11.7.3 Biostimulation and Bioaugmentation
Biostimulation is a method to stimulate the metabolic capacity of the indigenous
microbial flora of the contaminated site and thus enhance the degradation capabilities by provision of adequate aeration, nutrients, moisture, etc. Bioaugmentation
refers to the improvement of the metabolic capacity of the microbial flora at the
contaminated site by the introduction of active microbial communities. Either single
strains or mixtures of strains may be introduced (Ite and Ibok 2019). Several studies
have demonstrated that both biostimulation and bioaugmentation improve the biodegradation capability of weathered contamination sites.
A recent study compared biostimulation with nitrogen and phosphorous verses
bioaugmentation with native hydrocarbanoclastic microbes in contaminated soil.
The study revealed that improved biodegradation rates were obtained with
biostimulation, after 12 weeks test period. Bioaugmentation resulted in changes to
microbial composition, with the inoculated microbes quickly becoming predominant
with consequent reduction in microbial diversity (Wu et al. 2019). These results
indicate that reduction in biodegradation rates in a site that contained native petroleum hydrocarbon (PH) biodegraders may be associated with nutrient insufficiency.
Further, that stable maintenance of a diverse microbial composition may be more
beneficial, and achievable through adequate maintenance of nutrients.
11.7.4 Use of Dispersants/Surfactants
Use of surfactants during bioremediation of oil spills, especially in marine environment, is a common strategy. Frequently, chemical dispersants such as Tween 80 are
used (Tian et al. 2016). These chemicals emulsify the oil and convert them into
smaller droplets which are more easily utilized by microbes. However, these
chemicals deteriorate the water quality, may perturb the microbial composition in
the affected area, and can be fatally toxic to the aquatic fauna (Tian et al. 2016).
Additionally, reduction of the droplet size of the oil has been reported to result in
increased uptake of PAH by fish (Ramachandran et al. 2004), thus affecting the
aquatic life and or entering the food chain.
Recent studies, based on metagenome analysis of microbial clusters
experimented in marine microcosms, have shown that the use of biosurfactants
alongside microbial biodegradation may prove to be more suitable over chemical
surfactants due to their biodegradability, low toxicity, and efficiency imparted in
microbial remediation of petroleum hydrocarbons. Their studies indicate that expression of genes related to hydrocarbon degradation was stimulated by the biosurfactant
surfactin, while these genes were in fact decreased by the chemical surfactant
Ultrasperese II (Rattes de Almeida Couto et al. 2019). The difficulties in the
production of biosurfactants in bulk quantities required for the application in field
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S. Jayasena and M. Perera
Biostimulation is a method to stimulate the metabolic capacity of the indigenous
microbial flora of the contaminated site and thus enhance the degradation capabilities by provision of adequate aeration, nutrients, moisture, etc. Bioaugmentation
refers to the improvement of the metabolic capacity of the microbial flora at the
contaminated site by the introduction of active microbial communities. Either single
strains or mixtures of strains may be introduced (Ite and Ibok 2019). Several studies
have demonstrated that both biostimulation and bioaugmentation improve the biodegradation capability of weathered contamination sites.
A recent study compared biostimulation with nitrogen and phosphorous verses
bioaugmentation with native hydrocarbanoclastic microbes in contaminated soil.
The study revealed that improved biodegradation rates were obtained with
biostimulation, after 12 weeks test period. Bioaugmentation resulted in changes to
microbial composition, with the inoculated microbes quickly becoming predominant
with consequent reduction in microbial diversity (Wu et al. 2019). These results
indicate that reduction in biodegradation rates in a site that contained native petroleum hydrocarbon (PH) biodegraders may be associated with nutrient insufficiency.
Further, that stable maintenance of a diverse microbial composition may be more
beneficial, and achievable through adequate maintenance of nutrients.
11.7.4 Use of Dispersants/Surfactants
Use of surfactants during bioremediation of oil spills, especially in marine environment, is a common strategy. Frequently, chemical dispersants such as Tween 80 are
used (Tian et al. 2016). These chemicals emulsify the oil and convert them into
smaller droplets which are more easily utilized by microbes. However, these
chemicals deteriorate the water quality, may perturb the microbial composition in
the affected area, and can be fatally toxic to the aquatic fauna (Tian et al. 2016).
Additionally, reduction of the droplet size of the oil has been reported to result in
increased uptake of PAH by fish (Ramachandran et al. 2004), thus affecting the
aquatic life and or entering the food chain.
Recent studies, based on metagenome analysis of microbial clusters
experimented in marine microcosms, have shown that the use of biosurfactants
alongside microbial biodegradation may prove to be more suitable over chemical
surfactants due to their biodegradability, low toxicity, and efficiency imparted in
microbial remediation of petroleum hydrocarbons. Their studies indicate that expression of genes related to hydrocarbon degradation was stimulated by the biosurfactant
surfactin, while these genes were in fact decreased by the chemical surfactant
Ultrasperese II (Rattes de Almeida Couto et al. 2019). The difficulties in the
production of biosurfactants in bulk quantities required for the application in field
282
S. Jayasena and M. Perera