Does Duckweed Ponds Used for Wastewater Treatment Emit or Sequester Greenhouse Gases (GHG)?

R. H. R. Costa1* , G. Tonon1, R. A. Mohedano1, C.C. Teles1, S. R. Aguiar1 ,P. Belli Filho1 .
1 Federal University of Santa Catarina – UFSC/ CTC/ENS. Campus Reitor João David Ferreira Lima, s/n – Trindade, Florianópolis – SC. Postal code: 88040-900 – Brazil


Considering the problem of eutrophication in receiving water bodies, the duckweed ponds have shown a great potential for removing nutrients (N and P) from domestic and agroindustrial effluents. On the other hand, conventional treatment systems are also responsible for greenhouse gases (GHG) emission such as CO2 and CH4. Alternatively, duckweed ponds have been successfully used for polishing effluent and have become more popular in recent years because to the large capacity of these plants in nutrient removal and CO2 fixation. The present study aimed to evaluate the fluxes of greenhouse gases (GHG) emissions and carbon dioxide fixation by duckweed ponds applied to treat wastewater. To this, two pilot duckweeds ponds in series were operated with real wastewater with a flow rate of Beyond the common physicochemical parameters, the gases emissions from pond surface were measures by using a flux chamber according to method OM-8 by USEPA. The concentrations of CO2 and CH4 inside the chamber were measured by infrared probes. As results, during 123 days of monitoring, there was an important nutrient removal efficiency (TN = 92.6 % from 72.5 mg.L-1 and TP = 84% from f 8.1 mg.L-1), as well as organic matter (COD = 79% from 156.9 mg.L-1). The CO2 emission rate ranged from 3048 to 6017 mgCO2.m-2.d-1 and fixation rate ranged from 19592 to 42052 mgCO2.m-2.d-1. Methane emission was not detected (less than 0,1%) during  the whole study. The results showed that in presented conditions duckweeds ponds could fix at least three times more CO2 than emit.

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