Constructed wetlands are more economic to build and operate than conventional (mechanical) wastewater treatment systems, and there is an increasing move to consider them. However, although they are widely used in cold climates, winter operability often presents problems, and constructed wetlands normally only remove part of any nutrients (nitrogen and phosphorus compounds) in wastewaters being treated in them. What was needed was a new type of constructed wetland which removed nutrients as well as it did other contaminants, which operated better in cold weather, and which was able to handle especially difficult-to-treat wastewaters. The answer may be found with engineered wetlands, a type of constructed wetland in which process conditions and/or operations are modified, manipulated and/or controlled. Engineered wetlands have technical and economic advantages over conventional constructed wetlands. This paper presents mesocosm results for a pilot scale engineered wetland and demonstrates that ammonia nitrogen and phosphate removals can be increased by up to an order of magnitude using the engineered wetland configuration.).