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A Pilot Study for Wastewater Reclamation

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   Presented at the conference on Wastewater Reclamation and Reuse for Sustainability (WWRS2005), November 8–11, 2005, Jeju, Korea. Organized by the International Water Association (IWA) and the Gwangju Institute of Science and Technology (GIST). A pilot study for wastewater reclamation and reuse with MBR/RO and MF/RO systems L.S. Tam a , T.W. Tang a , G.N. Lau  b , K.R. Sharma  b , G.H. Chen  b * a  Drainage Services Department of the HKSAR Government, Revenue Tower, Wanchai, Hong Kong SAR, China b  Department of Civil Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, ChinaTel. + 852 2358-8752; Fax + 852 2358-1534; email: ceghchen@ust.hk Received 31 July 2005; accepted 23 December 2005 Abstract A pilot study was conducted to evaluate the quality of the effluent of an enhanced tertiary treatment processconsisting of MBR/RO or MF/RO units and explore the feasibility of reclamation of treated effluent for potableand non-potable reuse applications. The performance of both the MBR/RO and MF/RO pilot plants was excellent.The MBR or MF alone was able to bring down the concentrations of most of the pollutants under acceptablelimits for non-potable reuse applications. The application of RO further improved the treated water quality,especially the aesthetical and microbial qualities. Different strategies were employed to control membrane foulingin RO, and hypochlorite dosing showed the best results. The RO permeate quality in terms of conductivity,turbidity, organic content, ammonia, nitrate, hardness,  E. coli  and virus could meet the water quality requirementsfor many potable and non-potable reuse applications. In removal of total estrogens, the MBR/RO combination performed better than that of MF with RO, indicating the importance of the role of biomass. The rejection of virusin MBR and MF was greatly affected by the chemical membrane cleaning. It took more than 24h for the recovery,implying that the presence of membrane biofilm plays a key role in rejection of virus.  Keywords: Effluent reuse; Membrane bio-reactor; Reverse osmosis; Sewage treatment; Water reclamation 1. Introduction A dual-membrane process such as micro-filtration (MF) or ultra-filtration (UF) and reverseosmosis (RO) is becoming increasingly attractiveas a technology for the reclamation of municipalwastewater because of its efficiency and easyand economical operation [1,2]. In such a process,MF or UF is used for the treatment of secondaryeffluent prior to RO. The suspended solids and colloidal materials are removed by MF or UF,while the RO removes dissolved solids, organic *Corresponding author.Desalination 202 (2007) 106–113 0011-9164/06/$– See front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.desal.2005.12.045  107 and ionic matters. Membrane bioreactor (MBR)can achieve both the secondary treatment of sewageas well as the pretreatment for RO, and henceMBR/RO has a great potential for the treatmentof raw sewage to produce reclaimable water. Water from the Dongjiang River in GuangdongProvince of China accounts for 75% of the HongKong’s current fresh water supplies. Taking intoconsideration Hong Kong’s population growth incoming years as well as the development potentialof the Dongjiang river basin and the water demand of the whole region served by it, Hong Kongneeds to explore alternative water resources toreduce its reliance on the Dongjiang River water for the fresh water supplies. Thus, the interest of wastewater reclamation and reuse in Hong Konghas increased considerably in recent years;however, its implementation is still limited. Therefore, the Drainage Services Department(DSD) of the Hong Kong SAR Governmentconducted a pilot trial for testing two differentcombinations with different membrane filtrationtechnologies: MBR/RO and MF/RO at the Shek Wu Hui Sewage Treatment Works (SWHSTW).The overall objective of this pilot trial was toevaluate the quality of the effluent from each of these pilot plants and to explore the feasibilityof reclamation and reuse of the treated effluent.The study focused on the performance of both pilot plants under different operating conditionsand the quality of treated water. Microbiological,chemical and aesthetical qualities of the treated water were evaluated. 2. Materials and methods 2.1. Description of the pilot plants A schematic of the MBR/RO pilot plant is presented in Fig. 1, while that of MF/RO pilot plant is shown in Fig. 2. The details of the MBR,MF and RO units are presented in Table 1. Thedegritted sewage (for MBR/RO) and secondaryeffluent (for MF/RO) as the raw feed water wastransferred by a submersible pump through astrainer to the feed tank. The large suspended solids in the raw feed water were retained by astrainer to prevent the blockage of the membrane.Fouling of the MBR membrane was prevented  by providing intense aeration and intermittenteffluent discharge (13 min ON/2 min OFF),while the fouling of the MF membrane was min-imized by intermittent aeration and continuous NaOCl dosing. The fouling of RO membrane Recirculation PumpSuction PumpRO Feed Water Tank Air    I  n   f   l  u  e  n   t Feed Pump    A  g   i   t  a   t   i  o  n   P  u  m  p Raw WastewaterScreen    M  e  m   b  r  a  n  e Equalization Tank Anoxic Tank Aerobic Tank RO PermeateConcentrate BlowdownMembrane Bio-reactorReverseOsmosisBooster Pump    C  o  n  c  e  n   t  r  a   t  e   R  e  c   i  r  c  u   l  a   t   i  o  n Fig. 1. Schematic of the MBR/RO pilot plant.  L.S. Tam et al. / Desalination 202 (2007) 106–113  108 was controlled by dosing chloramines or PC11(biocide) and PC191 (antiscalant). The RO wasoperated at the water recovery ratio of 65–75%. 2.2. Pilot trials The MBR/RO and MF/RO pilot trial wasconducted in three operational phases. In Phase I,MBR/RO combination was used to treat thedegritted sewage of SWHSTW. In Phase II/III,MF/RO combination was used to treat the second-ary effluent of SWHSTW. Phase II of the pilottrial was conducted with a low fouling composite(LFC1) membrane in the RO unit, while anenergy saving ESPA1 membrane was studied inPhase III. The objective of studying the ROoperation and performance with two differentmembranes was to optimize the operating costof RO. During the pilot trial, 24-h compositesamples were collected daily and the sampleswere analyzed for pH, conductivity, turbidity,hardness, ammonia, nitrate, COD, BOD 5 , metals,color,  E. coli , and virus. Moreover, estrogensand chlorine disinfection byproducts (DBPs)such as THMs, HAAs, bromate and chlorite,and heavy metals in the treated water were alsoexamined periodically. 2.3. Analytical methods BOD 5 , TKN, ammonia, nitrate and nitrite,COD, TSS and  E. coli  measurements were doneas per the standard methods [3]. Virus level insamples was determined as “male-specific (F + ) Suction PumpFeedPumpSecondaryEffluentEqualizationTank Membrane FiltrationMembraneRO Feed Water Tank RO PermeateConcentrate BlowdownReverse OsmosisBooster Pump    C  o  n  c  e  n   t  r  a   t  e   R  e  c   i  r  c  u   l  a   t   i  o  n Fig. 2. Schematic of the MF/RO pilot plant.Table 1Details of the pilot plant units Parameters MBR MF RO Flow rate 40 m 3 /day 26 m 3 /day 19 m 3 /day Membrane Sterapore ®  SUR (Mitshubishi Rayon), pore size = 0.4µmLFC1, ESPA1 (Hydranautics)ConfigurationSubmerged Submerged Spiral wound Feed Degritted sewageSecondary effluentMBR/MF permeate  L.S. Tam et al. / Desalination 202 (2007) 106–113  109 coliphage” using EPA Method 1602 [4].Trihalomethanes (THMs) were measured accord-ing to the USEPA method 551.1 with slight mod-ifications. A gas chromatography (Finnigan)equipped with an electron capture detector (ECD)was used for THM measurement. Haloacetic acidswere measured according to USEPA method 552.2 (Rev. 1.0, 1995). Bromate and chlorite weremeasured according to the USEPA method 300.0(Rev. 2.2): Determination of inorganic anions byIon Chromatography with slight modifications.Dionex IC with an AS9 column (P/N 42025)was used for the measurement of bromate and chlorite. Enzyme-linked immunosorbent assay(ELISA) kit for total estrogens (Takeda ChemicalIndustries, Japan) was used for the determinationof total estrogen levels in the samples. 3. Results and discussion 3.1. Overall performance The performance of both the MBR/RO and MF/RO pilot plants was regularly monitored in terms of their operation and the treated water quality. The characteristics of the feed water and the performance of MBR/RO (Phase I) and MF/RO (Phase II/III) are summarized inTables 2 and 3, respectively. The performance of both the MBR/RO and MF/RO pilot plants was excellent. The MBR or MF alone was able to bring down the concentra-tions of most of the pollutants under acceptablelimits for non-potable water reuse applications.The application of RO further improved thetreated water quality, especially the aestheticaland microbial qualities. The color of the MBR/MF effluent ranged between 40 and 50 HazenUnit, which is higher than the limiting standard (20 Hazen Unit) of water quality criteria for reuse of treated effluent for flushing in HongKong. The results showed that the RO permeatecan be mixed with MBR/MF effluent to produce“optimized water” for its reuse in toilet flushingto save the treatment cost. 3.2. MBR/MF performance In Phase I, when the MBR was used for theremoval of organic matter and nitrogen fromraw sewage and also as the pretreatment of ROfeed water, the operation of the MBR was stableand its performance was excellent. The effluentBOD 5  was always below 2mg/L, while theaverage effluent COD was only 17.5mg/L. Thesuspended solids concentration in the MBR effluent was below 2mg/L. Despite the fluctuations Table 2Feed characteristics Parameters Phase I Phase II/IIIParameters Phase I Phase II/III Degritted sewage Secondary effluent Degritted sewage Secondary effluent TSS (mg/L) 201 2 Alkalinity (mg CaCO 3 /L)179 71 BOD 5  (mg/L)198 3 Silica (mg/L) 12.0 11.7 COD (mg/L) 391 23 Turbidity (NTU) 59.0 0.6 TKN (mg/L) 43.0 3.1  E. coli  (CFU/100 mL) 4.1 ´ 10 7  2.8 ´ 10 5   NO 3 –  +  NO 2 –  (mg N/L) 0.2 4.7 Virus (PFU/100 mL) 6.2 ´ 10 4  97 TDS (mg/L) 337 364 Total Estrogens  pH 7.2 7.2 (E1 to E3) ( m g/L) 182 38 Apparent color (Hazen unit)135 44 Odour (Threshold odour no.)/ 2  L.S. Tam et al. / Desalination 202 (2007) 106–113

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