Backwash Cycle Research Articles

Identification of microbiological genomes carrying antibiotic resistance genes and virulence factor genes for microbiological risk assessment in filter backwash water

Social development and environmental pollution have worsened the scarcity of global water resources. Recycling filter backwash water (FBW) can enhance water resource efficiency. Systematically investigating the biological risk of FBW for public health is essential. Biological risks such as widely publicized pathogens, emerging antibiotic resistance genes (ARGs), and virulence factor genes (VFGs) were studied. The sand filter backwash water (SFBW) and biological activated carbon filter backwash water (BACFBW) from a DWTP in southern China were sampled over two years. Pathogens and community structure were investigated using 16S and 18S rRNA gene sequencing. ARGs and VFGs were studied using metagenomic sequencing. The BACFBW contained 110 pathogens, 37 ARGs, and 740 virulence factors (VFs), and the SFBW contained 103 pathogens, 75 ARGs, and 832 VFs. The relative abundance of pathogens was higher in summer than in winter for BACFBW. The richness of both ARGs and VFGs in SFBW was higher than in BACFBW. Shortening the backwash cycle could reduce the relative abundance of pathogens in FBW but had no significant effect on ARGs and VFGs in FBW. BACFBW in summer can be reused after appropriately shortening the backwash cycle when controlling the risk of pathogens. The risk of SFBW cannot be reduced by shortening the backwash cycle when controlling ARGs and VFGs. This study provided a basis for safely reusing the sand filter backwash water and biological activated carbon filter backwash water.

Optimizing backwash control using data on seasonal changes in the invertebrate community of granular activated carbon filters

Problems associated with the colonization and leakage of invertebrates in the granular activated carbon (GAC) filters of waterworks have received increased attention in recent years. To study the effect of environmental factors and water quality on invertebrate abundances, and the backwash control for minimizing invertebrate abundance. A survey of the invertebrate community of GAC filters was carried out monthly from March 2021 to May 2022. A pilot-scale GAC system established in the laboratory alongside a lake, with a volume of 35.3 L. 45 invertebrate species were detected, and 40 of these were rotifers. Significant variation in abundance was observed among seasons before and after GAC filtration, the average invertebrate abundance in the inlet water was 11.1 times that in the filtrate. The GAC filter contained invertebrates that might be responsible for the large number of organisms in the filtrate. Invertebrate abundance in the GAC filter decreased gradually with the carbon layer depth, which the mean invertebrate abundances were 6,926, 5,232, and 3818 ind./kg in the top layer (TL), middle layer (ML), and bottom layer (BL), respectively. Invertebrate abundance was correlated with water temperature and varied seasonally. Among eight water quality parameters, chlorophyll a (Chla) and the total plate count (TPC) were most significantly correlated with invertebrate abundance. According to the statistical modeling and the optimization process of response surface methodology (RSM). The predicted optimal values were a flow rate of 6.36 L/h, a backwash cycle of 3.26 d, and a backwash intensity of 14.97 L/(m2·s) for a minimum invertebrate abundance of 3013 ind./kg in the GAC filter. To maintain invertebrate abundance within an acceptable range, some of these measures might need to be modified depending on the actual conditions.

Membrane Contamination Control in the Intermittent Aeration Mode of Operation of the C-MBR Process for Campus Wastewater Reuse

Filtration backwashing is necessary for the effective operation of membrane modules, and intermittent aeration helps to remove nutrients, which can save energy and effectively control the occurrence of membrane contamination. In this study, membrane contamination was controlled using an MBR in intermittent aeration operation mode and a filtration backwash cycle; difficult organic matter and nitrogen (COD and NH4+-N) were used as the main contamination indicators for this study; and the main membrane contamination components, extracellular polymers (EPs), and soluble microbial products (SMPs) were detected. The results show that the average removal of COD and NH4+-N could reach 86.45% and 92.47%, respectively, with a 2.0 day intermittent aeration time and 9/1 min filtration backwash cycle mode, and it also helped to reduce the membrane contamination, as shown by a decrease of 11.87% in bound EPs (EPSBound) and an increase of only 5.32% in SMPs. Microbiological analyses revealed that Proteobacteria and Acinetobacter, as dominant bacteria (50.90%), were the main causes of membrane contamination.

A Mechanistic Model for Hydrogen Production in an AnMBR Treating High Strength Wastewater.

In the global race to produce green hydrogen, wastewater-to-H2 is a sustainable alternative that remains unexploited. Efficient technologies for wastewater-to-H2 are still in their developmental stages, and urgent process intensification is required. In our study, a mechanistic model was developed to characterize hydrogen production in an AnMBR treating high-strength wastewater (COD > 1000 mg/L). Two aspects differentiate our model from existing literature: First, the model input is a multi-substrate wastewater that includes fractions of proteins, carbohydrates, and lipids. Second, the model integrates the ADM1 model with physical/biochemical processes that affect membrane performance (e.g., membrane fouling). The model includes mass balances of 27 variables in a transient state, where metabolites, extracellular polymeric substances, soluble microbial products, and surface membrane density were included. Model results showed the hydrogen production rate was higher when treating amino acids and sugar-rich influents, which is strongly related to higher EPS generation during the digestion of these metabolites. The highest H2 production rate for amino acid-rich influents was 6.1 LH2/L-d; for sugar-rich influents was 5.9 LH2/L-d; and for lipid-rich influents was 0.7 LH2/L-d. Modeled membrane fouling and backwashing cycles showed extreme behaviors for amino- and fatty-acid-rich substrates. Our model helps to identify operational constraints for H2 production in AnMBRs, providing a valuable tool for the design of fermentative/anaerobic MBR systems toward energy recovery.

Evaluation of Organic and Inorganic Foulant Interaction Using Modified Fouling Models in Constant Flux Dead-End Operation with Microfiltration Membranes.

The goal of this study was to elucidate the interaction of complex feed solutions under modified membrane fouling models for constant flux operation. The polyvinylidene fluoride membrane (PVDF) was tested for three types of solutions containing inorganic foulants (Al, Mn, and Fe), organic foulants, and suspended solids at 0.5 mM Ca2+ ionic strength. The membrane's performance was evaluated by measuring the increase in transmembrane pressure (TMP) during two different filtration scenarios: continuous filtration lasting 1 h and cyclic filtration lasting 12 min, with 3 min backwashing cycles included. Statistical analysis (linear regression results (R2), p-value) was used to verify the fouling model propagation along with the determination of the contributing constant of each fouling model. An increasing TMP percentage of 164-302%, 155-300%, and 208-378% for S1 (HA + Ca2+), S2 (inorganics + kaolin + Ca2+), and S3 (HA + inorganics + kaolin + Ca2+) was recorded for 1 h filtration, respectively. Furthermore, a five percent increase in irreversible resistance was noted for the S3 solution due to the strong adsorption potential of foulants for the PVDF membrane caused by the electrostatic and hydration forces of foulants. In addition to that, the participation equation elucidated the contribution of the fouling model and confirmed that complete blocking and cake layer contribution were dominant for the S1 and S3 solutions, while standard blocking was dominant for the S2 solution with a high significance ratio. Moreover, R2 and cyclic filtration analysis also confirmed the propagation of these fouling models. The statistical confirmation and regression results analysis of the modified model gave comparative results and satisfied the filtration mechanism and can be used for the constant flux dead filtration analysis of water treatment.

Sulfur-pyrite-limestone biological filter for simultaneous nitrogen and phosphorus removal from wastewater treatment plant effluent: Interaction mechanisms of autotrophic and heterotrophic denitrification

To efficiently remove nitrogen(N) and phosphorus(P) from wastewater treatment plant effluent (WWTPE) with insufficient carbon, sulfur-pyrite-limestone autotrophic denitrification (SPLAD) reactor and gravel heterotrophic denitrification (GHD) reactor were constructed. Results showed that SPLAD was successfully started after 8 days and was faster than GHD. Under optimal hydraulic retention time (30 min) and backwash cycle (2 d), SPLAD achieved higher removal rates for TP, TN, NO3−-N, NH4+-N at 70.49 %, 90.35 %, 92.82 %, 79.66 %, respectively, surpassing those of GHD. The N removal primarily occurred through nitrification and denitrification with a proportion of 2.42–2.51 between heterotrophic and autotrophic denitrification, while P removal predominantly relied on the combination with Fe2+/Fe3+ generated by FeS2 autotrophic denitrification. Microbial community analysis revealed that Thiobacillus (17.86 %), Thioalbus (7.30 %) and Geothrix (0.81 %), belonging to autotrophic denitrification bacteria using S0/FeS2 as electron donors to reduce NO3−-N, were existed exclusively in SPLAD. Besides, the denitrification genes, such as nitrate reduction (narG, narZ, nxrA, and narH, narY, nxrB) and nitrite reduction (nirB and nirD), were higher in PSLAD than that in GHD. High abundance of sulfur oxidation genes (soxA, soxX, soxB, soxY and soxZ) and iron oxidation gene (ccoN) for autotrophic denitrification were also found in SPLAD. This study highlights the practical engineering application potential of the sulfur/pyrite/limestone involved mixotrophic denitrification process due to its simplicity, cost-effectiveness, and efficient N and P removal.

Insight on the Properties of Pumice Mineral for the Combined Adsorption Distillation of Membrane Reject Water

The current study evaluated the use of pumice, a volcanic mineral and common sand, in treating reverse osmosis membrane reject water (ROR) using a novel combined adsorption distillation (CAD) method. The CAD method is developed to separate the dissolved solids through adsorption distillation, i.e., leaving the vaporized distillate as freshwater and concentrated brine. The adsorption potential of pumice and sand was investigated at different adsorbent doses, i.e., 2, 5, and 10 g, and consecutive CAD adsorbent backwashing cycles. The improved results were achieved at a 10 g pumice dose. However, its adsorption efficiency declined in longer CAD cycles, i.e., due to the separated deposition of solids. After backwashing, the adsorbed and accumulated salts were slightly removed, and pumice adsorption capacity was maintained for up to 20 cycles of CAD. The properties of the pumice, i.e., before and after five CAD cycles and after backwashing, were characterized with scanning electron microscopic (SEM), elemental disruptive spectroscopy (EDS), and X-ray diffraction (XRD), which revealed that the porous structure of the pumice was completely accumulated with deposits of ionic salts, which were slightly washed away after backwashing, but accumulation remained continued in post-CAD cycles. The explored method revealed a high potential of pumice in water filtration.

Efficient Water Softening in Heavy Oil Steamflood Operations

Summary Pigging of once through steam generators (OTSGs) has indicated various types of scales, the most predominant of these being silicates of hardness causing ions. It was noted that scaling propensity can potentially go up with higher steam quality (SQ) as the reject stream gets concentrated with ions. However, models suggested that there are benefits of higher SQ in enhancing fuel savings (8%) and electricity savings (2%) when SQ was increased by 20%. The challenges of higher SQ were noted in terms of increased scaling tendency and therefore the need for improved softening. In Field D, the service cycle, the backwash cycle, and the brining cycle were optimized leading to a gain in throughput and reduction in salt consumption. Service cycle improvement gained 30 to 130% in throughput between two regenerations, backwash cycle improvement by fluidizing the bed to nearly 35% helped gain 10% in throughput, and reduction of brining cycle from 75 to 48 minutes helped reduce salt consumption by 56% without impacting the throughput. In Field B, a 6-month pilot revealed that shallow shell resins where ion exchange is more efficient due to inert core (better intraparticle diffusion control) can enhance the throughput by 30 to 80% and simultaneously reduce the number of regenerations by 15 to 30%. Resin fouling is still a major challenge to contend with as oil can foul the resin and throughput can decline by 0.5 to 3 folds. In a plant operation, where there are multiple softener and brine vessels, there is a need to optimize them as a system. Reliability, availability, and maintainability (RAM) models are used in Field C to (a) address equipment configuration optimization with impact on capital capacity expansion project scope, (b) understand how net soft water delivery capacity was affected by increases in inlet hardness, and (c) assess through a comparison scenario if the large cost of addressing the valve issue in an upstream nutshell filter was worth the lost production opportunity related to unplanned downtime.

A metagenomic portrait of the microbial community responsible for two decades of bioremediation of poly-contaminated groundwater

Biodegradation of pollutants is a sustainable and cost-effective solution to groundwater pollution. Here, we investigate microbial populations involved in biodegradation of poly-contaminants in a pipeline for heavily contaminated groundwater. Groundwater moves from a polluted park to a treatment plant, where an aerated bioreactor effectively removes the contaminants. While the biomass does not settle in the reactor, sediment is collected afterwards and used to seed the new polluted groundwater via a backwash cycle. The pipeline has successfully operated since 1999, but the biological components in the reactor and the contaminated park groundwater have never been described. We sampled seven points along the pipeline, representing the entire remediation process, and characterized the changing microbial communities using genome-resolved metagenomic analysis. We assembled 297 medium- and high-quality metagenome-assembled genome sequences representing on average 46.3% of the total DNA per sample. We found that the communities cluster into two distinct groups, separating the anaerobic communities in the park groundwater from the aerobic communities inside the plant. In the park, the community is dominated by members of the genus Sulfuricurvum, while the plant is dominated by generalists from the order Burkholderiales. Known aromatic compound biodegradation pathways are four times more abundant in the plant-side communities compared to the park-side. Our findings provide a genome-resolved portrait of the microbial community in a highly effective groundwater treatment system that has treated groundwater with a complex contamination profile for two decades.

Treatment of Hydrothermal-Liquefaction Wastewater with Crossflow UF for Oil and Particle Removal.

This study aims to evaluate the application of ceramic ultrafiltration membranes in the crossflow mode for the separation of particles and oil in water emulsions (free oil droplets and micelles) from hydrothermal-liquefaction wastewater (HTL-WW) from the hydrothermal liquefaction of municipal sewage sludge. The experiments were carried out using one-channel TiO2 membranes with pore sizes of 30, 10 and 5 nm. The results showed that the highest stable permeability could be achieved with a membrane-pore size of 10 nm, which experienced less fouling, especially through pore blockage, in comparison to the two other pore sizes. Instead of observing an increase in the permeability, the application of a higher feed temperature as well as backwash cycles led to a clear increase in irreversible fouling due to the presence of surfactants in the HTL-WW. Among several physical and chemical cleaning methods, alkaline cleaning at pH 12 proved to be the most efficient in removing fouling and maintaining stable performance on a long-term basis. Ceramic-membrane ultrafiltration can be considered as an adequate first-stage treatment of real HTL wastewater.

Renewable energy powered membrane technology: Energy consumption analysis of ultrafiltration backwash configurations

In the field of ultrafiltration (UF) membranes for water treatment, fouling is a severe problem that limits the potential of the technology UF membranes and results in increased energy consumption. In this study, a small-scale photovoltaic-powered membrane system was employed to investigate the energy consumption of two UF backwashing configurations – a bladder tank and a backwash (BW) pump powered by supercapacitors – under varied solar irradiance conditions. Fouling was induced via the addition of bentonite, and then examined at varied BW intervals using the bladder tank to optimize the total specific energy consumption (TSEC) – determined for both UF BW and reverse osmosis (RO) desalination processes. Simulated fouling – realized via a pressure drop across a ball valve – was proposed to induce inorganic fouling without requiring the addition of foulants. The TSEC of both bentonite and simulated fouling was compared. Under simulated fouling and constant solar irradiance operating conditions, the bladder tank exhibits a BW SEC of 0.3 Wh/L, while the BW pump exhibits SEC of 0.09Wh/L. The TSEC is maintained at ∼ 4 Wh/L under varied real “solar days” with the bladder tank, indicating that the energetic penalty for implementing one BW cycle every 90 min is small. A BW interval of 60 min exhibited a TSEC of 3.7 Wh/L and provided a good compromise between TSEC and the mitigation of membrane fouling. The concept of using a valve to simulate fouling in the system can assist with the UF membrane fouling studies without inducing irreversible fouling to the membrane. Despite its higher BW SEC, the bladder tank was a more robust setup and is recommended for adding BW functionality to renewable-energy powered membrane filtration systems.

Treatment of hydrothermal liquefaction wastewater with ultrafiltration and air stripping for oil and particle removal and ammonia recovery

This study aims to evaluate the application of ultrafiltration technology for the separation of particles and oil droplets and the recovery of ammonia from hydrothermal liquefaction (HTL) wastewater. Real HTL wastewater from the hydrothermal liquefaction of municipal sewage sludge was used in this study. Experiments were carried out using a submerged polyethersulfone ultrafiltration membrane with molecular weight cutoff of 100 kDa in combination with air stripping and addition to acid and base traps for recovery of volatiles. Results showed, that the best operation mode of ultrafiltration is with backwash cycles of the permeate, maintaining a flux lower than the critical flux of 6 L/h·m2. The setup led to fast stripping of ammonia, which was successfully recovered by 88% in the acid trap. This application can be considered an adequate first stage treatment of the HTL wastewater. The importance of this work is that it proves that membrane technology can be successful in treating complex real HTL wastewater, and is not only limited for applications using model solutions.

Techno-economic assessment of a membrane-based wastewater reclamation process

Reclaimed water plays a crucial role in the water cycle since it constitutes an effective way to improve the utilization of water resources and can help to cope with the water crisis. Membrane technologies for wastewater reclamation, especially ultrafiltration (UF) and reverse osmosis (RO), have received great attention in the past decades. In this work, an integrated prototype (2.5 m3/h) based on the combination of UF and RO was operated in Vuelta Ostrera municipal wastewater treatment plant, located in the proximity of an industrial hub, to obtain water with the required quality for being industrially reused complying with Spanish law and the needs of industrial users. The influence of the process variables on water recovery was studied. Filtration time, backwash cycles duration and frequency, and the addition (or not) of coagulant, were the main variables studied during UF operation, while the recirculation rate of the concentrate stream and the UF permeate quality were the main variables for RO operation. Finally, the economic evaluation pointed to important savings in the OPEX of the process, when compared to the prize that industrial users are currently paying for water.

Pulsating CO2 nucleation radically improves the efficiency of membrane backwash

Although membrane filtration became a dominant water treatment technology globally, it suffers from membrane fouling which aggravates with time and imposes severe adverse effects on process performance, permeate quality and, eventually, its related costs. In this work, we introduce pulsating CO2 solution backwash with intermittent pressure drops to maximize CO2 bubbles yield and radically enhance membrane cleaning. The novel backwash technique was probed during ultrafiltration (UF) of feed waters containing sodium alginate, a model polysaccharide foulants, sea salts enriched in Ca2+, and SiO2. Transmembrane pressures (TMP) observed during the experiments with pulsating CO2 backwash acquired an up/down profile indicating that a considerable portion of TMP was recovered after each backwash cycle, in contrast to insufficient fouling removal and subsequent TMP build-up observed with continuous CO2 and Milli-Q backwashes. Notably, pulsating CO2 backwash alleviated irreversible membrane fouling in highly saline conditions with 30 g/L of sea salts and when it is combined with 1 mg/L of SiO2 (i.e., when conventional membrane backwash was not effective). Furthermore, intense cleaning of the membrane surface and its pores was resembled by a lower fouling resistance in the subsequent UF cycles implying potentially longer operation time with less cleaning frequency and substantial energy savings.

Long-Term Stability of Nitrifying Granules in a Membrane Bioreactor without Hydraulic Selection Pressure

To understand the long-term stability of nitrifying granules in a membrane bioreactor (GMBR), a membrane module was submerged in an airlift reactor to eliminate the hydraulic selection pressure that was believed to be the driving force of aerobic granulation. The long-term monitoring results showed that the structure of nitrifying granules could remain stable for 305 days in the GMBR without hydraulic selection pressure; however, the majority of the granule structure was actually inactive due to mass diffusion limitation. As a consequence, active biomass free of mass diffusion limitation only inhabited the top 60–80 µm layer of the nitrifying granules. There was a dynamic equilibrium between bioflocs and membrane, i.e., 25% of bioflocs attached on the membrane surface within the last nine days of the backwash cycle in synchronization with the emergence of a peak of soluble extracellular polymeric substances (sEPS), with a concentration of around 47 mg L−1. Backwash can eventually detach and return these bioflocs to the bulk solution. However, the rate of membrane fouling did not change with and without the biofloc attachment. In a certain sense, the GMBR investigated in this study functioned in a similar fashion as an integrated fixed-film activated sludge membrane bioreactor and thus defeated the original purpose of GMBR development. The mass diffusion problem and sEPS production should be key areas of focus in future GMBR research.

Alkali activated porous material with nano graphene oxide as adsorbent in wastewater treatment

Removal of contaminants, impurities and suspended solid matter are termed as water treatment. The possible water treatment methods are coagulation, filtration, ion exchange, aerobic and non aerobic methods. But all this involves high cost. Earlier filtration using granular sand was termed as the efficient way of water treatment. But due to the non-availability of sand this method is no more adopted. The most effective and easy means of treatment of water and waste water is adsorption method because it is an easy and convenient method. Though there are many adsorbents like activated carbon, clay minerals, zeolite, plant based and industrial based by products, the commonly used material is activated carbon which is again a costly investment. The next effective material is the zeolite. It has proved to perform well than the granular media and conventional activated carbon in removing heavy metals and ammonia. The advantage of using zeolite is that it adsorbs these contaminants in its pores and forms a strong bond which prevents leaching of these contaminants back to the ground water. The other advantages are the high specific surface area which facilities efficient adsorption, reduces the number of back-wash cycles, non-toxic and environmental friendly. Zeolites are hydrated aluminosilicates classified as natural and synthetic zeolites. The natural one is gluconites or green sand and the synthetic one is permutit which contains sodium in it. Inspite of many advantages in using zeolite the greatest disadvantage is that the treated water has Na+ ions which replaces the Ca2+ and Mg2+ ions. So when such waters are used sodium bicarbonate hydrolysis to sodium hydroxide which causes corrosion of boilers and also water having high turbidity cannot be effectively treated by this method. This research work will be focused on synthesizing alkali activated aerated concrete with graphene oxide which is porous and which can act as an efficient adsorbent in removing the contaminants from water and waste water respectively.

Accumulation of antibiotic resistance genes in full-scale drinking water biological activated carbon (BAC) filters during backwash cycles

Biological activated carbon (BAC) filtration, a process widely used in drinking water treatment, was recently reported to harbor antibiotic resistance genes (ARGs). This emerging contamination is poorly understood. This study was conducted to investigate the occurrence of ARGs and bacterial community in full-scale BAC filters during the backwash cycle using high-throughput qPCR and high-throughput sequencing. A total of 178 ARGs were detected in all biofilm samples, with relative abundance ranging from 0.1 to 1.37 copies per 16S rRNA and absolute abundance ranging from 4.48 × 107 to 3.09 × 109 copies/g carbon. Biofilms sampled from different filters shared most detected ARGs and dominant genera including Bryobacter, Pedomicrobium, Reyranella, and Terrimonas, though their bacterial community structure differed significantly. After backwashing, the relative ARGs abundance increased by 1.5- to 3.8-folds and the absolute ARGs abundance increased by 0.90- to 1.12-logs in all biofilm samples during filter ripening, indicating that ARGs accumulated in filters during this period. Redundancy analysis suggested that such ARGs accumulation was mainly driven by horizontal gene transfer in winter, but highly correlated with the increasing relative abundance of genera Bryobacter and Acidibacter in summer. It was observed that 80.6 %-89.3% of the detected ARGs persisted in the filters despite of the backwashing. Given the high richness and relative abundance of ARGs in BAC filter and the ineffectiveness of backwashing in ARG removal, more stringent downstream disinfection strategies are deserved and more research is necessary to assess potential human health risks due to the persistence of ARGs in drinking water.

Evaluating the effects of the flow direction on the performance of the rapid sand filter

The rapid sand downflow filter is widely used in water treatment plants. On the other hand, this filter has some drawbacks included the significant development of the head loss via the filter media because most of the rejected particles are removed by the upper layers. As well, the filter particles are redistributed during the backwash process causing the settling of fine particles on the upper part of the filter media, and this needs to increase the number of backwash processes. For these reasons, the cost of the produced water increases. The aim of the present study is to explore the possibility of using the upflow sand filter (UF-Filter) as a good alternative to the downflow sand filter (DF-Filter). To achieve the aims of the present study, a comparison was made between the performance of both filters through simultaneous experiments under different operating conditions. These conditions included changing of the filtering velocity from 5 m/h to 10 m/h and the initial water turbidity with a range of (10 – 200) NTU. The sand media with sizes of (0.6 - 1mm) and with 63 cm of depth was used. Experimental results show that the turbidity removal efficiency of the DF-Filter is of about 1.1 times that of the UF-Filter. On the other hand, the UF-Filter has higher turbidity removal efficiency than the DF-Filter by about 1.1 times when the initial turbidity of the influent water is greater than 150 NTU and the filtration velocity is equal to 10 m/hr. These differences in the removal efficiency between both filters can be considered as few values. The average filtration efficiency of the UF-Filter operated with the filtration velocity of 5 and 7.5 m/h is higher than that of the DF-Filter operated with the filtration velocity of 7.5 and 10 m/h, respectively under the same operating conditions. The filtration efficiency of both filters increases when the backwash was carried out before each experimental process instead of replacing the filter media. Also, the head loss of the DF-Filter is significantly increased due to redistribution of the sand media taking place during the backwash cycle, while the head loss of the UF-Filter is not affected. The head loss of the UF-filter at the end of each experimental run is less than that of the DF-Filter by about (18.18 % - 45.31 %) when the filter medium is replaced and this range is increased to about (53.31 % - 62.34 %) when the backwash is performed prior to the start of the experimental work. Thus, the decrease in head loss leads to an increase in the filter running time and decrease the number of backwash process.

Direct membrane heating for temperature induced fouling prevention

Particle deposition and fouling mainly hamper the applicability of porous membranes in filtration applications. Temperature has rarely been investigated or even used to manipulate deposition behavior at membranes and to increase membrane performances although strongly affecting the transport phenomena in and at membrane surfaces. Temperature modulates the hydrodynamic properties, the interaction between solutes and surfaces, and the molecular structure of particles. In this study, we present a novel approach to influence membrane performances and particle deposition by direct membrane heating.Novel inorganic porous hollow fiber membranes made from silicon carbide are directly heated by Joule heating using the electrical resistance of the membranes. The direct heat supply is used during yeast filtration for in-place membrane cleaning and advanced backwashing. Three different approaches are tested: (i) Power application of 70Wm−1 during permeation in cross-flow operation, (ii) 30Wm−1 during permeation in dead-end operation and (iii) 30Wm−1 during backwash operation after unheated dead-end permeation cycles. The power application features temperatures of 50∘C. The localized heating of the boundary layer at the surface of the membrane reduces the energy requirement by 40% compared to complete feed heating for the cross-flow configuration as the large feed stream remains partially unaffected. The viscosity-corrected fouling resistance of the membranes during heated permeation can be decreased by 27–31% in dead-end and cross-flow filtration through the heat treatment, respectively. We contribute the effect to small changes in shear induced cleaning by the thermal treatment. Membrane heating during backwashing results in a 30% reduction of the resistance over a course of 11 permeation–backwashing cycles compared with conventional backwashing.

Potential application of osmotic backwashing to brackish water desalination membranes

Brackish water Reverse Osmosis (RO) and Nanofiltration (NF) are an attractive technology for potable water production and wastewater reclamation. However, scaling and fouling remain common problems that limit the optimal use of membranes, cause flux decline, increase energy demand and require periodic cleaning by chemical means. Herein, we consider the use of osmotic backwashing, already reported in the literature for seawater RO, as a cleaning method for brackish RO and NF. Three commercial membranes were used in a bench-scale system along with three draw solutions, NaCl, Na2SO4 and MgSO4, to assess the osmotic flux induced during a backwash cycle. The backwash flux was found to be in good agreement with calculations made using a computational model, which was then used to reveal the role of solution chemistry as well as membrane support properties in controlling the backwash intensity and duration. Specifically, sulphate-based solutions showed a good ability to maintain an osmotic flux, better than NaCl, for which lower membrane selectivity restricts use as a draw agent. While preliminary experiments demonstrated the ability of an osmotic backwash to remove CaPO4 scale, achieving nearly complete flux restoration for some cases, the process requires further optimization.