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Renewable and Sustainable Energy Reviews

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New insights into algae factories of the future

Laurencas Raslavičiusa,⁎, Nerijus Striūgasb, Mantas Felnerisa,c

a Department of Transport Engineering at Kaunas University of Technology, Studentų str. 56, 51424 Kaunas, Lithuaniab Laboratory of Combustion Processes at Lithuanian Energy Institute, Breslaujos str. 3, 44403 Kaunas, Lithuaniac Department of Automobile Engineering at Vilniaus Gediminas Technical University, J. Basanavičiaus g. 28, 03224 Vilnius, Lithuania

A R T I C L E I N F O

Keywords:CO2 captureAlgal biomassFlue gasesCarbon captureBiofuelsGreen transport

A B S T R A C T

The total combined weight of biological material on planet Earth has been estimated in one source at about 75 ×109 t. Of this: crops comprise 2 × 109 t (2.7%) as well as microbes, fungi, algae and similar types ofmicroorganisms are estimated to comprise over 50% of the total amount. Microalgae is outstanding among allthe types of biomass sources in its ability to respond to the challenges of the future in terms of availability, highgrowth and production rates, yield per unit area, not competing for arable land, being most suitable optimalsources for both liquid and gaseous biofuels and valuable co-products within biorefineries. It is logical that theincreased ability to occupy new niches in the energy sector is determined by uptake of the new forms of biomassexploitation coupled with environmental impact reduction. This could explain the worldwide interest inexploiting algal biomass as an ideal attribute for photosynthetic capture of anthropogenic carbon that reached arecord high of ~ 10 Pg C yr−1 in 2014. In this review, we outline microalgae's potential to capture carbon in coal-fired power plant, discuss the advantages of photosynthetic organisms as a source for biodiesel and solid biofuelproduction, discuss the process engineering, different synergies and legislative factors needed to make theprocess efficient and economically viable. Before commercial-scale installations become feasible, however,numerous points still have to be resolved. In order to identify potentials and obtain recommendations foraction, co-authors have studied in detail various options for climate-beneficial recycling and trapping CO2 in thealgae factories of the future that potentially could be built in the European humid continental climate countries.

1. Introduction

Historically microalgae have been of interest since 1942 [1,2] whenHarder and von Witsch [3,4] proposed them as a source of vegetableoils. Even before that date, the relationship between nitrogen nutritionand lipid content of algae was already recognized [1]. After the WorldWar II the study of microalgae lipids was pursued by groups in theUnited States [5], England [6], and Germany [7]. One of the firstreports on biofuel processed from the lipids of Chaetoceros muelleri isdated 1990 [8]. Up till now algal biomass exhibits a range ofuncertainties, overflows, speculative dimensions, and above all mixedmodes of existence [9–16]. However, algal bio-crude is widely acceptedthese days by many researchers as a future source of biofuel worldwide[10,14,17–20].

Liquid, solid and gaseous biofuels from algae may become com-mercially available in the years 2020–2025 at the earliest, as theemerging algae-to-fuel systems has not been accomplished yet. Thereare various factors prompting application of algae-based fuels world-wide. The primary factor is limited petroleum resources predicted to

last for about another 50 years. The European Union member countriesalone consume approximately the fourth of the petroleum exploitedglobally per year. Global consumption of petroleum products has beengrowing as a result of rapid development of Asian economies (China,India) as well. EU authorities have recently started referring to newpollution and climate change control measures more frequently. Thereis unanimous consensus within the Community on securing long-termclean energy supplies for Europe in addition to the reduction ofgreenhouse gas emission from the energy and transport sectors [21].

Table 1 represents algae as universal product which can be used inmany cases: food industry, pharmacy, farming, environmental, oil, andbiofuel. European commission web page (http://cordis.europa.eu) wasused for the survey. Around 400 projects were overviewed and some ofthem are listed in the Table 1.

Table 2 shows that algae as the fuel source has some negativefactors which give impact for the high price, small payback, and lowpopularity. These factors led to the collapse of most of the projects.Expensive production and extraction processes determine high price ofan end-product, while production payback depends on algae species,

http://dx.doi.org/10.1016/j.rser.2017.08.024Received 5 September 2016; Received in revised form 28 May 2017; Accepted 10 August 2017

⁎ Corresponding author.E-mail address: laurencas.raslavicius@ktu.lt (L. Raslavičius).

Renewable and Sustainable Energy Reviews 81 (2018) 643–654

Available online 18 August 20171364-0321/ © 2017 Elsevier Ltd. All rights reserved.

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growing method, conditions, extraction method and many other factorsincluding state approach and support. We found that crude oil hasplayed significant role for the presented activities: at the moment of

projects implementation the price of oil has reached lows and remainedthe most popular energy source in the investigated period of time. Ofcourse, there is one key element which limits domination of crude oil in

Table 1Survey on the state of algae related research.

Programme (Year) Project Research

ENV-LIFE 2 (1997–1999)

Demonstration plant of recycling for vegetable wastes and algae [22] Composting plant where algae are used for the high quality organic productto be used for the farming.

IC-AVICENNE (1995–1998)

Use of wastewater for irrigation – a global approach blending watertreatment, irrigation with various systems on various crops andinstitutional/organizational aspects [23]

Algae usage for heavy metal reduction in wastewater.

FP1 (1985–1986) Production of liquid hydrocarbons from autotrophic biomass by lowtemperature autocatalytic conversion [24]

Biomass can be converted to oil relatively at low temperatures (250–380 °C). Such oil can be used as fuel source for transport or energy sectors.For example, biomass from algae are particularly suitable for thisconversion method. Oil is extracted from 60% of organic carbon whileapproximately 30% of organic carbon becomes coal. More than 65% of netenergy return is obtained using low temperature conversion method.

FP1 (1985–1987) Optimization and metabolic control of the production of autotrophicmicrobial biomass [25]

Tubular photobioreactor was constructed for algal biomass production.Microcomputer was involved to keep required temperature and pH level.The main goal was to achieve biomass rich in lipids growing under theLondon climate conditions. For the research Spirulina platensis(microalgae species) was used with reduced quantity of light. It has beenproven that even under that conditions algae biomass can be grownsuccessfully.

FP1 (1986–1987) Production of liquid hydrocarbons from autotrophic microbialbiomass by low temperature autocatalytic conversion. Part 3:harvesting procedures of microalgae in seawater [26]

Biomass conversion to oil needs oily and fast growing cultures, especiallyfor large scale oil production. Microalgae is one of the most promisingculture which can be harvested using flocculation process. Harvestingprocedure has high importance for further processes, whereas flocculationis simple and reliable. This technique is also economically acceptable (5–10US cents per kg of oil).

FP1 (1988–1992) Technology of high rate algal ponds for the photosynthetic reclamationof waste waters [27]

Improvement of algae ponds is required for a better efficiency treatingwaste water. Efficiency will be improved taking into account parameterssuch as pH, temperature, algae type, redox potential, dissolved oxygen,redox potential, bacterial strains.

FP4 (1996–1998) Production of polyunsatured fatty acids (PUFAs) by algae: a completebioprocessing concept for the large-scale production of high qualityDHA-containing oils [28]

Production of polyunsaturated fatty acids and docosahexaenoic acid,containing oil, which can be used later for infant food or pharmaceuticalpurposes.

FP5 (2000–2001) Hydroacustic tools for rapid industrial interest algae location [29] Hydroacoustics prototype is able to find algae concentration places. Usefulfor searching of algae in natural places including harvesting as additionalaspect.

FP7 (2009–2013) Marine algae as biomass for biofuels [30] Dictyota species from Mediterranean Sea was the oiliest 8.01% dry wt.basis, found in Turkey. Bifurcaria bifurcata species from Bantry Bay hadoil content of 5.9% dry wt. basis, found in Ireland. Other microalgae specieswere grown in photobioreactors: with highest oil content wasNannochloropsis oculata 20.83% dry wt. basis.

FP7 (2010–2011) Algae and aquatic biomass for a sustainable production of 2ndgeneration biofuels [31]

It was found that biomass, biodiesel and bioethanol can be produced from72 species of algae. 30 of them were produced commercially and 47 specieshad potential to be cultivated in seawater.

FP7 (2010–2013) Fuel making algae (Real-time non-invasive characterization andselection of oil-producing microalgae at the single-cell level) [32]

Not all algae species are suitable for the biofuel production. Iodine is one orthe factor which shows the quantity of saturation of its fatty acids.Increment in lipid production using this technology can be achieved.

FP7 (2010–2015) Biowaste and algae knowledge for the production of 2nd generationbiofuels [33]

The BioWALK4Biofuels Project aims to develop an alternative andinnovative system for the treatment of biowaste and use of GHG emissionsto produce biofuels, using macroalgae as a catalyser, in a multidisciplinaryapproach [33].

FP7 (2011–2015) Demonstration of integrated and sustainable enclosed raceway andphotobioreactor microalgae cultivation with biodiesel production andvalidation [34]

Biofuel production from algae on industrial scale. It has to meet EuropeanCommissions (EC) 20:20:20 objectives. Cultivated algae production isgoing to be around 90–120 dry tons per hectare by annum. Algae speciesand harvesting method must be selected responsibly in order to meetbiodiesel specifications.

FP7 (2011–2015) BIOfuel from algae technologies. [35] BIOFAT is a project with 10 ha of microalgae prepared for cultivation withannual productivity of 100 t/ha. Low energy centrifugation is used forbiomass harvesting, mechanical cell disruption is made for extraction andfinally biodiesel is made from oil by transesterification.

FP7 (2011–2016) All gas (Industrial scale demonstration of sustainable algae culturesfor biofuel production) [36]

Biofuel production on large scale using low-cost microalgae species. Projectincludes growing of algae, harvesting, production of biofuel and usage inthe vehicles. Algae yield is going to be around 200 t per hectare per yearand 20% of net oil content. Biogas will be produced from residues of algae.Wastewater will be used for the growth stimulation of algae and biogasproduction.

FP7 (2012–2017) DEMA – Direct Ethanol from MicroAlgae [37] Production of ethanol from microalgae using low cost bioreactors. Make itcheaper than from fossil fuel is the goal.

Horizon2020 (2016–2021)

Solenalgae. Improving photosynthetic solar energy conversion inmicroalgal cultures for the production of biofuels and high valueproducts [38]

Only 45% of sunlight can be used for the photosynthesis. Microalgae canachieve maximum 10% of sunlight for the photosynthesis. Even worsenumber can be achieved around 1–3% if low light conditions are evaluated.

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the market. It is environmental pollution. Each year more strictly lawsare released concerning air pollution including greenhouse effect allaround the world. Consequently, electric power companies started touse alternative energy sources such as biomass fuels. Expectations ofmicroalgae replacing fossil fuels is the most promising and anticipatedmoment. However, in most cases, energy return on investment (EROI)for algae industry projects does not show perfect values for the fossilfuel replacement. From literature analysis it can be seen that in themost cases EROI does not reach 1:1, i.e. net energy gain of 0.

It is believed that the projects on development and production ofalgae biofuels and co-products industry under economic and technicaluncertainties associated with the different synergies will improveperformance and reduce the cost of products as well as demonstrateon a large scale the readiness of the technology to enter the market inthe fields of energy and transport [45]. In other words, the dream of thealgae economy would be that of replacing fossil fuels. This can beachieved with the help of further research in the areas of carboncapture and sequestration [46,47], beneficial use of algal-biomasschain co-products [48], challenges in biotechnology [49,50] (applica-tion of light-emitting diodes [51], electromagnetic biostimulationstrategies [52,53], and use of wastewater as growth medium for algae[54,55]) to obtain economic algal biofuels.

2. Background and context for the study

2.1. Technology readiness assessment for combustion technologies

There are four fundamental methods of biomass conversion intosolid, liquid or gaseous fuels currently available, each with differenttechnological maturity level, efficiency, energy output, cost-effective-ness, and response to regional energy demands: (i) thermochemicalconversion (subcategories: combustion, gasification, torrefaction andpyrolysis), (ii) chemical conversion (biomass into liquid fuels), and (iii)biochemical conversion (subcategories: anaerobic digestion, and fer-mentation). Nevertheless, energy solutions developers are looking forspecific areas of focus, e.g. further development of stationary powerfuel cells, advanced thermochemical conversion systems (gasificationwith syngas upgrading to valuable products) or improved gas turbinesfor future combined-cycle plants, direct combustion remains amongthe most sought-after processes for industrial scale application.

Feedstock used are often residues such as bark, woodchips,sawdust, or crops grown specifically for use as fuel, like SRC biomass[56–62]. If comparing the calorific values of wood biomass fuels andde-oiled algae cake, we can derive at a conclusion, that it doesn't makea lot of difference (see Table 3). As hot algae-for-energy ideas go, thedirect combustion (incl. direct co-firing) [66,67] processes can success-fully find their application in the production of thermal energy andelectricity using de-oiled algae cake as fuel in the nearest future. It isworth mentioning that direct combustion processes are applied atindustrial facilities that operate on a vastly different scale – from fewkilowatts to hundreds of megawatts 300 MW. An exceptionally large

range of these systems with multiple possibilities in capacities andapplications presupposes the very high maturity level of a particulartechnologies (see Table 4).

Using the existing equipment, perhaps with some modifications,and co-firing it with de-oiled algae cake in conjunction with biologicalcarbon capture technology may represent a cost-effective means formeeting more stringent emissions targets as well as more efficient coal-based plants.

2.2. Biological systems for generating biomass and capturing carbon

Currently power from coal is cost competitive (for low-carbon andpollution permit prices) with other forms of electricity generation, likenuclear and hydroelectric power production (due to low variable costs)or renewable power generation (due to low variable costs and theirhigh-subsidization), except where there is direct access to low-costfossil fuels. US growth of shale gas extraction and usage in energysector influenced decreased coal demand and price in the worldmarket. The sharp decrease in prices of coal, together with thepollution allowance prices led to a significant decline in coal-firedpower production cost decrease, thus coal-fired power plants hasbecome much more competitive than gas-fired power plants. Anotherfact at an issue – founded in 2005 on the initiative of the EC, theEuropean Technology Platform for Zero Emission Fossil Fuel PowerPlants represents a unique coalition of stakeholders united in theirsupport for CO2 Capture and Storage (CCS) as a critical solution forcombating climate change [70]. Accordingly, CCS can technically beapplied to coal-fired power plants as well as their relative economicsdepend on power plant cost levels, fuel prices and market positioning,whereas applicability is mainly determined by load regime [70]. Theuse biological capture systems such as algae to remove CO2 from powerplant flue gases and yield by-products (biodiesel) that have value bothfinancially (subsidization, profits from a greater volume of sales of abiodiesel) and as an energy source (application of residual algalbiomass for further energy recovery) has received significant commer-cial interest in European humid continental climate countries. Apossibility to implement a cogeneration power plant using biologicalcapture system has been selected for in-depth analysis taking intoaccount major economic, technological, environmental and legalfactors facilitating development.

2.3. Energy balance for CO2 capture with microalgae

In contrast to southern countries, outdoor cultivation of microalgaein northern regions is hardly possible due to required climate condi-tions, i.e., the ambient temperature that should continuously exceed17 °C, and insufficient natural sunlight [71]. For instance, in India,which is an attractive region for growing aquatic biomass, the annualaccumulated solar radiation incident to a horizontal surface reaches upto 2000 kWh/m2/year, and only half as much in Lithuania –1000 kWh/m2/year. It is known that it is more efficient to cultivate

Table 2Unsuccessful or partially successful algae projects.

Ref. The outcome of a study

Zander [39] Pollution reduction. Algae are fed on the CO2 contained in the flue gases, which are produced by the power plants. However, it is cheaper to purchase pollutionallowances.

Ernsting [40] The yield of biofuel was far lower than company had expected or claimed. The company had to produce around 13 million gallons of biofuel per year, but theyhave produced 10 times less. Also company claimed to get 67–90 gallons from each ton of dry biomass, but actually 20–22 gallons per ton were achieved.

Wellinger [41] Power industry is more interested to maintain coal or oil as the main fuel source for the electric power plants, with the intensity fully recycling CO2 using e.g.algae. Biodiesel from algae is still in laboratories as samples.

Rapier [42] Algae grown using both methods (open ponds and photo bioreactors) are rather expensive. For the biofuel production is quite hard to compete growing algae inphoto bioreactors due to the price.

Biopact [43] Researchers could not reach high lipid yields from algae. Photo bioreactors are too costly. Various companies unsuccessfully attempt of using algae as thesource for the biofuel production.

Moss [44] Still high cost of microalgae compared to crude oil.

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micro algal biomass in photobioreactors than in open ponds [72].However, due to simpler technical complexity and low capital costs,this work will concentrate specifically closed ponds for algal biomasscultivation.

In order to estimate the main possible energy flows, the balances ofenergy flows were calculated (see Fig. 1) in order to identify a possibleenergy demand for cultivation of 1 tone of dry algal biomass per day. Itis known theoretically that it takes 1.83 t of carbon dioxide (CO2) tocultivate 1 t of dry algal biomass, assuming that the biomass contains50 wt% of elemental carbon. However, in a real system, consumption ofCO2 can increase up to several times due to irreversibility of processes[73]. In this way, the calculations assume that the CO2 consumptionefficiency reaches 50%, and it takes up to 2.745 t of CO2 to grow 1 t ofalgal biomass.

According to requirements of Directive 2010/75/EU of theEuropean Parliament and the Council on industrial emissions, thethreshold level of the pollutants in flue gases must be ensured thatcannot be exceeded and must be controlled continuously with an onlinemonitoring system. Consequently, the typical mass composition of fluegas at the standard 6 vol% O2 content in flue gas in a power plantfueled by coal should be close to that presented in Table 5 and close tothat declared by other authors [74]. Based on the calculated flue gascomposition and CO2 content, it is calculated that ~ 0.61 t/h of flue gasmust be supplied to the system to cultivate 1 t of microalgae. Typically,flue gas is heated to 120 °C upon exit from the flue gas treatmentsystem in a power plant fired with coal fuel, mostly upon exit from aSO2 scrubber if the chimney is not designed for wet operation.

In this particular case, the demand for flue gas increases to 13.7 t/h,because it is necessary to heat both water and air in the greenhouse(Fig. 1). The biomass growth cycle takes up to 1 day and the averagegrowth rate attains 1.5 g/L/day. In order to grow 1 tone of biomass, awater pond of approximately 667 m3 is needed with a recommendeddepth of 0.15–0.20 m due to limited light penetration [75]. Assumingthe planned depth of 0.2 m, the pond will occupy an area of 0.33 ha.Since the water is warm, it is expected to evaporate, and be removed bythe air circulation system installed in the greenhouse. Taking intoaccount the surface area of the pond and the water temperature, thewater evaporation rate can be estimated to be approximately 0.79 t/h.The water cooling rate of 3 °C/h due to circulation is also taken intoaccount. Thus, the heat demand for water heating makes 24 GJ per 1tone of algae.

In wintry regions, such as Lithuania which is situated in thehardiness zone of 5–6, the average annual air temperature is up to6 °C. Because of winter and large variation of air temperature, the pondmust be covered. This requires a greenhouse with an area of ~ 0.4 ha,height of up to 3 m and the volume of 12,000 m3. Assuming, thegreenhouse heat loss through the walls, air changes 2 times per hourand heating cold air from 6 to 25 °C, the heat demand for air heatingwas determined to be 8.3 GJ/t algae. Therefore, the total heat demandfor 1 tone of wet algal biomass cultivation per day amounts to 41.5 GJ.If in technological post-processing dry biomass is needed, additionalheat demand of 10 GJ for thermal drying from 70 to 5 wt% moistureafter mechanical dewatering is required.

In the analyzed region, annual sunshine hours make 1900 h/yearon average, while it can exceed 3000 h/year in southern regions. Thismeans, that in addition to heat energy, artificial lighting is alsonecessary for continuous cultivation of microalgae [76]. For the openponds typically employed light intensities varies between 100 and210 μE/m2/s [75]. Efficiency of modern LED lighting is > 75 lx/W,therefore recalculation into electrical energy yields the electrical powerof ~ 100 W/m2 in order to ensure the required light intensity. The lightand dark periods for microalgal cultivation is assumed to be 12:12 h.Consequently, the demand for electrical energy for cultivating 1 t ofalgae per day will be 14.4 GJ.

The preliminary energy balance for cultivation of 1 t/day dry algalbiomass with energy content of approximately 23.5 GJ would requireapproximately 51.5 GJ of thermal and 14.4 GJ electrical energy. Asseen from the diagram in Fig. 1 and Table 6, the thermal energy usedfor the process is recovered from the energy losses, i.e., each case ofutilization of waste heat energy increases directly the total power plantefficiency and additionally part of CO2 can be captured.

One of such alternatives using a standard condensing cogenerationpower plant in a small country with the installed thermal capacity of50 MW is presented in Table 6. It is seen here that this option will notcontribute a large energy value, because utilization of the total heatwaste of the flue gas from a power plant of the mentioned capacity canonly provide growth for up to 5.7 t/day of dry algal biomass.

Table 6 presents also other limit cases: the total capture of CO2, aswell as utilization of heat or electricity. The calculations show that thepresented amount of flue gas and carrying CO2 content can providecultivation of up to 168.5 t/day of dry algal biomass. However, therequired amount of heat and electrical energy for growth of thisamount of biomass would exceed the amounts produced in the powerplant. Another critical case would be utilization of the total electricalenergy produced in the power plant, because in this case, there wouldbe a shortage of heat energy to grow 90 t/day of algal biomass. Finally,the total utilization of the all heat energy produced in power plantwould ensure cultivation of up to 53 t/day of algae and a part ofelectrical energy would remain unused, but only one-third of CO2

would be captured.The performed analysis shows that cultivation of microalgae is not

efficient from the energy point of view and needs for more synergies.From the energy point of view, the most attractive case would be toutilize the waste heat leaved with flue gas. In this ideal case, up to 45%of energy could be recovered in form of biomass, and this approachwould increase the net efficiency of the power plant by up to 3%.Resuming that discussion, understanding the distinctive “footprints” offive different types of synergy assessed in this paper and internallinkages between them can help improve the way of planning andimplementing of the algae factories of the future. Combing these ideasgives us the first mutually exclusive and collectively exhaustive general-ization of the main influencing factors to make the dream of algaeeconomy in humid continental climate countries a reality.

Table 3Juxtaposition of calorific values and ash content of various biomass fuels, de-oiled algae cake, and coal.

Fuel type Wood biomass [63] De-oiled algae cake [64] Coal [65]

Coniferous wood(virgin wood)

Deciduous wood(virgin wood)

Bark materials(virgin wood)

Willow(SRC)/Poplar(SRC)

Chlamydomonas sp. JSC4 (foroil and biodiesel production)

Chlorella sorokinianaCY1 (for oil/biodieselproduction)

Anthracite/Bituminous/Sub-bituminous/Lignite

Calorific value,MJ/kg (drybasis)

18.8–19.8 18.5–19.2 19.0–21.0 18.4/18.5 17.4 20.4 30.0/18.8–29.3/8.3–25.0/5.5–14.3

Ash (wt%) 0.2–0.5 0.2–0.5 2.0–10.0 2.0/1.8 5.2 7.9 15.0–20.0

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Table 4Maturity assessment of two most commonly used coal direct combustion technologies [68,69].

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3. Understanding the factors facilitating the implementationof synergies in algal biofuel industry

3.1. Legislative factors

3.1.1. The role of public obligations quota in electricity sector. Thecase of Lithuania

The European Union has no common public service obligations(PSO) scheme: in each member state PSOs may operate in any field ofpublic service. Till now, mostly purchase price, investment subsidy andobligation to purchase energy produced from renewable energy sourceswere applied in the European countries if talking about the energysector. Another fact at an issue, Ministry of Energy of the Republic ofLithuania plans to abolish public service obligations levy for the

industry for their own use-produced electricity. The PSO levy is vitalto enable local industry to encourage local production of energy and atthe same time to enhance its competitiveness. Since 2016, natural gas-fired power plants in Lithuania are no longer supported by the fundscollected from consumers, because public service obligations (PSO)quotas were eliminated, i.e. gradual transition period from purchasingtariff to a method when the producers themselves will have to sell theelectricity in the market and to be responsible to maintain continuousbalance between electricity production and electricity consumption hasbeen completed. In 2015, the PSO quota for Lithuanian Power Plantwas up to 1.1 billion kWh, and for CHPs and gas-fired boiler-houses inother cities of Lithuania – 600 million kWh. Still, expensively producedelectricity was required to be ensured security of electricity supply inthe country. However, since 2016 new electricity connections betweenLithuania, Poland and Sweden started to operate which solved theaforementioned problem. Based on assessment of Litgrid that weremade in accordance with methodology of the European Network ofTransmission System Operators (ENTSO-E), two largest CHP plants(Vilnius CHPP and Kaunas CHPP) and one Combined Cycle PowerPlant (Panevezys CCPP) are not vitally necessary for Lithuanian powersystem's energetic security anymore. Specific problem occurred inKaunas where CHPP is required only for heat generation for districtheating system. However, hot water can be produced at a lower price ifswitching generated capacities from gas-fired plant to heat-only boilerplants using biomass as a fuel.

The changing energy market makes it vital for the second possibleoption – to build a power plants that could run efficiently on differentfuels. A plant's flexibility and a multi-fuel design, where fossil fuel likecoal is used in a combination with biomass fuels, coupled with CO2

capture with micro algae, constitute an effective way to optimize the

Fig. 1. Energy flow chart for cultivation of 1 t/day dry microalgae by capturing CO2 from coal combustion power plant.

Table 5Coal and flue gas composition used for calculation.

Composition of coal, wt%:Carbon (C) 62.2Hydrogen (H) 4.2Sulfur (S) 3.3Oxygen (O) 6.4Nitrogen (N) 1.2Ash 15.8Moisture 7Calculated theoretical flue gas composition, wt%:CO2 18.70N2 74.40SO2 0.04NOx 0.010O2 6.41

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prices of energy production and reduce air pollution.

3.1.2. Tradable carbon permitsIn terms of development of more efficient and sustainable processes

for heat and electricity production, microalgae can play an interestingrole through combining the use of flue gases from energy generatingsources and/or industrial wastewater (mainly that lacking fermentablecarbon) with cogeneration of valuable products (biodiesel, algalresidues for heat production), reducing carbon emissions and generat-ing tradable carbon permits. For producing one Carbon Permit (1 tCO2), an area less than 0.1 ha is (considering a biomass concentrationin the culture of 3 g/L and a pond with 0.2 m high of liquid) [77].

0.815H O + CO + 0.15HNO → CH N O + 1.37O2 2 3 1.78 0.15 0.52 2 (1)

Biological capture systems can play a very interesting role in thiscontext. While fixating carbon during growth (to be traded in themarket), industrial species of algae can accumulate lipids, which can befurther transformed into 3rd generation biodiesel to replace fuelsmined from ancient deposits. This is one of the untapped opportunitiesin the energy sector that receives more attention from the scientificcommunity and industry around the world.

3.2. Technological factors

3.2.1. Thermochemical treatment of algae residues to optimize thewhole cultivation cycle

The harvested algal biomass is a potential source for various kind ofbiofuels production [78]. During the thermochemical processing al-most all biomass is consumed and only negligible part of residuemostly in the form of the ash remains. However, producing biodiesel,bioethanol, biomethane, and other products, through biochemical orchemical processing leads to the higher amount of algal biomassresidues. The oil content of microalgae exceeds 80 wt% of the drybiomass [79]. The residual biomass obtained after extraction ortransesterification could be used for further energy recovery tooptimize the algae cultivation cycle in terms of energy efficiency. Thecomposition of residual biomass depends on the process used(Table 7). As can be seen from the Table 7, chemical composition ofextractive substances variate very negligible. The main differencecomparing with untreated algal biomass is a macromolecular composi-tion, i.e. the content of lipids decreases dramatically. However, the

remaining algal biomass residues are still rich in carbohydrates andproteins, and are very attractive for biomethane production viabiochemical conversion. However, the residual algal biomass is highlycalorific solid biofuel in comparison with ordinary woody biomass.Thus, the obtained residues are suitable for further thermochemicalconversion and production of heat or electricity, producer gas or cleansyngas, hydrogen, and Fischer-Tropsch diesel.

The thermochemical processing mainly includes such processes asdirect combustion, gasification, liquefaction and pyrolysis. The majorobstacle of algal biomass processing by thermochemical route is adrying stage as the treated or not microalgal biomass contains only 10–30 wt% dry solids. The second obstacle is high content of nitrogen (N)and sulfur (S) (Table 7). These compounds can lead to elevated NOx

and SOx emission to atmosphere during the high temperature oxida-tion during combustion process. There is lack of literature reviewaccording the algal biomass combustion, but theoretically, it could beeasily adapted for production of heat.

Alternatively, dried algal biomass could be converted to usefulgaseous products by means of gasification. The obtained gaseousproducts contain hydrogen (H2), carbon monoxide (CO), carbondioxide (CO2), methane (CH4) and other hydrocarbons [82]. After theprocessing of producer gas, the clean syngas containing only H2 and COis produced. Finally, for the transformation of synthesis gas intovaluable hydrocarbons, the catalytic Fischer–Tropsch (FT) synthesisis crucial [83].

Conversion of algal biomass into fuel and chemicals could be alsorealized by means of pyrolysis, which produces solid (bio-char), liquid(aromatic compounds, hydrocarbons, amides, amines, carboxylic acids,phenols) and gaseous fractions (H2, CO, CO2, CH4). The process isaccomplished at elevated 300–600 °C temperatures and according tothe process condition various yield of products could be obtained [84].The hydrothermal treatment seems to be most suitable for the biomasswith high moisture content. During the process, algal biomass istreated at the temperatures of 250–350 °C and high-pressure (5–15 MPa). The feedstock is mainly converted to the bio-oil fraction (31–45 wt%), residual solid (6–11 wt%), dissolved aqueous constituents(17–23 wt%), and gas phase products (30–41 wt%) [85].

3.2.2. Production of oil and biodiesel for transport and micro-cogeneration

According to energy input/output ratio to produce oil fuel and to

Table 6Alternatives for cultivation of microalgae from 50 MW coal combustion power plant.

Power plant capacity 50 MW (4320 GJ/day)El. power production 15 MWel (1296 GJ/day)Heat production 31.6 MWth (2730 GJ/day)Heat losses with flue gases 3.4 MWth (294 GJ/day)Coal usage 194 t/dayFlue gas yield 2474 t/dayCO2 yield 462 t/day

Algal biomass production CO2 capture Heat consumption Electricity consumption Pond area Algal biomass contentt/day t/day GJ/day GJ/day ha GJ/day toe

1 t/day dry algal production1 2.745 51.5 14.4 0.33 23.5 0.56

If all waste heat is used5.7 15.7 293.8 82.1 1.9 134.1 3.2

If all CO2 is captured168.5 462.4 8676.0 2425.9 55.6 3959.0 94.3

If all available heat is used53.0 145.5 2730.2 763.4 17.5 1245.8 29.7

If all available electrical power is used90 247.1 4635 1296 29.7 2115 50.4

* Counts in italic represent a constant of calculation, while in bold a limiting factor for each of the considered case.

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run diesel engines – oils are the most effective type of motor-fuel,taking an intermediate position between mineral diesel and petrol.They have CO2 neutral and usually decompose within 15–24 daysunder natural conditions having no impact on water pollution (Class 0pollution). Need to denote that algal oil production requires no toxic orchemically aggressive substances (methanol, esterification processadditives) as well as causes lower risk while being transported due toits non-toxic nature. More technical information about the character-istics of diesel fuel vs. different triglyceride oils is presented in Table 8.

Besides their ecological and economic benefits to the transport andenergy sectors, oils can't be used directly in diesel engines due to theirtoo high viscosity for modern high pressure pumps. The following threemethods were developed to reduce viscosity: heating, mixing of oil withmineral diesel fuel and transesterification of oil into biodiesel. Aneffective way to safely run an automotive diesel engine on algal oil is touse a one-tank (Fig. 2a) or dual tank systems (Fig. 2b). One-tanksystem can be applied for the small and average power diesel engines.It has numerous economic advantages for technique working inagriculture sector where seasonality is one of the most distinctiveand determinative features. Required set of equipment for the engineadaptation is displayed in Fig. 2a. Retrofitting concept helps tomaintain reliable supply of higher viscosity fuel and ensures its properatomization leading to mixture homogeneity throughout the entirecombustion chamber. Oil, if necessary, is heated by means of electricalheater during the start-up time of the engine in order to reduce fuelviscosity. When the engine reaches operating temperature, oil is heatedby means of plate heat exchanger, which is connected into the engine

cooling system.Other peripheral equipment that controls the engine function, i.e.

fuel pump, safety valves, air flow meter, fuel supply piping, remainunmodified. One-tank system allows to operate the retrofitted enginesat ambient temperatures no lower than + 5 °C. Dual tank (bi-fuel)system is more efficient for heavy duty diesel engines. To start thediesel engine requires mineral fuel contained in an auxiliary fuel tank(see Fig. 2b). The set works by sensing the engine temperature. It runson diesel fuel when engine temperature is low and allows the engine towarm to the designed temperature and then switches on oil afterrequired temperature is reached.

To sum it up, algal oil can be successfully produced as algal-biomasschain co-product from biological capture systems that are intended forCO2 capture in the industrial power plants and later be used as a fuelfor stationary engines (micro-CHPs for distributed renewable energysystems) and mobile engines (cars, buses, heavy duty vehicles, agri-cultural and forestry tractors). Because algae oil is a triglyceride, it canbe further converted to biofuels such as biodiesel, through the sameprocesses used to convert plant oils. Finally, power plants mustdistribute algal oil and/or biodiesel and sell their products: deliverthe product to business customers who then blend and distribute theproduct further [88,89], to use liquid fuels as a reserve fuel for CHPgeneration, or sell their products directly to consumers as a cleaneralternative at fuel stations across the country. Co-products and by-products of biodiesel production – oilcake and glycerine – areconsidered to be sold at the market as well [90].

Table 7The composition of algal biomass.

Parameter Type of treatment

1-butanolextraction[80]

Chloroform–

methanolextraction[80]

Ethanolextraction [81] Hot waterextractionextraction[81]

Acidcatalyzedtransesterification[80]

Untreated [80]

Ultimate analysis, daf:Carbon, wt% 47.45 46.63 55.1 55.57 44.77 53.82Hydrogen, wt% 7.05 7.17 7.41 7.07 7.46 8.48Nitrogen, wt% 9.89 10.13 12.61 11.25 9.39 7.25Oxygen, wt% 34.57 34.80 24.33 22.40 36.22 29.95Sulfur, wt% 1.04 1.28 0.81 0.74 2.15 0.50

Macromolecular composition, dry:Lipid, wt% 1.96 0.64 – – 0.19 28.3Carbohydrate,

wt%35.60 35.23 – – 39.62 26.2

Protein, wt% 62.44 64.13 – – 60.19 45.5Higher heating

value,MJ kg−1

22.32 22.36 22.41 21.43 21.76 26.09

Table 8Physical and chemical characteristics of different oils.

Diesel fuel vs. Type of oil Density (15 °C), Calorific value, Viscosity (20 °C), Cetane number Pour point, °C Ignition temperature, °C IOD numberkg/dm3 MJ/kg mm2/s

Diesel 0.84 42.7 4–6 50 – 80 –

Rapeseed 0.92 37.6 74.0 49 0…− 3 317 94–113Sunflower 0.93 37.1 66.0 35 − 16…− 18 316 118–144Soy 0.93 37.1 63.5 38 − 8…− 18 350 114–138Flax 0.93 37.0 51.0 52 − 18…− 27 – 169–192Olive 0.92 37.8 83.8 37 − 5…− 9 – 76–90Cottonseed 0.93 36.8 89.4 41 − 6…− 14 320 90–117Nut 0.91 37.2 71.0 51 – 340 103Coconut fat 0.87 35.3 21.7 – 14–25 – 7–10Palm 0.92 37.0 29.4 42 27–43 267 34–61Coconut kernel – 35.5 21.5 – 20–24 – 14–22Algae [86,87] 0.90–0.92 38.9 35.1–35.4 55.6 − 5 131 –

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3.2.3. Broad range of synergistic possibilities provided by 4thgeneration DH technologies and systems

On February 16th, 2016, the European Commission proposed anEU heating and cooling strategy (hereinafter Strategy) [91]. TheStrategy specifies that nascent electricity market in European Unionhas progressed over time to include more and more solar power andwind power generators. The number of small-scale decentralizedenergy producers increases as well. Direction is becoming clearer, thatenergy producers and consumers have to be flexible and adapt quicklyto the market conditions. For example, to accumulate cheaper energy atnight in the storage and use for own purposes or sell electricity duringperiods of peak demand, when electricity prices are highest.

District heating and cooling systems (DHCSs) is an excellentinfrastructure that is highly profitable from a national economyperspective: it enables the integration not only various energy re-sources but also energy producers and consumers. As stated in theStrategy, district heating systems (DHSs) can use a variety of renewableand local sources of energy: excess heat that is usually emitted byplants to the atmosphere, municipal waste, solar and geothermalenergy. Integration of heat pumps into DHSs is also considered asone of the methods to increase consumption of renewables basedelectricity [92]. Another viable function of DHSs is to purchase ofexcess heat and store in the underground reservoirs for several days(during weekends) or even weeks. Some district heating systems arealready buying cheaper (or "off peak") electricity and use for the waterheating. It reduces the need for primary fuels (coal or biomass) duringhigher heating energy consumption periods or accumulated energy canbe utilized for plant's own needs, such as heating of biological capturesystems among others. It should be noted, that in the well-functioningelectricity market, at different periods the price for electricity might becheaper than the price for biofuel.

A significant by-product of power generation plants is rejected heat.In large coal-fired plants process waste heat is commonly rejectedthrough the use of cooling towers or directly to lakes or rivers.Although these conventional methods are effective, they may not befeasible in every application due to lower overall efficiency of the plantor higher environmental impact. Study [93] considers several scenarios

for coal-fired power plants for rejecting or recovering the waste heat,including the use of the thermal heat for algae bioreactors and modifiedsolar updraft tower (SUT). Both alternatives generate secondarybenefits: the algae bioreactor and the modified SUT produce biodiesel,and electric power, respectively [93]. Finally, the authors of the Ref.[93] concludes that the algae bioreactor can be used to recycle CO2

from flue gases as well as reject heat from the plant and produce algalbiomass. However, the temperature of the algae bioreactor must beconstantly and precisely monitored for the health of the algae [93].Another study [94] came at a conclusion, that there are severalbeneficial uses for the heat that is rejected into the environment bypower plants: (i) it should be used to develop district heating andcooling systems, (ii) the potential of growing algae for generatingbiofuel from fossil fuel stack gases should be explored. This is in linewith our findings presented in Section 2.3.

It should be noted that synergies and feasible solutions (like abilityto utilize renewable heat as well as recycled and waste heat) are notachieved simply by combining the infrastructures of smart thermalgrid, smart electricity grid and energy storage automatically. Thedesign and configuration has to be carefully investigated [95,96].

3.3. The grand challenges in industrial biotechnology

3.3.1. Wastewater as a resourceReuse of industrial wastewater already happens although, cur-

rently, in many industries this is realized through general processimprovements (water conservation) or depends largely on an un-planned/indirect basis, resulting from the use of water (e.g. utilizationof seawater, controlled storm run-off, sewage treatment plant effluent)that has been contaminated with untreated or poorly treated waste-water [97]. It is recognized, however, that there needs to be a moresubstantial effort to move towards more planned use and a reframingof industrial wastewater from being a problem that determines thenegative financial impact on the production process in the form ofexpenditures to being a resource to be valued and exploited [98].

Power plants may not be able to reuse waste water from theirfacilities. In the power plant industry, large volumes of water are used

Fig. 2. Complete set of equipment for adapting the engine to work with oils: a – one-tank system (1 – oil fuel filter, 2 – heat exchanger, 3 – glow plugs, 4 – modified fuel injectors, 5 –

electric fuel pump, 6 – temperature relay, 7 –manual fuel pump, 8 – electronic control unit, 9 – relay kit, 10 – fuel hose connection, 11 – electrical cables), b – dual tank (bi-fuel) system(1 – fuel pump, 2 – fuel supply regulating valve, 3 – liquid cooled heat exchanger, 4 – electric fuel pump, 5 – oil filter, 6 – diesel fuel filter, 7 – diesel fuel pump, 8 – control unit, 9 –

auxiliary diesel tank, 10 – oil tank).

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by cooling systems [99]. Water is also used in the ash transport,demineralizer plant regeneration, boiler cleaning, flue gas desulfuriza-tion (technologies used to remove SO2 from the flue gas during thecombustion of fossil fuels), and water also accumulates from coalstockpile run-offs. As a consequence, the effluent from power plantindustry has higher temperature and also has heavy metals such aschlorine, copper (Cu), aluminum (Al), mercury (Hg) and phosphorus(P) [99]. It is difficult to grow algae in these effluents. However, somestrains (Nannochloropsis sp, Chlorella vulgaris and others) that havetolerance to heavy metal contamination (up to a maximum value of1000 ppm) and high temperature could possibly be grown [99,100].The phenomena lies in mixed algal compositions (Scenedesmus sp,Synechococcus sp, Nannochloropsis sp) able to proliferate on produc-tion process water, and to methods of obtaining an algal biomass fromsuch cultures for use in generating a biofuel [100].

Use of industrial wastewater effluent and industrial sources of CO2

as medium for closed pond could significantly reduce not only the needfor chemical enrichment of the medium itself, including their asso-ciated environmental burdens but also the use of freshwater (tocompensate water loss and to avoid salt buildup due to evaporation)during algae cultivation. For photosynthesis alone about 750 g of wateris needed per 1000 g biomass produced according to the reactionstoichiometry as given in Ref. [101]:

CO + 0.93H O + 0.15NO → CH O N + 1.42O + 0.15H2 2 3 1.72 0.4 0.15 2−− (2)

This means that per 1000 g (2.2046 lbs) of biodiesel produced,assuming a lipid content of 40% 1900 g (4.1887 lbs) of fresh water isrequired. However, in practice water use in production systems is muchlarger [101]. Increase of algae productivity especially in adverseenvironments such as industrial wastewater and improvement of theirharvest index – are the first two of the selected grand challenges inindustrial biotechnology.

3.3.2. Light-emitting diode systems for the cultivation of algaeThe tasks of many long-term applied research and development (R

&D) strategies for sustainable development of algal biofuels usuallycontain optimization of the biosynthesis of lipids and achievement ofmore efficient photosynthesis. A photometer with a detection range of400–700 nm and quanta meter are suitable for illumination andquanta measurements of the intensity of photosynthesis. The afore-mentioned spectral range characterizes the type of light needed forphotosynthesis and is called Photosynthetically Active Radiation orabbreviatedly, PAR. Absorption maxima in the blue and red portions inthe spectrum is 450–470 [102,103] and 650 nm [102], respectively,while the green spectrum has a wavelength region with its peak at550 nm that determine the less efficient process of algal photosynthesis[102]. Accordingly, all-three quanta in Photosynthetically ActiveRadiation are important in varying degrees for the biological reproduc-tion of microalgae [102,104]. So, further studies into the optimum ratiobetween the flux of quanta from the illuminator and its effect ondifferent species of microalgae is among today's challenges of industrialbiotechnology.

Light or electromagnetic radiation is nature's way of transferringenergy through atmosphere and available radiation must be exploitedwith the highest possible efficiency to optimize biomass output andmake the large scale cultivation of unicellular algae economically viableand energetically sustainable [105]. Chernova et al. [102] concluded,that the process of photosynthesis in plants can be very efficientlycontrolled by using modern light-emitting diode (LED) lighting sys-tems. Solid-state light-emitting diodes consume less power (efficiency∼ 200 lm/W) than traditional lamps (efficiency ∼ 20 lm/W) and emitup to 100% of light falling in the range of PAR [102]. Other distincttechnical properties of LED systems with huge untapped potential forsuccessful mass cultivation of microalgae that can enhance processefficiency are [104]:

• Distinct wavelength emission;

• Wide variety of available wavelengths;

• Small size;

• Low radiant energy dissipation;

• Electronically dimmable;

• Spectral and intensity shifts.

Basically, the wider application of internal light sources in the formof LEDs for algal biomass cultivation has two still unresolved issues: (i)LED heat dissipation, and (ii) reduced culture volume fraction by theinternal light sources volume [104]. Simulation of the entire sunlightspectrum (red, blue, green, white) in order to enable a deeper insight inthe photosynthetic mechanisms governing algae cells productivitythrough the various LED configuration can lead to breakthroughachievements in CO2 capture technologies as well. As described byGlemser et al. [104], sophisticated climate simulation by combininglight-emitting diode technologies with temperature and humidityadjustments would allow adaptation of algae processes (photosyntheticefficiency) to a particular global location.

4. Conclusions

Despite only a part of carbon dioxide being utilized when comparedto the total amount emitted by a 50 MW coal-firing power plant, all theinvestigated factors (facilitating the implementation of synergies inalgal biofuel industry) in this study are recommended for the creationof value from CO2. This mean that with significant rigor and effort it ispossible to obtain a positive net energy return for algae based carboncapture systems by developing them into viable chemical productionplatforms. Co-authors predict that future climate change mitigationwill rely on a synergistic combination of CO2 capture and utilizationtechnologies, with microalgal carbon capture and biomass productionplaying a significant role. In addition to technology aspects and energybalance described in this review, the implementation of microalgalcarbon capture technologies is highly dependent on other crucialfactors such as commitment to reducing carbon footprint, growth rateof 4th generation DH technologies and systems in different countries,governmental policies, incentives for implementation at national level,readiness of biotechnology solutions for a specific region and futuresocio-economic developments.

Acknowledgement

All-three co-authors have contributed equally. The authors declareno competing financial interests.

References

[1] Benemann JR, Tillett DM. Effects of fluctuating environments on the selection ofhigh yielding microalgae. Final report to the Solar Energy Research Institute undersubcontract XK-4-04136-06. Atlanta: Georgia Institute of Technology; 1987.

[2] Benemann J. Microalgae for biofuels and animal feeds. Energies 2013;6:5869–86.[3] Harder R, von Witsch H. Ueber Massenkultur von Diatomeen. Ber Dtsch Bot Ges

1942;60:146–53.[4] Harder R, von Witsch H. Bericht über Versuche zur Fettsynthese mittels

autotropher Microorganismen. Forsch Sonderh 1942;16:270–5.[5] Spoehr HA, Milner HW. Chemical compostition of Chlorella: effect of environ-

mental conditions. Plant Physiol 1949;24(1):111–9.[6] Fogg GE, Collyer DM. The accumulation of lipides in algae. In: Burlew JS, editor.

Algal culture from laboratory to pilot plant. Washington: Carnegie Institution ofWashington; 1953. p. 177–81.

[7] Von Witsch H, Harder R. Stoffproduktion dorch Gruenalgen und Diatomen inMassenkulutr. In: Burlew JS, editor. Algal culture from laboratory to pilot plant.Washington: Carnegie Institution of Washington; 1953. p. 154–65.

[8] Nagle N, Lemke P. Production of methyl ester fuel from microalgae. Appl BiochemBiotechnol 1990;24/25:355–61.

[9] Mackenzie A. Synthetic biology and the technicity of biofuels. Stud Hist Philos BiolBiomed Sci 2013;44:190–8.

[10] Raslavičius L, Semenov VG, Chernova NI, Keršys A, Kopeyka AK. Producingtransportation fuels from algae: in search of synergy. Renew Sust Energy Rev2014;40:133–42.

L. Raslavičius et al. Renewable and Sustainable Energy Reviews 81 (2018) 643–654

652

[11] Blin J, Brunschwig C, Chapuis A, Changotade O, Sidibe S, Noumi ES, et al.Characteristics of vegetable oils for use as fuel in stationary diesel engines—towards specifications for a standard in West Africa. Renew Sust Energy Rev2013;22:580–97.

[12] Esteban B, Riba J-R, Baquero G, Rius A, Puig R. Temperature dependence ofdensity and viscosity of vegetable oils. Biomass-Bioenergy 2012;42:164–71.

[13] Alcaine AA. Biodiesel from algae: final degree project. Royal School of Technology,Kungliga Tekniska Hogskolan; 2010, [Available from: ⟨http://upcommons.upc.edu/pfc/bitstream/2099.1/9406/1/micoralgae_thesis-Aullon2%5B1%5D.pdf⟩].

[14] Ahmad AL, Yasin NHM, Derek CJC, Lim JK. Microalgae as a sustainable energysource for biodiesel production: a review. Renew Sust Energy Rev2011;15(1):584–93.

[15] Mata TM, Martins AA, Caetano NS. Microalgae for biodiesel production and otherapplications: a review. Renew Sust Energy Rev 2010;14(1):217–32.

[16] Atabani AE, Silitonga AS, Ong HC, Mahlia TMI, Masjuki HH, Badruddin IA, et al.Non-edible vegetable oils: a critical evaluation of oil extraction, fatty acidcompositions, biodiesel production, characteristics, engine performance andemissions production. Renew Sust Energy Rev 2013;18:211–45.

[17] Stephenson PG, Moore CM, Terry MJ, Zubkov MV, Bibby TS. Improvingphotosynthesis for algal biofuels: toward a green revolution. Trends Biotechnol2011;29(12):615–23.

[18] Demirbas A. Biodiesel from oilgae, biofixation of carbon dioxide by microalgae. Asolution to pollution problems. Appl Energy 2011;88:3541–7.

[19] Zhu LD, Hiltunen E, Antila E, Zhong JJ, Yuan ZH, Wang ZM. Microalgal biofuels.Flexible bioenergies for sustainable development. Renew Sust Energy Rev2014;30:1035–46.

[20] Knothe G. A technical evaluation of biodiesel from vegetable oils vs. algae. Willalgae-derived biodiesel perform?. Green Chem 2011;13:3048–65.

[21] EUROPE 2020: a European strategy for smart, sustainable and inclusive growth.Communication from the Commission to the European Parliament COM 2020.Brussels, 3.3.2010; 2010.

[22] Demonstration plant of recycling for vegetable wastes and algae; Project ID:LIFE96ENV/E/000269. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/39190_en.html⟩.

[23] Use of wastewater for irrigation – a global approach blending water treatment,irrigation with various systems on various crops and institutional/organisationalaspects; Project ID: AVI*940002. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/24994_en.html⟩.

[24] Production of liquid hydrocarbons from autotrophic microbial biomass by lowtemperature autocatalytic conversion; Project ID: EN3B0020. Available fromInternet: ⟨http://cordis.europa.eu/project/rcn/13116_en.html⟩.

[25] Optimization and metabolic control of the production of autotrophic microbialbiomass; Project ID: EN3B0021. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/13117_en.html⟩.

[26] Production of liquid hydrocarbons from autotrophic microbial biomass by lowtemperature autocatalytic conversion. Part 3: harvesting procedures of microalgaein seawater; Project ID: EN3B0019. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/13119_en.html⟩.

[27] Technology of high rate algal ponds for the photosynthetic reclamation of wastewaters; Project ID: EV4V0071. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/11914_en.html⟩.

[28] PUFATECH; Project ID: FAIR973146. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/48033_en.html⟩.

[29] HYTRIAL; Project ID: Q5AW-CT-2000-01222. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/63129_en.html⟩.

[30] MABFUEL (Marine algae as biomass for biofuels); Project ID: 230598. Availablefrom Internet: ⟨http://cordis.europa.eu/result/rcn/144097_en.html⟩.

[31] AQUAFUELS; Project ID: 241301. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/93226_en.html⟩.

[32] Fuel making algae; Project ID: 256526. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/95036_en.html⟩.

[33] BIOWALK4BIOFUELS; Project ID: 241383. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/94338_en.html⟩.

[34] INTESUSAL; Project ID: 268164. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/100473_en.html⟩.

[35] BIOFAT (Biofuel from algae technologies); Project ID: 268211. Available fromInternet: ⟨http://cordis.europa.eu/project/rcn/100477_en.html⟩.

[36] ALL-GAS; Project ID: 268208. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/103638_en.html⟩.

[37] DEMA (Direct ethanol from microalgae); Project ID: 309086. Available fromInternet: ⟨http://cordis.europa.eu/result/rcn/169959_en.html⟩.

[38] SOLENALGAE; Project ID: 679814. Available from Internet: ⟨http://cordis.europa.eu/project/rcn/199416_en.html⟩.

[39] Zander VH. Microalgae: predators of the greenhouse gas. [Internet source;Published 02.05.2010; Cited: 02.03.2015]. Spiegel; 2010, [Available fromInternet: ⟨http://www.spiegel.de/wirtschaft/unternehmen/mikroalgen-fressfeinde-des-klimagases-a-688670.html⟩].

[40] Ernsting A. Biofuel or biofraud? The vast taxpayer cost of failed cellulosic and algalbiofuels. [Internet source; Published 14.03.2016; Cited: 16.03.2016]. IndependentScience News; 2016, [Available from Internet: ⟨https://www.independentsciencenews.org/environment/biofuel-or-biofraud-the-vast-taxpayer-cost-of-failed-cellulosic-and-algal-biofuels/⟩].

[41] Wellinger A. Algal biomass. Does it save the world?. IEA Bioenergy; 2009. p. 10–1,[Available from Internet: ⟨http://www.iea-biogas.net/files/daten-redaktion/download/publi-task37/AlgaeBiomass8-09.pdf⟩].

[42] Rapier R. Current and projected costs for biofuels from algae and pyrolysis.

[Internet source; Published 07.05.2012; Cited: 16.03.2016]. Energy trends; 2012,[Available from Internet: ⟨http://www.energytrendsinsider.com/2012/05/07/current-and-projected-costs-for-biofuels-from-algae-and-pyrolysis/⟩].

[43] An in-depth look at biofuels from algae. [Internet source; Published 19. 01.2007;Cited: 16.03.2016]. Biopact; 2007. Available from Internet: ⟨http://global.mongabay.com/news/bioenergy/2007/01/in-depth-look-at-biofuels-from-algae.html⟩.

[44] Moss B. Ultimate review: the unlimited biotech potential of algae. [Internetsource; Published 02.02.2016; Cited: 16.03.2016]. Green tech; 2016, [Availablefrom Internet: ⟨http://labiotech.eu/algae-review-industry-biotech-greentech-biofuels-nutrition-scrubbing/⟩].

[45] Brownbridge G, Azadi P, Smallbone A, Bhave A, Taylor B, Kraft M. The futureviability of algae-derived biodiesel under economic and technical uncertainties.Bioresour Technol 2014;151:166–73.

[46] Sayre R. Microalgae: the potential for carbon capture. BioScience 2010;60:722–7.[47] Ghorbania A, Rahimpour HR, Ghasemi Y, Zoughic S, Rahimpour MR. A review of

carbon capture and sequestration in Iran: microalgal biofixation potential in Iran.Renew Sust Energy Rev 2014;35:73–100.

[48] Collet P, Hélias A, Lardon L, Steyer J-P, Bernard O. Recommendations for LifeCycle Assessment of algal fuels. Appl Energy 2015;154(15):1089–102.

[49] Bux F, Chisti Y, editors. Algae biotechnology: products and processes. New York:Springer; 2016.

[50] Zhu L. Microalgal culture strategies for biofuel production: a review. BiofuelsBioprod Bioref 2015;9(6):801–14.

[51] Schulze PS, Barreira LA, Pereira HG, Perales JA, Varela JC. Light emitting diodes(LEDs) applied to microalgal production. Trends Biotechnol 2014;32(8):422–30.http://dx.doi.org/10.1016/j.tibtech.2014.06.001.

[52] Hunt RW, Zavalin A, Bhatnagar A, Chinnasamy S, Das KC. Electromagneticbiostimulation of living cultures for biotechnology, biofuel and bioenergy appli-cations. Int J Mol Sci 2009;10(11):4719–22.

[53] Patent WO2014027871A1: method and system of algal cells disruption andisolation of bioproducts therefrom. Inventors: Bendikiene V, Romaskevicius O,Kiriliauskaite V. International Application No.: PCT/LT2013/000005. PublicationDate: 20.02.2014.

[54] Guo Z, Liu Y, Guo H, Yan S, Mu J. Microalgae cultivation using an aquaculturewastewater as growth medium for biomass and biofuel production. J Environ Sci2013;25(1):S85–S88. http://dx.doi.org/10.1016/S1001-0742(14)60632-X.

[55] Dalrymple OK, Halfhide T, Innocent Udom I, Gilles B, Wolan J, Zhang Q, et al.Wastewater use in algae production for generation of renewable resources: areview and preliminary results. Aquat Biosyst 2013;9:2. http://dx.doi.org/10.1186/2046-9063-9-2.

[56] Kyriakopoulos GL, Chalikias MS, Kalaitzidou O, Skordoulis M, Drosos D.Environmental viewpoint of fuelwood management. In: CEUR workshop pro-ceedings, Vol. 1498, 2015, p. 416–25.

[57] Chalikias MS, Kyriakopoulos GL, Goulionis JE, Apostolidis GK. Investigation ofthe parameters affecting fuelwoods' consumption in the Southern Greece region. JFood Agric Environ 2012;10(1):885–9.

[58] Kolovos KG, Kyriakopoulos G, Chalikias MS. Co-evaluation of basic woodfueltypes used as alternative heating sources to existing energy network. J EnvironProt Ecol 2011;12(2):733–42.

[59] Kyriakopoulos GL, Kolovos KG, Chalikias MS. Woodfuels prosperity towards amore sustainable energy production. Commun Comput Inf Sci 2010;112(PART2):19–25, [CCIS].

[60] Chalikias MS, Kyriakopoulos G, Kolovos KG. Environmental sustainability andfinancial feasibility evaluation of woodfuel biomass used for a potential replace-ment of conventional space heating sources. Part I: a Greek case study. Oper Res2010;10(1):43–56.

[61] Kyriakopoulos G, Kolovos KG, Chalikias MS. Environmental sustainability andfinancial feasibility evaluation of woodfuel biomass used for a potential replace-ment of conventional space heating sources. Part II: a combined Greek and thenearby Balkan countries case study. Oper Res 2010;10(1):57–69.

[62] Kyriakopoulos GL. European and international policy interventions of imple-menting the use of wood fuels in bioenergy sector: a trend analysis and a specificwood fuels' energy application. Int J Knowl Learn 2010;6(1):43–54.

[63] Francescato V, Antonini E, Bergomi LZ, et al. Wood fuel handbook. Legnaro: AIEL– Italian Agriforestry Energy Association; 2009.

[64] Chen W-H, Huang M-Y, Chang J-S, Chen C-Y. Thermal decomposition dynamicsand severity of microalgae residues in torrefaction. Bioresour Technol2014;169:258–64.

[65] Williamson J (editor). The impact of ash deposition on coal fired plants:proceedings of the engineering foundation conference. CRC Press; 1994.

[66] Brennan L, Owende P. Biofuels from microalgae—a review of technologies forproduction, processing, and extractions of biofuels and co-products. Renew SustEnergy Rev 2010;14:557–77.

[67] Kadam KL. Environmental implications of power generation via coal-microalgaecofiring. Energy 2002;7:905–22.

[68] Raslavičius L, Kučinskas V, Jasinskas A. The prospects of energy forestry andagro-residues in the Lithuania's domestic energy supply. Renew Sust Energy Rev2013;22:419–31.

[69] Raslavičius L, Azzopardi B, Kopeyka AK, Šaparauskas J. Steep increases inbiomass demand: the possibilities of short rotation coppice (SRC) agro-forestry.Technol Econ Dev Econ 2015;21(3):483–506.

[70] The cost of CO2 capture, transport and storage: post-demonstration CCS in theEU. Technical paper, European technology platform for zero emission fossil fuelpower plants; 2011.

[71] Sudhakar K, Premalatha M, Rajesh M. Large-scale open pond algae biomass yield

L. Raslavičius et al. Renewable and Sustainable Energy Reviews 81 (2018) 643–654

653

analysis in India: a case study. Int J Sustain Energy 2014;33(2):304–15.[72] Pires JCM, Alvim-Ferraz MCM, Martins FG, Simões M. Carbon dioxide capture

from flue gases using microalgae: engineering aspects and biorefinery concept.Renew Sust Energy Rev 2012;16(5):3043–53. http://dx.doi.org/10.1016/j.rser.2012.02.055.

[73] Slade R, Bauen A. Micro-algae cultivation for biofuels: cost, energy balance,environmental impacts and future prospects. Biomass-Bioenergy 2013;53:29–38.http://dx.doi.org/10.1016/j.biombioe.2012.12.019.

[74] Van Den Hende S, Vervaeren H, Boon N. Flue gas compounds and microalgae:(bio-)chemical interactions leading to biotechnological opportunities. BiotechnolAdv 2015;30(6):1405–24. http://dx.doi.org/10.1016/j.biotechadv.2012.02.015.

[75] Yen H-W, Hu I-C, Chen C-Y, Chang L-S. Design of photobioreactors for algalcultivation. In: Pandey A, Lee D-J, Chisti Y, Soccol CR, editors. Biofuels fromAlgae. Amsterdam: Elsevier; 2014. p. 23–45, [ISBN 9780444595584].

[76] Schulze PSC, Barreira LA, Pereira HGC, Perales JA, Varela JCS. Light emittingdiodes (LEDs) applied to microalgal production. Trends Biotechnol2014;32(8):422–30. http://dx.doi.org/10.1016/j.tibtech.2014.06.001.

[77] Sydney EB, Novak AC, de Carvalho JC, Soccol CR. Respirometric balance andcarbon fixation of industrially important algae. In: Pandey A, Lee D-J, Chisti Y,Soccol CR, editors. Biofuels from algae. Elsevier; 2013. p. 67–110.

[78] Suganya T, Varman M, Masjuki HH, Renganathan S. Macroalgae and microalgaeas a potential source for commercial applications along with biofuels production: abiorefinery approach. Renew Sust Energy Rev 2016;55:909–41. http://dx.doi.org/10.1016/j.rser.2015.11.026.

[79] Chisti Y. Biodiesel from microalgae beats bioethanol. Trends Biotechnol2008;26:126–31.

[80] Ehimen EA, Connaughton S, Sun Z, Carrington GC. Energy recovery from lipidextracted, transesterified and glycerol codigested microalgae biomass. GCBBioenergy 2009;1:371–81. http://dx.doi.org/10.1111/j.1757-1707.2009.01029.x.

[81] Phyllis2, database for biomass and waste. Energy Research Centre of theNetherlands. Available from Internet: ⟨https://www.ecn.nl/phyllis2⟩.

[82] Striūgas N, Zakarauskas K, Džiugys A, Navakas R, Paulauskas R. An evaluation ofperformance of automatically operated multi-fuel downdraft gasifier for energyproduction. Appl Therm Eng 2014;73(1):1151–9. http://dx.doi.org/10.1016/j.applthermaleng.2014.09.007.

[83] Zhang Q, Kang J, Wang Y. Development of novel catalysts for Fischer–Tropschsynthesis: tuning the product selectivity. ChemCatChem 2010;2:1030–58. http://dx.doi.org/10.1002/cctc.201000071.

[84] Yanik J, Stahl R, Troeger N, Sinag A. Pyrolysis of algal biomass. J Anal Appl Pyrol2013;103:134–41. http://dx.doi.org/10.1016/j.jaap.2012.08.016.

[85] Vardon DR, Sharma BK, Blazina GV, Rajagopalan K, Strathmann TJ.Thermochemical conversion of raw and defatted algal biomass via hydrothermalliquefaction and slow pyrolysis. Bioresour Technol 2012;109:178–87. http://dx.doi.org/10.1016/j.biortech.2012.01.008.

[86] Singh BP. Performance of conventional engine with algae oil at varying injectiontiming and injection pressure. Distributed generation and alternative. Energy J2016;31(3):55–77. http://dx.doi.org/10.1080/21563306.2016.11745258.

[87] Tsaousis P, Wang Y, Roskilly AP, Caldwell GS. Algae to energy: engine perfor-mance using raw algal oil. Energy Procedia 2014;61:656–9.

[88] Raslavičius L, Bazaras Ž. The possibility of increasing the quantity of oxygenates infuel blends with no diesel engine modifications. Transport 2010;25(1):81–8.

[89] Raslavičius L, Bazaras Ž. The analysis of the motor characteristics of D–RME–Efuel blend during on-field tests. Transport 2009;24(3):187–91.

[90] Raslavičius L. Characterization of the woody cutting waste briquettes containing

absorbed glycerol. Biomass-Bioenergy 2012;45:144–51.[91] EU strategy for heating and cooling [Internet source; Cited 12 August]; 2016.

Available from Internet: ⟨https://ec.europa.eu/energy/en/topics/energy-efficiency/heating-and-cooling⟩.

[92] Lauka D, Gusca J, Blumberga D. Heat pumps integration trends in district heatingnetworks of the Baltic States. Procedia Comput Sci 2015;52:835–42. http://dx.doi.org/10.1016/j.procs.2015.05.140.

[93] Lefflera RA, Bradshaw CR, Groll EA, Garimella SV. Alternative heat rejectionmethods for power plants. Appl Energy 2012;92:17–25. http://dx.doi.org/10.1016/j.apenergy.2011.10.023.

[94] A Study of the feasibility of utilizing waste heat from central electric powergenerating stations and potential applications. Prepared for the ConnecticutAcademy of Science and Engineering (CASE) and The Connecticut EnergyAdvisory Board (peer reviewed by Academy Members Caspersson SA andHermann RJ); 2009.

[95] Mathiesen BV, Lund H, Connolly D, Wenzel H, Østergaard PA, Möller B, et al.Smart energy systems for coherent 100% renewable energy and transportsolutions. Appl Energy 2015;145:139–54.

[96] Lund H, Werner S, Wiltshire R, Svendsen S, Thorsen JE, Hvelplund F, et al. 4thGeneration District Heating (4GDH) integrating smart thermal grids into futuresustainable energy systems. Energy 2014;68:1–11.

[97] Mohsen MS. Treatment and reuse of industrial effluents: case study of a thermalpower plant. Desalination 2004;167(1):75–86. http://dx.doi.org/10.1016/j.de-sal.2004.06.115.

[98] Wastewater management. A UN-water analytical brief. Produced by the WorldHealth Organization (WHO), the United Nations Environment Programme(UNEP) and UN-Habitat, on behalf of UN-Water; 2015. Available fromInternet: ⟨http://www.unwater.org/publications/publications-detail/en/c/275896/⟩.

[99] Capture of CO2 emissions using algae: a research document by Oilgae [Internetsource; Cited: August 17]; 2016. Available from Internet: ⟨http://www.oilgae.com⟩.

[100] Patent WO2014060973 A1: improved microalgae strains and use thereof.Inventors: Kumar M, Singh MP, Singh D, Chopra A, Tuli DK, Malhotra RK.Application No.: PCT/IB2013/059407. Publication Date: 24.04.2014.

[101] Clarens AF, Resurreccion EP, White MA, Colosi LM. Environmental life cyclecomparison of algae to other bioenergy feedstocks. Environ Sci Technol2010;44(5):1813–9. http://dx.doi.org/10.1021/es902838n.

[102] Chernova NI, Korobkova TP, Kiseleva SV, Zaytsev SI, Radomskii NV. Microalgaeas source of energy: current situation and perspectives of use. In: Seliger G, editor.Sustainable manufacturing: shaping global value creation. Berlin Heidelberg:Springer-Verlag; 2012. p. 221–4.

[103] Terashima I, Fujita T, Inoue T, Chow WS, Oguchi R. Green light drives leafphotosynthesis more efficiently than red light in strong white light: revisiting theenigmatic question of why leaves are green. Plant Cell Physiol2009;50(4):684–97. http://dx.doi.org/10.1093/pcp/pcp034.

[104] Glemser M, Heining M, Schmidt J, Becker A, Garbe D, Buchholz R. Application oflight-emitting diodes (LEDs) in cultivation of phototrophic microalgae: currentstate and perspectives. Appl Microbiol Biotechnol 2016;100:1077–88. http://dx.doi.org/10.1007/s00253-015-7144-6.

[105] Simionato D, Basso S, Giacometti GM, Morosinotto T. Optimization of light useefficiency for biofuel production in algae. Biophys Chem 2013;182:71–8. http://dx.doi.org/10.1016/j.bpc.2013.06.017.

L. Raslavičius et al. Renewable and Sustainable Energy Reviews 81 (2018) 643–654

654