InspectAPedia ®

Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice
InspectAPedia
Home
| Air
Conditioning
| Electrical | Indoor
Environment
| Exteriors | Heating | Home
Inspection
| Insulate
Ventilate
| Interiors | Mold
Inspect/Test
| Plumbing
Water
Septic
| Roofing | Structure | Contact Us
Directory of Professionals to Inspect or Test a Building


SEPTIC SYSTEMS HOME
SEPTIC INFO ARTICLES
HOME BUYERS GUIDE to SEPTIC SYSTEMS
SEPTIC SYSTEMS ONLINE BOOK
SEPTIC PUMPING REPAIR
SEPTIC TREATMENTS
SEPTIC CONSULTANTS
SEPTIC AUTHORITIES
SEPTIC SYSTEM BOOKS REFS CODES
SEPTIC SYSTEM DESIGN MANUAL - Online
SEPTIC SYSTEM DESIGN BASICS
SEPTIC SYSTEM DESIGN ALTERNATIVES
  Wastewater Treatment Levels
  Wastewater Dispersal Methods
  Master List of Septic System Types
  AEROBIC SEPTIC SYSTEMS
  ALTERNATING BED SEPTIC SYSTEMS
  CESSPOOLS
  DRYWELLS
  SEPTIC EFFLUENT DISINFECTION SYSTEMS
  EVAPORATION-TRANSPIRATION SEPTIC SYSTEMS
  FIXED-FILM PROCESS SEPTIC SYSTEMS
  GRAVELLESS SEPTIC SYSTEMS
  GREYWATER SYSTEMS
  HOLDING TANK SEPTIC SYSTEMS
  LAGOON SYSTEMS
  GRAVITY/SIPHON DOSING SYSTEMS
    Methods of Effluent Distribution
    Bell Siphon Septic Dosing
    Dipping or Tipping Dosing
    Float Control Dosing Systems
    Products and Suppliers
  PRESSURE DOSING SYSTEMS
  HOW EFFLUENT IS DISTRIBUTED
  PRESSURE DOSING SPECIFICATIONS
  MANIFOLD DOSING SYSTEMS
  RIGID PIPE DOSING SYSTEMS
  DRIP DOSING SYSTEMS
  MEDIA FILTER SEPTIC SYSTEMS
  SEPTIC & GREYWATER FILTERS
  SEQUENCING BATCH SEPTIC SYSTEMS
  MOUND SEPTIC SYSTEMS
  RAISED BED SEPTIC SYSTEMS
  SAND BED SEPTIC SYSTEMS
  SEWAGE TREATMENT SYSTEMS
  TOILET ALTERNATIVES
  VEGETATED SUBMERGED SEPTIC BEDS
  WETLAND SEPTIC SYSTEMS
  ALTERNATIVE SEPTIC DESIGNERS
  ALTERNATIVE SEPTIC PRODUCTS

More Information

InspectAPedia® Home & Site Map
Air Conditioning & Heat Pumps
Bookstore
Electrical
Environment
Exteriors
Heating
Home Inspection
Insulate Ventilate
Interiors
Mold Inspect/Test
Plumbing Water Septic
Roofing
Structure
Accuracy & Privacy Policies
Contact Us



Vegetative submerged bed septic system design - EPA

Vegetative Submerged Bed Septic System Designs
InspectAPedia®  -    

  • Vegetative submerged bed septic system design applications
  • High-Specific-Surface Anaerobic Reactors for septic systems
  • Designs for various types of septic effluent dosing systems
  • Septic system designs using gravity dosing, effluent tipping buckets, drip systems
Our site offers impartial, unbiased advice without conflicts of interest. We will block advertisements which we discover or readers inform us are associated with bad business practices, false-advertising, or junk science. Our contact info is at InspectAPedia.com/appointment.htm.

This document discusses Vegetative submerged bed septic system design applications and High-Specific-Surface Anaerobic Reactors for septic systems, a variation for septic system effluent final treatment and disposal. US EPA information with supplemental documentation, references, and comments.

© Copyright 2010 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Vegetated Submerged Beds and Other High-Specific-Surface Anaerobic Reactor Septic System Designs

Onsite Wastewater Treatment SystemsTechnology Fact Sheet 5 - EPA 625/R-00/008

Description of Vegetated Submerged Bed Septic System Designs

A high-specific-surface anaerobic reactor (figure 1) is any tank or cavity filled with solid media through which wastewater flows with a high hydraulic retention time (HRT). In onsite treatment the two primary types are vegetated submerged beds (VSBs) and anaerobic upflow filters (AUFs).

The first is characterized by horizontal flow and prolific growth of macrophytes on the surface. The second comes in a variety of forms from upflow sludge blanket systems and fixed media anaerobic filters to partially fluidized beds of fine media. Both have long HRTs, produce anaerobic effluents, generally treat either high-strength or minimally pretreated wastewater, and usually require some form of posttreatment to meet surface discharge or water reuse requirements.

Figure 1. Generic high-specific surface anaerobic reactor

The primary removal mechanisms in all of these systems are physical, that is, floculation, sedimentation, and adsorption. Anaerobic biological reactions are extremely slow and do not have a significant impact on soluble BOD until HRTs become quite long. Some toxic organic compounds may be reduced through these mechanisms and chemical precipitation (e.g., sulfides) at shorter HRTs.

VSBs, as shown in figure 2, usually follow a septic tank and remove most of the suspended and larger colloidal particles, BOD, organic forms of nitrogen, and other particles. Although they are frequently identified as subsurface constructed wetlands, they do not fit the strict definition of a constructed wetland.

Figure 2. Elements of a vegetated submerged bed (VSB) septic systems

Submerged bed details EPA

Source: Toms Creek Project, VA.

Three types of AUFs can be used as pretreatment devices for high-strength wastewater and some onsite pretreatment applications in the United States. They are in shown in figures 3, 4, and 5. Figure 3, with a rock medium, is the most typical U.S. application.

Figure 3. Schematic of the upflow anaerobic filter process used in Vegetated Submerged Bed Septic System Designs

Figure 4. Schematic of the upflow anaerobic sludge blanket process used in Vegetated Submerged Bed Septic System Designs

Figure 5. Schematic of the anaerobic fluidized bed process used in Vegetated Submerged Bed Septic System Designs

Typical applications of Vegetated Submerged Bed Septic System Designs

AUFs are widely used in hot climates where domestic wastewaters are several times higher in strength than U.S. wastewaters. These systems can reduce high BOD and TSS to levels that can be readily treated by typical aerobic processes such as suspended and fixed growth aerobic units or recirculating/intermittent media filters. International literature contains numerous references to the three types of AUFs and their valuable contributions to water pollution abatement. Anaerobic rock upflow filters (figure 6) are also used to lower septic tank effluent BOD and TSS concentrations prior to discharge to the subsurface wastewater infiltration system (SWIS).

Figure 6. Anaerobic upflow filter for Vegetated Submerged Bed Septic System Designs

VSBs are extremely popular in the United States because of their aesthetic features and their ability to meet basic (secondary) effluent standards when treating septic tank effluent. Until recently they were purported to be capable of nitrification and nutrient removal at economically competitive HRTs. Since they are largely anaerobic, this would be biochemically impossible.

However, they are fully capable of meeting secondary BOD and TSS standards. They are also sometimes used before a SWIS and can meet the same effluent TSS and BOD standards as aerobic units (Technology Fact Sheets 1, 2, and 3). VSBs can be considered as pretreatment units regarding SWIS design requirements. They do not, however, remove more than 2 logs of fecal coliform and would likely require disinfection for direct surface discharge. They also require some form of aeration to meet effluent standards for dissolved oxygen (DO). These VSBs will capture rainfall and snowmelt, effluent standards for requiring adjustment to designs of SWIS following these units.

Both VSBs and AUFs are being used in rural areas in combination with aerobic processes to remove significant amounts of nitrogen through denitrification. These processes are included in the nutrient removal fact sheets.

Design assumptions for Vegetated Submerged Bed Septic System Designs

VSB design guidance for small communities is provided in table 1. In the first few months of operation, excellent phosphorus removal will occur until the rock medium becomes saturated with phosphorus and breakthrough occurs. (Note: USEPA guidance on design of VSBs can be found in Manual: Constructed Wetlands Treatment of Municipal Wastewater, posted at http://www.epa.gov/nrmrl/pubs/625r99010/625r99010.pdf)

Table 1. Summary of VSB Septic System Design Guide

Pretreatmenta Objective
Surface area
   BOD
   TSS
   TKN
   TP
Based on desired effluent quality and areal loading rates as follows:
6 g/m2-d (53.5 lb/ac-d) to attain 30 mg/L effluent
1.6 g/m2-d (14.3 lb/ac-d) to attain 20 mg/L effluent
20 g/m2-d (178 lb/ac-d) to attain 30 mg/L effluent
Use another treatment process in conjunction with VSB
VSBs not recommended for phosphorus removal
Depth
   Media (typical)
   Water (typical)

0.5 - 0.6 m (20 - 24 in)
0.4 - 0.5 m (16 - 20 in)
Length Minimum of 15 m (49 ft.)
Width As calculated
Bottom slope 0 - 1%
Top slope Level or nearly level
Hydraulic conductivity
   First 30% of length
   Last 70% of length

1% of clean K
10% of clean K
Media

   Inlet zone (1st 2 m [6.5 ft])
   Treatment zone
   Outlet zone (last 1 m [3.3 ft])
   Planting media (top 10 cm [4 in])

All media should be washed clean of fines and debris; more uniform rounded media will generally have more void spaces; media should be resistant to crushing or breakage.
40 - 80 mm (1.5 - 3.0 in)
20 - 30 mm (3/4 - 1 in) use clean K = 100,000, if actual K not known
40 - 80 mm (1.5 - 3.0 in)
5 - 20 mm (1/4 - 3/4 in)
Miscellaneous Use adjustable outlet control device with capability to flood and drain system and sizing of VSB and SWIS (if used) must include a water balance analysis
a Use after primary sedimentation (e.g., septic tank, Imhoff tank, primary clarifier); not recommended for use after ponds because of problems with algae.

Except for the anaerobic upflow rock filter, AUFs are rarely employed for U.S. onsite applications. Since the primary purpose of these systems is to improve the BOD and TSS of septic tank effluent, they are essentially physical processes.

Therefore, they must be designed to maximize their flocculation and sedimentation functions. Limited field studies indicate that successful removal of particulate BOD and TSS could be obtained with an average HRT between 16 and 24 hours, rounded media size of 1 to 2 inches or greater, and a means of periodically draining excess accumulated solids from the bottom of the unit. At higher temperatures, some partial digestion of accumulated organic solids occurs. This liquefaction may by accompanied by gas production. The amount and makeup of that gas depend on pH, wastewater constituents (e.g., protein, lipids, carbohydrates), sulfate, alkalinity, and other constituents.

Performance of Vegetated Submerged Bed Septic System Designs

VSB systems can treat septic tank effluent to a BOD of 20 to 30 mg/L, depending on the organic loading rate chosen. The VSB effluent TSS is almost always less than 30 mg/L. Some removal of all constituents (e.g., heavy metals, organic nitrogen and organic phosphorus, pesticides, and other toxic organics) can also be expected. Over and above these removals, there will be some small percentage of dissolved organic removal owing to anaerobic biological activity.

Rock AUFs after septic tanks have not been widely studied, but they appear to remove TSS by as much as 55 percent from septic tank effluent, while removing a similar percent of the BOD. Actual removals will depend on the specific fractions of particulate, colloidal, and soluble matter in the septic tank effluent. Little soluble or fine particulate removal is likely. Both systems will remove pathogens, with VSBs capable of removing from 1 to 3 logs (design average = 2 logs), while AUF removal is estimated to be closer to 1 log because of shorter HRTs.

Management needs for Vegetated Submerged Bed Septic System Designs

All of these anaerobic systems are passive in nature and require minimal O/M activity. AUF units may be constructed aboveground, but they usually are below the ground surface to provide insulation and protect against severe climatic conditions. The solid medium can be a coarse gravel or one of many commercially available synthetic media that will not easily clog with biomass. Access to inlet and outlet systems should be provided for purposes of cleaning and servicing. An easily accessible means to drain the unit and an effective alarm system should be provided.

VSB units are generally aesthetically pleasing additions to the landscape if sufficient area is available for their application. It is estimated that fewer than 4 hours per year will be required for O/M tasks, which will involve inspecting the system and making any adjustments required. Therefore, until more information becomes available, a site visit schedule of three to four times a year is suggested.

Residuals generate in VSB systems at a slow rate. Although the system inlet where most solids accumulate can be excavated or piped for high-pressure removal, it is more likely that a replacement system would be built after the service life of the original system ends.

AUF units will require periodic flushing of accumulated solids and inspection of inlet and outlet systems. If solids are allowed to accumulate, the filter may clog or release high solids "events" to the SWIS. This will clog the infiltrative surface or the distribution system. Therefore, a site visit schedule of three to four times per year is suggested until more information becomes available. This would entail from 6 to 8 hours per year of labor. Disposal and transport of excess solids will require similar management to septage.

Risk Management Issues Concerning Vegetated Submerged Bed Septic System Designs

VSB systems can usually handle the flow variations likely to occur from residential sources, as well as toxic shock loads and power outages. Reed and colleagues (1995) proposed some models to support the view that insulation provided by dead vegetation (litter) on the surface should aid these systems during typical winters in northern climates. The potential for odor is low for properly sized systems.

AUF systems should also accommodate typical flow variations, toxic shocks, and power outages. They should be insulated from cold weather. AUFs are inherently odor and corrosion generators, so corrosion-resistant materials should be employed. Odor (hydrogen sulfide) production may require the use of an odor-control system (e.g., soil filters) to deodorize off-gases.

Typical Costs of Vegetated Submerged Bed Septic System Designs

VSB systems for onsite application will cost about $20 per square foot (USEPA, 1999). Almost half of that cost is for the media, while excavation, liner, plants, control structures, and piping make up the rest. Operation and maintenance costs would run less than $100 per year if these services are professionally provided.

AUF systems are likely to cost about $1,000 to $1,500 per house, primarily related to the cost of the tank and related containment features. O/M costs would run around $200 per year, including solids transport as required.

Share this Article      

...

Technical Reviewers & References

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

SEPTIC SYSTEMS HOME
SEPTIC INFO ARTICLES
HOME BUYERS GUIDE to SEPTIC SYSTEMS
SEPTIC SYSTEMS ONLINE BOOK
SEPTIC PUMPING REPAIR
SEPTIC TREATMENTS
SEPTIC CONSULTANTS
SEPTIC AUTHORITIES
SEPTIC SYSTEM BOOKS REFS CODES
SEPTIC SYSTEM DESIGN MANUAL - Online
SEPTIC SYSTEM DESIGN BASICS
SEPTIC SYSTEM DESIGN ALTERNATIVES
  Wastewater Treatment Levels
  Wastewater Dispersal Methods
  Master List of Septic System Types
  AEROBIC SEPTIC SYSTEMS
  ALTERNATING BED SEPTIC SYSTEMS
  CESSPOOLS
  DRYWELLS
  SEPTIC EFFLUENT DISINFECTION SYSTEMS
  EVAPORATION-TRANSPIRATION SEPTIC SYSTEMS
  FIXED-FILM PROCESS SEPTIC SYSTEMS
  GRAVELLESS SEPTIC SYSTEMS
  GREYWATER SYSTEMS
  HOLDING TANK SEPTIC SYSTEMS
  LAGOON SYSTEMS
  GRAVITY/SIPHON DOSING SYSTEMS
    Methods of Effluent Distribution
    Bell Siphon Septic Dosing
    Dipping or Tipping Dosing
    Float Control Dosing Systems
    Products and Suppliers
  PRESSURE DOSING SYSTEMS
  HOW EFFLUENT IS DISTRIBUTED
  PRESSURE DOSING SPECIFICATIONS
  MANIFOLD DOSING SYSTEMS
  RIGID PIPE DOSING SYSTEMS
  DRIP DOSING SYSTEMS
  MEDIA FILTER SEPTIC SYSTEMS
  SEPTIC & GREYWATER FILTERS
  SEQUENCING BATCH SEPTIC SYSTEMS
  MOUND SEPTIC SYSTEMS
  RAISED BED SEPTIC SYSTEMS
  SAND BED SEPTIC SYSTEMS
  SEWAGE TREATMENT SYSTEMS
  TOILET ALTERNATIVES
  SEWAGE TREATMENT SYSTEMS
  TOILET ALTERNATIVES
  VEGETATED SUBMERGED SEPTIC BEDS
  WETLAND SEPTIC SYSTEMS
  ALTERNATIVE SEPTIC DESIGNERS
  ALTERNATIVE SEPTIC PRODUCTS

  • US EPA Onsite Wastewater Treatment Systems Manual - original citation epa.gov/nrmrl/pubs/625r00008/html/625R00008.htm and for vegetative submerged bed septics, see EPA http://www.epa.gov/nrmrl/pubs/625r00008/html/tfs5.htm
  • Septic Tank Soil Absorption Systems - Decentralized Sysetms Technology Fact Sheet, US EPA, EPA 932-F-99-075, September 1999 - original citation www.epa.gov
  • Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com
  • Victor Faggella, is a senior home inspector in New York and can be reached at Centurion Home Inspections, Inc. Mahopac, NY 10541. 845-628-0941 vjf@centurion-inspections.com The company has offices in Mahopac, NY, Woodbury CT., and Mansfield Center, CT.
  • Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
  • Rissy Plastics - Matt Cauthorn, Flout@engineer.com for text describing the Flout(TM) floating outlet valve dosing system control (see above).
  • InspectAPedia.com® - Daniel Friedman
  • Construction Guidelines for Gravity and Flood-Dose Trench Onsite (Septic) Systems, Indiana state health department
  • Maintenance of Low Pressure Distribution Septic Systems, Vermont Cooperative Extension
  • Dosing Gravity Drainfield Systems, Recommended Standards and Guidance for Performance, Application, Design, and Operation & Maintenance, Washington State Department of Health, July 1, 2007

References for Vegetated Submerged Bed Septic System Designs

Bauer, D.H., E.T. Conrad, and D.G. Sherman. 1979. Evaluation of Onsite Wastewater Treatment and Disposal Options. EPA/600/s2-81-178. U.S. Environmental Protection Agency, Cincinnati, OH.

Cowlter, J.B., S. Soneda, and M.B. Ettinger. 1957. Anaerobic contact process for sewage disposal. Sewage and Industrial Wastes Journal 29(4):468-477.

Crites, R., and G. Tchobanoglous. 1998. Small and Decentralized Wastewater Management Systems. WCB McGraw-Hill, San Francisco, CA.

DeRenzo, D.J. 1977. Energy from Bioconversion of Waste Materials. Noyes Data Corporation, Park Ridge, NJ.

Hamilton, J. 1975. Treatment of Septic Tank Effluent with an Anaerobic Filter. Master's of Science in Civil Engineering thesis, University of Washington, Seattle.

Hamilton, J. 1976. Proceedings of Northwest Onsite Wastewater Disposal Short Course. University of Washington, Seattle.

Jewell, W.J. 1987. Anaerobic sewage treatment. Journal of Environmental Science and Technology 21(1):14- 21.

Kennedy, J.C. 1979. Performance of Anaerobic Filters and Septic Tanks Applied to the Treatment of Residential Wastewater. Master's thesis, University of Washington, Seattle.

Lombardo & Associates, Inc. 1983. Design Report. Anaerobic Upflow Filters. Newton, MA.

Netter, R., E. Stubner, P.A. Wildner, and I. Sekoulov. 1993. Treatment of septic tank effluent in a subsurface biofilter. Water Science Technology 28(10):117-124.

Reed, S.C., R.W. Crites, and E.J. Middlebrooks. 1995. Natural Systems for Waste Management and Treatment. McGraw Hill, Inc, New York.

Switzenbaum, M.S. 1985. Proceedings of Seminar/Workshop-anaerobic Treatment of Sewage. Report No. Env.E. 88-85-5. University of Massachusetts, Amherst, MA.

Thaulow, H. 1974. Use of Anaerobic Filters for Onsite Treatment of Household Wastewater. Master's thesis, University of Washington, Seattle.

U.S. Environmental Protection Agency (USEPA). 1992. Wastewater Treatment/Disposal for Small Communities. EPA 625/R-92-005. U.S. Environmental Protection Agency, Cincinnati, OH.

U.S. Environmental Protection Agency (USEPA). 1993a. Nitrogen Control Manual. EPA 625/R-93/0010. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC.

U.S. Environmental Protection Agency (USEPA). 1993b. Subsurface Flow Constructed Wetlands for Wastewater Treatment: A Technology Assessment. EPA 832-R-93-008. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

U.S. Environmental Protection Agency (USEPA). 1999. Manual: Constructed Wetlands Treatment of Municipal Wastewater. EPA 625/R-99/010. U.S. Environmental Protection Agency, Cincinnati, OH

SEPTIC SYSTEMS HOME

More Information

InspectAPedia.comInspectAPedia ® Home & Site Map
InspectAPedia Blog - News Updates
Air Conditioning & Heat Pumps
Bookstore
Electrical
Environment
Exteriors
Heating
Home Inspection
Insulate Ventilate
Interiors
Mold Inspect/Test
Roofing
Plumbing Water Septic
Structure
Accuracy & Privacy Policies
Contact Us

More Information on Building Diagnostic Inspections and Repairs

InspectAPedia.comInspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.
GO TO the MOLD and INDOOR ENVIRONMENT INFORMATION CENTER for in-depth advice on avoiding testing for or cleaning up mold and other indoor environmental hazards, odors, gases, contaminants
The Mold Information Center:
What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
GO TO MOLD TEST KITS: This expert-recommended mold test kit is cheap and yet top performing *IF* you use a competent analysis laboratory!
Use this simple, economical mold test kit
by following our instructions on how to collect and mail mold samples to our lab
GO TO IAQ/MOLD-TEST LAB SERVICES: Mold, Pollen, indoor air quality, field and laboratory services by an expert.Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.
GO TO our PRE PURCHASE BUILDING INSPECTION SERVICES: Authoritative information for home buyers and home owners is included with your inspection.
Building Inspection, Problem Diagnosis
, Forensic Investigation & Testing, Repair Consulting

CONTACT Daniel Friedman - Dan is a senior ASHI home inspector, nationally recognized expert on building inspection, building failures, and sick building investigation
Contact Daniel Friedman for website content suggestions or for fee-paid consulting

10/23/2009 - 11/25/2006 - InspectAPedia.com/septic/Submerged_Septic_Beds.htm - © 2010 - 1988 Copyright Daniel Friedman All Rights Reserved - InspectAPedia® is a Registered U.S. Trademark