Improving mass transfer rates in microbial cell immobilization system for environmental applications: Synergistic interaction of cells on crude oil biodegradation.

Among the various techniques used to clean up polluted environments, bioremediation is the most cost-effective and eco-friendly option. The diversity of microbial communities in a consortium can significantly affect the biodegradability of hazardous organic pollutants, particularly for in situ bioremediation processes. This is largely attributed to interactions between members of a consortium. In this study, the effect of internal diffusion limitations in substrate model biodegradation was firstly examined by immobilized bacterial cells at different particle sizes produced by the electrospray technique. According to the obtained results, for particles with large size, the effectiveness factors (η) were about 0.58-0.67, and the resistance to diffusive on the biodegradation rate was significant, while with decreasing the particle size, η increases and approaches about 1. After selection of suitable bead size, heavy crude oil biodegradation was investigated using a consortium consisting of three oil-degrading bacterial strains at different treatment systems. The removal rate in the suspended co-culture system stands at minimum value of 38% with all three strains which is an indicator of negative interactions among consortium members. Independent immobilization of microorganisms minimizes the competition and antagonistic interactions between strains and leads to more crude oil removal, so that, the biodegradation rate reached 60%.

Enhanced biodegradation of light crude oil by immobilized Bacillus licheniformis in fabricated alginate beads through electrospray technique.

Petroleum contamination of marine environments due to exploitation and accidental spills causes serious harm to ecosystems. Bioremediation with immobilized microorganisms is an environmentally friendly and cost-effective emerging technology for treating oil-polluted environments. In this study, Bacillus licheniformis was entrapped in Ca alginate beads using the electrospray technique for light crude oil biodegradation. Three important process variables, including inoculum size (5-15% v/v), initial oil concentration (1500-3500 ppm), and NaCl concentration (0-30 g/L), were optimized to obtain the best response of crude oil removal using response surface methodology (RSM) and Box-Behnken design (BBD). The highest crude oil removal of 79.58% was obtained for 1500 ppm of crude oil after 14 days using immobilized cells, and it was lower for freely suspended cells (64.77%). Our result showed similar trends in the effect of variables on the oil biodegradation rate in both free cell (FC) and immobilized cell (IC) systems. However, according to the analysis of variance (ANOVA) results, the extent of the variables' effectiveness was different in FC and IC systems. In the immobilized cell system, all variables had a greater effect on the rate of light crude oil degradation. Moreover, to evaluate the effectiveness of free and immobilized B. licheniformis in bioremediation of an actual polluted site, the crude oil spill in natural seawater was investigated. The results suggested the stability of beads in the seawater, as well as high degradation of petroleum hydrocarbons by free and immobilized cells in the presence of indigenous microorganisms.

Investigation of Bacillus licheniformis in the biodegradation of Iranian heavy crude oil: A two-stage sequential approach containing factor-screening and optimization.

Oil pollution is a serious international concern due to its harmful effect on human health and the environment. This study aims to investigate the effective factors on the biodegradation of Iranian heavy crude oil by Bacillus licheniformis. For this purpose, oil removal from the artificial seawater was studied by response surface methodology (RSM). After the screening experiments, pH (4-10), NaCl concentration (0-10 g/L), and oil concentration (500-4500 ppm) were selected as influential factors. Moreover, to evaluate the bacterial capability in bioremediation of an actual polluted site, crude oil spill with a salinity of 35 g/L was experimentally simulated. The proposed model in this study clearly shows that both selected individual factors and their interactions are significantly effective on the crude oil biodegradation capacity. The results showed that Bacillus licheniformis was able to degrade crude oil at different concentrations of oil, especially at low concentrations, which are challenging in actual polluted sites. 15%-66% removal was achieved for 500-4500 ppm of crude oil after 14 days. Furthermore, according to the obtained results, this bacterium can tolerate the salinity up to 3.5%. At this salinity level, crude oil removal was 23.43 and 25.64% in neutral and alkaline conditions, respectively. Process factors were optimized, and 54.8% of crude oil was removed at optimum conditions i.e., 3500 ppm crude oil concentration, 2.5 g/L of NaCl and pH equal to 8.5. Finally, it can be concluded that the selected bacterium of this study can be more effective in harsh environments such as hypersaline and alkaline conditions.