Sponsored by Alan Schmidt

Program: Constructed Wetlands for Wastewater Treatment: A Nontechnical Overview

Speaker: James Lowery, previous Scientech Club speaker on Antarctica, the Wetumpka meteor crater, and the La Brea Tar Pits

Introduced By: Alan Schmidt

Attendance: NESC: 84; Zoom: 25

Guest(s): Bebe Axelrod, David Nimz                                                                                

Scribe: Dr. Alan Dale Schmidt

Editor: Bill Elliott

Talk’s Zoom recording found at: https://www.scientechclubvideos.org/zoom/10132025.mp4

James Lowery’s presentation explained an alternative wastewater treatment system that utilizes plants to naturally purify wastewater, including domestic wastewater, industrial wastewater, business building discharges, and stormwater.  He explained how plants clean wastewater and described the different types of constructed wetlands.  Wetlands are swamps, bogs, marshes, and other land that is underwater long enough to support plants that grow fully or partly in water.

There are willow trees that remove silver, ferns that thrive on arsenic, alpine herbs that hoard zinc, mustard plants that lap up lead, Indian Mustard plants that extract gold, clovers that eat oil, and poplar trees that destroy dry-cleaning solvents.  Poplar trees are so effective that people in the fast-growing “phytoremediation” business have a new name for them:  A stand of poplars is a self-assembling, solar-powered, pump-and-treat system. Wetlands duckweed is the smallest flowering plant and smallest fruit.  Wetlands feed oxygen to the bacteria through the plant roots, such as cattails and do not stink.  Anaerobic processes can be stinky.

There are documented cases of natural wetlands phytoremediation ameliorating mine drainage for zinc, iron, manganese, arsenic, cyanide, cadmium uranium, radium, copper, aluminum, lead, nickel, cobalt, and thallium in Canada, USA, and Australia.

Constructed wetlands are engineered systems designed to simulate the functions of natural wetlands for wastewater treatment. They use vegetation (duckweed, cattails, cypress trees, water hyacinths), soil, and microbial activity to remove contaminants from water.

Core Treatment Processes:

·       Sedimentation: Particles settle out of the water
·       Filtration: Media and plant roots trap solids
·       Microbial digestion: Bacteria break down organic matter.
·       Adsorption & Ion Exchange: Nutrients and metals bind to media surfaces.
·       Oxidation/Reduction: Chemical transformations of pollutants

Types of Constructed Wetlands:

·       Surface Flow Wetlands (SFW): Water flows over the soil surface, mimicking natural wetlands.
·       Subsurface Flow Wetlands (SSFW): Water flows below the surface through gravel or soil
·                Includes horizontal and vertical flow systems.
·       Hybrid Systems: Combine multiple types for enhanced treatment.

Design Components:

·       Liner: Prevents seepage
·       Inlet/Outlet Structures: Controls flow
·       Media Bed: Gravel, sand, or soil
·       Vegetation: Native plants preferred, organisms absorb & break down pollutants
·       Slope & Aspect Ratio: Influences hydraulic performance.  

Performance, Benefits, and Applications

Pollutant Removal Efficiency:

·       Reduces Biochemical Oxygen Demand (BOD)
·       Reduces Total Suspended Solids (TSS) sediment trapping.
·       Removes Nitrogen (Ammonia, Nitrate) nutrient removal.
·       Removes Phosphorus chemical detoxification.
·       Reduces Fecal Coliforms

Environmental and Operational Benefits:

·       Low energy use: Passive systems 40% of conventional cost
·       Minimal maintenance: Occasional media rinsing
·       No sludge production: Unlike mechanical systems
·       Wildlife habitat: Supports biodiversity.
·       Aesthetic value: Can be integrated into landscapes.

Limitations and Considerations:

·       Phosphorus removal may require specialized media.
·       Fecal coliform reduction often needs post-treatment.
·       Land area: Subsurface systems require less space but may have higher media costs.

Applications: Domestic wastewater, Industrial effluents, and Stormwater runoff

Site-specific factors: Climate, soil characteristics, and hydraulic loading rates can impact performance and must be carefully evaluated during system design. Additionally, regulatory requirements and ongoing monitoring may influence the choice and configuration of treatment wetlands.

                   James Lowery