Risk analysis for constructed wastewater treatment wetlands: A decision-making tool for regulatory agencies concerning human health and ecological risks associated with constructed wetlands

Constructed treatment wetlands are vegetated ponds designed for water quality improvement. Carefully planned and operated, they have a great potential for wastewater treatment. The main opportunities for constructed wetlands are to improve stormwater effluent quality and to replace small sanitary wastewater systems. However, the risks these systems contain are still unclear and controversial. Therefore, risks associated with constructed wetlands are identified in this document, focusing on urban stormwater effluent and sanitary wastewater from small households. Potential risks are then classified into low, medium and high attention stressors through a nominal and relative model, based on their likelihood of occurrence and ease of rectification. Improvement options in the areas of wetland assessment, design, monitoring and long-term management are given in order to minimize risks. It was found that most risks and potential problems occurring in constructed wetlands are well manageable if the necessary precautions are taken. Therefore, this promising technology should be promoted. However, an analysis of the regulatory framework for constructed wetlands in Alberta (Canada) and Switzerland showed that not only the lack of knowledge in terms of risks, but also the lack of a sufficient legal framework poses a great barrier to the construction of treatment wetlands. To improve the regulatory situation, this document serves as a decision-making tool in the approval process. It does so in proposing a nominal intervention assessment that can be adapted to a specific wetland proposal and in providing improvement options for the operation and regulation of constructed treatment wetlands.