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Patchy biofilm coverage can explain the potential advantage of BGAC reactors
Moshe Herzberg1, Carlos G Dosoretz, Sheldon Tarre
1Faculty of Civil and Environmental Engineering, Technion, Haifa 32000, Israel.
Environmental Science & Technology
|October 4, 2003
Summary
Biological GAC reactors show enhanced pollutant removal due to patchy biofilm coverage on granular activated carbon (GAC). This allows for adsorption and desorption, improving biofilm activity and treatment efficiency.
Area of Science:
- Environmental Microbiology
- Environmental Engineering
- Biotechnology
Background:
- Biological granular activated carbon (BGAC) reactors utilize adsorbing carriers, potentially leading to pollutant flux from both bulk liquid and the carrier itself.
- This dual-flux mechanism can enhance BGAC reactor performance over non-adsorbing carriers, particularly when pollutants partially penetrate biofilms.
- However, the effectiveness of adsorption in BGAC reactors under conditions requiring very low effluent concentrations is debated, necessitating exposed carrier surfaces.
Purpose of the Study:
- To demonstrate that patchy biofilm coverage with exposed granular activated carbon (GAC) areas occurs under typical BGAC fluidized bed reactor operating conditions.
- To establish that adsorption and desorption via these exposed GAC areas explain the observed higher biofilm activity in BGAC reactors.
Main Methods:
- Experimental verification of patchy biofilm coverage on GAC particles.
- Modeling tools to support experimental findings on biofilm distribution.
- Comparative analysis of BGAC reactors with adsorbing (GAC) and non-adsorbing carriers using an atrazine-degrading biofilm (Pseudomonas ADP).
Main Results:
- Patchy biofilm coverage on GAC particles was experimentally and computationally verified.
- BGAC reactors with atrazine-degrading biofilms exhibited higher biodegradation rates compared to non-adsorbing carriers.
- Lower effluent atrazine concentrations were observed in the BGAC reactor under conditions of partial pollutant penetration.
Conclusions:
- Patchy biofilm coverage on GAC is a characteristic of normal BGAC fluidized bed reactor operation.
- The presence of exposed GAC areas facilitates adsorption and desorption, contributing to the enhanced activity and efficiency of BGAC reactors.
- BGAC reactors offer superior performance in pollutant removal, especially for achieving low effluent concentrations, due to the combined effects of biodegradation and carrier adsorption.