Constructed wetlands are an appropriate technology for wastewater treatment in small communities. Appropriate technologies must be affordable, operable with local labor and resources, and reliably meet effluent standards. However, many small communities have inappropriately used activated sludge systems that are difficult to operate and maintain. Constructed wetlands, stabilization ponds, slow sand filters and land treatment systems fit the criteria of being affordable and operable treatment options for small communities. Constructed wetlands may require additional treatment processes to meet certain effluent standards for nutrients, and can be used alone or in combination with other appropriate technologies depending on treatment goals.

1.
Constructed Wetlands
Appropriate technology
for small communities

2. Constructed Wetlands
Appropriate technology for small communities
Appropriate technology is defined as a treatment system which meets the following key criteria:
Affordable ‐ Total annual costs, including capital, operation, maintenance and depreciation are within
the user’s ability to pay.
Operable ‐ Operation of the system is possible with locally available labor and support.
Reliable ‐ Effluent quality requirements can be consistently meet.
Unfortunately, many rural areas of the U.S. with small treatment plants (usually defined as treating less
than 3,800 m3/d (1 mgd)) have failed to consider this appropriate technology definition, and have often
adopted inappropriate technologies such as activated sludge. In 1980, small, activated sludge systems
constituted 39% of the small publicly owned treatment facilities. Recent information from one state
showed that 73% of all treatment plants of less than 3,800m3/d capacity used some form of the
activated sludge process. Unfortunately, the activated sludge process is considered by almost all U.S.
and international experts to be the most difficult to operate and maintain of the various wastewater
treatment concepts. Presently, small treatment plants constitute more than 90% of the violations of U.S.
discharge standards. At least one U.S. state, Tennessee, has required justification for the use of
activated sludge package plants for very small treatment plant applications.
Small community budgets become severely strained by the costs of their wastewater collection and
treatment facilities. Inadequate budgets and poor access to equipment, supplies and repair facilities
preclude proper operation and maintenance (O&M). Unaffordable capital costs and the inability to
reliably meet effluent quality requirements add up to a prime example of violating the prior criteria for
appropriate technology. Unfortunately, no consideration for reuse, groundwater recharge, or other
alternatives to stream discharge has heretofore been common, except in a few states where water
shortages exist.
Presently there are a limited number of appropriate technologies for small communities which should
be immediately considered by a community and their designer. These include stabilization ponds or
lagoons, slow sand filters, land treatment systems, and constructed wetlands. All of these technologies
fit the operability criterion, and to varying degrees, are affordable to build and reliable in their
treatment performance. Because each of these technologies has certain characteristics dNd
requirements for preand post‐ treatment to meet a certain effluent quality, they may be used alone or
in series with others depending on the treatment goals.
For example, the designer may wish to supplement stabilization ponds with a tertiary system to meet
reuse or discharge criteria consistently. Appropriate stabilization pond upgrading methods to meet
effluent standards include FWS wetlands, which can provide the conditions for enhanced settling to
attain further reduction of fecal coliforms and removal of the excess algal growth which characterizes
pond system effluents. FWS wetlands are normally used after ponds because of their ability to handle
the excess algal solids generated in the ponds. Although VSBs have been employed after ponds, excess
algal solids have caused problems at some locations, thus defeating the operability factor in the

3. appropriate technology definition. VSBs are more appropriately applied behind a process designed to
minimize suspended and settleable solids, such as a septic or Imhoff tank or anaerobic lagoon.
Constructed wetlands may also require post‐treatment processes, depending on the ultimate goals of
the treatment system. More demanding effluent requirements may require additional processes in the
treatment train or may dictate the use of other processes altogether. For example, the ability of
constructed wetlands to remove nitrogen and phosphorus has frequently been overestimated. Two
appropriate technologies that readily accomplish ammonium oxidation are intermittent and
recirculating sand filters. There is at least one case study of the successful use of a recirculating gravel
filter in conjunction with a VSB. FWS systems can both nitrify and denitrify, thus removing significant
portions of nitrogen from the wastewater, by alternating fully vegetated and open water zones in
proper proportions. If the municipal facility is required to have significant phosphorus removal (e.g., to
attain 1 mg/L from a typical influent value of 6 to 7 mg/L), constructed wetlands will need to be
accompanied by some process or processes that can remove the phosphorus.
In conclusion, constructed wetlands are an appropriate technology for areas where inexpensive land is
generally available and skilled labor is less available. Whether they can be used essentially alone or in
series with other appropriate technologies depends on the required treatment goals. Additionally, they
can be appropriate for onsite systems where local regulators call for and allow systems other than
conventional septic tank ‐ soil absorption systems.