In‐line Flocculation‐Submersed MF/UF Membrane Hybrid System in Tertiary Wastewater Treatment

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  In‐line Flocculation‐Submersed MF/UF Membrane Hybrid System in Tertiary Wastewater Treatment
  Author Queries  JOURNAL:  LSST  MANUSCRIPT:  297620 Q1  Please provide received and accepted dates for your article. Q2  Please provide Telephone / Fax numbers and E-mail address. Q3  Please check if the citation of figure 9 inserted in the text is ok. Citation Preview Dear Author,Below is a preview of the citation record for your article as it willappear on the journal Contents Page. Please review this record for author orderand author name spelling. The author list will be made available to indexingservices in the format on this page.Many thanks for your assistance. In-line Flocculation-Submersed MF / UF Membrane Hybrid System inTertiary Wastewater Treatment  L. Erdei, C.-Y. Chang, and S. Vigneswaran  In-line Flocculation-Submersed MF / UFMembrane Hybrid System in TertiaryWastewater Treatment Laszlo Erdei, 1 Chia-Yuan Chang, 2 and Saravanamuthu Vigneswaran 1 1 Faculty of Engineering, University of Technology, Sydney, Australia 2 Dept. of Environmental Engineering and Science, Chia Nan Universityof Pharmacy and Science, Tainan, Taiwan Abstract:  Coagulation / flocculation pre-treatment of feeds can successfully mitigatethe drawbacks of membrane micro- and ultra filtration processes: fouling and limitedability to remove organic pollutants. Laboratory experiments conducted with asynthetic wastewater (representing biologically treated secondary effluent) using0.1 m m pore size hollow fiber membrane showed that simple in-line flocculation pre-treatment with inorganic coagulants dramatically reduced membrane fouling rates.The hybrid system also ensured over 70% organic matter removal in terms of dissolved organic carbon (DOC). Indirect comparison experiments in in-line floccula-tion outperformed clarification pre-treatment at optimum coagulant dosages. Differ-ences in floc characteristics and elevated suspended solids concentrations in themembrane tank may explain this finding, but the exact causes were not investigatedin this study. The beneficial effects of in-line flocculation pre-treatment to MF / UF sep-aration were also confirmed in the treatment of septic tank effluent in a membrane bio-reactor (MBR). The fouling rate of the 0.4 m m pore size (flat-sheet) membrane wassubstantially reduced with 10–100 mg L 2 1 ferric chloride coagulant doses, and totaldissolved chemical oxygen demand (DCOD) removal also increased from 66% up to93%. These findings are consistent with the results of other experimental studies andshow that pre-treatment controls submersed MF / UF filtration performance. Keywords:  In-line flocculation, membrane, fouling, hybrid system, wastewater reuseReceived ???, Accepted ??? Q1 Address correspondence to Laszlo Erdei, Faculty of Engineering, Q2 University of Technology, Sydney, Australia. Separation Science and Technology , 43: 1–13, 2008Copyright # Taylor & Francis Group, LLCISSN 0149-6395 print / 1520-5754 onlineDOI: 10.1080/01496390801974548 123456789101112131415161718192021222324252627282930313233343536373839404142434445LSST297620 LSST_043_007 Techset Composition Ltd, Salisbury, U.K. 3/28/2008 1  INTRODUCTION In recent years low-pressure immersed (or submersed) micro- and ultrafiltration(MF / UF) membrane systems have become popular in water treatment andwastewater reuse applications. Such plants have low energy requirements,modest capital cost due to the open tankage and inexpensive membranematerial used, and easy operability. Another very important attribute is theirrobustness to provide good quality permeate even in rapidly changing feedquality conditions. Nonetheless, their widespread use is hindered by twomajor shortcomings.MF / UFhaslimitedabilitytoremovesmallcolloidalparticlesandpollutantsfromwater.In drinking water production, the presenceof natural organic matterleads to disinfection by-product formation, which is a public health concern.Similarly, the effective removal of organic matter is essential in high-gradewastewater reuse applications. Another shortcoming is membrane fouling,which is the transient or irreversible loss of membrane productivity in termsof transmembrane pressure (TMP) and permeability. Fouling may be abatedby various techniques, such as feed pre-treatment, using additional forcefields, system operation at low fluxes, manipulating the hydrodynamicconditions, backflushing the membrane with permeate and / or air, membranerelaxation (intermittent operation), and preventive chemical treatment (1).These methods, often in combination, have been used with varying degree of success.Coagulation and flocculation long have been employed to reduce foulingand improve organic matter removal in cross-flow MF / UF systems (2). Theterm “in-line flocculation” (or “in-line coagulation”) in this paper refers tothe use of inorganic coagulants before membrane filtration with no intermedi-ate settling step to separate / remove the solids. Immersed MF / UF systems canalso benefit from the use of coagulation / flocculation pre-treatment as firstshown by Benedek et al. (3). In such systems, the free tank volume canserve as reactor space. During the last five years, some important researchresults were published in this particular area, reflecting the growing share of immersed membrane applications in drinking water production and waste-water reclamation. However, several aspects of hybrid membrane systemsstill received little or no attention to date. This manuscript presents someresults obtained with feed pre-treatment using in-line flocculation prior tosubmersed hollow fibre and flat sheet MF / UF. EXPERIMENTALMaterials In the first phase of the study a synthetic wastewater (4) was used that rep-resented a biologically treated secondary effluent. The total dissolved L. Erdei et al.2 464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990LSST297620 LSST_043_007 Techset Composition Ltd, Salisbury, U.K. 3/28/2008  organic carbon (DOC) and pH of this wastewater were in the range of 11.4 to12.5 mg L 2 1 and 7.4 to 7.8, respectively, following variations in make-up tapwater. In some experiments septic tank effluent were used, with major charac-teristics listed in Table 1.The chemicals used in the experiments were of analytical grade,purchased from Sigma-Aldrich. For pH adjustment hydrochloric acid,sodium hydroxide and hydrated lime were used. Apparatus Figure 1 shows the schematic diagram of the laboratory scale immersedmembrane-flocculation hybrid system used in experiments with syntheticwastewater feed. Synthetic wastewater was pumped into the membrane tank (6 L active volume) at constant flow rates. A Tee fitting connected the feedand the coagulant dosing tubes, and a small diameter tube section of variable length ensured adjustable mixing times for coagulation. Compressed  Figure 1.  Schematic diagram of hollow fibre MF system. Table 1.  Raw wastewater characteristics (septic tank effluent)Parameter RangepH 7.2–8.5Temperature ( 8 C) 19–24DCOD (mg L 2 1 ) 97–138Turbidity (NTU) 140–220Suspended solids (mg L 2 1 ) 380–435Dissolved oxygen (mg L 2 1 )  , 1 In-line Flocculation 3 919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135LSST297620 LSST_043_007 Techset Composition Ltd, Salisbury, U.K. 3/28/2008  air was introduced for aeration (10 L min 2 1 rate) via a soaker hose placed atthe bottom of the membrane tank. At start-up the initial raw wastewater fill inthe tank was slug-dosed with the selected coagulant. Very importantly, themembrane was immersed only after sufficient flocculation time (40 minutes)to commence filtration. In experiments with clarified feeds, wastewater waspre-treated in a separate container and the supernatant was used after twohours quiescent settling. Feed was forced through the membrane by pumpsuction and permeate was collected in a container for backwash supply. Inthese experiments a Mitsubishi hollow fiber membrane module was used(hydrophilic PE material, 0.1 m m pore size and 0.05 m 2 total area). Dataacquisition and system control was provided by a PLC / SCADA system,described in detail elsewhere (5).Consecutive experiments used a bench-scale MBR system that treatedseptic tank effluent (Fig. 2). The MBR tank had 12.4 L active volume andprovided 5.3 hours hydraulic retention time. Dissolved oxygen (DO) levelswere in the relatively high 5–7 mg L 2 1 range, since dual (fine and coarse)aerators were used to satisfy biological oxygen demand and for membranebubbling. A relatively low 20 days sludge age was maintained with regardto the influent. The MBR system used a Kubota flat sheet type membrane(chlorinated PE material, 0.4 m m pore size and 0.059 m 2 area). In normaloperation the suction pump was stopped for one minute to allow membranerelaxation after each 11 minutes of filtration. In flux decline tests, the filtrationphase was maintained for two hours. Operational parameters (DO, tempera-ture, pH, and TMP) were monitored and logged by a computer. Experimentaldata were corrected to 20 8 C temperature.  Figure 2.  Schematic diagram of MBR system. L. Erdei et al.4 136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180LSST297620 LSST_043_007 Techset Composition Ltd, Salisbury, U.K. 3/28/2008
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