Potential of Echinodorus Cordifolius and Vallisneria Natans in Constructed Wetlands for the Removal of Water Pollution from Shrimp Farm Effluent

Management of shrimp aquaculture wastewater is still the major problems in fisheries. Objectives of this study are to set up laboratory-scale wetlands to evaluate the phytoremediator performance of Echinodorus Cordifolius and Vallisneria Natans in improving aquaculture wastewater as a treatment technology from the first day, 3 days, 7 days, 10 days, 14 days, 17 days and 21 days. The controlled and experimental design setup describes both constructed wetland by glass tank sizes with a circulation system. The controlled wetland dones’t have plants and an experimental wetland have plants with details as follows: Echinodorus Cordifolius had fresh weight 193.05±13.502 g, length of plant 55.5±2.081 cm, length of root 30.25 ±6.344 cm. Vallisneria Natans had fresh weight 57.58±0.05 g, length of plant 15cm, length of root 4cm. The results showed that the survival rate (SVR) of both aquatic plants in the experiment was 100% for Echinodorus Cordifolius and 16.7% for Vallisneria Natan in the 21-day experiment. Furthermore, the experimental wetland can be considered as an effective solution in reducing 95.68% of ammonium-nitrogen, 98.86% of nitrate-nitrogen, 60.02% of phosphate, 46,72% of chemical oxygen demand, 100% of iron, 97,4% of copper when compared with the concentration at the beginning of the experiment. To be concluded, the growth and development of Echinodorus Cordifolius and Vallisneria Natans in this wetland has a positive effect on reducing pollutants of shrimp aquaculture effluents in all the 21day experiment.


Introduction
In recent decades, considerable attention has been paid to the serious water pollution caused by the rapidly growing aquaculture industry. This industry has grown at an average rate around 8.9% per year since 1970, with 2.8% for farming systems of The State of World Fisheries and Aquaculture from FAO, 2004 and only 57% of the countries in the world had laws and regulations carefully designed in order to serve as a legal framework for fisheries management plans [1]. On the other hand, water quality is crucial to the success or failure of aquaculture. The raising of fish, crustaceans and mollusks is called aquaculture. Land aquaculture facilities have a great need for water resources because they require large amounts of high quality source water to feed and they also discharge wastewater into the water environment. The main source of waste water in aquaculture wastewater is the addition of industrial feed and antibiotics to promote the growth and development of aquaculture during the process of producing an excess of feed, antibiotics and stool. The wastes exist in water environment with high 1 ICCEIB 2020 IOP Conf. Series: Materials Science and Engineering 991 (2020) 012034 IOP Publishing doi: 10.1088/1757-899X/991/1/012034 2 nutrient concentration like N, P. Wastewater from aquaculture processes is not treated and discharged into the environment can lead to physical and chemical degradation of the receiving waters. High concentrations of phosphorus, nitrogen in water areas cause eutrophication. Eutrophication disturbs the natural nature of the aquatic system, pushing red, hot tides and leading to the death of aquatic animals. This phenomenon can occur in rivers, lakes, reservoirs and coastal waters and is one of the most important problems worldwide, unable to use eutrophic water sources for water sources or life support aquatic. Due to the effects of excess phosphorus and nitrogen, this nutrient needs to be removed. Phytoremediation using constructed wetlands (CWs) has become a logical solution to improve the quality of contaminated waters by acting as a sink for various contaminants [2]. Phytoremediation utilizes the natural properties of aquatic plants to remediate contaminated water, soils or sediments [3], [4]. It has received increased attention over the recent decades, as an emerging and eco-friendly approach. by using plant grasses, reducing or stabilizing unwanted substances (such as nutritional or toxic metal contamination to overcome contaminated areas [5]. Applying the submerged macrophytes reduces the residual aluminum (Al) [6]. Phyto-and Bio-remediation technologies based on artificial wetland in recent years [7].
Constructed wetlands also understood as artificial or treatment wetlands, use the same processes that locates in natural wetlands, it seems a feasible option to solve water pollution problems because of their low cost of maintenance and operation. Various types of CWs are now being combined into hybrid systems to achieve better treatment performance, the aquatic plant 's potential of CWs makes them very attractive from an economic and technical point of view, since they can adequately reduce contaminants in polluted waters [8]. Aquatic macrophyte diversity of Echinodorus occured in the Pantanal wetland and upper basin in Brazil [9] Echinodorus cordifolius was the best plant for arsenic removal [10]. Work presented the use of the plant E. cordifolius for remediating diethylene glycol (DEG) contaminated waters. E. cordifolius has the potential to reduce the concentration of all MEG, DEG, and TEG from wastewater by taking them up through the root and accumulating it in the leaf [11]. V. natans commonly coexist in nature and are commonly used in efforts to restore aquatic ecosystems. V. natans is relatively low growing, does not form a canopy and depends on light penetrating down near the sediment for growth. Its root is relatively well developed and a significant proportion of nutrient can be absorbed from the sediment [3], [12]. Re-vegetation in river using V. natans helped to improve water quality slightly more and change interactions of the water quality parameters substantially [13]. V. natans provide new insight into ecological-based removal of antibiotics in aquatic systems [14] These results demonstrate the suitability of the Echinodorus Cordifolius and Vallisneria Natans for phytoremediation of shrimp discharge, and the usefulness of CWs to improve the water quality. The aim of this study was to evaluate the potential of phytoremediation of waste waters using the E. cordifolius and V. natans in CWs on a laboratory scale.

Experimental Design
The experiment was arranged at the Environmental Monitoring Department, 3rd floor, Nguyen Tat Thanh University. Echinodorus Cordifolius and Vallisneria Natans are grown in styrofoam tanks with clean water and added nutrients to aquatic plants.  + The final compartment is used to regulate the outflow and is connected to a plastic tank with a circulating pump with a 27mm plastic tube.
Waste water when being put into a plastic tank will be pumped back to the glass tank with a capacity of 18.3ml/s, the wastewater will be circulated continuously for 21 days.

Sampling
Plants of group 2 has total of 4 plants of E. Cordifolius and 180 plants of V. Natans, to be cut trunks, leaves and roots and dried at 65 0 C (dried to constant weight after two weighing) to weigh amount of dry weigh, also known the control. The first purpose of a comparison a plant's dry weight between the control and the experiment was after 21 days of experimental setup. After 21 days, the plants were grown in which the waste water environment was collected and weighed, measured the size of rooting and dried at 65° C (dried to constant weight after 2 weighing) to weigh the dry weight.

Statistical Analyses
Mean values and standard errors of water quality parameters were calculated from replicates, to be done within each treatment on one sampling time to understand differences between the control and the experiment. This differences compared to National Standards of [15] or [16], and WHO Guidelines [17]. Table 1  The water temperature in this study ranged from 25.6 ± 0.14 ºC to 29.95 ± 0.07 ºC with an average 27.94 ± 1.13 ºC for the control and ranged from 25.7 ± 0.0 ºC to 29.95 ± 0.07 ºC with an average 27.98 ± 1.11 ºC for the experiment. In practical terms, this means that this water temperature affects the high solubility of many chemical compounds and thus the effects of some pollutants on aquatic life, for example, Optimal growth performance of plants with temperatures in the range of 20 -30ºC [18].  Figure 2 showed that the average pH value recorded for the control is 7.72 ± 0.29 and for the experiment is 7.56 ± 0.25. The pH concentration of the control range is from 6.89 ± 0.02 to 8.13 ± 0.06 and the pH concentration in the experimental range was from 6.82 ± 0.03 to 8.21 ± 0.01. This range is within the allowable limits of class B2 in (QCVN 08: 2015) and (World Health Organization, 2006) for conserving aquatic ecology and for animals with the threshold of pH 6-9. The electrical conductivity average recorded for the control was 1131 ± 19.7 µs/cm and for the experiment was 1132 ± 18.2 µs/cm. The conductivity in the control ranged from 1099 ± 1.41 to 1171 ± 1.14 µs/cm and the conductivity in the experimental ranged 1106.5 ± 2.12 to 1165.5 ± 0.70 µs/cm. As a result, the conductivity of both control and experiment had significantly changed during 21 days. The average concentration of total dissolved solids (TDS) in the control tank was 645 ±11.29 mg/l and ranges from 626.5 ± 0.07 to 667± 0.0 mg/l. The experiment average of TDS was 646 ± 10.33 mg/l and this range ranged from 632.5 ± 3.5 to 664.5 ± 0.7 mg/l. The trend of total dissolved solids in both control and experiment was a limit standard of National Standards as concentration of TDS < 1000 [16] -National technical regulation on drinking water quality and WHO in Table 1. The table 1 presented that the Fe concentration at the first day was 0.58 ± 0.01 mg/l and a trend of Fe concentration in both control and experiment tended to decrease at the end of this study at 21 th day. Results presented that the dissolved oxygen concentration (DO) in figure 2 of both control and experiment in the first day was worth 4.55 ± 0.07 mg/l and both trend decreased from the 3rd day to the 6th day. The dissolved oxygen concentration in the the control was only 1.15 ± 0.07 mg / l and the peak of the decrease in dissolved oxygen concentration was from the 3 rd day to the 6 th day fluctuating dissolved oxygen concentration around 0.65 to 0.7 m/l and tends to increase again at 7 days. Oxygen concentration from here and maintain a steady increase until day 12 is 5.6 ± 0.28 mg this trend was in 15th day with 9.2 ± 0.21mg/l and ranged from 7.15 to 8.25 mg/l until the end of 21 th day. Especially, the experiment also tended to decrease like the the control. On the second day, the dissolved oxygen was only 3.95 ± 0.35 mg/l, decreased to 0.6 mg/l compared the first day. The onset and peak of the decline in dissolved oxygen concentration was 3 rd day and 6 th day dissolved oxygen concentration, with a range from 0.65 to 0.7 mg/l and tends to increase gradually. On the 7 th day and maintain a steady increase on the 16 th day was 5.95 ± 0.77mg / l and increased to 7.6mg/l on the 21 th day. According to table 1, the average of dissolved oxygen (DO) between the 3rd day and the 6 th day was not in a limit of national Standards and WHO. Results provided useful information to better understand the adverse effects of algal blooms from water pollution, on survival rate of submerged macrophytes as Vallisneria Natans [19]. The figure 3 presented that NO3 --N concentration of the experiment was lower than the control level during the 21 days experimental set up. At the beginning of this study, NO3 --N concentration was 17.65 ± 0.49 mg/l, and this concentration was higher than the permitted limit of class B2 in (QCVN 08-MT: 2015 / BTNMT) regulating NO3-N < 5mg/l, but it was in a limit of WHO. In natural resources, if NO3 --N in surface water is less than 1mg/l nitrate NO3 --N, which is not a good thing for aquatic life. After 21 days of experiment, the concentration of NO3 --N in the control decreased to 3.55 ± 0.021mg/l. In the experiment, the concentration of NO3 --N was 0.2 ± 0.0mg/l. It is important that nitrates and nitrites in this wetland can be removed by plant uptake.

Water quality
The NH4 + -N concentration at the first day was 9.03 ± 0.09mg/l, and the water quality was higher than the permitted limit of national Standards and WHO regulations. Both trend of the control and the experiment decreased from the 3 rd day to the 21 th day. At the end of this study, the NH4 + -N concentration in the control decreased to 0.48 ± 0.02 mg/l and in the experiment reduced to 0.38 ± 0.01mg/l. Ammonium loading decreased dissolved oxygen concentrations and pH values, stimulated biofilms growth, increased growth of algae [20]. It happened in the control during experimental time. Another work [21] illustrated Echinodorus cordifolia and the non-vegetated control also removed high percentages of NO3− load (63% and 60%, respectively). Load decreases followed concentration decreases, where NO3 --N and NH4 + -N had variable load decrease efficiencies from the first day to the 21th day. Figure 4 showed that the PO4 3--P concentration at the first day was 77.4 ± 5.9mg/l, and this concentration was significantly higher than the permitted limit of national Standards and WHO regulations. Both trend of the PO4 3--P concentration in the control and the experiment decreased from the first day to the 21 th day. At the end of this study, the PO4 3--P concentration in the control decreased to 33,6 ± 1,69mg/l and in the experiment reduced to 30,8 ± 0,56mg/l mg/l. Phosphorus removal from domestic wastewater by E. cordifolius [22]. Another result mentioned that the TP removal by Echinodorus cordifolius from domestic wastewater was 16%. Similar [23]. PO4 3--P content of the experiment was significantly lower than that the control, which indicated that this aquatic plants could remove phosphorus from the water by plant uptake or plant-associated effects. V. natans has water purifying ability [24], could effectively absorb nitrogen, phosphorus and other nutrients from the water [25]. The trend of the PO4 3--P concentration in the experiment decreased because the processes and mechanisms for aquatic plants to take up phosphorus (P) in wetland soils and sediments by V. natans [26].  Figure 5 showed that an average of COD concentration at the first day was 107 ±1.41 mg/l, the COD concentration decreased to 17 ± 1.41 mg/l on the 14 th day of the control and 15 ± 1.4 mg/l the 14 th day & 17 th day of the experiment, to be the lowest concentration of COD. And the both trend of the con troll and the experiment had a slight increase to the 21 th day. E. cordifolius was reported to have the ability to remove reduce EG and COD in wastewater [7]. Figure 5 also presented the Cu concentration at the first day was 0.77 ± 0.01 mg/l. The Cu concentration in both control and experimental tanks tended to decrease to the 21 th day, this Cu concentration had a trend from the 3 rd day to the 21 th day, in a limit <2mg/l of WHO guidelines. This proves that it is possible for the V. natans growth to absorb Cu because V. natans are likely to reduce Cu concentrations in sediments [27].

Plant growth E.
Cordifolius and V. natans were harvested and washed and cleaned thoroughly with deionized water and then weighed to estimate the total biomass, root biomass and leaf biomass of each wetland.

Control Experiment
The first day The first day The 21 th day The 21 th day The results showed that the survival rate (SVR) of both aquatic plants in the experiment was 100% for E. Cordifolius and 16.7% for V. Natan in the 21-day experiment. the above-ground biomass of E. Cordifolius significantly increased with increasing ammonia-nitrogen concentrations in water body, indicating that excessive water ammonia-N can did not give significant toxicity to this plants. The below-ground biomass of V. natans significantly decreased, suggesting that excessive sediment pollution can result in significant damage to the root of V. natans. In addition, high ammonia-N levels place a greater stress on submerged plants than sediment [27].
Results in figure 6 & 7 showed that over 21 days, the survival rate of E. cordifolius 100% and weight increased over time until the end of the experimental arrangement. The fresh weight of E. cordifolius after 21 days increased from 193.6 grams to 367.75 grams. As for the dry weight after drying of E. cordifolius, the result of the first day was leaf weight of 13.30 ± 0.44 g, roots of 2.85 ± 0.74 g, stem of 1.69 ± 0.30 g. After 21 days, results showed an increase in leaf weight of 18.17 ± 5.33 g, with dead leaves 3.98 ± 1, 62 g, stem 1.85 ± 1.26 g, roots of 3.52 ± 2.52g and old roots 2.85 ± 1.02 g. Especially the production of young plants weighing 0.40 ± 0.22g. E. cordifolius will selected for constructed wetland by nutrient removal, stress resistant species, recycling of effluents [28]. After 21 days, results showed an increase in leaf weight of 0.55 g, root-in-blood of 0.14 g, which showed that E. cordifolius in the experiment were able to adapt to the discharge environment of shrimp farming, even though the water had P, N High, but the tree still shows good growth and development. The faster the plants adapt and grow, the more nutrients will be removed from the wastewater. V. Natan had a 100% survival rate in the first 9 days of the experiment and there was a death on the 10 days after 21 days of testing, the survival rate of the chives was only 16.7%. The fresh weight of V. Natan was reduced from 57.62 grams to 4.68 grams after 21 days. The dried weight of chives was found to have a weight of 2.12 g of leaves and a root of 0.6 g from roots. Results showed a higher N concentration led to declined abundance of V. natans, the decline being most pronounced for plants grown in high-nutrient sediment in this experiment [12]. The growth of plant weight during the experiments of the wastewater treatment system is technically and economically important. Last biomass of 16.7%. plants of V. Natan help a highly oxygenated zone around the root base because of changes protect roots against low oxygen conditions. V. natans that may help this plant adapt to submerged conditions in contaminated water [29]

Conclusion
Combined E. Cordifolius and V. natans in Constructed Wetlands on a laboratory scale successfully removed the contaminated pollutants. The survival rate (SVR) of plants in the experiment was 100% for Echinodorus Cordifolius and 16.7% for Vallisneria Natan at the 21 th day experiment. Results presented in the table 1 that the experiment can be considered as an effective solution in reducing Ammonium-Nitrogen (NH4 + -N) concentrations with 95.68%, Nitrate-Nitrogen (NO3 --N) with 98.86%, Phosphate (PO4 3--P) with 60.02%, COD 46,72%, Fe 100%, Cu 97,4% when compared to the first day of the experiment, and also in a limit of National standard and WHO guidelines. It is clear that the growth and development of Echinodorus Cordifolius with Vallisneria Natans in the experimental constructed wetland has a positive effect on reducing pollutants of shrimp aquaculture effluents in all 21day experiment because water parameter of the experiment was lower than the control, which indicated both plants improved the water quality from the shrimp farming effluent by plant uptake or plant-associated effects. The results support consistent comparisons can be used to identify and prioritize water-quality issues for further investigation. Particularly on large wetland, we need biological treatment of wastewater, focusing on the phytoremediation potential of selected aquatic plants of Echinodorus