Selection of suitable plant species for wastewater treatment by constructed wetland at the formosa Ha Tinh steel company

Vietnam Journal of Science and Technology 56 (2C) (2018) 157-163 SELECTION OF SUITABLE PLANT SPECIES FOR WASTEWATER TREATMENT BY CONSTRUCTED WETLAND AT THE FORMOSA HA TINH STEEL COMPANY Anh Thi Kim Bui1, *, Viet-Anh Nguyen2, Minh Phuong Nguyen3 1Institute of Environmental Technology, VAST, 18 Hoang Quoc Viet, Ha Noi 2Institute of Environmental Science and Engineering, Hanoi University of Civil Engineering, 55 Giai Phong, Ha Noi 3Department of Environmental Technology, Faculty of Environmental Sciences, VNU University of Sciences, 334 Nguyen Trai, Ha Noi *Email: buianh7811@gmail.com Received: 8 May 2018; Accepted for publication: 22 August 2018 ABSTRACT The study aimed to select suitable plant species in constructed wetland at Formosa Ha Tinh steel company and identify proper nutrient supplements for these plants growth. The tolerance of different aquatic plant species was tested with treated wastewater. Phragmites australis (Cav.), Typha angustifolia L. and Cyperus tegetiformis were selected for vegetation. In this experiment, removal efficiencies for monitored chemical parameters were in the range of 26.5 – 91.7 %, while elimination rates of total coliform were about 50 %. In the beginning, the plant nutrient demand for the first 3 months estimated based on theoretical mean annual nutrient uptake was 495 kg N, 153 kg P and 36 kg K per ha. When the wastewater entered CWs, the available nutrients in the influent could be enough for the plants growth. In fact, observations of the health status of the plants would serve as a basis for the fertilizer feeding decision, the concentration of mineral nutrients available in the wastewater are very important. Keywords: constructed wetland, nutrient, plant, wastewater. 1. INTRODUCTION Constructed wetlands (CWs) are eco-friendly technologies that utilize plants for wastewater treatment. Based on flow regime, CWs are classified as subsurface flow (SSF) and free water surface (FWS) systems. According to flow direction, SSFCWs could be horizontal flow (HF) or vertical flow (VF) [1]. By taking advantages of natural processes such as adsorption, precipitation, plant uptake, microbial transformations which are similar to natural wetlands but in a controlled conditions, CWs have been shown to be effective for pollutant removal from various types of wastewater [1, 2]. Wastewater from steel industry usually contains organics, colour, and toxicants such as Anh Thi Kim Bui, Viet Anh Nguyen, Minh Phuong Nguyen 158 phenol, cyanides and heavy metals which require proper treatment before discharging into environment. Treatment of wastewater from steel industry by CWs has been well-documented in some studies [3, 4, 5]. Xu et al. [4] evaluated the performance of CWs treating steel wastewater in China and the results showed that iron and manganese concentration were reduced by up to 98 %, meanwhile removal efficiencies of COD, turbidity, N-NH4+ and TP were 55 %, 90 %, 67 % and 93 %, respectively. In another study on the role of CWs treating wastewater from iron and steel enterprise, Huang et al. [3] reported that the mean reduction of COD, N-NH4+, turbidity, iron and manganese, were 77.3 %, 76.9 %, 95.8 %, 96.9 % and 92.5 %, respectively. After a marine life disaster in central Viet Nam in 2016 due to poorly treated steel industry wastewater and pipe cleaning solutions, the Formosa steel corporation has been requested to improve their wastewater treatment with enhanced physic-chemical and biological processes. A 10 ha pond – wetland system has been designed, including 4.3 ha for 4 constructed wetland (CW) cells in series.To the best of our recent knowledge, although the application of CWs in treating other wastewater types such as domestic wastewater [6] and mining wastewater [7] in Viet Nam has been reported, there is no its application for steel wastewater treatment yet. For plant establishment in wastewater treatment wetland system, the first thing needs to be done is selection of suitable plant species. Three plant species (Phragmites australis (Cav.), Typha angustifolia L. and Cyperus tegetiformis) were chosen for this research because they seem to be most tolerant to the expected conditions in this wastewater treatment wetland. These species can be found locally, have a good ability to grow in different types of wastewater, and are tolerant to relatively high levels of contaminants [3, 4, 7]. About 95 % of Fe and Mn were removed by CWs planted with Phragmites [3], whereas good treatment of COD, TSS, NH4+-N and TP was observed in CWs planted with Cyperus, with removal efficiencies were 96, 91, 92 and 99 %, respectively [8]. High removal rates of COD, TSS, NH4+-N and TP (76, 64, 50 and 48 %, respectively) were also obtained in Typha-CWs [9]. The contents of available nutrients N and P (based on daily wastewater analysis of FHS company) in the industrial wastewater were calculated to assess the necessary nutrients for plants to grow well in system. In many cases, nutrient supplement is very important for treatment wetlands [10]. The aims of our study to (1) evaluate the tolerance of selected plants to the treated steel wastewater from FHS and determine their treatment efficiencies; (2) calculate theoretical amount of fertilizers supplemented per hectare of CW. 2. MATERIALS AND METHODS 2.1. Materials The wetland plants Phragmites australis (Cav.) and Typha angustifolia L. were gathered from local province of Ha Tinh, whereas Cyperus tegetiformis was selected from a nearby province of Thanh Hoa. 2.2. Analytical methods Selected water quality parameters were measured weekly in the influent and effluent of each wetland cell. Standard methods for measurement and initial concentrations of those parameters before entering CWs are shown in Table 1. Selection of suitable plant species for wastewater treatment constructed wetland at .. 159 Table 1. Methods for measurement and initial concentrations of wastewater parameters. No. Parameters Initial value Unit Analytical methods 1 pH 7.5 – 8.3 (± 0.6) - TCVN 6492 : 2011 2 Turbidity 9.5 – 11 (± 1.1) NTU TCVN 6184:1996 3 Colour 70-72 (± 1.4) Pt/Co TCVN 6185 : 2008 4 COD 15 – 30 (± 10.6) mg/l SMEWW 5220C : 2012 5 TSS 14 – 26 (± 8.5) mg/l TCVN 6625 : 2000 6 Mn 0.2 – 0.4 (± 0.1) mg/l EPA.200.8:2012 7 T-N 2.1 - 5.7 (± 2.5) mg/l TCVN 6624-2:2000 8 NH4+-N 0.4 - 3.3 (± 2.1) mg/l TCVN 6179 -1 : 1996 9 T-P 1.2 – 1.4 (± 0.1) mg/l TCVN 6202-2008 10 Phenol <0.01 mg/l TCVN 6216 : 1996 11 CN- 0.03 – 0.06 (± 0.02) mg/l SMEWW 4500-CN- C:2012 12 Chlorophyll a 1.6 – 1.8 (± 0.1) µg/l TCVN 6662:2000 13 Total Coliforms 1600 (± 141) MPN/100ml TCVN 6187-2:1996 Other parameters such as BOD5, total grease, Hg, Cd, Cr (VI) were measured but results are not shown in this paper as they were not typical parameters in steel wastewaters, besides, concentrations of Hg, Cd and Cr (VI) were insignificant (lower than 0.0007, 0.0009 and 0.003 mg/l, respectively). 2.3. Experimental design The purpose of these experiments was to select suitable plants for CWs at FHS. In case non-regulated pollutants are present in the effluent, CW would be an important polishing step before wastewater can be discharged. These three plant species were planted in rectangular plastic pots (50 cm length x 35 cm width x 20 cm height) with three replicates for each. Substrate materials for plant growth were rock, gravel and sand. Pot TN1 was planted with Phragmites australis (Cav.), pot TN2 was planted with Typha angustifolia L, and pot TN3 was planted with Cyperus tegetiformis. Experiments to evaluate tolerance of plants to treated wastewater from industrial and bio-chemical treatment stations of FHS and the plants purification capacity were conducted in 35 days. The wastewater was taken from the FHS and renewed every 5 days depends on retention time in CW at Formosa. Water quality analysis has been carried out every 5 days. Calculation of fertilizers supplemented was estimated based on relevant published data from Tanner and Kadlec [11], Sohsalam et al. [12], Greenway [13], Land et al. [14], Nguyen My [15], and Kantawanichkul et al. [2] . 3. RESULTS AND DISCUSSIONS 3.1. Tolerance test Anh Thi Kim Bui, Viet Anh Nguyen, Minh Phuong Nguyen 160 After 35 days of experiment, all three plant species survived well in wastewater. The results indicated that plants were tolerant to this type of wastewater, number of leaves and new shoots grew significantly. Fresh biomass of plants increased in all TN1, TN2 and TN3 (Figure 1). Among three plant species, Cyperus tegetiformis (TN3) showed the highest increase in biomass (by 48.33 %, equivalent to 1.38 % day-1, from 120 to 178 g), followed by Typha angustifolia L. in TN2 (biomass increased by 33.33 %, equivalent to 0.95 % day-1, from 147 to 196 g and Phragmites australis (Cav.) in TN3 (biomass increased by 25.85 %, equivalent to 0.74 % day-1, from 205 to 258 g). Figure 1. Change in plant biomass during experimental period. The three emergent macrophytes in this study are commonly used in treatment wetlands due to their good nutrient uptake capacity, resistance to extreme environmental factors and high rate of biomass production [8]. Cyperus spp. has been suggested to be used as a source of biomass energy due to its remarkable high yield potential production, with net primary productivity ranges between 25.9 and 136.4 total dry matter ha−1 yr−1[2]. The average leaf elongation of Typha species has been found to be 4 cm per day [2], whereas the root growth rate of Phragmites australis (Cav.) has been reported to be in the range of 5 – 25 mm per day [11]. 3.2. Treatment efficiency of the experimental pots Treatment efficiencies of three experimental pots (TN1, TN2 and TN3) are presented in Table 2. The results revealed that all of the studied plants had good capacity of pollutant removal. Among three plants, best treatment performance was recorded in P. australis Cav and T. angustifolia L. (with no significant differences in removal efficiencies between two species), followed by C. tegetiformis. The parameter having highest treatment efficiencies was Mn, with 91.7 % was removed by P. australis Cav (TN1), while 86.3 % and 82 % of Mn concentrations was removed by T. angustifolia L. (TN2) and C. Tegetiformis (TN3), respectively. Treatment efficiency of colour by TN1 reached 86.6 %, while TN2 and TN3 experienced slightly lower efficiencies (82.4 and 79.2 %, respectively). Our results on color removal were in similar range of Bulc and Ojstršek [10], who found that color removal by CWs planted with P. Australis ranged from 70 % to 90 %. With regards to organic matters removal, TN1 achieved removal of COD of 60 %, while 44 and 35.6 % of COD was eliminated in TN2 and TN3, respectively. Those data are consistent with earlier findings on COD removal rates by CWs treating steel wastewater, ranging from 31.1 to 77.3 % [3, 5]. Regarding nitrogen and phosphorus removal, total nitrogen (TN) removal was in the range of 29.5- 36.7 %. Total phosphorus (TP) removal was in the range of 52.3 – 65.4 %, which matched with data on TP removal by CWs treating steel wastewater by Xu et al. [4] (59.8 – 66.2 %). Total coliforms removal efficiencies in our experiment were from 43.8 to 53.1 %, which were in 0 50 100 150 200 250 300 Before treatment After treatment Fr es h bi o m a ss (g) TN1 TN2 TN3 Selection of suitable plant species for wastewater treatment constructed wetland at .. 161 agreement with total Coliforms removal efficiency by Lemna (54 %) [12]. In general, all plants could effectively eliminate pollutants. However, differences in removal rates by Phragmites and Typha were only negligible, while removal efficiencies by Cyperus were lowest, which were in accordance with results published by Vymazal [1]. Table 2. Treatment efficiencies of three experimental pots. Parameters Initial value Unit TN1 Effi- ciency (%) TN2 Effi- ciency (%) TN3 Effi- ciency (%) pH 7.9 - 7.6 - 7.6 - 7.6 - Turbidity 10.2 NTU 4.7 54.6 5.6 45.4 5.9 42.8 Colour 71 Pt/Co 9.5 86.6 12.5 82.4 14.8 79.2 COD 22.5 mg/l 9 60.0 12.6 44.0 14.5 35.6 TSS 20 mg/l 11.3 43.7 12.0 40.3 12.0 40.0 Mn 0.3 mg/l 0.03 91.7 0.04 86.3 0.05 82.0 TN 3.9 mg/l 2.5 36.7 2.6 33.6 2.8 29.5 NH4+_N 1.9 mg/l 1.05 43.2 1.3 30.8 1.4 26.5 TP 1.3 mg/l 0.5 65.4 0.5 61.5 0.6 52.3 Phenol < 0.01 mg/l < 0.01 < 0.01 < 0.01 CN-/ Cyanide 0.05 mg/l < 0.004 < 0.004 < 0.004 Chlorophyll a 1.7 µg/l 1.1 37.1 1.5 10.6 1.6 5.3 Total Coliforms 1600 MPN/100ml 750 53.1 800 50.0 900 43.8 3.3. Estimation of the need for nutrients in the wetland cells In order to assess the need for additional nutrients, the plant nutrient demand was estimated based on mean nutrient uptake data from literature (Table 3). The nutrient content in the wastewater inflow was used as an assessment of available nutrients. Table 3. Calculation of nutrient demand based on theoretical uptake. Plant nutrient uptake T a n n er & K ad le c 20 03 K an tw a n ic hk u l e t a l 2 00 9 G re en w a y 20 03 La n d et a l., 20 16 So hs a la m et a l., 20 08 So hs a la m et a l., 20 08 Ng u ye n M y H o a , 20 03 Ng u ye n M y H o a , 20 03 Mean nutrient uptake Nutrient demand in 1 ha total (kg/day) Nutrient demand in 1 ha total (kg/ 3 months) g/m2.day N 0.6 0.86 0.15 0.73 0.59 5.9 531.0 P 0.064 0.276 0.17 1.7 153.0 K 0.02 0.06 0.07 0.7 63.0 Although the growth of plants depends on many factors not only the excess of TN, TP and TK, however N, P and K are considered as the most important nutrients for plant growth, besides certain amounts of organic carbon and trace metals are also available in the wastewater. Anh Thi Kim Bui, Viet Anh Nguyen, Minh Phuong Nguyen 162 Therefore, nutrient demand of TN, TP and TK were calculated in the study. It is obvious from Table 3 that the values differ a lot between different studies; this probably depends on whether the authors are referring to max uptake during a certain part of the year, or uptake during the entire year (also when the season is less favorable to plant growth). An estimation for the three months after growing the plants to the cells would be 531 kg N, 153 kg P and 63 kg K per ha. This would best be split on at least three different occasions. The input flow of 4.3 ha CWs in FHS company was 15,000 (m3/d), the mean concentration (mg/l) of T-N, T-P and T-K in inflow wastewater was 3.9, 1.3 and 0.4 mg/l, respectively. We calculated the mean inflow load of N, P and K, as the nutrient supply for the plant grown. Mean inflow load of T-N, T-P and T-K per ha were 13.6, 4.5 and 1.4 while nutrient demand were 5.9, 1.7 and 0.7 kg/day, respectively. From some public data, it ensures that no need nutrients to be added to the CWs system during the operation. The result from figure 1 also show that, during 35 days experiment, without addition of fertilizer, the biomass of selected plant species increase from 25.85 to 48.33 %. The results close with theoretical calculation above. However in practice, observations of the health status of the plants would serve as a basis for the fertilizer feeding decision, together with frequent nutrient analyses of the wastewater effluent from the CW system. 4. CONCLUSIONS Phragmites australis (Cav.), Typha angustifolia L. and Cyperus tegetiformis could be tolerant with the treated wastewater from the steel industry company FHS. The CW system has substantially improved the wastewater quality, where the highest removal efficiencies were achieved in the cell with Phragmites australis (Cav.) and Typha angustifolia L. The estimated nutrients need for the plants at a stage of three months after plantation would be 495 kg N, 153 kg P and 36 kg K per ha. 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