Shallow pond systems planted with Lemna minor treating azo dyes

•Basic Red 46 was successfully treated in the laboratory-scale shallow ponds.•The small molecular weight of simple Basic Red 46 and neutral pH enhanced uptake.•Low removal efficiencies for Acid Blue 113, Direct Orange 46 and Reactive Blue 198.•Ponds containing Lemna minor outperformed corresponding algae and control ponds.•L. minor and algae growth were inhibited by the presence of any of the four dyes.

A higher demand on textile materials has resulted in an increase of the number of textile factories particularly in the developing world, which consequently negatively effects the environment due to their contaminated effluents. Textile effluents are highly coloured and mixed with different chemicals and pollutants. Shallow pond systems are a promising, cheap and effective technique for the treatment of contaminated wastewater. The aim of this study is to assess the performance of pond systems vegetated by Lemna minor L. (duckweed) for textile dye removal under controlled laboratory conditions. The key objectives of this study are to assess the influence of design variables on water quality parameters, the dye and chemical oxygen demand (COD) removal of dyes, and the effect of dye accumulation as a function of the relative growth rate of L. minor. Findings indicate that the simulated shallow pond system (as a polishing step) is able to remove only Basic Red 46 (BR46) in low concentrations, and ponds containing L. minor significantly (p < 0.05) outperformed algae-dominated ponds and control ponds. The simple chemical structure, absence of sulpho-group and small molecular weight associated with neutral pH values enhanced the capacity of the uptake of BR46 molecules. Furthermore, the total dissolved solid concentrations were within the threshold set for discharge to the aquatic environment.

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