Environmental Engineering Reference
In-Depth Information
26
Lower Plants
Michael A. Borowitzka
Murdoch University
contents
26.1 Introduction ........................................................................................................................ 653
26.2 Methane .............................................................................................................................. 653
26.3 Ethanol and Butanol ........................................................................................................... 654
26.4 Pyrolysis ............................................................................................................................. 655
26.5 Lipids and Biodiesel ........................................................................................................... 656
26.6 Hydrocarbon Producers ...................................................................................................... 659
26.7 Large-Scale Production of Microalgae ............................................................................... 659
26.8 Open Pond Culture versus Closed Photobioreactors .......................................................... 662
26.9 The Future .......................................................................................................................... 662
References ......................................................................................................................................664
26.1 IntroductIon
The algae are an extremely diverse group of (mainly) photosynthetic organisms, ranging in size
from approximately 1 µm for some picoplanktonic species to over 30 m in length for some of the
large kelps. They are mainly aquatic, growing in fresh to hypersaline waters, but they are also
found in soils and on many surfaces such as rocks, trees, and buildings. As photoautotrophs, algae
use light energy to fix carbon dioxide (CO
2
) into sugars during photosynthesis, and these are then
further metabolized. Algae are being explored and developed as a source of a range of renewable,
CO
2
-friendly energy sources such as biodiesel, bioethanol, hydrogen, and methane (Chynoweth
et al. 1987; Sheehan et al. 1998; Miyura 2002; Benemann 2004; Chisti 2007; Brennan and
Owende 2010).
This chapter aims to provide a detailed overview of biofuels and energy production from algae,
both the seaweeds and the microalgae.
26.2 methane
The extremely large biomass of seaweeds available in many parts of the world has the potential to
be used as a source of renewable biofuel, either by fermentation to produce methane or through the
production of ethanol from the sugars in the biomass. Renewable fuel production by the pyrolysis of
macroalgae is also being considered (Ross et al. 2009).
The commercial use of seaweeds, especially the brown algae such as
Laminaria
(
Saccharina
)
and
Macrocystis
and red algae such as
Kappaphycus
and
Gracilaria
, is a well established and very
large industry. The industry uses wild stocks and cultivated biomass to produce biomass for use as
foods and the production of hydrocolloids such as agar, carrageenan, and laminaran (Zemke-White
and Ohno 1999; McHugh 2003). The annual harvest of wild seaweeds is estimated at approximately
1,000,000 t wet weight, and the amount produced by aquaculture at approximately 15,000,000 t wet
weight (FAO 2006).
653
