Surfactin production from potato process effluent by Bacillus subtilis in a chemostat.

The biosurfactant surfactin has potential to aid in the recovery of energy resources (oil recovery) or subsurface organic contaminants (environmental remediation). However, high medium and purification costs limit its use in these high-volume applications. In previous work, we showed that surfactin could be produced from an inexpensive low-solids potato process effluent with minimal amendments or pretreatments. Previous research has also shown that surfactin can be both produced in Bacillus subtilis cultures and recovered by foam fractionation in an airlift reactor. Results using both purified potato starch and unamended low-solids potato process effluent as substrates for surfactin production indicate that the process is oxygen limited and that recalcitrant indigenous bacteria in the potato process effluent hamper continuous surfactin production. The research reported here features the use of a chemostat operated in batch mode for producing surfactin with concomitant use of antifoam to prevent surfactant loss. The antifoam did not interfere with surfactin recovery by acid precipitation or its efficacy. Initial trials took about 48 h to produce 0.9 g/L of surfactin from potato process effluent. Increasing the oxygen mass transfer by increasing the stirring speed and adding a baffle decreased production time to 12-24 h and produced about 0.6 g/L of surfactin from two different potato-processing facilities.

Characterization of surfactin from Bacillus subtilis for application as an agent for enhanced oil recovery.

Surfactin produced by Bacillus subtilis (ATCC 21332) was used to examine the effect of altering salt concentration, pH, and temperature on surfactin activity (as measured by reductions in surface tension). These parameters are some of the conditions that define oil reservoir characteristics and can affect the application of surfactants. The Biotechnology for Oilfield Operations research program at the Idaho National Engineering and Environmental Laboratory (INEEL) has successfully produced surfactin from potato process effluents for possible use as an economical alternative to chemical surfactants for improved oil recovery. Surfactants enhance the recovery of oil through a reduction of the interfacial tension between the oil and water interfaces, or by mediating changes in the wettability index of the system. We investigated changes in surfactin activity under a range of conditions by measuring surface tension. Surface tension was determined using video image analysis of inverted pendant drops. Experimental variables included NaCl (0-10%), pH (3.0-10.0), and temperature (21-70 degrees C). Each of these parameters, as well as selected combinations, resulted in discrete changes in surfactin activity. It is therefore important to consider the exploration of the studied surfactin as an enhanced oil recovery agent.

Development of continuous surfactin production from potato process effluent by Bacillus subtilis in an airlift reactor.

The biosurfactant surfactin has the potential to aid in the recovery of subsurface organic contaminants (environmental remediation) or crude oils (oil recovery). However, high medium and purification costs limit its use in these high-volume applications. In previous work, we showed that surfactin can be produced from an inexpensive low-solids (LS) potato process effluent with minimal amendments or pretreatments. Previous research has also shown that 95% or more of the surfactin in Bacillus subtilis cultures can be recovered by foam fractionation. In this work, we present the results of research to integrate surfactin production with foam fractionation. Experiments were performed in an airlift reactor, with continuous collection of the foam through a tube at the top of the column. Preliminary results using both purified potato starch and unamended low-solids potato process effluent as substrates for surfactin production indicate that the process is oxygen limited and that recalcitrant indigenous bacteria in the potato process effluent may hamper continuous surfactin production.