Presentation on theme: "Constructed Wetlands pp.117-121. CIDWT Disclaimer These materials are the collective effort of individuals from academic, regulatory, and private sectors."— Presentation transcript:
Constructed Wetlands pp.117-121
CIDWT Disclaimer These materials are the collective effort of individuals from academic, regulatory, and private sectors of the onsite/decentralized wastewater industry. These materials have been peer-reviewed and represent the current state of knowledge/science in this field. They were developed through a series of writing and review meetings with the goal of formulating a consensus on the materials presented. These materials do not necessarily reflect the views and policies of the Consortium of Institutes for Decentralized Wastewater Treatment (CIDWT). The mention of trade names or commercial products does not constitute an endorsement or recommendation for use from these individuals or entities, nor does it constitute criticism for similar ones not mentioned.
NDWRCDP Disclaimer This work was supported by the National Decentralized Water Resources Capacity Development Project (NDWRCDP) with funding provided by the U.S. Environmental Protection Agency through a Cooperative Agreement (WPA No. X-830851-01-0) with Water Environment Research Foundation (WERF) in Alexandria, Virginia. These materials have not been reviewed by the U.S. Environmental Protection Agency, NDWRCDP, or WERF. The contents of these materials do not necessarily reflect the views and policies of the NDWRCDP, WERF, or the U.S. Environmental Protection Agency, nor does the mention of trade names or commercial products constitute their endorsement or recommendation for use.
Learning Objectives Upon completion of this chapter, you should be able to: 1. Understand the treatment process in constructed wetlands. 2. Understand the relationship between hydraulic detention time and the quality of the effluent. 3. Understand and be able to accurately complete Operational Checklist 7-3. Constructed Wetlands (CW).
Constructed Wetlands Recreate the treatment processes that occur in natural wetlands
Constructed Wetland Basin/cell containing microorganisms, media and plants that provide treatment of incoming effluent Effluent flows horizontally through the bed
Treatment The pathogens and nutrients entering the system are removed by microbes living on the surfaces of the media and plant roots Processes such as sedimentation, nitrification, denitrification, and adsorption help in removing pathogens and nutrients.
Hydraulic Detention Time The amount of time effluent is in contact with and in the treatment media The longer the wastewater is in the wetland… the better the quality of the exiting effluent! Typical warm weather design 3 days Typical warm weather design 3 days Typical cold weather design 10 days Typical cold weather design 10 days
Detention Time An average daily flow of 390 gpd and the CWS is 10’ x 43’ x 1.5’ of operating depth and 25% void space. What is the detention time? 10’x 43’x 1.5’x 0.25 x 7.5 g/ft 3 = 1209 gal 1209 gal ÷ 390 gpd = 3 days (3.1)
Operation and Maintenance Form 7.3 Operational Checklist: Constructed Wetland (CW)
Layout One Cell One cell that provides treatment One cell that provides treatment Lined- used as a pretreatment component Lined- used as a pretreatment component Multiple Cells Flexibility for flow changes Flexibility for flow changes Second cell can be unlined- used as the final treatment and dispersal component- Should be treated as a Soil treatment option Second cell can be unlined- used as the final treatment and dispersal component- Should be treated as a Soil treatment option
1. Constructed wetland Cell # : ___/___ Evaluate the wetland system one cell at a time and use a new sheet for every cell.
1. Constructed wetland (cont.) a.Media: None None Gravel, Average Diameter: in Gravel, Average Diameter: in Other : Other : Note the type of media and size of media
1. Constructed wetland (cont.) b. Flow regime: Surface Subsurface Combination Identify the type of wetland system being used c. Distribution: Pressure Gravity
2. Conditions at the constructed wetland a.Evaluate presence of odor within 10 feet of perimeter of system: None Mild Strong Chemical Sour b. Source of odor
2. Conditions at the constructed wetland (cont.) c. Type of border material: d.Border material in good repair
2. Conditions at the constructed wetland (cont.) e. Evidence of water/soil entering wetland f. Fence present and operable
2. Conditions at the constructed wetland (cont.) g.Animal activity at wetland surface g.Animal activity at wetland surface Prevent pets from digging in the wetlands, destroying vegetation, and moving substrate and mulch.
Water Level Control As wastewater flows through the media, it exits through a water level control sump A water level control device allows water levels to be raised or lowered as needed to prevent overflow and maintain enough effluent for plant growth
3. Water level management a. Header distribution plugged Maintain water at wetland inlet below media surface. Solids may accumulate at wetland inlet
3. Water level management (cont.) b. Water level control option available Maintain the water level in the bed during extended periods of no flow (e.g., long vacations).
3. Water level management (cont.) Check adjustable standpipe or hose in the water level control structure to ensure that effluent is not leaking from joints. Repair as necessary.
3. Water level management (cont.) c. Water level adjustment needed Adjust wastewater level using the pipe/tubing in the water level control structure.
4. Vegetation a.Is species appropriate Check the vegetation for signs of disease or other stress Yellowing Yellowing Browning Browning Withering Withering Spots Spots Prevent excessive shading
5. Effluent quality Effluent quality monitored to determine system performance Turbidity Turbidity Clarity Clarity Oily film Oily film Dissolved Oxygen Dissolved Oxygen pH pH Temperature Temperature Color and Odor of exiting effluent Color and Odor of exiting effluent
6. Additional tasks for subsurface flow wetlands a.Media surface level Standing water on the substrate surface is the probable cause of objectionable odor.
6. Additional tasks for subsurface flow wetlands (cont.) b.Water level below media surface: in
6. Additional tasks for subsurface flow wetlands (cont.) Excessive flows above the design basis Clogging of the substrate by excessive solids from the septic tank Roots that have blocked the under drain
7. Additional tasks for recirculating wetlands a.DO in recirculation tank: b.Inspected recirculating device c.Cleaned recirculating device
7. Additional tasks for recirculating wetlands (cont.) d. Design recirculation ratio: e. Actual recirculation ratio: f. Recirculation changed to: *If dam configuration, recirculation device cannot be inspected or cleaned