Influencia de los tipos de regímenes terapéuticos

between pH, dissolved oxygen and chloride concentrations with contaminant treatment efficiencies within tested ICW mesocosms. Three advanced statistical tools (PCA, RDA, and SOM) were subsequently employed to carry out further investigations of subtle relationships. Findings showed that dissolved oxygen concentration and conductivity can be linked to treatment efficiencies of NH4-N, MRP, and COD. Furthermore, redox potential values related

to MRP and COD removal. Temperature and pH values contributed to the treatment of NH4-

N and (NO3+NO2)-N. The key results associated with all four techniques were similar.

However, this is likely to be a coincidence related to this particular case study.

Although no reduction of the overall performance has been found in the multi-cellular ICW sites 7 and 11 over an operational period of 15 years, the long-term performance of individual

cells and the cascading transfer of intercepted contaminants is less known. Wetland aging, which might cause the loss of contaminant removal, is seen as a perceived challenge for their management. Scholz et al. (2007) calculated theoretical desludging frequencies between 9 and 46 years (mean of 23 years) for six ICW systems located in Ireland. However, based on this laboratory research study, a much higher desludging frequency of about 5 to 10 years for the first wetland cell might be more appropriate. Alternatively, other management strategies including a change in vegetation and water depth as well as dewatering or allowing the first wetland cell to dry out in summer could also be tested.

3. Conclusions

(1) Findings suggest that the treatment performance of mature wetland were relatively poor and the mesocosms acted rather as contaminant sources than sinks. Due to long-term operation and high nutrient loads entering the full-scale ICW systems, contaminants accumulated within the sediment layer at the base of the first wetland cell. However, contaminants may remobilize when environmental and chemical conditions change. As to maintain the effectiveness of ICW systems, sustainable sediment management such as entire sediment removal from the first wetland cell is recommended if a saturation point (i.e. wetland becomes a source for contaminants) has been reached.

(2) The relationships between physico-chemical parameters and contaminant treatment efficiency were sequentially investigated using four statistical tools (multiple regression, PCA, RDA, and SOM). The obtained results provided complementary information for the retention and/or release processes inside ICW systems.

(3) No reduction in treatment performance has been found in the multi-cellular ICW sites 7 and 11 according to monitoring results. In addition, the operational conditions are well controlled for laboratory-scale ICW systems. Therefore, the application of these findings to the management of the long-term operating ICW system is limited. The full-scale ICW dataset should be further analyzed to improve the tested techniques and models. However, the results still provide valuable warning hints regarding decreasing treatment efficiency in long- term operating ICW systems.

Acknowledgements

We wish to acknowledge the technical support and assistance by Ms. Susan Cook (Waterford County Council), Mrs. Tanya Peshkur (The University of Edinburgh), Mr. Shane Doolin (The University of Edinburgh), Mr. Gerard Noone (The University of Edinburgh), and Ms.

Morgane Biehler (Ecole de Biologie Industrielle, France). Funding for Mr. Yu Dong’s PhD study was provided by The University of Edinburgh and the China Scholarship Council (CSC).

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The influence of clogging on effluent water quality and performance of