Abstract
This study compares the performance of simulated
shallow ponds vegetated with Lemna minor L. under controlled
and semi-natural conditions for the treatment of simulated
wastewater containing textile dyes. The objectives were
to assess the water quality outflow parameters, the potential of
L. minor concerning the removal of chemical oxygen demand
(COD) and four azo dyes (Acid blue 113, reactive blue 198,
Direct Orange 46 and Basic Red 46) and the plants’ growth
rate. Findings show that all mean outflow values of COD, total
dissolved solids (TDS) and electrical conductivity (EC) were
significantly (p < 0.05) lower within the outdoor compared to
the indoor experiment except the dissolved oxygen (DO). The
COD removal was low for both experiments. The outflow
TDS values were acceptable for all ponds. The pond systems
were able to reduce only BR46 significantly (p < 0.05) for the
tested boundary conditions. Removals under laboratory conditions
were better than those for semi-natural environments,
indicating the suitability of operating the pond system as a
polishing step in warmer regions. The mean outflow values
of zinc and copper were below the thresholds set for drinking
and irrigation waters and acceptable for L. minor. The dyes
inhibited the growth of the L. minor.