The objective of research is to build CNST using TVTS to treat pig waste water after microbiological treatment, to minimize environmental pollution. Technology is feasible when applied in practice.
Trang 1VU 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
GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY
Trang 2
-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
The dissertation can be reached at:
- Library of the Academy of Science and Technology
- Vietnam national library
Trang 3INTRODUCTION
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 technological conditions, contributing to minimize 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 wastewater after microbial treatment process in order to reduce environmental pollution The technology is feasible and practical
Trang 43 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,
NH4 , NO3-, pH, and their ability to treat COD, nitrogen, phosphorus in pig 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
Trang 5liters/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 andneeds 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
- Pollutant removing mechanism: Nitrogen is removed by 3 mechanisms, nitrification/denitrification, ammonia evaporation 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
Trang 61.4 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 m 3 /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,
Trang 7Ipomoea 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, NH 4 + , NO 3 - , pH
Tolerance of aquatic plants to COD, NH 4 + , NO 3 - 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
Trang 8layer: 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
(floating plant system), the last one for Vetiveria zizanioides
(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, NO3-, T-N, PO4-3, 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
Trang 9Chapter 3 Results and discussion 3.1 Tolerance and treatment ability of the aquatic plants
3.1.1 Plant tolerance to the pollutants
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 evaluate the tolerance of selected aquatic plants to COD, NH4 , NO3- and
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 NH4levels on the growth of aquatic plants 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)
- NH 4 + tolerance: Nitrogen is an important nutrient for plants growth
Although NH4+ can be assimilated by plants, NH4+ turns to toxic if the amount is high due to part of ammonia will convert into NH3 Based on the
Trang 10results of the NH4 tolerance assessment (Figure 3.2), NH4 tolerance of the
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
alternifolius can resist NH4+ < 250 mg/l Pistia stratiotes, Rorippa nasturtium aquaticum can tolerate to NH4 <150 mg/l Enydra fluctuans and
Ipomoea aquatica can resist NH4 < 100 mg/l, all of which is corresponding
to the research of Korner (2001), Liao X (2000) and Piyush Gupta et al.,
2012
- Tolerance to NO 3 - : NO3- is an essential compound for the growth and
development of plants With appropriate levels, NO3- along with PO4-3promotes 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 Figure 3.4 The effect of different pH
levels on the growth of aquatic plants The results of evaluating the effect of NO3- on the growth of aquatic plants in Figure 3.3 showed that the NO3- tolerance of the experimental aquatic plants was higher than the NH4 Based on growth data, the tolerant order of the plants to NO3- is descripted as follows: Eichhornia crassipes,
Enydra fluctuans, Cyperus alternifolius > Phragmites australis, Rorippa nasturtium aquaticum, Vetiveria zizanioides > Ipomoea aquatica, Pistia
stratiotes Eichhornia crassipes, Enydra fluctuans, Cyperus alternifolius
can be resistant to NO3- < 300 mg/l; Phragmites australis, Rorippa nasturtium aquaticum, Vetiveria zizanioides can tolerate to NO3- <250 mg/l;
Pistia stratiotes and Ipomoea aquatica can be resistant to NO3- <200 mg/l 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,
Trang 11Enydra 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
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
Trang 12Figure 3.5: Efficiency of COD
removal (%)
Figure 3.6: Efficiency of TSS
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
NH4 (%)
Figure 3.8: Efficiency of TN removal (%) 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)
Figure 3.9: Efficiency of PO43-
removal (%)
Figure 3.10: Efficiency of TP removal (%) The efficiency of PO43- removal by the plants was ranked in order:
Eichhornia crassipes > Pistia stratiotes, Enydra fluctuans, Ipomoea
Trang 13aquatica, Phragmites australis, Cyperus alternifolius > Rorippa nasturtium aquaticum, Vetiveria zizanioides (figure 3.9)
The efficiency of PO43- 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)
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 in semi-continuous experiments
The results presented in Fig 3.12 and Fig.3.14, the efficiency of COD and NH4 removal by the plants was ranked in order: Eichhornia
crassipes, Enydra fluctuans, Phragmites australis>Vetiveria zizanioides, Ipomoea aquatica, Pistia stratiotes, Cyperus alternifolius, Rorippa nasturtium aquaticum
Figure 3.12: Efficiency of COD
treatment (%)
Figure 3.14: Efficiency of NH4 treatment (%)
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)