1. What are the keys to planning a successful transition or start-up of a biofiltration process?
Utilities have reported acclimation periods of 2 weeks to 6 months. It is important to initiate biofiltration start-up so that ample time is provided for acclimation prior to needing a functioning biofilter.
2. What water quality and performance data should I monitor during the start-up phase and long-term operation of the biofiltration process?
Key parameters include turbidity, headloss, run time, unit filter run volume, temperature, nutrients, biomass (e.g., ATP), and total organic carbon removal across the filter.
3. What operational impacts can occur after converting to biofiltration?
While biofilters often perform similarly to conventional filters, some utilities have reported operational impacts including shortened filter run times, monitoring equipment fouling, and increased post-filter chlorine demand.
4. What mitigation strategies can I use to address these issues?
Mitigation strategies largely focus on reducing unwanted biomass, specifically EPS, development. WRF 4215 and 4346 have shown that in some cases adding nutrients (e.g., phosphorus, nitrogen) to avoid a nutrient-limited condition can reduce the production of EPS. Other mitigation strategies include the periodic use of an oxidant such as chlorine, hydrogen peroxide, or potassium permanganate to help address overproduction of EPS.
5. What levels of removal are achievable with long-term biofiltration?
Removal rates are specific to the facility and target contaminant, but utilities have reported TOC removal rates ranging from 10 to 20 percent, MIB/geosmin removal of greater than 99 percent, and removal of disinfection byproduct formation potential by 20 to 50 percent.
6. How should I handle my filter-to-waste and backwash wastewater?
Currently, utilities generally recycle filter-to-waste and backwash wastewater to the head of the plant prior to chemical addition.
7. What are common practices for filter shutdown, idling, and restart?
Few utilities reported best practices for biofilter idling. Some reported the ability to bring biofilters online that have been idled for less than two weeks with repeated backwash and drain cycles. One utility reported using a caustic wash of the filter bed followed by a backwash prior to start-up. For extended shutdown periods reaching months in duration, media change out and disinfection of the filter box may be required.
8. What impacts are experienced after start-up?
Start-up dynamics are largely dependent on filter media selected. GAC biofilters leverage initial high-rate adsorption and will achieve excellent organics removal when brought on line. Non-GAC biofilters will require acclimation before significant contaminant removal can be expected.
9. How do biofilters perform when short-term process upsets occur?
No full-scale operations reported impacts of short-term process upsets.
10. How long does it take biofilters to reach acclimation/steady-state?
Utilities have reported acclimation periods of 2 weeks to 6 months. Treatment schemes using ozone generally acclimate more quickly than non-ozonated systems due to the increased availability of biodegradable organic carbon.
11. Are there ways to accelerate biofilter acclimation in full-scale operation?
No full-scale operations reported methods for accelerating acclimation. This could be an area of future research.
12. What parameters should I monitor for biological stability?
Parameters such as assimilable organic carbon or biodegradable organic carbon can be use to directly quantify biological stability. Indirect measures of biological stability include disinfectant residual stability, and the occurrence of distribution system nitrification or corrosion.
13. What operations and maintenance costs are associated with biofiltration?
Incidental biofiltration does not require additional investment to maintain beyond additional monitoring of biomass (e.g., ATP). In cases where nutrients or oxidants are used, ongoing relatively minor chemical costs will incurred.
14. What are best practices for biofiltration training?
One of the best ways to train operations staff is to engage them in the pilot testing phase of biofiltration. While training for sample collection and data analysis is important, it is also important that operators know how media in a healthy biological filter looks and what various headloss trends might indicate. Operators should also understand the basic biological processes including the role of nutrients and temperature in process performance.
15. Should I use supplemental chemicals to manage the biofiltration process?
Supplemental chemicals may be helpful if your source water is nutrient limited or you are experiencing increase headloss due to EPS development.