Effects of Co-current and Cross Flows on Circular Enhanced Gravity Plate Separator Efficiencies

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1 Environ. Eng. Res June,19(2) : Reserch Pper pissn eissn X Effects of Co-current nd Cross Flows on Circulr Enhnced Grvity Plte Seprtor Efficiencies Lock Hei Ngu 1, Puong Ling Lw 2, Kien Kuok Wong 1 1 Fculty of Engineering, Computing nd Science, Swinurne University of Technology Srwk Cmpus, Kuching, Srwk 93350, Mlysi 2 Deprtment of Civil Engineering, Universiti Mlysi Srwk, Kot Smrhn, Srwk 94300, Mlysi Astrct This study compres the effects of flow on oil nd suspended solids removl efficiencies in circulr enhnced grvity plte seprtor equipped with colescence medium. Colescence medium cts to cpture rising oil droplets nd settling solid prticles nd ssist in the colescence of oil nd cogultion of solid. The circulr seprtor uses n upflow center-feed perforted-pipe distriutor s the inlet. The co-current flow is chieved using 4 incresing sizes of frustum, wheres cross flow uses inclined colescence pltes running long the rdius of the seprtor. The different rrngement gve the cross flow seprtor higher colescence pln re per opertionl volume, miniml nd constnt trvelling distnce for the oil droplets nd prticles, lower retention time, nd higher opertionl flowrte. The cross flow seprtor exhiited 6.04% nd 13.16% higher oil nd totl suspended solids removl efficiencies s compred to co-current flow. Keywords: Circulr enhnced grvity plte seprtor, Colescence medium, Co-current flow, Cross flow, Oil droplets nd solid prticles removl 1. Introduction Regultory requirement for oil nd suspended solids content llowle in sewge nd industril effluent dischrge re 10 mg/l nd 100 mg/l, respectively, for most countries, such s the United Stte, Cnd, Colomi, Mlysi, nd some Europen countries [1]. Effluent from oil nd gs industry or shipping ctivities contins high mount of oil [2]. Wstewter high with suspended solids prticles due to erosion re introduced into the environment from lnd clering nd erthworks ctivities [3]. Most seprtors used to tret oil or solids re rectngulr seprtor [4]. Some of these seprtors currently in use include 1) the Americn Petroleum Institute seprtors, 2) colescing plte seprtors, 3) colescing tue seprtors, nd 4) pcking type seprtors [5]. Rectngulr seprtor hs constnt horizontl velocity, v h throughout. In rectngulr seprtor, co-current flow is fvorle for solid prticles removl wheres cross flow is preferle for oil seprtion [6]. A circulr seprtor tkes dvntge of the continul decrese in horizontl velocity, v h s surfce re increses long the rdius. The decrese in horizontl velocity, v h enhnces seprtion. The circulr seprtor is more compct s compre to rectngulr seprtor [7]. The im of this study is to determine which flow pttern long colescence medium is preferle for light phse (d) hevy phse (c) plte 1 Fig. 1. Physics of processes in plte settler [9]. principle interfce plte 2 oil nd solid seprtion in circulr seprtor. Colescence mediums in the form of prllel pltes re pplied in enhnced grvity seprtors to increse the seprtion efficiency y mking the settling distnce smller nd the interfcil re for the colescence lrger. In these seprtors, the oil droplets rise to the upper plte nd form trickling film which flows long the plte following the hydrosttic pressure grdient to the principl interfce s shown in Fig. 1 [8-10]. Droplets of oil then colesce on the trickling film [9]. This is n Open Access rticle distriuted under the terms of the Cretive Commons Attriution Non-Commercil License ( which permits unrestricted non-commercil use, distriution, nd reproduction in ny medium, provided the originl work is properly cited. Received Ferury 19, 2014 Accepted My 02, 2014 Corresponding Author E-mil: lngu@swinurne.edu.my Tel: Fx: Copyright 2014 Koren Society of Environmentl Engineers 151

2 Lock Hei Ngu, Puong Ling Lw, Kien Kuok Wong c Fig. 2. Co-current flow () plte rrngement nd () oil-wter-solid seprtion mechnism. Fig. 3. Cross flow () plte rrngement (top view), () plte rrngement (cross sectionl view), nd (c) oil-wter-solid seprtion mechnism. Circulr oil-wter-solid seprtor with colescing pltes re suitle for pplictions on smll-scle wstewter flow for workshop, oil terminl, lnd clering nd erthwork surfce runoff, residentil t rurl or low popultion density res where the trnsporttion of wstewter to centrl tretment system is costly [11]. This seprtor is lso suitle for wstewter tretment where vilility of lrge re is constrint, such s on oil nd gs pltforms nd shipping ctivities. 2. Mterils nd Methods Co-current nd cross flow were chieved in circulr seprtor y utilizing n upflow center-feed perforted-pipe distriutor s the inlet [12] directing flow to different rrngement of inclined colescence pltes. Fig. 2() illustrtes how inclined pltes were rrnged to chieved co-current flow. The rrngement consists of four series of inclined frustums. Ech series consists of severl successive lyers of frustums. The frustums were inclined t n ngle of 55 (up-right) [13] nd 125 (inverted) tht susequently form multiple-ngle rrngement. All frustums hd n inclined length of 10.0 cm. The mount of frustums increses with ech susequent series, nd the intervl etween frustum decreses with ech susequent series [7]. Fig. 2() shows the mechnism of oil-wter-solid seprtion for co-current flow. Fig. 3() nd () illustrtes the rrngement of pltes to chieve cross flow. The rrngement consists of 6 set of colescing pltes, ech covering 60 of the circulr seprtion tnk. Ech 152

3 Effects of Flow Directions on Circulr Seprtor Efficiencies colescing pltes set consists of severl prllel successive lyer of pltes inclined t ngle θ, 55 nd 125 to form the dul ngle colescing pltes rrngement. The intervls etween inclined pltes re constnt, nd the intervls etween stcks of inclined pltes form the oil nd sludge port [11]. Fig. 3(c) shows the mechnism of oil-wter-solid seprtion for cross flow Oil-Wter-Solid Seprtion Mechnism Colescence pltes promote lminr flow nd fcilitte the colescence of oil droplets nd the cogultion of solid prticles. Pltes re kept t miniml spcing to reduce the verticl distnce tht the oil droplets nd solids prticles need to trvel efore encountering plte. Droplets nd prticles cptured on the pltes would increse in size. When they re lrge enough the uoyncy forces will overcome the ttrctive forces holding the droplets nd prticles to the plte [14]. Then the lrge droplets rose to the surfce to e skimmed out nd the cogulted prticles settled to the ottom. In rectngulr seprtor the pltes extend from one side of the seprtor ll the wy to the opposite side of the seprtor; ll cptured oil/solids must progress long the entire length of the plte efore exiting to the surfce t the opposite side of the seprtor [15]. In lrge seprtor, this could mesure 2.5 m in length, or more. This mens tht the mount of oil running long the undersides of pltes increses s it moves upwrd long the sloped surfce of the pltes. In circulr seprtor, oil/sludge ports re plced t intervls long the rdius (co-current) or verticlly ligned long the rdius (cross flow) for the quick relese of oil droplets nd solid prticles from the pltes to rise to the surfce or fll to the ottom of the tnk. These re illustrted in Figs. 2() nd 3(c) Different etween Co-current nd Cross Flow Circulr Seprtor Both the seprtors were designed with 86 L of opertionl volume [16]. The colescence plte rrngements for cross flow seprtor gve higher colescing pln re per opertionl volume of m²/l s compred to co-current flow with m²/l [17]. Higher colescing pln re provides more surfce re for oil droplets to colesce nd solids prticles to cogulte, hence theoreticlly enle higher removl cpcities of oil droplets nd solid prticles. Due to this, seprtor with cross flow cn operte t higher opertionl flowrtes which llow more wste wter to e treted Experimentl Procedure Influent oil wter mixtures were prepred from used plm olein oil with mss density (ρ o ) of 917 kg/m³. Different influent oil concentrtions, C io were prepred (50, 75, 100, 150, 200, nd 250 mg/l). Oil concentrtions in wter were mesured using n oil-in-wter nlyzer which is non-dispersive infrred sorption method. The mesurement error for this instrument is ±0.2 mg/l (oil content nlyser OCMA-310; Hori, Tokyo, Jpn). Influent suspended solids wter mixtures were prepred from sieved silt nd cly prticles tht pssed through mm sieve (with specific grvity of 2.72) [18]. Seven different influent suspended solids concentrtions, C iss, were prepred: 100, 150, 200, 250, 300, 350, nd 400 mg/l. Totl suspended solids (TSS) were mesured y spectrophotometer (DR/2400; HACH, Lovelnd, Fig. 4. Schemtic digrm of experimentl setup. Fig. 5. Averge oil removl efficiencies, Eo of vrious Cio t different Qi for cross flow seprtor. CO, USA) using the photometric method t 810 nm. The instrument wvelength ccurcy is ±1 nm nd clirted utomticlly vi internl filter. The prepred influent mixtures were tested t four different influent flowrtes (Q i ; , , , nd m 3 /s). Fig. 4 indictes the schemtic digrm of the experimentl setup. 3. Results nd Discussions 3.1. Oil Removl Fig. 5 illustrtes the verge oil removl efficiencies, E o of vrious C io t different Q i of the cross flow seprtor. The verge E o of vrious C io increses with decreses in Q i. The verge E o t Q i of , , , nd m 3 /s were 83.8%, 78.4%, 72.4%, nd 64.3%, respectively. The R 2 correltion of Q i reltion with verge E o ws The eqution E o = (Q i 10-5 ) cn e used to determine the verge oil removl efficiency of cross flow t given Q i. Fig. 6 compres the oil removl efficiencies of co-current flow nd cross flow for circulr seprtor t C io of 100 mg/l [11]. It indictes tht oil removl for cross flow is pproximtely 13.16% higher compred to co-current flow

4 Lock Hei Ngu, Puong Ling Lw, Kien Kuok Wong Fig. 6. Oil removl efficiencies t influent oil concentrtion of 100 mg/l nd vrious flowrte for co-current nd cross flow Suspended Solids Removl Fig. 7 shows the reltionship of verge TSS removl efficiencies, E ss of vrious C iss t different Q i for the co-current flow nd cross flow seprtors. Similr to oil removl trend, it ws lso oserved tht verge E ss of vrious C iss increses when Q i decreses. For cross flow seprtor the verge E ss t Q i of , , , nd m 3 /s were 67.1%, 62.6%, 56.7%, nd 46.9%, respectively. The R 2 correltion of Q i reltion with verge E ss ws The eqution E ss = (Q i 10-5 ) cn e used to determine the verge TSS removl efficiency of the cross flow seprtor t given Q i. For co-current flow seprtor the verge E ss t Q i of , , , nd m 3 /s were 60.70%, 54.91%, 50.06%, nd 43.45%, respectively. The R 2 correltion of Q i reltion with verge E ss ws The eqution E ss = (Q i 10-5 ) represents the reltionship etween verge TSS removl efficiency of the co-current flow seprtor with Q i. Comprtively, cross flow hs n verge 6.04% higher TSS removl rte s compred to co-current flow. It is pproximtely 12% higher t lower influent concentrtion of 100 nd 150 mg/l. Fig. 7. Averge totl suspended solid removl efficiencies, Ess of vrious Ciss t different Qi for () co-current flow seprtor nd () cross flow seprtor. TSS: totl suspended solids Discussion Circulr plte seprtor with cross flow exhiits 6.04% nd 13.16% higher oil nd TSS removl efficiencies s compred to co-current flow. Cross flow colescence medium rrngement return higher colescing pln re per opertionl volume of m²/l s compred to co-current flow with m²/l. This gve cross flow more surfce re for oil droplets to colesce nd solids prticles to cogulte, nd hence increses its removl cpcity. The rrngement of colescence pltes with reltion to the flow direction gve cross flow constnt distnce (denoted s x in Fig. 8) for oil droplets/solid prticles to trvel efore it meet colescence plte. With co-current flow rrngement the distnce might vries from x to y depending on the size of the droplets/prticles. Therefore, in cross flow rrngement, oil droplets/ solid prticles regrdless of its size need only to trvel the minimum x distnce efore it encounter colescence plte. These fctors enhnce seprtion nd performnce in the cross flow seprtor. With cross flow rrngement seprtor cn e operted t higher flowrte nd shorter retention time to chieve comprle results with co-current flow seprtor. Fig. 8. Distnce trvel y oil droplets/solid prticles efore encountering colescence plte. 4. Conclusions Circulr enhnced grvity plte seprtor with cross flow exhiits 6.04% nd 13.16% higher oil nd TSS removl efficiencies s compred to co-current flow. Cross flow colescence medium rrngement hs etter removl performnces due to its higher colescing pln re per opertionl volume nd minimum nd constnt droplets/prticles trvelling distnce etween colescence pltes. 154

5 Effects of Flow Directions on Circulr Seprtor Efficiencies Acknowledgments The uthors wish to thnk the Mlysin Ministry of Science, Technology nd Innovtion which funded the reserch work relted to this pper. Nomenclture θ colescence plte ngle ρ o kg/m³ used plm olein oil with mss density C io mg/l influent oil concentrtion C iss mg/l influent TSS concentrtion E o % oil removl efficiencies E ss % TSS removl efficiencies Q i m 3 /s influent flowrtes TSS mg/l totl suspended solids v h m/s horizontl velocity References 1. Mohr KS. An overview of US nd interntionl regultions regrding hydrocrons in wter effluents. Proceedings of the Wter Environment Federtion nd Purdue University Industril Wstes Technicl Conference; 2000 My 21-24; St. Louis, MO. p LRusic A, Mohr KS. Design nd instlltion of hydrocron removl seprtor for industril storm runoff. Proceedings of the British Columi Wter nd Wste Assocition Annul Conference; 1998 Apr; Whistler, BC. 3. Mlysi Deprtment of Environment. Mlysi environmentl qulity report Kul Lumpur: Deprtment of Environment; Tchonoglous G, Burton FL, Stensel HD. Wstewter engineering: tretment nd reuse. 4th ed. New York: McGrw- Hill; Mohr KS. Stormwter tretment for contminnt removl. In: Pulic works nd the humn environment: proceedings of the Interntionl Symposium of the Americn Pulic Works Assocition; 1995 Apr 19-21; Settle, WA. 6. Schlegel S, Stein A. Design mesures to increse the efficiency of secondry sedimenttion tnks. Wter Sci. Technol. 2000;41: Ngu LH. Development nd performnce test of seprtion system for removl of physiclly emulsified nd free oils from wstewter [disserttion]. Kot Smrhn: Universiti Mlysi Srwk; Meon W, Rommel W, Blss E. Plte seprtors for dispersed liquid liquid systems: hydrodynmic colescence model. Chem. Eng. Sci. 1993;48: Rommel W, Blss E, Meon W. Plte seprtors for dispersed liquid liquid systems: multiphse flow, droplet colescence, seprtion performnce nd design. Chem. Eng. Sci. 1992;47: Rommel W, Blss E, Meon W. Plte seprtors for dispersed liquid liquid systems: the role of prtil colescence. Chem. Eng. Sci. 1993;48: Ngu LH. Development nd optimiztion of circulr phse seprtor with dul ngle colescence pltes for removl of suspended solids, free nd physiclly emulsified oils [disserttion]. Kot Smrhn: Universiti Mlysi Srwk; Ngu LH, Lw PL, Wong KK. A study on flow chrcteristics of verticl perforted-pipe distriutor in circulr seprtor. J. Civil Eng. (IEB) 2004;32: Demir A. Determintion of settling efficiency nd optimum plte ngle for plted settling tnks. Wter Res. 1995;29: Lw PL, Ngu LH, Wong KK, Yusof AA. Development nd performnce tests of seprtor for removl of physiclly emulsified nd free oils from wstewters. J. Inst. Eng. Mlysi 2006;67: Deininger A, Gunthert FW, Wilderer PA. The influence of currents on circulr secondry clrifier performnce nd design. Wter Sci. Technol. 1996;34: Ngu LH, Lw PL, Wong KK, Yusof AA. Oil droplets nd solid prticles removl using circulr seprtor with inclined colescence mediums: comprison etween co-current nd counter-current flow. Wter Sci. Technol. 2010;65: Ngu LH, Wong KK, Lw PL. Optimiztion of circulr plte seprtors with cross flow for removl of oil droplets nd solid prticles. Wter Environ. Res. 2012;84: Ghni AA, Zkri NA, Kssim M, Nsir BA. Sediment size chrcteristics of urn drins in Mlysin cities. Urn Wter 2000;2: