Application of multi-barrier membrane filtration technologies to reclaim municipal wastewater for industrial use

1 REVIEWING THE APPLICATION OF MULTI-BARRIER MEMBRANE 1 FILTRATION TECHNOLOGIES TO RECLAIM MUNICIPAL WASTEWATER 2 FOR INDUSTRIAL WATER USE 3 4 Ruth Ordóñez a, Daphne Hermosilla a, Noemí Merayo a, Antonio Gascó b, Carlos Negroa 5 and Ángeles Blanco a 6 7 a Department of Chemical Engineering, Universidad Complutense of Madrid, 8 Avda. Complutense, s/n. 28040 Madrid, Spain. 9 10 b IE University, B.Sc. in Biology, Campus de Santa Cruz la Real, Cardenal Zúñiga 12, 11 40003 Segovia, Spain. 12 13 Running Head: Reclaimed sewage for industrial use 14 15 Address correspondence to Prof. Daphne Hermosilla, Dept. of Chemical Engineering, 16 Complutense University of Madrid, Avda. Complutense s/n. 28040 Madrid, Spain. Tel.: 17 (+34) 91 394 4245; Fax: (+34) 91 394 4243; E-mail: [email protected] 18 19 2 ABSTRACT 1 The significant percentage of the world’s water consumption devoted to industrial use, 2 along with an increasingly higher environmental concern of society, have awaken the 3 interest of industry on using municipal reclaimed water for replacing fresh water use 4 coming from utilities or natural resources. Depending on the type of industry and the 5 specific application, water must meet certain quality requirements. Therefore, those 6 water quality standards that are required for those most relevant industrial applications 7 wherein the use of reclaimed water has noticeably been reported are herewith reviewed. 8 Although the use of internal water treatments for recycling and reusing their own 9 effluents has recently and widely been reported within many industrial sectors 10 worldwide, the substitution of fresh water by reclaimed municipal wastewater has not 11 been much extended yet. The increasing proportion of municipal wastewater 12 reclamation plants that rely on membrane filtration technologies versus the total number 13 of reclamation facilities that are worldwide distributed is also assessed within this 14 review, including the discussion of their main related drawbacks. 15 16 Keywords: membrane filtration, municipal wastewater reclamation, industrial water 17 quality, ultrafiltration, reverse osmosis. 18 19 3 1. INTRODUCTION 1 Water shortage, an increasing population, and a more stringent legislation regarding 2 water conservation and environmental compliance, are imposing severe restrictions to 3 industrial water use since its activity entails about a quarter of the world’s total water 4 consumption (1). Moreover, predictions inferred from climate change considerations 5 may even suppose more stringent water use policies in the short term because a 6 significant impact is expected on water resources quality and availability (2). 7 Although water recycling within industrial facilities leads to reduce water 8 consumption figures, it is very difficult to achieve a total closure of their water circuits 9 because residual contaminants eventually accumulate in reused water (3), and fresh 10 water intake is always somewhat needed to compensate losses (e.g. by evaporation) in 11 any case (4). As a consequence, and despite industrial process-water consumption is 12 progressively being reduced as a result of a higher closure level of water circuits, the 13 demand for this resource will still be large in the close future. Fortunately, the 14 remaining water demand after closing water circuits might alternatively be satisfied by 15 reclaimed water from municipal sewage treatment plants in many cases. 16 Despite its great application potential, the market for reclaimed water is nowadays 17 still awaiting a wider exploitation. The major factors limiting the use of reclaimed water 18 in industry are: availability to ensure continuous operation without water shortage, 19 meeting quality standards, volume, cost, and reliability (5, 6). In short, reclaimed water 20 use only satisfied about the 0.4% of the total water use worldwide demanded for 21 industrial purposes in 1995 (7); whereas this alternative only reached the 1% ten years 22 later (2005) (8). Agriculture is the main user of reclaimed water (70%), followed by 23 industry (20%), and domestic uses (10%) (9). 24 4 Beyond these average figures, there are strong significant differences among how 1 the volume of reclaimed wastewater is distributed in each country. For example, Tunisia 2 devotes an 86% water use for agricultural purposes, for which a 30-45% of the treated 3 sewage is also used (10). On the other hand, USA, Singapore, and Germany, 4 respectively devote a 45%, 51% and 69% of their fresh water capacity to industrial 5 purposes, and many recycling and reuse projects have therefore been implemented 6 within their industry (9). Finally, only about the 10% of the fresh water resource of 7 Spain is consumed by industrial applications (11). Correspondingly, only a 0.3% of the 8 Spanish reclaimed sewage capacity was consumed by industry in 2009 (≈1 hm3/year) 9 (12); although an enterprising plan aiming to boost the use of reclaimed water in all 10 sectors is currently being implemented, estimating an accumulated industrial use of 38 11 hm3/year (6.2%) at a 2015 horizon (12). 12 In tune with these considerations, there is much available information regarding 13 municipal wastewater reclamation initiatives for irrigation purposes in agriculture or 14 environmental applications (13-15); as well as for implementing treatments to reclaim 15 the effluent within specific industrial facilities (16-18). However, the use of reclaimed 16 municipal wastewater for industrial applications is still much less extended; with the 17 exception of cooling systems, where municipal reclaimed water has been used from 18 long time ago after a conventional tertiary treatment (19). In addition, reclaimed 19 municipal water has been also used in several other industrial auxiliary applications, 20 significantly replacing fresh water intake, such as washing and flushing, and in general 21 cleaning and watering plants (7, 8). 22 Nevertheless, the interest in using reclaimed sewage as industrial process water is 23 expected to increase in the close future, provided its economical (4, 20-21) and constant 24 quality features (21), and new initiatives being developed and reported within several 25 5 industrial sectors (4, 20, 22, 23). Particularly, it may represent a very interesting 1 alternative for industrial facilities located within areas suffering water scarcity; 2 furthermore when authorities (24) and climate change forecast (2) are progressively 3 imposing more stringent limitations to fresh water consumption. In short, many 4 companies may also find that the substitution of fresh water by municipal reclaimed 5 water may be an economically feasible complement to compensate water losses within 6 their own closed circuits, and/or a good alternative to building on-site specific 7 treatments for recycling their own effluents (4, 23). 8 n general terms, guidelines defining water quality parameters that reclaimed 9 water must fulfil for its different potential use alternatives follow two main orientations: 10 (a) those who prefer limiting health hazard to the maximum extent possible, being the 11 “Californian Title 22” (24) regulation a major example; and (b) those who pretend to be 12 more realistic and feasible, such as the World Health Organisation’s “Guidelines for the 13 safe use of wastewater and excreta in agriculture and aquaculture” (1989) (10). In 14 short, most countries (even states or regions within) have developed their own 15 guidelines regarding the use of reclaimed water combining quality standards from both 16 legislation types, so there are no universal water quality standards defined (20). 17 Nevertheless, although every state has its own legislation within the USA, all of 18 them are collected within the “Guidelines for Water Reuse” (25). Correspondingly, 19 some Australian jurisdictions have together implemented the “Australian Guidelines for 20 Water Recycling: Managing Health and Environmental Risks” (26); as well as they 21 have developed specific validation requirements for recycled water schemes (27). On 22 the other hand, there are no current formal definitions or guidelines for water reuse at 23 the European level. Conversely, there are very different water reuse practices from 24 North to South, and even among Mediterranean countries (28). In fact, the European 25 6 Union is at least making a big effort to solve this legislation disagreement creating the 1 “Mediterranean-EU Water Initiative Working Group for Wastewater Reuse”, which is 2 first one collecting information regarding the current status of wastewater reuse within 3 the EU and the Mediterranean area in order to implement specific demand-driven 4 actions (29). Within this framework, “Aquarec” EU’s project has defined seven water 5 quality categories including microbial and chemical limits for each one (30). 6 Despite water quality guidelines for industrial use differ among countries and the 7 standards required for each specific application, health hazard is the main issue that is 8 always mentioned within all available legislations because special attention should be 9 paid when workers might be in direct contact with water. In this sense, both 10 “Californian Title 22” and the Australian guidelines define a minimal water reclamation 11 process based on a secondary treatment followed by coagulation-flocculation, filtration 12 or flotation, and disinfection. On the other hand, they differ in the limits related to the 13 allowed presence levels of microorganisms. For example, “Californian Title 22” 14 establishes a total coliforms threshold of <23 colony-forming units (CFU)/100 mL for 15 specific sampling (<2.2 weekly) (24); whereas the Australian standards set <10 16 CFU/100 mL for E. Coli (26); but both legislations agree limiting turbidity to <2 NTU. 17 Beyond these considerations, current reclamation treatment trends are focused on 18 obtaining the highest water polishing grade in order to avoid any health hazard or 19 operational risk. In this sense, membrane processes (microfiltration, MF; ultrafiltration, 20 UF; nanofiltration, NF; and reverse osmosis, RO) are taking competitive advantage over 21 those physico-chemical processes specified in historically used standards within 22 municipal wastewater treatment plants (mWWTP) (9). In short, membrane processes 23 produce high quality water regardless the variations in the characteristics of the 24 inflowing feed water in comparison to other treatment processes (31). Particularly, MF 25 7 and UF are applied as the preferred processes for the retention of microbial and 1 suspended solids; and as pre-treatments for NF or RO stages, which are able to generate 2 process water with a very high quality standard, even drinking water (32, 33). 3 Industrial water use is herein reviewed considering water quality requirements for 4 different uses, and the possibility of using municipal reclaimed water as an alternative 5 to fresh water use. Municipal wastewater reclamation facilities that produce treated 6 water for industrial purposes are also located worldwide providing an overall water 7 reclamation assessment. In particular, membrane filtration alternatives, including their 8 potential drawbacks, for reclaiming municipal wastewater for industrial purposes are 9 also reviewed, provided these technologies are currently taking the lead within the 10 alternatives to polish sewage. 11 12 2. ASSESSING CURRENT AND POTENTIAL APPLICATIONS FOR 13 RECLAIMED MUNICIPAL WASTEWATER IN INDUSTRY 14 Most standards for water use are set to maintain a proper operation of industrial systems, 15 to preserve the quality of manufactured products, and to protect public and 16 environmental health. Main water quality guidelines that are applicable to major 17 industrial water consumers are reviewed next. 18 19 2.1 Utilities 20 2.1.1 Cooling water 21 More than 50% of the fresh water consumed by industry is used for cooling (34). 22 Power generation plants, petroleum refineries, chemical manufacturers, metal 23 processors, and food (i.e. mainly meat and dairy products) and beverage manufacturers, 24 are the major consumers of cooling water. In 2004, power generators from the USA 25 8 accounted for approximately the 40% of the freshwater withdrawal within the country 1 (35). Although this value finally only accounts for about the 3% of the total freshwater 2 consumption in the USA (the rest 37% is returned back), it still represents a significant 3 demand of freshwater use (36). The United States Environmental Protection Agency 4 (USEPA) established the cooling tower water quality requirements within their 5 “Guidelines for water reuse” (EPA/625/R-92/004), published in 1992 (37) (Table 1), 6 which have not been modified so far. 7 Figure 1 shows water use intensity for different fuel types and cooling systems in 8 thermoelectric power plants where cooling towers are typically placed (38). In short, the 9 amount of required water depends on the type of cooling system and the efficiency of 10 the turbine, which increases as the difference between steam and condensation 11 temperatures increases as well. Therefore, more efficient plants require less cooling 12 effort to produce the same amount of energy. For example, coal plants nowadays 13 operate at higher temperatures than nuclear ones, so they consume less water. 14 In recirculating cooling systems, such as cooling towers or spray ponds, water 15 evaporates as it dissipates process heat, so the water solution become concentrated 16 many times (typically 4-8 times) (39). As a consequence of both an elevated 17 concentration of diverse matter and such high water temperature, scaling, corrosion and 18 biofouling trouble may be promoted in the system. Particularly, ammonia is a critical 19 compound that may form metal complexes affecting metals solubility and release, as 20 well as it may also promote biological growth and bio-corrosion. In fact, it is especially 21 corrosive to copper alloys at a concentration greater than 2 mgN/L (40). In addition, 22 silica may precipitate when its concentration threshold favours silicic acid 23 polymerization until the solubility limit of amorphous silica is reached, which is further 24 decreased by the presence of trace amounts of aluminum (41); as well as iron content is 25 9 able to deactivate polymers that are used to inhibit calcium phosphate scaling (421). 1 Finally, organic matter content thresholds that may induce the formation of metal 2 complexes, which may further increase metal release as well, or promote biological 3 growth and consequent bio-corrosion trouble in cooling systems, may be controlled 4 monitoring total organic carbon (TOC) concentration in the solution (1). 5 Moreover, cooling water systems (particularly open recirculating ones such as 6 cooling towers) provide a favourable environment (i.e. T= 25-45 ºC; pH= 5.5-8.5) for 7 the growth of bacteria, algae, fungi, protozoa, and viruses (43-44); being the gram 8 negative aerobic bacteria Legionella pneumophila especially dangerous for public 9 health, as it is the responsible to cause the fatal infectious Legionellosis disease. All 10 these microorganisms can be drifted into the environment through cooling equipment 11 aerosols causing other diverse illnesses (45-49). In short, all of them may enter the 12 system in makeup water, through the air, or from process leaks; and they will then begin 13 to proliferate if an effective preventive monitoring and maintenance programme is not 14 implemented. Finally, microbial growth on wetted surfaces ultimately leads to the 15 formation of biofilms, which are made up by the accumulation of microorganisms 16 themselves, extra-cellular secreted products, and other organic and inorganic debris. 17 These biofilms affect equipment performance adversely and also promote metal 18 corrosion (43, 50-51). 19 The key to limit bio-growth, and the consequent slime formation, in any water 20 system reside in controlling nutrients contents circulating in water streams. Besides 21 nitrogen- and phosphorous-based compounds, nutrients may be provided by scale (Ca 22 and Mg based), suspended solids, corrosion products, or trapped organic or inorganic 23 molecules supplied by the incoming water (43). Although corrosion and scaling are 24 relatively easy to control in cooling systems keeping water chemical contents under the 25 16 Materials (ASTM), Semiconductor Equipment and Materials International (SEMI), 1 Balazs Labs, or Sematech. Particularly, ASTM D5127-99 corresponds to the “Standard 2 Guide for Ultrapure Water Used in the Electronics and Semiconductor Industry” (82). 3 In short, general reference specifications for water quality within the electronic industry 4 are collected in Table 1 as well (83). 5 6 2.2.5 Chemical industry 7 It has been recently reported that the chemical industry is consuming the 11% of 8 the total water withdrawal in Europe (84), which approximately represents the 3% of the 9 water directly abstracted by all industry (85). Nevertheless, the general trend is showing 10 a significant reduction of these values; that is, the European Chemical Industry Council 11 (CEFIC), for example, has reported that chemical industrial facilities have reduced their 12 water consumption about an 8% from 2003 to 2007. 13 Water quality requirements and consumption figures widely differ among 14 chemical industrial applications, provided this sector includes such a great diversity of 15 manufactured products (e.g. basic chemicals, steel, fuel, petrochemicals, coal, other 16 mining products, plastics, detergents and toiletries, medicines, paint, pesticides, etc.) 17 For example, the total amount of water that is used in oil refineries has been estimated as 18 0.25-0.34 m3 of water per crude oil barrel (86); and extracting 1 barrel of bitumen from oil 19 sand takes 2 to 3 barrels of water (87). In short, Table 1 also summarizes USEPA’s 20 general guidelines for process water quality demands in the chemical industry, and the 21 basic quality standards that are required in the petrochemical and coal sectors (88). 22 23 3. MEMBRANE TECHNOLOGIES FOR WATER RECLAMATION 24 Membrane filtration is basically based on placing a selective barrier between two phases. 25 17 As a result of exerting a driving force to one side of the membrane, components are 1 transported towards the membrane surface. Therefore, some components pass through 2 the membrane (permeate) and others are retained according to their size (retentate). 3 Considering a particular industrial application, different membrane systems and 4 configurations might be arranged, including pre-treatments and other treatment stages 5 based upon different technologies, in order to meet those target water quality standards 6 that this industrial application may specifically demand from reclaimed municipal 7 wastewater. 8 9 3.1. Types of membrane systems available for wastewater reclamation 10 In general terms, membrane technologies may be classified according to the nature of 11 the applied driving force (i.e. type of pressure or vacuum), or by the operating size 12 ranges for filtration. In short: microfiltration (MF) can separate 0.1-10 μm particles 13 from solvents or other low-molecular components, for which an operating pressure of 14 0.1-2 bar is required; ultrafiltration (UF) is applied to retain macromolecules or sub-15 micrometrical particles (0.002-0.1 m), requiring operating pressures of 0.1-5 bar; 16 nanofiltration (NF) is very useful for removing micro-pollutants, herbicides, and 17 bivalent ions (Ca2+, Mg2+, SO42-, CO32-) due to its 0.5-2 nm pore-size filtration range, 18 for which a 3-20 bar pressure is necessary; and reverse osmosis (RO) is able to separate 19 macromolecules and low molecular mass compounds (>1-0.1 nm), such as monovalent 20 ions (Na+, K+, Cl-, NO3-, etc.) and sugars, working at higher pressure thresholds (5-120 21 bar) in order to overcome higher osmotic pressure values in the solution (89). 22 A complete membrane treatment unit comprises membranes (in assembled 23 modules), a pressure support structure, a feed inlet, a concentrate outlet, and an overall 24 support structure. The main types of membrane modules that are used for wastewater 25 18 treatment are: plate-and-frame, pleated cartridge, tubular, capillary, hollow fibre and 1 spiral wound. Each type of module shows specific advantages and disadvantages 2 depending on feed water quality, their design, and maintenance protocols (90); whereas 3 main differences among them are related to the allowed filtration area and their capacity 4 to promote turbulence to reduce fouling occurrence. 5 In addition, manufacturers offer membrane modules made of a wide variety of 6 materials (e.g. polypropylene, polysulfone, polyvinylidene difluoride, polyether-7 sulfone, cellulose acetate, aromatic polyamide, regenerated cellulose, titanium oxide, 8 etc.) showing different physico-chemical behaviours (e.g. mechanical strength, oxidant 9 tolerance, pH operating range, etc.). In short, their compatibility to each specific 10 operational set of conditions should be verified by end-users (89-91). 11 The direction of feed-water flow in relation to the surface of the membrane 12 determines the type of filtration in MF and UF systems. For example, an encased 13 membrane system may use a cross-flow design, where part of the feed stream is 14 withdrawn as permeate, whereas the other part is forced to flow across the membrane 15 surface; or it may operate in dead-end mode, where the total feed water volume passes 16 through the membrane, leaving all components that are larger than its pores in the feed’s 17 phase. This option results effective when the concentration of particles in the feed 18 stream is low (turbidity <10 NTU), or the packing tendency of the filtered material does 19 not produce large pressure drop across the membrane (90). On the other hand, water 20 streams characterized by a higher concentration of particles or macromolecules (i.e. 10-21 100 NTU) will rapidly compact the cake if operated in dead-end mode, so an 22 unacceptable quick pressure drop will be driven (92). 23 Similarly, semi-permeable membranes of NF and RO systems do not allow the 24 passage of organics or salts, so dead-end filtration will result in plugging or fouling(90); 25 19 although NF filtration may be operated at both modes. In this sense, cross-flow systems 1 are the best alternatives to keep stable filtration rates; despite they consume more 2 energy because their pumping systems have to guarantee high superficial velocities (1-6 3 m/s) through a constant recirculation loop (90, 93, 94). 4 Summing up, although any membrane design can be applied for wastewater with 5 a low suspended solids content, only specifically designed membranes and operation 6 modes would be able to handle effluents carrying high amounts of solids. Particularly, 7 higher cross-flow velocities would be required in these cases. In short, it is highly 8 recommended to perform optimization trials whenever a specific membrane filtration 9 system is designed and implemented for reclaiming a specific wastewater quality. 10 Besides an encased design, membrane modules can be arranged conforming a 11 submerged membrane system inside a tank containing wastewater, where filtration is 12 performed by the application of vacuum. A lower sensitivity to fouling and a lower 13 filtration pressure requirement are the main advantages of submerged systems; whereas 14 some disadvantages can be also addressed, namely: i) foam episodes; ii) fouling may be 15 boosted by high recovery rates, as a higher discharge frequency is required; iii) a higher 16 potential health hazard as a consequence of the exposition of workers to wastewater 17 contact; and iv) the operation of bubbling agitation (which facilitates filtration and 18 reduces fouling) has to be balanced with its operational cost (4). 19 In addition, the direction and orientation of feed water across the surface of the 20 membrane define inside-out and outside-in operation modes. Feed water surrounds the 21 membrane in outside-in systems, so filtrate is collected inside the hollow fibre (lumen). 22 In an inside-out system, feed water enters to the fibres at one end of the membrane 23 element, and discharge stream passes through the element exiting at the opposite side. 24 In this system, filtrated water is collected inside the element on the outside of the fibres. 25 20 In general, inside-out systems are more sensitive to fouling; therefore requiring more 1 intense wastewater pre-treatment, and more frequent cleaning (95). 2 Finally, membrane bioreactors (MBRs) represent a particular configuration of 3 submerged systems, where biological degradation of waste products is integrated with 4 membrane filtration (96). As a consequence, the separation of solids does not depend on 5 settling, and a smaller reactor volume is needed. In addition, they may be used with 6 high filamentous bacteria contents and floating sludge, allowing a very long retention 7 time for solids and generating much less sludge (96-99). In addition, MBR effluents are 8 suitable for feeding RO polishing stages without installing additional pre-treatment 9 processes in between. On the other hand, MBRs are relatively expensive to install and 10 operate; as well as they address other limitations imposed by a low oxygen transfer 11 efficiency (due to a high organic presence), pressure, temperature, and pH requirements 12 (96-99). 13 There are two main MBR configurations: 1) submerged membranes (S-MBR), 14 where the filtration unit is integrated inside the bioreactor; and 2) side-stream MBR 15 (external circulation), where a separate membrane module recycles the rejected stream 16 back to the bioreactor. As permeate flux is relatively low in S-MBR configurations, it 17 can be held for extended periods of time without decline; but membrane permeability 18 could suffer rapid losses if solids content is high (>20 g/L), as well as an important 19 membrane fouling may be generated at low mean cell residence times ( 2 days) (98). 20 On the other hand, both flux and fouling rates are much higher in side-stream MBRs; as 21 well as they require more frequent, and rather more aggressive, cleaning operations, 22 which can be properly performed backwashing or adding chemicals. 23 Summing up both operational and cost issues, it has been reported that submerged 24 configurations operate more effectively than side-stream ones when they are applied to 25 21 reclaim domestic wastewater, considering both energy consumption and cleaning 1 requirements (99). Specifically, aeration results to represent the main operating cost 2 component of these systems because it is required for both mixing and transferring 3 oxygen. In addition, S-MBRs operate at lower flux regimes requiring a greater 4 membrane area, which also implies a greater associated investment. In particular, it has 5 been demonstrated that a side-stream UF-MBR system fed with urban wastewater may 6 produce reclaimed water of enough quality for municipal watering, toilet flushing, and 7 car washing. Moreover, it could be also used for cooling; even as process water after 8 softening (100). 9 10 3.2. Challenges to improve the application of membrane filtration to reclaim 11 municipal wastewater 12 Although membrane filtration generally produce high grade quality water requiring low 13 footprint, and its implementation is nowadays following an increasing trend for 14 municipal wastewater reclamation, they must also face some drawbacks and challenges 15 for a future wider application. 16 17 3.2.1 Fouling and cleaning 18 It is widely known that fouling is the main cause for membrane’s loss of performance 19 because it leads to flux decline, trans-membrane pressure increase, higher energy 20 requirements, membrane biodegradation, and a greater salt passage rate (101, 102). 21 Several types of membrane fouling have been identified, including those caused by 22 suspended solids and particles, colloids, scaling, metal oxidation, organics, extracellular 23 polymeric substances (EPS), and biological organisms (102-105) In fact, membranes 24 22 are usually affected by one or two different types of fouling at the same time, which are 1 summarized in Table 2 (104, 106-109). 2 In general, dissolved organic matter (effluent organic matter, EfOM) typically 3 present in municipal wastewater (TOC ≈ 5-20 mg/L; BOD5 ≈ 3-10 mg/L) (110), is 4 composed of a wide range of constituents (polysaccharides, proteins, aminosugars, 5 nucleic acids, humic and fulvic acids, organic acids, EPS, and cell components). 6 Together to other colloidal matter is able to partially pass (depending on the pore size) 7 through MF or UF membranes causing important fouling to those subsequent NF or RO 8 membranes that are disposed in serial (111). In particular, polysaccharides have been 9 found to play the most important role in fouling NF and UF membranes (112); as well 10 as the presence of soluble EPS (biomass supernatant) has been widely reported to play 11 the main role in the formation of biofouling on MBR’s membranes (109). 12 Although effluents from mWWTPs contain much lower total dissolved solids 13 contents than seawater (1,500 versus 38,000 mg/L, respectively), scaling may also 14 cause special trouble in RO membrane systems (113). Rivers, groundwater, rainfall, 15 seawater, and municipal wastewater, contain basic or acidic inorganic species that are in 16 equilibrium with precipitates, or with other potential scaling components, mainly: OH-, 17 F-, CO32-, SO42-, PO43- and Si(OH)4; whereas cationic species that (directly or indirectly) 18 are more likely to form precipitates in water include: Ca2+, Mg2+, Fe3+ and Al3+. All 19 these inorganic species are responsible to form those main precipitates (phosphates, 20 sulphates, carbonates, hydroxides, and fluorides) that have been identified to cause 21 scaling in reclaiming municipal wastewater RO systems (108). 22 Hydrophobicity, surface charge, pore size, and roughness, are membrane 23 properties that have been related to greater fouling occurrence. In fact, it has been 24 reported that if there are no crevices in the surface of the membrane, no material will be 25 23 deposited there because the boundary layer formation becomes less pronounced, and 1 cross-flow will be then able to remove it at a faster rate than it could be deposited (114). 2 In addition, the effect of membrane charge is mainly reflected by its role in 3 controlling electrostatic adsorption and pore clogging. Particles populating wastewater 4 are generally negatively charged due to the presence of organic matter that came from 5 every source of water that made it up (original drinking water, human activity, surface 6 run-off, etc.), as well as from the bacterial activity that may have been developed along 7 sewage transport (115, 116). Therefore, membranes showing a neutral to negative net 8 surface charge tend to show hydrophilic interaction or electrostatic repulsion with these 9 constituents, further reducing biofouling episodes (117, 118). Finally, other water 10 quality properties, such as pH value or its ionic strength, may also influence organic 11 matter deposition (119). For example, these compounds usually show carboxyl 12 (−COOH) or phenolic (−OH) functional groups, which further increase the 13 concentration of negative charges as the pH value turns higher (120). 14 The diversity of materials that may be used to manufacture commercial UF/MF 15 membranes span the range from fully hydrophilic polymers (e.g. cellulose acetate, CA) 16 to fully hydrophobic ones (e.g. polypropylene, PP; and polyethylene, PE). Between 17 both well-defined groups of polymers, the polysulfone (PS) - polyethersulfone (PES) 18 family, polyacrylontrile (PAN), and polyvinylidene fluoride (PVDF) show an 19 intermediate behaviour; and they may be blended with additives and pore formers in 20 order to design moderate hydrophilic membranes (121). Particularly, sulfone (e.g. PS 21 and PES) polymers are characterized by their mechanical strength, thermal and 22 chemical stability, and excellent film forming properties; as well as their hydrophilic 23 character, and their consequent biofouling resistance as well (122), may be easily 24 24 increased blending them with other polymers thanks to their high inherent solubility. As 1 a result, they may even achieve CA membranes hydrophilicity figures (123-124). 2 Considering all these properties favouring or preventing membrane fouling, much 3 research effort has been recently devoted to modify membrane surface properties in 4 order to further enhance their anti-fouling behaviour (125-127). Particularly, a double 5 repulsive NF hollow fiber membrane, with a positively charged selective layer and a 6 negatively charged substrate, has recently been developed with the ability to effectively 7 retain diverse dye molecules contained in textile industrial wastewater over a wide 8 range of pH values (127). 9 Another common strategy to control fouling relies on installing aeration devices 10 in MF, UF, or even in some NF, systems in order to enhance surface membrane shear 11 and therefore reduce foulant layer thickness. Bubbling can be applied within membrane 12 modules, or externally to them in submerged systems; its effectiveness has been 13 reported to be the same (128). In contrast, aeration may represent the 70% of the total 14 energy cost of the treatment, so current research efforts aim to optimize this operation 15 and its associated cost figures. In fact, it has already been reported that only the 10% of 16 the actual operational time is optimally devoted to perform this task (129). Finally, 17 enhancing shear rate via mechanical means seems it would be a potential alternative to 18 bubbling as a mean for fouling control, as it has been shown by magnetically induced 19 membrane vibration in MBRs (130). 20 Furthermore, fouling can be classified as reversible or irreversible depending on 21 the effectiveness of both, fouling controlling strategies and selected cleaning 22 technologies. Reversible fouling can be described as the fraction that can be effectively 23 removed by one or a combination of the following methods: 1) flow inversion 24 (backwashing or permeate backflushing); 2) forward flush (cross-flow at high flow 25 25 rates); and 3) membrane surface scouring using relaxation breaks like it has been 1 reported in MBR systems (131), or just bubbling air (128), among other alternatives. 2 In short, flux decline caused by irreversible fouling cannot be recovered unless 3 membranes are cleaned by chemical agents, or ultimately replaced (90). Particularly, NF 4 and RO membranes do not allow backwashing, so chemical treatment (namely the 5 clean-in-place (CIP) operation) is the only feasible alternative for them (4, 90). The 6 selection of those chemicals that are going to be used in CIP operation mainly depends 7 on the type of foulant; although they generally belong to one of the following six 8 categories: acids (e.g. HCl, HNO3, H2SO4, H3PO4, oxalic acid, and citric acid), caustics 9 (e.g. NaOH, KOH, and NH4OH), sequestering complexes (e.g. EDTA), detergents (e.g. 10 alkyl sulphate, and sodium dodecyl sulphate), enzymatic chemicals (e.g. alpha-CT, CP-11 T, and perozidase), oxidizing disinfectants (e.g. NaOCl, H2O2, and KMnO4), and 12 commercial blends (e.g. 4Aquaclean, Divos, Triclean, and Ultrasil/Aquaclean) (132, 13 133). 14 In addition, cleaning effectiveness may be enhanced combining physico-chemical 15 cleaning methods, which are those mechanical cleaning processes (i.e. backwashing) 16 that are assisted by the addition of certain chemical agents (i.e. NaOCl or citric acid). 17 For example, a chemically enhanced cleaning operation that is generally applied for 18 cleaning MBRs daily consist on performing backwash using permeate to which certain 19 chemical products have been added in small quantities (109). 20 Summing up, the selection of the best cleaning strategy (type of chemical, 21 cleaning conditions, and frequency) for backwashes and CIP is the key to achieve both, 22 a constant membrane system performance, and the lowest possible contribution to 23 operational cost (4, 134). While mechanical cleaning is directly related to the 24 operational cost of membrane treatment because energy consumption is mainly derived 25 32 Particularly, those plants located in Peterborough (UK) and Madrid (Spain) are based on 1 multi-barrier membrane systems. The first one (MF+RO) started up in 2002, and it 2 produces 1,200 m3/day of permeate for steam generation at Peterborough’s Power 3 Station (178). Madrid’s one (UF+RO) is currently being built inside “Cuenca Media-4 Alta de Arroyo Culebro” mWWTP, and it will provide more than 10,000 m3/day of 5 reclaimed water to Holmen Paper Company, which will become the first paper mill in 6 Europe producing 100% recovered paper from 100% reclaimed water (4). In addition, 7 plants located in Florence (Italy) and Villefranque (France) rely on MBR technology 8 (179-180); whereas UF membranes were installed in Turin (Italy) and Katowice 9 (Poland) (180-181). 10 All water reclamation projects that have been found within the African continent 11 are located in South Africa (Figure 4), and all of them reclaim municipal wastewater for 12 pulp and paper mills; although treatment characteristics are only available for Durban’s 13 water reclamation plant, which supplies 47,000 m3/day of tertiary treated water 14 (sedimentation + ozonation + activated carbon filtration + chlorination) to Mondi Paper 15 Mill (182). 16 Finally, the USA gather most of the municipal wastewater reclamation projects 17 aiming to supply process water to industrial applications that were found in America; 18 whereas only two were found in Mexico, and another one in Canada. None were found 19 located in Central and South America (Figure 4). Among them, there are two well 20 differentiated types of facilities: a) those based on membrane technologies; and b) those 21 consisting on tertiary treatments based on “Californian Title 22” recommendations or 22 slight modifications of them. The main difference between both treatment schedules is 23 whether the main objective is obtaining water just for cooling use, or if higher water 24 quality standards are required, for which multi-barrier membranes systems would be 25 33 installed (Table 6). In short, most plants located from Florida to Massachusetts produce 1 make-up water for cooling operations through conventional tertiary treatments; whereas 2 membrane filtration is preferred in those plants located from Middle to West USA 3 (California and Arizona, mainly), and they are generally of bigger capacity. This may be 4 expected provided California pioneered water reclamation initiatives creating Title 22 5 quality guidelines, and starting-up the first municipal facility using RO systems for 6 water reclamation in 1977 (183). 7 8 5. GENERAL OVERVIEW AND DISCUSSION CONSIDERING ACTUAL 9 FACILITIES RECLAIMING WATER WORLDWIDE 10 Conventional tertiary treatment (typically, flocculation + clarification + filtration + 11 disinfection) is usually applied when reclaimed water would just be used for cooling 12 applications; whereas membrane filtration is further required for the production of 13 boiler make-up water at least, or when reclaimed water is going to be used within the 14 process (Tables 3-6). Most of the facilities that use membrane systems to reclaim 15 sewage rely on the combination of MF or UF with RO; and less are based on MBRs. 16 Although there were approximately 3,000 MBRs operating worldwide in 2008, 17 the number of facilities that are nowadays applying this technology to reclaim 18 municipal wastewater for industrial applications is still very low (Tables 3-6); although 19 it is progressively increasing, and several pilot trials have been carried out to 20 demonstrate the feasibility of combining MBR+RO technologies in new water 21 reclamation projects (184-186). 22 Regarding NF treatment, it has been successfully used for reducing hardness, 23 color and high organic content in feed water, at the same time that it represents an 24 effective barrier for cysts and viruses (187). In comparison to RO, NF works at a lower 25 34 operating pressure and at a higher permeate flux; but it only achieves partial 1 nitrites/nitrates reduction (188), it reaches lower salts rejection results (e.g. 78% in NF 2 versus 95% in RO), and COD would not totally be removed (189). Even considering 3 RO treatment superiority, actual NF application to filtrate secondary effluents of 4 municipal wastewaters is still very limited (190-191). Nevertheless, some good essays 5 considering the implementation of NF technology to reclaim biologically treated 6 wastewater from textile, and pulp and paper industries, have been reported to date (127, 7 192-194). In short, NF may be considered a promising water reclamation alternative to 8 RO filtration in order to reduce the cost of the treatment in those applications where NF 9 limitations would not be limiting the accomplishment of those defined target water 10 quality requirements. 11 In general, and regardless the type of membrane being used, membrane 12 processes are widely extended for treating industrial effluents and recycle them back 13 into the process. For example, there are twenty Indian dyeing mills that have already 14 implemented zero liquid discharge systems to recycle their effluents and reduce fresh 15 water consumption; and even though each one has implemented its own specific 16 wastewater treatment system, all of them use RO technology as the final treatment stage 17 (156). Other companies within the textile industry, or other mills belonging to other 18 industrial sectors, provide other good application alternatives. In short, it may be: an 19 MBR treating bleaching water of cotton raw material (156); a combined UF+NF 20 membrane system reducing freshwater use to its maximum extent in a mill producing 21 fine and magazine quality papers (194-195); an MBR followed by an RO stage 22 generating boiler feed water from a frozen-vegetables processing plant effluent (1); or 23 an UF+RO membrane system implemented in order to satisfy boiler make-up water 24 35 demand in a power plant (196). They all succeeded in recycling effluents inside their 1 industrial processes keeping a competitive product fabrication cost. 2 Nevertheless, it is also very important to highlight one more the fact that using 3 drinkable water quality in some industrial applications would not be necessary (e.g. 4 cooling, or sealing applications). For example, some paper mills use clarified water 5 from dissolved air flotation units for this purpose (197); and evaporator and boiler 6 condensed streams can also be used as pump sealing water (198). In addition, other 7 mills and facilities have reported the use of municipal tertiary treated effluent 8 (biological oxidation + alum coagulation + filtration + disinfection) (199). In short, 9 water and energy savings may turn crucial in the future against a higher water scarcity 10 threshold that would be imposed under the foreseen climate change. On the other hand, 11 even though it would not always be required to generate water of drinkable grade for 12 many industrial applications, the inherent health hazard that is attributed to municipal 13 sewage management will always be a major concern. 14 Industrial effluent recycling is probably the most extended option used to reduce 15 freshwater consumption because the facilities are generally located far away from 16 mWWTPs; and wastewater transport to a mill may not result economically feasible. 17 Besides, municipal wastewater reclamation usually faces a general population 18 disapproval, sometimes even for irrigation purposes (200), due to the presence of micro-19 pollutants (i.e. natural and synthetic hormones, pesticides, pharmaceuticals or personal 20 care products), and microorganisms meaning potential health hazard. In short, final 21 reclaimed water quality is always suspicious of carrying undesired hazards. As a 22 consequence, many surveys have been performed in order to guess which would be the 23 potential public willingness to use reclaimed sewage (201-202). Its main conclusion 24 stated that the best way for promoting its acceptance is providing factual information 25 36 regarding the production process, rather than launching persuasive campaigns. 1 Moreover, in the same way people are nowadays concerned about plastic, glass, and 2 paper recycling, the society should work on achieving the same concern for water use 3 (industrial water use, particularly). 4 Summing up, Table 7 shows a summary of the general treatment removal 5 efficiencies that are achieved for those main water quality parameters (e.g. TSS, TDS, 6 COD, BOD5, TOC, inorganic concentrations, biological contents, etc.) after applying 7 different technological alternatives to reclaim municipal wastewater (4, 203). In short, 8 Table 7 provide a first approximation to an appropriate reclamation treatment selection 9 chart considering average municipal wastewater quality figures, and the requirements 10 that should be considered for a specific industrial application, which were previously 11 reviewed. 12 13 4. CONCLUSIONS 14 Environmental sustainability may be significantly enhanced reclaiming municipal 15 wastewater. Particularly, it enables the replacement of fresh water use for industrial 16 purposes in areas suffering water scarcity. 17 Depending on the type of industry, and on the specific application where 18 reclaimed water is going to be used, water quality requirements that should be fulfilled 19 are variable, so the implementation of those suitable reclamation technologies must be 20 timely designed. The most important challenges that reclaimed facilities using 21 membrane technologies must face are fouling and the management of the generated 22 rejected streams. 23 The number of facilities that reclaim urban wastewater for different industrial 24 applications has recently increased very quickly. Most of them rely on the use of multi-25 37 barrier membranes systems consisting of MF, UF or MBR units followed by RO 1 systems, which are able to produce water of a very high quality (drinkable grade). 2 Screening worldwide mWWTPs relaying on the use of membrane systems for 3 producing reclaimed water for industrial applications, it has been found that 19 4 membrane filtration-based facilities over a total 28 water reclamation plants are 5 currently located in Asia (6 of them placed in Singapore); 15 of 45 in America, 9 of 10 6 in Australia, and 4 of 6 in Europe. 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Parameter Cooling (37) Boiler (37, 38) Sealing (55) PAPER GRADES (61) TEXTILE (5) Electronic (83) Chemical (88) Pharmaceutical a (56) Petrochem / Coal (88) Groundwood Soda & sulphate (Kraft) Kraft bleached Unbleached Bleached Recycled (high pressure showers) Sizing suspension Scouring, bleaching, dying T,ºC - - <20-30 <55 27 - - 15-27 - - 19-21 - - - pH 6.9-9.0 8.2-10.0 >7.0 - - - - - 6.5-7.5 - - 6.5-7.5 6.2-8.3 - 6-9 TSS, mg/L 100 5 - 40 10 10 10-30 10-30 <5 5 5 - 5 - 10 TDS, mg/L 500 700 <1000 250-1000 250-1000 300 75-650 75-650 <300 100 100 - 1000 - 1000 Conductivity, mS/cm - - <2.0 - - - - - <0.5 - - - - ≤1.1 - Turbidity, NTU 50 - - 70 35 40 140 14-56 - - - - - - - Colour, PCU - - - 30 5 25 30-100 5-25 <30 5 5 - 20 - - COD, mg/L 75 5 - - - - - - <5 - - - - - - BOD5, mg/L 25 - - - - - - - - - - - - - - TOC, mg/L - - - - - - - - - - - 0.25 - 0.5 - Hardness, mgCaCO3/L 650 1.0 <200 100-200 100-200 100 200 100 <200 25 25 - 250 - 350 Alkalinity, mgCaCO3/L 350 100 - 75-150 75-150 75 150 75-125 <100 - - - 125 - - Ammonia-N, mg/L 1.0 0.1 - - - - - - <0.5 - - - - - - PO43-, mg/L 4.0 - - - - - - - - - - - - - - HCO3- , mg/L 24 120 - - - - - - - - - - 128 - - NO3-, mg/L - - - - - - - - - - - - 5 ≤0.2 - Si, mgSiO2/L 50 10 - 50 20 50 100 9-20 <5 - - 50 - - aData are for highly purified water class; bHeavy metals in general must be ≤ 0.1 mg/L. 66 Table 1 (continuation). Quality guidelines that reclaimed water must fulfill for its use as fresh water in different industrial applications. Parameter Cooling (37) Boiler (37, 38) Sealing (55) PAPER GRADES (61) TEXTILE (5) Electronic (83) Chemical (88) Pharmaceutical a (56) Petrochem / Coal (88) Groundwood Soda & sulphate (Kraft) Kraft bleached Unbleached Bleached Recycled (high pressure showers) Sizing suspension Scouring, bleaching, dying Al, mg/L 0.1 0.1 - - - - - - 0.1 - - - - - - Fe, mg/L 0.5 0.3 - 0.3 0.1 0.2 1.0 0.1 <0.1 0.3 0.1 - b 0.1 1.0 Mn, mg/L 0.5 0.1 - 0.1 0.05 0.1 0.5 0.03 <0.05 0.05 0.01 - b 0.1 - Ca, mg/L 50 0.4 - - - - - - <60 - - - - 68 75 Mg, mg/L 0.5 0.25 - - - - - - <15 - - - - 19 30 SO42-, mg/L 200 - <200 trace - - - 100-300 <100 - - - - 100 - Cl-, mg/L 500 - <200 75 75 200 200 200 <50 - - - - 500 300 Cu, mg/L - 0.05 - - - - - - <0.001 0.01 - - b - 0.05 Zn, mg/L - 0.01 - - - - - - - - - - b - - Na, mg/L - - - - - - - - - - - 0.01 - - - Dissolved oxygen, mg/L - 0.007 - - - - - - - - - - - - - Methylene-blue active substances - 1 - - - - - - - - - - - - - Carbon tetrachloride extract - 1 - - - - - - - - - - - - - Evaporation residue, mg/L - - - - - - - - - - - 0.5 - - - Resistivity, MΩ·cm at 25ºC - - - - - - - - - - - >18 - - - Abrassive matter (>10µm) - - <40-50 - - - - - - - - - - - - Aerobic bacteria (CFU/mL) - - - - - - - - - - - - ≤10 - - Bacteria endotoxins (IU/mL) - - - - - - - - - - - - ≤0.25 - - aData are for highly purified water class; bHeavy metals in general must be ≤ 0.1 mg/L. 67 Table 2. Effect of common foulants on membrane performance (104, 106-109). FOULANT TYPE SALT PASSAGE PRESSURE DROP PRODUCT FLOW Inorganic salts 10-15% increase 10-40% increase <10% decrease Metal (hydro)oxides >200% rapid increase >200% rapid increase 20-40% decrease Colloids >200% gradual increase >200% gradual increase >50% gradual increase Organic matter increase or decrease small increase >50% decrease Biofouling > 200% rapid decrease >200% rapid increase >50% decrease 68 Table 3. Wastewater reclamation facilities based on membrane systems located in Australia. FACILITY NAME LOCATION SYSTEM APPLICATION Bundamba AWTPa (162) Ipswich MF + RO + UV Cooling water Eraring Power Station (1) Lake Macquarie MF + ROe Boiler makeup water Cooling water Gibson Island AWTPa (163) Brisbane MF + RO + UV Power stations Kwinana Water Reuse Project (204) Perth MF + ROe - d Luggage Point WTPb (160) Brisbane MF + ROe - d Luggage Point AWTPa (161) Brisbane MF + ROe Boiler feed water Cooling tower make-up Other process uses Northern Water Plant (205) Victoria UF + ROe Refinery Illawarra RWPc (160) Sydney MF + ROe At Bluescope Steel facility WRAMS-2000 Olympic Site (206) Sydney MF + RO + UV -d Secondary treatment is specified when RO is used without membrane pretreatment. aAWTP: Advanced Water Treatment Plant; bWTP: Water Treatment Plant; cRWP: Recycled Water Plant; dIndustrial, but not specified; eNot specified whether disinfection exists after RO. 69 Table 4. Wastewater reclamation facilities based on membrane systems located in Asia. FACILITY NAME LOCATION SYSTEM APPLICATION Bedok NEWater plant (23, 207) Bedok/Singapore UF + RO + UV Electronics industry Wafer fabrication Air conditioning Cooling water Boiler feed water Kranji NEWater plant (23, 209) Kranji/Singapore MF + RO + UV Electronics industry Wafer fabrication Air conditioning Cooling water Boiler feed water Seletar NEWater plant (23, 209) Seletar/Singapore MF + RO + UV Electronics industry Wafer fabrication Air conditioning Cooling water Boiler feed water Changi NEWater (210) Changi/Singapore UF + RO + UV Electronics industry Wafer fabrication Air conditioning Cooling water Boiler feed water Ulu Pandan NEWater plant (23, 186) Ulu Pandan/Singapore MF + RO + UV Electronics industry Wafer fabrication Air conditioning Cooling water Boiler feed water Xinxinban WWTPa (209) Hohhot/China MBR + IEl Cooling water Secondary treatment is specified when RO is used without membrane pretreatment.aWWTP: Wastewater Treatment Plant; bWRP: Water Recycling Plant; cSTP: Sewage Treatment Plant; dIndustrial, but not specified; eNot specified whether disinfection exists after the last treatment; fSF: Sand filter; gEDI: Electrodeionization; hCMF: Classical matched filter; iCF: Cartridge filter; jGF: Gravity filter; kAC: Activated carbon; lIE: Ionic exchange. 70 Table 4 (continuation). Wastewater reclamation facilities based on membrane systems located in Asia. FACILITY NAME LOCATION SYSTEM APPLICATION Jurong WRPb (210) Jurong Island/Singapore SFf + ROe -d Jurong WRPb (210) Jurong Island/Singapore MBRe -d CNPC Dalian Petrochemical Company Ltd. (211) Dalian/China UF + ROe Boiler feed water ShanXi DaTong Co-gen Ltd. (212) DaTong/China UF + RO + EDIg Boiler feed water Tianjin Ji Zhuang Zi STPc (8) Tianjin/China MFe -d Tianjin TEDA STPc (8) Tianjin/China MF + ROe -d STP of Beijing EDA (176) Beijing/China CMFh + ROe Process water Gajwa WWTP (9) West Inchen/North Korea Flocculation + media filtration + ROe (MF is applied to protect RO against process breakdown) Cooling water Sewage Treatment of Changshou industry park (176) Changshou/China UFe Cooling water Boiler make-up water Industrial process water Madras Fertilizers Limited (8) Chennai/India SFf + ammonia stripping + carbonation + chlorination + filtration +dechlorination +CFi +ROe Cooling tower makeup Petromin Refinery (Aramco) (213, 214) Riyadh/Saudi Arabia Lime clarification + GFj + ACk + RO + decarbonation + IEl Cooling tower makeup Desalter water makeup Boiler feed water Sulaibiya WWTP (215, 216) Sulaibiya/Kuwait UF+RO+UV -d Secondary treatment is specified when RO is used without membrane pretreatment. aWWTP: Wastewater Treatment Plant; b WRP: Water Recycling Plant; cSTP: Sewage Treatment Plant; dIndustrial, but not specified; eNot specified whether disinfection exists after the last treatment; fSF: Sand filter; gEDI: Electrodeionization; hCMF: Classical matched filter; iCF: Cartridge filter; jGF: Gravity filter; kAC: Activated carbon; lIE: Ionic exchange. 71 Table 5. Wastewater reclamation facilities based on membrane filtration systems located in Europe. FACILITY NAME LOCATION SYSTEM APPLICATION Cuenca Media-Alta de Arroyo Culebro WWTPa (4) Madrid/Spain SF + AC + UF + RO + UV Process water in a paper mill Cooling tower makeup Boiler feed water Flag Fen Sewerage Treatment Plant (217) Peterborough/UK MF+ chloramines +RO +IE Boiler feed water E.C. Katowice Power Plant (181) Katowice/Poland UF Cooling water Villefranque (180) Villefranque/France MBR Washing water in a tannery Empoli MWRF (179) Florence/Italy MBR Industrial (but not specified) Collegno (180) Turin/Italy SF + UF + AC Industrial (but not specified) Secondary treatment is specified when RO is used without membrane pretreatment aWWTP: Wastewater Treatment Plant; b *Type of disinfection not specified; ** Not specified whether disinfection exists after RO. MWRF: Municipal Water Reclamation Facility. SF: Sand filtration; CF: Cartridge filtrate; IE: Ionic exchange; AC: Activated carbon; DMF: Dual media filters. 72 Table 6. Wastewater reclamation facilities based on membrane systems located in America. FACILITY NAME LOCATION SYSTEM APPLICATION South Bay ARWTFa ICF (218) Sta. Clara & S. Jose/ California MF+RO+UV Cooling and processing Toppan Electronic WWTPb (219) San Diego/California MF + ROd Process water Millender-McDonald Carson Regional WRPc (8) Carson/California MF + ROd Cooling tower makeup Mobil Boiler Feed Facility (8) Torrance/ California MF + ROd Boiler feed water West Basin WRPc (220) El Segundo/California MF + ROd Boiler feed water Terminal Island Treatment Plant (8) Los Angeles/California MF + RO + chlorination Boiler feed water Pinellas County Resource Recovery Facility (221) Pinellas/Florida MF + RO + chlorination Boiler feed water City of North Las Vegas WRPc (222) Las Vegas/Nevada MBR + chlorination Cooling water Kyrene WRPc (223) Tempe/Arizona MBR + UV Industrial processing Wyodak Power Plant (200) Gilette/Wyomin SF +CF +RO + recarbonation +IE Boiler make-up Dust suppression Redbud Power Plant (224) Luther/Oklahoma Secondary + ROd Cooling tower makeup Boiler feed water Harlingen WWTPb (225) Harlingen/Texas SF + ROd Process water Honouliulu WWTPb (226) Eva Beach/Hawaii MF + RO + disinfectione Boiler feed water City of Edmonton Gold Bar WWTPb (227) Edmonton/Canada UF + ROd Hydrogen and steam production Process alternate feedstocks Met-Mex Peñoles (228) Torreon/Mexico DMFf + ACg + CFh + ROd Cooling tower makeup Boiler feed water Zinc electrolytic process Secondary treatment is specified when RO is used without membrane pretreatment. aARWTF: Advanced Recycled Water Treatment Facility; bWWTP: Wastewater Treatment Plant; cWRP: Water Reclamation Facility; dNot specified whether disinfection exists after RO; eType of disinfection not specified; fDMF: Dual media filters; gAC: Activated carbon; hCF: Cartridge filter. 73 Table 7. Removal efficiencies (%) of different treatments applied to reclaim municipal sewage (4, 203). Parameter CASa CAS + filtration CAS +BNRb CAS +BNR + filtration MBR MBR +IE CAS +MF / UF +RO MBR+RO TSS, mg/L 96-94 98 95-96 99 >98 >98 >99 TDS, mg/L 0 0-19 0-19 0-19 0-19 - 85-98 VOCs, µm 90 90 90-95 90-95 90-95 90-95 >99 COD, mg/L 84-90 88-91 92-95 92-96 >96 >96 96-99 BOD5, mg/L 93-95 94-95 95-96 98-99 >99 >99 >99 TOC, mg/L 85-88 88-90 90-92 98-99 >98 >98 99.0-99.9 Total nitrogen, mg/L 25-50 25-50 85-89 90-93 >86c >80 >95 Total phosphorous, mg/L 0-17 0-33 75-83 >83 58-93d >80 >86 Metals, mg/L 33-40 33-40 33-40 33-40 trace trace - Total coliforms, CFU/100mL 99.0-99.9 >99.9 99.0-99.9 99.0-99.9 >99.9 >99.9 ~100 Protozoan cysts and oocysts, CFU/100 mL 0-99.9 >99.9 >99.9 >99.9 >99.9 >99.9 ~100 Viruses, PFU/100mL 0-90.0 0-99.9 0-90.0 0-90.0 >90 >90 ~100 aCAS: conventional activated sludge + nitrification. bBNR: biological nutrient (N and P) removal ; cWith anoxic stage; dWith coagulant addition.