Effectiveness and economic feasibility of our hollow fiber bioreactor system

To determine the effectiveness and economic feasibility of our hollow fiber bioreactor with E. Coli which has been engineered to express a mercury transport system and metallothionein, we modelled its impact when applied to a current real situation, mercury pollution in Onondaga Lake, Syracuse, NY.

It has been shown that similar hollow fiber bioreactors are able to reduce the concentration of mercury from 2mg/L to about 5 µg/L.[1] This corresponds to a promising 99.8% reduction in mercury levels. Furthermore as discussed in our case study, Onodaga Lake has a capacity of 35 billion gallons and about 165,000 lbs of mercury has been dumped into the lake over the years.[2] This corresponds to an approximate mercury concentration of 0.56 mg/L. Thus, the mercury concentration is Onodaga Lake is within the limits that the engineered E. Coli is able to sequester.

In Nov 2004, the estimated cost of dredging to remove the mercury contaminated mud in the lake was determined to be $451 million.[3] Currently the cost of our hollow fiber bioreactor system is about $560 with the cost being largely due to the reactor itself ($490) and the remainder of the cost was for the pump and filters.

However, it should be noted that the scale of the hollow fiber bioreactor system is much smaller as its volume is about 1L. Hence, the hollow fiber bioreactor would have to be scaled up significantly (by about 10E11 times!) in order to have any impact. To give a better idea of the scale, if the lake were the size of an Olympic swimming pool, the volume of the hollow fiber bioreactor would be equivalent to a drop of water. While we would need to scale up the volume of our hollow fiber bioreactor, it should also be noted that by placing the bioreactors in series, better mercury sequestration is achieved. [1]

Therefore, even though it has been shown that the hollow fiber bioreactor is successful on a pilot scale, more tests would be required to determine if it is as effective on a larger scale. As there are several variables that might change eg. flow rates and membrane area, the performance of the engineered E. Coli might not simply scale up as expected. Nevertheless, given the environmental costs associated with existing remediation methods such as dredging, it is important to look into how biological systems are able to complement these solutions and solve the problem of mercury contamination in an effective, safe and cost efficient manner.

References

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1. Chen, S., Kim, E., Shuler, M., & Wilson, D. (1998). Hg2+ Removal by Genetically Engineered Escherichia coli in a Hollow Fiber Bioreactor. Biotechnology Progress, 667-671
2. Moriarty, Rick. "Discovering What Lies at the Bottom of Onondaga Lake." Syracuse.com. Syracuse.com, n.d. Web. 24 Sept. 2014.
3. Collin, Glen. "Onondaga Lake Dredging Begins for Season; Could End a Year Early (video)." Syracuse.com. N.p., 7 Apr. 2014. Web. 11 Aug. 2014.