Bioslurping involves the simultaneous application of vacuum enhanced extraction/recovery, vapor extraction, and bioventing to address LNAPL contamination. Vacuum extraction/recovery is used to remove free product along with some groundwater, vapor extrac tion is used to remove high volatility vapors from the vadose zone, and bioventing is used to enhance aerobic biodegradation in the vadose zone and capillary fringe.
The bioslurping system is made up of a well into which an adjustable length 'slurp tube' is installed. The slurp tube, connected to a vacuum pump, is lowered into the LNAPL layer, and pumping begins to remove free product along with some groundwater (vac uum enhanced extraction/recovery). The vacuum-induced negative pressure zone in the well promotes LNAPL flow toward the well and also draws LNAPL trapped in small pore spaces above the water table. When the LNAPL level declines slightly in response to p umping, the slurp tube begins to draw in and extract vapors (vapors extraction). This removal of vapors promotes air movement through the unsaturated zone, increasing oxygen content and enhancing aerobic bioremediation (bioventing). When mounding due to the introduced vacuum causes a slight rise in the water table, the slurp cycles back to removing LNAPL and groundwater. This cycling minimizes water table fluctuations, reducing 'smearing' associated with other recovery techniques.
Liquid (product and groundwater) removed through the slurp tube is sent to an oil/water separator, and vapors are sent to a liquid vapor separator. Aboveground water and vapor treatment systems may also be included, if required. However, in some cases, system design modifications have allowed discharge of groundwater and vapor extracted via bioslurping without treatment. Results of field tests of bioslurping systems have shown that LNAPL and vapor recovery are directly correlated with the degree of vac uum. A comparison of bioslurping to conventional methods of LNAPL recovery reported that bioslurping achieved the greater recovery rates than either skimming or dual-pump methods.
Reported advantages of bioslurping, as compared to other LNAPL recovery/treatment techniques, include lower project costs (because less groundwater is extracted and because vapor and groundwater may not require treatment) and a reduction in aquifer 'smear ing.' Disadvantages cited as associated with bioslurping include potential 'biofouling' of well screens due to active aeration and lack of treatment of residual LNAPL contamination in saturated soils.