Water Science & Technology Vol 55 No 1-2 pp 121–128 © IWA Publishing 2006 doi:10.2166/wst.2007.030

Effect of external organic matter on nutrient removal and growth of Phragmites australis in a laboratory-scale subsurface-flow treatment wetland

A.K. Karunarathna^*, N. Tanaka^** and K.B.S.N. Jinadasa^*

Coconut dust, which is used intensively in horticultural applications, was tested as an external organic additive in a series of laboratory-scale subsurface-flow constructed wetlands planted with Phragmites australis. The systems were fed with a mixture of NO^-₃‐N, NH⁺₄‐N, and SRP in tap water to simulate high nutrient loads. In the absence of plants, TN removal efficiency was 66%, and the efficiency increased to >80% in the microcosm wetlands. TN and NO^-₃ removal efficiencies were marginally increased by coconut-dust treatment in comparison with sand-bed microcosms. Analysis by ANOVA showed that the TN removal from a coconut dust-supplemented sand-bed microcosm was significantly different from a sand-bed microcosm (0.0437 < p<0.05). All the systems showed an equal capacity to treat NH⁺₄ nitrogen under low influent concentration levels. Phosphorus removal efficiencies were >98% in all three systems, and a difference between planted and unplanted systems was not observed. Shoot height and shoot densities of P. australis grown in the coconut dust-supplemented medium were significantly higher than those grown in the sand-bed medium. The difference in P. australis growth in response to the coconut dust addition revealed that the added material has the potential to create favourable conditions for plant growth.

Keywords: ANOVA model; coconut dust; denitrification; organic carbon; phosphorus sorption

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