MINISTRY OF EDUCATION
AND TRAINING
VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY
GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY ---------------------------
VU THI NGUYET
RESEARCH ON THE
APPLICATION OF AQUATIC PLANTS
IN THE TREATMENT OF SWINE WASTEWATER
Major: Environmental technology
Code : 62 52 03 20
SUMMARY OF DOCTORAL THESIS OF
ENVIRONMENTAL TECHNIQUE
Ha Noi - 2018
The work was completed at the Academy of Science and
Technology, Vietnam Academy of Science and Technology
Supervisors:
1. Dr. Trần Văn Tựa – Environmental technology academy
2. Prof. Dr. Đặng Đình Kim - Environmental technology
academy
Counter-argument 1:
Counter-argument 2:
Counter-argument 3:
The dissertation will be defended at the Academic Review
Board of the Institute, meeting at the Academy of Science and
Technology - Vietnam Academy of Science and Technology at
... on …’,
The dissertation can be reached at: - Library of the Academy of Science and Technology - Vietnam national library
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INTRODUCTION
1. The necessary of the project
In recent years, with the vigorous development of our nation, the economy of rural area has also increased significantly; in which livestock activities have contributed major income for many farmers. However, the negative side of this quick development is environmental pollution caused by the waste of livestock activities. It is estimated that only 40-50% of total livestock waste is properly treated before discharging to environment, the rest is directly released into ponds, lakes and canals.
To solve the environmental problem, several technologies have been proposed and conducted to treat livestock waste like physical methods which separate solid and liquid waste, or biological methods based on anaerobic or aerobic condition. Among biological methods, biogas technique has been proved to be an appropriate method to treat livestock waste, and it has been widely used nowadays. However, some limitations of biogas technique such as high P and N in outlet water that does not meet the permitted standards lead to the necessary to construct an extra-treatment step before discharging into the environment.
The extra-treatment step aims to reduce the remained P, N and organic matters in effluent to meet standards before discharging. One of the potential methods that are suitable for such a goal is eco-technology that uses aquatic plants as a factor to treat the pollutants. This method has been reported to have several advantages compared to regular wastewater treatment system. Eco-technology is environmentally friendly, low cost, easy to operate, and has a high and stable treatment efficiency. Many countries in the world have studied to apply this method.
Vietnam is a promising country for applying Eco-tech to use aquatic plants in water pollution treatment. However, the research and application of this technology in Vietnam remains limited and/or unsystematic, only in small experimental scale and lack of practical research to put the technology into practice. Therefore, we conduct the study entitled: "Research on the application of aquatic plants in the treatment of pig waste water" aiming to propose an effective technology for livestock waste treatment, suitable for Vietnam to minimize technological conditions, contributing environmental pollution in residential areas. This is a promising strategy to develop sustainable livestock farming along with environmental protection and life quality improvement. 2. Study objectives
To propose Eco-tech model using aquatic plants to treat pig reduce treatment process
in order
to
wastewater after microbial environmental pollution. The technology is feasible and practical.
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+, NO3
3. Research content Content 1: Overview of the current status of pig wastewater pollution and the treatment technologies; overview of Eco-tech using aquatic plants in wastewater treatment in general, including waste water from pig farms. Content 2: Evaluate the tolerance of some selected aquatic plants to COD, -, pH, and their ability to treat COD, nitrogen, phosphorus in pig NH4 wastewater after microbial treatment. Content 3: Evaluate the efficiency of the treatment in different technological types using aquatic plants with different wastewater loads. Content 4: Establish and evaluate the treatment efficiency of the aquatic plant system in reducing nitrogen (N), phosphorus (P) and organic matters from pig farm wastewater after the microbial treatment. 4. Novel contributions of the study
- Selection of suitable aquatic plants for pig wastewater treatment
after microbial process based on the efficiency of COD, N, P removal.
- Selection of the suitable Eco-tech type using aquatic plants to treat
swine wastewater.
- Integration of the selected Eco-tech type into a treatment system of 30 m3 per day- night, effectively additional treating COD, N and P in effluent from pig farms with low cost, simple operation, potential enlargement and adaptation for farm conditions of Vietnam. 5. Thesis structure
The thesis is presented in 131 pages with 25 tables, 54 figures, and 166 references, including: 3-page introduction, 41-page literature review, 11-page experimental and research methods, 74-page result and discussion, 2-page conclusion and recommendation.
CONTENTS OF THE THESIS Chapter 1: Literature overview
1.1 The situation of pig farm
Livestock farming is the development orientation of the stock-raising sector. According to statistic number stated in 2016, there have been total 29 millions pigs in Vietnam, in which the Red River Delta reaches the largest number with 7.4 million pigs (~26%), and this number has been increasing over the years. This quick development, however, leads to many problems to our environment caused by the increasing livestock waste. 1.2. Survey results of waste from pig farming and treatment technology 1.2.1. Environmental pollution caused by pig farming
A total of 20 pig farms were surveyed in five provinces: Hanoi, Vinh Phuc, Hung Yen, Thai Binh and Hoa Binh. Water consumption in the farms differs significantly from one to another, varying from 15 to 60
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liters/pig/day.night, leading to the amount of waste water is a considerable high number.
In terms of pollutant composition and level in pig wastewater before biogas treatment; the COD, TN and TP in wastewater were very high reaching to 3587 mg/l, 343 mg/l and 92 mg/l, respectively. After biogas treatment, the parameters were reduced to 800 mg/l, 307 mg/l and 62 mg/l, respectively. The amount of dissolved oxygen in wastewater before and after biogas treatment was almost zero. Coliform index was multiple times higher than the permitted standards. Therefore, the pollution caused by piggery farm waste is an urgent situation and needs to be solved. 1.2.2. Current status of wastewater treatment technology
There are four typical types of technology applied by farms to treat
animal wastewater. 1 - The wastewater is treated with anaerobic ponds and then through facultative ponds and then discharged into the environment (8.3%). 2 - Livestock wastewater is treated through biogas digester and then discharged into canals (50%). 3 - Livestock wastewater is treated with biogas, followed by biological ponds (25%). 4 - Livestock wastewater is treated by anaerobic stabilization, then treated by anaerobic biological filter or aerotanks, finally through aquatic plant ponds and then discharged (8.3%). The remaining 8.3% of the farms do not apply any treatments but directly discharge into the canals, causing serious pollution to the surrounding environment. 1.3. Ecological technology in livestock wastewater treatment
- Types of aquatic plants in wetlands can be divided into three main groups: semi-submerged aquatic plants, floating aquatic plants and submerged aquatic plants.
- Types of technology used in Eco-tech for wastewater treatment: surface flow technology, submerged flow technology, and floating aquatic plant system.
evaporation
ammonia
- Pollutant removing mechanism: Nitrogen is removed by 3 mechanisms, nitrification/denitrification, and absorption. Regarding P, the removal includes: absorption, via bacterial metabolism, adsorption, precipitation and deposition with Ca, Mg ions... The treatment process starts with microbial activities to form biofilms on the surface of the aquatic plant shoots and roots; then the microbes digest organic matters in water, releasing nutrient elements like N and P for plant utilization.
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1.4. Application of aquatic plants in wastewater and pig wastewater treatment
- Situation of research in the world: Research and application of Eco-tech with aquatic plants for livestock wastewater treatment in the world has developed for a long time by extensive and intensive researches, not only in small experimental scale, but in large practical scale (from 200 m2 to 15 ha). Common types of technology are surface flow technology and submerged flow technology. In Europe, it is popular to combine surface and submerged flows. Commonly used aquatic plants are Phragmites australis, Miscanthus sacchariflorus, Vetiveria zizanioides, Cyperus alternifolius, Eichhornia crassipes, Typha latifolia, Schoenoplectus californicus. This system is environmentally friendly, low cost, easy to operate, with high efficiency, and stability (COD removing efficiency: 30 - 68.1%, TN: 20 - 98%, 13 - 95%).
- Situation of VN research: Research and application of Eco-tech with aquatic plants for livestock wastewater treatment in Vietnam is still limited, only in small scale from few liters to less than 1 m3, short-term trials, and without a reliable model to put the technology into practice.
For the reasons above, it is necessary to set up Eco-tech using
aquatic plants for pig wastewater treatment to higher levels such as:
- Evaluating the tolerance and treatment ability of different aquatic plant species (Eichhornia crassipes, Pistia stratiotes stratiotes, Ipomoea aquatica, Enydra fluctuans, Rorippa nasturtium aquaticum, Phragmites australis, Vetiveria zizanioides, Cyperus alternifolius), the selected plants will be used for pilot scale test.
- Selection of technology types (surface flow technology, submurged flow technology, combined technology), that is suitable for the field treatment model of pig farms in Vietnam.
- Based on the specific conditions of the farm, construction and evaluation of treatment efficiency of the aquatic plant system will be calculated to effectively reduce N, P and COD from effluent after the microbial treatment at 30 m3/day scale, in Hoa Binh Green Farm, Luong Son, Hoa Binh.
- Orientate to apply and extend the ecological model in practice. Chapter 2. Materials and Methods
2.1. Research subjects
Swine wastewater: The wastewater collected from the outlet of
microbial treatment process.
Some aquatic plants have been reported to have ability to treat piggery wastewater: Eichhornia crassipes, Pistia stratiotes stratiotes,
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Ipomoea aquatica, Enydra fluctuans, Rorippa nasturtium aquaticum, Phragmites australis, Vetiveria zizanioides, Cyperus alternifolius. 2.2. Research methods 2.2.1. Evaluation of plant tolerance to pollutants and their ability treatment a. Evaluation of tolerance to COD, NH4
+, NO3
-, pH
+, NO3
Tolerance of aquatic plants to COD, NH4
- and pH levels was assessed by plant growth. The experimental plants were placed in 4 liters pots containing 3 liters of hydroponic growth medium. b. Evaluating the plant ability in eliminating some pollutants in the pig wastewater + Batching experiment: The experimental plants were placed in 6-liter pots containing 4 liters of pig wastewater with approx. 250 mg/l of COD. The experiment was repeated three times with the control (without plants). + Semi-continuous experiment: The experiment was set up as in batching experiment. Daily, one liter from the pots is replaced by one liter of new wastewater with the same concentration. COD is maintained at about 250 mg/l with glucose supplement. c. Evaluate the growth of aquatic plants
Fresh biomass of plants before and after experiments was measured by Sartorius balance (Germany). For weighing, the plant was removed from the pots, let it drained. 2.2.2. Evaluate the capability of pig wastewater treatment of various types of technology - Experiment with floating aquatic plant systems: The experiment was conducted in a tank of the following sizes: High x Long x Width = 60 cm x 200 cm x 50 cm with two compartments: distributing compartment with volume of 10 liters of water; treating compartment with volume of 360 liters. The Eichhornia crassipes was deployed on 4/5 of the water surface area. Experiment with 2 loading flows: 50 liters/day and 100 liters/day. - Experiment with surface flow technology: The experiment was conducted in a tank with size: Height x length x Width = 60 cm x 200 cm x 50 cm with 20 cm soil layer for planting. Water level is 20 cm with Phragmites australis, 5 cm with Ipomoea aquatica with water capacity is 180 liters and 45 liters, respectively. Phragmites australis density at 15 cm x 20 cm and Ipomoea aquatica at 5 cm x 5 cm. Wastewater load was 50 l/day and 100 l/day for Phragmites australis and 25 l/day and 50 l/day for Ipomoea aquatica. - Experiment with submerged flow system: The experiment was conducted in a tank with size: Height x length x Width = 60 cm x 200 cm x 50 cm, total water capacity 160 liters. Plating substrates included the first
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layer: crab 4-5 cm (25 cm), second layer: gravel 2 to 3 cm (25 cm), third layer: gravel and small stones ø 0.5 cm (20 cm). Plant density was 15 cm x 20 cm, test loading flow was 25 l/day, 50 l/day and 100 l/day. - Experiment with combined flow technology
Combination system of Phragmites australis & Eichhornia crassipes: Size of the system: Height x Length x Width = 60 cm x 200 cm x 50 cm comprise two tanks. Tank 1 with Eichhornia crassipes (360 liters), tank 2 with Phragmites australis (360 liters including the 20 cm-soil layer and 180 liters of wastewater), the loading flow was 100 l/day. Combination system of Phragmites australis, Cyperus alternifolius, Eichhornia crassipes and Vetiveria zizanioides: The experiment system comprises four compartments: one for Phragmites australis (surface system), one for Cyperus alternifolius and Vetiveria zizanioides (floating plant system), one for Eichhornia crassipes the last one for Vetiveria zizanioides (floating plant system), (submerged flow system). The size of each compartment: Height x Length x Width = 30 cm x 44 cm x 30 cm. Test loading flow: 25 liters/day (equivalent to 47.35 liters/m2.day)
2.2.3. Evaluate the efficiency of pig wastewater treatment
The ecological system consists of: - Surface flow using Phragmites australis - Floating plant systems include Cyperus alternifolius, Vetiveria
zizanioides and Eichhornia crassipes.
- Submerged flow with Vetiveria zizanioides The ecological model has a total area of 600 m2 divided into 3 compartments, built on flat ground. Wastewater flows into compartment 1, through compartment 2 and compartment 3, the outlet at the end of compartment 3 after submerged flow. 2.2.4. Analytical methods The pollutants (NH4
-, T-N, PO4
+, NO3
-3, T-P, COD, TSS ...) were analyzed according to ISO standard methods by UV-Vis 2450, Shimadzu - Japan. 2.2.5. Data processing methods
Analyzed data were processed by Origin Pro and Excel software.
2.2.6. Equipment used in research
Equipments used in the study were dosing pump: 2.5 - 3 m3/h, water distillation machine, nitrogen distillation Keldahl, technical and analytical balances, portable device Oxi 330 WTW - Germany, pH 320 WTWW - Germany, HACH COD Reactor (United States), TOA (Japan) multi- indicator water meter, Japan's Shimadzu UV-2450 spectrometer.
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Chapter 3. Results and discussion
3.1. Tolerance and treatment ability of the aquatic plants 3.1.1. Plant tolerance to the pollutants
+, NO3
In order to have a basis for the selection and application of aquatic plants for pig wastewater treatment, it is necessary to assess the tolerance of the aquatic plants. Pig farm wastewater is usually characterized by a high organic content while plants in general or aquatic plants in particular are able to tolerate to a certain level. Therefore, we conducted an experiment to - and evaluate the tolerance of selected aquatic plants to COD, NH4 pH in different levels via monitoring plant growth. - COD tolerance: COD parameter indicates the level of organic matter pollution of wastewater. In pig wastewater, COD is usually very high value. Results of the assessment of COD tolerance (Figure 3.1) showed a difference among eight plants, ranking from highest to lowest: Eichhornia crassipes, Enydra fluctuans, Cyperus alternifolius > Vetiveria zizanioides > Phragmites australis, Ipomoea aquatica, Pistia stratiotes stratiotes > Rorippa nasturtium aquaticum.
+
Figure 3.1. Effect of different COD levels on the growth of aquatic plants
Figure 3.2. Effect of different NH4 levels on the growth of aquatic plants
+ can be assimilated by plants, NH4
The results indicated that COD was an important factor that influenced on the growth of the plants. When the COD level was increased, the plant growth was gradually decreased. The higher the COD was, the worse the plants developed. The first group including Eichhornia crassipes, Enydra fluctuans, Cyperus alternifolius was able to tolerate to 250-750 mg/l COD. The second group of Phragmites australis, Vetiveria zizanioides, Pistia stratiotes could tolerate to COD a bit lower, from 250 - 500 mg/l. The third group of Ipomoea aquatica and Rorippa nasturtium was able to tolerate at COD < 500 mg/l. The results of this study are in consistent with those of Liao X (2000), Jingtao Xu et al (2010) and Tran Van Tua (2011). + tolerance: Nitrogen is an important nutrient for plants growth. - NH4 + turns to toxic if the Although NH4 amount is high due to part of ammonia will convert into NH3. Based on the
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-: NO3
- along with PO4
+ tolerance of the + tolerance assessment (Figure 3.2), NH4 results of the NH4 eight plants can be ranked as follows: Eichhornia crassipes > Phragmites australis, Vetiveria zizanioides, Cyperus alternifolius > Pistia stratiotes, Rorippa nasturtium aquaticum > Enydra fluctuans >Ipomoea aquatica. Eichhornia crassipes, Phragmites australis, Vetiveria zizanioides, Cyperus + < 250 mg/l. Pistia stratiotes, Rorippa alternifolius can resist NH4 + <150 mg/l. Enydra fluctuans and nasturtium aquaticum can tolerate to NH4 + < 100 mg/l, all of which is corresponding Ipomoea aquatica can resist NH4 to the research of Korner (2001), Liao X (2000) and Piyush Gupta et al., 2012. - is an essential compound for the growth and - Tolerance to NO3 -3 development of plants. With appropriate levels, NO3 promotes the development of plants. Compared with ammonium, nitrate is considered less toxic but does not mean that the plants can tolerate any levels
- Figure 3.3.Effect of different NO3
levels on the growth of aquatic plants
The results of evaluating the effect of NO3
Figure 3.4. The effect of different pH levels on the growth of aquatic plants - on the growth of aquatic - tolerance of the experimental plants in Figure 3.3 showed that the NO3 +. Based on growth data, the tolerant aquatic plants was higher than the NH4 - is descripted as follows: Eichhornia crassipes, order of the plants to NO3 Enydra fluctuans, Cyperus alternifolius > Phragmites australis, Rorippa nasturtium aquaticum, Vetiveria zizanioides > Ipomoea aquatica, Pistia stratiotes. Eichhornia crassipes, Enydra fluctuans, Cyperus alternifolius - < 300 mg/l; Phragmites australis, Rorippa can be resistant to NO3 - <250 mg/l; nasturtium aquaticum, Vetiveria zizanioides can tolerate to NO3 - <200 mg/l. Pistia stratiotes and Ipomoea aquatica can be resistant to NO3 Ayyasamy and cs. (2009), Gupta and cs. (2012), Liu (2012) also reported the similar results. - pH tolerance: In general, the appropriate pH for plant growth is around 6- 8. The pH tolerance of the experimental plants is as follows: Eichhornia crassipes, Ipomoea aquatica, Cyperus alternifolius > Vetiveria zizanioides,
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Enydra fluctuans > Phragmites australis > Pistia stratiotes, Rorippa nasturtium aquaticum. Eichhornia crassipes, Ipomoea aquatica and Cyperus alternifolius can tolerate to pH of 5 - 9. Vetiveria zizanioides and Enydra fluctuans can tolerate to pH 5 - 8. Phragmites australis, Pistia stratiotes and Rorippa nasturtium aquaticum can be resistant to pH <8, the similar results were also reported by Gendy et al. (2004), Lu (2009), Gupta et al. (2012) and Tran Van Tua (2011).
Considering the effect of all the four factors, Eichhornia crassipes is likely the highest tolerant plants, followed by Vetiveria zizanioides, Enydra fluctuans, Cyperus alternifolius and Phragmites australis. The species Pistia stratiotes, Ipomoea aquatica and Rorippa nasturtium aquaticum are the least tolerant plants under the effect of the four factors. The results of the tolerant study are sum up in Table 3.1.
Table 3.1. The tolerance aquatic plants to environmental factors
TVTS PH COD (mg/l) NH4
+ (mg/l) NO3
- (mg/l)
TT 1 5-9 Up to 1000 Over 250 Over 300
6-8 5-8 Up to 500 Up to 750 Up to 150 Up to 250 Up to 200 Up to 250 2 3 4 6-8 Below 500 Up to 150 Up to 250
5-9 5-8 5-8 Below 500 Up to 750 Up to 750 Up to 100 Up to 100 Up to 250 Up to 200 Up to 300 Up to 250 5 6 7 8 5-9 Up to 500 Up to 250 Up to 300 Eichhornia crassipes Pistia stratiotes Phragmites australis Rorippa nasturtium aquaticum Ipomoea aquatica Enydra fluctuans Vetiveria zizanioides Cyperus alternifolius
Based on the results of tolerant study, it is difficult to use directly aquatic plants for pig wastewater treatment, especially in case of COD and +. This suggests for a combination of different treatment processes, in NH4 which Eco-tech is considered as the last step of the process. 3.1.2. The efficiency of pollutant removal by selected aquatic plants 3.1.2.1. The efficiency of pollutant removal in batch experiments
Based on the data of COD removal (Figure 3.5), the efficiency of the plants is ranked from the highest to lowest as follow: Eichhornia crassipes, Pistia stratiotes > Enydra fluctuans, Phragmites australis > Cyperus alternifolius, ipomoea auqatic, Rorippa nasturtium aquaticum > Vetiveria zizanioides.
The efficiency of TSS treatment by the plants was ranked in order (Figure 3.6): Eichhornia crassipes, Pistia stratiotes > Enydra fluctuans, Vetiveria zizanioides, Phragmites australis, Ipomoea aquatica, Rorippa nasturtium aquaticum, Cyperus alternifolius.
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Figure 3.6: Efficiency of TSS removal (%)
Figure 3.5: Efficiency of COD removal (%) The efficiency of NH4
+ removal by the plants was ranked in order: Eichhornia crassipes >Pistia stratiotes, Ipomoea aquatic > Phragmites australis, Enydra fluctuans>Vetiveria zizanioides, Cyperus alternifolius, Rorippa nasturtium aquaticum (Figure 3.7).
Figure 3.7: efficiency of removing
+ (%)
Figure 3.8: Efficiency of TN removal (%)
NH4
The efficiency of TN removal by the plants was ranked in order: Eichhornia crassipes >Pistia stratiotes, Water buffalo, Ipomoea aquatica, Phragmites australis >Vetiveria zizanioides, Cyperus alternifolius, Rorippa nasturtium aquaticum (Figure 3.8).
3-
Figure 3.9: Efficiency of PO4 removal (%)
Figure 3.10: Efficiency of TP removal (%)
The efficiency of PO4
3- removal by the plants was ranked in order: Eichhornia crassipes > Pistia stratiotes, Enydra fluctuans, Ipomoea
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aquatica, Phragmites australis, Cyperus alternifolius > Rorippa nasturtium aquaticum, Vetiveria zizanioides (figure 3.9).
The efficiency of PO4
3- removal by the plants was ranked in order: Eichhornia crassipes > Pistia stratiotes, Enydra fluctuans, Ipomoea aquatica, Phragmites australiss > Rorippa nasturtium aquaticum, Vetiveria zizanioides, Cyperus alternifolius (Figure 3.10).
in semi-continuous
The optimal remaining time for the aquatic plants to remove pollutants was seven days, which is in accordance with the practical treatment systems. Results of other researches using the same aquatic plant system to treat livestock wastewater have also reported a similar observation such as: Sooknah and cs (2004), Tran Van Tua (2007), Ho Bich Lien (2014), Vo Hoang Hoang and cs (2014), Nguyen Hong Son (2016). 3.1.2.2. The efficiency of pollutant removal experiments
The results presented in Fig. 3.12 and Fig.3.14, the efficiency of + removal by the plants was ranked in order: Eichhornia COD and NH4 crassipes, Enydra fluctuans, Phragmites australis>Vetiveria zizanioides, Ipomoea aquatica, Pistia stratiotes, Cyperus alternifolius, Rorippa nasturtium aquaticum.
Figure 3.14: Efficiency of
Figure 3.12: Efficiency of COD treatment (%)
+treatment (%)
NH4
The efficiency of TN removal by the plants was ranked in order: Eichhornia crassipes> Ipomoea aquatica, Enydra fluctuans, Phragmites australis, Vetiveria zizanioides, Cyperus alternifolius>Pistia stratiotes, Rorippa nasturtium aquaticum (Figure 3.16).
The efficiency of TP removal by the plants was ranked in order: Eichhornia crassipes > Enydra fluctuans, Phragmites australis, Ipomoea aquatica, Vetiveria zizanioides,Cyperus alternifolius > Pistia stratiotes, Rorippa nasturtium aquaticum (Figure 3.17).
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Figure 3.16: Efficiency of TN treatment (%)
Figure 3.17: Efficiency of TP treatment (%)
For the all results above, it could be concluded that the COD, TN and TP removal efficiency of different plants was not the same. This dissimilar efficiency might be caused from the different tolerance of those plants to the pollutants.
From the results of tolerant and treatment efficiency study, five plants of 8 tested plants were selected for the further study to assess the ability of pig wastewater treatment after microbial process with different loadings. The five plants are Eichhornia crassipes, Ipomoea aquatica, Phragmites australis, Cyperus alternifolius and Vetiveria zizanioides. 3.2. Efficiency of pig wastewater treatment after microbial treatment stage by some types of Eco-tech using aquatic plants with different loading wastewater 3.2.1. Floating leaves technology - Eichhornia crassipes
The floating leave system effectively remove COD, TN and TP, with COD removal efficiency: 61.5% - 84.9%; TN: 41% - 65.8% and TP: 43.3% - 55.2% (table 3.2). The loads added into the system were 5.1 - 11.6 g COD/m2.day; 4.5 - 10 g TN/m2.day; 0.8 - 1.3 g TP/m2.day. The removal amounts from the system were 4.4 - 11.6 g COD/m2.day; 2.9 - 4.1 g TN/m2. day; 0.4 - 0.45 g TP/m2. Table 3.2. Efficiency of treatment system with Eichhornia crassipes
FLOW – 50l/day FLOW – 100l/day
input output H% input output H%
Parame ters (mg/l) - NO3 + NH4 TN 3- PO4 41.19 ± 4.67 10.52 ± 2.01 89.79 ± 11.2 13.08 ± 3.24 10.92 ± 3.76 2.24 ± 1.09 30.71 ± 4.15 6.19± 0.63 73.5 78.7 65.8 52.7 47.89 ± 3.90 32.67 ± 4.12 100.3 ± 7.86 9.08 ± 3.92 13.86 ±3.73 14.78 ±3.76 60.53 ±8.04 5.59 ± 0.71 71.1 54.8 41 38.4
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TP COD TSS pH DO 15.69 ± 1.13 102.5± 8.42 316.7± 61.9 7.26 ± 0.67 3.96 ± 0.39 7.03 ±0.71 15.51 ± 2.00 88.33 ± 29.3 7.37 ± 0.46 2.96 ± 0.29 55.2 84.9 71.2 73.5 78.7 12.52 ± 1.05 115.7± 22.27 338.3± 57.76 7.17 ± 0.28 4.07 ± 0.30 7.10 ± 1.57 44.5± 10.60 133.3± 0.65 7.58 ± 0.34 3.40 ± 0.15 43.3 61.5 60.6
3.2.2. Surface flow technology
3.2.2.1 Surface flow technology using Phragmites australis
Surface flow system with Phragmites australis effectively removed COD, TN and TP. The removal efficiency of COD was 56.8% - 72.9%; TN: 35% - 53.5%; TP: 33.0% - 42.8% (Table 3.3). The loads added into the system were 5.1 - 11.6 g COD/m2.day; 4.5 - 5 g TN/m2.day and 0.79 - 1.25 g TP/m2.day. The removal amounts from the system were 2.5 - 7.8 g COD/m2.day, 2.4 - 3.5 g TN/m2.day, 0.34 - 0.4 g TP/m2.day.
Table 3.3. Efficiency of treatment system with Phragmites australis
FLOW – 50l/ day FLOW – 100l/day Input Output H% Input Output H%
41.2 ± 4.67 10.5 ± 2.01 89.8 ± 11.17 13.1 ±3.24 15.7 ±2.13 102.5±8.42 316.7±61.9 7.26±0.67 3.96±0.39 14.4 ± 3.73 4.04 ± 1.12 41.7 ± 2.99 7.56 ±0.56 8.97 ±1.69 21.7±3.19 121.7±33.1 7.28±0.58 3.06±0.24 65 61.6 53.5 42.2 42.8 72.9 61.6 47.9 ±3.90 32.7 ±4.12 100.3±7.86 8.58 ±3.26 12.5 ±1.05 115.6±22.2 338.3±57.8 7.17±0.27 4.02±0.34 19.1 ±3.07 16.5 ±3.76 65.2 ±12.8 6.17 ±1.34 8.35 ±2.56 50.0±13.3 163.3±21.6 7.47±0.34 3.05±0.11 60.0 49.4 35.0 28.0 33.0 56.8 51.7 Param eter (mg/l) - NO3 + NH4 TN 3- PO4 TP COD TSS pH DO
3.2.2.2. Surface flow technology with Ipomoea aquatica
The efficiency of COD, TN and TP removal of Ipomoea aquatica system was lower than those with Phragmites australis . The COD removal efficiency was 35.5% - 54.3%,; TN: 25.7% - 36.8%; TP: 28.6% - 42.2% (Table 3.4).
Table 3.4. Efficiency of treatment system with ipomoea aquatica FLOW – 50l/day
FLOW – 25l/day
Input 47.9 ±3.90 32.7 ±4.12 100.3 ±8.26 Output 11.3 ±1.88 15.9 ±2.94 63.3 ±15.5 H% 76.4 51.5 36.8 Input 41.2 ±3.75 10.5 ±2.01 89.8 ±11.17 Output 22.1 ±3.47 5.4 ±1.20 66.7 ±3.90 H% 46.4 49.2 25.7 parameter (mg/l) - NO3 + NH4 TN
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3- PO4 TP COD TSS pH DO
8.58 ±3.26 12.52 ±1.05 115.8±22.3 338.3±57.8 7.17±0.29 4.07±0.30 5.03 ±0.56 7.24 ±1.84 52.9 ±16.7 151.7 ±29.3 7.83 ±0.22 2.87 ±0.24 41.4 42.2 54.3 55.2 13.1 ±3.24 15.7 ±2.13 102.5 ±8.42 316.7 ±61.9 7.26 ±0.67 3.96 ±0.39 8.1 ±0.44 11.2 ±2.22 66.2 ±6.56 198.3 ±33.1 7.01 ±0.33 2.85 ±0.36 38.1 28.6 35.5 37.4
The loads added into the system were 2.3 - 5.1 g COD/m2.day; 2.5 - 4.5 g TN/m2.day; 0.31 - 0.75 g TP/m2.day. The removal amounts from the system were 1.2 - 1.8 g COD/m2.day; 0.9 - 1.2 g TN/m2.day; 0.13 - 0.22 g TP/m2.day. 3.2.3. Surmerged flow technology 3.2.3.1. Surmerged flow technology with Phragmites australis
The system with Phragmites australis effectively removed COD, TN and TP, with COD removal efficiency was 30.2% - 79.4%; TN: 27.8% - 83.7%; TP: 25.0% - 66.3%. The loads added into the system were 2.7 - 12.1 g COD/m2.day; 2.3 - 10.7 g TN/m2.day; 0.3 - 1.2 g TP/m2.day. The removal amounts from the system were 2.1 - 3.7 g COD/m2.day; 1.9 - 3.0 g TN/m2.day; 0.18 - 0.3 g TP/m2.day.
Figure 3.18: Efficiency of surmerged flow technology to treat COD, TN and TP using Phragmites australis
3.2.3.2. Surmerged flow technology with Vetiveria zizanioides
The surmerged flow system with Vetiveria zizanioides effectively removed COD, TN and TP, with COD removal efficiency was 38.7% - 81.5%; TN: 38.6% - 88.7%; TP: 27.6% - 65.4%. The loads added into the system were 2.7 - 12.1 g COD/m2.day; 2.3 - 10.7 g TN/m2.day; 0.28 - 1.2 g TP/m2.day. The removal amounts from the system were 2.2 - 4.68 g COD/m2.day; 2.05 - 4.13 g TN/m2.day; 0.18 - 0.33 g TP/m2.day.
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Figure 3.19: Efficiency to treat COD, TN and TP of the system using Vetiveria zizanioides
3.2.4. Combined system of aquatic plants 3.2.4.1 Eichhornia crassipes and Phragmites australis
The COD removal efficiency of the system was 69.9%, TN: 76.8%, and TP: 68.8% (Table 3.7). The loads added into the system were 7.8 g COD/m2.day; 5.4 g TN/m2.day; 0.61 g TP/m2.day. The removal amounts from the system were 5.4 g COD/m2.day; 4.1 g TN/m2.day; 0.42 g TP/m2.day. Table 3.7. Efficiency of Eichhornia crassipes and Phragmites australis system
FLOW - 100 l/ngày HB1% 61.6 44.5 51.2 54.6 57.8 53.5 57.3 60.2 37.5 52.6 37.1 43.4 35 59.1 Parameter (mg/l) NO3 NH4 TN PO4 TP COD TSS pH DO Input 79.5 ± 3.54 20.81 ±2.71 107.4 ±3.66 9.84 ±0.75 12.14 ±0.97 155.9±11.13 320.1±93.7 6.98±0.79 3.77±0.49 ĐR-B1 30.56± 8.5 11.55 ± 5.1 52.45 ±15.9 4.47 ± 1.11 5.78 ± 1.76 72.42±11.4 136.6±56.9 7.61±0.38 2.49±0.39 ĐR-B2 12.17± 7.44 7.22 ±4.37 24.87 ± 11.9 2.81 ±1.46 3.79 ± 1.71 47.10±9.7 55.86±26 7.68±0.18 3.49±0.27 HB2 % H% 84.9 65.3 76.8 71.4 68.8 69.8 82.6
Note: ĐR-B1: Output of the Eichhornia crassipes tank; HB1: Treatment efficiency of the Eichhornia crassipes tank; ĐR-B2: Output of the Phragmites australis tank; HB2: Treatment efficiency of the Phragmites australis tank; H: Treatment efficiency of the whole system. 3.2.4.2. Combined system of Phragmites australis, Cyperus alternifolius, Eichhornia crassipes and Vetiveria zizanioides
The application of the combined technology allows taking advantage of the each type, improving the efficiency of pollutant removal as well as reducing treatment area.
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The combination system of Phragmites australis, Cyperus alternifolius, Eichhornia crassipes and Vetiveria zizanioides effectively removed COD, TN and TP. The COD removal efficiency was 71.7%; TN: 79.3%; TP: 69.7%. The loads added into the system were 9.6 g COD/m2.day; 5.3 g TN/m2.day; 0.64 g TP/m2.day. The removal amounts from the system were 6.89 g COD/m2.day, 4.2 g TN/m2.day; 0.45 g TP/m2.day.
For all the results above, it could be concluded that the combination of the surface system (Phragmites australis), the floating plant system (Cyperus alternifolius, Vetiveria zizanioides and Eichhornia crassipes) and the submerged flow system (Vetiveria zizanioides) showed the most effective treatment in comparison with other regular systems.
3.21. Efficiency to treat
Figure 3.20. Efficiency to treat COD of the system
TN of the system
3.22. Efficiency to treat TP of the system
3.2.5. Comparison of the efficiency of TN, TP and COD treatment by different types of Eco-technology
Table 3.8. Comparison of the efficiency of TN, TP and COD treatment of different technology types.
Technology aquatic plant TN Treatment efficiency TP COD % g/m2.ng % g/m2.ng % g/m2.ng
25.7 1.15 28.6 0.22 35.5 1.8 Surface flow 53.5 2.40 42.8 0.34 72.9 3.7
65.8 2.95 55.2 0.43 84.9 4.4 Floating plant
76.8 4.13 68.8 0.42 69.8 5.4
Combined system
79.3 4.20 69.7 0.45 71.7 6.9 Ipomoea aquatica Phragmites australis Eichhornia crassipes Eichhornia crassipes - Phragmites australis Phragmites australis- Cyperus
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63.5 3.24 39.6 0.21 64.8 6.8
Surmerged flow system 56.0 2.85 42.6 0.23 62.2 6.6 alternifolius- Water papyrus- Vetiveria zizanioides Vetiveria zizanioides Phragmites australis
The results in Table 3.8 indicate that: + Three eco-tech types having the most effective removing TN, TP, and COD are the combination system, floating plant system - Eichhornia crassipes and Vetiveria zizanioides surmerged system.
+ The surface system with Ipomoea aquatica is less effective when
applied in the treatment of highly polluted wastewater in TN and TP.
+ With the aim to construct an extra-treatment step for TN, TP and COD in pig wastewater after the microbial treatment in the most economical and effective way, we propose to use combination system including surface technology, floating plant systems and surmerged flow system with Phragmites australis, Cyperus alternifolius, Eichhornia crassipes and Vetiveria zizanioides. 3.3. Installation, operation and evaluation of COD, N and P removal efficiency in ecological model (MHST) 3.3.1. Installation
System design: The main specifications of ecological model to treat pig wastewater after aerobic treatment are shown in table 3.9. The model occupies a total area of 600 m2 with capacity 30 m3/day built at Hoa Binh Xanh farm, Luong Son district, Hoa Binh province.
TT 1 2
Table 3.9. Specifications of the ecological model Standard designs Parameter ≤ 450 mg/l - 4500 kg/ha/day COD ≤ 200 mg/l – 2000 kg/ha/ day TN (including N-NH4) ( ≤150 mg/l - 1500 kg/ha/day ) 30 m3/day Capacity
3 4 Time of flow 5 Plants
9 days Phragmites australis, Eichhornia crassipes , Vetiveria zizanioides, Cyperus alternifolius, 0,35 m 6
Depth of water: - Phragmites australis zone - Floating plants zone - Underground flow zone 0,60 m 0,60 m
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Model operation: Seedlings were previously prepared and cultivated in the spring. After one month for rooting and stable growth, the system started with gradual increasing load flow: 0.3-0.6-0.9-1.3 m3/h. 3.3.2. Evaluation of efficiency 3.3.2.1. COD removal efficiency
After 2 months of starting system, MHST was operated to increase the capacity from 0.6 m3/h to 0.9 - 1.3 m3/h to evaluate the treatment efficiency, stability and economic efficiency. - 0.6 m3/h load: COD treatment efficiency of MHST in this period was not stable, around 52.1% in average (ranging from 42.7% to 58.5%). The COD load added into the system was about 5.5 g COD/m2.day, and the removal amount was 2.87 g COD/m2.day. - 0.9 m3/h load: COD treatment efficiency of MHST in this period was 55.8% in average (ranging from 49.34% to 68.2%). The COD load added into the system was about 6.3 g COD/m2.day, and the removal amount was 3.5 g COD/m2.day. - 1.3 m3/h load: COD treatment efficiency of MHST in this period was 59.3% in average (ranging from 53.6% to 65.7%). The COD load added into the system was about 14.7 g COD/m2.day, and the removal amount was 8.7 g COD/m2.day.
Figure 3.23: MHST COD removal efficiency in Luong Son, Hoa Binh
As shown in Figure 3.23, the COD treatment efficiency changed drastically in the initial time, but quickly gained the stability at the load of 1.3m3/h. The COD removal amount increased accordingly with the increase of the COD load added into the system. The COD removal amount by MHST system was 2.8 - 8.7 g COD/m2.day.
The similar results were also reported in previous studies conducted by Poach (2004), Kalipci (2011), Vymazal and Kröpfelová (2011), Luu Huy Manh and cs. (2014), Nguyen Thanh Loc and cs. (2015).
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- and NH4
- removal efficiency was 74.1%, and NH4 - and NH4
3.3.2.2. Nitrogen removal efficiency - Load flow 0.6 m3/h: The TN, NO3 + removal efficiencies were 73.8%, 73.8%, and 44.6%, respectively. The average TN load added into the system was 4.1 g TN/ m2.day. The removal amount was 3.02 g TN/m2.day. - Load flow 0.9 m3/h: The average treatment efficiency reached to 67.8%, + was 59.2%. The system with NO3 +. The average TN load effectively removed both TN and NO3 added into the system was 2.4 g TN/ m2.day and the removal amount was 1.62 g TN/m2.day.
- and NH4
Figure 3.24: TN removal efficiency of MHST in Luong Son, Hoa Binh - Flow load 1.3 m3/h: The TN, NO3 + removal efficiencies were 66.2%, 68.5% and 51.8%, respectively. The average TN load added into the system was 5.5 g TN/m2.day, and the removal amount was 3.6 g TN/m2.day. At this stage, despite the high variation of TN input, the efficiency and stability of the system remained in a high performance. This proved that the system in this study well adapted to a high range of load flow and input content.
In summary, the load added into the system was 2.4-5.5 g TN/m2.day and the removal amount from the system was 1.6 - 3.6 g TN/m2.day. The results of this study are in consistent with previous studies carried out by Sohsalam and cs. (2008), Zhang (2016) and Le Tuan Anh (2013).
removal of
The pollutant
the combined ecological system demonstrated a higher efficiency than those with only one plant species in a system which was reported by López and cs (2016) and Luu Huy Manh and cs. (2014). These positive results were derived from the combination of different aquatic plants, which clearly improved the pollutant removal efficiency of the treatment system . The diversity of plants in the system is
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able to increase plant tolerance to changing environmental conditions as well as stability in biochemical processes (Eviner and Chapin, 2003), limiting the effects of seasonal factors, pests... 3.3.2.3. Phosphorus removal efficiency - Load flow 0.6 m3/h: The TP removal efficiency was 50.7% in average (ranging from 47.9% to 54.4%). The average TP load added into the system was 0.8 g TP/m2.day, and the removal amount was 0.41 g TP/m2.day.
Figure 3.25. TP removal efficiency of MHST in Luong Son, Hoa Binh.
- Load flow 0.9 m3/h: The TP removal efficiency was 48.8% (ranging from 47.4% to 51.7%). The average TP load added into the system was 1.4 g TP/m2.day and the removal amount was 0.68 g TP/m2.day. - Load flow 1.3 m3/h: The TP removal efficiency was 45.3% (ranging from 41.9% to 48.8%). Data from Figure 3.25 indicated that the efficiency in this load flow was relatively stable. The average TP load added into the system was 1.9 g TP/m2.day, and the removal amount was 0.86 g TP/m2.day.
The TP load applied to the system ranged from 0.8 to 1.9 g TP/m2.day and the removal from the system ranged from 0.41 to 0.86 g TP/m2.day. The results of this study are in consistent with González (2009), Zhang and cs (2016). Like N, the efficiency of MHST is much higher than that of one-type TVs by Zheng and cs (2016), Valipour and cs (2015) and Pham Khanh Huy (2012).
3.3.2.4. Changes of the hydrological parameters of the ecological model
In general, the hydrological parameters of the wastewater were not significant different among the four loading inputs, the output of Phragmites australis, the floating system and the last output of the model except the EC, pH and temperature factors. The average value of DO parameter was in between 2.99 ± 1.29 due to the air supply during treatment process.
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The pH values of MHST were significant different between the input and output points (P <0.05), ranging from 7.96 to 8.42. The pH was alkaline at the input of treatment process (around 8.42 ± 0.31), then gradually decreased to 7.96 ± 0.52 at the output. This meant that the pH of output water was almost neutral. Similarly to pH values, conductivity (EC) of MHST was significant different (P <0.05) between the two points. The average EC values at input was about 3.47 ± 1.94 mS/cm, then reduced to 1.77 ± 0.99 mS/cm at the output. The temperature at the input was about 23.41 ± 3.93, and reduced to 22.93 ± 3.78 at the output.
Table 3.9.Hydrological parameters of the ecological model
Parameters Input Output P- value Floating plant system Phragmites australis system 2.79±1.57 EC (mS/cm) 3.47±1.94 2.11±1.07 1.77±0.99 0.03 Sal. (‰) 1.83±1.09 1.51±0.96 1.19±0.83 0.94±0.59 0.09 TDS (m/L) 2.16±1.17 1.78±0.99 1.38±0.75 1.14±0.62 0.98 pH 8.42±0.31 8.31±0.3 8.10±0.36 7.96±0.52 0.04 Temperature 23.4±3.93 23.2±4.2 22.8±3.89 22.9±3.78 0.02 DO (mg/l) 2.99±1.29 2.1±0.93 2.70±0.91 2.40±0.68 0.14 0.75 Turbidity (NTU) 109±112 99±90 94±142 57±112
In summary, when the MHST system worked at full designed capacity (1.3 m3/h or 30 m3/day), with the inputs of COD, TN and TP 323.7 mg/l; 102.7 mg/l and 31.46 mg/l, the treatment efficiency of those parameters reached to 59.3%; 66.2% and 45.3%, respectively. The output values of the treated wastewater were 123.69 mg/l COD; 32.54 mg/l TN and 17.03 mg/l, which meets the A standard for wastewater according to QCVN 62-MT: 2016-BTNMT for COD and TN. 3.3.2.5. Preliminary calculation of economic efficiency
Eco-tech uses aquatic plants as a low cost technology, simple technology, easy to operate and can use local resources. Investment costs include the cost of designing, building and purchasing materials. The preliminary cost for MHST (scale of 600 m3, capacity of 30 m3 wastewater per day) is 201.5 million VND. With the above mentioned cost, the investment rate is 6.7 million VND/m3 wastewater.
Operation and management costs: Operation costs include the cost of quality control of flow, maintenance of the system, weeding, collecting plants, etc. Operating MHST does not require electricity, machines, and
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need only one-hour labor per day for examination, flow adjustment, plant caring and harvesting. The operation cost for 1 m3 wastewater treatment is canculated:
VND 150,000 (one day salary): 8 hours: 30 m3 = VND 625 vnd/m3 Therefore, the application of Eco-tech as an extra-step for livestock wastewater treatment after microbial process is suitable for economic and technical conditions for the most of livestock farms in Vietnam. The 600 m2 treatment model at Hoa Binh Green Farm have proved the high treatment efficiency of the technology when 66.2% of TN; 45.3% TP and 59.3% COD were removed from wastewater after the treatment process.
3.4. Evaluation of treatment efficiency of MHST in the integrated model in Luong Son, HoaBinh province.
The overall model of pig waste disposal (wastewater, solid waste and odor) was built on a 1.300 m2 area outside the livestock farming. MHST system was installed as the final stage of the overall model, to treat COD, N and P to the permitted standards for wastewater discharging to environment. Separated treatment steps are not substitutable but support each other. The role of MHST in the overall model is described as bellow:
COD, TN and TP treatment efficiency of the model is presented in
Table 3.11. Table 3.11. COD, TN and TP treatment efficiency of waste water treatment model
parameters Input Anaerobic output Aerobic- anoxic output MHST output H%
COD (mg/l) 6339 1958 316 119 98.1
1 ± 1309 1359 82 23 0.34
H of each stage (%) 69.1 83.9 62.3
TN (mg/l) 1042 875 99.27 32.97 96.8 2 ± 129.3 102.3 52.47 14.4 1.36 H of each stage (%) 16.03 88.7 66.8
TP (mg/l) 149.2 67.4 31.4 16.63 88.9 3 ± 27.8 27.0 5.71 5.6 3.03 H of each stage (%) 54.83 53.41 47.04
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The efficiency of COD treatment was relatively high; average value was about 98.1%, in which treatment efficiency of ecological step was 62.3%. The output COD amount was 119 mg/l, which meets the B standard according to QCVN 62-MT: 2016/BTNMT
In terms of TN treatment, although the TN in the effluent was very high (1041.7 mg/l), the overall system was able to remove approx. 96.8% TN. The efficiency of MHST system itself gained to 66.8%, leading to the TN of output effluent of the system was 33 mg TN/l, which is lower than the A standard (50 mgTN/l) according to QCVN 62-MT: 2016/BTNMT.
Average TP input of the system was 149.2 mg/l, the overall system removed 88.9% of TP out of the system. The efficiency of MHST system itself gained to 47%, with 31.4 mg TP/l input and 16.6 mg TP/l output. It should be considered that when the amounts of COD, TN and TP are low but still higher than permitted standards, using Eco-tech with aquatic plants is the most efficient and economical way to apply for the treatment. Other methods like physico-chemical or microbial technologies will require higher investment and more complicated operation compared to the Eco-tech. Because the Eco-tech is low cost and simple, it can be operated by any farmer or organization who want to develop their livestock farming in a sustainable way.
+, NO3
