Desalination and Water Treatment
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Reverse osmosis desalination system and algal blooms part II: seawater intake technologies Mohamed A. Darwish, Hassan K. Abdulrahim, Ashraf S. Hassan & Basem Shomar To cite this article: Mohamed article: Mohamed A. Darwish, Hassan K. Abdulrahim, Ashraf Ashraf S. Hassan & Basem Shomar (2016): Reverse osmosis desalination system and algal blooms part II: seawater intake technologies, Desalination and Water Treatment, Treatment, DOI: 10.1080/19443994.2016.1159619 10.1080/19443994.2016.1159619 To link to this article: http://dx.doi.org/10.1080/19443994.2016.1159619
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Date: 07 Date: 07 September 2016, At: 22:21
Desalination and Water Treatment
(2016) 1–37
www.deswater.com doi: 10.1080/19443994.2016.1159619
Reverse osmosis desalination system and algal blooms part II: seawater intake technologies Mohamed A. Darwish, Hassan K. Abdulrahim, Ashraf S. Hassan, Basem Shomar* Shomar* Qatar Environment and Energy Research Institute, HBKU, Qatar Foundation, P.O. Box 5825, Doha, Qatar, Tel. +974 4454 2892;
[email protected] (M.A. (M.A. Darwish),
[email protected] Darwish),
[email protected] (H.K. (H.K. Abdulrahim),
[email protected] Abdulrahim),
[email protected] (A.S. (A.S. Hassan), emails:
[email protected] emails:
[email protected] (B. Shomar)
[email protected] (B. Received 21 January 2016; Accepted 23 February 2016
ABSTRACT
While thermal desalination processes require minimum pretreatment (mainly screening and chemic che mical al additi additions ons to preven preventt scaling scaling), ), seawat seawater er revers reversee osmosi osmosiss (SWRO) (SWRO) desalin desalinati ation on plants require extensive pretreatment of the feedwater before entering the membranes. As the Arabian Gulf (AG) countries depend on seawater desalination, there is a strategic decision to move gradually to SWRO desalination technologies. The algal bloom (AB) events that have happened in the AG countries raise more concerns about seawater pretreatment. A seawater intake is a key limiting factor and is a real part of pretreatment for high performance desalination process. This paper (second part of a series of three parts) reviews several eral in inta take ke op opti tion onss an and d thei theirr effe effect ctss on the the qu qual alit ity y of feed feed seaw seawat ater er an and d th thee majo majorr parameters causing membrane fouling, especially bio-fouling. These include the concentrations of algae, bacteria, total organic carbon, particulate and colloidal transparent exopolymer particles (TEP), and the biopolymer fraction of natural organic carbon. Several forms of algal organic matter (AOM) are produced by ABs with varying concentrations and include intracellular intrac ellular organic matter formed due to autolysis autolysis consisting consisting of proteins, proteins, nucleic acids, lipids and small molecules; and extracellular organic matter formed via metabolic excretion and composed composed mainly of exopolysac exopolysaccharid charides. es. Being comparatively comparatively large macromolecu macromolecules, les, exopoly exo polysac saccha charid rides es are most most often often ins insolu oluble ble in water. water. A sig signifi nifican cantt fractio fraction n of the these se exopolysaccharides, known as TEP, are highly surface-active, sticky, and play a significant role in the aggregation dynamics of algae during AB events. This paper reviews the different seawater intake technologies and highlights advantages and disadvantages of each. It aims at recommending the best intake technology for the site-specific conditions of a given desalination project. Keywords: Membrane Keywords: Membrane desalination; Seawater intake systems; Biofouling; Arabian Gulf region
1. Introduction
Thermal desalination methods such as multi effect (M (ME) E) dist distil illa lati tion on,, mult multii-st stag agee fla flash sh (M (MSF SF), ), an and d
ME-thermal ME-ther mal vapor vapor compres compressio sion n (ME-TV (ME-TVC) C) system systemss were the first desalination technologies applied in the Gulf Gu lf Coop Cooper erat atio ion n Coun Countr trie iess (GCC (GCC)) to prod produc ucee desalted seawater (DW). DW satisfies good portions of freshwater demands in the GCC, (Fig. 1). 1 ). DW satisfies
*Corresponding author. 1944-3994/1944-3986 2016 Balaban Desalination Publications. All rights reserved.
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M.A. Darwish Darwish et al. / Desalinati Desalination on and Water Treatment Treatment
Fig. 1. Percentage of desalinated water in total water consumption (in billion cubic meters per year) [1 [ 1].
the main munici municipal pal water needs needs in the GCC (about (about 99% in Qatar, 96% in Kuwait, 60% in Saudi Arabia). The ME, MSF, and ME-TVC systems are known to be very reliable; need simple pre-treatment, have a
lular toxins. In thermal thermal desalinati desalination on systems, systems, volatile organi org anics cs with with boilin boiling g points points lower than than that that of SW may ma y be carr carrie ied d ov over er in th thee ge gene nera rate ted d va vapo porr an and d ve vente nted d out out in th thee proce process ss.. It is of often ten assu assume med d th that at
3 lar large capaci ty per unit, uni t, but hav e aa high high high cost energy energy use pergemcapacity of produced DW, andhave thus of product duct water water.. Th Thee GCC GCC are are now now fo foll llow owin ing g the the worl world d tren trend d by movi moving ng gr grad adual ually ly to the the us usee of se seaw awate aterr reverse osmosis (SWRO) desalination systems to produce duce DW be beca caus usee of their their lo low w sp speci ecific fic energ energy y co connsumption sumpt ion (SEC) and production production cost. Pretr Pre treat eatme ment nt of fe feed ed seaw seawat ater er (S (SW) W) to therm thermal al desalinati desal ination on processes processes is simple simple and consists consists mainly mainly of scr screen eening ing and chemic chemical al condit condition ioning ing.. Screeni Screening ng removes large particles by coarse and fine screens of vertica vert icall and rot rotati ating ng types. types. Chemic Chemical al pretrea pretreatmen tmentt includes chlorination, alkalinity reduction by pH control, and adding scale inhibitors. In general, chemical pret pretre reat atme ment nt is us used ed to av avoi oid d sc scal alin ing g of CaCO CaCO3,
high hi gh mo lecul cular ar ain we weig ight httheorga orbrine gani nics csrejected wi with thd hi high ghk bo boil ing g. points poi ntsmole will remain rem in rejecte back bac to ilin sea. sea Evaporation of organics from SW and their condensation tion int into o distil distillat lates es are governe governed d by severa severall fac factor torss such such as th thee te temp mpera eratu ture re an and d press pressure ure of th thee MSF MSF stages stages or ME effect effectss and their their concen concentrat tration ion,, vapor vapor pressur pres suree and the lat latent ent heat of condens condensati ation on of the individual compounds. Fo Forr co comp mpar aris ison on,, pr pret etre reat atme ment nt of fe feed ed SW fo forr SWRO SWR O desali desalinat nation ion is much much more more compli complicate cated d and general gen erally ly cla classi ssified fied to pri primar mary y and second secondary ary treattreatments men ts to remove remove suspen suspended ded solids solids (parti (particul culate, ate, col col-loidal, microbial and some organic foulants, etc.), oil, an and d grea grease se fr from om fe feed edwa wate ter. r. The The prim primar ary y pretr pretrea eattment usually consists of coagulation and flocculation
MgCO3, an and d CaSO CaSO4. The The MSF MSF is very very robu robust st wi with th allowable particle size in feed SW in the range of 5– 15 mm. The ME proces processs needs needs finer finer water water filt filtrat ration ion,, with the allowable particle size for SW going through the spray spray nozzle nozzless less less than than 0.5 mm. mm. Therma Thermall plants plants’’ inta intake ke scree screens ns do not not remov removee fin finee pa part rtic icula ulates tes an and d algal cells. Chemical conditioning (like chlorination) is applied to cooling SW to the MSF heat rejection section tion,, and and antianti-sc scal alan antt is appl applie ied d to makeu makeup p water water (feed) (feed) to prevent prevent scalin scaling g on the heat heat exchan exchanger ger surfaces. Moreover, antifoaming agents are continuously added to thermal processes to prevent foaming in the de-aer deaerato atorr and flash flash chambe chambers. rs. Neithe Neitherr antifo antifoami aming ng chemic che micals als (poly(poly-pro propyle pylenene-pol polyet yethyl hylene ene oxide, oxide, isoisopropanol) propan ol) nor the anti-scalan anti-scalants ts (commonly (commonly poly-acry-
in combin combinati ation on with with a cla clarifi rificat cation ion proces processs such such as sedimenta sedime ntatio tion n or dissol dissolved ved air flotati flotation on (DAF). (DAF). The second sec ondary ary pretrea pretreatme tment nt consis consists ts of a filt filtrat ration ion proce cess ss,, an and d can can be cl clas assi sifie fied d as conv convent entio iona nall when when granular media filters (GMF) are used and advanced (or low pressu pressure re membra membranes nes)) when when microfil microfiltra tratio tion n (MF)) and ult (MF ultrafil rafiltrat tration ion (UF) (UF) membra membranes nes are used. used. The The SW SWRO RO pretr pretrea eatm tment ent is nece necess ssit ity y to av avoi oid d (o (orr reduc reduce) e) memb membra rane ne fo foul ulin ing g ca caus used ed by de depo posi sits ts of part partic icle less on memb membra rane ne surf surfac acee or in memb membra rane ne po pore ress th that at de degr grad adee it itss perfo perform rman ance ce.. It was was fo foun und d that that at le leas astt 63 63% % of al alll RO memb membra rane ne fa fail ilure uress ar aree rela related ted to th thee in inad adequ equat atee de desi sign gn an and d opera operati tion on of Membra rane ne fo foul ulin ing g ca can n pr pretr etreat eatme ment nt syst system emss [2]. Memb caus causee flux flux de decl cline ine an and d af affec fectt th thee perm permea eate te wate waterr
lactes, poly-carboxylic acids) are expected to assist in the removal of algal cells or detoxification of extracel-
quality. qualit y. There There are variou variouss types types of foulan foulants, ts, which which can be summarized as:
M.A. Darwish et al. / Desalination and Water Treatment
(1) Particulate Particulate (suspended (suspended solids of clay, flocs, and silt). (2) Colloidal Colloidal (0.001–1 (0.001–1 μ m colloidal silica and iron). (3) Mineral Mineral scaling (mainly (mainly salts of calcium, calcium, magnesium, and metal oxides of iron, manganese, copper, etc.). (4 (4)) Orga Organi nicc (o (oil ils, s, po poly lyele elect ctro roly lyte tes, s, nega negati tivel vely y charge cha rged d humic humic and ful fulvic vic aci acids, ds, and residu residual al organics). (5 (5)) Bio Biolo logi gica call (b (bac acte teria ria,, fu fung ngi) i),, an and d mi micr crob obia iall (poly-saccharides and proteins from algal and bacterial cells).
turbid tur bidity ity,, total total suspen suspended ded solids solids (TSS), (TSS), silt silt density density index (SDI), index (SDI), total total organi organicc carbon carbon (TOC) (TOC) determi determinin ning g the natural organic matters (NOM), algae, oil & gas, and chloro chlorophy phyllll-a. a. Details Details of the pretreat pretreatmen mentt processes are given in part three of this series. Process options Schemee A Open intake Schem intake coagflocculation sedimentation granular media filter (GMF) ultrafiltration (UF) cartridge filter RO Scheme Sch eme B Open Open intake intake coagflocculation sedimentation GMF cartridge filter RO Schemee C Open intake Schem intake coagflocculation sedimentation UF cartridge filter RO Schemee D Open intake Schem intake coag-flocculation dissolved air flotation (DAF) GMF UF cartridge filter RO Schemee E Open intake Schem intake coagflocculation DAF GMF cartridge →
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Fouling can be reversible or irreversible based on attachment strength of particles to the membrane surfac face. e. While While reversi reversible ble fouling fouling can be removed removed by a fir firm m shea shearr fo forc rcee or ba back ck-w -was ashi hing ng in lowlow-pre press ssure ure membrane memb rane processes processes such as UF, back-washi back-washing ng cannot cannot be applied for reverse osmosis (RO) membranes. Formation mat ion of a str strong ong matrix matrix of foulin fouling g layer layer with with the solu solute te du duri ring ng a cont contin inuou uouss fil filtr trat ation ion proces processs will will result in reversible being transformed an irr irrever eversib sible le foulin fouling g fouling layer. layer. Irrever Irre versib sible le foulin fouling g into is the stur sturdy dy atta attach chme ment nt of pa part rtic icle les, s, whic which h cann cannot ot be removed by physical cleaning. [4] showed sevVillacorte [3 [3] and Missimer et al. [4 erall SWRO era SWRO pretr pretrea eatm tment ent opti option onss as illu illust stra rate ted d in Figs. 2 and 3, respec respecti tivel vely. y. Th Thee inta intake kes, s, show shown n in and 3 can be open intake (onshore or offshore) Figs. 2 and Figs. with coarse and fine screening; and subsurface intake (vertical, (verti cal, horizontal, horizontal, slant wells; wells; and onshore, beach, and offshore infiltration galleries) where SW is using naturall geological natura geological properties of sediments sediments and rocks to provide high-quality feed SW. After open intakes, small particulates in SW have to be agglomerated for easy eas y sedime sedimenta ntatio tion n and filt filtrat ration ion by (in-li (in-line ne or ful full) l)
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Scheme Sch eme F filter Open Open intake intRO ake coagflocculation DAF UF cartridge filter RO Schemee G Open intake Schem intake in-line coagulation cartridge filter RO Scheme H Open intake in-line coagulation UF cartridge filter RO Schemee I Subsurface Schem Subsurface intake intake in-line coagulation UF cartridge filter RO Schemee J Subsurface Schem Subsurface intake intake UF cartridge filter RO Schemee K Subsurface Schem Subsurface intake intake cartridge filter RO →
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coa coagul gulati ation. on. ) This Thi s is or to dissolved be fol follow lowed ed sedime sedimenta ntation tion (clarification (clari fication) tanks disso lved air by floatation (DAF) to separate agglomerated particles. When coagulation is not enough, it is followed by flocculation. The clarifie fied d SW is th then en filte filtered red by co conv nvent entio iona nall gran granul ular ar media filers (operated by gravity or under pressure); or by low pressure membranes such as UF or microfiltratio tration n (MF). (MF). A final final precaut precaution ionary ary measure measure to save save the SWRO SWRO membra membranes nes is passin passing g the filtered water thro throug ugh h cartr cartrid idge ge filter filters. s. Th Thee trai trains ns a, b, an and d c in desired d simpli simplified fied system system with with open Fig. 3 are the desire intake, while train d in Fig. 3 is for subsurface intake. A subsurface intake is utilized to produce high-quality feed SW that can bypass the pretreatment system and flows directly to the cartridge filters [4 [ 4].
The water intake system to the desalination plant (DP) is considered as part of the feed SW pretreatment process as shown in Figs. 2 and and 3. The intake system shou should ld ensu ensure re re reli liab able le quali quality ty an and d quant quantit ity y of th thee incoming SW to the DP. The choice of the SW intake design and its siting to the SWRO DPs is an important issue that highly affects the quality of the feed SW in ter terms ms of nature nature and quantity quantity of foulan foulants, ts, and comcomplexity of the pretreatment system. system. The pretreatment process removes debris, suspended suspended solids, solids, and organic co comp mpou ound ndss th that at adve advers rsel ely y im impa pact ct th thee pr prim imar ary y memb me mbra rane ne proc proces ess. s. Th Thee in inta take ke syst system em af affe fect ctss th thee
Th Thee pretr pretrea eatm tmen entt syst system em sele select ctio ion n opti option onss are are based on feed SW characterization by determining its
SWRO pl SWRO plan antt capi capita tall co cost st;; adop adopte ted d pr pret etre reat atme ment nt method to achieve the required feedwater quality for
2. Water intake systems
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M.A. Darwish Darwish et al. / Desalinati Desalination on and Water Treatment Treatment
Fig. 2. Pretreatmen Pretreatmentt options options and process schemes schemes applicable applicable for SWRO plants [3 [3].
Fig. 3. Diagram Diagram showing showing typical pretreatment pretreatment process trains for an SWRO plant [4 [4].
the membranes; and reduce the negative impact of DP on the environment. environment. Th Thee nega negati tive ve impa impact ct on mari marine ne envir environ onme ment nt is caused by fish impingement and entrainment into the intake system. Fish impingement occurs when fish get stuck to the intake screen due to high intake velocity, while whi le entrai entrainme nment nt occurs occurs when when organi organisms sms smalle smallerr than the screen mesh are drawn into the intake. The intake to the DP can be classified as open intake (also
Single-pu Single -purpos rposee direct direct int intake akess can be used used for the DP only, or dual purpose intake for both DP and a power pow er plant; plant; and can extract extract SW from from surfac surface, e, shalshallow, or deep water on shore, near shore, or offshore. Shallow SW can be considered as that taken from 0 to 15 m depth while deep SW is considered as that from 20 to 35 m depth. The possibility of having deep-water inta intake ke is li limi mited ted by th thee fe feas asib ibil ilit ity y of findi finding ng de deep ep water wa ter cl clos osee to th thee DP. DP. A float floating ing intake intake is an anot othe herr
called(Fig. 4a direct) sub-surface intake (called indir indirect) ect) type (Fig. 4a)) [5 [and 5]. sub-surface
direct an example us usin ing g system float floatin ing gwith pump pump syst system em;; proposed some some 20 2000 for m Sicily fr from om DP th thee
M.A. Darwish et al. / Desalination and Water Treatment
shore to take SW from the open sea site one meter below the SW surface and connected to the DP by a flexible pipe [6 [6]. Sub-surface intakes extract seawater from beneath the the seaflo eafloor or or beac beach h; an and d ca can n be lo loca cate ted d on or
Fig. 4a. Marine intake systems for seawater DPs [5 [ 5].
]. Fig. 4b. Co-location of a power plant with a DP [11 [11].
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offshore. Onshore offshore. Onshore subsurface subsurface intakes intakes include include vertical vertical wells wel ls (e.g. (e.g. beach beach well), well), slant slant wells, wells, horizo horizonta ntall radial radial wells, wel ls, and beachbeach-infi infiltr ltrati ation on galleri galleries. es. Further Furthermor more, e, offshore offsh ore indirect indirect intakes intakes include include horizontal horizontal directionall ally y dri drille lled d wells, wells, and seabed seabed infiltr infiltrati ation on galleri galleries. es.
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M.A. Darwish Darwish et al. / Desalinati Desalination on and Water Treatment Treatment
Fig. 4c. Three configuration of combining SWR DP with PP [ 12]. 12].
Examples of existing seawater intake systems for DPs of more more th than an one one mi mill llio ion n ga gall llon onss pe perr da day y (MGD (MGD)) capacity are given in Table 1 Table 1 [ [77]. Subsurf Sub surface ace int intakes akes contri contribute bute greatl greatly y to the prepretreatment process, as the feed SW is filtered through natural nat ural soil soil or sand sand bed withou withoutt adding adding chemic chemicals als;; and bacteri bacteria, a, algae, algae, and bio-pol bio-polyme ymers rs (e.g. (e.g. protein proteinss and polysa polysacch cchari arides des)) are remove removed d before before pumpin pumping. g. This reduces drastically the membrane bio-fouling. For example, the Fukuoka, Japan DP using a seabed infiltration gallery supplies seawater of SDI below 3 to the UF pretreatment step. This allows the UF to operate
infil infiltra trati tion on ga gall llery ery,, an and d US$6 US$650 50 mi mill llio ion n fo forr be beac ach h wells. These estimated cost data given by Pankratz are Voutchkov kov reporte reported d signifi significan cantly tly not not confi confirm rmed ed [9]. Voutch ]. The intake smaller than those given by Pankratz [11 [11]. of the Gold Coast plant is only US$ 26 million and thatt of Carlsb tha Carlsbad ad is only US$ 16 millio million n becaus becausee the Carlsbad DP is collocated with a power plant and it uses its existing existing intake. A scie scienc ncee te tech chni nica call ad advi viso sory ry comm commit itte teee fo foun und d 3 recentl rec ently y that that a 380,00 380,0000 m /d off offsho shore re gallery gallery for the Huntington Beach SWRO plant (50 MGD) would cost about US$ 900 million.
for long long periods periods withou withoutt back-w back-wash ashing ing.. Moreov Moreover, er, subsurface subsu rface intakes intakes inherently inherently eliminate eliminate impingement impingement and entrai entrainme nment, nt, and elimin eliminate ate marine marine lif lifee impact impact compared with open intakes [8 [ 8]. The cost of the intake system can be a significant share of DP capital cost. Pankratz [9 [ 9] gave two cost examples, one for the 35 MGD SWRO in Gold Coast, Australia where, the SWRO facility cost was US$ 557 million with Intake/outfall cost was US$ 280 million, or about 50% of the plant cost. The other example is the SWRO plant plant of 50 MGD in Carlsb Carlsbad, ad, Californ California ia where whe re the SWRO fac facili ility ty cost cost was US$ 300 million, million, while the additional intake/outfall cost was estimated fo forr se seve veral ral type typess of in inta take kess as: as: US$ 150 150 mi mill llio ion n fo forr new open sea, US$ 415 million for slant well, US$438 millio mil lion n for horizo horizontal ntal Ranney Ranney’, ’, US$ 638 millio million n for
Th Thee choi choice ce of in inta take ke ty type pe de depen pends ds on th thee si site, te, plant capacity, needed feedwater quantity and quality, and environmental regulations. The type of the intake system sys tem can be decided decided by the DP capaci capacity ty from the beginning. Low capacity DP (200 MGD, (>2 MGD, or 76,000 76,000 m3/d) normally normally uses the open intake intake system system,, and mid-ra mid-range nge capaci capacity ty (5–20 (5–20 MGD) MGD) uses multiple alternatives alternatives [7]. The effect of algal blooms (AB) on membrane fouling depends on the type of the intake. In open intake system using deep SW, the amounts of algae species may ma y be le less ss th than an th that at at th thee surf surfac ace, e, bu butt stil stilll ne need ed algae alg ae pretrea pretreatme tment. nt. Subsur Subsurfac facee intake intakess provide provide SW with almost no algae, and thus the AB is not an issue in th thiis ca casse. More Moreo ove ver, r, open open int ntak akee is usua usuall lly y
M.A. Darwish et al. / Desalination and Water Treatment
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Table 1 Water intake examples of some DP of more than one MGD Capacity [7 [7] Owner
Location
Intake type
Capacity
United Arab Emirates Morro Bay Antigua N.V. Energie en
UAE Morro Bay, California, USA Antigua Leiden, Netherlands
Floating intake on barge Beach wells Open sea intake Beach collector wells
1 mgd (3,800 m3/d) 1.4 mgd (5,300 m3/d) 2.5 mgd (9,500 m3/d) 2.6 mgd (9,800 m3/d)
Rijnland USWatervoorziening Naval Base Ghar Lapsi Veolia Bay of Palma Pemex Refinery Fukouka District Waterworks Agency Pembroke Veolia Aqualectra Production Tampa Bay Water Desalcott San Pedro del Pinatar Public Utilities Board Sydney Water Veolia
Guantanamo Bay, Cuba Malta Kindasa, Saudi Arabia Mallorca, Spain Salina Cruz, Mexico Fukuoka, Japan
Open intake with fish trap Beach wells Open intake Beach wells Beach collector wells Seabed infiltration gallery
5 mgd (19,000 m3/d) 6.3 mgd (24,000 m3/d) 7 mgd (26,500 m3/d) II mgd (42,000 m3/d) 12 mgd (45,500 m3/d) 13.2 mgd (50,000 m3/d)
Malta Sur, Oman Santa Barbara, Curacao Tampa, Florida, USA Point Lisas, Trinidad and Tobago Cartagena, Spain Tuas, Singapore Kumell, Australia Ashkelon, Israel
Beach wells Open intake and beach wells Permeable pit intake Shared power plant intake Bar screen intake Horizontal bedrock wells Open intake Passive intake screen risers Multiple-head open intakes
14.3 mgd (54,000 m3/d) 21 mgd (79,500 m3/d) 22 mgd (83.000 m3/d) 25 mgd (95,000 m3/d) 28.8 mgd (109,000 m3/d) 35 mgd (132,000 m3/d) 36 mgd (136,000 m3/d) 66 mgd (250,000 m3/d) 22 222 mgd (840,000 m3/d)
disinfect disinf ected ed by chlori chlorine ne (eithe (eitherr contin continuou uouss or shock shock chlorination), and chlorine can damage the algae cells. Periodic shock chlorination of the open intake system is now the most common practice for biological control. This can prevent the cells from entering the DP, but the destroyed cell will produce high levels of sticky algal organic matter (AOM) containing polysaccharides chari des and proteins, proteins, transparent transparent exopolymer particles (TEP), and biopolymers. These materials are more di diffi fficu cult lt to remov removee th than an the the ce cell llss an and d caus causee majo majorr SWRO fouling problems. These materials also create a favora fav orable ble environ environmen mentt for bacteri bacteriaa to thrive thrive,, exacerexacer-
It is a necessity to combine any thermal DP with a power plant to secure moderately low pressure bleeding steam rather than using expensive steam directly generated from a boiler. When a SWRO DP is used, its its co comb mbin inat atio ion n wi with th a po powe werr pl plan antt is op opti tion onal al,, although it has some benefits. The main benefit is to overcome the problem of low SW feed temperature in winter that results in decreased output and increased SEC. SEC. When When a SWRO SWRO DP is comb combin ined ed wi with th a powe powerr plant, the return cooling SW from the power plant at a temperature higher than that of ambient SW is used as a feed to the SWRO. Another benefit is to blend the
bating biofouling issues in the SWRO [10]. 10].
discharged high salinity SWRO brine with the return power plant cooling SW (at ambient SW salinity). This reduces the salinity of the discharge from SWRO DP and the tempera temperature ture of the power power plant plant discha discharge rge,, which negatively negatively affect the marine marine environment environment.. Benefits also include: reduction in capital cost for the SW intake and outfalls structures, as well as screening the incoming SW. Several arrangements of co-located the SWRO with power plant are given in Fig. 4c Fig. 4c..
3. Intake system for cogeneration power/DPs
In the Arabian Gulf (AG) area, most DPs are com bined with power plants forming what is called cogenerat gen eration ion power power desali desalinat nation ion plants plants (CPDP). (CPDP). The inta intake ke of DP is co-l co-loc ocat ated ed with with that that fo forr the the po powe werr 4b.. Co-location of a power plant with a DP plant, Fig. Fig. 4b enab enable less the the us usee of on onee inta intake ke fo forr both both,, an and d this this reduces red uces the int intake ake’s ’s constru constructi ction on cost cost 10–30% 10–30%,, and allows use of the same screening facilities. Moreover, by using one outfall for the DP and power plant dilutes the DP rejects and reduces its negative impact on the marine marine environment environment..
4. Open intakes
Open intakes extract SW from surface, and shallow or de deep ep wate waterr fo forr th thee DP (o (orr CPDP CPDP)) wi with th onsh onshor oree lagoon lag oon and channe channels ls and offshore offshore pipe pipe as shown shown in
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M.A. Darwish Darwish et al. / Desalinati Desalination on and Water Treatment Treatment
Fig. 5. Typical onshore (lagoon and channels) and offshore (pipe) open wet-well intake, line, and screen configurations [7].
Fig. Fig. 6b. Exampl Examplee of band band type type travel traveling ing screen screen over over an intake [5 [5].
Fig. 5 [7]. The open intakes are suitable for all plant capacities, but gives inferior feed SW quality. In the case of onshore intake systems, SW is directed ted to a conc concre rete te conv convey eyan ance ce chan channe nell with with co coar arse se screens, then to mechanical fine screens just before the pump station. The coarse screens prevent large debris and aquati aquaticc life life from from enteri entering ng the intake intake str struct ucture. ure. Thes Thesee ar aree us usua uall lly y stat statio iona nary ry and and have have low low de desi sign gn velocity to minimize impingement of aquatic life. The lo low w velo veloci city ty desi design gn incr increa ease sess the the inta intake ke area area to account for partial area blockage by shellfish growth and debris accumulated on the surface of the coarse bars as in the offshore velocity cap intake shown in Fig. 6a Fig. 6a.. Bar screens are used in onshore intakes and have an automa automated ted raking raking mechan mechanism ism that that period periodica ically lly remo remove vess the the ac accu cumu mula late ted d debr debris is an and d allo allows ws fo forr
Fig. 6c. Sydney SWRO plant intake drum screens [14 [ 14]. ].
maintenance. The fine screens’ (3–10 mm) function is to protect protect the int intake ake pumps from damage damage.. They are placed following the course screens, and usually have rotating screens of band type, Fig. 6b or drum type, 6c,, and both should have automated water-sprayFig. 6c Fig. ing ing cl clea eani ning ng syst system em to re remo move ve th thee de debr bris is fr from om th thee screen surface. 4.1. Onshore open intake
]. Fig. 6a. Coarse bar screen of open offshore cap intake [13 [ 13].
A traditional conventional surface water intake for CP CPDP DP usin using g an in inta take ke wate waterr chan channel nel is show shown n in Fig. 7a Fig. 7a [ [99] and a water lagoon is shown in Fig. 7b Fig. 7b [ [15 15]. ]. Open intakes should have a suitable location such as adequat ade quatee submer submergen gence ce at low tides, tides, protect protected ed from from storm wave motion, and away from near-shore sediment me nt tr tran ansp spor ortt zo zone ne (sil (siltt and and se sedi dime ment nt de depo posi sits ts). ).
M.A. Darwish et al. / Desalination and Water Treatment
Fig. 7a. Convention Conventional al channel channel intake [9 [ 9].
Fig. 7b. Convention Conventional al channel channel intake and outfall for Carlsbad Carlsbad seawater CPDP [15 [ 15]. ].
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Fig. 8a. Al Fujairah CPDP plant [9 [ 9].
Some intake locations should be avoided such as: in indust ind ustria riall ports, ports, at wastew wastewate aterr treatme treatment nt plants plants disdis-
vertically vertica lly openin opening g off offsho shore re cap int intake akess are prone prone to draw fish down as shown in Fig. 8b Fig. 8b..
charge, in terminals. ship channels, in area of frequent dredging, and in oil Vertica Ver ticall travel traveling ing band band scr screen eenss are used used over over the intake, intak e, Fig. 6b [5], wi with th inco incomi ming ng SW pa pass ssin ing g the the moving mesh panels to the DP. High-pressure water sprays are used to eject the accumulated debris. These scr screen eenss are specifi specifical cally ly design designed ed with with low incomi incoming ng SW velocity to reduce the entrainment and impingement. A through-screen velocity of 0.15 m/s has been dete determ rmin ined ed to be pr prot otec ecti tive ve of impi imping ngem ement ent si size zed d ]. The open intakes are the most-used type of fishes [16 [16]. intake for large (>10 MIGD, or >45,000 m 3/d, production) plants. One example of onshore intakes for large DP of SWRO type is the 109,000 m3/d Port Lisas in Trinid Trinidad ad equipped equipped with with coarse coarse and fine scr screens eens and
velocity cap is utilized of the the Aof offs fsho hore re in inta take ke pi pipe pe in to orde orfit derrthe tovertical gu guid idee riser aq aqua uati tic c organisms away from the intake structure in order to reduce entrainment, see Fig. 8c [17]. 17]. The velocity cap has a horizontal, flat cover located slightly above the vertical riser to convert a vertical flow into a horizontal flow at the intake’s entrance, and works on the premise that fish will avoid rapid changes in horizontal flow, and typically operates at an entrance velocity of about 0.1–0.3 m/s. An intake intake terminal terminal using velocity 10,15]. In Fig. 8d the upper cap is shown in Fig. 8d [10,15].
vertical turbine pumps [13 [13]. ]. intake is shown in Fig. 8a An offshore-submerged [9] with with veloci velocity ty cap-ty cap-type pe inlet inlet structu structure re and one or more pipelines (or an intake tunnel) to on shore intake cham ch ambe ber, r, tra trash sh ra rack cks, s, fin finee sc scree reens ns,, an and d SW inta intake ke pump station. The offshore intake should have a minimum distance of 30 m offshore. 4.2. Offshore open intake using velocity cap The offshore open intake usually consists of a vertical riser open intake connected to a horizontal pipe to the the inta intake ke pu pump mp stat statio ion. n. Th Thee inta intake ke speed speed can can cause a vertical downward velocity which fish cannot cope with. The results are a large number of entrained fis fish h le lead adin ing g to mari marine ne envi enviro ronm nmen entt impa impact ct.. Many Many
Fig. 8b. View of the Gold Coast SWRO plant velocity cap intakee interior intak interior during operation operation [14]. 14].
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Fig. 8c. Velocity Velocity cap for entrainment entrainment reduction [17 [17]. ].
Fig. 8d. Velocity cap intake structure [4,13 [4,13]. ].
top and lower area sured from SWintake level preferential are as 13 and 16 of m,the thecap seameabed is at 20.1 m below sea level, and thus, the top of the cap is about 8 m above the bottom. Fig. 8e Fig. 8e shows the Sydney SWRO plant intake structure from the velocity cap on the seabed to the water tunnel. Very large velocity-cap intake structure is used at the the Go Gold ld Co Coas astt SWRP SWRP plant plant,, and and pre-c pre-cas astt inta intake ke ]. coarsee screen structure/screen coars structure/screen [16,17,18 [ 16,17,18]. Exampl Exa mples es of open open off offsho shore re intake intakess for large SW ]: DPs are [20 [20]: (1 (1)) Th Thee 300, 300,00 0000 m3/d Adel Adelai aide, de, Aust Austra rali liaa wi with th 0.15 m/s maximum entrance velocity of SW at 18 m depth below SW surface, and 0.5 m above bottom of sea, one inlet structure of 9.5 m
length, and 100 mm located screen size. m diameter concrete tunnel 1,000Am2.8 from shore is used. (2) The 170,00 170,0000 m3/d Al Fuja Fujair irah ah 1, UAE UAE wi with th 0.10 m/s maximum entrance velocity of SW at 10 m depth below SW surface, and 6 m above the bottom of the sea, one 3 inlet structure of 3 m le leng ngth th,, an and d 80 mm scre screen en si size ze.. Thre Threee 2.0 m diameter GRP pipes located 380 m from shore are used. (3 (3)) Th Thee 24 240, 0,00 0000 m3/d Al Dur, Bahrain, with 0.10 m/s maximum entrance velocity of SW at 4 m depth below SW surface, and 2.3 m above bottom of sea, one 4 inlet structure of 7.2, and 80 mm screen screen size. size. Four Four 2.4 m diamet diameter er GRP pipes located 1,500 m from shore are used.
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Fig. 8e. Sydney intake structure from the velocity cap on the seabed to the water tunnel, very large velocity-cap intake structure used at the Gold Coast SWRP plant, pre-cast intake coarse screen structure/screen [ 14,19]. 14,19].
The maximum entrance velocity in the cap shown in Fig. 8d Fig. 8d can be calculated by dividing the intake volume by the intake area of the velocity cap, shown in Fig. 8d as π(9.5 m) × 3 m = 90 m2, and due to the screen bar existence, the effective area would be only 80% of total area, or equal to 0.8 × 90 = 72 m 2. If the DP capacity, say 240,000 m3/d of recovery ratio 1/3, the intake volume would be 720,000 m 3/d (8.333 m3/ s), and the maximum intake horizontal velocity would be 0.115 m/s. The feed SW is conveyed from the intake point to a wet well housing the intake pump through a tunnel or conveya conveyance nce pipelin pipeline. e. Convey Conveyanc ancee pipes pipes are typitypically concrete, high-densi high-density ty polyethylen polyethylenee (HDPE), or fiber-reinfo fiber-r einforced rced polymer polymer pipes with concrete concrete collarscollarsanchors, Fig. Fig. 9a 9a.. It can be laid directly on the seabed, 9b,, but the portion of the pipeline that extended Fig. 9b Fig. through the surf zone and onshore to the pump station is usually laid in a dredged trench and backfilled. An emergent HDPE pipeline is usually installed by welding its segments on shore line, and plugging the ends. It is then withdrawn by a boat to the final location before being connected to the intake offshore, and the pumping well inlet at the shore, see Fig. 9c Fig. 9c..
Due to shellfish growth on internal walls of intake pipes, the pipes are usually oversized (typically 130%) and need need periodi periodicc cle cleani aning. ng. Chemic Chemicals als are usuall usually y inadequ ina dequate ate to suppres suppresss shellfi shellfish sh growth growth in the pipepipelin linee and this all allows ows shellfish shellfish growth in the pretreatpretreatsuggested ted additi addition on of mentt system men system.. Voutch Voutchkov kov [13] 13] sugges sodium hypochlorite, and sulfuric or hydrochloric acid for that purpose. In Australia, tunnels were adopted for five SWRO plants connecting the intake pump stations of the DPs on shore shore with with their their open open int intake akes’ s’ screen screenss and brine concentrate outfall systems. Schematic diagrams of the tunnels used in both Gold Coast and Sydney SWRO plants pla nts seawat seawater er int intake akess are shown shown in Figs. Figs. 10a and 10b,, respectively. Fine 3 mm screens, Fig. 10c, 10c , are usu10b ally ally pl plac aced ed upstr upstrea eam m of th thee pumps pumps to capt capture ure an any y mater ma teria iall th that at may may pass pass th thro roug ugh h th thee coar coarse se ocea ocean n intake screens, including algae and non-motile marine life such as jellyfish, and to protect the pumps from damage. The intake pump moves SW from the intake lo loca cati tion on to th thee DP. DP. Pe Peri riod odic ic scre screen en main mainte tena nanc ncee requires raising and/or removal of screens for cleaning. The pumping station onshore must be equipped wi with th tra travel velin ing g wate waterr fine fine scree screens ns or rota rotati ting ng dr drum um
M.A. Darwish et al. / Desalination and Water Treatment
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Fig. 9a. Conveyance pipelines with installing concrete ballasts [[99].
Fig. 9b. Conveyanc Conveyancee pipes laid directly on seabed, seabed, suggested suggested for a Qatar’s Qatar’s DP.
Fig. Fig. 9c. Inst Installa allatio tion n of convey conveyanc ancee pipelin pipelinee for an intake intake system using the float, transport and sink method at Abu]. taraba, Libya [21 [21].
scr screen eenss to protec protectt downst downstream ream pumps pumps and pretrea pretreattment equipment. Debris and particulate matter (both
organic and inorganic) are removed from screens by the cleaning system. SW from open intakes requires significant pretreatmentt to remove men remove partic particles les,, dissol dissolved ved NOMs, NOMs, aquatic aquatic orga organi nism sms, s, float floatin ing g or susp suspen ende ded d debris debris,, oi oill an and d grease, and anything else that could foul or affect the membranes within the main treatment system. While screens for MSF or MED DPs require a traveling water scr screen een or rot rotati ating ng drum drum screen screen with with 6–9.5 6–9.5 mm wire wire mesh openings, screens for SWRO plants require finer level of screening wire mesh panels having openings ranging from 0.5 to 5 mm to reduce entrainment (up 10d.. SW veloci velocity ty throug through h to 80%), see Figs. 10c and 10d screens is usually less than 0.15 m/s. In offshore openintake, small screen mesh size and slow inlet flow rate (< (. [35] R.M. Rachman, S. Li, T. Missimer, SWRO feed water qu qual alit ity y im impr prov ovem emen entt us usin ing g su subs bsur urfa face ce inta intake kess in Oman, Oma n, Spain, Spain, Turks Turks and Caicos Caicos Island Islands, s, and Saudi Saudi Arabia, Desalination Desalination 351 (2014) 88–100. [36] [36] D. William Williams, s, Sla Slant nt well well intake intake system systems: s: Design Design and construction, in: T.M. Missimer, B. Jones, R.G. Maliva (Eds.) (Ed s.),, Chapte Chapterr 13 Intake Intakess and Outfal Outfalls ls for Seawat Seawater er Reverse-Osmosis Desalination Facilities, Environmental Sci Scienc encee and Engine Engineeri ering, ng, Spring Springer er Intern Internati ationa onall Publishing Switzerland, (2015), doi: 10.1007/978-3-319doi: 10.1007/978-3-31913203-7-13.. 13203-7-13 [37] D. William, Results of Drilling, Drilling, Construction, Construction, Development, and Testing of Dana Point Ocean Desalination Project Test Slant Well, Subsurface System Intake Feasibility sibilit y Assessmen Assessment, t, Desalinati Desalination on and Water Purification Research and Development Program Report No. 152, US Department of the Interior, Bureau of Reclamation, Denver Federal Center, PO Box 25007, Denver CO 80225-0007, 80225-0007, 2009.
SWRO SWR O pilot pilot plant plant in Abu Dhabi, Dhabi, The Intern Internati ationa onall Desalination Association World Congress on Desalinati tion on an and d Wate Waterr Re Reus usee 20 2015/ 15/Sa San n Dieg Diego, o, CA, CA, RE REF: F: IDA15WC Okamoto-51441, 2015. [41] [41] K. Gaid Gaid,, C. Vent Ventre resq sque ue,, C. Pi Pita tavy vy,, J. Th Thub uber ert, t, J. Leparc, Pretreatment of RO desalination: Success stories for variou variouss water water qualit qualities ies,, The Intern Internati ationa onall Desalination Association World Congress on Desalinati tion on an and d Wate Waterr Re Reus usee 20 2015/ 15/Sa San n Dieg Diego, o, CA, CA, RE REF: F: IDA15WC- Gaid-51758, 2015. [42] A. Dehwah, S. Al-Mashharaw Al-Mashharawi, i, N. Kammourie, Kammourie, T.M. Missimer, Impact of well intake systems on bacterial, algae, and organic carbon reduction in SWRO desalinat nation ion system systems, s, SAWACO SAWACO,, Jeddah Jeddah,, Saudi Saudi Arabia Arabia,, Desalin. Desal in. Water Treat. Treat. 55 (2015) 2594–2600. [43] [43] R. Ra Rach chma man, n, A. Dehw Dehwah ah,, S. Li, Li, H. Wi Wint nter ers, s, S. Al-Mash Al-M ashhar harawi awi,, T. Missim Missimer, er, Effect Effectss of well well int intake ake system sys temss on remova removall of alga algae, e, bacter bacteria, ia, and natura naturall orga organi nicc matt matter er,, in in:: T.M. T.M. Miss Missim imer er,, B. Jone Jones, s, R. R.G. G. Malvia, Malv ia, (Eds.) (Eds.),, Chapte Chapterr 9 Intake Intakess and Outfal Outfalls ls for Seawat Sea water er Revers Reverse-O e-Osmo smosis sis Desalin Desalinati ation on Facilit Facilities ies,, Enviro Env ironme nmenta ntall Scienc Sciencee and Engine Engineeri ering, ng, Spring Springer er Int Intern ernati ationa onall Publis Publishin hing g Switze Switzerlan rland, d, (20 (2015), 15), doi: doi: 10.1007/978-3-319-13203-7-9 . 10.1007/978-3-319-13203-7-9. [44] A. Dehwah, T. Missimer, Impact of intake well age in impr improv ovin ing g th thee qu qual alit ity y of raw raw wate waterr for for a SWRO SWRO desalination plant, Jeddah, Saudi Arabia, The Internatio tional nal Desalin Desalinati ation on Associ Associati ation on World World Congre Congress ss on Desalin Des alinati ation on and Water Water Reuse Reuse 2015/Sa 2015/San n Diego, Diego, CA, REF: IDAWC15- Dehwah-51661, 2015.
