Acquire reliable information that shows:
- Demonstrate The overall technical applicability and the economical feasibility of BA;
- That the application of BACad will result in a significant reduction in the volume of the groundwater contamination off-site: 50% in 5 years and 80% in 10 years. The current volume of the off-site groundwater contamination is estimated at approximately 500000 m³.
- That a practically feasible methodology for the transfer of the CAH-degrading microbial population from one remediation zone to another can be developed;
- That a significant decrease in remediation costs (approx. 50%) and time (approx. 35%) can be realized applying BA;
- The environmental benefits of this technique compared to traditional remediation techniques: we aim at (1) a reduction of use of electricity of approximately 70%, (b) a reduction of water consumption of approx. 50%, (c) a reduction of waste streams (active carbon, contaminated slib, …) use of approx. 60%
The project has demonstrated that bio-augmentation is technically feasible. Even at a site with very challenging environmental conditions (acidic and oxidized groundwater) it was possible to
- reach the required geochemical conditions in a part of the contaminated area (in the other part of the area they are evolving in the right direction)
- rstablish and maintain a halorespiring microbial population (although it is not growing as fast as we had anticipated)
- accomplish the remediation targets in the zone that is fully inoculated with halorespiring bacteria.
Even with the knowledge of the difficulties encountered at this site, bio-augmentation should still be recommended for its further remediation. At other sites with better (or optimal) geochemical conditions the results of bio augmentation are likely to be achieved faster.
Regarding the reduction of the contaminated volume, we do not have enough data at this point to estimate if it can be achieved or not as anticipated initially (50% reduction in five years, 80% in ten years). Because of the delays that we have encountered, the full scale demonstration has not been fully operational for long enough to be able to extrapolate its results.
VITO has developed a method for ensuring strict anaerobic conditions during groundwater transfer from one site to another. A mobile prototype has been constructed which includes a groundwater buffer tank with nitrogen gas blanketing, pumps, filters, a chemical dosing station and inline mixing. The prototype has been used to perform transfers during the small and full scale demonstrations.
For the evaluation of the financial aspects of the remediation, it was calculated that bio-augmentation would lead to a cost reduction of 23% compared to a traditional pump & treat system (in the Grant Agreement it was estimated that there would be a cost reduction of 50% compared with traditional techniques). When looking at the time needed to remediate the plume, we must conclude that bio-augmentation should lead, specific for the Punch Metals site, to a reduction of time span by 55% (estimated 35% in the Grant Agreement). This number is site specific. For the Punch Metals site, a downstream extraction of groundwater is present, which speeds up the spreading of the bacteria. If this extraction would not be present, the time necessary for the bio-augmentation with the concept of microbial transfers may be longer when compared to a pump & treat system. We conclude that bio-augmentation for very large plumes like this one only can lead to a decrease of time when a groundwater extraction system is applied (the extent of the extraction needs to be confirmed with a groundwater model). For smaller/less extended plumes, where the natural groundwater velocity can cover the whole plume in a relevant time frame, bio-augmentation may be applied without an additional extraction of groundwater.
For the evaluation of the environmental aspects of the remediation, it was calculated that bio-augmentation would emit 89% less CO2 than a pump & treat system.
A carbon footprint evaluation has been made. The method recommended by the Flemish soil administration (OVAM) has been used to do this. This method can be found at http://www.ovam.be/batneec-evaluatie-met-co2-calculator. We have compared a pump & treat system (P&T) with bio-augmentation.
It has been calculated that the total amount of CO2 emitted with the P&T-system would be 4858.7 tons or 5.2 tons/kg pollution removed. For the bio-augmentation, the CO2 calculator has calculated a total production of 575.8 tons or 0.4 ton/kg pollution removed. For the amount of CO2 produced, that means a reduction of 89.1% for bio-augmentation as compared to P&T.
It was also estimated that bio-augmentation has resulted in a 60% reduction of waste (sludge and spent activated carbon) and a 50% reduction of volumes of extracted groundwater compared to P&T.
The CO2-calculator output also has shown that the P&T-system would remove 943 kg of contaminants whereas the BA approach did remove 1321 kg, which is 378 kg or 29% more than P&T.
A P&T system not only consumes more resources, but it also produces waste streams like activated carbon , contaminated sludge, iron sludge, etc. Most of these streams are not recyclable and must be burned or landfilled. In an ideal bio-augmentation system with no groundwater extraction none of these streams are produced and hence this means a 100% reduction. Specific for the Punch Metals site, an extraction of groundwater at the end of the plume is present. The extracted groundwater needs to be cleaned before it can be discharged. In June 2016 a total of 199 005.68 m³ groundwater is extracted. The cleaning of this groundwater produced 14680 kg sludge and 5000 kg activated carbon waste. The numbers are summarized in the table below and an estimation of produced waste is made for the whole duration of the bio-augmentation. For the P&T system the same exercise has been made.
|Groundwater extracted (actual after 3.5 years) (m³)||Estimated until end of remediation (m³)||Estimated produced sludge until end (kg)||Estimated use of activated carbon (kg)|
The P&T system would extract 7.116.407 m³ more groundwater (+90.3%), would produce 524.954 kg more sludge and 178.799 more kg activated carbon would needed.
The consumption of electricity is summarized in the table below:
|kWh||Time (days)||Total kW|
The calculations show that a P&T system would use 61% more electricity than BA.