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*Installation costs – is the system difficult to install? How much excavation is required for installation? |
*Installation costs – is the system difficult to install? How much excavation is required for installation? |
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*Aesthetics – how will the system impact the aesthetics of the site? Are above-ground systems attractive? How many risers do below-ground systems require? Will there be an unsightly raised disposal bed? |
*Aesthetics – how will the system impact the aesthetics of the site? Are above-ground systems attractive? How many risers do below-ground systems require? Will there be an unsightly raised disposal bed? |
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==External Links== |
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http://www.buzzardsbay.org/etiresults.htm |
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http://www.epa.gov/etv/verifications/vcenter9-3.html |
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http://www.shelterpub.com/_shelter/ssom_advanced-02.html |
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http://www.swrcb.ca.gov/ab885/docs/techonsite/chapter6.pdf |
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http://cfpub.epa.gov/owm/septic/index.cfm |
Revision as of 19:55, 23 August 2007
The biological treatment of wastewater with a trickling biofilter is among the oldest and most well characterized on-site or decentralized sewage treatment technologies. Onsite sewage facilities (OSSF) are recognized as viable, low-cost, long-term, decentralized approaches to wastewater treatment if they are planned, designed, installed, operated and maintained properly (USEPA, 1997). These systems have also been described as intermittent filters, packed media bed filters, trickling filters, alternative septic systems, attached growth processes, and fixed film processes.
Description
Trickling biofilters are used to treat sewage wastewaters in areas not serviced by municipal wastewater treatment plants (WWTP). Systems are typically installed in areas where the traditional septic tank system is failing, cannot be installed due to site limitations, or where improved levels of treatment are required for environmental benefits such as preventing contamination of ground water or surface water. Sites where there is a high water table, high bedrock, high clay, small land area, or where minimal site destruction (tree removal) is desired are ideally suited to trickling biofilters.
Approvals
Third-party verification of trickling biofilters has proven these systems to be a reliable alternative to septic systems with increased levels of treatment performance and nitrogen removal. Typical effluent quality parameters are Biochemical Oxygen Demand (BOD), Total suspended solids (TSS), Total Kjeldahl Nitrogen (TN), and fecal coliforms. The leading testing facility in the US is the Massachusetts Alternative Septic System Test Center, a program of the Buzzards Bay National Estuary Program. Testing conducted here includes the stringent Environmental Technology Initiative (ETI) where systems are tested in triplicate over two years, and the Environmental Technology Verification (ETV) program which is funded by the US Environmental Protection Agency (EPA) and includes stress testing as well as evaluation of nitrogen removal over 14 months. Systems are approved for installation by local, state and federal regulations and controls.
Technology
All trickling biofilter systems share the same fundamental components: a) a septic tank for primary settling of solids, b) a filter medium upon which beneficial microbes (biomass, biofilm) are promoted and developed, b) a container which houses the filter medium, c) a distribution system for applying wastewater to be treated to the filter medium, and d) a distribution system for disposal of the treated effluent. By treating septic tank effluent before it is distributed into the ground, higher treatment levels and smaller disposal means such as leach field, shallow pressure trench or area bed.
Systems can be configured for single-pass use where the treated water is applied to the biofilter once before being disposed of, or for multi-pass use where a portion of the treated water is cycled back to the septic tank and re-treated via a closed-loop. Multi-pass systems result in higher treatment quality and assist in removing Total Nitrogen (TN) levels by promoting nitrification in the aerobic media bed and denitrification in the anaerobic septic tank.
Trickling biofilters differ primarily in the type of filter media used to house the microbial colonies. Types of media most commonly used include plastic matrix material, open-cell polyurethane foam, sphagnum peat moss, recycled tires, sand and geotextiles. Ideal filter medium optimizes surface area for microbial attachment, wastewater retention time, allows air flow, resists plugging and does not degrade. Some systems require forced aeration units which will increase maintenance and operational costs.
System Considerations
There are many considerations to take into account when choosing a trickling biofilter:
- System footprint – will there be sufficient space at the installation site to accommodate the treatment unit?
- Robustness – how will the system be affected by seasonal use or in the event of a power outage?
- Treatment performance – will the system’s expected level of treatment ensure the receiving environment is not affected?
- Service requirements – are there many moving parts that will require regular maintenance and replacement?
- Electricity usage – what is the cost of operating the system? How many pumps, fans, or aeration units does it require?
- Sludge production – will the treatment unit produce unwanted sludge that must be trucked off site at the owner’s expense?
- Costs – is the cost of the system justified by its effectiveness?
- Installation costs – is the system difficult to install? How much excavation is required for installation?
- Aesthetics – how will the system impact the aesthetics of the site? Are above-ground systems attractive? How many risers do below-ground systems require? Will there be an unsightly raised disposal bed?
External Links
http://www.buzzardsbay.org/etiresults.htm http://www.epa.gov/etv/verifications/vcenter9-3.html http://www.shelterpub.com/_shelter/ssom_advanced-02.html http://www.swrcb.ca.gov/ab885/docs/techonsite/chapter6.pdf http://cfpub.epa.gov/owm/septic/index.cfm