Resource efficient wastewater treatment in a developing area-Climate change impacts and economic feasibility

- Wastewater treatment by constructed wetland shows to be an energy efficient method in warm climate areas.
- Wastewater treatment by constructed wetland gives savings in greenhouse gas emissions compared to conventional treatment processes.
- When operated properly, wastewater treatment by constructed wetland is an economic method due to its energy saving and production.

Resource efficiency in wastewater treatment (WWT) is widely needed, not least in developing areas. Natural, less capital intensive processes in wastewater purification may offer developing economies an alternative to traditional biological processes. In this paper, we compare a constructed wetland (CW) based wastewater treatment plant to an activated sludge process (ASP) in Matamoros, Mexico. Greenhouse gas (GHG) emissions are calculated using life cycle assessment (LCA) and an economic viability assessment is carried out. Based on a literature review, both treatment methods are considered to produce sufficient treatment efficiency.Water hyacinth was chosen as the aquatic plant in the CW due to its fast growth rate and the possibility of using it in anaerobic digestion (AD) to produce energy and fertiliser for agricultural land. In our calculations, the biogas produced from the water hyacinth biomass is the decisive factor when the two methods are compared. Direct GHG emissions from both methods are of the same order and are dominated by the GHG releases from the purification phase. However, if the water hyacinth can be used for energy production, the CW-based WWT not only fares better in economic terms, but also produces significant net climate benefits. Both methods studied have their downsides, increasing the need for risk evaluation. Although water hyacinth's fast growth rate is a crucial factor in the analysis, careful management is needed when cultivating the plant, as it has led to serious problems due to uncontrollable spreading. Furthermore, environmental and health risks must be identified and managed properly if wastewater-derived digestate is to be used on arable land, as assumed in the analysis. Additionally, N2O leakages from the ASP and CH4 and N2O releases from the CW must be studied further to obtain reliable values for future analyses.

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