) was considerably less than that of 0.1M NaCl (Js/Jw=0.37g/L) because the complexion between Na(+) and HPO4(2-) at pH9 led to the reduction of free Na(+) ions, which subsequently reduced the reverse salt diffusion substantially. Moreover, for a feed solution with an initial sludge concentration of 3500mg/L, the sludge concentration could be concentrated to 19,800 and 22,000mg/L in the pressure-retarded osmosis (PRO) and FO membrane orientations, respectively, after 15h of operation. Four types of MD membranes were selected for draw solution recovery; of these, a polytetrafluoroethylene membrane with a pore size of 0.45µm was the most effective in achieving a high water flux (10.28L/m(2)h) and high salt rejection (approximately 100%) in a diluted Na3PO4 draw solution.

A novel osmosis membrane bioreactor-membrane distillation hybrid system for wastewater treatment and reuse.

A novel approach was designed to simultaneously enhance nutrient removal and reduce membrane fouling for wastewater treatment using an attached growth biofilm (AGB) integrated with an osmosis membrane bioreactor (OsMBR) system for the first time. In this study, a highly charged organic compound (HEDTA(3-)) was employed as a novel draw solution in the AGB-OsMBR system to obtain a low reverse salt flux, maintain a healthy environment for the microorganisms. The AGB-OsMBR system achieved a stable water flux of 3.62L/m(2)h, high nutrient removal of 99% and less fouling during a 60-day operation. Furthermore, the high salinity of diluted draw solution could be effectively recovered by membrane distillation (MD) process with salt rejection of 99.7%. The diluted draw solution was re-concentrated to its initial status (56.1mS/cm) at recovery of 9.8% after 6h. The work demonstrated that novel multi-barrier systems could produce high quality potable water from impaired streams.

Effects of hydraulic retention time and bioflocculant addition on membrane fouling in a sponge-submerged membrane bioreactor.

The characteristics of activated sludge and membrane fouling were evaluated in a sponge-submerged membrane bioreactor (SSMBR) at different hydraulic retention times (HRTs) (6.67, 5.33 and 4.00h). At shorter HRT, more obvious membrane fouling was caused by exacerbated cake layer formation and aggravated pore blocking. Activated sludge possessed more extracellular polymeric substances (EPS) due to excessive growth of biomass and lower protein to polysaccharide ratio in soluble microbial products (SMP). The cake layer resistance was aggravated by increased sludge viscosity together with the accumulated EPS and biopolymer clusters (BPC) on membrane surface. However, SMP showed marginal effect on membrane fouling when SSMBRs were operated at all HRTs. The SSMBR with Gemfloc® addition at the optimum HRT of 6.67h demonstrated superior sludge characteristics such as larger floc size, less SMP in mixed liquor with higher protein/polysaccharide ratio, less SMP and BPC in cake layer, thereby further preventing membrane fouling.

Innovative sponge-based moving bed-osmotic membrane bioreactor hybrid system using a new class of draw solution for municipal wastewater treatment.

For the first time, an innovative concept of combining sponge-based moving bed (SMB) and an osmotic membrane bioreactor (OsMBR), known as the SMB-OsMBR hybrid system, were investigated using Triton X-114 surfactant coupled with MgCl2 salt as the draw solution. Compared to traditional activated sludge OsMBR, the SMB-OsMBR system was able to remove more nutrients due to the thick-biofilm layer on sponge carriers. Subsequently less membrane fouling was observed during the wastewater treatment process. A water flux of 11.38 L/(m(2) h) and a negligible reverse salt flux were documented when deionized water served as the feed solution and a mixture of 1.5 M MgCl2 and 1.5 mM Triton X-114 was used as the draw solution. The SMB-OsMBR hybrid system indicated that a stable water flux of 10.5 L/(m(2) h) and low salt accumulation were achieved in a 90-day operation. Moreover, the nutrient removal efficiency of the proposed system was close to 100%, confirming the effectiveness of simultaneous nitrification and denitrification in the biofilm layer on sponge carriers. The overall performance of the SMB-OsMBR hybrid system using MgCl2 coupled with Triton X-114 as the draw solution demonstrates its potential application in wastewater treatment.

A breakthrough biosorbent in removing heavy metals: Equilibrium, kinetic, thermodynamic and mechanism analyses in a lab-scale study.

A breakthrough biosorbent namely multi-metal binding biosorbent (MMBB) made from a combination of tea wastes, maple leaves and mandarin peels, was prepared to evaluate their biosorptive potential for removal of Cd(II), Cu(II), Pb(II) and Zn(II) from multi-metal aqueous solutions. FTIR and SEM were conducted, before and after biosorption, to explore the intensity and position of the available functional groups and changes in adsorbent surface morphology. Carboxylic, hydroxyl and amine groups were found to be the principal functional groups for the sorption of metals. MMBB exhibited best performance at pH 5.5 with maximum sorption capacities of 31.73, 41.06, 76.25 and 26.63 mg/g for Cd(II), Cu(II), Pb(II) and Zn(II), respectively. Pseudo-first and pseudo-second-order models represented the kinetic experimental data in different initial metal concentrations very well. Among two-parameter adsorption isotherm models, the Langmuir equation gave a better fit of the equilibrium data. For Cu(II) and Zn(II), the Khan isotherm describes better biosorption conditions while for Cd(II) and Pb(II), the Sips model was found to provide the best correlation of the biosorption equilibrium data. The calculated thermodynamic parameters indicated feasible, spontaneous and exothermic biosorption process. Overall, this novel MMBB can effectively be utilized as an adsorbent to remove heavy metal ions from aqueous solutions.

Influence of micelle properties on micellar-enhanced ultrafiltration for chromium recovery.

An investigation of micelle properties on the recovery of chromium for micellar enhanced ultrafiltration (MEUF) process was conducted using cationic surfactant of cetyltrimethylammonium bromide (CTAB). The relationship between degree of ionization, micellar sizes and chromium removal were determined in this study. The results showed that the complete ionization for CTA+ and Br- was observed for CTAB lower than 0.72 mM and aggregation initiated at concentration of CTAB higher than 0.72 mM to yield attraction of counterion. The micellar sizes increased with increase in concentration of CTAB (higher than 4.02 mM) to generate micron-sized micelles. The distribution of micellar sizes was used to estimate the molecular weight cutoff of membrane used in the MEUF process. As chromium was added into aqueous CTAB solution, the chromate was dominant and bound on the micellar surface instead of Br-. Moreover, the presence of micelle formed a gel-layer to slightly shrink the membrane pore, therefore, UF membrane of 30k Da molecular weight cutoff (pore size≈7.9 nm) was selected in the MEUF process to achieve the removal efficiency of Cr(VI) higher than 95%.