ACHIEVEMENT OF ZERO EMISSIONS BY THE BIOCONVERSION OF FISHERY WASTES INTO FERTILIZER - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 76

R ESULTS AND D ISCUSSION

Seaweed fertilizer has been found superior to chemical fertilizer due to the high level of
organic matter aids in retaining moisture and minerals in the upper soil level that are available
to the roots (Blunden, 1991). This finding is because seaweed contains not only nitrogen,
phosphorus and potash content but also trace elements and metabolites, which increase its
fertilizing value (Booth, 1969). In this chapter, therefore, biodegradation characteristics for
various types of seaweeds were determined, and the fertilizing values of the biodegraded
culture broths of the seaweeds were evaluated.

Biodegradation of Seaweed Polysaccharides

Compared with terrestrial plants, seaweeds possess a high water content of approximately
70-90%, a relatively high protein content of approximately 10% and varying levels of
carbohydrates (Park et al., 2008). The carbohydrate contents of green, red and brown
seaweeds are 25-50, 30-60 and 30-50%, respectively, depending on species, habitat, season,
part of the seaweed body, and maturity. The different chemical compositions of seaweeds are
shown in Table 1. Major polysaccharides that are contained in seaweeds vary and thus, are
composed of different chemical bonds. To reutilize the seaweed waste, the complicated
molecular structure must be hydrolyzed. Recently, aerobic biodegradation was offered as an
ecologically acceptable alternative for the treatment of fishery wastes (Kim & Lee, 2012).

Table 1. Chemical composition of seaweeds

Seaweed Water a Carbohydrate b Protein b Lipid b Ash b

Green c 88.0-92.0 38.0-55.4 8.5-26.0 1.4-7.9 19.6-49.8

Red d 70.0-90.0 43.8-68.3 27.0-38.6 0.3-6.2 8.1-38.5

Brown e 86.0-94.0 30.3-68.5 5.6-20.0 0.2-4.2 5.1-46.0

a Fresh weight %
b Dry weight %
c Data that were obtained from Aguilera-Morales et al. (2005), Lahaye and Robic (2007), Pena-Rodriguez et
al. (2011), Wong and Cheung (2000), and Yaich et al. (2011).
d Data that were obtained from Dawczynski et al. (2007), Gressler et al. (2010), Marinho-Soriano et al.
(2006), and Matanjun et al. (2009).
e Data that were obtained from Dawczynski et al. (2007), Kim et al. (2011), McDermid and Stuercke (2003),
and Marinho-Soriano et al. (2006).
Green Seaweed
A time course monitoring the degradation of green seaweed polysaccharides by B.
licheniformis TK3-Y is shown in Figure 1. As shown in Figure 1A, the pH steadily increased
from 6.05 to 8.24 after 5 d as the biodegradation proceeded. The cell number increased from
4.7×10 5 CFU ml -1 to 8.8×10 7 CFU ml -1 after 3 d, and then decreased somewhat to 6.5×10 7
CFU ml -1 near the end. The concentration of reducing sugar was 2.94 g l -1 and decreased until
3 d. Then, the concentration of reducing sugar slightly increased to 0.52 g l -1 after 5 d.
Reducing sugars that were present at the beginning of biodegradation were due to the
pretreatment of Ulva powder to improve its solubility.