The Hierarchical Mosaic of Aquatic Ecosystems (HMAE ®) was originally developed in Belgium by applying the ecological adaptations of hydrophyte plants to flooded and polluted conditions. The system consisted of a stabilization pond (stage I) followed by a semi-aquatic ecosystem planted with helophytes (stage II) and by a terrestrial ecosystem (stage III) where ligneous species are planted. An HMAE ® experimental system net treatment area of 9.4 m 2 per one equivalent inhabitant (e.i.) showed a high average performance for SS (66.5%); COD (89%); BOD 5 (87.5%) and fecal bacteria (99.997%). The decrease of the treatment area of 2.8 m 2 /e.i. showed a average high performance for SS (75%); COD (80%); BOD 5 (82%) and fecal bacteria (99.9%). An HMAE ® system was built in Bustillo de Cea (Leon, northwest of Spain) and their removal efficiency was studied. Organic matter, nutrients and fecal bacteria were fortnightly analyzed. The whole system showed removal efficiencies in start-up as high as 98% for solids, 95% for BOD 5 and up to 99.99% for fecal bacteria.

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The viability of Parascaris equorum eggs was studied in two experimental pilot-scale high-rate algal ponds (HRAPs) working in parallel with 4 and 10 days hydraulic retention time respectively. Semi-permeable bags of cellulose (15000 daltons pore size) were used to study the effect of physico-chemical conditions on the survival of these helminth eggs. Three thousand eggs were used in each bag. Replicates of these bags were submerged for 4 and 10 days in the HRAPs and egg viability was compared with that in control bags submerged in sterile water. After 4 days exposure, 60% reduction in viability was achieved, reaching 90% after 10 days, much higher than the 16% and 25% found in the control bags for 4 and 10 days respectively. Ionic conditions of the HRAP may have been responsible for up to 50–60% of the egg mortality, suggesting that mortality due to the ionic environment could be more important than physical retention and other potential removal factors.

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Research into a constructed wetland for wastewater treatment using M.H.E.A. (Hierarchical Mosaic of Artificial Ecosystems) pilot system was carried out over a vegetative period in 8 different flow and vegetable composition series. The system consisted of a free water pond as a first step working as primary treatment followed by a zone with Typha sp. and surface flow and finally a woody zone with a subsurface flow and planted with ligneous species (Salixsp., Populus sp., Fraxinus sp. and Alnus sp.). Removal efficiency in the study reflects an optimal result: 80-99% total suspended matter removal, 82-98% organic matter removal, 70-98% nutrients removal and up to 99.9% faecal bacterial disinfecting. Effluent characteristics were in accordance with European Union legislation criteria for wastewater treatment systems.