Misbah Majid, Samia Shafqat, Hafsa Inam, Uzair Hashmi, and Alvina Gul Kazi

Contents

13.1 Introduction…………………………………………………………………………………………………… 208

13.2 Cultivation of Algae………………………………………………………………………………………… 210

13.2.1 Internal and External Factors Required for Growth of Algal Biomass………………… 210

13.2.2 Methods for Cultivation of Algal Biomass…………………………………………………. 212

13.2.3 Comparison of Different Cultivation Techniques………………………………………….. 213

13.3 Cultivation Systems………………………………………………………………………………………… 213

13.3.1 Open Ponds……………………………………………………………………………………… 213

13.3.2 Closed Photobioreactors……………………………………………………………………….. 214

13.3.3 Hybrid Production System……………………………………………………………………. 215

13.4 Problems Associated with Production of Algal Biomass……………………………………………… 216

13.4.1 Production Cost…………………………………………………………………………………. 216

13.4.2 Large-Scale Production………………………………………………………………………… 216

13.4.3 Temperature……………………………………………………………………………………… 216

13.4.4 Salinity…………………………………………………………………………………………… 217

13.4.5 Mixing…………………………………………………………………………………………… 217

13.4.6 Contamination…………………………………………………………………………………. 217

13.5 Harvesting of Algal Biomass……………………………………………………………………………… 217

13.5.1 Flocculation……………………………………………………………………………………… 218

13.5.2 Chemical Coagulation………………………………………………………………………… 218

13.5.3 Combined Flocculation………………………………………………………………………… 219

13.5.4 Gravity Sedimentation…………………………………………………………………………. 219

13.6 Reservoirs of Algal Biomass………………………………………………………………………………. 220

13.7 Main Hurdles and Possible Solutions……………………………………………………………………. 221

13.8 Conclusions………………………………………………………………………………………………….. 221

References ………………………………………………………………………………………………………….. 222

M. Majid • S. Shafqat • H. Inam • U. Hashmi • A. G. Kazi (*)

Atta-ur-Rahman School of Applied Biosciences (ASAB), National University of Sciences and Technology (NUST), Islamabad, Pakistan e-mail: alvina_gul@asab. nust. edu. pk

K. R. Hakeem et al. (eds.), Biomass and Bioenergy: Processing and Properties,

DOI 10.1007/978-3-319-07641-6_13, © Springer International Publishing Switzerland 2014

Abstract Among renewable resources, algae have proven to be an attractive feedstock for rapid generation of carbohydrates and lipids by utilizing its photosynthetic ability to present itself as an alternative energy source. Different species of algae, being environmental friendly, are strong candidates for generation of biomass, and are used in production of biogas and biofuel. Continuous efforts are being made to increase its large-scale production by application of specific methods chosen on the basis of desired downstream processing and final application of algal biomass. Biomass production is dependent upon cultivation methods for harvesting, followed by quantification of biochemical composition of biomass. Harvesting of algal mass is a major concern playing crucial role in determination of process economy required for further applications including biofuel production. Although algal biomass appears to be an efficient substrate for biofuel production, the progress is hindered by ammonia inhibition and ion toxicity. Further research is needed to replace the con­tinuously depleting energy sources with renewable, eco-friendly sources.

Keywords Algal biomass • Biofuels • Feedstock • Bioreactors • Algae

13.1 Introduction

With an immense increase in world population over the past few decades, man has been forced to endeavor the alternative energy sources to meet the ever-increasing energy demands. Renewable sources are the areas of interest for researchers of which biomass and biodegradable organic wastes have shown high potential to be used in the production of biofuels (Chynoweth et al. 2001). Most bioenergy is generated from organic matter through the process of anaerobic fermentation. Anaerobic fermentation of biomass results in the production of biogas that is useful and eco-friendly fuel and releases quite a fewer amount of greenhouse gases and other toxic particulate matter than any other conventional fuel. There are a number of materials utilized in producing biofuel through anaerobic fermentation such as edible oil, maize seeds, and sugarcane (Mussgnug et al. 2010). Among these materi­als, algae have appeared to be the most attractive feedstock. This is due to the fact that algae are prokaryotic or eukaryotic photosynthetic microorganisms with high rate of productivity, rich in lipid content and depicts no competition with food crops since it does not require arable land and can grow in any harsh conditions owing to their simple organization (Vandamme et al. 2011). Algae contain high content of biodegradable components, which can be renewed to methane-rich biofuels (Sialve et al. 2009). Microalgae are well adapted to all ecosystems of the earth including aquatic as well as terrestrial environments. There are approximately 50,000 species of microalgae on earth indicating the immense variety of strains adaptable to variety of environmental conditions (Richmond 2004). Microalgae have been divided into three broad categories based on their pigment; one is red seaweed also known as Rhodophyceae, second is green seaweed or Chlorophyceae, and third is brown sea­weed or Phaeophyceae. First time in 1952, a paper on “Algal culture from labora­tory to pilot plant” was published by the Carnegie Institution of Washington demonstrating the work done on algal culture during World War II era. This paper illustrated the promising potential of algae as a source of agricultural and chemical commodities (Burlew 1953). The first use of algal biomass was as feed supplement for animal proteins to be consumed by humans directly. An aspect of using micro­algae biomass is that there is a minimal nutrient requirement so it can be grown on a range of sewage and waste water from where it derives its nitrogen and phospho­rus requirement (Malik and Prajapati 2012). For the production of algal biomass, water, CO2, and essential nutrients are provided according to the strains used while oxygen is removed. Nutrients can also be provided from runoff water from nearby lands. Microalgae can also grow on large ponds and pools adding to its benefits as economically feasible and the most successful candidates for biogas production. Cultivation of microalgae is done using sunlight in covered or open ponds or pools or closed photobioreactors depending upon the designs. However, closed systems are more expensive than open ponds and present more technical problems. Individual closed system unit cannot be extended beyond 100 m2 due to gas exchange limita­tions and other problems (Demirbas 2010). Another important aspect in the eco­nomics of algal biomass production is the harvesting and CO2 supplementation as elevated levels of CO2 help in increased growth of algal biomass and subsequently increased bioenergy production (Yoo et al. 2010; Prajapati et al. 2013; Chinnasamy et al. 2009; Jiang et al. 2011). The method of harvesting algal biomass depends upon its application. Since the harvesting of algal biomass is energy requiring pro­cess, it should be carefully designed. A major challenge is the small size of algal cells and their subsequent low concentration in the culture medium ranging between

0. 5 and 2.0 g/L approximately (Prajapati et al. 2013; Christenson and Sims 2011; Vandamme et al. 2011). Algae cultures may contain either a single or multiple spe­cific strains in order to optimize the production of desired product. There have been a number of microalgae species used for the production of biogas. It includes the Chlorella spp., Oscillatoria spp., Euglena spp., Scenedesmus spp., and Synechocystis spp. along with a number of others. However, there are certain limitations that have been encountered using algal biomass during anaerobic digestion (Sialve et al.

2009) . These include low digestibility of algal cell wall, ammonia inhibition, and the sodium toxicity to methanogens (Mussgnug et al. 2010). In the first phase of anaerobic digestion of algal biomass, hydrogen gas is released which may lead to feedback inhibition to acetate forming bacteria (Gerardi 2003). To counter the low digestibility of algal biomass and to obtain maximum amount of biogas, high hydraulic retention time (HRT) is required under mesophilic conditions (Zamalloa et al. 2012). Therefore a number of pretreatment methods have been established to remove or rupture the algal cell walls to reduce HRT (Alzate et al. 2012).

There is a great need to replace petroleum-derived transport fuels with renewable biofuels, which are more long-lasting and least contributing towards global warm­ing. The most attractive of these renewable resources for transport fuel is biodiesel and bioethanol. Agricultural crops have been used for the production of bioethanol and biodiesel, however, the present techniques failed to substantially replace fossil fuel-based transport fuels; therefore a more attractive alternative is the use of microalgae (Chisti 2008). Even the most widely used oil crops including oil palm and sugarcane can not match the amount of bioenergy produced through microalgae. Production of biodiesel involves the process of transesterification in which ester compound’s alk — oxy group is exchanged by specific alcohol. Transesterification involves fat or oil reaction with the alcohols to produce esters and glycerol. When algal oil product is combined with alcohol and H+ or OH — group, fatty acid methylesters are produced to form biodiesel. The important requirement in this regard is to select those algal strains, which are rich in oil, since most of the microalgae are rich in oils and some even exceeds 80 % of dry mass of algae biomass, thus there is a great potential in the use of algal biomass in biodiesel production (Demirbas 2010).

Structurally activated carbon is a disorganized form of graphite due to impurities and the method of preparation (activation process) where the layers are held by carbon-carbon bonds. Its precise atomic structure comprised of curved fragments containing pentagons, hexagons in addition to other non-hexagonal rings. Pentagonal rings structure is naturally porous, due to the curvature of the carbon layers, and relatively hard compared to other carbons, because of the absence of parallel gra­phene layers, the most expected arrangement or structure of activated catalyst is represented in Figs. 15.2 and 15.3 (Harris et al. 2008).

It explains the microporosity and many other properties of the carbon. Recently it has been suggested that fullerenes structure is quite associated with the activated car­bon structure, pentagonal rings are visible at 2,000 °C, showing that the carbons bear fullerene-related structure. This type of structure helps to explain the properties of activated carbon, and also gives an important implication for the modeling of adsorp­tion on microporous carbons. Cross-links consist of domains containing sp3 bonded atoms (Ergun and Tiensuu 1959; Ergun and Alexander 1962) however neutron diffrac­tion studies entirely discounted that non-graphitizing carbons consist entirely of sp2

(Mildner and Carpenter 1982). Presence of pentagonal rings in the structure leads to extremely porous, due to the curvature of the carbon layers (Harris et al. 2008).

The impact of biofuels on environment cannot be neglected. The main issues concerning environmental impacts of J. curcas production system are the impact on global warming, biodiversity, and land use. GHG emissions from biodiesel are found to be less compared to fossil diesel (Tobin and Fulford 2005; Prueksakorn and Gheewala 2006; Silitonga et al. 2011) and hence have less negative impact on environment. In comparison to fossil diesel production and use (Sheehan et al. 1998) , GHG emissions from biodiesel production and use (Wenzel et al. 2000; IPCC 2001) have 73 % less global warming potential (Prueksakorn and Gheewala 2006; Tiwari et al. 2007) (Fig. 17.2). Over 90 % of GHG are emitted during use phase from both diesel and biodiesel.

Biodiesel produced by Jatropha emits 100 % less SO2 than fossil diesel. Since biodiesel is of biomass origin, carbon dioxide emissions from its use in engines are considered GHG neutral as Jatropha plants during growth absorb them from the atmosphere. Furthermore, every year around 7.9 kg of CO2 is absorbed by a full — grown Jatropha plant (PSO 2010). Thus one hectare Jatropha plantation can poten­tially sequester about 18.1 ton of GHG from environment per year (Nhar and Homptan 2011).

250

50

Fig. 17.2 Comparison of

GHG emission from life

cycle of biodiesel and diesel

(source: Prueksakorn and 0

Gheewala 2006)

Although as compared to fossil diesel, biodiesel production from J. curcas showed a reduction of GHG emissions but reallocating of (semi-) natural forest for J. curcas cultivation will result in negative effect on the overall GHGs balance.

Since at most growing areas Jatropha is an exotic species, introduction and cultivation of J. curcas is expected to have negative impact on biodiversity (Achten et al. 2008). As Jatropha is believed to sequestrate carbon, reduce/prevent soil ero­sion and hence leading to soil structure improvement, its land impact on soil due to Jatropha land occupation is expected to be positive.

There are some alternative methods for recovering ethanol from aqueous solutions, in this termed as fermentation broth. These include distillation, membrane perme­ation, vacuum stripping, gas stripping, solvent extraction, adsorption, and various hybrid processes. The most common method applied is distillation process. However, depending on the concentration of the feed solution and other factors, some of these methods have the potential to be less energy intensive than distillation. For instance, solvent extraction of dilute feeds of 2 % ethanol has been reported to have substantially energy savings (Richard et al. 2008).

When SSF is completed, the liquid fraction of the fermentation broth contains mainly ethanol, but also a large numbers of other organic compounds, such as residual sugars, acetic acids, and amyl alcohols. The concentration of ethanol depends on the concentration solid used in the SSF. In most cases, the solid concentration is chosen to result in at least 4-5 % w/w ethanol. The broth also contains solid residue, con­sisting mainly of lignin, some unreacted cellulose, and yeast. The main challenges in terms of separation processes in ethanol production are downstream of the fermentation. The interesting products in the broth are ethanol, solid, and residual low molecular weight organic substances. Important separation challenges in ethanol production from fermentation broth are shown in Fig. 20.4.

In brief, separation is employed at various stage of the process. There are some alternative methods for recovering ethanol from aqueous solutions, in this termed as fermentation broth. These include distillation, membrane permeation, vacuum stripping, gas stripping, solvent extraction, adsorption, and various hybrid processes. The most common method applied is distillation process. The fermentation broth is first distilled in a stripper column, in order to separate the ethanol content from the broth and concentrate the ethanol to above 20 % v/v (Galbe et al. 2013). After the stripper, the ethanol stream is further concentrated in rectifier column. As ethanol and water form azeotrope, the distillate from the rectifier column will only be concentrated to near azeotropic concentration, 96 % v/v ethanol. To be blended with gasoline, dehy­dration process in order to yield water-free ethanol must be done.

Fuel ethanol or absolute alcohol is produced by dehydration of rectified product. Ethanol dehydration technologies are now very interesting to develop. Several ethanol dehydration methods, such as azeotropic distillation, extractive distillation, molecular sieve adsorption, pressure swing adsorption (PSA), pervaporation and vapor perme­ation (Bastidas et al. 2010), azeotropic distillation, and molecular sieve technology, are commercially available. However, PSA process is prospective to replace the com­mon technology due to performance, cost, and environmental reason. In the PSA, two steps of adsorption and desorption are carried out in two adsorbent beds operated

in tandem, so that a continuous process can be operated. The adsorbent is regenerated by rapidly reducing the partial pressure of the adsorbed component by lowering the total pressure or by using a purge gas (Galbe et al. 2013).

Bamboo when treated with caustic soda of different concentration, show significant decrease in percent elongation at break with the increase in concentration of caustic soda (Das and Chakraborty 2008).

2.4.2 Flexural Strength

Bamboo fiber reinforced mortar laminates with reformed bamboo plate on bottom as tensile layer and a fiber reinforced mortar sheet at the top as compressive layer are exposed to have flexural strength of upto 90 MPa (Yao and Li 2003). Flexural strength shows a considerable increase at 50 % volume fraction of extracted bamboo fibers in composites (Chattopadhyay et al. 2010). Flexural strength ofbam — boo fiber reinforced epoxy resins is calculated to be 230.09 MN m-2 (Jain et al. 1992). Flexural strength of maleic anhydride treated bamboo polyester composite is increased by 50 % (Kushwaha and Kumar 2010). Autoclaved bamboo fibers rein­forced cement composites have a flexural strength greater than 18 MPa. By screen­ing out fines found in original bamboo pulp, flexural strength can be increased upto 20 MPa (Coutts and Ni 1995). Flexural strength of bamboo fibers shows a signifi­cant increase on addition of amino propyl trimethoxysilane and tetramethoxy ortho­silicate after alkali treatment (Lee et al. 2009). Bamboo glass composite fibers at bamboo to glass ratio of 1:4 show flexural strength of 140 MPa (Dieu et al. 2004). Bamboo fiber reinforced cementitious plate (FRC) is found to have a very high flexural strength, which may be upto 96 MPa (Li et al. 2002).

Physical properties of bagasse fibers can be evaluated by Image Analysis and is as follows:

4.4.1.1 Image Analysis

Image analysis method can be used for the determination of physical characteristics of bagasse fibers. AGFA Duoscan T1200 scanner can be used to measure the length of the fibers through a digital imprint. The images collected from the scanner were in JPEG (Joint Photographic Experts Group) format. The length of the fiber was directly measured using the Scion Image software (SIS). Fiber imprint contour of Scion Image software was used to measure the length of each individual fiber. The SIS software is used to take, display, and measure the output images. It is also used for the analysis of images. For the determination of cross-sectional area, the fibers were chopped to a length of 1 mm and stick with the cross-section using “Spot-o-gold” labels. The process involves coating of the cross-sections with 25 nm gold palla­dium using a Hummer II Sputter Coater. The cross-sections of the bagasse fibers were visualized by using scanning electronic microscope (SEM) with a magnifica­tion range upto 50,000 and a resolution of 10-29 nm (Chiparus 2004).

Regarding the performance of the machine, firstly, its productivity was determined based on the time evaluations carried out for fiber production in the four plantations evaluated. The data obtained showed the amount of plants and leaves consumed per hour and their equivalents in green and dried fiber. The production costs for each kilogram of dried fiber were also calculated. Regarding fiber color, a variance analy­sis was applied to L*,a*,b*, and ДЕ* parameters obtained from the three bleaching treatments used, in order to determine whether there were any differences between the values of green fiber and thus detect differences between the fiber from the first and the fiber from the second crop. Next, the values of the three treatments in the bleaching and drying stages were compared; the ANOVA tests and the Tukey test with 0.01 significance were applied in order to find which treatments varied. SAS

8.1 (SAS Institute Inc., Cary, NC) and STATISTICA 9.1 Windows programs were used for both the analysis and for the Kolmogorov-Smirnov test.

Table 10.4 also shows the comparison of the effect of chemical treatment on TS, YM, EB, FS and FM of OBF-PFR composites. Untreated fibre composite is taken as control for comparison. It shows that the AN-grafted OBF-PFR composite shows higher TS than those of untreated, alkali-treated and bleached OBF-PFR composites. It is also observed that alkali-treated and bleached OBF composites showed higher properties than untreated OBF composite. Bleached fibre composite shows higher strength and modus than alkali-treated fibre composites. The bleaching operation can able to increase surface energy of the fibre. Besides, fibre becomes cleaner due to removal of huge amount of impurities, i. e. pectin, waxes, part of hemicellulose and lignin. The fibre surface roughness becomes prominent; this is suitable for better adhesion with polymer resin. On the other hand, fibre surface layer covered by polyacrylonitrile (PAN) after modification with acrylonitrile monomer. At the same time, hydrophobic nature of AN-grafted OBF is developed which causes better adhesion with PFR matrix and forms stronger interfacial bond between them.

It is clearly observed that the highest value of YM is found for AN-grafted OBF — PFR composite. This may be due to the increase of surface free energy by chemical treatment of fibres. Consequently, the hydrophobic nature of AN-grafted fibre causes better adhesion with PFR and forms strong interfacial bond between them. Again, fibre surface area is increased by the removal of impurity from OBF surface and also by the removal of impurity from OBF surface by alkali treatment and bleaching operation. Both treatments have the same mechanism, which breaks the intermolecular and intramolecular hydrogen bonding of hydroxyl groups of cellu­lose molecule. Due to the presence of more reactive hydroxyl group after both chemical treatments, fibres easily form chemical bonds with PFR. That is why higher YM is found from alkali-treated and bleached OBF composites than untreated OBF composite.

By comparing the effect of chemical treatment of FS and FM composites, it is evident that treated OBF-PFR composites have higher FS and FM than that of untreated OBF composites. Because they contain more surface free energy, treated fibre composites are more stable against flexural load. Besides, due to the presence of better adhesion of treated fibre, PFR matrix forms strong interfacial bond between them given the higher FS and FM. Similar observations are also found in betel nut fibre-reinforced polypropylene composites (Khan et al. 2012).

After light, temperature plays the most significant role in determining the effectiveness of algal growth. Some species of microalgae have the ability to endure temperature that is approximately 15 °C lower than their optimum temperature but a rise in temperature of only 2-4° may result in absolute loss of culture. When it comes to maintaining temperature in closed cultivating systems, favorable results have been shown by employment of evaporative water coolers.

13.4.3 Salinity

Dealing with salinity is a main problem while cultivating algae. Salinity plays a role in determining the growth and composition of algal cell. In high temperature, the salinity of algal biomass can increase due to evaporative losses. Deviation in the optimum salinity conditions can affect the algal strain by producing an osmotic and ionic stress. In addition to that, there occurs a change in the ionic ratios of the algal cell. These problems can be managed by addition of water or salt according to the need.

13.4.4 Mixing

Blending is another important factor when it comes to cultivating algae. It is important for regulating the distribution of cells and heat. It also dispenses the metabolites and aids in the transportation of gases. While cultivating algae in a reactor, a system is required that transfers the algae from the light to dark region, which is accomplished by generating a certain magnitude of turbulence. An unchecked increase in the velocity of mixer leads to cell damage owing to shear stress.

13.4.5 Contamination

Biological elements that pollute the algal culture include undesirable strains of algae, yeast, mould, bacteria, and other strains of yeast. Degree of contamination is high in raceway ponds because the culture is more susceptible to contaminants like protozoa and foreign algal species. Studies have shown that contaminants can be elimi­nated by temporarily exposing the culture to an environment with extreme conditions of growth factors like temperature, light, pH, etc.

16.4.1 Erosion of Soil

Soil erosion may be controlled by minimizing the raindrops and the speed of running water on the surface soil (Andraski et al. 1985). This involves the protection of soil surface with the help of mulching as well as preventing the rain water from striking the soil water directly and keeping away the practices such as compacting the soil or excessively pulverizing it. Soil erosion may be reduced when sugarcane straw would be harvested mechanically without straw burning resulting to mulching effect. Nutrient losses were noticed after burning the sugarcane field due to soil erosion. Izidorio et al. (2005) reported that soil nutrients such as phosphorus (1.07 kg/ha), potassium (1.59 kg/ha), calcium (10.24 kg/ha), and magnesium (1.91 kg/ha) may be reduced in the soil of sugarcane fields. Andrade et al. (2011) observed the nutrient loss through soil erosion that has economic and technical impacts in sugarcane cultivation in Brazil. On the other hand, burned sugarcane lost more soil nutrient than the unburned sugarcane.