Effectiveness of constructed wetlands on water quality improvement at the National Hydraulic Research Institute of Malaysia lake

The use of biological method of constructed wetlands to improve water quality of freshwater bodies in developing countries especially those in the tropical region with high water quality issues have been underutilized and reported. Therefore, the objective of this study is to establish the baseline water quality parameters concentrations of the NAHRIM lake, assess the effectiveness of the constructed wetlands in improving the water quality of the lake as well as determining the level of improvement in the water quality. Sampling and laboratory analysis of the lake water, constructed wetland water, sediment and plant samples were conducted according to the standard water, sediment and plants laboratory methods. Quality control and assurances were used to ensure the accuracy of the methods. ANOVA and Pearson correlation, in addition to water, sediment, plants indices were used to understand the parameters studied. The results shows the total mean concentration of dissolved oxygen (DO): 6.77±1.4mgL-1, chemical oxygen demand (COD): 10.13±1.5mgL-1, biochemical oxygen demand (BOD): 4.54±0.62mgL-1, total suspended solids (TSS): 12.89±5.12mgL-1, total coliform (8671±1762CFU/100mL), Fe (1.33±0.62mgL-1), Mn (0.26±0.09mgL-1) and Al (0.19±0.08mgL-1) of water samples in the lake to be between the national water quality standard class I and II, and exhibited significant difference (p<0.05) across the sampling sites. The total mean concentration of COD (20.51±3.4mgL-1), biochemical oxygen demand (5.04±1.8 mgL-1), total suspended solids (53.91±23.72mgL-1), pH (6.51±0.62mgL-1), E. coli (6330±2053.23CFU/100mL), total coliform (65700±21884.4CFU/100mL) and Al (8.16±3.5mgL-1) also shows a significant difference (p<0.05) in water samples across the wetland sampling sites. COD and BOD are in a strong positive significant correlation (r = 0.700**). Fe (7499.14±762.03mgkg-1), Al (4753.24±990.8mgkg-1), Mn (85.10±25.3mgkg-1), Zn (15.74±4.17mgkg-1), Cr (14±2.73mgkg-1), Pb (3.11±0.78mgkg-1), Ni (2.30±0.41mgkg-1), Cu (1.56±1.1mgkg-1) and Cd (0.90±0.22mgkg-1) also revealed a significant difference (p<0.05) in the sediment samples of the wetlands while Al and Fe (r = 0.933**), Cr and Ni (r = 0.84**), Cu and Fe (r = 0.886**) exhibited a very strong positive correlations. Ten heavy metals were observed for plants samples with total mean concentration of Fe (3338.5±3082mgkg- 1), Al (1071.91±944.6mgkg-1), Mn (240±143.07mgkg-1), Zn (25.94±17.21mgkg-1), Ba (13.6±12.1 mgkg-1), Cr (2.8±1.97mgkg-1), Cu (1.86±1.33mgkg-1), Ni (1.00±0.91mgkg-1), Pb (0.8±0.71mgkg-1) and Cd (0.78±0.17mgkg-1) across their tissues. Thalia sp., Cyperus papyrus, Nelumbo nucifera have the best phytoremediation potential for the heavy metals. As compared with the previous study of the lake water pre-constructed wetlands period, with a reported mean of Water Quality Index (WQI) class III (63.01) status, there is an improvement in the water quality due to the achievement of the WQI class II (86.01) status suitable for recreation. This is attributed to the constructed wetland through its accumulation of more contaminants before they get to the lake. Thus, this study suggests that constructed wetlands improve water quality; and this method can be replicated in other lake.

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