Research On Phytoremediation For Pollution Control In Water Environment

In recent decades, urban wastewater contains increasingly higherconcentration of contaminants such as nitrogen, phosphorus andespecially heavy metals, which caused serious pollution problems inwaters. Phytoremediation offers a cost-effective, non-intrusive,environmental friendly and safe alternative to conventional cleanuptechniques. This technique was extensively used in constructed wetlandsfor wastewater treatment, which particularly would be a promising fieldfor China. Constructed wetland is potentially a low-cost solution to treatdomestic and industrial wastewater in developing countries. Thoughphytoremediation is developed fast recent years, there are still manyproblems to be solved. In this study, we used hydrophytes as constructedwetlands to treat urban wastewater and electroplating wastewater,involving the aspects of selecting wetland species, mechanism ofphytoremediation, adjusting conditions of wetland ecosystem andapplication of strengthening measure. The major results and conclusionare summarized as below:1. Total nitrogen (TN), total phosphorus (TP), biological oxygendemand (BOD₅), chemical oxygen demand (COD) and heavy metals (Cd,Cr, Pb) concentration of urban heavy metal sewage in both planted andunplanted pots were detected to evaluate whether this ornamental hydrophytes (Reinekea carnea, Acorus gramineus, Alisma orientale,Acorus calamus, Iris pseudacorus and Lythrum salicaria) can be used inscavenging urban heavy metal wastewater. Results showed that most ofthe ornamental hydrophytes adapted to the heavy metal wastewater well,and were fairly efficient in scavenging BOD₅, COD, TN, TP and heavymetals (Cr, Pb, Cd) in the wastewater. However, the efficiency varied alot for various species to different contaminants, Iris pseudacorus andAcorus gramineus were good choices for decontaminatingcomposite-polluted water such as urban heavy metal sewage. On theother hand, interaction of different components in the wastewater mighthave had some effects on phytoremediation.2. In order to evaluate the decontaminant ability of by tenhydrophytes (Typha minima, Phragmites australis, Lythrum salicaria,Arundo donax var. versicolor, Juncus effusus, Pontederia cordata,Cyperus alternifolius, Typha orientalis, Acorus calamus, Iris pseudacoruset al.), a model constructed wetland experiment was conducted to studythe growth of plants in electroplating wastewater and the improvedefficiency of constructed wetland by these plants. Results showed thatLythrum salicaria, Phragmites australis and Iris pseudacorus are suitableto remove heavy metals in electroplating wastewater in constructedwetlands.3. Floating bed technology was used to study the growth of plants in electroplating wastewater and the improved efficiency of constructedwetland by these plants, in order to evaluate the decontaminant ability ofby nine aquatic weeds (Eichnornia crassipes, Alternanthera philoxcroide,Commelina commelis, Setcreasea purpurea, Lolium perenne, Oenanthedecumbens, Leersia hexandra, Verena hybrida, Ophiopogon bodinieri etal.). The results showed that Oenanthe decumbens and Eichnorniacrassipes are suitable to remove heavy metals in electroplatingwastewater in constructed wetlands.4. Tolerance of hydrophytes are exhibited in keeping good conditionin root growth, root activity and enhancing antioxidative enzyme activityto avoid or lower the damage of heavy metal in electroplating wastewater.5. Mechanism of absorption and translocation of metals byhydrophytes was studied on Lythrum salicaria, Phragmites australis andIris pseudacorus using Inductively Coupled Plasma EmissionSpectrometry. The results indicated that most of the Cr, Fe and Zn wereaccumulated in the root of plants, while the translocation from roots toaboveground of Cu are easy in plants; Phragmites australis emphasizeparticularly on phytoextraction, Lythrum salicaria on rhizafiltration andIris pseudacorus on accumulation in roots.6. FTIR was also used to understand the mechanism of absorptionand translocation of metals by hydrophytes in present study. The spectraof cell wall of Cr-treated root and control of Eichhornia crassipes and Alternanthera philoxeroides were determined directly with FourierTransform Infrared (FTIR) spectrometry and OMNI-sampler. Absorptionpeaks were identified to the corresponding functional groups andhalf-quantitative analysis was also used. The results showed that asignificant shift of—OH absorption peaks can be seen when comparingthe FTIR spectra of control and Cr-treated plants, absorbency of—OHand COO- groups went up in E. crassipes root cell wall while drop in A.philoxeroides root cell wall. It is suggested that—OH and COO^- groupswere referred in binding Cr⁶⁺ in aqueous solutions, and it may be includedin the mechanism of Cr accumulation in E. crassipes roots. Therefore,FTIR spectrometry could be widely used to monitor changes in chemicalcomposition of plant parts under stresses and environmental restoration.7. Effect of organic acids on mobilization of Cr and Zn inelectroplating wastewater and plants was also studied. In this experiment,thcitric acid, oxalic acid and tartaric acid were applied in the constructedwetland planted with Canna glauca L.. Results indicated that 4～8 mmol/L thcitric acid and 8 mmol/L tartaric acid are available in enhancingthe removal efficiency of Cr and Zn in electroplating wastewater.8. Biomass, chlorophyll content, F_v/F_m, antioxidative ability as wellas Cr ⁶⁺ removal efficiency are studied on Eichhornia crassipes underdifferent pH conditions. Results indicated that pH had effects on plantnutrition and the Cr ⁶⁺ removal efficiency, the most suitable pH was at 3.