Influence of Flocculation and Adsorption as Pretreatment on the Fouling of Ultrafiltration and Nanofiltration Membranes: Application with Biologically Treated Sewage Effluent (original) (raw)
Related papers
Journal of Membrane Science, 2004
Reuse of wastewater can help in maintaining environmental quality and relieving the unrelenting pressure on conventional and natural freshwater sources. Membrane processes find an important place in the wastewater treatment for reuse. Nonetheless, reverse osmosis (RO) and nanofiltration (NF), i.e. non-porous membranes require higher operational costs and energy. Thus, in this research NTR 7410 ultrafiltration (UF) membrane which is porous was used without and with pretreatment to treat biologically treated sewage effluent (BTSE). Four different pretreatment methods, namely, ferric chloride (FeCl 3) flocculation, powdered activated carbon (PAC) adsorption, flocculation followed by adsorption, and granular activated carbon (GAC) biofilter were used in this study to compare their relative merits. Experimental results indicate that the most suitable pretreatment was flocculation followed by adsorption leading to a total organic carbon (TOC) removal of 90%. To assess the suitability of the membranes, it is important to conduct a detailed membrane characterization. The fouled NTR 7410 membrane surface was analyzed in terms of contact angle, zeta potential, attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), flux decline, and TOC removal. The contact angle of the fouled membrane surface was lower than that of the clean membrane surface. This suggests that the majority of the foulants may have been the hydrophilic organic compounds such as polysaccharides, urea, etc. which are the extracellular enzyme of microorganisms in BTSE. But, the fouled membrane surface after the pretreatment of flocculation followed by adsorption had nearly the same contact angle as that of the clean membrane, suggesting that the hydrophobicity of the membrane is preserved by this pretreatment. According to attenuated total reflection-Fourier transform infrared spectroscopy results, the peaks observed on the fouled membrane were ether (C-O-C) and urea (R-NH-CO-NH-R). On the other hand, the peaks obtained after the pretreatment of flocculation followed by adsorption were similar to those of clean membranes. The highest effluent organic matter (EfOM) concentration on the fouled membranes without any pretreatment was measured up to 0.011 mg EfOM/cm 2 membrane surface. The pretreatment of flocculation followed by adsorption reduced the EfOM concentration on the membrane to 0.005 mg EfOM/cm 2. The SEM images on the membrane cross-section revealed that there was practically no foulant layer on the membrane when a pretreatment of flocculation followed by adsorption was used.
Fouling Control of Membranes with Pretreatment
Membrane Technology and Environmental Applications, 2012
The impediment of the membrane technology is the fouling problem and consequently higher operating and membrane replacement cost. Pretreatment is very important for developing the best treatment process train to secure better membrane treatability and producing acceptable effluent qualities. This chapter addresses the state of the art pretreatment techniques and their applications to low pressure (MF/UF) and high pressure (NF/RO) membranes in water and wastewater treatment as well as desalination. The impacts of different pretreatment processes on membrane performance and membrane fouling control have been extensively reviewed. 19.1 Introduction Application of membrane technology has expanded over the last decades for advanced water and wastewater treatment. Particularly, membrane bioreactors (MBRs) for separation and retention of biological solids have been widely applied as one of the alternatives to conventional treatment processes. However, as various factors govern the operating cost of a membrane system, such as power requirements, power cost, labor cost, material cost, membrane cleaning costs, scale inhibition costs, membrane life and replacement cost, some limitations remain in using membranes for water and wastewater treatment (Bennett, 2005). The major obstacle for the application of membrane processes is the rapid decline of the permeate flux over time as a result of membrane fouling. That is to say, without proper pretreatment, rapid membrane fouling (or clogging) may occur, which will reduce permeate flux, increase feed pressure, reduce productivity, increase system downtime, increase membrane maintenance and operation costs due to membrane cleaning, and decrease the lifespan of the membrane modules (Bai and Leow, 2002; Seidel and Elimelech, 2002). Micro-biological organisms: the microbiological category covers vegetative matter such as algae and microorganisms (e.g., bacteria), which can adhere to the membranes and cause biofouling (biofilm formation). Raw waters contain a wide distribution of materials that can cause membrane fouling, such as fine particles, dissolved organic compounds, colloids, less soluble salts and nutrients for biological growth. Fouling by different foulants can be considered to occur by different mechanisms. Recent research has identified six principal fouling mechanisms: (a) pore blocking; (b) cake formation; (c) concentration polarization; (d) organic adsorption; (e) inorganic precipitation; and (f) biological fouling.
Effect of adsorption of organic matter on fouling of ultrafiltration membranes
Journal of Membrane Science, 1993
This study examined the effect of organic matter adsorption on ultrafiltration membrane blocking and fouling. A hydrophilic cellulose derivative membrane and a hydrophobic acrylic polymer membrane, both with a hollow fiber configuration, were tested. The experiments were performed using synthetic, particle free solutions of a low molecular weight dextran and tannic acid. The effect on fouling of pretreatment of the synthetic solutions by preozonation and by preadsorption on powder activated carbon (PAC) was also evaluated. The level of adsorption was assessed by measuring the quantity of each compound adsorbed, reversibly or irreversibly, by mass or per surface unit of membrane. The level of fouling was assessed by monitoring the loss in specific flux under actual filtration conditions. The study showed that the highest level of adsorption occurred in the ultrafiltration of the aromatic compounds through the hydrophobic membrane. The filtration of a 15 mg/l tannic acid solution led to the adsorption of 6 mg of tannic acid per gram of dry membrane. This resulted in severe fouling with an 80 percent loss of initial flux after only three hours of filtration, despite the absence of particulate matter. Preozonation was very effective in preventing adsorption of tannic acid by-products on the hydrophilic membrane, but only partially reduced the fouling caused by adsorption of the hydrophobic membrane. Similarly, preaclsorption on PAC was effective when the membrane used for subsequent filtration was hydrophilic.
Physicochemical pretreatment of seawater: fouling reduction and membrane characterization
Desalination, 2009
The pretreatment of raw seawater is necessary to minimize the organic fouling of seawater reverse osmosis (SWRO) membranes. To predict the membrane fouling of the pretreated seawater, the modified fouling index (MFI) with ultrafiltration (UF) was investigated in terms of molecular weight distribution (MWD) and membrane characterization. The study was conducted with seawater drawn from Collioure, France. The concentration of total dissolved solids was 32,760 mg/L. The molecular weight (MW) of the initial seawater organic matter (SWOM) ranged from about 14160 Da to 280 Da. FeCl 3 flocculation removed the majority of SWOM, while PAC adsorption could not remove the lowest MW fraction of organic matter (1110, 750 and 280 Da). The UF membranes with 30 kDa and 100 kDa MW cut-off removed the majority of of organic matter corresponding to the peaks 14,160 Da and 6560 Da in MWD. The MFI values obtained when using UF membranes of 30 kDa and 100 kDa with MF pretreatment were 19,700 s/L 2 and 31,000 s/L 2 , respectively. The MFI values after pretreatments of FeCl 3 flocculation and PAC adsorption significantly decreased to 6900 s/L 2 and 6700 for 30 kDa UF and to 2300 s/L 2 and 2500 s/L 2 for 100 kDa UF, respectively. Some relation does exist for both membranes between the MFI-UF values and S pb values obtained during the first peiod of filtration (pore blocking). The pore blocking zone significantly decreased after flocculation and adsorption pretreatment. This suggests that the pore blocking can be used as an indicator to predict membrane propensity. The detailed membrane characterization on the clean and fouled membrane surface after MFI-UF experiments was made in terms of contact angle, zeta potential, functional group and microscopy.
Correlations of relevant membrane foulants with UF membrane fouling in different waters
Water Research, 2013
Membrane fouling Biopolymer Humic substance Particulate matter a b s t r a c t Correlations between potential fouling-relevant substances and membrane fouling during ultrafiltration (UF) of different waters were investigated, including water samples from Lake Tegel, from a Berlin canal (Landwehrkanal) and from a wastewater treatment plant (WWTP) secondary effluent. The biopolymers quantified with liquid chromatographyorganic carbon detection (LC-OCD) showed a remarkable correlation with UF membrane fouling for all the three water sources at different seasons. This finding suggests that the biopolymer content in water can be employed as a universal indicator for predicting membrane fouling potential in UF processes. The particulate matter in the two surface waters Lake Tegel and Berlin canal, as characterized by suspended solids and turbidity, also exhibited a distinct correlation with UF membrane fouling, although its correlation was slightly weaker than that of biopolymers. However, the humic substances, which are generally believed to be major membrane foulants, did not show any reliable correlation with the UF membrane fouling of the different waters. This work may provide useful information for the development of optimized fouling control strategies for sustainable UF operation. ª journal homepage: www.elsevier.com/locate /wa tres w a t e r r e s e a r c h 4 7 ( 2 0 1 3 ) 1 2 1 8 e1 2 2 8
Treatability of wastewater and membrane fouling
Desalination, 2007
Municipal wastewater from the secondary treatment stage was treated using various types of membranes such as regular filter paper, microfilter (MF) and UF membranes of molecular weight cut off (MWCO) of 10, 50 and 100 kDa. The membrane performance was assessed by measuring the absorbance, the BOD 5 and the COD of the filtrate. The results indicated that most of the suspended solids are removed and the BOD 5 and the COD were reduced by 98% and 40% respectively. The results indicate that regular filter paper is equally capable of treating the wastewater as UF and MF membranes. Membrane fouling by wastewater was investigated. Results showed that small particles cause severe membrane fouling by adsorbing within its pores. The MFI-UF index was calculated as a function of time where no stable value was reached. A new equation to calculate the fouling index was suggested. The new equation is based on measuring the relative volumes of suspension and distilled water filtered during a specific period of time. The fouling index calculated by the suggested equation was found stable with time. It has many advantages over the previously defined indices: It is easy to apply, does not involve tedious mathematical calculations, can be employed with any type of membrane and its values ranges between 0 and 1. Testing the effect of applied pressure shows that the fouling index is proportional to the applied pressure.
Clarification: Impact on Ultrafiltration Membrane Fouling in Drinking Water Treatment
Journal AWWA, 2015
The impact of different pretreatment conditions (powdered activated carbon [PAC] addition, iron chloride coagulation, and anionic polymer addition) on ultrafiltration membrane fouling was studied. Experiments were carried out at laboratory scale with new membranes and at pilot scale with used membranes. Results show that PAC has a positive effect—or at least, no negative effect—as long as backwashing allows effective removal of the filtration cake. On the other hand, excess PAC can generate irreversible fouling. Iron chloride has no negative impact for either native or used fibers as long as acid backwashes are effective. Inversely, an anionic polymer has a negative impact in every case—causing irreversible membrane fouling—despite its effectiveness in the clarification process. Test results also confirm that aged membranes are more sensitive to fouling than are pristine membranes. Their more hydrophobic structure is caused by the consumption of the hydrophilic agent under the effec...
Pre-treatment for ultrafiltration: effect of pre-chlorination on membrane fouling
Scientific reports, 2014
Microbial effects are believed to be a major contributor to membrane fouling in drinking water treatment. Sodium hypochlorite (NaClO) is commonly applied in membrane cleaning, but its potential use as a pretreatment for controlling operational fouling has received little attention. In this study, the effect of adding a continuous low dose of NaClO (1 mg/l as active Cl) in combination with alum, before ultrafiltration, was compared with only alum as pretreatment. The results showed that the addition of NaClO substantially reduced membrane fouling both in terms of the rate of TMP development and the properties of the membrane cake layer. Although the size of nano-scale primary coagulant flocs changed little by the addition of NaClO, the cake layer on the membrane had a greater porosity and a substantially reduced thickness. NaClO was found to inactivate bacteria in the influent flow, which reduced both microbial proliferation and the production of proteins and polysaccharides in the c...