Cardno ERI Fluidized Bed Bioreactor Operation
Cardno ERI and faculty from the University of California at Davis have collaborated to develop a line of compact, practical, and effective bioreactor systems to treat contaminated groundwater. Bioreactor-based water treatment involves pumping groundwater out of the ground, mixing it with active microorganisms in a bioreactor system, and discharging the newly treated water. The treated water is either sent back into the ground, to a municipal sewer system, or into surface water.
The bioreactor groundwater treatment technology developed by Cardno ERI and UC Davis includes an above-ground tank containing trillions of microorganisms, primarily bacteria that attach themselves to the surfaces of fine grains of sand. The grains are distributed throughout the tank by the upward flow of the water passing through the tank for treatment. As the contaminated water mixes with them, the microorganisms consume MTBE and other dissolved gasoline components as food.
Cardno ERI bioreactors can treat a wide range of contaminant concentrations because of the way their distinct water recycle loop dilutes water coming out of the ground. Cardno ERI's bioreactors have handled extremely high concentrations (up to a million parts per billion of gasoline constituents), reducing them to non- detectable levels. Laboratory analyses of water samples leaving Cardno ERI bioreactors are able to detect little if any MTBE or other gasoline traces.
Cardno ERI bioreactors are quiet and odor-free and can be efficiently moved—along with their microbial communities—to new treatment sites.
Cardno ERI bioreactors offer the following features and benefits:
Applicable Compounds
The bacteria biodegrade ethers such as MTBE, DIPE, TAME, and ETBE, as well as tertiary butyl alcohol (TBA). They also biodegrade, and actually prefer, gasoline petroleum hydrocarbons such as BTEX. The bioreactor can be used to treat oxygenated compounds and petroleum hydrocarbons. However, if extremely high concentrations of petroleum hydrocarbons are present, the water should be pretreated using a more conventional technology such as activated carbon or air stripping; ethers and alcohols will break through the pre-treatment process for subsequent removal in the bioreactor.
Mass Loading
Cardno ERI bioreactors are sized to treat a specific mass loading, which is equal to the flow rate of water from the site recovery wells times the total volatile organic compound (VOC) concentration in the recovered water. In a well executed remediation project, initial VOC concentrations typically decrease over time as the site is remediated. As VOC concentrations decrease, the influent flow rate of water from the recovery wells can be increased such that a constant mass loading enters the bioreactor system for treatment. Cardno ERI's bioreactor design incorporates a partial recycle loop that provides operational flexibility by allowing the influent flow rate to be adjusted as VOC concentrations change, thus maintaining bioreactor operation at peak efficiency. Here is how it works.
Schematic Operation of Fluidized Bed
Water from the site recovery wells (1) enters the feed tank, where it is diluted with treated water exiting from the bioreactor.
The mixed water stream (2) is pumped to the bottom of the bioreactor, where it flows upward through the sand medium which is colonized by microorganisms. The microorganisms consume the TBA, MTBE, and other VOCs present in the water, converting them to carbon dioxide and water and using dissolved oxygen in the process.
Treated water with a decreased dissolved oxygen content (3) flows from the bioreactor through an oxygenator where it is reoxygenated to near saturated levels (typically around 8 mg/l). Most of the treated water is recycled to the feed tank to dilute the incoming well water; however, an amount equal to the incoming well water (4) is discharged from the system. The treated water typically has effluent VOC concentrations that are near or below detection limits.
Handling of Bioreactor Effluent
The water exiting the bioreactor is often filtered and then passed through a pair of activated carbon canisters before final discharge to groundwater, surface water, or municipal sewer system. Since the TBA, MTBE, and other gasoline constituents have been consumed, the carbon is not necessary for treatment under normal conditions but merely serves as a backup should there be a sudden increase in influent VOC concentrations from the site or an upset in the bioreactor.
An alternate strategy is to discharge the oxygenated treated water directly to groundwater without final carbon polishing. This provides oxygenated, treated water containing bacteria to the subsurface, thus promoting in situ bioremediation at the site at the same time that the ex situ treatment is taking place.
Ancillary Equipment
Sufficient oxygen must be provided for the aerobic microorganisms to consume the VOCs, and the mass loading that can be handled by the bioreactor can be increased by delivering more oxygen to the system. Use of an oxygen booster can double the bioreactor capacity by elevating dissolved oxygen (DO) concentrations. DO concentrations as high as 38 mg/l have been achieved.
When the water is oxygenated, dissolved iron, manganese, and hardness can form nuisance precipitates that can cause clogging and other problems. These precipitates are removed by means of a bead filter or filter pad. In addition to food (VOCs) and oxygen, the biomass requires nutrients—particularly nitrogen, phosphorus, and potassium. A nutrient solution is metered into the feed tank to satisfy this need.
A flow switch and autodialer are included in Cardno ERI bioreactor systems to notify the operator should the recirculation flow be interrupted. Finally, water temperature and pH must be maintained within a normal operating range. When necessary, Cardno ERI bioreactors are equipped with systems for heating and/or pH adjustment.
Cardno ERI-4000 Fluidized Bed Reactor
Cardno ERI-500 Fluidized Bed Bioreactor
Specifications for Standard Cardno ERI Fluidized Bed Bioreactors
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