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Knowledge Base

Planning Phase

The implementation of biofiltration requires significant up-front evaluation and planning Perhaps the most important elements for biofiltration planning are identifying and evaluating drivers for implementation. The water treatment performance and finished water stability are well-known benefits associated with the implementation of biofiltration. In addition, other advantages of biofiltration may be realized, including a low relative cost (when compared to separation-based technologies), decreased upstream/downstream chemical/energy requirements, and improved treatment process sustainability. Conversely, consideration must also be given to the potential negative impacts of biofiltration implementation. Uncontrolled biological fouling may lead to challenges with filter production and/or the failure of filter mechanical and structure components. Public perception and regulatory support may also serve as factors that limit the feasibility of implementation. At a minimum, outreach and education must be considered as mitigating tools to improve acceptance of what is incorrectly perceived as a new or unproven technology. Ultimately, any utility planning to implement biofiltration should consider performing a cost-benefit analysis that balances treatment performance, reliability, costs, regulatory approval requirements, and unforeseen consequences. Frequently asked questions are listed below.

1. What are the drivers for biofiltration?

Common drivers for biofiltration include the need to reduce disinfection byproduct formation potential for regulatory compliance, to improve distribution system biostability, to remove manganese, and/or to remove taste and odor causing compounds.

2. What contaminants can biofiltration address?

Biofiltration can effectively reduce total organic carbon (TOC), manganese, iron, ammonia, MIB, geosmin, and a wide range of biodegradable micropollutants.

3. What are the benefits of using biofiltration?

Biofiltration uses naturally occurring microorganisms to enhance current treatment schemes at a relatively low cost with minimal to moderate impacts on facility operations. In some cases, biofiltration may be a cost effective alternative to more costly treatment processes such as post filter GAC adsorption or ion exchange.

4. What are the key factors to successfully implementing biofiltration?

Biofiltration may not be as effective as other, more costly treatment processes (e.g., GAC) so care must be takento ensure that the desired treatment objectives are appropriate. Further, biofiltration relies on water quality that will support the growth of microorganisms and treatment of target contaminants. Not all water sources, regardless of geographic location, will support biofiltration. Pilot testing for a full year prior to full-scale demonstration is strongly recommended.

5. What are the regulatory requirements associated with using biofiltration?

Requirements vary from state to state. Please check with you primacy agency for requirements in your area.

6. What process modifications are needed to accommodate biofiltration?

In retrofit applications, most utilities stop carrying an oxidant residual through their filters. Other possible modifications may include providing a backwash supply without an oxidant, installing an air scour system, or changing filter media. More significant facility modifications could include the installation of pre-ozonation or chemical feed systems for nutrient addition. Lastly, utilities must install or purchase appropriate monitoring equipment for observing ongoing biofilter performance.

7. What unintended consequences are typically experienced with biofiltration?

Most utilities have not experienced unintended consequences, however some have reported shortened filter runs, increased headloss, increased monitoring equipment maintenance, and increased chlorine demand.

8. What does it cost to implement biofiltration?

Costs are relative to the facility and treatment objectives. For new construction, the cost of implementing biofiltration need not differ significantly from the cost of implementing conventional filtration. In retrofit applications, implementation costs can range from minimal to significant depending on the planned facility modifications

9. How do I assess long-term operational cost for leveraging biofiltration?

Operational costs beyond those associated with conventional filtration may include chemical nutrient addition, cleaning of monitoring equipment, and backwash water usage.

10. What factors make biofiltration a sustainable technology?

In most applications, treatment performance targets are met without the use of chemical addition. This is accomplished by harnessing the power of microorganisms indigenous to the raw water supply. This resource-efficient process also addresses a wide range of contaminants and often converts contaminants to harmless end products instead of sequestering or concentrating them into a waste stream.

11. Is the application of biofiltration limited to certain geographies?

No. Although water temperature is a factor in biofiltration performance, it has proven effective in full-scale facilities across the United States and Canada.

Water Research Foundation Reports

Cost-Effective Regulatory Compliance With GAC Biofilters
Microbial Impact of Biological Filtration
Balancing Multiple Water Quality Objectives
Optimizing Filtration in Biological Filters
Use of Chlorine Dioxide and Ozone for Control of Disinfection By-Products
Removal of DBP Precursors by GAC Adsorption
Microbial Activity on Filter-Adsorbers
Treating Algal Toxins Using Oxidation, Adsorption, and Membrane Technologies
Biological and Ion Exchange Nitrate Removal Evaluation
Biological Treatment and Downstream Processing of Perchlorate-Contaminated Water