Groundwater metal removal

Normally, treatment of coproduced groundwater during hydrocarbon recovery operations will include, as a minimum, oil-water separation and the removal of dissolved volatile hydrocarbon fractions (i.e., benzene, toluene, and total xylenes). In addition, removal of inorganic compounds and heavy metals (i.e., iron) is often required. Dissolved iron, a common dissolved constituent in groundwater, for example, may require treatment prior to downstream treatment processes to prevent fouling problems in air-stripping systems. Heavy metals removal is normally accomplished by chemical precipitation. 

Alternative 1 consists of preliminary treatment for heavy metals removal with the primary concern being iron removal (Figure 8.3). The levels of iron observed in the groundwater at this site would be very detrimental to the downstream treatment processes. This pretreated water would then be used for cooling tower makeup water followed by biological treatment. This approach would be the easiest and cheapest alternative. This combined process should provide effective removal of BTEX. 

Metals removal may require pretreatment. Other applications may require equalization tank, oil/water separator, sludge dewatering, postcarbon adsorption or filter. Certain applications may require off-gas control system. It may also be unsuitable for groundwater with a chemical oxygen demand less than 40 mg/liter. 

Metals removal via peat is an in situ, passive treatment technology being developed to treat groundwater contaminated with heavy metals and radionnclides. Bench-scale tests indicate that peat may be an inexpensive and effective material for trapping metals. 

The Unipnre Environmental, Unipnre process technology is a unique iron co-precipitation method for removal of heavy metals from waste streams or groundwater. It can act as a primary metal-removal system or as a polishing step to an existing treatment system. The reactor mod-nle replaces the nentrahzation tank in a conventional wastewater treatment system. The process prodnces solids that are extremely insolnble in water and mild acid solutions. 

Metal removal from surface water, groundwater or wastewater streams is more straightforward than that from soils. Typically, removal is achieved by concentration of the metal within the wastestream using flocculation, complexation, and/or precipitation. For example, the use of lime or caustic soda will cause the precipitation and flocculation of metals as metal hydroxides. Alternatively, ion exchange, reverse osmosis, and electrochemical recovery of metals can be used for metal removal (Chalkley et al., 1989 Moore, 1994). Unfortunately, these techniques can be expensive, time-consuming and sometimes ineffective, depending on the metal contaminant present. 

Metal reclamation from acid mine drainage and contaminated surface- and groundwater and wastewaters has been extensively studied. Technologies for metal removal from solution are based on the microbial—metal interactions discussed earlier the binding of metal ions to microbial cell surfaces the intracellular uptake of metals the volatilization of metals and the precipitation of metals via complexation with microbially produced ligands. 

Microbial mat formation may also stimulate metal removal through sulfate reduction. Barnes, Scheeren Buisman (1994) have developed a process that specifically uses sulfate-reducing bacteria to treat metal-contaminated groundwater. In this process, as groundwater is pumped through the water treatment plant, sulfide produced by sulfate-reducing bacteria precipitates the metals in the water. Metal concentrations in the treated water were reportedly reduced to fig/l quantities and the water was suitable for release into the environment. 

Sang et al. [94] used nanoflbrous membrane prepared from chloridized PVC by high-voltage electrospinning for the removal of divalent metal cations (Cu2+, Cd +, and Pb +) from the simulated groundwater. To obtain the best heavy metal removal, several experimental methods were investigated, including static adsorption, direct filtration, soil-addition filtration, diatomic-addition flltration, and micellar-enhanced... 

Groundwater is vulnerable to pollution by chemicals carried by rainwater, leaching from waste sites or from waste water carrying industrial or agricultural effluent. Treatment of drinking water may remove some, but not all, of these contaminants. Some polycarbonate or metal water pipes that are lined with epoxy resin lacquers may release bisphenol A. 

Ortiz-Bernad I, RT Anderson, HA Vrionis, DR Lovley (2004b) Vanadium respiration by Geobacter metal-lireducens novel strategy for in situ removal of vanadium from groundwater. Appl Environ Microbiol... 

Membrane filtration processes have been successfully applied to the field of environmental engineering for air pollution control,34 potable water purification,22-24 groundwater decontamination,35,36 industrial effluent treatment,37 hazardous leachate treatment,35,36 and site remediation,36 mainly because membrane filtration can remove heavy metals and organics. 

The technology is commercially available and has been applied to leachates, wastewater processing, and contaminated groundwater. The technology has been modified to remove hexavalent chrominm and immobilize heavy metals in situ, but demonstration results have not been reported. 

The INCA system can recover virtually any target metal in any aqueous waste stream containing up to 60% solids. Applications include on-site remediation of mining effluents and contaminated groundwater. The INCA system can also be used as an in-process treatment system for manufacturing processes where metals in solution are a problem. The modular unit can easily be used in tandem with other technologies, such as those that remove hydrocarbons, as part of a total treatment train. 

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