A breakthrough dynamic-osmotic membrane bioreactor/nanofiltration hybrid system for real municipal wastewater treatment and reuse.

This study designed a Dynamic-Osmotic membrane bioreactor/nanofiltration (OsMBR/NF) system for municipal wastewater treatment and reuse. Results indicated that a continuously rotating FO module with 60 RPM in Dynamic-OsMBR system could enhance shear stress and reduce cake layer of foulants, leading to higher flux (50%) compared to Traditional-OsMBR during a 40-operation day. A negligible specific reverse salt flux (0.059 G/L) and a water flux of 2.86 LMH were recorded when a mixture of 0.1 M EDTA-2Na/0.1 M Na2CO3/0.9 mM Triton114 functioned as draw solution (DS). It was found that the Dynamic-OsMBR/NF hybrid system could effectively remove pollutants (∼98% COD, ∼99% PO43-P, ∼93% NH4+-N, > 99% suspended solids) from wastewater. In short, this developed system can be considered a breakthrough technology as it successfully minimizes membrane fouling by shear force, and achieves high water quality for reuse by two membrane- barriers.

Water and nutrient recovery by a novel moving sponge - Anaerobic osmotic membrane bioreactor - Membrane distillation (AnOMBR-MD) closed-loop system.

For the first time, a novel sponge-based moving bed-anaerobic osmosis membrane bioreactor/membrane distillation (AnOMBR/MD) system using mixed Na3PO4/EDTA-2Na as the draw solution was employed to treat wastewater for enhanced water flux and reduced membrane fouling. Results indicated that the moving sponge-AnOMBR/MD system obtained a stable water flux of 4.01 L/m2 h and less membrane fouling for a period lasting 45 days. Continuous moving sponge around the FO module is the main mechanism for minimizing membrane fouling during the 45-day AnOMBR operation. The proposed system's nutrient removal was almost 100%, thus showing the superiority of simultaneous FO and MD membranes. Nutrient recovery from the MF permeate was best when solution pH was controlled to 9.5, whereby 17.4% (wt/wt) of phosphorus was contained in precipitated components. Moreover, diluted draw solute following AnOMBR was effectively regenerated using the MD process with water flux above 2.48 L/m2 h and salt rejection > 99.99%.

Characteristics of sediment affecting monomethylmercury accumulation in benthic fish of the Mekong Delta.

The Mekong River Delta (Vietnam) is a flat, low-lying area formed by a dense network of main tributaries of the Tien and Hau Rivers, providing a nourishing habitat for aquatic organisms. A sediment survey of the total mercury (Hg), monomethylmercury (MMHg), and geochemical variables was carried out from the coast to 131 km upriver to establish an overview of the environmental factors affecting the bioaccumulation of Hg and MMHg in delta fish. The survey results revealed that the total Hg (12-90 ng g-1 ) and MMHg (0.014-1.5 ng g-1 ) concentrations were in the range of uncontaminated sediment. Statistical analysis using various geochemical factors demonstrated that sediment MMHg concentrations and fractions of MMHg over total Hg in sediment were higher at sites with higher total organic carbon (TOC) and total nitrogen sites. The current levels of TOC in Mekong Delta sediment are relatively low (0.2-1.5%); however, expanding dam constructions and aquacultures related to salinity intrusion are reinforcing the carbon burial rate by increasing the fine fractions. Based on the positive relationship found between MMHg and TOC in sediment, proper management efforts are necessary to reduce MMHg production in the Mekong River Delta sediment. Environ Toxicol Chem 2019;38:503-510. © 2018 SETAC.

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.

Morphological and elemental properties of urban aerosols among PM events and different traffic systems.

Morphology and elemental composition of individual fine ambient particles varied among types of PM events and between two different urban environments having different major transportation systems (gasoline/diesel vehicles versus motorcycles). Carbonaceous particles were the most dominant in PM events, whereas S-rich particles were the highest in non-events at urban Gwangju in Korea. The aged soot, semi-volatile organic (SVO), and non-volatile organic (NVO) particles were more abundant in the polluted-long range transport (LTP) event than those in the dust-LTP event and non-event. In the dust-LTP event, the aged mineral dust particles outnumbered the fresh ones, suggesting the mineral dust particles were aged during their long-range transport. At HoChiMinh (HCM) in Vietnam, the fraction of carbonaceous particles was much higher than Gwangju (66% versus 30%) possibly due to more abundant two-stroke motor vehicles at HCM. Of the carbonaceous particles, combustion soot (19%) was the highest, followed by NVO (18%), SVO (17%), and biological particles (11%) at HCM, whereas SVO (11%) and NVO (10%) particles were the highest, followed by combustion soot particles (8%) at Gwangju. The higher fraction of mineral dust particles was also observed at HCM, indicating the sampling site was influenced by dust from unpaved roads and construction sites.

Laboratory-scale membrane up-concentration and co-anaerobic digestion for energy recovery from sewage and kitchen waste.

This study assessed an alternative concept for co-treatment of sewage and organic kitchen waste in Vietnam. The goal was to apply direct membrane filtration for sewage treatment to generate a permeate that is suitable for discharge. The obtained chemical oxygen demand (COD) concentrations in the permeate of ultrafiltration tests were indeed under the limit value (50 mg/L) of the local municipal discharge standards. The COD of the concentrate was 5.4 times higher than that of the initial feed. These concentrated organics were then co-digested with organic kitchen wastes at an organic loading rate of 2.0 kg VS/m(3).d. The volumetric biogas production of the digester was 1.94 ± 0.34 m(3)/m(3).d. The recovered carbon, in terms of methane gas, accounted for 50% of the total carbon input of the integrated system. Consequently, an electrical production of 64 Wh/capita/d can be obtained when applying the proposed technology with the current wastes generated in Ho Chi Minh City. Thus, it is an approach with great potential in terms of energy recovery and waste treatment.

Application of diffusive gel-type probes for assessing redox zonation and mercury methylation in the Mekong Delta sediment.

The vertical profiles of PO4(3-), Mn, Fe, S(2-), Hg, and CH3Hg(+) in sediment pore water were investigated using DGT and DET probes in the Tien River, the northern branch of Vietnam's Mekong Delta. Although some of the DGT measurements could be lower than the actual pore water concentrations due to the depletion of the species, the measurements provided information for understanding redox zonation and Hg methylation. The gradual increases in the measured species concentrations with the sediment depth were observed and the diffusive fluxes of the species to overlying water were expected. The vertical profiles suggested that (1) SO4(2-) seemed to be reduced before Fe(3+), or the two electron acceptors were reduced simultaneously; (2) the release of PO4(3-) was more closely related to S(2-) than Fe release; and (3) Hg methylation was active in the micro-niche between the aerobic and anaerobic transition zones. The maximum pore water CH3Hg(+) concentrations were observed at depths just above where the maximum S(2-) concentrations were detected. Hence, the maximum CH3Hg(+) concentration was observed near surficial sediments (less than 1 cm from the surface) in brackish water, and at a depth of 3 cm in fresh water. The different vertical profiles led to a CH3Hg(+) diffusive flux eight-times greater in brackish than in fresh water. The present study showed that the in situ application of DGT and DET probes was helpful to understand coupled biogeochemical reactions and mercury methylation by measuring pore water redox species.

Low flux submerged membrane bioreactor treating high strength leachate from a solid waste transfer station.

A submerged membrane bioreactor was employed to treat high strength leachate generating from a solid waste transfer station. The reactor was operated at low fluxes of 1.2; 2.4; 3.8 and 5.1 LMH. The organic loading rate (OLR) ranged from 2 to 10 kg COD/m(3)day. Results show that 97% removal efficiency of COD at flux of 2.4 LMH. The highest removal of ammonia nitrogen and total nitrogen was 92.0 ± 1.5% and 88.0 ± 2.0% respectively at flux of 3.8 LMH. Fouling rates were observed to be 0.075; 0.121; 3.186 and 6.374 kPa/day for the fluxes of 1.2; 2.4; 3.8 and 5.1 LMH, respectively. Membrane fouled very slowly at low flux operation. The sustainable flux was identified to be less than 2.4 LMH for treating high strength leachate. It reveals less fouling was able to achieve for high strength wastewater by reducing the membrane flux.