DOI: 10.14457/tu.the.2017.233
title: A study on removal of lead (Pb) from synthetic wastewater by submerged aquatic plants

description: Heavy metals contaminated water is the one of the important water pollution problems in Thailand. Improper wastewater treatment and management are resulting in contamination of groundwater, surfacewater, and drinking water. Humans are exposed to the metals by ingestion or inhalation and they can be accumulated in living organisms causing various diseases and disorders. Aquatic plants were discovered to be phytoaccumulator for metal contaminated water environment, especially lead (Pb). Hydrilla verticillata (L.f) Royle, Ceratophyllum demersum L., Limnophila heterophylla, Hygrophila difformis (L.f.) Bi, and Echinodorus amazonicus were selected to study the Pb uptake. Screening of plants for Pb hyperaccumulators was conducted at 10 mg/L as lead nitrate [Pb(NO3)2] supplemented with  10%  Hoagland’s nutrients solutions for 11 days. To study effect of Pb concentration on plants uptake, the concentration of Pb was varied from 20, 40, 60, 80, and 100 mg/L. Moreover, the effect of nutrients and amount of plants at 20 and 40 g were also investigated by adding 10 and 20% of Hoagland’s nutrients solution to contaminated water with 10 mg/L of Pb concentration. Pb concentration in water and plant samples were analyzed by ICP-OES. Screening of plants for Pb hyperaccumulators, C. demersum, and L. heterophylla, showed Pb removal of 86.97 and 83.43%, respectively, after day 11th. The highest concentration of lead was found in C. demersum (6269.6 mg/kg DW) and L. heterophylla (5171.7 mg/kg DW). Based on the uptake, C. demersum, and L. heterophylla were selected for further study. C. demersum, and L. heterophylla looked unhealthy with increasing metals concentration and exposure time, due to Pb toxicity which caused the relative growth reduction. However C. demersum could remove Pb more than 80% within short period of time (1 day). Whereas L. heterophylla could remove Pb more than 40% at day 1. They were able to remove Pb within 10-14 days when the concentration increased from 20-100 mg/L. BCFs show that C. demersum and L. heterophylla could be moderate accumulator at concentration from 20-100 mg/L. Even though these two species could remove Pb in the contaminated water more than 90% at concentration 10-100 mg/L, but Pb concentration in water was still higher than the standard of industrial wastewater effluent and their appearance was changed due to increasing concentration. They completely died when exposed to Pb 60-100 mg/L. Thus, the tolerant of these two plants to Pb should not exceed more than 40 mg/L as the plant health is also important concern. Nutrients concentration employed in this study did not have much effect on heavy metals uptake by plants. Relative growth, heavy metal removal efficiency, heavy metal accumulation, and BCF were not influenced by amount of nutrient. Increasing mass of plant between 20 and 40 g supplemented with 10 and 20% of Hoagland’s nutrient solution, it was found that Pb concentration in water was lower than the industrial wastewater effluent standard (&lt;0.2 mg/L) when the mass of C. demersum was 40 g supplemented with 10 and 20% of Hoagland’s nutrient solution. Similarly, 40 g of L. heterophylla supplemented with 10% Hoagland’s nutrient solution could remove Pb from wastewater to lower than 0.2 mg/L as well. It can be summed that high biomass can result in higher uptake by plants. Additionally, plants looked unhealthy due to oxygen deficiency in the medium when time increased. Thus, larger containers should be employed. These results indicated the potential application of C. demersum and L. heterophylla for phytofiltration of lead by constructed wetland or introducing these plants into the contaminated water bodies.