Microalgae Harvesting And Processing: A Literature Review; A .
SERI/STR-231-2396UC Category: 61aDE84013036Microalgae Harvesting andProcessing: A LiteratureReviewA Subcontract ReportG. ShelefA. SukenikM. GreenAugust 1984Technion Research and DevelopmentFoundation ltd.Haifa, IsraelPrepared under Subcontract No. XK-3-03031-01SERI Technical Monitor: Robins P. McintoshSolar Energy Research InstituteA Division of Midwest Research Institute1617 Cole BoulevardGolden, Colorado 80401Prepared for theU.S. Department of EnergyContract No. 0 E-AC02-83CH 10093
Printed in the United States of AmericaAvailable from:National Technical Information ServiceU.S. Department of Commerce5285 Port Royal RoadSpringfield, VA 22161Price:Microfiche A01Printed Copy A04NOTICEThis report was prepared as an account of work sponsored by the United StatesGovernment. Neither the United States nor the United States Department of Energy,nor any of their employees, nor any of their contractors, subcontractors, or theiremployees, makes any warranty, express or implied, or assumes any legal liabilityor responsibility for the accuracy, completeness or usefulness of any information,apparatus, product or process disclosed, or represents that its use would notinfringe privately owned rights.
FOREWORDThis report is a literature review on microalgal harvesting and processing submitted aspartial fulfillment of subcontract XK-3-03031-01. The work was performed undersubcontract to SERI with funds provided by the Biomass Energy Technology Division ofthe U.S. Department of Energy. t! /- Robins P. McIntosh, CoordinatorAquatic Species Programtein, Coordinatorram OfficeStari1eYR'. BtillirectorSolar Fuels Research Divisioniii
SUMMARYObjectiveThe objective of this report is to present a discussion of the literature review performedon methods of harvesting microalgae.DiseussionThere is no single best method of harvesting mieroalgae. The choice of preferableharvesting technology depends on algae species, growth medium, algae production, endproduct, and production cost benefit.Algae size is an important factor since low-cost filtration procedures are presentlyapplicable only for harvesting fairly large microalgae. Small microalgae should beflocculated into larger bodies that can be harvested by one of the methods mentionedabove. However, the cells' mobility affects the flocculation process, and addition ofnonresidual oxidants to stop the mobility should be considered to aid flocculation.The decision between sedimentation or flotation methods depends on the densitydifference between the algae cell and the growth medium. For oil-laden algae with lowcell density, flotation technologies should be considered. Moreover, oxygen release fromalgae cells and oxygen supersaturation conditions in growth medium support the use offlotation methods.If high-quality algae are to be produced for human consumption, continuous harvesting bysolid ejecting or nozzle-type disc centrifuges is recommended. These centrifuges caneasily be cleaned and sterilized. They are suitable for all types of microalgae, but theirhigh operating costs should be compared with the benefits from their use.Another basic criterion for selecting the suitable harvesting procedure is the final algaepaste concentration required for the next process. Solids requirements up to 30% can beattained by established dewatering processes. For more concentrated solids, dryingmethods are required.The various systems for algae drying differ both in the extent of capital investment andthe energy requirements. Selection of the drying method depends on the scale ofoperation and the use for which the dried product-is intended.ConclusionsThe literature review on microalgae harvestfng technologies does not reveal anyrevolutionary conceptual advances since the first comprehensive study done by Goluekeand Oswald (1965). Nevertheless, optimizing various trains of processes can not onlyreduce the cost, but can render the whole scheme economically feasible. The existingliterature is not conclusive enough to propose such optimal train of harvesting processes,and the continued work of the Technion Group on this project will try to establish theseoptimal processes.iv
TABLE OF CONTENTS1.Introduction2.The stability of microalgae with respect to their1separability from aqueous suspensions.42.1Colloidal character of microalgae suspension42.2Algae sedimentation rate93.Flocculation of microalgae114.Algae harvesting technologies164.1Filtration screening & rifugation405.Algal drying496.Summary and conclusion56v
1.INTHooucnorlMass culture of microalgae carl beobjectivesor gan i csuchas: racticeato attain diflerentproduction of hydrocarbons,proteins,var i oussubs t anc e s , wastewater treatment, solar energy conversioncombination ofAn blgalabove. henia s s cu I tureisatsu i t ab I e climatic conditions.photosyntheticintendedt a l nab l e in outdoor ponds uncrerHigh rate algal pond (HHAP) is anr eact.or wh i ch is operated for mass blbBlmixingofaissha ll ow rc.:lCe-way or meande r Lngprovidedtokeepthealgaeinor-encu I t ur eto maY/mize algal production per unit of area.t he Tile op e r at i o na l kr.owhot, and the scientific b ack grou nd of micro-algaeproductionscientificinHRAP are well based on longexperience.foundamentals, the oper .ltional strotegies and theThevarioususes of the IlRAP are beyond the scope of this review, and the da t athatontopics is available in the literature (Sheler et al., 19BO, Azove t a I , , 19b:::, Oswald 19'(4, Soeder, 19(0).The product of the HHAP is an effluent of 81gal culture whichcontains up to 600 mg/lpr cduc t i onculturemediumseparationessentialpr-oduc t isystems(O.OGI )microalgae.As in otLer microorganismthe separ at i on or the suspendedc e l Lsis an essential and important step.Thef rornefficientdewatering und drying of microalgae is rr.ostn.i c ro cl gaeon system.In combined system of HRAP for wastewater treatment, waterrenovationand protein production, the algal swateraanddualb)concentration of protein ricll algal biomass available for animal feed.In'clean'systems that their media are consisted of1amixtureof
defineds a l t s wLich are di s s oLved in water, the a Lga l separ a t i cnconcentration is essential for the further processing stepstothedesired end produc t nyfromande t. a IthatinandaccordingThe resultant algal I'r e e culture med i ur,addition,iviicroalgae by their swall size (5-50chargedsome casesr:theirtheintost.abl e/lEAP.their negativelymobility,st.ao lf'orrnhereby difficulties in their separation ane. 1fj6i3).anderecoveryTechnological solutions for separation of algaesuspensions shouldbegi venintLE:processingsequence of mi c ro a I g ae production (Fig. 1.1).The term algae harvesting refers to the concentration of fairlydiluted (ca. e suspension until a slurry or me more is ob t a i ued ,concentrated rocesswhichwloseof5-25 T ;ST S)or by twoslurryste As it is i nd i cat.ed inisattainableprocess consistingbyofoneresultantsubsequential1 -25%TSS.stepharvestingbrings the algal slurry to 2-7% TSS, dnd dewateringend product is an algal past{;: ofthepastestepThe ion (Hahn 1978 & 1980).The methods and devices I-.'hich ore suitable for microalgCies ep ar at.i onfromHRAPeffluent dependontheal gaespecies,production system and the objectives of the final product.1980,n.ett.odsDocd , 19bO).ofmicr-oa Lgae(liohnThis review deals with separation andmic r ou Lgaesuspensions,from the pond effluent.and the principles2whichThemaytheprocessings t ab i Li t.ybeusedofto
Onestep--Twoconcentration'--Production stepHighAlgae1steps concentrationr--------rjRateAlgal SlurryAlgal cakeEffluentharvestinga) 0.02 - 0.06%I--- )Idewateringa) 2 - 7%--- a) 15 - 25%Ib) 100 - 200b)2 - 1014------'La)algal concentration % TSSb)concentration factorFig.1.1 -Schematic presentation of algal production and processing.ProcessingI!I-- III extraxtiondrying
mended lcroal8ae2.thealgaeseparation step, areandcritic singUpdatedseparationandtechnologiesarefurther improvement end applicationforoilladenseparation.TfiE STJWILITY OF MICROALGAE WITH RESPECT TO THEIR SEPARABILITYFROM AQUEOUS SUSPENSIONSThe HRAP effluent consists of a culture medium containing microalgaebiomasswhichaffectelectricwhich form stable suspension.thechargerepulsion forces.There arestability of that algalsurfaceintercellularb) tiny cell diffiensions and cell densityclosetothat of the medium cause slow cell sinking rate.2.1The colloidal character of an algal suspension.Both the electric repulsion interactions between algal cells andcell interactions with the surrounding water contribute to thestability of the algal suspension (Tenny et al., 1968).Most ofthe planktonic algae are characterized as negatively chargedsurfaces.The intensity of that charge is a function of algalspecies, ionic strength of medium, pH "nd other environmentalconditions (lves 1959 & Hegewald 1972).The sources of thealgal surface electric charge are: ionization of ionogenicfunctional groups at the algal cell wall (Golueke & Oswald 1970)and selective adsorption of ions from the culture medium (Shaw1969).4
The electric state of a surface depends on the spatial distribution of free charges (ions) in its neighborhood (Stumm &Morgan 1981) and is idealized as an electrochemical doublelayer.One layer is described as a fixed charge attached to aparticle surface and is called the Stern layer.The other iscalled Gouy layer or diffuse layer which contains an excess ofcounter ions (ions of opposite sign to the fixed charge) and adeficit of co-ions (of the same sign as the fixed charge).Thedistribution of ions and potential at solid solution interface isdescribed in Figure 2.1.1.::loUd-solutionInterfacee,.I .I . IVdPotential:. f)ul\ Concentration (rnM)Counter ions" ( )orCo-ions (-)Fig. 2.1.1 - The distribution of ions and potential at solidsolution interface.5
Neither the potential at the surface (1); ) nor the Sternapotential (1); ),nor the potential at the border of Stern and diffuse layerpotential ( d)can be directly measured.Instead, the zeta- the potential measured at the shear plane (thatseparates the solid surface and the mobile liquid), is the onegenerally used and is obtained by simple electrokinetic methods.The zeta potential is assumed to be equal to 1);d although it isnot necessarily correct.A simplified formulation (valid for small potentials) showsthe potential decreases exponentially with the distcJOce(2.1.1)where 1); is the potential at a distance X and K is the reciprocalof the double layer thickness and is defined by equation(2.1.2.)where Z is the charge of counter ion whose concentration is n ok is bolzman constant,! Kelvin temperature and e is a basiccharge.The above equations show that the electric potential at agi ven distance in the diffused layer is affected by the valencyof the counter ion and its concentration.Compression of theelectric double layer is attainable either by increasing thecounter ion concentration or by using counter ions of higher6
valency.The interaction between colloidal particles are affected bythe electric repulsion forces on one hand and attraction forcesof Van-der-Waals on the other hand.The combined effect of thosetwo energies is shown in Figure 2.1.2.There is a potentialbarrier to be overcome if attachment is to be attained.It canbe exceeded by the kinetic energy of the particles or alternatively by the reduction of the energetic barried.This is done bycompressing the double layer (increasing K) through addition ofelectrolytes to the solution or ions of higher valences.Double-layer repulsion,VRResultant potential of interaction,VTPotential barrierIParticle distanceder Waals attraction,VIAIIFig. 2.1.2 - Combined effect of electric repulsion andVan-der-Waals attraction energy (Ref. Stumm &Morgan 1981).7
Although the double layer theory is of great theoreticalimportance, its use is restricted to cases where specificchemical interactions do not playa role in colloid stability(O'Melia 1978).Destabilization of colloidal suspension as aresult of specific chemical interaction is attainable by thepresence of polyelectrolytes or polyhydroxy complexes.Hydrolysis of metal ions (for example Fe(H 0)3. 26andAI(H O)3 ) is described as a stepWise consecutive replacement ofL.H206molecules in the hydration shell by OHions (Stumm &C'Melia, 1968), according to the scheme shown in Fig. 2.1.3.Theeffects of ferric and 21uminium salts are brought about by theirhydrolysis products and not try the simple aqua-metal ion themselves.Over dose of the hydroxo complexes can restabilizedispersions by a reversal of the charge of the colloidalparticlesFig. 2.1.3 - Stepwise conversion of a positive aluminium ion intonegative one (Ref: Stumm and O'Melia 1968).8
Organic polymers, usually those of quite highare considered as good flocculants.molecul rweightThe polymeric flocculationis explained by bridging model says that a polymer can attachitself to the surface of a colloidal particle by several segmentsbeing remainder segments extended into solutions. These segmentsare then able to attach on vacant sites on other particle forminga three dimensional floc network (Gregory 1979).Destabilization and flocculation of algal suspension is animportant procedure in most of the various algal separationprocess and is described separately in a following section.2.2Sinking rate of microolgae.Planktonic algal cell can be considered as a body which falls inaqueous medium and is affected by theand drag forces on the other.gra ityforce on one hand,Within a short time this bodyexceeds constant sinking velocity which is described by Stokeslaw (eq. 2.2.1)v (2.2.1)9
where V is the fall ing velocity, g - gravity force, d - particlediameter, p and pI the density of the mediulTl and the particle,respectively, and ri is the medium viscosity.Ac ordineto Eq. 2.2.1, the falling velocity of a odydecreases either by increasing medium viscosity or reducing thecell-medium density difference or by decreasing cell diameter.Stokesi s ;'ipplicatJle i or spherical bodies and any di versi ty1cll,from sphericity reduces the sinking rate, inversely, to thecoefficient of form resistent v ""(2.2.2)while is a dimensionless parameter and calculated from ther atio ofof thethe sinking rate of sphere of the same diameter and that ctualbOdY.The sinking velocity of planktonic algae in natural habitatis disturbed by cell mobility, water turbulence and upwellingcaused by winds and temperature stratification (Hutchinson,1967).Planktonic algae in ecosystem reduce their sinking rateby the f'oLl ow.i ng methods: a) motility, b) reducing celldimensions, c) increament of the drag forces as in Scenedesmusspecies which contain seta (Conway & Trainer 1973), d) reducingcell density as in many blue green algae which contain gasvacuoles (Fogg 1975, Pearl & Ustach 1982).In8reasing of algal cell sedimentation rate can be obtainedby increasing cell dimensions, i.e., by cells aggregation into10
large body.This principle is applied in algal separationprocesses where chemical flocculants are added and cause largealgal floes which settle rapidly to the container bottom.Alternatively, tiny air bubbles which may adsorbe to the alreadyformed algal floes will reduce dramatically the floc density andcause the floc to float.Increasing the gravity force willincrease the sedimentation rate of algal cells and is attainableby3.centrifugal forces on algal suspensions.applyi gMICROALGAE FLGCCULATIONAddition of chemiCals to algal cultures in order to induce algaeflocculation is a routine procedure in various separation &(Golueke & Oswald 1965, Moraine et al.centrifugationflotationand1980).Therefore, a brief discussion is dedicted herein to algal flocculationmethods and flocculants.The variousbebroadlypolyvalentchemic lsdivided into two groups:metalcomplexeswhich were studied as algal flocculants canationsasAl 3a) inorganicand Fe 3agentswhichformsuitable pH as shown in figure n is a common technique in water and wastewater treatment.Itinvolves raising the pH with lime to the point at which Mg(OH)2 isformedandacts asFriedman et al. 1977).anionic,generallycationicusedtoandultimate flocculant (Folkman& Wachs1973,b) Polymeric organic flocculants which maynon culantsinclUdingbeisthe
nonionic species, synthetic and natural polymers (Stumm & Ivlorgan 1981)as is shown in Table 3.1.Various flocculants were evaluated either by batch flocculation xperimer.ts('Jarsummarizesthete ts')or by pilot scale apparatus.different flocculants whichHereTable 3.2testedforalgalflocculation and their operating conditions, primarily pH and optimalreported in the literature.dose asAlum, Al 2 (SOL;) 3 x 18 H2flocculantsOswaldalum,wasother salts of aluminium were used asbranch and field scale experimentsI'lcGarry et a l , 1970, Hor a me e t a l ,1965,sulfatemanyin orused(GoluekeFerric1980).too, but found to be inferior in&comparisonwithregarding the optimal dose, pH and the quality of the resultantwaterandslurryTable 3.1(bareeta1.r';oraine1975,eta1.1980) - Some ;jynthetic and Natural Polymeric ---- ------------ - - --------- - hetic polymersfCH2-CH2-N H2 Jr: H-CH2-1L CONH2npolY :.icrylamidepol yeth yleneamine-('H-CH,-J" J- CH'-r(-\:,\,,-jj(so,Polyvinyl alcoholb)Natur lttr "",Polystyrene / . Polyvinyl Pyridinium[CH'OHchitosane-------------- -------------------------------------- - - - -- - - - - - - - - - - -12NH'] -. 0
FLOCCULANTTYPEOPTIMAL DOSEmg/lOPTIMAL pHTESTING SCALENOTSS5.3 - 5.6Sedimentation &I flotation batchEXI er. Pilot scaleexperimentswa s t ewat e rREFERENCESAlum A12(S04)3'18 H2 OPolyvalent metalion80-250Ferric sULfatePolyvalent m,:,talion50-903. - 9.0batch and pilotflotation unitsclean andwastewatersystemsFunk et al. 1968Bare et al. 1975Lime treatmentinduces Ng(OH)precipitationposit ively chargedmetal hydroxideprecipitates500-70010.5-11.5batch sedimentation experimentswas t evat e rFolkman & Wachs 1974Friedman et al. 1977wastewatersyscemslsystemsystemsMoraine et al. 1980Friedman et al. 1977Cationic polymersPurifloc-353.5batchMoraine et al.Zetay 51polyethylene amine10. 9batchDow 21MPolyethylene amine104 -·7batchcleansystemTilton et al.Dow C31Polyamine2 - 4batchcleansystemTenny et al.Chitosandiacetylated polymerof chitin.8.4batchcleansys temVenkataraman et al.1980Table 3.211005Different flocculants and their optima (pH and dose) for algae flocculation.IIII
Although goodclart fication of algal pond effluent- has beenachieved by lime treatment (Folkman & Wachs 1973, Shelef et al.1978,Fr-Ledman et a I , 19'(7) that flocculant is restricted to cultureswhichcontain magnesium concentrationconsistedmore0"-abov 10 mg/l and the resultant sludgelime t han of algae, containing up to 25 % calcium.Organic polymers were tested as algal flocculant on hatch scale.the c at.ion i c polymers were found as efficient flocculants (TennyOnlyet1968, Tilton et a l , 1972, Hor-a I ne et a1. 1980).81.polymersbe used in conjunction with alum or ferriccanimprovetheInadditionsulfateseparation process, while anionic polymers improveto1 imeflocculation (Friedman et al. 1977).Tenny et al. (1968) and Tilton et al. (1972) explainedpolymericfewflocculation by adsorption and bridging modelparameterswhichaffect the phenomena.Low lgalandstudiedmolecularweig tcationic polymers either do not cause any flocculation or are requiredinvery high concentrations.optimalverydose will decrease with increasing molecular weight, however,highchargeAt higher molecular weight polymers themolecular weight polymer will reversed thestabilizeandthe suspension (Tiltoneta1.algalsurfaceThe1972).hydrogen ion concentration as well as medium electrolite concentrationinfluence the surfa-.oe charge density of the algal surface, theofionizationsubsequentlycharge density and the extention ofwhole flocculation uired for a given degree ofdefinitedosageforstechiometry between algalalgalfloccul at i onpolymerVariationsconcentrations (algal surface area) would influence andconcentrationandeta1.1969),
The chemical composition of algal medium may affect theflocculationoptima(1. e.dose and pH).For limetreatmentprocesswhere Mg(OH)2 precipitates and act as a flocculant, it was foundthatthe higher dissolved organic substanceS (measured by ,COD) in the, algalsuspension,thehigher was the dose of Mg(OH)2algae (Folkman & Wachs 1973).flocculationofflocculationprocesses caused by the ecliningther equ.i r-edofforgoodInhibitiondissolvedorganicbiologic origin was observed by other invstigations& Bernhardt 1980, Narkis & Rebhun 1981).etal ,decreasegrowthshowed that algal(1969)the optimal flocculantphase,theexocellulardosewhereas ysubstancesduring the late growth stages increases the optimal dose evidently dueto the organics which serve as protective colloid.Moraine et al. (1980) pointed out that the soluble P04concentration is an important factor which influence the alum optimalriose.The required dose of alum may be described by(2.3.1)is the alum dose mM, (PO-43)S the soluble phosphatewheremt-';,TSS, the suspended solid concentration gil and k is alum specific dosem moleAl 3/gTS8.characteristics.asThe coefficient k should be a function of effluentHowever, it was not correlated with suchparametersalkalinity, NIl 3 ' BOD, but weakly correlated with temperaturealgal type (Shelef et a1. 1981).15and
The many variables which affect the flocculation process make theprediction of the operational conditions impossible and they should beevaluated by bench scale experiments as 'jar test'.The apparant spontaneous floc formation and settling of microalgaehasphenomenonbeenmentioned in the literature for sesthisphenomenon is associated with elevated pH due to photosynthetic CO2consumption corresponding with precipitation of inorganic ).formationwhich cause theflocculation(Sukenik&Aside from this coprecipitative autoflocculation,of algal aggregates can also be dueto:a)excretedorganic macromolecules (Pavoni et ale 1974, Benemann et ale 1980),b)inhibited release of microalgae daughter cells (Arad et ale 1980)andc)aggregation between microalgae and bacteria (Kogura et ale4.ALGAE HARVESTING TECHNOLOGIES1981).Solid-liquid separation processes can be classified into twokindsofseparation. (Svarovsky 1979a).constrainedinaIn the first,the liquidvessel and particles can movefreelywithinliquid.Sedimentation and flotation fall into this econstrainedthrough which the liquid can flow.fit this definition.of these ermeableandscreeningFig. 4.1 shows further sub-divisions withinDensity difference between the solidsfor16gravity orcentrifugalandsedimentation.
separationParticles constrained,Liquid Constrained,particles issolved air,Ct h i c k e ne r s ,electrolytic)clarifiers)CentrifugalCake filtrationsedimentation(vacuum,pressure,Deep-bed filtration(sand and coke)centrifugal)(dewateringvibratingscreens)Fixed wallRotating wallChydrocyclones)Csedimentingcentrifuges)Figure 4.1:ScreeningClassification of common industrial solid-liquid separation techniques
Filtration and processesbothseparatesolidsby p as s i ng a s u s p e n s t.on through permeable medium thatliquidsfromretainst.he solids.Screen ngThe principle of screening is introducing particles onto a screenof g i ve n aperture size.ontheThe particles either passscreen accordingtheirsize.Although this method is usedso Li d-is o l i d s e p a r a t i on itprimarily forseparation.tothrough or collectis also usedfor solidliquidFor algae harvestIng two screening devices were employed:ffilcrostralners and vibrating screen filters.FiltrationIIImediumallfiltrationo rd erintor e q u t re dmagnitudedrivingforceaforceofdropf lu i dflowtopr e s s ur neoracrosstheDepending centrifugal.Two basic types of filtration are used:I.Surfacefiltersin whichthesolidsareform of a cake on the face of a thin filter medium.of cakeandtheappearsmediumr e s i s tanc eentheactsto flowfilteronlyasi.nc r e as e s .face,aAstntheAs soon as a layerdeposition shiftssupport.Thus,depositedthefor a cons tantto cake itselfcakegrows,thepressure drop thefeed rate declines.II.Depth filters(deep bed f i l rr at i on ) - in which the solids aredeposited within thE filter medium.The problem with using filtration to clarify algae pond effluentISthatrapidly,amediafineenoughrequiring frequenttoretainallbackwashing.Asthealgaea resulttendtoblindfilter size has*Filters description and operation mode were taken from "Solids Li qu i d sSeparation" by 1. Svarovsky, Chemical Eng. July 2, 1979.18
fectiveoftheandbiomassefficientst reammeansdecreases.offiltrationcontinues, due to its potential advantages In reduced cost and energy,and avoidance of chemlcals and their impact on feed quality.f i l t r a t, ion methodsSe ve r a Ihavebeen tested with varying degreesof resforalgaeharvesting are presented in the following sections.Filtration and Screening Devices4.1.24.1.2.1 Pressure FiltersIn pressure filters the driving force for filtration is the liquidpressure developed by pump i.n g orfeed vessel.10%fi 1 t e r sPressureplate-and-frameInforce of gas pressure in thePressure filters can treat feed with concentrations up tos o l i.d s .elements.by thefilterpresses(Sv a r ov sk themaybegroupedintoand pressure vesselstwocategories,containing enceofperforated, square or rectangular plates alternating with hollow framesis mounted on suitable supports and pressed together with hydraulic- orscrew-drawnrams.Theslurry is pumpedplatesareinto theframescategoryofcovered wi t hafiltercloth.Theand the filtrate is drained from lters,MohnCyl cludesvesselfilters,tank vertical leaf nthorizontal tank verticaland ho-iaontal leaf filters.(1980)harvesting:4.1.1.asverticalleaf filters,thatpressuretester:!fivedi f f e r en tpressure filtersfor ColastrumChamber filter press, Belt press, Pressure Suction Filter,Si eveandFi I terBasket.Hisr e.su I tsareshownIntableFinal TSS concentratlons were in the range of 5 to 27% and eration,reliabi l i ty and concentrat ing c ap ab i lity the chamber filter press,c y I i nd r i.cSIeveandfiltering systems.thefilterThe beltbasketwererecommendedfilter press was not19asthepotetentrecommended because
Table 4.1.1Devices for harvesting through pressure filtration(Mohn - 1980)%T8S of theconcentrateEnerg Deviceper mAlgae SpeciesRemarksChamber filter press22-27%0.88 kWhCoelastrumDiscontinuous method, very higreliabilityBelt Press18%CoelastrumContinuous method, needpreconcentrating ofFlocculant, low reliabilityPressure SuctionFilter16%CoelastrumDiscontinuous Method, goodr e l i ab i lityConsumedNo(15 ppmFlocc.)0.5 kWhCylindric s i.eve(pressure c used byrotators)7.5%0.3 kWhCaelastrumContinuous method, goodreliabilityFi Her basket5%0.2 kWhCae last rumDiscontinuous method, forpreconcentrating,good reliabil
te wasPressure suction filter was notdense mmended because ofexpensesandbecauseoflowfiltration ratio and high investment costs.4.1.2.2 Vacuum FiltersInthevacuumfiltersap p I i c a t i.o nAlthough theof[he driving force for filtration results al pressure drop available for vacuum filtrationis 100 kPa 1n practice it is limited to 70 or 80 kPa.In applicationswhereslurrytheproport ionoffinepart ic lesi.nthefeed1Slow,relatively cheap vacuum filters can yield cakes with moisture filters.truly continuousFurthermorefiltersbuiltinthi slargecategorysizesthatcan provide for washing, drying and other process requirements.Vacuum filtersare usually classified as either batch operated or1979).continuous (Svarovsky uentchangesThe vacuum-leaf,rectangularleaves,leaveswhich aresequence,arefiltrationfilterandne xp e n s r.v etthe vacuum-Nutscheandvery versatile,(or batch-and can copeIn process conditions.or Mooremanifoldedfilter ,consistssimply of a number oftogether and connectedto vacuum.carried by an overhead c r.arie duringdippedtakesThe two most common slurrythetank,where ing cont
This report is a literature review on microalgal harvesting and processing submitted as partial fulfillment of subcontract XK-3-03031-01. The work was performed under . There is no single best method of harvesting mieroalgae. The choice of preferable harvesting technology depends on algae species, growth medium, algae production, end .
nowadays for the growth of microalgae in photo-bioreactors. In Section 1.3 is explained what is the purpose of this thesis. 1.1 Microalgae Microalgae are microscopic unicellular organisms that live in aquatic environments. They have a simple reproductive structures and they do not have stems, roots or leaves [6].
Janette Worm and Tim van Hattum . Rainwater harvesting for domestic use 4 Contents 1 Introduction 6 2 Need for rainwater harvesting 8 2.1 Reasons for rainwater harvesting 9 2.2 Advantages and disadvantages 10 3 Basi
research needs to address these technical gaps, and lessons learned from previous harvesting campaigns. The document also describes a process for planning future harvesting campaigns; such a plan would include an understanding of the harvesting priorities, available materials, and the planned use of the materials to address the technical gaps.
The Goal of Tax-Loss Harvesting. The strategy aims to realize losses on individual stocks in conjunction with an investment objective, such as: Earning index returns. Tilting on quality factors. Lowering carbon footprint. Tax-loss harvesting may materially affect return-risk profiles of standard strategies. Tax-Loss Harvesting
increasing in world food price and food crisis. Microalgae have high CO 2 absorption capacity, high oil content, and high growth rate. Mass microalgae cultivation can be performed on unexploited land, therefore, avoiding competition for ag
Photobioreactors for microalgae cultivation - An Overview M. K Egbo, A. O Okoani, I. E Okoh Abstract - One of the ways to combat global warming is to substitute the conventional fossil fuels that are used to meet most of the world energy demand with cheaper, cleaner, renewable and therefore sustainable energy (heat, electricity, and transport fuel) sources.
microscopic organisms are unicellular. Question: How are unicellular organisms similar to multicellular organisms? 1. Observe: Compare the microalgae, the Elodea leaf cells, the maple leaf cells, and the root hair cells at 400x. Sketch each below: Microalgae Elodea Maple leaf Root hair A.
Rumki Basu, (2004) Public Administration: Concepts and Theories, Sterling Publication, Delhi. 22. Bhogale Shantaram, (2006) Lokprashasanache Siddhant aani Kaeryapadhati, Kailas Prakashan, Aurangabad. 23. Patil B. B., Public Administration (Marathi), Phadake Prakashan, Kolhapur, 2004. 8 SYLLABUS FOR TYBA POLITICAL SCIENCE (S-4) INTERNATIONAL POLITICS Course Rationale: This paper deals with .
