The optimal combination of entrapped bacteria for diesel remediation in seawater

• This is the first study evaluating calcium-gel entrapped bacteria in diesel degradability in seawater.
• Among the four deisgns, the optimal combination CC-HCCH11: CC-JG39 = 5: 1.
• The entrapped bactera, as a seeding process, can continuously be released for diesel degradation in seawater.
• The suspended free cells only achieved half of the degradability of the entrapped bacteria cells.

The objective is to determine an optimized combination of immobilized cell when remediating diesel-oil contaminated seawater. Experiments were conducted using the diesel-degrading bacteria: Rhodococcus pyridinivorans CC-HCCH11, Gordonia alkanivorans CC-JG39, and Alcaligenes piechaudii CC-ESB2. They were entrapped in calcium alginate gel beads. All of the combinations were evaluated with the total petroleum hydrocarbon-diesel (TPHd) degradability in modified Bushnell Haas medium by baffled flask tests. Design I (dominant CC-HCCH11) achieved the highest TPHd degradation percentage (78%), followed by Design II (75%), Design III (70%), and Design IV (61%). Design I reduced TPHd from initial 2342 mg/L to 504 mg/L, and also achieved the highest 1st order kinetic rate (0.0049/hr) followed by Design III (0.0046/hr), Design IV (0.0042/hr), and Design II (0.0022/hr). A parallel batch result showed that the free-cell Design I revealed only about half of the TPHd degradability. Nutrient test showed that Bushnell Haas medium was adequate for the remediation.