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Knowledge Base

Evaluation Phase

A well-thought-out process evaluation is a critical step for utilities that decide to test biofiltration for their treatment scheme. This step is primarily composed of identifying the desired biofiltration performance metrics and then evaluating and optimizing the process around those metrics. Common metrics include turbidity removal, filter run time, TOC removal, DBP precursor removal, taste and odor removal, manganese removal, and micropollutant removal. It is also important to evaluate the range of water quality conditions upstream of the planned biofiltration process as this can significantly impact treatment performance. Key water quality factors include temperature, pH, alkalinity, nutrients, solids loading, and the concentration of target contaminants. Biofiltration is most effectively tested at the pilot or demonstration (full) scale, though some utilities have successfully conducted bench-scale evaluations. The smaller-scale tests encounter the typical challenges of scale that can significantly impact the utility of testing. Scale evaluations should be conducted to capture the full range of water quality conditions believed to be representative of the intended source water. Some utilities recommend testing for at least one year. Frequently asked questions are listed below.

1. How important is it to perform bench, pilot, and/or demonstration-scale evaluations?

While bench-scale evaluations may have value for establishing treatability, pilot- and demonstration-scale testing is a critical precursor to full-scale implementation. These tests will support optimization of design and operational parameters.

2. What are the costs associated with performing these evaluations?

Evaluation costs are generally a function of scale, duration, equipment procurement, and analytical requirements. Short duration bench-scale evaluations can cost $30,000, while longer-term, large-scale evaluations where pilot equipment is procured can be over $1.5 million.

3. Water are target performance criteria for these evaluations?

Typical performance criteria include maintaining filtered turbidity below 0.1 NTU, filter run time greater than 24 hours, unit filter run volume greater than 10,000 gal/ft2, and target contaminant removal (e.g., greater than 20 percent TOC removal). In all cases, these performance criteria should be tailored to the specific needs of the facility.

4. Are there performance data available in the knowledge base?

Full-scale operational data are summarized in the knowledge base report and in select case studies.

5. How long should I run an evaluation?

It is recommended that evaluations be run long enough to achieve biological operation mode followed by a period that includes seasonal fluctuations in water quality. Pilot- or full-scale evaluation durations can be as short as six months, but are recommended to be at least one year.

6. How do the evaluation results translate to full scale?

Some utilities have had difficulty in achieving full-scale performance predicted by bench- or pilot-scale tests. Therefore, it is valuable to run a demonstration-scale evaluation on a single full-scale filter once process optimization has been achieved at pilot-scale.

7. What media and media configuration should I use for the evaluation?

Most utilities have dual-media filters comprised of anthracite and sand or GAC and sand. There are various types of GAC available for evaluation. Most utilities use bituminous GAC.

8. Can I expedite the acclimation of the biofilters?

Acclimation of biofilters has been reported to range from two weeks to six months. At this time, there are no reliable methods for expediting biofilter acclimation.

9. What water quality and operational data should I collect during the evaluation phase?

At a minimum water quality and operational parameters should include typical parameters for filter evaluations (e.g., turbidity, headloss, temp, pH, alkalinity), target contaminants (e.g., TOC, manganese, iron, MIB, geosmin, micropollutants), nutrients (e.g., orthophosphate, ammonia) and biomass (e.g., adenosine triphosphate).

10. Are there regulatory guidelines available for developing an evaluation plan?

Regulatory guidelines vary from state to state. Please consult your primacy agency for pilot testing requirements.

Water Research Foundation Reports

Biological Drinking Water Treatment Perceptions and Actual Experiences in North America
State of Knowledge of Endocrine Disruptors and Pharmaceuticals In Drinking Water
Case Studies of the Impacts of Treatment Changes on Biostability in Full-Scale Distribution Systems
Radionuclides in drinking water
Microbial Impact of Biological Filtration
Removal of DBP Precursors by GAC Adsorption
A Simulation Tool to Assess Contaminant Warning System Sensor Performance Characteristics
Case Studies of the Impacts of Treatment Changes on Biostability in Full-Scale Distribution Systems
Microbial Activity on Filter-Adsorbers
Advances in Taste-and-Odor Treatment and Control
Colonization of Biologically Active Filter Media With Pathogens
Biological Treatment and Downstream Processing of Perchlorate-Contaminated Water