! ! A!Realistic!Technology!and!Engineering!Assessment! of!Algae!Biofuel!Production! ! ! T.J.!Lundquist12,!I.C.!Woertz1,!N.W.T.!Quinn2,!and!J.R.!Benemann3! ! 1!Civil!and!Environmental!Engineering!Department! California!Polytechnic!State!University! San!Luis!Obispo,!California! ! 2!Earth!Sciences!Division! Lawrence!Berkeley!National!Laboratory! Berkeley,!California! ! 3!Benemann!Associates! Walnut!Creek,!California! ! ! ! ! ! Energy!Biosciences!Institute! University!of!California! Berkeley,!California! ! ! October!2010! ! ! ! ! ! ! EXECUTIVE!SUMMARY! ! This!report!assesses!the!economics!of!microalgae!biofuels!production!through!an!analysis!of! five!production!scenarios.!These!scenarios,!or!cases,!are!based!on!technologies!that!currently! exist!or!are!expected!to!become!available!in!the!near"term,!including!raceway!ponds!for! microalgae!cultivation,!bioflocculation!for!algae!harvesting,!and!hexane!for!extraction!of!algae! oil.!!Process!flow!diagrams,!facility!site!layouts,!and!estimates!for!the!capital!and!operations! costs!of!each!case!were!developed!de!novo.!!This!report!also!reviews!current!and!developing! microalgae!biofuel!technologies!for!both!oil!and!biogas!production,!provides!an!initial! assessment!of!the!US!and!California!resource!potential!for!microalgae!biofuels,!and! recommends!specific!R&D!efforts!to!advance!the!feasibility!of!large"scale!algae!biofuel! production.!! Contents!of!the!Report! Chapter!1!introduces!microalgae!biofuels!production.!!Chapter!2!reviews!the!biology!and! biotechnology!of!microalgae,!including!major!taxa,!cell!composition,!resource!requirements,! productivities,!and!possible!algae!strain!improvement!through!genetic!methods.!!! Chapter!3!addresses!the!engineering!of!microalgae!production!systems,!emphasizing!those!for! commercial!production!of!nutritional!supplements,!which!are!the!main!current!application!of! microalgae!cultivation.!!Also!discussed!are!past!and!current!efforts!to!advance!microalgae! biofuels!research!to!larger!scales,!as!well!as!the!existing!large"scale!use!of!microalgae!in! wastewater!treatment.!!Wastewater!is!an!attractive!resource!for!algae!production!due!to!its! nutrient!content!and!low!cost.!!Closed!photobioreactors!are!reviewed!briefly.!!Although!they! are!unsuitable!for!large"scale!biomass!production,!they!have!applications!for!producing!starter! cultures!(inocula).!!Similarly,!heterotrophic!algae!production!is!not!considered!extensively!due! to!the!high!cost!of!the!needed!reactors!and!feedstocks.! Chapter!4!addresses!the!potential!resource!base!for!microalgae!biofuels!production!in!the!US,! with!California!analyzed!in!more!detail.!!The!availability!of!the!resources!required!for! microalgae!production—land,!climate,!water,!and,!perhaps!most!critically,!carbon!dioxide—at! the!same!site,!will!likely!limit!the!US!potential!for!algae!oil!production!to!less!than!a!few!billion! gallons!annually.!!While!minor!compared!to!total!US!transportation!fuels!consumption!(about! 200!billion!gallons!per!year),!renewable!algae!oil!could!be!a!major!contributor!to!biofuel! resources,!particularly!in!specific!markets,!such!as!aviation!fuel.!!! Chapter!5,!the!major!chapter!of!this!report,!details!five!microalgae!biofuel!production! scenarios,!or!cases,!for!a!hypothetical!location!in!the!Imperial!Valley!in!southern!California,!a! ! i promising!region!for!algae!production.!!In!all!five!cases,!water!and!nutrients!(N!and!P)!are! supplied!by!municipal!wastewater,!which!also!provides!some!of!the!carbon!needed!for!algae! growth.!!Additional!CO2!is!supplied!by!flue!gas!from!a!natural!gas"fired!power!plant.!!! The!cases!differ!in!three!main!ways:!!(1)!primary!process!objective—either!biofuel!production! or!wastewater!treatment,!(2)!biofuel!outputs—either!biogas!only!or!biogas!plus!oil,!and!(3)! farm!size—growth!ponds!covering!either!100!or!400!hectares!(250!or!1,000!acres).!!! Sale!of!algae!co"products,!such!as!pigments!or!animal!feeds,!could!improve!the!economics!of! algae!biofuel,!but!it!is!not!considered!in!this!analysis!because!the!higher!value!co"product! markets!would!likely!become!saturated!before!significant!biofuel!quantities!were!produced,! while!commodity!animal!feed!co"production!would!likely!not!have!a!decisive!effect!on!biofuels! production!costs!without!other!production!improvements!in!addition.! Unlike!most!prior!techno"economic!reports!on!microalgae!biofuel!systems,!discussed!below,! this!study!fully!incorporates!wastewater!treatment!in!process!design!and!economics.!!In! addition,!the!design!details!and!cost!updates!in!this!study!were!developed!independently,!with! many!distinct!design!features,!and!thus!is!not!directly!comparable!to!prior!studies.!! Technology!Assumptions! The!technologies!used!in!the!facility!designs!were!selected!to!meet!three!feasibility!criteria:!! scalability,!low!parasitic!energy!demand,!and!low!cost.!!The!cultivation!systems!are!open,! raceway,!paddle!wheel"mixed!ponds!(“high!rate!ponds”),!a!technology!already!used!in! commercial!microalgae!production!plants!and!some!pilot"scale!biofuels!projects.!!The!pond! designs!of!this!report!differ!from!existing!commercial!designs!in!having!larger!individual!ponds! and!in!mostly!being!lined!with!compacted!clay!instead!of!plastic.!!The!biomass!harvesting!is!by! bioflocculation!(natural!flocculation!of!the!algae)!followed!by!sedimentation.!!This!process!is! based!on!experience!with!small"scale!algae!systems!and!is!analogous!to!conventional!(non" algal)!wastewater!treatment!processes.!!Thickening!of!the!resulting!algae!slurry!is!by!gravity! sedimentation,!and,!for!the!oil!producing!cases,!biomass!drying!is!done!primarily!with!solar! heat.!!For!the!methane"only!production!cases,!no!drying!is!required.!!! The!algae!farm!designs!are!based!on!methods!and!standards!of!agricultural!engineering!rather! than!on!more!costly!civil!engineering!and!municipal!standards.!!For!example,!the!clarifiers!and! anaerobic!digesters!use!plastic"lined!earthen!basin!designs!rather!than!concrete!tank!designs.! For!recovery!of!the!algae!oil!(triacylglycerides)!from!the!dried!biomass,!a!hexane!extraction! process!similar!to!that!used!for!soybean!oil!extraction!was!selected.!!Such!extraction!plants! must!be!large!(~4,000!metric!tons/day)!for!economies!of!scale,!which!requires!a!centralized! processing!plant!and!two"way!hauling!of!raw!and!extracted!biomass!from!a!multitude!of!algae! ! ii farms!(e.g.,!fifty!400"ha!farms!for!a!4,000!mt/d!extraction!plant).!!Despite!this!limitation,!solvent! extraction!is!the!most!economical!method!currently!available.!!Other!approaches!may!be! developed!in!the!future!(e.g.,!cell!breakage!followed!by!oil!emulsification!and!centrifugation).!! The!major!technical!assumptions!for!all!five!cases!are!25%!recoverable!triacylglyceride!content! in!algae!biomass!and!22!g/m2"day!(80!mt/ha"yr)!annual!average!total!biomass!productivity,!of! which!20!g/m2"day!is!harvested.!!The!resulting!oil!yield!is!about!20,000!liters/ha"yr!(2,100! gal/acre"yr).!!The!individual!ponds!are!4!hectares!(10!acres)!in!size!(690!m!by!60!m,!with!30"m! wide!channels)!and!mixed!with!paddle!wheels!at!a!nominal!water!velocity!of!25!cm/sec.!!The! hydraulic!residence!time!in!the!ponds!is!3!to!5!days,!depending!on!season.!!Flue!gas!CO2!is! supplied!by!countercurrent!sumps!within!the!ponds!to!eliminate!any!carbon!limitation!on!the! algae!growth!rate.!!! To!provide!the!starter!cultures!of!selected!or!improved!microalgae!strains!assumed!to!be! developed!for!this!process,!an!algae!inoculum!production!system!is!provided.!!It!uses!a!small! area!of!photobioreactors!(not!a!significant!cost),!followed!by!small!covered,!plastic"lined!ponds,! and!finally!4"ha!plastic"lined!ponds.!!! For!the!oil"producing!cases,!after!oil!is!extracted!from!the!dried!algae!biomass,!the!residual! biomass!is!returned!to!the!pond!facility,!re"wetted,!and!anaerobically!digested.!The!biogas! produced!is!used!for!electricity!generation!with!the!flue!gas!providing!CO2!to!the!ponds.!!The! digester!residuals,!with!their!carbon!and!nutrients,!are!recycled,!as!needed,!to!the!algae! production!ponds.!!For!the!cases!that!produce!only!biogas,!the!algae!biomass!is!not!dried!or! extracted,!only!digested.!! As!examples!of!the!processes!analyzed,!Figure!ES1!shows!the!process!schematic!for!the!case! having!wastewater!treatment!as!the!main!objective,!with!biogas!as!the!byproduct.!!Figure!ES2! shows!the!case!with!oil!production!as!the!main!objective,!with!treated!wastewater!as!the! byproduct.!!The!major!differences!in!Figure!ES2!compare!to!Figure!ES1!are!the!large!proportion! of!water!recirculated!and!the!use!of!solvent!extraction.!!The!cases!with!the!primary!objective!of! biofuel!production!do!not!produce!more!oil!or!biogas!per!hectare!than!the!cases!emphasizing! wastewater!treatment,!but!rather,!they!are!meant!for!larger!scales!in!which!wastewater!is!used! only!for!make"up!of!lost!water!and!nutrients.! The!microalgae!cultivation!and!harvesting!facilities!for!the!five!cases!are!designed!with!enough! detail!to!allow!a!preliminary!level!of!cost!estimation!(i.e.,!with!process!designs,!sizing!of!unit! operations,!mass!balances,!and!selection!of!the!construction!materials!and!methods).!!The! construction,!operation,!and!land!costs!are!specific!to!the!Imperial!Valley!or!nearby!areas!of! southern!California.!!! ! ! iii CO2 Recirculation 1o High Rate 2o Treated Screened Clarifiers Ponds Clarifiers Wastewater Wastewater Sludge Algae Biomass Digestate CO2 Anaerobic Gravity Generator Digesters Thickeners CH4 Algae + Biomass CO2 Electricity ! Figure!ES1:!!Process!schematic!for!Case!2!(wastewater!treatment"emphasis!with!production!