Description:

Bioreactors degrade contaminants in water with microorganisms through attached or suspended biological systems. In suspended growth systems, such as activated sludge, fluidized beds, or sequencing batch reactors, contaminated ground water is circulated in an aeration basin where a microbial population aerobically degrades organic matter and produces CO₂, H₂O, and new cells. The cells form a sludge, which is settled out in a clarifier, and is either recycled to the aeration basin or disposed. In attached growth systems, such as upflow fixed film bioreactors, rotating biological contactors (RBCs), and trickling filters, microorganisms are established on an inert support matrix to aerobically degrade water contaminants.

One promising methodology includes the use of active supports (such as activated carbon, which adsorbs the contaminant and slowly releases it to the microorganisms for degradation). The microbial population may be derived either from the contaminant source or from an inoculum of organisms specific to a contaminant. Other applications include wetland ecosystems and column reactors.

Nutrients are often added to the bioreactors to support the growth of microorganisms.

Bioreactors are a long-term technology. The process may take up to several years.

Trickling Filter

Another aerating wastewater treatment is the trickling filter. The trickling filter consists of a bed of highly permeable media, a water distributor, and an underdrain system. Wastewater is distributed over the top of the filter bed through which wastewater is trickled. The organic contaminants in wastewater are degraded by the microorganisms attached to the filter medium. The filter media may be rocks, plastic, or wood. The filter bed is normally round with depth varying from 3 to 8 ft (0.9 to 0.5m) and average 6 ft (1.8m). As wastewater flows over the solid filter media, it is aerated and the organic contaminants are degraded by the microorganisms attached to the media surface. The underdrain system is used to collect the treated water and any biomass detached from the filter media. It is also important as a porous structure through which air can circulate.

The duration of operation and maintenance of sprinkler irrigation depends on the amount of time needed to capture and treat the contaminated waste; monitoring of treated water; and monitoring of potential metal accumulation.

Synonyms:

Applicability:

Limitations:

• The dilute nature of contaminated ground water often will not support an adequate microbial population density, and this is especial true for suspended growth reactors. Nutrient addition may be necessary.
• Very high contaminant concentrations may be toxic to microorganisms and require special design approaches.
• Air pollution controls may need to be applied if there is volatilization from activated sludge processes.
• Low ambient temperatures significantly decrease biodegradation rates, resulting in longer cleanup times or increased costs for heating.
• Nuisance microorganisms may preferentially colonize bioreactors, leading to reduced effectiveness.
• Residuals from sludge processes require treatment or disposal.
• Discharge of treated effluents may still be regulated.

Data Needs:

Data requirements include contaminants and their concentrations, pH, presence of compounds toxic to microorganisms, contaminant biodegradability, BOD₅, COD, suspended solids, flow rate, temperature, and nutrient concentrations.

Performance Data:

Startup time can be slow if organisms need to be acclimated to the wastes; however, the existence of cultures that have been previously adapted to specific hazardous wastes can decrease startup and detention times.

DOE has demonstrated another biological process, biological destruction of tank waste (BDTW), on the laboratory scale. This process is a separation and volume-reduction process for supernatant and sluiced salt cake waste from underground storage tanks. These wastes are usually composed of various radionuclides and toxic metals concentrated in a nitrate salt solution. The bacteria act as metal and radionuclide adsorbers and also as denitrification catalysts that reproduce themselves at ambient temperature and pressure. Some degradation of organic contaminants may also occur during the process.

The field demonstration bioreactor tank size is about 100 cubic meters, which corresponds to a waste treatment rate of 2 gpm, sufficient to treat a 1-million gallon tank in 1 year. At the 2-gpm size, the BDTW system is transportable. The current bioreactor is able to process salt solutions having nitrate concentrations up to 300,000 ppm. The maximum salt tolerance is being explored. Power usage is estimated at 20 kW for pumping and agitation.

Cost:

The key cost driver information and cost analysis was developed using the 2006 version of the Remedial Action Cost Engineering and Requirements (RACER) software.

Key Cost Drivers 

·        Chemical Oxygen Demand (COD)

o       The COD a given waste exerts is the primary cost driver.

·        pH Adjustment

o       The secondary cost driver is the amount of acid/base required to neutralize the pH of the waste stream.

Cost Analysis

The following table represents estimated costs (by common unit of measure) to apply bioreactor technology at sites of varying size and complexity.   A more detailed cost estimate table which includes specific site characteristics and significant cost elements that contributed to the final costs can be viewed by clicking on the link below.

Detailed Cost Estimate

References:

Innovative Remediation Technologies:  Field Scale Demonstration Project in North America, 2nd Edition

Groundwater Cleanup: Overview of Operating Experience at 28 Sites, September 1999, EPA 542-R-99-006,

Abstracts of Remediation Case Studies, Volume 4,  June, 2000, EPA 542-R-00-006

Guide to Documenting and Managing Cost and Performance Information for Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007

DOE, 1994. Technology Catalogue, First Edition. February.

EPA, 1980. Innovative and Alternative Technology Assessment Manual, EPA, Office of Water Program Operations, EPA/430/9-78/009.

EPA, 1984. Design Information on Rotating Biological Contactors, EPA/600/2-84/106.

EPA, 1987. Rotating Biological Contactors: U.S. Overview, EPA/600/D-87/023.

EPA, 1991. BioTrol - Biotreatment of Groundwater, EPA RREL, series includes Technology Evaluation, EPA/540/5-91/001, PB92-110048; Applications Analysis, EPA/540/A5-91/001; Technology Demonstration Summary, EPA/540/S5-91/001; and Demonstration Bulletin, EPA/540/M5-91/001.

EPA, 1993. BioTrol, Inc. - Methanotrophic Bioreactor System, EPA RREL, series includes Emerging Technology Bulletin, EPA/540/F-93/506; Emerging Technology Summary, EPA/540/SR-93/505; and Journal Article, AWMA, Vol. 43, No. 11, November 1993.

Opatken, E.J., H.K. Howard, and J.J. Bond, 1987. "Biological Treatment of Hazardous Aqueous Wastes", EPA Report EPA/600/D-87/184.

Opatken, E.J., H.K. Howard, and J.J. Bond, 1989. "Biological Treatment of Leachate from a Superfund Site," Environmental Progress, Vol. 8, No. 1.

Stinson, M., H. Skovronek, and T. Chresand, 1992. "EPA SITE Demonstration of BioTrol Aqueous Treatment System," Journal of the Air Waste Management Association, Vol. 41, No. 2, p. 228.

• DOI Demo Bureau of Mines
• EPA Demo MacGillis & Gibbs Superfund Site, MN
• DOI Demo Late Summer
• DOI Demo Bureau of Mines, NV
• DOI Demo Bureau of Mines, UT
• Navy Demo, Naval Weapons Station Seal Beach, CA
• EPA Demo St. Joseph, MI
• Air Force & DOE Demo Tinker AFB, OK
• Hanscomb AFB, MA
• Dow Chemical Site, TX
• 

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A list of vendors offering Ex Situ Biological Water Treatment is available from EPA REACH IT which combines information from three established EPA databases, the Vendor Information System for Innovative Treatment Technologies (VISITT), the Vendor Field Analytical and Characterization Technologies System (Vendor FACTS), and the Innovative Treatment Technologies (ITT), to give users access to comprehensive information about treatment and characterization technologies and their applications.

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