Ultrafiltration Of River Water Research Articles

Assessing irreversible fouling behavior of membrane foulants in the ultrafiltration of natural water using principal component analysis of fluorescence excitation-emission matrices

Natural river water is comprised of different foulant components such as natural organic matter and colloidal/particulate matter. Both individual and combined contributions of these foulant components results in different fouling behaviour. The ability to characterize these contributions that lead to reversible and irreversible membrane fouling would be beneficial for the implementation of fouling monitoring and control strategies for membrane-based drinking water treatment operations. A fluorescence excitation-emission matrix and principal component analysis-based approach was able to qualitatively estimate the accumulation of humic substances (HS)-, protein- and colloidal/particulate matter-like foulant components in membranes during the ultrafiltration (UF) of natural river water. A bench-scale flat sheet UF cross-flow set-up and successive permeation and membrane backwashing cycles were used. Analysis of the accumulation of these foulant components revealed that the increased levels of colloidal/particulate matter accumulation in the membranes appeared to have increased the extent of irreversible fouling by HS-like matter whereas lower irreversible fouling by protein-like matter was observed with increased colloidal/particulate matter accumulation. The results also indicate that the combined contributions by these foulants are important in the fouling of membranes during the UF of river water.

Use of carbon black nanoparticles to mitigate membrane fouling in ultrafiltration of river water

Abstract The performance of hybrid adsorption–membrane filtration processes can drop owing to limited adsorption capacity and increased membrane fouling. Here we compared preadsorption by carbon black (CB) nanoparticles and powdered activated carbon (PAC) on subsequent membrane fouling in the ultrafiltration of river water containing natural organic matter (NOM), using an unstirred batch setup with four cycles of filtration and backwashing. PAC was ineffective at reducing fouling although PAC enhanced removal of micromolecular NOM. CB had a high capacity to adsorb macromolecular NOM, and subsequently prevented irreversible fouling. The CB cake was more easily detachable by backwashing than the PAC cake because of structural differences. Our results demonstrate that CB mitigated irreversible fouling and reduced the deposition of transphilic NOM on the membrane surface.

Consecutive chemical cleaning of fouled PVC membrane using NaOH and ethanol during ultrafiltration of river water

Chemical cleaning of fouled hollow-fiber polyvinyl chloride (PVC) membrane with the consecutive use of NaOH and ethanol during ultrafiltration of river water was investigated in the study. Results showed that through the chemical cleaning with 1% NaOH for 30min, a negative cleaning efficiency of −14.6% was observed for the PVC membrane. This might be due to the increase of membrane hydrophobicity, which was reflected by the increase of contact angle from 69.7° to 87.6°. On the other hand, the cleaning efficiency of 85.1% was obtained by the consecutive cleaning with 30min of 1% NaOH and 30min of ethanol. Individual ethanol cleaning could remove 48.5% of the irreversible resistance, indicating that NaOH cleaning also made its contribution (36.6%) to the removal of membrane foulants. Scanning electronic microscopy (SEM) and atomic force microscopy (AFM) analyses demonstrated that both NaOH and ethanol were not only able to eliminate the foulants on membrane surface, but also able to remove the in-pore fouling of the PVC membrane. The synergetic effects for removing membrane foulants were observed between the NaOH and ethanol. Furthermore, ethanol could also restore the hydrophilicity of the membrane by decreasing the contact angle from 87.6° to 71.4°. Considering that ethanol is easy to be used and reclaimed, the consecutive chemical cleaning by alkali and ethanol is recommended for PVC membrane in filtration of surface water.

Ultrafiltration of natural organic matter and black carbon: Factors influencing aggregation and membrane fouling

There are concerns about black carbon (BC), due to its potential for sorption of toxic pollutants and inevitably entering drinking water sources. This study aimed to evaluate factors affecting BC aggregation and membrane fouling in the ultrafiltration of river water. Hydrophilic carbon black (CB) was selected as a surrogate of submicron BC in natural waters. Calcium, pH, and natural organic matter (NOM) were found to influence CB aggregation. Calcium induced interparticle interactions in a pH range of 4.3–7.7. In river water at 0.3 mM Ca 2+, CB remained as fine aggregates (<300 nm) that caused substantial filtration resistance. At 1.3 mM Ca 2+, CB size increased to 2.2–3.3 μm and membrane fouling was reduced. Interactions between particles and NOM enhanced organic rejection and eliminated irreversible membrane fouling. BC in water resources is a noxious substance, but it was easily aggregated in hard waters and could enhance NOM removal in the ultrafiltration process.

Impacts of Hydrophilic Membrane Additives on the Ultrafiltration of River Water

One of the most serious disadvantages of membrane applications in water treatment is the decreasing water permeation rate with time, which is often called fouling. This study investigates surface modification of polyethersulfone (PES) ultrafiltration membranes as a fouling reduction strategy for drinking water treatment applications. Surface modification was achieved through the addition of three different tailor-made hydrophilic surface modifying macromolecules (LSMM200, LSMM400, and LSMM600). Flat sheet membranes were prepared via a single-step casting procedure; their surface hydrophilicity was quantified via contact angle measurements. The incorporation of hydrophilic additives produced slightly more hydrophilic membranes (contact angle reduction of up to 8° ) and improved membrane performance compared with the PES membrane without blending. In the treatment of highly colored river water, LSMM400- and LSMM600-modified membranes achieved up to 32% higher final fluxes. Surface modification resulted in s...

Study of a hybrid process combining ozonation and microfiltration/ultrafiltration for drinking water production from surface water

A hybrid process, consisting of ozonation and membrane filtration, followed by activated carbon filtration, was studied in pilot scale for drinking water production from river water. The main focus of this study centred on tests to determine the effect of ozone on the filtration and fouling behaviour of ceramic microfiltration and ultrafiltration membranes with pore sizes of 0.1 gm and 20 kD as well as on the quality of the water produced. The results showed that a certain ozone concentration in the permeate was required to maintain stable and high permeate fluxes during microfiltration and ultrafiltration of river water without backflushing. For the membranes under study, a minimum concentration of 0.05 mg ozone per litre in the permeate was needed. Furthermore, as the ozone dosage was increased, permeate fluxes rose to the values of pure water permeability depending on ozone doses. Ultrafiltration of the river water with the addition of ozone showed that yields of 99% can be achieved without reducing membrane permeability while obviating the need for membrane backflushing. In order to assess the treatment process and the water qualities generated, the most important chemical and microbiological analytical parameters were determined in the feed river water and in the treated water after each treatment stage and were then compared. The results of the analysis showed that, due to this treatment process, the concentration of the organic components in the water, determined as total organic carbon (TOC), chemical oxygen demand as permanganate demand (COD), adsorbable organic halogens (AOX) and spectral absorption coefficient (SAC 254), could be reduced to values under the respective determination limit. Moreover, microbiological analysis showed that coliform bacteria, E. coli, Pseudomonas aeruginosa, Clostridia and faecal streptococci, which were sometimes present in the river water, could be eliminated completely. Therefore all the parameters analysed for the fresh water produced, fulfilled the requirements of the German Drinking Water Regulations.

Air sparging in ultrafiltration hollow fibers: relationship between flux enhancement, cake characteristics and hydrodynamic parameters

The gas sparging process consists in injecting a gas with the feed during the filtration period. Many studies have recently demonstrated the interest of gas sparging for various membrane configurations to enhance the flux or to modify the membrane selectivity. This study focuses on gas sparging in ultrafiltration hollow fibers to prevent a particulate deposit. New experimental results on ultrafiltration of river water are introduced and demonstrate that air sparging is more interesting for waters having a high fouling ability (low critical flux). On the basis of experimental results for clay suspensions, an analysis of the influence of the two-phase flow parameters on the cake characteristics (porosity, thickness and specific resistance) is then introduced and allows to demonstrate that the notion of cake deposit is no more available with a gas/liquid flow. Hydrodynamics of the gas/liquid two-phase flow was characterized, in order to identify the parameters responsible for deposit prevention and for flux enhancement. Mixing or turbulence near the membrane surface seems to control the flux enhancement whereas the cake structure seems to be linked either to mixing or to the flow intermittence. To conclude, perspectives of future processes which could involve air sparging are discussed.

Temporal variations in the fractionation of the rare earth elements in a boreal river; the role of colloidal particles.

Rare earth element (REE) data from weekly sampling of the filtered (<0.45 μm) and suspended particulate phase during 18 months in the Kalix River, Northern Sweden, are presented together with data on colloidal particles and the solution fraction (<3 kDa). The filtered REE concentration show large seasonal and temporal variations in the river. Lanthanum varied between approximately 300 and 2100 pM. High REE concentration in the filter-passing fraction is related to increased water discharge and there is a strong correlation between the REE concentration, organic carbon, Al and Fe. Physical erosion of detrital particles plays a minor role for the yearly transport of particulate REE in this boreal river system. The suspended particulate fraction, which is dominated by non-detrital fractions, accounted for only 35% of the yearly total transport of La in the river. Approximately 10% of the REE were transported in detrital particles during winter. At spring-flood in May, about 30% of the LREE and up to 60% of the HREE where hosted in detrital particles. Ultrafiltration of river water during spring-flood shows that colloidal particles dominate the transport of filter-passing REE. Less than 5% of the filtered REE are found in the fraction smaller than 3 kDa. The colloidal fraction shows a flat to slightly LREE enriched pattern whereas the solution fraction (<3 kDa) show an HREE enriched pattern, compared with till in the catchment. Suspended particles show a LREE enriched pattern. Data indicate that the REE are associated with two phases in the colloidal (and particulate) fraction, an organic-rich phase (with associated Al–Fe) and an Fe-rich (Fe–oxyhydroxide) inorganic phase. The Ce-anomaly in the suspended particulate fraction in the river shows systematic variations, and can be used to interpret fractionation processes of the REE during weathering and transport. There was no anomaly at maximum spring-flood but during the ice-covered period the anomaly became more and more negative. The temporal and seasonal variations of the Ce-anomaly in the suspended particulate phase reflect transport of REE–C–Al–Fe-enriched colloids from the upper section of the till (and/or from mires) to the river at storm events.