Agriculture Reference
In-Depth Information
Addition of SMC results in enhanced PAH-degrading efficiency (82%) as compared to the
removal by sorption on immobilized SMC (46%). It was observed that the addition of SMC
to the contaminated medium reduced the toxicity, added enzymes, microorganisms, and
nutrients for the microorganisms involved in degradation of PAHs (Lau, et al., 2003).
Organic wastes like banana skin, spent mushroom compost and brewery spent grain in
earlier studies were found to enhance the biodegradation of used lubricating oil up to 90%
loss of oil within the period of 3 months (Abioye, et al., 2009b, 2010). Also the results of our
studies revealed the potential of melon shell to stimulate 75% crude oil degradation in soil
contaminated with crude oil within the period of 28 days (Abioye, et al., 2009a).
Depending on the nature of the contaminated soil, some of these nutrients could become
limiting, hence the additions of nutrients are necessary to enhance the biodegradation of oil
pollutants (Choi et al., 2002; Kim et al., 2005). Pelletier et al. (2004) assessed the effectiveness
of fertilizers for crude oil bioremediation in sub-Antarctic intertidal sediments over a one-
year and observed that chemical, microbial and toxicological parameters demonstrated the
effectiveness of various fertilizers in a pristine environment. Frederic et. al., (2005), observed
that addition of commercial oleophilic fertilizers containing nitrogen and phosphorus to
hydrocarbon contaminated soil increased the hydrocarbon-degrading microbial abundance
and total petroleum hydrocarbon degradation, and also reported 77 - 95% loss of total
alkanes and 80% of PAHs in hydrocarbons contaminated soil within the period of 180days.
In another study using poultry manure as organic fertilizer in contaminated soil,
biodegradation was reported to be enhanced in the presence of poultry manure alone, but
the extent of biodegradation was influenced by the incorporation of alternate carbon
substrates or surfactants (Okolo et al., 2005). However, excessive nutrient concentrations can
inhibit the biodegradation activity (Challain et al., 2006), and several authors have reported
the negative effect of high NPK levels on the biodegradation of hydrocarbons (Oudot et al.,
1998; Chaıneau et al., 2005) and more especially on the aromatics (Carmichael and Pfaender,
1997).
3.2.2 Bioaugmentation
This is an approach that involves introduction of microorganisms that possessed
biodegradation potential into the contaminated environment to assist the indigenous
microbes with biodegradative processes. This may sometimes involved addition of
genetically engineered microorganisms suited for biodegradation of the hydrocarbon
contaminants into the contaminated soil. Bioaugmentation is a promising and low-cost
bioremediation strategy in which an effective bacterial isolate(s) or microbial consortium
capable of degrading xenobiotics is administered to contaminated sites (Gentry et al., 2004).
Successful bioremediation of soil contaminated with hydrocarbon sources through
bioaugmentation has been reported by various authors. Bagherzadeh et al., (2008) evaluated
the efficiency of pollutant removal by selected microorganisms and reported thus: Five
mixed cultures and 3 single bacteria strains,
Pseudomonas
sp.,
Arthrobacter
sp. and
Mycobacterium
sp. were isolated from hydrocarbon-contaminated soils by enrichment on
either crude oil or individual hydrocarbons, as the sole carbon sources. The strains were
selected based on their ability to grow in medium containing crude oil, used engine oil or
both. Their ability to degrade hydrocarbon contaminants in the environment was
investigated using soil samples contaminated with used engine oil. The mixed starter
culture #1 degraded 66 % of aliphatic compounds in the engine oil, after 60 days of
