ACHIEVEMENT OF ZERO EMISSIONS BY THE BIOCONVERSION OF FISHERY WASTES INTO FERTILIZER - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 83

Properties of the culture broths
The biodegraded culture broth of seaweed could be used as a fertilizer because this broth
contained compounds that are potentially useful for plant growth. However, the application of
the culture broth depends on the absence of any toxicity and on the abundance of organic and
inorganic sources of nutrients. To assess the feasibility of liquid fertilizers, hydroponics was
used in this chapter because this method could provide a convenient means of studying the
nutrient uptake by plants. In addition, this method is free of confounding or uncontrollable
variations in the soil nutrient supply (Nhut et al., 2006).
Figure 6. TLC of the degradation products in the biodegraded culture broth of brown seaweed. M1-M3
indicates standard markers. Lane 1, day 0; lane 2, day 1; lane 3, day 2; lane 4, day 3; lane 5, day 4; and
lane 6, day 5 of cultivation.
Phytotoxicity
In aerobic biodegradation, sufficient aeration promotes the conversion of organic matters
into nonobjectionable stable products, such as CO 2 , SO 4 2- , NO 3 - , etc. However, in incomplete
aeration, organic acids can accumulate, which have harmful effects on plant growth if the
fertilizer is incorporated into the soil (Jakobsen, 1995). To examine the fertilizing value of the
biodegraded culture broths of seaweeds, their GI tests were accomplished at various dilution
ratios, with the criterion of phytotoxin-free at GIs that were higher than 50% (Zucconi et al.,
1985). As shown in Figure 7, the filtered culture broth of red seaweed showed the lowest
phototoxicity even at low dilutions, and all filtered culture broths were phytotoxin-free at the
dilution ratios of more than 500-fold. Low values of GI indicate that some characteristics that
existed had an adverse effect on the root growth of cress seeds. This adverse effect may be
attributed to the release of high concentrations of ammonia and low molecular weight organic
acids (Wong, 1985; Fang & Wong, 1999) because cress is known to be sensitive to the toxic
effect of these compounds (Fuentes et al., 2004). At the dilution ratio of 1000, GI values of
the filtered culture broths of green, red and brown seaweeds were 94.5, 89.9 and 90.5%,
respectively, which indicates almost no existence of any compounds that adversely affecting
root growth after seed germination.