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#environmental cleanup

5 public questions tagged with this topic.

Bioremediation

Which plant family is extensively used for phytoremediation?

Brassicaceae also called Cruciferae mustard family dominates phytoremediation literature due to hyperaccumulation capacity, rapid growth biomass 5 to 20 tons per hectare, high seed production and genetic tractability with Arabidopsis thaliana as model enabling molecular characterization. Genera include Thlaspi caerulescens now Noccaea accumulating zinc up to 30,000 and cadmium 3,000 mg per kg, Brassica juncea for lead up to 10,000, selenium, chromium and uranium, Alyssum bertolonii and murale hyperaccumulating nickel above 10,000 mg per kg in serpentine soils, and Brassica napus for radionuclides. Underlying traits involve overexpression of metal transporters ZIP ZNT1 and HMA4 P-type ATPase critical for xylem loading confirmed by QTL mapping and transgenic overexpression enhancing accumulation 3-fold, plus histidine chelation and antioxidant glutathione-ascorbate cycle for reactive oxygen scavenging. Fast doubling and extensive roots allow multi-cropping. Compared to Poaceae grasses used for rhizosphere oxidation, Fabaceae for nitrogen fixation, and Malvaceae minor, Brassicaceae provides optimal compromise between accumulation intensity and biomass, supported by genome resources and transformation protocols enabling engineering via overexpressing HMA4 or MTP1.

Ref: Baker 1997 Brassicaceae hyperaccumulators New Phytol; Peer et al. 2006 Brassica phytoremediation Plant Biology; EPA Brassicaceae plant family guide.

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Bioremediation

Bioslurping is limited to approximately:

Bioslurping practical effectiveness limited by physics of lifting liquid column against gravity using available vacuum, which imposes maximum operational depth. Field experience compiled in EPA engineering bulletins and US Army Corps of Engineers guidance indicates product recovery feasible only where water table depth less than approximately 25 feet below ground surface when using typical regenerative blowers 15 to 25 horsepower generating 20 to 30 inches mercury vacuum. Beyond this, hydrostatic head exceeding vacuum capability, increased friction losses in riser pipe, product viscosity particularly weathered diesel, and capillary retention in fine-grained sediments trapping residual NAPL prevent efficient slurping and cause water upconing rather than product collection. Radius of influence declines exponentially with depth due to reduced pressure differential, leading to channeling. Performance curves from demonstration sites at Hill Air Force Base show recovery rate dropping from 10 gallons per day at 10 feet to less than 0.5 at 30 feet. Shallower sites with thick floating layer yield higher initial rates then transition to bioventing polishing phase once free product depleted. Engineering calculations using modified Theis equation for multiphase flow incorporate vacuum limit, guiding selection between bioslurping and more energy-intensive dual-pump or skimmer systems for deeper aquifers exceeding threshold.

Ref: EPA Bioslurping depth limitations 1996; Khan et al. Bioslurping design considerations Bioslurping; USACE depth guidance.

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Bioremediation

Bioslurping is effective for removal of:

Bioslurping represents hybrid technology merging vacuum-enhanced free product recovery with bioventing to address sites where light non-aqueous phase liquid LNAPL such as gasoline, diesel and jet fuel accumulates as floating layer 2 to 100 centimeter thick on top of water table, serving as persistent secondary source dissolving into groundwater. Technique deploys adjustable slurp tube inside well connected to high-vacuum blower generating 20 to 30 inches mercury, extracting groundwater, free-phase hydrocarbon and soil vapor simultaneously through same conduit via Venturi effect; liquid rises into knockout separator where LNAPL skimmed for off-site recycling or disposal while water treated via air stripping or carbon adsorption. High vacuum expands capture zone radius 10 to 30 feet enhancing mobility of floating product toward extraction well through increased hydraulic gradient. Concurrent soil gas extraction induces airflow through smear zone stimulating aerobic biodegradation of residual sorbed phase via alkB bearing microbes, polishing source zone after bulk liquid removal. Unlike heavy metal or chlorinated solvent DNAPLs denser than water, floating hydrocarbons uniquely amenable because they reside at air-water interface accessible to slurp tube. Pilot tests measuring transmissivity and product thickness determine viability versus dual-phase extraction.

Ref: EPA Bioslurping Fact Sheet 1996; Afentoulis et al. Remediation Journal 1996 bioslurp effectiveness; US Army Corps design guide.

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