Cost Considerations

The primary advantages in using constructed wetlands to treat sewage effluent, particularly in rural locations, are the low technology and the reasonably inexpensive and safe method they provide for treating wastewater. The cost of each constructed wetland project will vary depending on a number of factors and these may include the needs of the user, the site location, the pollutant load and the amount of land available. There are, however, cost factors that can be useful to consider.

Constructed Wetland vs. Package Treatment

Research has shown that a conventional sewage treatment plant typically costs between two to ten times more than a constructed wetland system. For example, a conventional sewage treatment plant proposed for an oil refinery in North Dakota was estimated to cost between $1 million and $3 million dollars. The constructed wetland system that was built cost $250,000.

Space Constraints

The amount of land required to operate a constructed wetland system is considerably larger than that required for a conventional sewage treatment plant. The size will depend on the hydraulic loading rate of effluent per day, which is based on the number of users and the type and efficiency of the water delivery system, as well as the size of the lagoon used for primary treatment. Where land is scarce this cost is considerable but where land is readily available it becomes a minor cost factor.

Design and Construction

A constructed wetland is usually built in tandem with a sewage lagoon or some other primary treatment source and often the lagoon and the constructed wetland are bid for design together. The scope of work for these projects is highly variable, however beyond the engineering and design costs there are some specific considerations when placing a constructed wetland for sewage treatment in a community.

It is not always necessary to install an impermeable liner in the constructed wetland, however if such a liner is needed it would increase the construction costs. Moose and caribou hooves could easily puncture the lining, allowing untreated effluent to seep into the surrounding terrain. Human use of the area, such as travel by snowmachines or four-wheelers, could potentially impact the ability of the macrophytes to regenerate and colonize successfully and degredation of berms or other specifically engineered landscaping could cause the effluent flow in the constructed wetland to short circuit, thus reducing treatment. Depending on the resolution of these issues, a sturdy fencing system may be necessary and costs will vary with the size of the constructed wetland as well as material and installation costs.

Water Quality Testing

Once a constructed wetland is operational, followup water testing is essential to determine if the system is performing adequately to the State of Alaska DEC standards. The method of collecting water samples is specific and sampling may require followup site visits. The cost of analysis will vary depending on the parameters being tested. If test results indicate problems with the water quality, a professional consultation will be necessary to identify the cause and the cost of correcting the problem will vary depending on the situation.