Bioresource Technology xxx (2014) xxx–xxx
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Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and bio-oil production encompassing biorefinery Omprakash Sarkar, Manu Agarwal, A. Naresh Kumar, S. Venkata Mohan ⇑ Bioengineering and Environmental Sciences (BEES), CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad 500 007, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Fresh microalgae and oil extracted
microalgae showed potential as pyrolytic feedstock. Pyrolysis of algae produced biogas, bio-oil and bio-char. Bio-oil showed fuel properties. Sand additive pyrolysis improved biogas from oil extracted microalgae.
a r t i c l e
i n f o
Article history: Received 30 July 2014 Received in revised form 14 September 2014 Accepted 15 September 2014 Available online xxxx Keywords: Lipids Oil extracted microalgae Sand additive Biohydrogen Adsorbent
a b s t r a c t Algal biomass grown hetrotrophically in domestic wastewater was evaluated as pyrolytic feedstock for harnessing biogas, bio-oil and bio-char. Freshly harvested microalgae (MA) and lipid extracted microalgae (LEMA) were pyrolysed in packed bed reactor in the presence and absence of sand as additive. MA (without sand additive) depicted higher biogas (420 ml/g; 800 °C; 3 h) and bio-oil (0.70 ml/g; 500 °C; 3 h). Sand addition enhanced biogas production (210 ml/g; 600 °C; 2 h) in LEMA operation. The composition of bio-gas and bio-oil was found to depend on the nature of feedstock as well as the process conditions viz., pyrolytic-temperature, retention time and presence of additive. Sand additive improved the H2 composition while pyrolytic temperature increment caused a decline in CO2 fraction. Bio-char productivity increased with increasing temperature specifically with LEMA. Integration of thermo-chemical process with microalgae cultivation showed to yield multiple resources and accounts for environmental sustainability in the bio-refinery framework. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Renewable and sustainable energy production from photosynthetic microalgae has attracted a considerable interest in the domain of energy and environment (Alcantara et al., 2013; Christenson and Sims, 2011; Watanabe et al., 2014). Due to high
⇑ Corresponding author. Tel./fax: +91 40 27191664. E-mail address: [email protected] (S. Venkata Mohan).
photosynthetic efficiency and rapid growth rates associated with microalgae cultivation, microalgae are being considered as an attractive biomass for the production of chemicals and fuels. Cultivation of microalgae biomass for biodiesel production has gained wide interest from researchers across the world (Devi et al., 2013, 2012; Venkata Mohan and Devi, 2014). After extracting the lipid, attention is being given to reuse residual algal biomass to other value-added co-products (Lam et al., 2014; Venkata Subhash and Venkata Mohan, 2014; Maddi et al., 2011). To make microalgal based biofuel production process sustainable it is
http://dx.doi.org/10.1016/j.biortech.2014.09.070 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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imperative to mimic integrated biorefinery concept facilitating production of diverse value added by-products from microalgae biomass. Usually pyrolysis is employed to covert a variety of biomass residues including municipal solid waste, plastic waste, agricultural residues, sludge, etc. into various forms of energy and materials. Pyrolysis facilitates the thermal decomposition of a material in the absence of oxygen or any other oxygen-containing reagent (air, water, carbon dioxide) and as a result, a solid material (char), gas and condensable liquids fractions (oils) are obtained (Lorenzo et al., 2014). As a fuel, bio-oil has several environmental advantages over fossil fuels since it is renewable, locally produced and has lower environmental impact (close to CO2/GHG neutral, no SOx emissions, 50% lower NOx emissions). There are several reviews focused on biomass pyrolysis for liquid fuel production (Oasma and Czernik, 1999; Czernick and Bridgwater, 2004; Mohan et al., 2006). The solid bio-char is similar to fossil coal, and this is useful as it can be used as bio-fuel (high calorific value), as chemical adsorbent (as a substitute for activated carbon) or for soil amendment (Brennan et al., 2014; Agarwal et al., 2015). The pyrolysis product quality and distribution depends mainly on pyrolytic temperature, heating rate, residence time, type of reactor, type of feedstock, etc. (Zanzi et al., 1996; Bridgwater, 2003). After extracting lipids from microalgae, the leftover biomass residue (deoiled) needs to be effectively utilized. In this regard, an attempt was made in this communication to explore the potential of harvested microalgae (MA) as well as lipid extracted microalgal biomass (LEMA) as pyrolytic feedstock. The influence of sand additive on biogas, bio-char and bio-oil composition was studied in comparison to and feedstock composition variation. 2. Methods 2.1. Feedstock Heterotrophically cultivated microalgae (mixed consortia) were used as pyrolytic feedstock in two diverse forms. After dual mode cultivation viz., growth and stress phases in domestic wastewater, the harvested algae biomass (MA) was solar dried. Half of the solar dried microalgal biomass was used as feedstock for pyrolysis directly. Remaining half was subjected for lipid extraction and the resulting residual biomass (LEMA) was also used as feedstock along with MA separately. 2.2. Experimental setup and operation The pyrolysis set-up broadly consists of three parts: pyrolysis reactor, furnace and condenser (Agarwal et al., 2013). The length of the reactor was 45.72 cm (25.4 mm diameter; 3 mm thick; SS316) with one end welded to a 6 mm pipe (SS316) and the other to a 3 mm thick flange of 50.8 mm diameter (SS304). The former serves as the inlet and the latter as outlet. The flange joints are closed by four 25 mm bolts with an asbestos packing. The reactor was placed inside a furnace (40.64 cm 10.16 cm) with 35.56 cm heating zone insulated with glass-wool through ceramic tube. Heating coil (3 kW) was wound around the ceramic tube. The inlet and outlet were connected to nitrogen cylinder and ice-bath condenser, respectively. The ice-bath condenser was used to cool the gas produced and to separate the condensable gases. The pyrolysis experiments were carried out in nitrogen rich atmosphere in a packed bed reactor on batch mode basis after loading MA and LEAM separately. A fixed amount of dry algae sample (3 g) was packed in the reactor and purged with pure nitrogen (99.99%) to remove the trapped air inside the reactor. The nitrogen gas was not purged during the course of pyrolysis operation.
Coarse sand (0.63–1 mm) was used as an additive for equal distribution of heat during the reaction in some specified experiments. It was mixed with algae in the ratio of 1:9, prior to being packed in the reactor. The most common constituent of sand is silica in form of quartz with sodium, calcium and iron silicates being the minor constituents. The reactor was heated at a constant rate of 12 °C per min. The decomposition of the sample was evaluated at selected temperatures and retention times with sand additive (SA; 600 °C; 1 and 2 h) and without sand additive (SL; 500, 600 and 800 °C; 3 h). The volatile substances evolved during pyrolysis were passed through ice-bath condenser to separate the condensable gases from the non-condensable ones (bio-oil). Transesterification of bio-oil was performed by refluxing in chloroform/methanol and hexane with methanol in the presence of H2SO4 as a catalyst. Refluxing was performed at 65–70 °C for 2 h in a round bottom flask and later washed in a retort funnel with distilled water to maintain neutral pH. After washing, diethyl ether was added to the reaction mixture and the Fatty Acid Methyl Esters (FAME) were collected from the organic phase which was separated from aqueous phase using a separating funnel. Pinch of anhydrous sodium sulphate was added to the organic layer to remove traces of water and finally the organic phase was subjected to evaporation for solvent recovery leaving FAME content in the tube. The concentrated samples were analysed for the presence of fatty acid methyl esters (FAME) by gas chromatography. 2.3. Analysis The volume of biogas evolved from pyrolysis was measured through water displacement technique. The compositional analysis of bio-gas was evaluated by gas chromatograph (NUCON 5765) using thermal conductivity detector (TCD) with 1/800 2 m Hayesep Q column employing nitrogen as carrier gas. The injector and detector were maintained at 60 °C each and the oven was operated at 40 °C isothermally. The biogas was quantified with the calibration gas supplied by Span Gas & Equipments Ltd., Navi Mumbai, India. FAME composition were analysed by using GC with FID (flame ionization detector) (Nucon-5765) through capillary column (Valcobond (VB) 30 mm (0.25 mm 0.25 lm)) using nitrogen as carrier gas (1 ml/min). The temperature of the oven was initially maintained at 140 °C (for 5 min), later increased at a rate of 4 °C/ min to reach 240 °C and maintained for 10 min. The injector and detector temperatures were maintained at 280 and 300 °C, respectively with a split ratio of 1:10. FAME (fatty acid methyl ester) composition was compared with the standard FAME mix (C8–C22; LB66766, SUPELCO). Thermo-gravimetric analysis (TGA) was studied with Mettler Toledo (TGA/SDTA 851e) system. 3. Results and discussion 3.1. Cultivation of microalgae biomass and lipid extraction Microalgae cultivation was performed by sequentially integrating growth and stress phase each with seven days of retention time. The growth phase was operated in heterotrophic mode using domestic wastewater. Stress phase was induced by transferring the 7th day biomass from growth phase into tap water which provides nutrient limiting conditions. After stress phase the microalgae was harvested, dried and subjected to lipid extraction (Chandra et al., 2014). The total lipid productivity of 21.2% was obtained. The fresh microalgal biomass (after 14 days; MA) were sun dried and then lipid were extracted (LEAM) and sealed in container prior to use in pyrolysis studies. Both algae based feedstocks were subjected to thermogravimetric analysis (TGA) in nitrogen atmosphere (Fig. 1). For the fresh
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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microalgae (MA), biomass has undergone three phases of weight loss, one between 50 and 100 °C, the second at 300 °C–400 °C (24%) and a third loss around 750 °C–800 °C (57.13%). The first shift represents weight loss caused by dehydration of the microalgae sample. Nearly 60% weight was reduced in the first shift of physical change representing evaporation of water content in the sample. The second and third weight shifts are attributed to losses of organic compounds and decomposition of the algae biomass, respectively. For deoiled algae (LEMA) also the first peak was seen at 50–100 °C (1.84%) followed by 300 °C–400 °C (21.19%), and at 750 °C–800 °C (54%). In MA and LEMA the TGA curve illustrated a reduction in the peak between 750 °C and 800 °C, proved reduction in the volatile matter content. This supports that with increase in temperature and retention time the reaction rate increased and therefore, the volatile matter might evolve in the form of bio-gas (Peng et al., 2001). 3.2. Biogas The biogas yield and composition were found to depend on the pyrolysis temperature, retention time and presence of additive (Fig. 1). During all the conditions the gas volume increased progressively as a function of temperature. Operation with sand as an additive and retention time variations documented marked improvement in the biogas yield as well as composition. Maximum biogas yield was documented at 800 °C with SL operation for both MA (420 ml/g) and LEMA (320 ml/g). Increase in thermal decomposition time for MA and sand addition influenced the total gas volume. With SL operation at 500, 600 and 800 °C the gas volume increased to 200 ml/g, 240 ml/g and 420 ml/g, respectively. Operating with SA increased the gas production at 600 °C varying with decomposition time [1 h – 230 ml/g (MA) and 200 ml/g (LEMA); 2 h – 240 ml/g (MA) and 210 ml/g (2 h)]. For LEMA, biogas yield with SA operation (200 ml/g) at 600 °C is comparable with the gas obtained (180 ml/g (500 °C; 3 h); 220 ml/g (600 °C; 3 h)) with SL operation because of uniform distribution of heat inside the reactor. The results depicted that the oil extracted algae biomass can be reutilized for pyrolytic biogas production in a sustainable and biorefinery route. Pyrolytic time, temperature and sand
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addition also influenced the biogas composition significantly apart from the volume. 3.2.1. Bio-hydrogen H2 yield was observed to vary with the biomass nature, pyrolytic temperature and retention time (Fig. 2). MA pyrolysis under SL condition (800 °C) documented highest H2 yield (110.5 ml/g; 3 h), followed by LEMA (100 ml/g; 3 h). SL operation showed lower H2 yield at lower decomposition temperature for both the algal feedstocks used [MA – 7.56 ml/l (500 °C); 18.50 ml/g (600 °C); LEMA – 3.40 ml/g (500 °C); 41.58 ml/g (600 °C)] attributing its effect on product formation. Moreover, operation with LEMA and SL also documented higher biogas yields at high temperature (800 °C: 36.8 ml/g) compared to lower temperature operations (500 °C: 1.1 ml/g and 600 °C: 13.86 ml/g) (Table 1). This signifies the functional role of temperature on biohydrogen yields as a function of feedstock composition. Effect of retention time with SA operation was also evaluated in both the pyrolytic operations (MA and LEMA). Initially with low RT, MA operation (SA: 600 °C, 1 h) showed higher H2 production (93.3 mg/g) followed by 2 h RT (SA: 55.4 ml/g (600 °C)). Whereas, with LEMA SA condition with 1 h RT at 600 °C documented lower biogas yield (10.3 mg/g) than 2 h operation (18.4 ml/g). The presence of sand as additive reduced the activation energy and maximized H2 yield without need to reach high decomposition temperature for extended time. However, variations in the H2 production varied with the composition of feedstock. This ascribes the influence of biomass composition and decomposition time on the biogas composition/yields with the function of temperature. The H2 content is probably caused by the poly-condensation of free radicals generated during the pyrolysis process and by dehydrogenation reactions with the oil and char. It is evident from results that LEMA pyrolysis showed relatively lower yield of H2 compared to oil bound microalgae. 3.2.2. Bio-methane The maximum bio-methane (CH4) production was observed at 800 °C with LEMA-SL operation (100 ml/g) followed by MA-SL (47.8 ml/g). Lower decomposition temperature documented comparatively less CH4 yields with MA-SL [1.2 ml/g (500 °C);
Fig. 1. TGA curves of microalgae/oiled (MA) and deoiled/lipid extracted microalgae (LEMA) at different heating rate.
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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Fig. 1 (continued)
10.6 ml/g (600 °C)] than LEMA [31 ml/g (500 °C); 50 ml/g (600 °C)]. Overall, LEMA pyrolytic operation showed maximum bio-methane yields compared to MA. RT has a significant influence on the bio-methane yields. Initially MA with 1 h decomposition time (SA: 600 °C) showed 10.3 ml/g of CH4 yield, which increased to 50.1 ml/g with RT of 2 h. whereas, in case of LEMA, 1 h operation (SA: 600 °C) yielded 31 ml/g followed by 50 ml/g at 2 h. The formation of CH4 can be attributed to the release of methyl radicals. Similar to the H2 yield, with increasing temperature, the CH4 production from both the types of algae feedstock improved with an exception that the CH4 yield from LEMA at 800 °C was less than that from MA. 3.2.3. Carbon dioxide Among the biogas composition, CO2 was observed as major component in all the experimental variations studied (Fig. 1). However, specifically CO2 fraction was lower with deoiled algal (LEMA) pyrolysis compared to lipid bound microalgae (MA). Based on the pyrolytic feedstock used, MA operation showed a increasing trend with CO2 production with an increase in decomposition temperature or time. On the contrary, LEMA operation showed marginal drop with increment in decomposition temperature or time. Comparatively SL operation yielded higher CO2 with MA operation. Decomposition temperature showed direct correlation with CO2 yield with MA pyrolytic operation. At 500 °C (3 h) operation with SL mode, 191.2 ml/g yield of CO2 was recorded followed by 600 °C (SL; 210.8 ml/g; 3 h) and 800 °C (SL; 261.6 ml/g; 3 h) (Fig. 3). LEMA operation with SL (3 h) mode operation documented marginal variation in CO2 production (175.4 ml/g (500 °C); 164.5 ml/g (600 °C); 172.5 ml/g (800 °C). However, in both the pyrolytic operations, the influence of RT on CO2 production was evident. With lower RT (1 h, 600 °C), MA process showed 126.2 ml/g followed by 155 ml/g (4 h). Similarly with LEMA at 600 °C operation for 1 h RT resulted in 178.5 ml/g yield followed by a drop in the production (146 ml/g). The influence of SA was marginal with CO2 production. In general, the pyrolysis of biomass produces a gas rich in oxides of carbon due to the high oxygen content of the feed material. The formation of the gaseous compounds
is a consequence of cracking reactions and the reactions between the species formed during pyrolysis. The origin of CO2 can be attributed primarily to the existence of carboxyl groups in the protein and saccharides in the algae as well as lipids particularly with MA feedstock. 3.3. Bio-oil profile Oil produced during pyrolysis is one of the important value added product (Mata et al., 2009; Sharif Hossain and Salleh, 2008; Yanik et al., 2013; Demirbasß, 2007). MA (lipid bound microalgae) only showed bio-oil production. Due to lipid extraction, LEMA did not yield pyrolytic oil. Both increments in decomposition time as well as temperature have had a negative effect on the pyrolytic oil production. Higher oil production was specifically observed at lower temperatures. With SL operation, higher oil yields were observed (0.70 ml/g) at 500 °C (3 h) operation followed by 600 °C (3 h; 0.30 ml/g) and 800 °C (3 h; 0.27 ml/g). Sand addition did not show any impact on bio-oil yields, whereas retention time affected the productivity (0.20/0.17 ml/g (1/2 h); 600 °C). Lipid bound microalgae (MA) with SL operation at 500 °C (3 h) and 600 °C (3 h) yielded higher bio-oil and were selected for oil profile analysis after transesterification. The composition of transesterified pyrolytic algal-oil showed good properties that enable its use as fuel (Table 2). Heptadecanoic acid (C17:0) was the major component observed with 500 °C operation which is a good fuel property desirable for use in diesel engines. At higher pyrolytic temperature (600 °C), the oil showed comparatively broader contour depicting the presence of butyric acid (C4:0), lauric acid (C12:0), stearic acid (C18:0), cis-11-eicosanoic acid (C20:1) and cis-11,14,17-eicosatrienoic acid (C20:3). Among these, butyric acid can be used for the preparation of butyrate methyl esters or stearic acid which has fuel based applications. Algal based oil has low oxygen content, higher carbon and hydrogen content and a lower density than bio-oil produced from lignocelluloses materials (Du et al., 2011). Bio-oil from fast pyrolysis of microalgae has low oxygen content with a higher heating value of 29 MJ/kg, a density of 1.16 kg/1 and a viscosity of 0.10 Pas which makes it suitable for
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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H2
CH4
CO2
Total biogas
SL
SA
500 400
200 300 150 200
100
100
50
(b) 300
500/ 3 600/ 3 800/ 3 600/ 1 600/ 2 0 Experimental variations (Temp ( C)/RT (h)) H2
LEMA
250
CH4
CO2
SL
0
Biogas 500
SA
400
200 300 150 200
100
100
50 0
Total biogas (ml/g)
250
0
Biogas composition (ml/g)
MA
Total biogas (ml/g)
Biogas composition (ml/g)
(a) 300
500/ 3 600/ 3 800/ 3 600/ 1 600/ 2 Experimental variations (Temp (0C)/RT (h))
0
Fig. 2. Effect of decomposition time and temperature on biogas production from microalgae (MA) and lipid extracted microalgae (LEMA) with sand additive (SA) and sand less (SL) pyrolytic conditions.
fuel oil (Miao et al., 2004). Fatty acid composition showed the presence of higher saturated fatty acids (SFA) over unsaturated fatty acids (USFA) depicting the lower risk on the combustion characteristics and ignition delay (Benjumea et al., 2011). The distribution of straight-chain alkanes of the saturated fractions from microalgae bio-oils were similar to diesel fuel (Miao et al., 2004).
3.4. Bio-char Bio-char is as potential value addition to improve soil fertility and thus allow increased crop production. Bio-char act as a sink for atmospheric carbon dioxide in terrestrial ecosystems (Lehmann and Joseph, 2006; Grierson et al., 2011; Wang et al., 2013). Fig. 4 depicts the yield of bio-char from MA and LEMA in SA
Table 1 Comparative evaluation of products obtained from pyrolysis of microalgae (MA) and lipid extracted microalgae (LEMA) pyrolysis at different operation conditions. Pyrolysis conditions
Retention time (h)
Biogas (ml/g)
H2 (ml/g)
CH4 (ml/g)
CO2 (ml/g)
H2 (%)
CH4 (%)
CO2 (%)
Bio-char (mg/g)
Bio-oil (ml/g)
MA SL 500 °C SL 600 °C SL 800 °C SA 600 °C SA 600 °C
3 3 3 1 2
200 240 420 230 240
7.56 18.50 110.46 93.36 28.80
1.20 10.66 47.88 10.35 56.16
191.24 210.84 261.66 126.29 155.04
1.26 2.57 8.77 13.53 4.00
0.20 1.48 3.80 1.50 7.80
95.62 87.85 62.30 54.91 64.60
0.43 0.33 0.56 0.63 0.53
0.70 0.30 0.27 0.20 0.17
LEMA SL 500 °C SL 600 °C SL 800 °C SA 600 °C SA 600 °C
3 3 3 1 2
180 220 320 220 220
3.40 41.58 110.59 31.09 55.44
1.13 13.86 36.86 10.36 18.48
175.46 164.56 172.54 178.55 146.08
0.63 6.30 11.52 4.71 8.40
0.21 2.10 3.84 1.57 2.80
97.48 74.80 53.92 81.16 66.40
0.45 0.51 0.50 0.58 0.55
– – – – –
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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H2
MA
CH4
MA
CO2
80
LEMA
SL
SA
0.6
Biochar yield (mg/g)
Biogas composition (%)
60 10
0 100
LEMA
SA
SL
80 60
0.4
0.2
10 0
500/ 3
0.0
600/ 3 800/ 3 600/ 1 600/ 2 Experimental variations: Temp (( 0C )/ RT(h))
500/ 3
600/ 3
800/ 3
600/ 1
600/ 2
0
Experimental variations: Temp( C/ RT(h))
Fig. 3. Influence of experimental conditions on composition of bio-gas evolved during pyrolysis (nitrogen atmosphere).
and SL operation. More or less similar trend of bio-char formation was seen from both MA and LEMA. SL operation showed relatively higher productivity than SA. Pyrolytic time, temperature and sand addition did not have much effect on bio-char production (MA – 0.426 mg/g to 0.555 mg/g; LEMA – 0.447 mg/g to 0.507 mg/g). Generally during pyrolysis, dehydration stage occurs up to 200 °C which leads to weight loss due to moisture removal from the algal biomass. The next stage (200–600 °C) is the devolatilisation; where about 60% weight loss occurs due to the loss of volatile components. The last stage (600–800 °C) is called solid decomposition; where the weight loss is much slower. In the devolatilisaton stage between 200 and 600 °C, the biogas production was highest with MA compared with LEMA, which indicates that highest volatile matter was released resulting in highest yield of bio-oil. The thermal decomposition breaks the compound and volatile gases were released as temperature increases to a specific point (Grierson et al., 2009). There exists a relationship between the chemical structure of solid bio-char and the composition of released gases at different temperatures (Singh et al., 2014). Algal bio-char has a lower carbon content, surface area and cation exchange capacity compared with the lignocellulose bio-char but has a higher pH and gives a higher content of nitrogen, ash and inorganic elements (Chaiwong et al., 2012). The addition of bio-char to soils enhances microbial activity. Bio-char produced from algal feedstocks have higher nutrients including minerals (Peacocke, 2001). Good amounts of nitrogenous compounds are present in algae which are derived from the pyrolysis of peptides or the decomposition and condensation of amino acids (Lorenzo et al., 2014). Bio-char has demonstrated its potential as a soil ameliorant capable of improving water holding capacity and nutrient status of many soils (Lehmann and Joseph, 2009). Biochar also helps to uptake polycyclic aromatic hydrocarbons (PAHs) and toxic elements from soil which results in
Fig. 4. Bio-char at different temperatures with varying pyrolysis time from microalgae (MA) and lipid extracted microalgae (LEMA) in presence and absence of sand additive.
improving crop productivity (Brennan et al., 2014). Bio-char after applying appropriate pretreatment can be used as an adsorbent for removing pollutants from wastewater (Agarwal et al., 2015; Brennan et al., 2014). Based on the multiple utilities, bio-char can be considered as one of the potential value addition to algal cultivation in the context of biorefinery. 4. Conclusions Pyrolysis of hetrotrophically cultivated algae resulted in production of bio-char, bio-oil and bio-gas. The profile of pyrolytic products was found to depend on the nature of feedstock, decomposition time/temperature and presence of sand as additive. Higher temperature and long decomposition time favoured biogas yield with lipid bound algae. Sand additive pyrolysis of lipid extracted algae showed good bio-gas production with increased H2 yield and decreased CO2 production even at lower decomposition temperature/time. Pyrolytic algae-oil showed good fuel properties. Study depicted the potential of algal biomass as a renewable feedstock for multi-product recovery that contributes for the development of sustainable biorefinery platform. Acknowledgements Authors acknowledge the Director, CSIR-IICT for kind support and encouragement in carrying out this work. Research was supported by Council of Scientific and Industrial Research (CSIR), New Delhi, India, in the form of XII five year network project (BioEn (CSC-0116); SETCA (CSC-0113) and by Department of Biotechnology (DBT) in the form of SAHYOG-EU-FP7-KBBE project (BT/IN/ EU/07/PMS/2011).
Table 2 Composition of pyrolysis bio-oil from microalgal (MA) pyrolysis at 500 °C; 3 h (3 h) and 600 °C (3 h). Parameter
Sample
Temperature Fatty acids
500 °C Common name Heptadecanoic acid
Lipid number C17:0
Property Combustion of diesel engines
600 °C Common name Butyric acid, lauric acid, stearic acid, cis-11eicosenoic acid, cis-11,14,17-eicosatrienoic acid
Lipid number C4:0 C12:0 C18:0 C20:1 C20:3
Property Preparation of butyrate esters like methyl butyrate, medicinal properties. As biofuel in engines lubricant, drying of oils
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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References Agarwal, M., Tardio, J., Venkata Mohan, S., 2013. Biohydrogen production from kitchen based vegetable waste: effect of pyrolysis temperature and time on catalyzed and non-catalyzed operation. Bioresour. Technol. 130, 502–509. Agarwal, M., Tardio, J., Venkat Mohan, S., 2015. Pyrolysis biochar from cellulosic municipal solid waste as adsorbent for azo dye removal: equilibrium isotherms and kinetics analysis. I. J. Environ. Sci. Dev. 6, 67–72. Alcantara, C., Encina, G.P.A., Munoz, R., 2013. Evaluation of mass and energy balances in the integrated microalgae growth-anaerobic digestion process. Chem. Eng. J. 221, 238–246. Benjumea, P., John, R.A., Andres, F.A., 2011. Effect of the degree of unsaturation of biodiesel fuels on engine performance, combustion characteristics and emissions. Energy Fuels 25, 77–85. Brennan, A., Jimenez, E.M., Alburquerque, J.A., Knapp, C.W., Switzer, C., 2014. Effects of biochar and activated carbon amendment on maize growth and the uptake and measured availability of polycyclic aromatic hydrocarbons (PAHs) and potentially toxic elements (PTEs). Environ. Pollut. 193, 79–87. Bridgwater, A.V., 2003. Renewable fuels and chemicals by thermal processing of biomass. Chem. Eng. J. 91, 87–102. Chaiwong, K., Kiatsiriroat, T., Vorayos, N., Thararax, C., 2012. Biochar production from freshwater algae by slow pyrolysis. Maejo Int. J. Sci. Technol. 6, 186–195. Chandra, R., Rohit, M.V., Swamy, Y.V., Venkata Mohan, S., 2014. Regulatory function of organic carbon supplementation on biodiesel production during growth and nutrient stress phases of mixotrophic microalgae cultivation. Bioresour. Technol. 165, 279–287. Christenson, L., Sims, R., 2011. Production and harvesting of microalgae for wastewater treatment, biofuels, and bioproducts. Biotechnol. Adv. 29, 686–702. Czernick, Bridgwater, A.V., 2004. Overview of applications of biomass fast pyrolysis oils. Energy Fuels 18, 590–598. Demirbasß, A., 2007. Oily products from mosses and algae via pyrolysis. Energy Sources Part A 28, 933–940. Devi, M.P., Swamy, Y.V., Venkata Mohan, S., 2013. Nutritional mode influences lipid accumulation in microalgae with the function of carbon sequestration and nutrient supplementation. Bioresour. Technol., 278–286. Devi, M.P., Venkata Subhash, G., Venkata Mohan, S., 2012. Heterotrophic cultivation of mixed microalgae for lipid accumulation and wastewater treatment during sequential growth and starvation phases: effect of nutrient supplementation. Renew. Energy, 276–283. Du, Z., Li, Y., Wang, X., Wan, Y., Chen, Q., Chen, Q., Wang, C., Lin, X., Liu, Y., Chen, P., Ruan, R., 2011. Microwave-assisted pyrolysis of microalgae for biofuel production. Bioresour. Technol. 102, 4890–4896. Grierson, S., Strezov, V., Ellem, G., Mcgregor, R., Herbertson, J., 2009. Thermal characterisation of microalgae under slow pyrolysis conditions. J. Anal. Appl. Pyrolysis 85, 118–123. Grierson, S., Strezov, V., Shah, P., 2011. Properties of oil and char derived from slow pyrolysis of Tetraselmis chui. Bioresour. Technol. 102, 8232–8240.
7
Lam, M.K., Tan, I.S., Lee, K.T., 2014. Utilizing lipid-extracted microalgae biomass residues for maltodextrin production. Chem. Eng. J. 235, 224–230. Lehmann, J., Joseph, S., 2006. Bio-char sequestration in terrestrial ecosystems – a review. Mitig. Adapt. Strat. Global Change 11, 403–427. Lehmann, J., Joseph, S., 2009. Biochar for Environmental Management: Science and Technology. Earthscan publication, pp. 1–12. Lorenzo, N.F., Fuente, E., Suárez-Ruiz, R.R., Gil, B., 2014. Pyrolysis characteristics of a macroalgae solid waste generated by the industrial production of Agar-Agar. J. Anal. Appl. Pyrolysis 105, 209–216. Maddi, B., Viamajala, S., Varanasi, S., 2011. Comparative study of pyrolysis of algal biomass from natural lake blooms with lignocellulosic biomass. Bioresour. Technol. 102, 11018–11026. Mata, T.M., Martins, A.M., Caetano, N.S., 2009. Microalgae for biodiesel production and other applications: a review. Renew. Sustain. Energy Rev. 14, 217–232. Miao, X., Wu, Q., Yang, C., 2004. Fast pyrolysis of microalgae to produce renewable fuels. J. Anal. Appl. Pyrolysis 71, 855–863. Mohan, D., Pittman, C.U., Steele, P.H., 2006. Pyrolysis of wood/biomass for bio-oil: a critical review. Energy Fuels 20, 848–889. Oasma, S., Czernik, 1999. Fuel oil quality of biomass pyrolysis oils state of the art for the end users. Energy Fuels 13, 914–921. Peacocke, O.C., 2001. A Guide to Physical Property Characterisation of Biomass Derived Fast Pyrolysis Liquids. Technical Research Centre of Finland, Espoo, Finland (VTT Publication No. 450). Peng, W., Wu, Q., Tu, P., Zhao, N., 2001. Pyrolytic characteristics of microalgae as renewable energy source determined by thermogravimetric analysis. Bioresour. Technol. 80, 1–7. Sharif Hossain, A.B.M., Salleh, A., 2008. Biodiesel fuel production from algae as renewable energy. Am. J. Biochem. Biotechnol. 4, 250–254. Singh, C.R., Kataki, R., Bhaskar, T., 2014. Characterization of liquid and solid product from pyrolysis of Pongamia glabra deoiled cake. Bioresour. Technol. . Venkata Mohan, S., Devi, M.P., 2014. Salinity stress induced lipid synthesis to harness biodiesel during dual mode cultivation of mixotrophic microalgae. Bioresour. Technol. . Venkata Subhash, G., Venkata Mohan, S., 2014. Deoiled algal cake as feedstock for dark fermentative biohydrogen production: an integrated biorefinery approach. Int. J. Hydrogen Energy 39, 9573–9579. Wang, K., Brown, R.C., Homsy, S., Martinez, L., Sidhu, S.S., 2013. Fast pyrolysis of microalgae remnants in a fluidized bed reactor for bio-oil and biochar production. Bioresour. Technol. 127, 494–499. Watanabe, H., Li, D., Nakagawa, Y., Tomishige, K., Kaya, K., Watanabe, M.M., 2014. Characterization of oil-extracted residue biomass of Botryococcus braunii as a biofuel feedstock and its pyrolytic behavior. Appl. Energy 132, 475–484. Yanik, J., Stahlb, R., Troegerb, N., Sinagc, A., 2013. Pyrolysis of algal biomass. J. Anal. Appl. Pyrol. 103, 134–141. Zanzi, R., Sjostrom, K., Bjornbom, E., 1996. Rapid high-temperature pyrolysis of biomass in a free-fall reactor. Fuel 75, 545–550.
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Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and bio-oil production encompassing biorefinery Omprakash Sarkar, Manu Agarwal, A. Naresh Kumar, S. Venkata Mohan ⇑ Bioengineering and Environmental Sciences (BEES), CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad 500 007, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Fresh microalgae and oil extracted
microalgae showed potential as pyrolytic feedstock. Pyrolysis of algae produced biogas, bio-oil and bio-char. Bio-oil showed fuel properties. Sand additive pyrolysis improved biogas from oil extracted microalgae.
a r t i c l e
i n f o
Article history: Received 30 July 2014 Received in revised form 14 September 2014 Accepted 15 September 2014 Available online xxxx Keywords: Lipids Oil extracted microalgae Sand additive Biohydrogen Adsorbent
a b s t r a c t Algal biomass grown hetrotrophically in domestic wastewater was evaluated as pyrolytic feedstock for harnessing biogas, bio-oil and bio-char. Freshly harvested microalgae (MA) and lipid extracted microalgae (LEMA) were pyrolysed in packed bed reactor in the presence and absence of sand as additive. MA (without sand additive) depicted higher biogas (420 ml/g; 800 °C; 3 h) and bio-oil (0.70 ml/g; 500 °C; 3 h). Sand addition enhanced biogas production (210 ml/g; 600 °C; 2 h) in LEMA operation. The composition of bio-gas and bio-oil was found to depend on the nature of feedstock as well as the process conditions viz., pyrolytic-temperature, retention time and presence of additive. Sand additive improved the H2 composition while pyrolytic temperature increment caused a decline in CO2 fraction. Bio-char productivity increased with increasing temperature specifically with LEMA. Integration of thermo-chemical process with microalgae cultivation showed to yield multiple resources and accounts for environmental sustainability in the bio-refinery framework. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Renewable and sustainable energy production from photosynthetic microalgae has attracted a considerable interest in the domain of energy and environment (Alcantara et al., 2013; Christenson and Sims, 2011; Watanabe et al., 2014). Due to high
⇑ Corresponding author. Tel./fax: +91 40 27191664. E-mail address: [email protected] (S. Venkata Mohan).
photosynthetic efficiency and rapid growth rates associated with microalgae cultivation, microalgae are being considered as an attractive biomass for the production of chemicals and fuels. Cultivation of microalgae biomass for biodiesel production has gained wide interest from researchers across the world (Devi et al., 2013, 2012; Venkata Mohan and Devi, 2014). After extracting the lipid, attention is being given to reuse residual algal biomass to other value-added co-products (Lam et al., 2014; Venkata Subhash and Venkata Mohan, 2014; Maddi et al., 2011). To make microalgal based biofuel production process sustainable it is
http://dx.doi.org/10.1016/j.biortech.2014.09.070 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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imperative to mimic integrated biorefinery concept facilitating production of diverse value added by-products from microalgae biomass. Usually pyrolysis is employed to covert a variety of biomass residues including municipal solid waste, plastic waste, agricultural residues, sludge, etc. into various forms of energy and materials. Pyrolysis facilitates the thermal decomposition of a material in the absence of oxygen or any other oxygen-containing reagent (air, water, carbon dioxide) and as a result, a solid material (char), gas and condensable liquids fractions (oils) are obtained (Lorenzo et al., 2014). As a fuel, bio-oil has several environmental advantages over fossil fuels since it is renewable, locally produced and has lower environmental impact (close to CO2/GHG neutral, no SOx emissions, 50% lower NOx emissions). There are several reviews focused on biomass pyrolysis for liquid fuel production (Oasma and Czernik, 1999; Czernick and Bridgwater, 2004; Mohan et al., 2006). The solid bio-char is similar to fossil coal, and this is useful as it can be used as bio-fuel (high calorific value), as chemical adsorbent (as a substitute for activated carbon) or for soil amendment (Brennan et al., 2014; Agarwal et al., 2015). The pyrolysis product quality and distribution depends mainly on pyrolytic temperature, heating rate, residence time, type of reactor, type of feedstock, etc. (Zanzi et al., 1996; Bridgwater, 2003). After extracting lipids from microalgae, the leftover biomass residue (deoiled) needs to be effectively utilized. In this regard, an attempt was made in this communication to explore the potential of harvested microalgae (MA) as well as lipid extracted microalgal biomass (LEMA) as pyrolytic feedstock. The influence of sand additive on biogas, bio-char and bio-oil composition was studied in comparison to and feedstock composition variation. 2. Methods 2.1. Feedstock Heterotrophically cultivated microalgae (mixed consortia) were used as pyrolytic feedstock in two diverse forms. After dual mode cultivation viz., growth and stress phases in domestic wastewater, the harvested algae biomass (MA) was solar dried. Half of the solar dried microalgal biomass was used as feedstock for pyrolysis directly. Remaining half was subjected for lipid extraction and the resulting residual biomass (LEMA) was also used as feedstock along with MA separately. 2.2. Experimental setup and operation The pyrolysis set-up broadly consists of three parts: pyrolysis reactor, furnace and condenser (Agarwal et al., 2013). The length of the reactor was 45.72 cm (25.4 mm diameter; 3 mm thick; SS316) with one end welded to a 6 mm pipe (SS316) and the other to a 3 mm thick flange of 50.8 mm diameter (SS304). The former serves as the inlet and the latter as outlet. The flange joints are closed by four 25 mm bolts with an asbestos packing. The reactor was placed inside a furnace (40.64 cm 10.16 cm) with 35.56 cm heating zone insulated with glass-wool through ceramic tube. Heating coil (3 kW) was wound around the ceramic tube. The inlet and outlet were connected to nitrogen cylinder and ice-bath condenser, respectively. The ice-bath condenser was used to cool the gas produced and to separate the condensable gases. The pyrolysis experiments were carried out in nitrogen rich atmosphere in a packed bed reactor on batch mode basis after loading MA and LEAM separately. A fixed amount of dry algae sample (3 g) was packed in the reactor and purged with pure nitrogen (99.99%) to remove the trapped air inside the reactor. The nitrogen gas was not purged during the course of pyrolysis operation.
Coarse sand (0.63–1 mm) was used as an additive for equal distribution of heat during the reaction in some specified experiments. It was mixed with algae in the ratio of 1:9, prior to being packed in the reactor. The most common constituent of sand is silica in form of quartz with sodium, calcium and iron silicates being the minor constituents. The reactor was heated at a constant rate of 12 °C per min. The decomposition of the sample was evaluated at selected temperatures and retention times with sand additive (SA; 600 °C; 1 and 2 h) and without sand additive (SL; 500, 600 and 800 °C; 3 h). The volatile substances evolved during pyrolysis were passed through ice-bath condenser to separate the condensable gases from the non-condensable ones (bio-oil). Transesterification of bio-oil was performed by refluxing in chloroform/methanol and hexane with methanol in the presence of H2SO4 as a catalyst. Refluxing was performed at 65–70 °C for 2 h in a round bottom flask and later washed in a retort funnel with distilled water to maintain neutral pH. After washing, diethyl ether was added to the reaction mixture and the Fatty Acid Methyl Esters (FAME) were collected from the organic phase which was separated from aqueous phase using a separating funnel. Pinch of anhydrous sodium sulphate was added to the organic layer to remove traces of water and finally the organic phase was subjected to evaporation for solvent recovery leaving FAME content in the tube. The concentrated samples were analysed for the presence of fatty acid methyl esters (FAME) by gas chromatography. 2.3. Analysis The volume of biogas evolved from pyrolysis was measured through water displacement technique. The compositional analysis of bio-gas was evaluated by gas chromatograph (NUCON 5765) using thermal conductivity detector (TCD) with 1/800 2 m Hayesep Q column employing nitrogen as carrier gas. The injector and detector were maintained at 60 °C each and the oven was operated at 40 °C isothermally. The biogas was quantified with the calibration gas supplied by Span Gas & Equipments Ltd., Navi Mumbai, India. FAME composition were analysed by using GC with FID (flame ionization detector) (Nucon-5765) through capillary column (Valcobond (VB) 30 mm (0.25 mm 0.25 lm)) using nitrogen as carrier gas (1 ml/min). The temperature of the oven was initially maintained at 140 °C (for 5 min), later increased at a rate of 4 °C/ min to reach 240 °C and maintained for 10 min. The injector and detector temperatures were maintained at 280 and 300 °C, respectively with a split ratio of 1:10. FAME (fatty acid methyl ester) composition was compared with the standard FAME mix (C8–C22; LB66766, SUPELCO). Thermo-gravimetric analysis (TGA) was studied with Mettler Toledo (TGA/SDTA 851e) system. 3. Results and discussion 3.1. Cultivation of microalgae biomass and lipid extraction Microalgae cultivation was performed by sequentially integrating growth and stress phase each with seven days of retention time. The growth phase was operated in heterotrophic mode using domestic wastewater. Stress phase was induced by transferring the 7th day biomass from growth phase into tap water which provides nutrient limiting conditions. After stress phase the microalgae was harvested, dried and subjected to lipid extraction (Chandra et al., 2014). The total lipid productivity of 21.2% was obtained. The fresh microalgal biomass (after 14 days; MA) were sun dried and then lipid were extracted (LEAM) and sealed in container prior to use in pyrolysis studies. Both algae based feedstocks were subjected to thermogravimetric analysis (TGA) in nitrogen atmosphere (Fig. 1). For the fresh
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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microalgae (MA), biomass has undergone three phases of weight loss, one between 50 and 100 °C, the second at 300 °C–400 °C (24%) and a third loss around 750 °C–800 °C (57.13%). The first shift represents weight loss caused by dehydration of the microalgae sample. Nearly 60% weight was reduced in the first shift of physical change representing evaporation of water content in the sample. The second and third weight shifts are attributed to losses of organic compounds and decomposition of the algae biomass, respectively. For deoiled algae (LEMA) also the first peak was seen at 50–100 °C (1.84%) followed by 300 °C–400 °C (21.19%), and at 750 °C–800 °C (54%). In MA and LEMA the TGA curve illustrated a reduction in the peak between 750 °C and 800 °C, proved reduction in the volatile matter content. This supports that with increase in temperature and retention time the reaction rate increased and therefore, the volatile matter might evolve in the form of bio-gas (Peng et al., 2001). 3.2. Biogas The biogas yield and composition were found to depend on the pyrolysis temperature, retention time and presence of additive (Fig. 1). During all the conditions the gas volume increased progressively as a function of temperature. Operation with sand as an additive and retention time variations documented marked improvement in the biogas yield as well as composition. Maximum biogas yield was documented at 800 °C with SL operation for both MA (420 ml/g) and LEMA (320 ml/g). Increase in thermal decomposition time for MA and sand addition influenced the total gas volume. With SL operation at 500, 600 and 800 °C the gas volume increased to 200 ml/g, 240 ml/g and 420 ml/g, respectively. Operating with SA increased the gas production at 600 °C varying with decomposition time [1 h – 230 ml/g (MA) and 200 ml/g (LEMA); 2 h – 240 ml/g (MA) and 210 ml/g (2 h)]. For LEMA, biogas yield with SA operation (200 ml/g) at 600 °C is comparable with the gas obtained (180 ml/g (500 °C; 3 h); 220 ml/g (600 °C; 3 h)) with SL operation because of uniform distribution of heat inside the reactor. The results depicted that the oil extracted algae biomass can be reutilized for pyrolytic biogas production in a sustainable and biorefinery route. Pyrolytic time, temperature and sand
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addition also influenced the biogas composition significantly apart from the volume. 3.2.1. Bio-hydrogen H2 yield was observed to vary with the biomass nature, pyrolytic temperature and retention time (Fig. 2). MA pyrolysis under SL condition (800 °C) documented highest H2 yield (110.5 ml/g; 3 h), followed by LEMA (100 ml/g; 3 h). SL operation showed lower H2 yield at lower decomposition temperature for both the algal feedstocks used [MA – 7.56 ml/l (500 °C); 18.50 ml/g (600 °C); LEMA – 3.40 ml/g (500 °C); 41.58 ml/g (600 °C)] attributing its effect on product formation. Moreover, operation with LEMA and SL also documented higher biogas yields at high temperature (800 °C: 36.8 ml/g) compared to lower temperature operations (500 °C: 1.1 ml/g and 600 °C: 13.86 ml/g) (Table 1). This signifies the functional role of temperature on biohydrogen yields as a function of feedstock composition. Effect of retention time with SA operation was also evaluated in both the pyrolytic operations (MA and LEMA). Initially with low RT, MA operation (SA: 600 °C, 1 h) showed higher H2 production (93.3 mg/g) followed by 2 h RT (SA: 55.4 ml/g (600 °C)). Whereas, with LEMA SA condition with 1 h RT at 600 °C documented lower biogas yield (10.3 mg/g) than 2 h operation (18.4 ml/g). The presence of sand as additive reduced the activation energy and maximized H2 yield without need to reach high decomposition temperature for extended time. However, variations in the H2 production varied with the composition of feedstock. This ascribes the influence of biomass composition and decomposition time on the biogas composition/yields with the function of temperature. The H2 content is probably caused by the poly-condensation of free radicals generated during the pyrolysis process and by dehydrogenation reactions with the oil and char. It is evident from results that LEMA pyrolysis showed relatively lower yield of H2 compared to oil bound microalgae. 3.2.2. Bio-methane The maximum bio-methane (CH4) production was observed at 800 °C with LEMA-SL operation (100 ml/g) followed by MA-SL (47.8 ml/g). Lower decomposition temperature documented comparatively less CH4 yields with MA-SL [1.2 ml/g (500 °C);
Fig. 1. TGA curves of microalgae/oiled (MA) and deoiled/lipid extracted microalgae (LEMA) at different heating rate.
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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Fig. 1 (continued)
10.6 ml/g (600 °C)] than LEMA [31 ml/g (500 °C); 50 ml/g (600 °C)]. Overall, LEMA pyrolytic operation showed maximum bio-methane yields compared to MA. RT has a significant influence on the bio-methane yields. Initially MA with 1 h decomposition time (SA: 600 °C) showed 10.3 ml/g of CH4 yield, which increased to 50.1 ml/g with RT of 2 h. whereas, in case of LEMA, 1 h operation (SA: 600 °C) yielded 31 ml/g followed by 50 ml/g at 2 h. The formation of CH4 can be attributed to the release of methyl radicals. Similar to the H2 yield, with increasing temperature, the CH4 production from both the types of algae feedstock improved with an exception that the CH4 yield from LEMA at 800 °C was less than that from MA. 3.2.3. Carbon dioxide Among the biogas composition, CO2 was observed as major component in all the experimental variations studied (Fig. 1). However, specifically CO2 fraction was lower with deoiled algal (LEMA) pyrolysis compared to lipid bound microalgae (MA). Based on the pyrolytic feedstock used, MA operation showed a increasing trend with CO2 production with an increase in decomposition temperature or time. On the contrary, LEMA operation showed marginal drop with increment in decomposition temperature or time. Comparatively SL operation yielded higher CO2 with MA operation. Decomposition temperature showed direct correlation with CO2 yield with MA pyrolytic operation. At 500 °C (3 h) operation with SL mode, 191.2 ml/g yield of CO2 was recorded followed by 600 °C (SL; 210.8 ml/g; 3 h) and 800 °C (SL; 261.6 ml/g; 3 h) (Fig. 3). LEMA operation with SL (3 h) mode operation documented marginal variation in CO2 production (175.4 ml/g (500 °C); 164.5 ml/g (600 °C); 172.5 ml/g (800 °C). However, in both the pyrolytic operations, the influence of RT on CO2 production was evident. With lower RT (1 h, 600 °C), MA process showed 126.2 ml/g followed by 155 ml/g (4 h). Similarly with LEMA at 600 °C operation for 1 h RT resulted in 178.5 ml/g yield followed by a drop in the production (146 ml/g). The influence of SA was marginal with CO2 production. In general, the pyrolysis of biomass produces a gas rich in oxides of carbon due to the high oxygen content of the feed material. The formation of the gaseous compounds
is a consequence of cracking reactions and the reactions between the species formed during pyrolysis. The origin of CO2 can be attributed primarily to the existence of carboxyl groups in the protein and saccharides in the algae as well as lipids particularly with MA feedstock. 3.3. Bio-oil profile Oil produced during pyrolysis is one of the important value added product (Mata et al., 2009; Sharif Hossain and Salleh, 2008; Yanik et al., 2013; Demirbasß, 2007). MA (lipid bound microalgae) only showed bio-oil production. Due to lipid extraction, LEMA did not yield pyrolytic oil. Both increments in decomposition time as well as temperature have had a negative effect on the pyrolytic oil production. Higher oil production was specifically observed at lower temperatures. With SL operation, higher oil yields were observed (0.70 ml/g) at 500 °C (3 h) operation followed by 600 °C (3 h; 0.30 ml/g) and 800 °C (3 h; 0.27 ml/g). Sand addition did not show any impact on bio-oil yields, whereas retention time affected the productivity (0.20/0.17 ml/g (1/2 h); 600 °C). Lipid bound microalgae (MA) with SL operation at 500 °C (3 h) and 600 °C (3 h) yielded higher bio-oil and were selected for oil profile analysis after transesterification. The composition of transesterified pyrolytic algal-oil showed good properties that enable its use as fuel (Table 2). Heptadecanoic acid (C17:0) was the major component observed with 500 °C operation which is a good fuel property desirable for use in diesel engines. At higher pyrolytic temperature (600 °C), the oil showed comparatively broader contour depicting the presence of butyric acid (C4:0), lauric acid (C12:0), stearic acid (C18:0), cis-11-eicosanoic acid (C20:1) and cis-11,14,17-eicosatrienoic acid (C20:3). Among these, butyric acid can be used for the preparation of butyrate methyl esters or stearic acid which has fuel based applications. Algal based oil has low oxygen content, higher carbon and hydrogen content and a lower density than bio-oil produced from lignocelluloses materials (Du et al., 2011). Bio-oil from fast pyrolysis of microalgae has low oxygen content with a higher heating value of 29 MJ/kg, a density of 1.16 kg/1 and a viscosity of 0.10 Pas which makes it suitable for
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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H2
CH4
CO2
Total biogas
SL
SA
500 400
200 300 150 200
100
100
50
(b) 300
500/ 3 600/ 3 800/ 3 600/ 1 600/ 2 0 Experimental variations (Temp ( C)/RT (h)) H2
LEMA
250
CH4
CO2
SL
0
Biogas 500
SA
400
200 300 150 200
100
100
50 0
Total biogas (ml/g)
250
0
Biogas composition (ml/g)
MA
Total biogas (ml/g)
Biogas composition (ml/g)
(a) 300
500/ 3 600/ 3 800/ 3 600/ 1 600/ 2 Experimental variations (Temp (0C)/RT (h))
0
Fig. 2. Effect of decomposition time and temperature on biogas production from microalgae (MA) and lipid extracted microalgae (LEMA) with sand additive (SA) and sand less (SL) pyrolytic conditions.
fuel oil (Miao et al., 2004). Fatty acid composition showed the presence of higher saturated fatty acids (SFA) over unsaturated fatty acids (USFA) depicting the lower risk on the combustion characteristics and ignition delay (Benjumea et al., 2011). The distribution of straight-chain alkanes of the saturated fractions from microalgae bio-oils were similar to diesel fuel (Miao et al., 2004).
3.4. Bio-char Bio-char is as potential value addition to improve soil fertility and thus allow increased crop production. Bio-char act as a sink for atmospheric carbon dioxide in terrestrial ecosystems (Lehmann and Joseph, 2006; Grierson et al., 2011; Wang et al., 2013). Fig. 4 depicts the yield of bio-char from MA and LEMA in SA
Table 1 Comparative evaluation of products obtained from pyrolysis of microalgae (MA) and lipid extracted microalgae (LEMA) pyrolysis at different operation conditions. Pyrolysis conditions
Retention time (h)
Biogas (ml/g)
H2 (ml/g)
CH4 (ml/g)
CO2 (ml/g)
H2 (%)
CH4 (%)
CO2 (%)
Bio-char (mg/g)
Bio-oil (ml/g)
MA SL 500 °C SL 600 °C SL 800 °C SA 600 °C SA 600 °C
3 3 3 1 2
200 240 420 230 240
7.56 18.50 110.46 93.36 28.80
1.20 10.66 47.88 10.35 56.16
191.24 210.84 261.66 126.29 155.04
1.26 2.57 8.77 13.53 4.00
0.20 1.48 3.80 1.50 7.80
95.62 87.85 62.30 54.91 64.60
0.43 0.33 0.56 0.63 0.53
0.70 0.30 0.27 0.20 0.17
LEMA SL 500 °C SL 600 °C SL 800 °C SA 600 °C SA 600 °C
3 3 3 1 2
180 220 320 220 220
3.40 41.58 110.59 31.09 55.44
1.13 13.86 36.86 10.36 18.48
175.46 164.56 172.54 178.55 146.08
0.63 6.30 11.52 4.71 8.40
0.21 2.10 3.84 1.57 2.80
97.48 74.80 53.92 81.16 66.40
0.45 0.51 0.50 0.58 0.55
– – – – –
Please cite this article in press as: Sarkar, O., et al. Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and biooil production encompassing biorefinery. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.09.070
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O. Sarkar et al. / Bioresource Technology xxx (2014) xxx–xxx 100
H2
MA
CH4
MA
CO2
80
LEMA
SL
SA
0.6
Biochar yield (mg/g)
Biogas composition (%)
60 10
0 100
LEMA
SA
SL
80 60
0.4
0.2
10 0
500/ 3
0.0
600/ 3 800/ 3 600/ 1 600/ 2 Experimental variations: Temp (( 0C )/ RT(h))
500/ 3
600/ 3
800/ 3
600/ 1
600/ 2
0
Experimental variations: Temp( C/ RT(h))
Fig. 3. Influence of experimental conditions on composition of bio-gas evolved during pyrolysis (nitrogen atmosphere).
and SL operation. More or less similar trend of bio-char formation was seen from both MA and LEMA. SL operation showed relatively higher productivity than SA. Pyrolytic time, temperature and sand addition did not have much effect on bio-char production (MA – 0.426 mg/g to 0.555 mg/g; LEMA – 0.447 mg/g to 0.507 mg/g). Generally during pyrolysis, dehydration stage occurs up to 200 °C which leads to weight loss due to moisture removal from the algal biomass. The next stage (200–600 °C) is the devolatilisation; where about 60% weight loss occurs due to the loss of volatile components. The last stage (600–800 °C) is called solid decomposition; where the weight loss is much slower. In the devolatilisaton stage between 200 and 600 °C, the biogas production was highest with MA compared with LEMA, which indicates that highest volatile matter was released resulting in highest yield of bio-oil. The thermal decomposition breaks the compound and volatile gases were released as temperature increases to a specific point (Grierson et al., 2009). There exists a relationship between the chemical structure of solid bio-char and the composition of released gases at different temperatures (Singh et al., 2014). Algal bio-char has a lower carbon content, surface area and cation exchange capacity compared with the lignocellulose bio-char but has a higher pH and gives a higher content of nitrogen, ash and inorganic elements (Chaiwong et al., 2012). The addition of bio-char to soils enhances microbial activity. Bio-char produced from algal feedstocks have higher nutrients including minerals (Peacocke, 2001). Good amounts of nitrogenous compounds are present in algae which are derived from the pyrolysis of peptides or the decomposition and condensation of amino acids (Lorenzo et al., 2014). Bio-char has demonstrated its potential as a soil ameliorant capable of improving water holding capacity and nutrient status of many soils (Lehmann and Joseph, 2009). Biochar also helps to uptake polycyclic aromatic hydrocarbons (PAHs) and toxic elements from soil which results in
Fig. 4. Bio-char at different temperatures with varying pyrolysis time from microalgae (MA) and lipid extracted microalgae (LEMA) in presence and absence of sand additive.
improving crop productivity (Brennan et al., 2014). Bio-char after applying appropriate pretreatment can be used as an adsorbent for removing pollutants from wastewater (Agarwal et al., 2015; Brennan et al., 2014). Based on the multiple utilities, bio-char can be considered as one of the potential value addition to algal cultivation in the context of biorefinery. 4. Conclusions Pyrolysis of hetrotrophically cultivated algae resulted in production of bio-char, bio-oil and bio-gas. The profile of pyrolytic products was found to depend on the nature of feedstock, decomposition time/temperature and presence of sand as additive. Higher temperature and long decomposition time favoured biogas yield with lipid bound algae. Sand additive pyrolysis of lipid extracted algae showed good bio-gas production with increased H2 yield and decreased CO2 production even at lower decomposition temperature/time. Pyrolytic algae-oil showed good fuel properties. Study depicted the potential of algal biomass as a renewable feedstock for multi-product recovery that contributes for the development of sustainable biorefinery platform. Acknowledgements Authors acknowledge the Director, CSIR-IICT for kind support and encouragement in carrying out this work. Research was supported by Council of Scientific and Industrial Research (CSIR), New Delhi, India, in the form of XII five year network project (BioEn (CSC-0116); SETCA (CSC-0113) and by Department of Biotechnology (DBT) in the form of SAHYOG-EU-FP7-KBBE project (BT/IN/ EU/07/PMS/2011).
Table 2 Composition of pyrolysis bio-oil from microalgal (MA) pyrolysis at 500 °C; 3 h (3 h) and 600 °C (3 h). Parameter
Sample
Temperature Fatty acids
500 °C Common name Heptadecanoic acid
Lipid number C17:0
Property Combustion of diesel engines
600 °C Common name Butyric acid, lauric acid, stearic acid, cis-11eicosenoic acid, cis-11,14,17-eicosatrienoic acid
Lipid number C4:0 C12:0 C18:0 C20:1 C20:3
Property Preparation of butyrate esters like methyl butyrate, medicinal properties. As biofuel in engines lubricant, drying of oils
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References Agarwal, M., Tardio, J., Venkata Mohan, S., 2013. Biohydrogen production from kitchen based vegetable waste: effect of pyrolysis temperature and time on catalyzed and non-catalyzed operation. Bioresour. Technol. 130, 502–509. Agarwal, M., Tardio, J., Venkat Mohan, S., 2015. Pyrolysis biochar from cellulosic municipal solid waste as adsorbent for azo dye removal: equilibrium isotherms and kinetics analysis. I. J. Environ. Sci. Dev. 6, 67–72. Alcantara, C., Encina, G.P.A., Munoz, R., 2013. Evaluation of mass and energy balances in the integrated microalgae growth-anaerobic digestion process. Chem. Eng. J. 221, 238–246. Benjumea, P., John, R.A., Andres, F.A., 2011. Effect of the degree of unsaturation of biodiesel fuels on engine performance, combustion characteristics and emissions. Energy Fuels 25, 77–85. Brennan, A., Jimenez, E.M., Alburquerque, J.A., Knapp, C.W., Switzer, C., 2014. Effects of biochar and activated carbon amendment on maize growth and the uptake and measured availability of polycyclic aromatic hydrocarbons (PAHs) and potentially toxic elements (PTEs). Environ. Pollut. 193, 79–87. Bridgwater, A.V., 2003. Renewable fuels and chemicals by thermal processing of biomass. Chem. Eng. J. 91, 87–102. Chaiwong, K., Kiatsiriroat, T., Vorayos, N., Thararax, C., 2012. Biochar production from freshwater algae by slow pyrolysis. Maejo Int. J. Sci. Technol. 6, 186–195. Chandra, R., Rohit, M.V., Swamy, Y.V., Venkata Mohan, S., 2014. Regulatory function of organic carbon supplementation on biodiesel production during growth and nutrient stress phases of mixotrophic microalgae cultivation. Bioresour. Technol. 165, 279–287. Christenson, L., Sims, R., 2011. Production and harvesting of microalgae for wastewater treatment, biofuels, and bioproducts. Biotechnol. Adv. 29, 686–702. Czernick, Bridgwater, A.V., 2004. Overview of applications of biomass fast pyrolysis oils. Energy Fuels 18, 590–598. Demirbasß, A., 2007. Oily products from mosses and algae via pyrolysis. Energy Sources Part A 28, 933–940. Devi, M.P., Swamy, Y.V., Venkata Mohan, S., 2013. Nutritional mode influences lipid accumulation in microalgae with the function of carbon sequestration and nutrient supplementation. Bioresour. Technol., 278–286. Devi, M.P., Venkata Subhash, G., Venkata Mohan, S., 2012. Heterotrophic cultivation of mixed microalgae for lipid accumulation and wastewater treatment during sequential growth and starvation phases: effect of nutrient supplementation. Renew. Energy, 276–283. Du, Z., Li, Y., Wang, X., Wan, Y., Chen, Q., Chen, Q., Wang, C., Lin, X., Liu, Y., Chen, P., Ruan, R., 2011. Microwave-assisted pyrolysis of microalgae for biofuel production. Bioresour. Technol. 102, 4890–4896. Grierson, S., Strezov, V., Ellem, G., Mcgregor, R., Herbertson, J., 2009. Thermal characterisation of microalgae under slow pyrolysis conditions. J. Anal. Appl. Pyrolysis 85, 118–123. Grierson, S., Strezov, V., Shah, P., 2011. Properties of oil and char derived from slow pyrolysis of Tetraselmis chui. Bioresour. Technol. 102, 8232–8240.
7
Lam, M.K., Tan, I.S., Lee, K.T., 2014. Utilizing lipid-extracted microalgae biomass residues for maltodextrin production. Chem. Eng. J. 235, 224–230. Lehmann, J., Joseph, S., 2006. Bio-char sequestration in terrestrial ecosystems – a review. Mitig. Adapt. Strat. Global Change 11, 403–427. Lehmann, J., Joseph, S., 2009. Biochar for Environmental Management: Science and Technology. Earthscan publication, pp. 1–12. Lorenzo, N.F., Fuente, E., Suárez-Ruiz, R.R., Gil, B., 2014. Pyrolysis characteristics of a macroalgae solid waste generated by the industrial production of Agar-Agar. J. Anal. Appl. Pyrolysis 105, 209–216. Maddi, B., Viamajala, S., Varanasi, S., 2011. Comparative study of pyrolysis of algal biomass from natural lake blooms with lignocellulosic biomass. Bioresour. Technol. 102, 11018–11026. Mata, T.M., Martins, A.M., Caetano, N.S., 2009. Microalgae for biodiesel production and other applications: a review. Renew. Sustain. Energy Rev. 14, 217–232. Miao, X., Wu, Q., Yang, C., 2004. Fast pyrolysis of microalgae to produce renewable fuels. J. Anal. Appl. Pyrolysis 71, 855–863. Mohan, D., Pittman, C.U., Steele, P.H., 2006. Pyrolysis of wood/biomass for bio-oil: a critical review. Energy Fuels 20, 848–889. Oasma, S., Czernik, 1999. Fuel oil quality of biomass pyrolysis oils state of the art for the end users. Energy Fuels 13, 914–921. Peacocke, O.C., 2001. A Guide to Physical Property Characterisation of Biomass Derived Fast Pyrolysis Liquids. Technical Research Centre of Finland, Espoo, Finland (VTT Publication No. 450). Peng, W., Wu, Q., Tu, P., Zhao, N., 2001. Pyrolytic characteristics of microalgae as renewable energy source determined by thermogravimetric analysis. Bioresour. Technol. 80, 1–7. Sharif Hossain, A.B.M., Salleh, A., 2008. Biodiesel fuel production from algae as renewable energy. Am. J. Biochem. Biotechnol. 4, 250–254. Singh, C.R., Kataki, R., Bhaskar, T., 2014. Characterization of liquid and solid product from pyrolysis of Pongamia glabra deoiled cake. Bioresour. Technol. . Venkata Mohan, S., Devi, M.P., 2014. Salinity stress induced lipid synthesis to harness biodiesel during dual mode cultivation of mixotrophic microalgae. Bioresour. Technol. . Venkata Subhash, G., Venkata Mohan, S., 2014. Deoiled algal cake as feedstock for dark fermentative biohydrogen production: an integrated biorefinery approach. Int. J. Hydrogen Energy 39, 9573–9579. Wang, K., Brown, R.C., Homsy, S., Martinez, L., Sidhu, S.S., 2013. Fast pyrolysis of microalgae remnants in a fluidized bed reactor for bio-oil and biochar production. Bioresour. Technol. 127, 494–499. Watanabe, H., Li, D., Nakagawa, Y., Tomishige, K., Kaya, K., Watanabe, M.M., 2014. Characterization of oil-extracted residue biomass of Botryococcus braunii as a biofuel feedstock and its pyrolytic behavior. Appl. Energy 132, 475–484. Yanik, J., Stahlb, R., Troegerb, N., Sinagc, A., 2013. Pyrolysis of algal biomass. J. Anal. Appl. Pyrol. 103, 134–141. Zanzi, R., Sjostrom, K., Bjornbom, E., 1996. Rapid high-temperature pyrolysis of biomass in a free-fall reactor. Fuel 75, 545–550.
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