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fermentation productivity [21]. The bacterial immobilization can provide remarkable stability and prevent the loss of bacteria. A packed bed or fluidized bed reactor containing the immobilized biomass also can effectively remove contaminants using a much smaller reactor than biosorption processes containing free cells.

17.4.2 Groundwater Treatment

The biosorption process can be applied in situ without the expense of pumping out the contaminated groundwater or excavating the soil. This technique provides low-cost, easy operating, and safe treatment of contaminants in groundwater. The immobilized microbial stratum may be placed in an engineered trench across the flow path of a contaminated plume to create a BPB (biological permeable barrier). Contaminated groundwater enters the BPB, to which electron donor and nutrients may be supplied through the groundwater gradient, while the remediated groundwater exits the BPB. Selective removal has the potential and flexibility to treat a wide range of wastewater contaminants beyond nitrates. The most relevant work on true bacterial biosorption has been done by Brierley [60]. He found that the biosorption process was useful for cost-effective treatment of high-volume, low-concentration wastes such as mine runoff using artificial wetlands with undefined biota.

17.4.3 Protection from Pollutant Plumes

The migration of contaminants from a hazardous site is a concern for the protection of downstream resources. Biobarriers serve as an alternative technology for controlling the migration of contaminants from hazardous waste sites. The biobarrier can be applied in the field by injecting starved bacteria and then nutrients into a series of injection wells. The pore space is sealed by bacterial growth and EPS production and then a biobarrier is formed in soil [61]. The biobarrier has applicability as an alternative liner material in landfills to the contaminated sites. It is able to immobilize heavy metals in situ, thus protecting environments from the hazardous lechate.

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