American Journal of Engineering Research (AJER)2015 American Journal of Engineering Research (AJER) e-ISSN: 2320-0847p-ISSN : 2320-0936 Volume-4, Issue-8, pp-140-144 www.ajer.org Research PaperOpen Access w w w . a j e r . o r g Page 140 Flocculator Design for a Water Treatment Plant in a Rural Community with a River or Stream Water Source around Maiduguri Area, Borno State, Nigeria Hussaini A Abdulkareem, Nuhu Abdullahi, Bitrus I Dangyara, Gideon I Orkuma Department of Mechanical Engineering , School of Industrial Engineering , College of Engineering, Kaduna Polytechnic, Nigeria ABSTRACT:Flocculator,amajorcomponentofwatertreatmentplantisrequiredforattainingthe International Standard for a potable drinking water is hereby design for rural domestic water supply. This is for anestimatedpopulationof260,000peoplewithanaverageconsumptionrateof0.057mgd(milliongallons daily). The dimension of the flocculator is 2m x 2m x 2.5m i.e. 10m3in volume with a power input of 0.0036kw anddetentiontimeof54.36min.Provisionisalsomadeforfutureexpansionintheeventofanincreaseinthe communitiespopulation.Thesinuouschannelsprincipleusedaidedinminimalpowerrequirementforthe system.Key words: flocculator, sinuous channel, head loss, velocity gradient I.INTRODUCTION The use of gentle stirring in water, which floc has formed to induce the particles to coalesce and grow is known as flocculation. The bigger and denser the floc particles, the quicker are the rate of settlement.Thesourceofpowerforflocculatingdevicesaremechanicalandpneumatically.Generallyspeaking,seldom usedinlargeplants,eventhoughtheypossessquiteusefulfeatures[2].Whenthedosedwatercarryingfloc finallypassesintotheflocculatorthroughtheinletport,acertainrollingmotionisinevitable,whichcanbe accentuated by baffles in Horizontal flow basin or in an upward flow basin by the sludge blanket. [1] However inmany basins thereis ampleevidence thatbetter resultscan beobtained ifmixing and flocculation can be intensified. In recent years much research has been done on both and sound theoretical rules have been laid down. Therearemethodsoftheoreticalapproach,themixingandflocculationcanbecarriedouteitherby mechanicalmeansinspeciallybuiltchambersorinsuitablebaffledchannelorinterconnectedchambers.The latter methods requires no mechanical equipment butlacksflexibility,becausethesystemcanbe designed formaximumefficiencyonlyatonerateofflowandatonetemperature,where-asthespeedofmechanical paddles can be adjusted to suit the variations of flow,temperature and silt conditions. However, the cost added tothecomplexityofmechanicalequipmentintroducesadditionalcomplicationstobeavoidedinadeveloping country,andinpracticeasinuousinletchannelprecededbyviolentmixinggenerallyprovidesareasonable effective solution [1]. IfthepipeorchannelthroughWHICHtheincomingwaterentersthebasinissodimensionedasto ensureavelocity>1m/s,andifthechannelordirectedatanendwallsothattheflowisforcedtoreverse abruptlythrough180o,anycoagulantintroducedintothewaterbeforethatsuddenreversalwillbeadequately mixed and floc will form almost instantaneously. Unliketheabsolutenecessityfor thoroughmixing, theneed for flocculation as aseparate process may ormay notbeessentialmuchdependsonthenatureofthesuspendedsolids,forriverscarryingcoarseandheavy sedimentthemainproblemistopreventthesiltsettlingandblockingtheinletchannelsbeforeitreachesthe basin[1].Shallowdepthsettlingmaypresentoperationaldifficultiesindevelopingcountries,soseparate flocculators aremostly found beforeconventionalhorizontal flow basinswherecolloids area problem and the complication of additional machinery may be avoided by having the flocculating action imparted to the water by the gently rolling motion resulting from passing water along a sinuous channel. In practice a channel providing a velocity of flow of about 0.3m/swithcross-wallsensuring12-20changesofdirection though180o (with well rounded corners), has often proved to be very effective, The emphasis must be placed on the comparative smoothness of flow required. Under no circumstances should velocity or turbulence be such as to break up the floc. American J ournal of Engineering Research (AJ ER)2015 w w w . a j e r . o r g Page 141 II.THEORETICAL APPROACH: Thestirringofwatercreatesdifferenceofvelocityandthereforevelocitygradients.Theaverage temporal mean velocity gradient in a shearing fluid is denoted by G. For baffled basins or sinuous channels: - G = ( ) 1/2. (1) Also T = . (2) Where,G is the velocity gradient, s-1 g is the weight of water per unit volume h is the head loss due to friction, m Is the dynamic viscosityT is the detention time, s. For mechanical agitation, the velocity gradient relation G is given by; G = ( )1/2.(3) Where,P is the power consumption, W V is the volume of fluid, m3 The total number of particle oscillation is proportional to GT, and is greater when there is a degree of turbulence as opposed to general rotation. It has been observed that in many of the more successful mixing and flocculating basinswhicharemechanicallystirredtheGTvaluesareasshownintables(1&2)below.Increasein contact time above 120 seconds achieves little, and excessive G values can be harmful [1]. Table: 1 Recommended GT Values for Flash Mixers [1] Contact time T,sVelocity Gradient G,s-1GT 20100020,000 3090027,000 407530,000 41-12070030,000 Table 2: Recommended GT Values for Flocculation [1] Type Velocity Gradient G,s-1GT Turbidityorcolourremoval (without solids recirculation20-10020,000-150,000 Turbidity or colour removal (with solids recirculation)75-7525,000-200,000 Softeners (solid contact reactors)30-200200,000-250,000 Softener (ultra-high solid)250-300300,000-400,000 III.SINOUS CHANNELS The permissible loading on a sinuous channel at any given value of GT is (from eqn. 2.0) = ( )1/2/ GT =)1/2/ GT.. (5) Where,Q is the rate of flow, m3/s V is the channel volume, m3 g is the acceleration due to gravity (9.81 m/s2) is the kinematic viscosity of the water, m2/s The useful power input isP = Q gh.. (6) wherePisthepowerwattsforeachmeterofheadlost,theusefulpowerinputis9.8x103wattsperm3/s,in practice, head losses are commonly 0.15-0.6m, velocities 0.15-0.5m/s and detention times 10.60min.For channel with baffles (over and under or round the bend), the extra loss of head in the channel (in addition to normal channel friction) is,h= .... (4) Where,h is the addition head loss, mAmerican J ournal of Engineering Research (AJ ER)2015 w w w . a j e r . o r g Page 142 n is the number of bafflesv1 is the velocity between the baffles, m/sv2 is the velocity at the baffles slots, m/sToapproximatethetotalchannelfrictioncanbeobtainedbycalculationusingaHazenWilliamsdischarge coefficient c= 50 [5]. IV.FLOCCULATOR DESIGN Since,thedesignisforaruralsettlement,whichshouldavoidexcessiveuseofpowerandatlowercost,the flocculator should be a sinuous flow baffled channel type. The number of baffles (n) is chosen to be 7, (over and under) [3] with an entry velocity V1 = 0.36m/s (Velocity of water from mixer) [3] and a velocity between baffles V2 = 0.5m/s. The detention time in the channel is given by equation 2 T=ForturbidityorcolourremovalwithoutrecirculationGistakentobe23s-1(table2).Theheadlossdueto friction (hf) is given by Haizen Williams eqn with c = 50 hf = ( )1.85 x x Q1.85 Where L is the length of pipe which is 2md is the pipe diameter which is 0.1mQ = 0.003m3/s hf = ( ) 1.85 x x 0.0031.85 hf = 0.0054m g and at 35oC are 9.747x103N/m2 and 0.7255x103Ns/m2respectively(Appendix II) Addition head loss in the channel is given by equation 4, h = h = h = 0.123m Total head loss = head loss due to friction + additional head loss. Total head loss = 0.123 + 0.0054 = 0.1284m Thus substituting values of head loss, g andin equation (2), The detention time T = = 361sec = 54.35minThus from flow rate Q = Q =V = 0.003 x 3261 = 9.8m3 10m3 The dimension of the flocculator is 2m x 2m x 2.5m; hence the useful power inputs given by equation (6) P =gQh P = 9.747 x 103 x 0.003 x 0.1230 P = 3.6watts = 0.0036Kw The permissible loading Q/V is given by equation (1) Q/V = = 0.03s-1and the GT value is thus, GT = 23 X 3261 = 75003. This is within the recommended range as given in table 2. The floor of the flocculator slopes from entry by 10% of the height. Thus 10% of 2m = 0.2, hence the height at entry = 2-0.2which is equals to 1.8m. Thickness of the baffles are chosen to be 50mm, there are 3 upper baffles spaced 587.5mm apart and each 1.2m deep. The upper and lower baffles should lap by 0.4m (400mm) as shown in the diagram appendix I. Theflocculatorbasinistobebuiltwithbricksandthesurfaceisplasteredtoasmoothfinish,thefloorofthe basinisofconcrete.Sincetheflocculatorisaccompaniedbyasettlementbasin,almostallflocformedwill settle at the settlement basin and the remaining that settled at the flocculator is to be hand cleaned monthly. The top of the flocculator is to be left open so as to assist further disinfection by ultraviolet radiation. The outlet diameter of the flocculator is to be the same with the inlet, i.e. 0.1m American J ournal of Engineering Research (AJ ER)2015 w w w . a j e r . o r g Page 143 V.CONCLUTION Forfutureexpansionofthetreatmentplantduetoincreasedwaterdemandorpopulationincreaseas pre-determined based on data of the1963 censusreport, this expansionwill bebasedon thepopulationfigure projected to that year. The provision for expansion has already been provided in the design and the addition of morechamberssuchasintheflocculatorandsettlementbasinsmaybefoundnecessary.Thefilterhasbeen designed to last the life span of the project. REFERENCES [1]Smsrthurst G.: Basic Water Treatment 1979; Thomas Telford Ltd, London. [2]M. Fair, Gordon C. Geyer, John A. Okun, Daniel. Water and Waste water Engineering Vol.1, 1968, John Willey and Sons Inc. [3]H. A.Abdulkareem,S. B. Abdurrahman and Isyaku Umar, (Nov., 2014), Design of awater treatment Mechanical Mixer for a pre-chlorinationtankasaneffectivealgaecontrol,aerationandcoagulationprocessing"InternationalJournalofEngineering ScienceInventionISSN(Online):2319 6734,ISSN(Print):2319 6726www.ijesi.orgVolume3Issue11November2014, PP.25-36 [4]M. Fair, Gordon/C. Geyer, John/A. Okun, Daniel; Water and Waste water Engineering Vol. 2, 1968, John Willey and Sons Inc. [5]Dunn, P.D.: Appropriate Technology Macmillan Press Ltd 1978 American J ournal of Engineering Research (AJ ER)2015 w w w . a j e r . o r g Page 144 APPENDIX II Table A-2a Physical properties of water in English units Temperature, oF Specific weight lb. ft3 Density Slugs ft./ Viscosity x103,lb. sec ft2 Kine-matic viscosity x 103 ft2/sec Heat of vapor-ization, Btu.lb Vapor pressure p Pascal Vapor pressure head p h ft. Bulk modulus of elasticity Etx 103 Pascal 3262.42 1.9403.7461.9311075.50.090.20293 4062.431.9403.2291.6641071.00.120.28294 5062.411.9402.7351.4 101065.30.180.41305 6062.371.9382.3591.2171059.70.200.59311 7062.301.9362.0501.0591054.00.360.84320 8062.221.9341.7990.930104 8.40.511.17322 9062.1 1 1.9311.5950 8261042.70.70I .61323 10062. 00 1.9271.4240.7391037.10.952.19327 11061.861.9231.2840.6671031.41.272.95331 12061.711.9181.1630.6091025.61.693.91333 13061.551.9131.0690.5581019.82.225.13334 14061 381.9080.9810.5141014.()2.896.62330 15061 201.9020 9050.4761008.13.728.58328 16061.001.8960.8380.4121002.24.7410.95 326 17060.801.8900.7800.413996.25.9913.83 322 18060. 581.8830.7260 385990.27.5117.33 318 19060. 361.8760.6780.362984.19.3421.55 313 20060.121 8680.6370 341977.911.5226.59 308 21259.831.8600.5930.319970.314.7033.90 300 Table A - 2 A Physical properties of water in SI units Temperature, C Specific weight kN m3 Density kg m3 Viscosity x103N sec m2 Kine-matic viscosity x 103 m2 sec Heat of vapor-ization J gm. Vapor pressure p kN m\ abs Vapor pressure head p m Bulk modulus of elasticity Et x 10-6kN m: 09.805999.81.7811.7852500.30.610.062.02 59.8071000.01 5181.5192488. 60.870.092.06 109.804999.71.3071.3062476.91.230.122.10 159.798999.11.1391.1392465.11.700.172.15 209.789998.21.0021.10032453.02.340.252.18 259.777997.00.893244 1.33.170.332.22 309.764995.70.7980.80024 29.64 240.442.25 409.730992.20.6530.6582405.77.380.762.28 509.689988.00.5470.5532381.812.331.262.29 609.642983.20.4660474 ,2357.619.92 2.032.28 709.589977.80.4040.4132333.331.163.202.25 809.530971.80.3540.3642308.247.344.962.20 909.466965.30 315.0.3262282.670.107.182.14 100 9.399958.40.2820.2942256.7101.3310.332.07