Pilot-scale production and in-situ application of petroleum-degrading enzyme cocktail from Alcanivorax borkumensis

Petroleum degrading enzymes can be used as an alternative way to improve petroleum bioremediation approaches. Alcanivorax borkumensis is an alkane-degrading bacteria that can produce petroleum degrading enzymes such as alkane hydroxylase and lipase. In this study, pilot-scale Alcanivorax borkumensis fermentation was developed for producing large volumes of petroleum degrading enzymes cocktail (similar to 900 L). Different process conditions, such as inoculum age 72 h and size 4% v/v, temperature 30 +/- 1 degrees C, agitation speed at 150 rpm and, fermentation period 3 days were determined as the optimum for producing alkane hydroxylase and lipase activity. The oxygen transfer capacity was studied for obtaining better bacterial growth and higher enzyme activities in bioreactor process optimization as well as scale-up. Results showed that the maximum values of oxygen mass transfer coefficient (k(L)a), oxygen uptake rate (OUR), oxygen transfer rate (OTR), alkane hydroxylase, lipase, and cell count were 196.95 h(-1), 0.92 mmol O-2/L/h, 1.8 mmol O2/L/h, 222.49 U/mL, 325 U/mL, and 8.6 x 10(10) CFU/mL, respectively. Compared with the bench-scale bioreactors, the 150 L fermenter showed a better oxygen transfer rate which affected the cell growth that doubled the number and enzymes production that increased. Then, the enzyme cocktail was used for a field test in a diesel source zone using a 5-spot well pattern. The results showed a significant reduction in concentrations of C10 - C50 (from 36% to > 99%) after one injection of enzyme cocktail, mainly for the contaminated soils located in the saturated zone of the unconfined aquifer. This study confirmed the scaling-up ofalkane-degrading enzyme production to an industrial-scale and its application for effective bioremediation of petroleum contaminated sites.

Automated summary

This study developed a pilot-scale fermentation method for producing a large quantity of petroleum degrading enzyme cocktail using Alcanivorax borkumensis. Optimum process conditions were determined for high enzyme activity and bacterial growth. The study also demonstrated the successful application of the enzyme cocktail in effectively remediating petroleum contaminated sites.