Simultaneous removal of nitrate and sulphate from greenhouse effluent by artificial wetlands.
Gruyer, N., Dorais, M., Alsanius, B.W., and Zagury, G.J. (2013). "Simultaneous removal of nitrate and sulphate from greenhouse effluent by artificial wetlands.", Journal of Environmental Quality, 42(4), pp. 1256-1266. doi : 10.2134/jeq2012.0306 Access to full text
This study evaluated the effectiveness of C-enriched subsurface-flow constructed wetlands in reducing high concentrations of nitrate (NO3−) and sulfate (SO42−) in greenhouse wastewaters. Constructed wetlands were filled with pozzolana, planted with common cattail (Typha latifolia), and supplemented as follows: (i) constructed wetland with sucrose (CW+S), wetland units with 2 g L−1 of sucrose solution from week 1 to 28; (ii) constructed wetland with compost (CW+C), wetland units supplemented with a reactive mixture of compost and sawdust; (iii) constructed wetland with compost and no sucrose (CW+CNS) from week 1 to 18, and constructed wetland with compost and sucrose (CW+CS) at 2 g L−1 from week 19 to 28; and (iv) constructed wetland (CW). During 28 wk, the wetlands received a typical reconstituted greenhouse wastewater containing 500 mg L−1 SO42− and 300 mg L−1 NO3−. In CW+S, CW+C, and CW+CS, appropriate C:N ratio (7:3.4) and redox potential (−53 to 39 mV) for denitrification resulted in 95 to 99% NO3− removal. Carbon source was not a limiting factor for denitrification in C-enriched constructed wetlands. In CW+S and CW+CS, the dissolved organic carbon (DOC)/SO42− ratios of 0.36 and 0.28 resulted in high sulfate-reducing bacteria (SRB) counts and high SO42− removal (98%), whereas low activities were observed at DOC/SO42− ratios of 0.02 (CW) to 0.11 (CW+C, CW+CNS). On week 19, when organic C content was increased by sucrose addition in CW+CS, SRB counts increased from 2.80 to 5.11 log[CFU+1] mL−1, resulting in a level similar to the one measured in CW+S (4.69 log[CFU+1] mL−1). Consequently, high sulfate reduction occurred after denitrification, suggesting that low DOC (38–54 mg L−1) was the limiting factor. In CW, DOC concentration (9–10 mg L−1) was too low to sustain efficient denitrification and, therefore, sulfate reduction. Furthermore, the high concentration of dissolved sulfides observed in CW+S and CW+CS treated waters were eliminated by adding FeCl3.
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