Regeneration of Sorptive Capacity

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1 Quick Reference: Technical Bulletin 4.1 Regeneration of Sorptive Capacity PlumeStop binding site bio regeneration Extended functional longevity Background PlumeStop Liquid Activated Carbon is composed of very fine particles of activated carbon (1 2µm) suspended in water through the use of unique organic polymer dispersion chemistry. Once in the subsurface, the material behaves as a colloidal biomatrix binding to the aquifer matrix, rapidly removing contaminants from groundwater, and expediting permanent contaminant biodegradation. Wide Area Dispersive Distribution Unlike any other sorbent technology, PlumeStop can be emplaced in the subsurface through dispersive flow from low pressure injection (without fracturing the formation), providing a widearea thin film coating of the aquifer matrix through which it passes. It does not create preferential flow pathways, plug the formation, or compromise monitoring wells through extreme carbon loading in contrasting respect to the majority of the surrounding porosity (i.e. the porosity external to the fractures or soil partings themselves) as may be the case with pressure emplaced powdered activated carbon products. More information on low pressure ease of distribution and dispersive emplacement of PlumeStop can be found in PlumeStop Technical Bulletin 1.1: Distribution through a Permeable Medium. Rapid Removal of Contaminants from Groundwater PlumeStop rapidly sorbs organic contaminants from aqueous solution (hours). Pollutants partition directly into the PlumeStop particles sorbed to the soil formation, removing the pollutants from groundwater. Contaminant advection in the aqueous phase is therefore eliminated (i.e. the plume is stopped) and partitioning into the vapor phase is also reduced (Henry s Law). Results can be dramatic, with groundwater cleanup objectives often met within days of PlumeStop application. Information on the sorption of contaminants by PlumeStop can be found in PlumeStop Technical Bulletin 2.1: Sorption of Contaminants from Solution. 1

2 Acceleration of Contaminant Biodegradation Once in place and with contaminants partitioned onto its surface, PlumeStop is colonized by contaminant degrading bacteria. These may be naturally present or applied as an inoculum. The bringing together of a degradative microflora and the target contaminant in local abundance (i.e. concentrated on the PlumeStop rather than dispersed in the groundwater and formation) reduces mass transfer kinetic constraints and supports greater speed and efficiency of degradation. The net result is a substantial increase in the instantaneous rate and extent of contaminant destruction. Further information on the stimulation of contaminant biodegradation by PlumeStop can be found in PlumeStop Technical Bulletin 3.1: Stimulation of Biodegradation Rates. Regeneration In Place Once in place with particles coating aquifer pore surfaces, PlumeStop continues to regenerate inplace by the continual cycle of contaminant sorption and biodegradation: 1) Dissolved phase contaminants partition out of the groundwater and are concentrated on sorption sites of the PlumeStop particles. 2) Opportunistic contaminantdegrading microbes colonize the PlumeStop. These together form the bio matrix. 3) Biodegradation of contaminants within the bio matrix frees up sorption sites allowing further contaminant to partition out of the groundwater. Sorption sites become available for additional contaminant Contaminant sorbs to sites available on PlumeStop particle Microbes biodegrade sorbed contaminants This cyclical pattern results in on going contaminant capture and destruction and regeneration of the PlumeStop bio matrix. This allows a one time application of PlumeStop to remain functional for an extended / indefinite period of time. 2

3 Data Supporting the In Place Regeneration To demonstrate the in place regeneration of PlumeStop, a laboratory study was undertaken comparing the removal of perchloroethene (PCE) from soil/water slurries treated with PlumeStop versus a sterile control. Test Procedure Twenty seven microcosm samples were prepared in 8 oz amber serum bottles sealed with Mininert valves (Figure 1). Each bottle contained site soil (20 g), PlumeStop (50 mg/l), microbial consortia (1 x 10 6 cells/ml Dehalococcoides ethenogenes), and sodium lactate as an electron donor to promote biological reductive dechlorination (1,000 mg/l). The experiment was initiated with the addition of 2.3 mg of PCE to each bottle, bringing the total mass of each sample mixture to 250 g. Similarly, twenty seven sterile control samples were prepared with autoclaved site soil (20 g), sodium lactate (1,000 mg/l), and sodium azide (200 mg/l), a biocide added to inhibit biological activity. PCE (2.3 mg) was then added to each control bottle to give a total sample mass of 250 g. Figure 1. Experimental set up test microcosms All bottles were placed on an orbital shaker at room temperature throughout the entire experiment. After 24 hours, three PlumeStop treated samples and three control samples were chilled prior to removing a 1 ml aliquot for headspace analysis by GC ECD in order to determine the PCE concentration in water. The same sample bottles were then sacrificed and subjected to a 48 hour hexane extraction (total system extraction both soil and water phases). The hexane extract was analyzed by GC ECD to give the total mass of PCE within each bottle. After two weeks, the same sampling procedure described above was repeated on six more sample bottles, three from each condition. At the same time, all remaining sample bottles were spiked with an additional 2.3 mg of PCE and 25 mg of sodium lactate. The freshly spiked bottles were allowed to equilibrate for six hours before an additional six sacrificial bottles were sampled and analyzed in the manner described in order to establish a new post spike baseline. 3

4 The identical procedure described above of analyzing spiking analyzing was repeated at the four week and six week time points of the experiment, such that PCE was spiked and analyzed through four complete cycles. Two additional PCE analysis only cycles (no spikes) were also conducted at the eight and ten week time points. Results PCE concentrations present in the aqueous phase, as measured by headspace analysis, indicated that in the test vials with PlumeStop, the majority of the PCE was almost immediately sorbed by the PlumeStop (same day) and thus removed from aqueous solution (Figure 2). Within the control vials (no PlumeStop or biological activity), the data show a PCE build up in the aqueous phase over time with the addition of each successive PCE spike. Figure 2. Comparison of dissolved phase PCE concentration on cumulative loading with and without PlumeStop. Data from the total system extraction (Figure 3) clearly indicates the rapid degradation of PCE within the PlumeStop amended vials. At the time of each sampling, less than 10% of the added PCE remained in the PlumeStop amended vials prior to re spiking with additional PCE. Conversely, in the control vials absent PlumeStop and biological activity, PCE concentration increased with each additional PCE spike. 4

5 Figure 3. Comparison of dissolved phase PCE concentration on cumulative loading with and without PlumeStop total system extract. Summary and Conclusion The laboratory test conducted clearly demonstrated the ability of PlumeStop to re generate in place: 1) PCE rapidly partitioned onto the PlumeStop particles removing PCE from the aqueousphase. 2) Once partitioned onto the PlumeStop particles the PCE was degraded, leaving negligible PCE in the system (sorbed phase or aqueous phase). 3) After sorbed PCE was degraded, the regenerated PlumeStop particles were again able to sorb additional PCE from solution, thereby providing capacity for continued contaminant sorption and degradation. The manner in which the sorptive capacity of PlumeStop regenerates during contaminant biodestruction suggests extended if not indefinite treatment longevity. 5

6 PlumeStop is manufactured and distributed for sale by REGENESIS, San Clemente, CA, USA. For more information or to contact a technical representative visit Calle Sombra San Clemente, CA