DOI: 10.14457/tu.the.2015.155
title: A STUDY ON REMOVAL OF HEAVY METALS FROM WASTEWATER BY FLOATING PLANTS

description: Heavy metal contaminated water is the major environmental problem and has been increasing with the discharge of industrial wastewater untreated or partially treated. They affect human, fauna, and flora systems. The cost effective and environmental friendly technology, phytoremediation, uses plants to remove heavy metals from wastewater or to render them harmless. Water hyacinth (WH), Water lettuce (WL), Creeping waterprimrose (CM), Floating moss (FM), and Common duckweed (CD) were selected to study the Cd and Pb uptake. Screening of plants for Cd and Pb hyperaccumulators was conducted at 4 and 10 mg/L, respectively. To study the effect of heavy metals concentration on plants uptake, the concentration of Cd was varied from 5, 10, 20, 30, 40, 60, 80 and 100 mg/L, and 10, 30, 50, 70, 100, 200, 300 and 400 mg/L for Pb. Moreover, the effect of nutrients was also investigated by adding 3, 10, 20 and 30% of Hoagland’s nutrients solution to contaminated water with heavy metals. The heavy metals in water and plant samples were analyzed by ICP-OES. Based on the uptake, CM and WH were selected as Cd and Pb hyperaccumulator, respectively. FM was selected as both Cd and Pb hyperaccumulators. During the experiments, plants looked unhealthy with increasing metals concentration and exposure times (except WH at 10 and 30 mg/L of Pb, and FM at 10 mg/L of Pb), due to Cd and Pb toxicity which caused the relative growth reduction. However, they could remove heavy metals within short duration (1day). In Cd contaminated water, CM and FM were able to remove Cd within 6-8 days when the concentration increased from 5 to 100 mg/L. The Cd removal efficiency decreased when the concentration increased. At 5 mg/L, CM and FM could remove Cd 76.1 and 89.2%, respectively, and 39.7 and 53.2% were removed at 100 mg/L, respectively. Although Cd removal efficiency of plants was high, the Cd remained in water was still higher than the standard of industrial wastewater effluent. However, biomass productivity was high at the studied Cd concentration (up to 92.1 and 93.9% for CM and FM, respectively). The Cd accumulation in CM and FM increased with increasing Cd concentration, except Cd accumulation in FM at 100 mg/L. BCFs for plants indicated as moderate accumulators at concentration from 5 to 10 mg/L for CM and at concentration from 5 to 60 mg/L for FM, respectively. For other concentration, plants were poor Cd accumulator. In Pb contaminated water, the highest Pb removal efficiency of WH was found at 10 mg/L (98.3%). It can be noted that Floating moss at concentration from 10 to 100 mg/L, Pb was almost removed 100%. The lowest Pb removal efficiency was 32.8 and 61.3 % at 400 mg/L for WH and FM, respectively. The results also show that plants had high biomass productivity which was over 78% for WH and 89% for FM. The Pb accumulation in WH and FM increased with increasing concentration, expect at 100 mg/L for FM. BCFs show that FM could be moderate accumulator at concentration from 10 to 400 mg/L. In contrast, WH was the moderate accumulator at concentration from 10 to 70 mg/L and poor accumulator at other concentration. Based on the high removal efficiency of plants at 10 mg/L of Pb (including screening experiment), Pb removed by WH, CM, FM and Common duckweed could be discharged to environment without any treatment. For the effect of nutrients, the results show that it did not have any effect on heavy metals uptake by plants. CM (for Cd), WH (for Pb) and FM (for Cd and Pb) were selected to study the effect of nutrients.  Relative growth, biomass productivity, heavy metals removal efficiency, heavy metals accumulation and BCFs were not influenced by the amount of nutrients. A comparison of Cd and Pb at 30 and 100 mg/L, it indicates that Cd  was more toxic than Pb. Based on all results, the floating plants can uptake Cd and Pb, and also can be used as bio-indicators of water, especially CM (for Cd), WH (for Pb) and FM (for both Cd and Pb).