Yes the combination of two or more plant species will improve removal efficiency in constructed wetlands treating domestic waste water. Eichhornia crassipes, Hydrilla verticillata, Lemna minor, Nelumbo nucifera etc. like aquatic plants can be used in combination for domestic  waste water treatment.

Please check the following links for more information on the subject.

http://fourthcornernurseries.com/the-use-of-aquatic-plants-to-treat-waste-water/

There are some publications discussing about this issue, and looks like it is still controversial. Recently, I have just conducted a series of experiments to answer this question, though it is not completely finished yet, I can say it's not a "yes" or "No" results, in another word, it depends. 

I mean it depends on many factors, like the plant species, target contaminants, environmental conditions, etc. Example 1, plant A+Plant B might be better than any of them separately, but plant A+plant C might not be better than plant A and Plant C separately. Example 2, Plant A+Plant B might showed better result for TN, but this conbination might not be always better for TP or COD. Example 3, when the environmental conditions like the temperature change, the effectiveness of the combination of two plant species might depend more on the habit (their response of temperature change), if they are complementary, then this combination is probably better than single plant. 

hi Mr. Lahbib,

i had experience with constructed wetlands, combining 2 different species in one constructed wetlands is almost always had better efficiency than just using one species. different plants species means different  physiological characteristic, and microclimate characteristic. as long as you used complementary species you could get maximum efficiency in treating domestic wastewater.

as we know many plants having ability to degrading pollutants in many different wastewater characteristic, but we mus admit that constructed wetlands is a complex system, not only plants that contribute in degrading the pollutants in wastewater, but also microorganism that living in that system, so it's not "absolute" depending on the plants ability actually, but also depending on how the plants initiate the interactions between plants-wastewater and plants-microorganism to treat the wastewater,

regards :)

 My answer is “Yes”.  In my opinon, it is a good choice to combine 2 or more different species in one constructed wetlands，which  had better efficiency than just using one species. Different plants species means different  physiological characteristic, and microclimate characteristic. as long as you used complementary species you could get maximum efficiency in treating domestic wastewater. Also, it is beacauce of that different plant species had their own  best efficiency in removing pollutants in differrent season, we can obtain synergistic effects. 

Dear All,

I would like to thank you very much for your answers and suggestions.

L Latrach

hi.

I had experience with constructed wetlands, combining 4 different species[ in oEichhornia ,Lemna, Lemna minor , Pistia.]one constructed wetlands .