A novel approach to measure carbonate alkalinity in aqueous solutions using a total organic carbon analyzer.

Carbonate alkalinity is crucial in regulating the pH and buffering capacity of natural water systems. Thus, its accurate measurement is essential to understand various water environments that affect water quality and ecosystem health. However, conventional potentiometric titration has some limitations. It results in inaccurate measurements of carbonate alkalinity when the alkalinity levels are low or when high dissolved organic matter or inorganic ion levels exist. Herein, we propose a novel approach to accurately measure carbonate alkalinity using a total organic carbon (TOC) analyzer. An extensive study comparing the accuracy and reliability of the conventional potentiometric titration method with those of the newly developed TOC method was conducted to develop and verify highly accurate measurements of carbonate alkalinity. The TOC method has several advantages over the conventional potentiometric titration methods, such as its ability to accurately measure carbonate alkalinity in the presence of high dissolved organic matter or inorganic ion levels and its ability to provide rapid and automated measurements with high reproducibility. Because, the limit of detection, limit of quantification, and the variation coefficient of the measurements was 0.016 mM (0.2 mgC/L), 0.050 mM (0.6 mgC/L), and 3.68 % respectively. Thus, the development of a novel TOC method has significant environmental implications as it provides a reliable and accurate means to measure carbonate alkalinity in solutions containing various organic matter types.

Effects of two-step cleaning sequences on foulant extraction from multibore ultrafiltration membranes in a pilot-scale membrane filtration system for surface water treatment.

The cleaning efficiencies of fouled multibore ultrafiltration membrane (UFMB) operated from a pilot-scale UF process for surface water treatment were systemically investigated according to the sequences of two different cleaning solutions. The experimental results decisively confirmed that HPI DOM and HPO DOM/multivalent ions complexation significantly resulted in the fouling formations on UFMB due to their neutral charge characteristic. The basic cleaning agent effectively extracted the organic foulants attached on UFMB, indicating that the type of cleaning agent was a critical factor influencing on the cleaning efficiency of fouled UFMB. However, the cleaning sequence 1 (CS-1: 0.1 M NaOH >0.1 M HCl; the total DOC = 725.77 mgC∙m-2; the total TN = 146.35 mgN∙m-2, total inorganic contents = 132.62 mg m-2) much more effectively extracted the foulants on the UFMB surfaces than the cleaning sequence 2 (CS-2: 0.1 M HCl >0.1 M NaOH; the total DOC = 604.49 mgC∙m-2; the total of TN = 121.79 mgN∙m-2, total inorganic contents = 73.43 mg m-2). The morphological results also clearly showed that the cleaned UFMB surface using CS-1 were effectively recovered, as compared with those using CP-2. Overall, this study implied that the hydroxide ions from the basic cleaning agent promoted the infiltration of the acidic cleaning agent into the densely formed fouling layers on the UFMB surfaces and demonstrated that the cleaning sequences strategy could significantly govern the restoration of UFMB performance during the pilot-scale surface water treatment system operation.

Urine Treatment on the International Space Station: Current Practice and Novel Approaches.

A reliable, robust, and resilient water recovery system is of paramount importance on board the International Space Station (ISS). Such a system must be able to treat all sources of water, thereby reducing resupply costs and allowing for longer-term space missions. As such, technologies able to dewater urine in microgravity have been investigated by different space agencies. However, despite over 50 years of research and advancements on water extraction from human urine, the Urine Processing Assembly (UPA) and the Water Processor Assembly (WPA) now operating on the ISS still achieve suboptimal water recovery rates and require periodic consumables resupply. Additionally, urine brine from the treatment is collected for disposal and not yet reused. These factors, combined with the need for a life support system capable of tolerating even dormant periods of up to one year, make the research in this field ever more critical. As such, in the last decade, extensive research was conducted on the adaptation of existing or emerging technologies for the ISS context. In virtue of having a strong chemical resistance, small footprint, tuneable selectivity and versatility, novel membrane-based processes have been in focus for treating human urine. Their hybridisation with thermal and biological processes as well as the combination with new nanomaterials have been particularly investigated. This article critically reviews the UPA and WPA processes currently in operation on the ISS, summarising the research directions and needs, highlighted by major space agencies, necessary for allowing life support for missions outside the Low Earth Orbit (LEO). Additionally, it reviews the technologies recently proposed to improve the performance of the system as well as new concepts to allow for the valorisation of the nutrients in urine or the brine after urine dewatering.

Energy recovery through reverse electrodialysis: Harnessing the salinity gradient from the flushing of human urine.

Urine dilution is often performed to avoid clogging or scaling of pipes, which occurs due to urine's Ca2+ and Mg2+ precipitating at the alkaline conditions created by ureolysis. The large salinity gradient between urine and flushing water is, theoretically, a source of potential energy which is currently unexploited. As such, this work explored the use of a compact reverse electrodialysis (RED) system to convert the chemical potential energy of urine dilution into electric energy. Urine' composition and ureolysis state as well as solution pumping costs were all taken into account. Despite having almost double its electric conductivity, real hydrolysed urine obtained net energy recoveries ENet of 0.053-0.039 kWh/m3, which is similar to energy recovered from real fresh urine. The reduced performances of hydrolysed urine were linked to its higher organic fouling potential and possible volatilisation of NH3 due to its high pH. However, the higher-than-expected performance achieved by fresh urine is possibly due to the fast diffusion of uncharged urea to the freshwater side. Real urine was also tested as a novel electrolyte solution and its performance compared with a conventional K4Fe(CN)6/K3Fe(CN)6 couple. While K4Fe(CN)6/K3Fe(CN)6 outperformed urine in terms of power densities and energy recoveries, net chemical reactions seemed to have occurred in urine when used as an electrolyte solution, leading to TOC, ammonia and urea removal of up to 13%, 6% and 4.4%, respectively. Finally, due to the migration of K+, NH4+ and PO43-, the low concentration solution could be utilised for fertigation. Overall, this process has the potential of providing off-grid urine treatment or energy production at a household or building level.

Intrinsic pKa of Nanofiltration Membrane Surfaces to Assess Fouling and Cleaning Behaviors Induced by Foulant-Membrane Electrostatic Interactions.

The fouling and cleaning behaviors of m-phenylenediamine (MPD), coumarin-3-carboxylic acid (CCA), and d-(+)-glucose (DG) on polyamide nanofiltration (NF) membrane surfaces were investigated with a focus on the two intrinsic equilibrium constants (pKa,intr.) of carboxylic and amine functional groups determined using potentiometric titration. The charged foulants (MPD and CCA) strongly influenced the pKa,intr. of the membrane surface after the fouling layer formed via electrostatic interactions (Virgin = 3.4 and 9.2; MPD-fouled = 4.1 and 8.1; CCA-fouled = 1.5 and 12.4). Moreover, the pKa,intr. of electrostatically fouled membranes substantially recovered when using cleaning agents that released electrostatic interactions (cleaned MPD-fouled = 3.5 and 9.0; cleaned CCA-fouled = 3.3 and 9.6). In contrast, the neutral foulant (DG) did not affect the pKa,intr. (DG-fouled = 3.5 and 9.2); however, the ζ-potential of DG-fouled membrane was closer to zero than the virgin membrane (Virgin = -28.1 mV and DG-fouled = -7.2 mV at pH 7). The pKa,intr. value accurately represented the electrostatic interactions between organic foulants and membrane surfaces. Potentiometric titration is a facile method of determining the pKa,intr. that gives an in-depth understanding of the electrostatic interactions at the membrane surface associated with the membrane fouling and cleaning mechanism.

Enhancing the removal efficiency of osmotic membrane bioreactors: A comprehensive review of influencing parameters and hybrid configurations.

The amount of research conducted on osmotic membrane bioreactors (OMBRs) has increased over the past decade because of the advantages of these reactors over conventional membrane bioreactors (MBRs). OMBR process is a hybrid process involving a forward osmosis membrane and biologically activated sludge. It is a promising technology to reduce membrane fouling, enhance effluent water quality, and lower energy consumption compared to conventional MBR processes. Eleven years since the OMBR process was first proposed, about 60 papers regarding the OMBR process have been published. In this article, we address recent advances in OMBR technology based on a review of the literature. Typical factors that influence the performance of the OMBR process are discussed to provide a clear understanding of the current state of this technology. We also provide a critical review of OMBR applications in organic matter, nutrient, and micropollutant removal as well as direct recovery of nutrients from wastewater. We propose several hybrid configurations that can enhance the removal efficiency of OMBR systems. Finally, we present potential research directions for future OMBR research.

Human urine as a forward osmosis draw solution for the application of microalgae dewatering.

Human urine is a unique solution that has the right composition to constitute both a severe environmental threat and a rich source of nitrogen and phosphorous. In fact, between 4-9% of urine mass consists of ions, such as K+, Cl-, Na+ or NH4+. Because of its high ionic strength, urine osmotic pressure can reach values of up to 2000 kPa. With this in mind, this work aimed to study the effectiveness of real urine as a novel draw solution for forward osmosis. Water flux, reverse nitrogen flux and membrane fouling were investigated using fresh or hydrolysed urine. Water flux as high as 16.7 ± 1.1 L m-2 h-1 was recorded using real hydrolysed urine. Additionally, no support layer membrane fouling was noticed in over 20 h of experimentation. Urine was also employed to dewater a Chlorella vulgaris culture. A fourfold increase in algal concentration was achieved while having an average flux of 14.1 L m-2 h-1. During the algae dewatering, a flux decrease of about 19% was noticed; this was mainly due to a thin layer of algal deposition on the active side of the membrane. Overall, human urine was found to be an effective draw solution for forward osmosis.

Abiotic Formation of Humic-Like Substances through Freezing-Accelerated Reaction of Phenolic Compounds and Nitrite.

A previously unknown abiotic humification pathway which is highly accelerated in frozen solution containing phenolic compounds and nitrite was investigated and proposed. The production of humic-like acids (HLA) and fulvic-like acids (FLA) was observed in the frozen solution (-20 °C) whereas it was negligible in aqueous solution (20 °C). Inorganic nitrogen was transformed into organic nitrogen during the humification process. Mass spectrometry (MS) and elemental analyses, including pyrolysis-GC/MS and FT-ion cyclotron resonance/MS, showed that humification products (HLA and FLA) have chemical structures and compositions similar to nature humic substances. The enhanced humification reaction could be attributed to the freeze-concentration effect, whereby nitrite ions in the unfrozen grain boundary region are transformed into nitrosonium ions which oxidize phenols to phenolic radicals. Confocal Raman microscopy confirmed that catechol and nitrite ions are preferentially concentrated at the ice grain boundary and electron paramagnetic resonance spectroscopic analysis of catechol/nitrite solution detected the phenolic radicals only in frozen solution, not in aqueous solution. The freezing-induced generation of phenolic radicals should lead to the formation of humic-like substances through polymerization. This study identifies and proposes a new humic formation pathway that might work as a model abiotic "bottom-up" mechanism in frozen environmental conditions.

Techno-economic feasibility of recovering phosphorus, nitrogen and water from dilute human urine via forward osmosis.

Due to high phosphorus (P) and nitrogen (N) content, human urine has often proven to suitable raw material for fertiliser production. However, most of the urine diverting toilets or male urinals dilute the urine 2 to 10 times. This decreases the efficiency in the precipitation of P and stripping of N. In this work, a commercial fertiliser blend was used as forward osmosis (FO) draw solution (DS) to concentrate real diluted urine. During the concentration, the urea in the urine is recovered as it diffuses to the fertiliser. Additionally, the combination of concentrate PO43-, reverse Mg2+ flux from the DS and the Mg2+ presents in the flushing water, was able to recover the PO43- as struvite. With 50% concentrated urine, 93% P recovery was achieved without the addition of an external Mg2+. Concurrently, 50% of the N was recovered in the diluted fertiliser DS. An economic analysis was performed to understand the feasibility of this process. It was found that the revenue from the produced fertilisers could potentially offset the operational and capital costs of the system. Additionally, if the reduction in the downstream nutrients load is accounted for, the total revenue of the process would be over 5.3 times of the associated costs.

Sorption of pharmaceuticals to soil organic matter in a constructed wetland by electrostatic interaction.

There is a growing interest in the removal of pharmaceuticals from wastewater because pharmaceuticals have potential ecotoxicological effects. Among several removal mechanisms, the sorption of pharmaceuticals to sediment organic matter is an important mechanism related to the mobility of pharmaceuticals. This study investigated the sorption of pharmaceuticals to soil organic matter (SOM) by electrostatic interactions. SOM located on the surface of soil/sediment generally has a negative charge because of the functional groups present (i.e., carboxylic and phenolic groups). Thus, the electrical characteristics of SOM can induce electrical attraction with positively charged chemical compounds. In this study, SOM was extracted from soils under different aquatic plants (Acorus and Typha) in a constructed wetland in Korea. Experiments were carried out with the following three pharmaceuticals with different electrical characteristics at pH 7: atenolol (positive charge; pKa 9.5), carbamazepine (neutral; no pKa), and ibuprofen (negative charge; pKa 4.9). The SOM in the Acorus pond had a higher hydrophobicity and electrical charge density than that in the Typha pond. Regarding the sorption efficiency between SOM and charged pharmaceuticals, atenolol showed highest sorption efficiency (~60%), followed by carbamazepine (~40%) and ibuprofen (<~30%). In addition, the removal efficiency of the targeted pharmaceuticals in the constructed wetland was estimated by comparing the concentrations of the pharmaceuticals at sampling points with flowing water. The results showed that the removal efficiency of atenolol and carbamazepine was almost 50%, whereas that of ibuprofen was only ~10%. A comparison of the results of lab-scale and field experiments showed that electrostatic interaction is one of the major pharmaceutical removal mechanisms in a constructed wetland.

Simultaneous phosphorous and nitrogen recovery from source-separated urine: A novel application for fertiliser drawn forward osmosis.

Re-thinking our approach to dealing with waste is one of the major challenges in achieving a more sustainable society. However, it could also generate numerous opportunities. Specifically, in the context of wastewater, nutrients, energy and water could be mined from it. Because of its exceptionally high nitrogen (N) and phosphorous (P) concentration, human urine is particularly suitable to be processed for fertiliser production. In the present study, forward osmosis (FO) was employed to mine the P and N from human urine. Two Mg2+-fertilisers, i.e. MgSO4 and Mg(NO3)2 were selected as draw solution (DS) to dewater synthetic non-hydrolysed urine. In this process, the Mg2+ reverse salt flux (RSF) were used to recover P as struvite. Simultaneously, the urea was recovered in the DS as it is poorly rejected by the FO membrane. The results showed that, after concentrating the urine by 60%, about 40% of the P and 50% of the N were recovered. XRD and SEM - EDX analysis confirmed that P was precipitated as mineral struvite. If successfully tested on real urine, this process could be applied to treat the urine collected in urban areas e.g., high-rise building. After the filtration, the solid struvite could be sold for inland applications whereas the diluted fertiliser used for direct fertigation of green walls, parks or for urban farming. Finally, reduction in the load of N, P to the downstream wastewater treatment plant would also ensure a more sustainable urban water cycle.

Validation of a biotic ligand model on site-specific copper toxicity to Daphnia magna in the Yeongsan River, Korea.

The objective of this study was to determine whether the water effect ratio (WER) or biotic ligand model (BLM) could be applied to efficiently develop water quality criteria (WQC) in Korea. Samples were collected from 12 specific sites along the Yeongsan River (YSR), Korea, including two sewage treatment plants and one estuary lake. A copper toxicity test using Daphnia magna was performed to determine the WER and to compare to the BLM prediction. The results of the WER from YSR samples also indicated significantly different copper toxicities in all sites. The model-based predictions showed that effluent and estuary waters had significantly different properties in regard to their ability to be used to investigate water characteristics and copper toxicity. It was supposed that the slight water characteristics changes, such as pH, DOC, hardness, conductivity, among others, influence copper toxicity, and these variable effects on copper toxicity interacted with the water composition. The 38% prediction was outside of the validation range by a factor of two in all sites, showing a poor predictive ability, especially in STPs and streams adjacent to the estuary, while the measured toxicity was more stable. The samples that ranged from pH 7.3-7.7 generated stable predictions, while other samples, including those with lower and the higher pH values, led to more unstable predictions. The results also showed that the toxicity of Cu in sample waters to D. magna was closely proportional to the amounts of acidity, including the carboxylic and phenolic groups, as well as the DOC concentrations. Consequently, the acceptable prediction of metal toxicity in various water samples needs the site-specific results considering the water characteristics such as pH and DOC properties particularly in STPs and estuary regions.

Evaluation of Humic Acid and Tannic Acid Fouling in Graphene Oxide-Coated Ultrafiltration Membranes.

Three commercially available ultrafiltration (UF) membranes (poly(ether sulfone), PES) that have nominal molecular weight cut-offs (5, 10, and 30 kDa) were coated with graphene oxide (GO) nanosheets. Field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, confocal laser scanning microscopy, water contact angle measurements, and X-ray photoelectron spectroscopy were employed to determine the changed physicochemical properties of the membranes after GO coating. The water permeability and single-solute rejection of GO-coated (GOC) membranes for humic acid (HA) molecules were significantly higher by approximately 15% and 55%, respectively, compared to those of pristine UF membranes. However, the GOc membranes for single-solute tannic acid (TA) rejection showed similar trends of higher flux decline versus pristine PES membranes, because the relatively smaller TA molecules were readily adsorbed onto the membrane pores. When the mixed-solute of HA and TA rejection tests were performed, in particular, the adsorbed small TA molecules resulted in irreversible membrane fouling due to cake formation and membrane pore blocking on the membrane surface for the HA molecules. Although both membranes showed significantly higher flux declines for small molecules rejection, the GOc membranes showed better performance than the pristine UF membranes in terms of the rejection of various mixed-solute molecules, due to higher membrane recovery and antifouling capabilities.

Removal of N-nitrosamines in a membrane bioreactor and nanofiltration hybrid system for municipal wastewater reclamation: Process efficiency and mechanisms.

This study investigated the removal efficiency and mechanisms of water contaminants (mainly N-nitrosamines) during municipal wastewater reclamation by a membrane bioreactor (MBR) and nanofiltration (NF) hybrid system. The removal of bulk water contaminants was governed by the microbial activities in the MBR and molecular weight cut-off (MWCO) of the NF membranes. The removal of N-nitrosamines by the MBR was primarily attributed to biodegradation by aerobic bacteria, which can be determined by the reactivity of the amine functional groups with the catabolic enzymes (removal efficiency=45-84%). Adsorption and formation of membrane fouling can enhance the removal of N-nitrosamines by the NF membranes. However, size-exclusion is found to play a major role in the removal of N-nitrosamines by the NF membranes since the removal efficiencies of N-nitrosamines varied significantly depending on molecular weight of the N-nitrosamines and MWCO of the NF membranes (removal efficiency: NE90>NE70).

The role of a combined coagulation and disk filtration process as a pre-treatment to microfiltration and reverse osmosis membranes in a municipal wastewater pilot plant.

A pilot study was conducted to assess the performance of a municipal wastewater reclamation plant consisting of a combined coagulation-disk filtration (CC-DF) process, microfiltration (MF) and reverse osmosis (RO) membranes, in terms of the removal of water contaminants and changes in characteristics of effluent organic matter (EfOM). The CC-DF and MF membranes were not effective for the removal of dissolved water contaminants. However, they could partially reduce the turbidity associated with the cake layer formation by particulate materials on the membrane surfaces. Furthermore, most of water contaminants were completely removed by the RO membranes. Although the CC-DF process could remove approximately 20% of turbidity, the aluminium concentrations considerably increased after the CC-DF process due to the residual coagulants complexed with both carboxylic acid and alcohol functional groups of EfOM. Those aluminium-EfOM complexes had a lower negative charge and higher molecular weight (>0.1 µm pore size of the MF membranes) compared to non-complexed EfOM. These results indicate that the control of the formation of the aluminium-EfOM complexes should be considered as a key step to use the CC-DF process as a pre-treatment of the MF and RO membranes for mitigation of membrane fouling in the tested pilot plant.

Role of wetland organic matters as photosensitizer for degradation of micropollutants and metabolites.

Overall photodegradation of pharmaceuticals, personal care products (PPCPs) and pharmaceutical metabolites were investigated in order to evaluate their photochemical fate in aquatic environments in various natural organic matter (NOM) enriched solutions. Tested PPCPs exhibited different rates of loss during direct and indirect photolysis. Here, only ultraviolet (UV) light source was used for direct photolysis and UV together with (3)DOM(*)for indirect photolysis. Diclofenac and sulfamethoxazole were susceptible to photodegradation, whereas carbamazepine, caffeine, paraxanthine and tri(2-chloroethyl) phosphate (TCEP) showed low levels of photodegradation rate, reflecting their conservative photoreactivity. During indirect photodegradation, in contrast to the hydrophilic autochthonous NOM, allochthonous NOM with relatively high molecular weight (MW), specific ultraviolet absorbance (SUVA) and hydrophobicity (e.g., Suwannee River humic acid (SRHA)) revealed to significantly inhibit the photolysis of target micropollutants. The presence of Typha wetland NOM enhanced the indirect photolysis of well-known conservative micopollutants (carbamazepine and paraxanthine). And atenolol, carbamazepine, glimepiride, and N-acetyl-sulfamethoxazole were found to be sensitive to the triplet excited state of dissolved organic matter ((3)DOM(*)) with Typha wetland NOM under deoxygenated condition. This suggests that photolysis in constructed wetlands connected to the wastewater treatment plant can enhance the degradation of some anthropogenic micropollutants by the interaction with (3)DOM(*) in wetlands.

Humification of effluent organic matters through a surface-flow constructed wetland.

Dominant fractions of wastewater effluent organic matter (EfOM) were changed from polysaccharides (PS) to polyhydroxyaromatics (PHA), throughout the constructed treatment wetland connected to a wastewater treatment plant, as measured using pyrolysis gas chromatography-mass spectrometry (Py-GC/MS). The changes in the fractions were also identified, with respect to molecular weight (MW) distributions of the effluent organic matters, as measured using high performance size exclusion chromatography equipped with both UV and fluorescence detectors, for aromatic/hydrophobic and protein-like organic substances, respectively; organic matter, with MWs of approximately 2,500 and 20,000 Da, and approximately 38,000 Da, as measured by the UV and fluorescence detectors, respectively, were newly formed after the wetlands, especially for the samples of the Typha wetland in June and August against in December. Thus, with the above two different analyses, the humification type of transformation of EfOM through the treatment wetland, was believed to occur, probably due to biological transformation (from the comparison of results in June and August with those in December). It was anticipated that the humification of EfOM could reduce biodegradable organic portions of wastewater effluents even though total organic carbon levels were not reduced that much after the treatment wetland.

Advanced characterization of algogenic organic matter, bacterial organic matter, humic acids and fulvic acids.

Advanced characterization techniques of organic matter, including bulk organic characterization, size-exclusion chromatography, three-dimensional excitation-emission matrix, Fourier transform infrared spectroscopy, and fractionations using Amberlite XAD-8/4 resins, were used to investigate differences and similarities in the physicochemical properties of four different organic matter, namely algogenic organic matter (AOM), bacterial organic matter (BOM), Suwanee River humic acids (SRHA) and Suwanee River fulvic acids (SRFA). From the comparison of characteristics of the AOM, BOM, SRHA, and SRFA, it was identified that the specific UV absorbance, molar ratio of organic nitrogen to organic carbon, molecular weight, fluorescence characteristics, functional group compositions, and relative hydrophobicity/hydrophilicity of all the tested organic matter were considerably different from their sources. The SRHA and SRFA were mainly composed of hydrophobic fractions while the AOM and BOM included more hydrophilic fractions than the SRHA and SRFA due to the alcohol and amide functional groups. This indicated that the origin of organic matter in natural waters can be predicted by their physicochemical characteristics, and the source identification of organic matter provides a better understanding of the interactions between the origin of organic matter and water treatment processes (e.g., coagulation and membrane filtration).

A pilot-scale hybrid municipal wastewater reclamation system using combined coagulation and disk filtration, ultrafiltration, and reverse osmosis: removal of nutrients and micropollutants, and characterization of membrane foulants.

A pilot-scale municipal wastewater reclamation system using combined coagulation and disk filtration (CC-DF), ultrafiltration (UF), and reverse osmosis (RO) membrane has been built to investigate removal of water contaminants and fouling mitigation. The reclaimed water using the pilot system could meet draft regulations on wastewater reuse of the California Department of Public Health (DOC: 0.5 mgC/L; TN: 5 mgN/L). The removal of micropolluants by the CC-DF process and UF could not be evaluated by their MW, Log D, and charge characteristics. However, they were identified as governing factors affecting the removal of micropollutants by the RO. The CC-DF process might effectively remove particulate materials capable of contributing to cake layer formation on the UF membrane surfaces but the residual coagulants provided a strong effect on fouling formation of the UF membrane. Thus, hydrophobic fractions of the desorbed UF membrane foulants were higher than those of the desorbed RO membrane foulants.

Fouling characteristics of a membrane bioreactor and nanofiltration hybrid system for municipal wastewater reclamation.

A laboratory-scale membrane bioreactor (MBR) and nanofiltration (NF) hybrid system has been built to investigate effects of changes in characteristics of effluent organic matter by the MBR on fouling characteristics of the NF membranes. Large amounts of polysaccharide-like substances with small molecular weight and strong fluorescence intensity at the excitation wavelength of 230nm and the emission wavelength of 420nm were produced by microbial growth in the MBR. These substances had a great influence on fouling formation of the NF membranes. Fouling characteristics of the MBR were governed by both hydrophobic and hydrophilic fractions while hydrophilic fractions were found as major constituents of the desorbed NF membrane foulants. Flux decline rates of the NF membranes were closely associated with differences in their fouling layer compositions, meaning that performances of the NF membranes (i.e., flux decline) could be influenced by the membrane characteristics (i.e., surface zeta potential and contact angle).