the use of some aquatic plants to improve the effluents of an aerated lagoon system more

THE USE OF SOME AQUATIC PLANTS TO IMPROVE THE EFFLUENTS OF AN AERATED LAGOON SYSTEM. Hussein E. Tuleibah2, Mohamed A. M. Salem1, Ahmed A. M. Khalafallah2 and Hany A. E. El Gerum2 1 Ismailia Waste water Treatment Plant, Ismailia, Egypt. 2 Botany Department, Faculty of Girls for Arts, Science & Education, Ain Shams University, Egypt. Corresponding author: salemm32@yahoo.com ABSTRACT Pilot-Scale study was conducted at the outlet of Ismailia Wastewater Treatment Plant in Egypt, to determine the efficiency of some aquatic plants and to improve the quality of the effluents. Their efficiency in upgrading the lagoon effluents was studied over a period of one year. This was done through studying the efficiency of three aquatic plants individually and in series. The three plants which were used are the common reed (Phragmites australis); Water Hyacinth, (Eichhornia crassipes) and the duckweed (Lemna gibba). The results showed that BOD5, COD, TSS, nutrients and heavy metals contents were reduced significantly through using of these plants individually and in series. Also, the algae species and their numbers in the lagoon effluents were reduced significantly due to nutrients uptake competition with these higher plants. The produced effluents after the pilot study have an excellent quality and can be used safely in agriculture or for discharge on an aquatic environment. Keywords: Aquatic plants - algae - wastewater treatment - BOD5 – Fecal coliform INTRODUCTION Ismailia Wastewater Treatment Plant was established in 1996 at Serapeum area, Ismailia governorate. The Plant type is an aerated lagoon system. It depends mainly on the mechanical aeration of the sewage to activate the aerobic bacteria, which break down the organic substances to inorganic minerals. The algae are playing an important role in the final stage of the treatment process. The algae take the inorganic substances and give the oxygen to the water through the photosynthetic activity and the produced effluents have a good characteristic. Some studies were carried out in the past for evaluating the performance of Ismailia waste water treatment plant, concerning the removal efficiency of different pollutants [Abdel-Shafy, and Salem, 2007]. These studies showed that the plant performance is variable with the different seasons. The plant efficiency reduces in the winter compared with the other seasons, where the bacterial activity is reduced. The long retention time of the system is playing an important role in improving the physico-chemical and microbiological characteristics of the effluents. In the summer, the long retention time results in algal blooming in the effluents. Sarkar and Chattopadhyay, [2003 ] demonstrated that the high concentrations of algae in the lagoons can be followed by an increase of pH values up to 10. This can severely hamper or damage the biocenosis both in the lagoons and in sensitive receiving waters with small or intermittent flows. As a consequence, protein degradation is induced and foaming can be observed in the effluent as well as in the receiving water during times of high photosynthetic production. Furthermore, algae in the effluent show up in the form of suspended solids and exert an oxygen demand on the receiving stream by bacterial degradation. Thus, algae should be removed in order to meet the sensibility of the biocenosis in small receiving waters. To solve this problem in many countries, the corrected BOD5 and TSS are considered to avoid the effect of algae, where a definite value is subtracted by theoretical equation depends on the measurement of chlorophyll A.. In other countries, many methods are used to upgrade the effluents of lagoon systems, such as rock filters, gravel filters, sand filters, or by using some aquatic plants such as water hyacinth, reed plants, or duckweed. In Aquatic plants, the competition for nutrients uptake is grown up and the higher plants take up the most available nutrients. The chance of algae is reduced to get the food and their huge growing. These experiments proved that all the treated waste water characteristics are improved well and with an excellent quality [Middlebrooks, 1995]. Contamination of the aquatic environment by the heavy metals has become a serious concern in the developing world. Heavy metals unlike organic pollutants are persistent in nature, therefore, tends to accumulate in the different components of the environment. The heavy metals are highly toxic to the aquatic plants and animals as well as do not vanish easily from the environment. Their treatment usually requires removal through some technology. The technologies used for their treatment are reverse osmosis, ion exchange, electro dialysis, adsorption, etc. Most of these technologies are quite costly, energy intensive and metal specific [ Bodar et al.,2006]. Contrary to this phytoremediation, i.e. removal of pollutants by the use of plants offers a promising technology for heavy metals removal from waste water. Aquatic plants have great potential to accumulate heavy metals inside their bodies. These plants can accumulate heavy metals 100,000 times greater than in the associated water. Therefore, these aquatic plants have been used for heavy metal removal from a variety of sources. The aquatic plants are thought to remove metals by three patterns (a) metals are restricted from entering the plant and attaches to the cell wall (b) metals are accumulated in the root, but translocation to the shoot is constrained (c) hyper accumulators, metals are concentrated in the plant parts. The hyper accumulative capacities of the aquatic plants are beneficial for the removal of heavy metals [Liu et al., 2008]. The capacity for wastewater purification by both natural and artificial wetlands is well documented. Wetlands remove aquatic pollutants through a complex variety of biological, physical and chemical processes. The major mechanisms for pollutant removal in these wetland systems include bacterial transformations and physico-chemical processing including adsorption, precipitation and sedimentation. The higher plants play an important role in wastewater purification. The plant rhizome provides surfaces for bacterial growth as well as for filtration of solids. More importantly, plants are known to translocate oxygen from the shoots to the roots [Evangelou et al.,2007]. The rhizosphere or root zone will therefore offer an oxidized micro-environment in an otherwise anaerobic substrate, which stimulates both the decomposition of organic matter and the growth of nitrifying bacteria, the latter which can convert ammonia to nitrate. The nitrate so formed can then diffuse or percolate through to the oxygen-poor zones where it will be removed from the system by dentrification [Cao et al,2007]. MATERIALS AND METHODS. 1-Ismailia wastewater treatment plant description The plant has been in operation since 1996. It is located 15 Km to the south of Ismailia city. The plant has facilities to measure flow, screening, sand removal and that is followed with two parallel treatment series; each designed for 45,000 m3/day, with a total design flow of 90,000 m3/day. Each one consists of an aerated lagoon, an aerated facultative lagoon and a polishing lagoon. Earthen berms form the walls of lagoons and a synthetic liner prevents sewage from entering groundwater [EPA, 1971]. Effluent structures with control weirs are provided at the end of the aerated facultative and polishing lagoons to collect sewage from the surface layers and to maintain the water depth. Effluent is discharged by gravity to El-mahsama drain. 2- Purifier Hydrophytes Experiment Design: The final wastewater effluent pipe was divided into two branches. Duplicate 40 L plastic tanks used for each species of plant and were connected to one of the effluent pipes .Three types of plants were used as purifier hydrophytes and are floating plants as Duckweeds, emerged plants Eichornia, marginal plants as Reed plants (phragmites). and the phytoremediator plants applied by two designs: 1- Each plant in separated tanks. 2- The three plants in a series as water flows with a constant Analytical Methods 1-Physico-chemical and Bacteriological Analyses Sampling: The sampling regime to evaluate the plant and pilot study performance included 24 hrs weighed composite samples and grab samples. The composite samples were used to analyse the parameters TSS, VSS, TDS, BOD5 and COD. The grab samples were used to analyse the parameters: trace metals, mineral salts, TKN, ammonia, nitrate, chlorophyll A, total phosphorus, orthophosphate, pH, T. alkalinity and fecal coliform bacteria. All the physical, chemical and bacteriological analyzed were determined according to Standard Methods for Examination of Water and Wastewater [APHA, 1995]: pH, Total Suspended Solids (TSS; filtration at 45 µm and drying at 103–105oC), Biological Oxygen Demand (BOD5; polarization method), ammoniacal nitrogen (NH4–N); preliminary distillation step, KCl and MgO, with titrimetric method), total phosphorus (total P, persulfate digestion method, colorimetry with vanadomolibdo- phosphoric acid). Heavy metals were measured using the Inductively Coupled Plasma- Emission Spectrometry (ICP-ES) with Ultra Sonic Nebulizer (USN). This Nebulizer decreases the instrumental detection limits by 10%. The ICP is Perkin Elmer optima 3000, USA. The samples were filtered by filtration system through membrane filter of pore size 0.45 um before analyses. Bacteriological analyses, fecal coliform of water samples were determined using membrane filter technique. Chlorophyll a concentration: was determined through the following equation [APHA, 1995]: Chlorophyll a (Ca) = 11.85 E664 – 1.54 E647 – 0.08 E630 Where: E664 = O.D664 – O.D750, E647 = O.D647 – O.D750, E630 = O.D630 – O.D750. O.D664, O.D647 and O.D630 are the optical densities readings at the wave lengths 664 nm, 647 nm and 630 nm respectively. The final calculation of chlorophyll a content is given by the following formula: Chlorophyll a (mg/L) = Ca X V’ V”X N Where: V’ = Volume of 90% acetone extract in ml, V” = Volume of sample filtered in ml N = light path length in cm (1cm) RESULTS AND DISCUSSION I- The plant removal efficiency During the period from January 2007 to December 2007, based on a monthly sampling regime, the plant performance was evaluated. The plant was receiving raw sewage with a mean of 104196 m3/d . The mean retention time (HRT) was 7.4 day. The dissolved oxygen was increased through the system and the mean was 7.3 mg/l in the effluent. The total dissolved solids (TDS) content was increased in the effluent, due to the high evaporation rate from the lagoons surface. Organic load removal The overall removal efficiency of organic load in the system was 74 % of BOD5, 74.2 % of COD, 88.5 % of VSS and 89.1 % of TSS . The statistical analysis showed that there was a very strong (+ve) correlation between TSS and VSS (r=0.97; p<0.05), indicating that the algae were responsible for increasing TSS in the effluent. Also, there was a (+ve) correlation between retention time and BOD5, TSS, VSS and Chlorophyll A (r = 0.45, 0.39, 0.41 and 0.41; p<0.05), respectively. Nutrients (Nitrogen and Phosphorus) removal The removal efficiency of TKN and ammonia in the system was 22.6 and 9.3%. The reason for low removal efficiency of ammonia could be the insufficient supply of oxygen demand. However, the surface aerators may did not supply enough dissolved oxygen to oxidize the released ammonia and other products of the anaerobic digestion in the bottom of the lagoon. Another reason was the weak activity of nitrifying bacteria. Therefore, the released ammonia from the anaerobic digestion was not oxidized to nitrate. Also, this low removal efficiency is due to the presence of anaerobic zones in the polishing lagoon bottom. Li et al., [1991] concluded that the algae had the most significant effects on the removal of nutrient salts. When the bacterial colony prevailed over the algal colony, the ammonia in water tended to increase and subsequently the ammonia in the effluent became higher than that in the influent, i.e. with negative removal of ammonia. However, when the algal colony was dominant, the ammonia in water tended to decrease and that in the effluent was correspondingly less than that in the influent, i.e. with positive removal of ammonia. In addition, ammonia in the polishing lagoon, under favourable pH condition, can be converted to ammonia nitrogen, which then leaves the liquid phase as ammonia gas into air due to the large lagoon surface area and long retention time. Mara and Pearson [1987] reported that ammonia concentration above 28 mg/l is toxic to algae with the pH range experienced during daylight hours in the lagoons. Ammonia becomes more toxic above pH 8, since a larger proportion is then in the unionized NH3 state, which rapidly penetrates the algal cell. Inhibition of photosynthesis by high ammonia can cause polishing lagoons to become slightly anaerobic, even when the BOD surface loading is low. The orthophosphate also increased due to biodegradation of polyphosphate by microorganisms. Our results showed also that there was no removal efficiency of total phosphorus in the polishing lagoon . The overall removal efficiency of phosphorus and orthophosphate in the system was -33.4 and -39.5 % respectively . Li et al. [1991] stated that the negative removal of orthophosphate was due to the conversion of phosphorus by bacteria. They concluded that there is a dynamic equilibrium of phosphorus in the lagoons system, i.e. the transition between organic and inorganic phosphorus and the precipitation in the lagoon. Horan [1990] reported that the factors affecting the growth of nitrifying bacteria, are: the substrate content, temperature, D.O and pH. The results showed that the increase in temperature was correlated with decrease in ammonia and alkalinity and increase in orthophosphate. The orthophosphate increased due to the acceleration of biodegradation of polyphosphate by microorganisms. The increase in pH and D.O was correlated with a decrease in the ammonia. Heavy metals removal The mean removal efficiencies of the heavy metals cadmium, chromium and mercury, were 33.3, 100 and 66.7 %, respectively. On the other hand, no removal efficiencies took place for nickel, lead, copper, zinc, cobalt and manganese [Table: 1]. The removal mechanism occurs mainly by precipitation and microbial activity. The pH value of water is very important, as it affects the solubility of the metal hydroxides and the kinetics of the oxidation and hydrolysis processes. Metallic ions tend to precipitate as hydroxides at high pH values. The relationship between pH and heavy metals removal is extremely complex, as it is different for each metal and for biotic and abiotic processes. The availability of dissolved oxygen will affect oxidation processes and microbial activity. Heavy metals that are present may be associated with the suspended solids via adsorption to their surfaces [Maynard et al., 1999]. Faecal coliform removal The overall removal efficiency of the system varied from 96.3750 to 99.9928 % and the mean was 99.5762 %. However, the system does not comply with the national regularity standards (≤ 5000 cfu/100 ml). The present results showed that the faecal coliform bacteria were little reduced with the increase of retention time (r =-0.15; p< 0.05). Pearson et al. [1996] found that increasing the depth of maturation pond (= polishing lagoons) in order to increase the retention time, leads to decrease the removal efficiency for faecal coliforms. The depth of the polishing lagoon in our system is 3.5 m, which is inconvenient to achieve a good removal. Meanwhile, the depth of 1.5 m was recommended by Mara et al. [1992]; the shallower lagoons are more effective in pathogen removal. Tertiary treatment by using aquatic plants The data which recorded in Table 1 indicated that the treated water of the final effluent has good physical properties (Temperature, pH, T. alkalinity and TDS), in addition these properties slightly affected when treated by using three aquatic plants in three separated basins (Lemna gibba, Eichhornia crassipes and Phragmites australis) or by using a serial of the three plants in three connected basins. Lemna gibba and Eichhornia crassipes nonsignificantly decreased DO from 7.3 mg/L to 6.1 and 6.8 respectively, while Phragmites australis and the series of the three plants approximately did not affect the DO concentration of the treated water. Nitrates when treated by using aquatic floating plants (Lemna gibba and Eichhornia crassipes) were reduced by 9 and 14.3% respectively, but when treated using emergent plants (Phragmites australis) and a series from the three plants were reduced by 25.4 and 41.3% respectively. Chlorophyll A represents an indication on density of algal flora in the treated water. Chlorophyll A concentration significantly reduced in the treated water by using aquatic plants, the lowest reduction recorded when used Lemna gibba plants (83.8%) while the maximum reduction recorded by using Phragmites australis plants and the series from the three plants (100%). Pandy [2001] reported that algal growth is suppressed by duckweed because of competition for both sunlight and nutrients; it has also been hypothesized that the rhizosphere complex may secrete organic substances which suppress and kill algae cells. The present results indicated that Phragmites australis plants are strong competitor to algal flora than Lemna gibba plants due to their height and their dense vegetation. Table (1): Physic-chemical characteristics of the final effluents of the aerated lagoons system and the effluents of the pilot study. (Mean ± standard deviation and range). Locations Final effluent Lemna gibba Eichhornia crassipes Phragmites australis Three plants in series Temp 0C D.O mg/l pH 7.4 ± 0.1 (7.1- 7.6) 7.5 ± 0.1 (7.3- 7.8) T. alkalinity mg/l 255 ± 20 (225 - 283) 255 ± 21 (220 - 285) 252 ± 20 (220 - 280) 251 ± 21 (218 - 278) 250 ± 21 (216 - 278) TDS mg/l NO3-N Chlorophyll A mg/l mg/l 0.08 ± 0.03 (0.02- 0.12) 0.013 ± 0.011 (0.001- 0.04) 0.001 ± 0.0 (0.001- 0.002) 0.0 ± 0.0 (0.0- 0.001) 0.0 ± 0.0 (0.0- 0.0) 22.9 ± 4.5 7.3 ± 0.4 (16.1 - 29) (6.5 – 7.8) 6.1± 0.4 22.7 ± 4.4 (5.5 – 6.5) (16 - 29) 22.7 ± 4.4 (16 - 29) 585 ± 71 12.6 ± 4.1 (498 - 682) (6-20) 11.4 ± 3.7 581 ± 72 (6-19) (490 - 680) 573 ± 73 (480 - 675) 565 ± 73 (475 - 660) 538 ± 182 (495 - 680) 10.8 ± 3.3 (6-18) 9.4 ± 3.2 (4-17) 7.4 ± 2.3 (4-12) 6.8 ± 0.3 7.7 ± 0.1 (6 – 7) (7.5- 7.9) 7.1 ± 0.2 22.7 ± 4.4 7.8 ± 0.1 (6.8 – 7.5) (16 - 29) (7.5- 7.9) 22.7 ± 4.4 (16 - 29) 7.2 ± 0.2 7.9 ± 0.1 (7 – 7.5) (7.67- 8) Table 2 showed that the tertiary wastewater treatment by using aquatic plants is effective in removing TSS, VSS, BOD5, TKN, T-P and fecal coliform. Lemna gibba plants significantly reduced the above mentioned parameters by 33.5, 31.0, 45.0, 52, 7.9, 33.3 and 19% respectively, these efficiencies is low when compared to the efficiency of Phragmites australis plants in reducing the same parameters (80.5, 91.7, 84, 71.7, 53, 45 and 50% respectively). Eichhornia crassipes plants have moderate efficiency in reducing these parameters; however these parameters were reduced by 50.0, 49.7, 62.7, 65.0, 35.4, 40.5, and 31.0% respectively. The reduction efficiency of these parameters maximized when using the three plants in a series with the following order, Lemna gibba, Eichhornia crassipes and Phragmites australis, the reduction percentage of these parameters were 88.5, 93.6, 96.7, 77.2, 70.1, 54.8 and 59.9% respectively. Falabi [2002]reported that fecal coliform could be reduced by 62% of domestic wastewater by using duckweed plants and Zimmo et al., [2005] found that higher phosphorus removal efficiency was achieved in the duckweed system than in the algae system.El -Shafai et al., [2007] recorded that the removals of COD, BOD and TSS from the anaerobic effluent bed to three duckweed ponds reached about 64%, 73% and 43%, during the warm season and 72%, 75% and 63% in the winter, respectively. Rousseaua et al., [2004] found that reed plants in vertical flow (VF) wetlands reduced COD, TSS, TN, and TP, by 94%, 98%, 52% and 70% respectively. Solano et al. [2004] found that using two plants, cattail (Typha sp.) and reed (Phragmites sp.) in constructed wetland are more efficient in removal of BOD, COD and TSS. In this respect, the present study recommended using Phragmites australis plants or a series from the three plants in tertiary water treatment. The high efficiency of reed plants, duckweed and water hyacinth in removal or decreasing pollutants is due to their ability to oxygenate the rhizosphere, however, Brix, [1997] reported that roots and rhizomes of reeds and all other wetland plants are hollow and contain air-filled channels that are connected to the atmosphere for the purpose of transporting oxygen to the root system. The majority of this oxygen is used by the roots and rhizomes themselves for respiration, but as the roots are not completely gastight, some oxygen is lost to the rhizosphere. The differences in the removal efficiencies in the present study and the previous studies may be due the differences in system design, climate, and behavior of plants in the different geographical provinces and concentration of the pollutants in the wastewater. Table (2): Removal efficiency of the pilot study. (Mean ± standard deviation, range and removal %). TSS mg/l Final effluent Lemna gibba Eichhornia crassipes Phragmites australis Three plants in series VSS mg/l BOD5 mg/l TKN NH4-N T-P Fecal coliform mg/l mg/l mg/l cfu/100 ml 32.5 ± 25.4 ± 2.1 4.2 ± 0.5 4 x 103 ± 2 x 103 11.7 (20-28) (3.4-5.2) (1.1 x 103-8 x 103) (18-52) 15.5 ± 6.7 (9-30) 52 % 11.3 ± 4.8 (6-20) 65 % 9.2 ± 4.7 (5-19) 71.7 % 7.4 ± 3.6 (4-15) 77.2% 23.4 ± 1.4 (20-25) 7.9 % 16.4 ± 2.3 (12-20) 35.4 % 11.9 ± 1.7 (8-14) 53 % 7.4 ± 0.8 (6 - 8) 70.1 % 2.8 ± 0.7 (1.6-4.2) 33.3 % 2.5 ± 0.6 (1.5-3.3) 40.5 % 2.3 ± 0.5 (1.4-3) 45 % 1.9 ± 0.3 (1.3-2.6) 54.8 % 3.4 x 103 ± 1.7 x 103 (1 x 103-6 x 103) 19 % 2.9 x 103 ± 1.7 x 103 (0.5 x 103-5.5 x 103) 31 % 2.1 x 103 ± 1.2 x 103 (400 - 4.2 x 103) 50 % 1.7 x 103 ± 1.1 x 103 (300 -3.8 x 103) 59.9 % 20 ± 3 15.7 ± 2 51 ± 31 (16-25.5) (12 – 19.5) (9.6 - 101) 13.3 ± 3 (8-18) 33.5 % 10 ± 3 (5-14) 50 % 3.9 ± 1 (2-6) 80.5 % 2.3 ± 1 (1-4) 88.5 % 10.8 ± 3 (6 – 16) 31 % 7.9 ± 2 (4 – 12) 49.7 % 1.3 ± 1 (0.5 – 2) 91.7 % 1.0 ± 0 (0.4 – 2) 93.6 % 28 ± 17 (8 - 60) 45 % 19 ± 12 (4 - 40) 62.7 % 8±4 (2 - 15) 84 % 2±1 (2 - 4) 96.7 % The data which recorded in the Table 3 represents the mean values of heavy metals in the final effluent water of the treated plant and tertiary treated water by using aquatic plants and their removal efficiency. The data indicated that Cd, Ni, Cu, and Mn were found in very low concentrations. The used aquatic plants have been successfully removed the heavy metals from the treated water, this ability maximized when used the three plants in series to 100% for the most heavy metals. Lemna gibba and Eichhornia crassipes have moderate ability in removing Cd metals (50%), in addition, Hg removed by 62.5% from the total concentration when treated by Lemna gibba plants. The recorded data indicated that Phragmites australis plants are best plants in removing the studied heavy metals when compared to Lemna gibba and Eichhornia crassipes, while using the three plants in series was more effective. Table (3): Heavy metals removal efficiency of the pilot study. (Mean, range and removal %). Cd mg/l Final effluent 0.0002 (0 0.0006) 0.0001 (0 0.0001) 50 % 0.0001 (0 0.0001) 50 % 0.000 (0 0.0001) 100 % 0.0 (0 - 0) 100 % Ni mg/l Hg mg/l Pb mg/l 0.045 (0 - 0.04) Cu mg/l 0.015 (0-0.02) Zn mg/l 0.113 (0.07-0.159) Mn mg/l 0.017 (0.01-0.02) 0.007 0.2 (0- 0.021) (0.1 - 0.4) Lemna gibba Eichhornia crassipes Phragmites australis Three plants in series 0.0008 0.075 0.0008 0.0008 0.0035 0.001 (0- 0.001) (0.0 - 0.1) (0.0001-0.001) (0.0001-0.001) (0.07-0.159) (0.0001-0.002) 88.6 % 62.5 % 98.2 % 94.7 % 96.9 % 94.1% 0.0008 0.0028 (0- 0.001) (0 - 0.01) 88.6 % 98.6 % 0.0003 (0 - 0.001) 99.3 % 0.0006 0.0013 0.0006 (0.0001-0.001) (0.001-0.002) (0.0001-0.001) 96 % 98.8 % 96.6 % 0.0001 (0.00010.0001) 99.9 % 0.0001 (0- 0.0001) 99.9 % 0.0001 (0.00010.0001) 99.4 % 0.0000 (0- 0.0001) 100 % 0.0001 0.0001 0.0001 0.0006 (0- 0.0001) (0-0.0001) (0 - 0.0001) (0.0001-0.001) 98.6 % 99.9 % 99.8 % 96 % 0.0001 0.0 0.0 (0- 0.0001) (0-0.0001) (0 - 0.0001) 98.6 % 100 % 100 % 0.0001 (0- 0.0001) 99.3 % The ability of the used aquatic plants in removing heavy metals may be due to their uptake with water absorption and accumulation in plants tissues or through metal precipitation however, Maynard et al., [1999] reported that the availability of dissolved oxygen will affect oxidation processes and microbial activity. Heavy metals that are present may be associated with the suspended solids via adsorption to their surfaces. Phytoremediation using vegetation to remove, detoxify, or stabilize heavy metal pollutants is an accepted tool for cleaning polluted soil and water [Cheng et al., 2002]. The studied plants were successfully used previously in removing heavy metals from the wastewater, Lokeshwari and Chandrappa [2006] found that water hyacinth plants accumulated high concentration of Cr in their tissues in proportion to Zn. Zayed [1998] concluded that duckweed shows promise for the removal of Cd, Se, and Cu from contaminated wastewater since it accumulates high concentrations of these elements. Furthermore, the growth rates and harvest potential make duckweed a good species for phytoremediation activities. Lesage et al., [2007] reported that Phragmites australis was the best plant species adapted to tannery wastewater in terms of survival and propagation among three plans examined. 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