Study on potential plants for use in constructed wetlands to strengthen phosphorus treatment performance from swine wastewater

VIETNAM NATIONAL UNIVERSITY, HANOIVIETNAM JAPAN UNIVERSITY VU THI THOM STUDY ON POTENTIAL PLANTS FOR USE IN CONSTRUCTED WETLAND TO STRENGTHEN PHOSPHORUS TREATMENT PERFORMANCE FROM SWINE

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

VU THI THOM

STUDY ON POTENTIAL PLANTS FOR USE IN CONSTRUCTED WETLAND TO STRENGTHEN PHOSPHORUS TREATMENT PERFORMANCE

FROM SWINE WASTEWATER

MASTER'S THESIS

Hanoi, 2019

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

VU THI THOM

STUDY ON POTENTIAL PLANTS FOR USE IN CONSTRUCTED WETLAND TO STRENGTHEN PHOSPHORUS TREATMENT PERFORMANCE

FROM SWINE WASTEWATER

MAJOR: ENVIRONMENTAL ENGINEERING

CODE: PILOT SUPERVISORS

DR NGUYEN THI AN HANG ASSOC PROF DR SATO KEISUKE

DR NGUYEN THI HOANG HA

First of all, I would like to express the sincere gratitude to my principalsupervisor, Dr Nguyen Thi An Hang at VNU Vietnam Japan University, foraccepting me as her master student and continuous teaching and supporting me inthe process of doing experiments as well as writing essays and makingpresentations She always encourages and is willing to help me when I havedifficulties She is always beside me to teach me how to work effectively This helps

me grow up in both personal and professional aspects A special thanks also go toAssoc Prof Dr Sato Keisuke for his recommendations to my research He provided

me with the best conditions for implementing my experiments during my internship

in Japan He is wholeheartedly devoted to his students I would like to express mydeepest thanks to Dr Nguyen Thi Hoang Ha She gave me valuable supports indeveloping research methods, and enthusiastically guided me to fullfil my thesis Ialways feel grateful to her for accompanying me for such a long time

The second, I would like to send my sciencere thanks to Prof Dr JunNakajima for supporting not only me but also all of memerbers in my class duringMaster course He cares for us like his children And he is our respected father

The third, I am grateful to Ms Nguyen Thi Xuyen, the project staff, foralways supporting me in conducting experiments as well as analyzingenvironmental parameters

This research is funded by Vietnam National Foundation for Science andTechnology Development (NAFOSTED) under grant number 105.99-2018.13,

2018 Asean Research Center (ARC) research grant of Vietnam NationalUniversity, Hanoi (VNU), and Japan International Cooperation Agency (JICA)research grant for the academic year of 2018-2019

My heartfelt thanks and gratitudes to my family for their unconditionalhelps with plant sampling, the love and encouragement

Hanoi, June 9th, 2019

Vu Thi Thom

i

TABLE OF CONTENTS

ACKNOWLEDGMENTS i

LIST OF TABLES ii

LIST OF FIGURES iii

LIST OF ABBREVIATIONS v

INTRODUCTION vi

CHAPTER 1: LITERATURE REVIEW 1

1.1 Overview of the situation of pig husbandry in Vietnam 1

1.1.1 Current status and development orientation of pig breeding 1

1.1.2 Environmental pollution due to swine wastewater 2

1.1.3 Technologies for the treatment of swine wastewater 4

1.2 Phosphorous pollution and treatment technologies 5

1.2.1 Phosphorus pollution and its consequences 5

1.2.2 Phosphorus treatment technologies 6

1.3 Constructed wetland for wastewater treatment 7

1.3.1 Definition and classification of CWs 7

1.3.2 Influential factors and treatment performance 9

1.4 Removal phosphorus by plants in the CWs 12

1.4.1 Classification of plants used in CWs 12

1.4.2 Removal P mechanisms by plants 14

CHAPTER 2: MATERIALS AND RESEARCH METHODOLOGY 18

2.1 Research object, scale, and scope 18

2.1.1 Research object 18

2.1.2 Research scale & scope 18

2.2 Materials, chemicals and equipment 19

2.2.1 Materials 19

2.2.2 Experimental design 20

2.2.3 Plant sample preparation and P analysis 25

2.2.4 Analysis of other water quality parameters 26

2.3 Data calculation 27

2.4 Data statistical analysis 28

CHAPTER 3: RESULTS AND DISCUSSION 29

3.1 Screening potential plants for use in the CWs 29

3.1.1 Selection of potential plants based on their P content and biomass growth 29

3.1.2 Selection of CWs plants based on other growth characteristics 33

3.2 Factors influencing the growth and uptake of p of Cymbopogon citratus and Ubon paspalum 35

3.2.1 Effect of initial P concentration 35

3.2.2 Effect of pH 42

3.2.3 Effect of plant age 45

3.2.4 Effect of plant density 49

3.2.5 Effect of water level 52

3.3 Applicability of the selected plants in the constructed wetland 54

CHAPTER 4: CONCLUSION AND RECOMMENDATION 57

4.1 Conclusion 57

4.2 Recommendations 57

REFERENCE 58

APPENDIX 62

LIST OF TABLES

Table 1.1 Annual growth rate of culture sector (%) 1

Table 1.2 Composition and characteristics of swine wastewater 3

Table 1.3 Methods for handing and using liquids at systems 4

Table 1.4 3 main parameters of swine wastewater after biogas treatment 5

Table 1.5 P removal by Constructed Wetland 11

Table 1.6 Plant species are used to treat swine wastewater 13

Table 1.7 P removal efficiency by plants in CW (Jesus et al., 2017) 15

Table 2.1 The list of investigated plants 19

Table 2.2 Methods for examination of water quality parameters 27

Table 3.1 The P content in plants use for phytoremediation or CWs 31

Table 3.2 The P removal potential of the studied plants 33

Table 3.3 Growth characteristics of potential plants 34

Table 3.4 The P removal efficiency by different plant species 39

Table 3.5 Biomass growth rate of Ubon paspalum at different plant ages 48

Table 3.6 Effect plant density on the biomass growth rate of Ubon paspalum 51

LIST OF FIGURES

Figure 1.1 Eutrophication: cause and effect 5

Figure 1.2 P removal in CWs 9

Figure 2.1 Scheme of horizontal constructed wetland 23

(at the start of experiment) 23

Figure 2.2 The structure of filter media in CWs and adsorption units 24

Figure 2.3 Plant sample preparation and analysis 25

Figure 2.4 Images of apparatus used in this study 26

Figure 3.1 The P content and its distribution in the studied plants 29

Figure 3.2 Images of the investigated plants in this study 34

Figure 3.3 Effect of initial P concentration on the removal efficiency of Cymbopogon citratus 37

Figure 3.4 Effect of initial P concentration on the removal efficiency of Ubon paspalum 37

Figure 3.5 P concentration left in solution plant with Ubon paspalum 38

Figure 3.6 P concentration left in solution planted with Cymbopogon citratus 38

Figure 3.7 Effect of intial P concentration on P removal rate of Ubon paspalum 40

Figure 3.8 Effect of intial P concentration on P removal rate of Cymbopogon citratus 40

Figure 3.9 Ubon paspalum died at the highest P concentration 41

Figure 3.10 Cymbopogon citratus could adapt with a wide range of initial P concentration 41

Figure 3.11 Normal growth of Cymbopogon citratus at all pH values 42

Figure 3.12 The death of Ubon paspalum at pH values of 9&11 43

Figure 3.13 Speciation of P in solution at various pH conditions 43

Figure 3.14 Effect of pH on P removal efficiency of Ubon paspalum and Cymbopogon citratus 44

Figure 3.15 Effect of pH on P removal rate of Ubon paspalum and Cymbopogon citratus 45

iii

Figure 3.16 Effect of plant age on P removal efficiency and P removal rate of Ubon

paspalum (hydroponic experiment) 47

Figure 3.17 The effect of plant age on the growth of root system 47

Figure 3.18 Effect of plant age on the biomass growth of Ubon paspalum 48

(experiment with garden soil) 48

Figure 3.19 Effect of plant density on P removal rate of the investigated plants 50

Figure 3.20 Effect of plant density on the P removal efficiency of the investigated plants 50

Figure 3.21 The root growth of Ubon paspalum at different plant densities 52

Figure 3.22 Effect of Ph on P removal rate of plants 53

Figure 3.23 Effect of water level on root growth of Ubon paspalum 54

Figure 3.24 The change of phosphorus in the effluent over the time 54

Figure 3.25 P removal efficiency and Ph after treatment of HFCWs 55

Figure 3.26 The plants growth well after 2 weeks of system operation 56

Hydraulic loading rateHydraulic retention timeSubsurface water flowSurface flow

Total nitrogenTotal phosphorusTotal suspended solidsVertical flow

White hard clam

v

In Vietnam, in recent years, pig breeding industry has developed rapidly Sincemost of pig farms have not designed and operated appropriately, wastewater from pigfarms cause serious environmental pollution, which poses a high risk to public healthand surrounding ecosystems Therefore, the proper treatment of swine wastewater isurgent and necessary At present, swine wastewater in Vietnam is normally treated bybiogas technology However, the concentration of pollutants in the effluent is still high,exceeding national discharge standards (QCVN 01-79: 2011/BNNPTNT) Thus, furtherprocessing after biogas treatment of swine wastewater is mandatory

Constructed wetlands (CWs) is a promising technology, which possesses manyadvantages, such as cost-effective, green technology (Wu et al., 2015; Yang et al,2018;), low land, energy, and less-operational requirements (Wu et al., 2015);simple construction and operation (Bunce et al., 2018) However, the wideapplication of CWs is limited by intensive land requirement, long-termunsustainability (Bunce et al., 2018) Especially, although CWs can achieve highremoval efficiency with TSS, COD, BOD, it is demonstrated to be inefficient innutrient elimination It is well-known that the treatment performance of phosphorus

by CWs is low and unstable Hence, the enhancement of phosphorus removal by

CW is of great significance Since phosphorus is eliminated by CWs mainly viasubstrate adsorption, plant uptake, microbial degradation, selection and application

of potential plants in CWs plays an important role

Plant-based treatment technology is known as phytoremediation, which receivesthe great interests of scientists in the world So far, a numerous number of studies onsuccessful phytoremediation of wastewater polluted by phosphorus The most commontypes of plant species for nutrient removal are Typha latifolia, Cyperus papyrus,Phragmite australiis (Almuktar et al., 2018) TP removal efficiency of

Phragmites communis, Typha orientatlis and Sparganium stoloniferum was 72.67%,73.39%, 71.54%, respectively (Liu et al., 2012) TP was considerably eliminated byPersicaria hydropiper, representing 97.63% (Zheng et al., 2013) However, these arewildlife grass type with no or less economic value There is still lack of informationabout potential plants with high economic value for phytoremediation and CWs totreat P- rich water and wastewater Also, very few studies on factors influencing thegrowth and utapke of phosphorus by plants.

The objectives of this study comprise (1) to search for potential plants forphosphorus decontamination from wastewater, (2) to investigate five factors

influencing the growth and phosphorus removal efficiency of Ubon paspalum and

Cymbopogon citratus, (3) to evaluate the applicapability of selected plant (Ubon paspalum) in the constructed wetlands for treatment of synthetic swine wastewater.

Thesis’ outline

The thesis has been completed by 5 chapters The main contents of eachchapter are provided as below

Introduction: Introduce the research content, identify research issues, tasks,

purposes, research scope

Chapter 1: Literature review - Providing information on the characteristics

of P factor, the negative impact of P on the environment, technological solutions

implemented to eliminate P, the removal efficiency of Contructed Wetland, rolesand mechanisms P removal of plants

Chapter 2: Materials and methods - Describe potential plant selection

methods, methods of analyzing P content in plants and water, methods of setting upexperiments to study absorption capacity of plants under the influencing factors

Chapter 3: Results - Focus on describing the results of plant uptake rates and

assess the role of plants in the P removal in CWs

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Chapter 4: Discussion and recommendation - Summarizes major findings

of this study Additionally, the unique contributions of this study to the field of

phosphorus removal by plants are provided Provide limitations and for futureresearch direction

Appendices – provides some pictures in research activities

CHAPTER 1: LITERATURE REVIEW 1.1 Overview of the situation of pig husbandry in Vietnam

1.1.1 Current status and development orientation of pig breeding

According to FAO, Asia will become the region, which produces andconsumes livestock products the most Like other countries in the region, Vietnamneeds to maintain high growth level to meet the demand of domestic consumptionand export In recent years, the livestock industry in Vietnam has developed rapidly.The annual growth rate of livestock in the period of 2006-2010 was 8.5%

Table 1.1 Annual growth rate of culture sector (%)

Year

1986-1990 1990-1996 1997-2005 1986-2005 2006-2010Sectors

Source: Vietnam Agricultural Economics Institute, 2009 Recently, there is a trend to

develop centralized animal husbandry As a result, the number of large-scale farms

is increasing By 2006, Vietnam has 17,721 farmsthroughout the country, of which there is 7,415 pig farms, accounting for 42.18%.The number of pig farms has increased from 3,293 to 14,481 in the period of 2011-2016

Among Asian countries, Vietnam has to suffer from high pressure of landuse The fast population growth and urbanization have resulted in a reduction ofagricultural land In order to ensure food security, Vietnam has no choice but

1

implementation of intensive animal husbandry Of which, pig raising plays animportant role According to Decision No 10/2008/QĐ-TTg dated on 16 January

2008 by the Prime Minister on the approval of livestock development strategy to

2020, the proportion of livestock in the agriculture will increase from 32% (2010) to38% (2015) and reach 42% (2020)

1.1.2 Environmental pollution due to swine wastewater

a Characteristics of swine wastewater

The swine wastewater can pose a high risk to the environment, due to highcontent of organic matter, TSS, N, P, and pathogen According to the report toassess the current status of the environment by Institute for Animal Husbandry(2006), in centralized pig farms in Ha Noi, Ninh Binh, Nam Dinh, Quang Nam,Binh Duong, Dong Nai, the swine wastewater is characterized as follows:

- Organic matter accounts for 70-80%, including cellulose, protein, acid amine, lipid, hydrate carbon, …

- Inorganic matter represents 20-30%, including, salts (chloride, sulfate, etc.)

- Nutrients (N and P): The swine wastewater usually contains high levels of N and

P (e.g TN 200-350 mg/ L of which N-NH4 accounts for 80-90%, TP 60-100 mg/ L)

- Pathogens: Swine wastewater may contain microorganisms, virus, eggs of

parasites, etc

2

Table 1.2 Composition and characteristics of swine wastewater

No Parameters Unit Value Category A, QCVN

Source: Xuyen Viet Environment Company

b Swine wastewater management

In recent years, the pig breeding industry has developed rapidly However,most of them have been developed spontaneously and have not met the technicalstandards for breeding facilities Therefore, breeding productivity is usually low andthe surrounding environment is seriously polluted The wastewater from pig farmsincludes urine, wastewater from pig bathing and facilities cleaning A majority ofpig farms discharge directly the wastewater into surrounding water bodies, causingunpleasant smells (H2S and NH3) especially in the hot and sunny days Theineffective management of swine wastewater is due to huge amount of wastewater

is generated, which cannot be used all for arable lands in surrounding areas It isestimated that the need of clean water for cleaning breeding facilities, pig bathing,pig drinking is 30-50 L/ pig head/ day The bad smell, hindering its transport forlong distances for purposes of agriculture and aquaculture development

3

Table 1.3 Methods for handing and using liquids at systems

m3

3.87 ±5.43 4.41±1.28 3.73±1.83 3.98 ±2.98wastewater

treatment environment m3

2.22 ±2.23 4.91±2.95 3.98 ±5.75 3.50±5.40

1.1.3 Technologies for the treatment of swine wastewater

Numerous technologies have been used for treatment of swine wastewater,which can be divided into (1) Mechanical treatment method, (2) Physio-chemicaltreatment method, and (3) Biological treatment method Of which, biologicaltreatment method is mainly used after mechanical and physio-chemical treatment

Biological treatment methods comprise both aerobic and anaerobic treatment.The anaerobic treatment processes include biogas, anaerobic tank, anaerobicbiological trickling filtration, upflow anaerobic slug blanket (UASB), expandedgranular sludge bed (EGSB) The commonly used aerobic processes are aerotank,aerobic biological filtration, biological lagoon, algae, aquatic plants In order to cutdown the price of pig breeding, farm owners in Vietnam tend to simply apply biogasinstead of combining various technologies The commonly used treatment train is:Swine wastewater => Biogas tank => Lagoon => Environment Consequently, theeffluent after biogas treatment is heavily polluted, and far above the dischargestandard (QCVN 40:2011/BTNMT)

4

Table 1.4 3 main parameters of swine wastewater after biogas treatment

40:2011/BTNMT1

Ammonium (NH

+ ) mg/L ISO 5664 (TCVN 5988) 180-340 104

SMEWW 4500P E

1.2 Phosphorous pollution and treatment technologies

1.2.1 Phosphorus pollution and its consequences

Phosphorous is an element essential for plant growth It is actively involved

in main functions of plants, such as photosynthesis, energy conveyance, activation

of protein, control of metabolic processes, etc (Vo et al., 2017) However, theexcessive level of phosphorus may cause the eutrophication in natural water bodies

Figure 1.1 Eutrophication: cause and effect

This results in many water quality issues, including deterioration of waterquality and algal bloom Degradation of algal reduces O2 but increase CO2 in water,thus influencing the life of aquatic organisms The lack of oxygen leads anaerobicdecomposition of organic matter, producing foul smell (H S, NH , CH ) (Thongtha et

5

activities Natural activities include earthquake, soil erosion, etc Human activitiescan release phosphorus into aquatic medium, such as agriculture, wastewater, stormwater, etc The contribution of domestic sewage, agriculture and industry to theglobal phosphorous load is 54, 38, and 8% respectively The phosphorus load fromagriculture in USA increased by 27%, from 579,000 to 734,000 tons in 2010.

1.2.2 Phosphorus treatment technologies

Phosphorus decontamination from wastewater can be done via physical,chemical or biological methods Physical methods include membrane, magneticseparation, adsorption, ion exchange etc Chemical processes are precipitation,crystallization

Biological methods comprise EBPR, phytoremediation, constructed wetlands,etc Each method has both advantages and limitations Typically, the chemicalprecipitation is widely used for phosphorus treatment, because it is flexible, easy toinstall, high P removal, less space requirement However, its application is limited due

to high chemical demand, chemical sludge generation, effluent neutralizationrequirement, difficult to identify optimal dosing conditions, low bioavailability of end-products, unsuitable for wastewater with low P levels Another method for phosphorusremoval is adsorption This method is favored because of simple operation, lesschemicals use, no sludge formation, suitability for P-poor wastewater Nevertheless,limitations of this method are high cost, disposal problems after use, etc In a studyconducted by Gustafsson et al (2008) using naturally occurring materials, thephosphorus removal efficiency reached 95% In another study, Seo et al (2013)reported that phosphorus could be removed up to 90% In recent years, phosphorusremoval using enhanced biological methods has received great interests of scientists inthe world, due to the dominant advantages of modest cost, minimal sludge formation orability to remove phosphorus to very low levels According to Smith et al (2014) Sun

et al (2013), 88% of phosphorus was removed from wastewater by membranebioreactor integrated into a continuous flow EBPR Besides to advantages, this methodhas some constraints, including external carbon source

requirement, complex configuration and operating regimes, more energy and spacerequirement (Nguyen et al., 2015) The utilization of biological process is not onlylimited to EBPR but also using algal or aquatic plants Sukacova et al (2015) statedthat fixed growth algal bioreactor could eliminate up to 97% phosphorus inwastewater The ability of macrophyte in phosphorus decontamination fromwastewater will be discussed thoroughly in other section of thesis.

1.3 Constructed wetland for wastewater treatment

1.3.1 Definition and classification of CWs

a Definition

Artificial wetlands are human wetland areas designed to treat wastewater.The system of artificial wetlands has low operating and maintenance costs, lowenergy consumption, does not require high operational and environmentally friendlytechniques (Viet et al., 2019)

Components of CWs include substrate, plant, microorganism, animal(earthworm), water (Davis, 1985) The biomass of plants in the system can be used

as animal feed, as a fiber material or as an organic fertilizer However, the land areafor construction of artificial wetlands is relatively large, which is an obstacle to theselection of this treatment method, so artificial wetlands are suitable for crowdedareas with wide and unfocused land area

b Advantages and limitations

CWs are inexpensive (building, maintenance), simple operation, tolerant to variousflow, habitat of many submerged species, wild animals; improve the surroundings,get the community's approval (Davis, 1995)

CWs need to be a large land area, effectively processing inconsistently affectedexternal environmental conditions such as rainfall, droughts, seasons, sensitive totoxic chemicals (Davis, 1995)

c Classification

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There are many ways to classify CWs which are based on water level,direction of water (Vymazal, 2008) Based on CWs water levels are classified intocategories: Surface flow CWs, Subsurface flow CWs (VF-CWs, HF-CWs), Hybrid /integrated / combined CWs The water level in the

SF system is higher than the substrate surface while it is equal to or lowerthan the substrate surface in the SSF system (Davis, 1995)

Based on the flow direction of water, SSF is divided into 2 types of horizontalflow (HF) and vertical flow (VF) Water in HFCWs flooded the substrate in the systembefore exiting through water level control While water in the VFCWs system drainswith the intermittent application of water to the system (Stefanakis et al 2014)

d Mechanisms of CWs for P removal

Numerous studies shown that the phosphorus in constructed wetlands isremoved mainly by absorption of plants, accumulation of microorganisms,absorption and precipitation of matrix (Lu, 2006) Firstly, the inorganic phosphorus

is synthesized ATP, DNA and RNAetc.by uptake and assimilation of plants, andremoved from the system through the plants harvested Secondly, phosphorus isnecessary to microbial, phosphorus bacteria converted poorly soluble organicphosphorus and phosphorus to dissolved inorganic phosphorus which is conducive

to absorption by plants Finally, phosphorusis removed by adsorption of media orion exchange, the iron, aluminum, calcium compounds will affect the adsorptioncapacity of the media, and PAOs excess polyphosphate phosphorus also has acertain role to removal phosphorus Since the constructed wetland have a specialaerobic and anaerobic conditions, PAOs can be adsorbed an excess of phosphorus inthe aerobic state, and released excess phosphorus in anaerobic conditions, some ofphosphorus will spread with the water transport, other will adsorption by themedium, because of the release of phosphorus, adsorption by media in favor ofphosphorus in the local where concentration of phosphorus is higher

Figure 1.2 P removal in CWs (Hristina Bodin, 2013)

The most important way to remove phosphorus is adsorption and precipitation

of matrix in constructed wetland system, there is less effect for plant adsorption oforganic phosphorus, but the absorption of plant is given priority to remove inorganicphosphorus, which may be related to the large plants, like reed plants, need forinorganic phosphorus with a longterm growth.( LI jianbo, 2008) considered that: theadsorption by plants is a major way when at a low concentration of phosphorus, and theabsorption by plants appear to be negligible when at a higher concentrations However,the adsorption of medium is limited, that is the absorption effect will be reduced afterreaching saturation (Qin and Chen, 2016)

1.3.2 Influential factors and treatment performance

a Influence factors Substrates (medium)

The substrate is the critical design parameter in CWs and SSF CWs in particular,because it can provide a suitable growing medium for plant and also allow successfulmovement of wastewater (Kadlec and Wallace, 2009) Moreover, substrate sorptionmay play the most important role in absorbing various pollutants such as phosphorus(Ju et al., 2014) Selection of suitable substrates to use in CWs for industrial wastewatertreatment is an important issue The selection of substrates is determined in terms of thehydraulic permeability and the capacity of absorbing pollutants Poor

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hydraulic conductivity would result in clogging of systems, severely decreasing theeffectiveness of the system, and low adsorption by substrates could also affect thelong-term removal performance of CWs (Wang et al., 2010) Many studies alsosuggest that substrates such as sand, gravel, and rock are the poor candidate forlong-term phosphorus storage, but by contrast, artificial and industrial products withhigh hydraulic.

HRT (Hydraulic retention time)

HRT determines the average contact time of microbial communities withpollutants (Lee et al., 2009) Furthermore, the effect of HRT may differ betweenCWs depending on the dominant plant species and temperature, as those factors canaffect the hydraulic efficiency of wetlands

HLR (Hydrologic loading rate)

HLR is defined as following formular:

/

= 100

Where q is defined as the volume per time per unit area (cm day -1); A is thewetland surface area (m2), Q is the flow rate (m3 day-1) Avila et al (2014) alsostudied the feasibility of hybrid CW systems used for removing emerging organiccontaminants, and demonstrated that the removal efficiency for most compoundsdecreased as the HLR increased (Yan and Xu, 2014; Huang et al., 2000)

Feeding mode

The influent feeding mode is another crucial design factor that can affect theperformance of a wetland system (Zhang et al., 2012) Wetlands can be fed incontinuous, batch, and intermittent modes These modes affect the oxidation andreduction conditions as well as the oxygen to be transferred and diffused in thesystem resulting in treatment efficiency modification

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b P removal efficiency

Table 1.5 P removal by Constructed Wetland

sandy loam soil

S pungens

HFWs seem to be more effective in P elimination than VFWs because of the longer flowing distance and treatment time (Lüderitz and Gerlach, 2002).

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1.4. Removal phosphorus by plants in the CWs

1.4.1 Classification of plants used in CWs

a Role of plants in CWs

Plants is one of factors will affect the performance of CWs Plants provide anenvironment for microorganisms to attach and release oxygen from the root systemwhich affect removal efficiency of plants (Jethwa and Bajpai, 2016) Using greenplants to reduce pollutant concentration in soil and water was defined asphytoremediation (“Phyto” meaning plants, “remediation” meaning to restore andclean) (Cunningham et al., 1997)

Phytoremediation is more attractive than other technologies thanks to lowmaintenance, far-reaching, reducing pollution emissions, dust and by-products,preventing soil erosion, surface water flow, permeability, noise reduction, andincreased aesthetics, carbon dioxide absorption, improved soil supply aftertreatment (Champagne, 2007)

In addition, phytoremediation (phytoremediation) is economically viable.According to Champagne (2007), this method is at least 40% cheaper than other on-site processing methods and 90% less than ex situ technologies

b Classification of plants used in CWs

Wetland plants can be categorized under four main classes, namely,emergent plants, floating leave macrophytes, submerged plants, and freely floatingmacrophytes Wu et al (2014)

Macrophytes frequently used in CW treatments include emergent plants,submerged plants, floating leaved plants and free floating plants Although more than

150 macrophyte species have been used in CWs globally, only a limited number ofthese plant species are very often planted in CWs in reality Emergent species are

Phragmitesspp (Poaceae), Typha spp (Typhaceae), Scirpus spp.(Cyperaceae), Iris spp (Iridaceae), Juncus spp (Juncaceae) and Eleocharis spp.(Spikerush) The most

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frequently used submerged plants are Hydrilla verticillata, Ceratophyllum demersum,Vallisneria natans, Myriophyllum verticillatum and Potamogeton crispus The floatingleaved plants are mainly Nymphaea tetragona, Nymphoides peltata, Trapa bispinosaand Marsilea quadrifolia The free-floating plants are Eichhornia crassipes, Salvinianatans, Hydrocharis dubia and Lemna minor In addition, Ornamental flowering plants,especially Canna indica (Sandoval et al., 2019).

P.australis is the most common species in Asia and Europe while T latifolia

is the most popular plant used in North America The most used plants in Africa areCyperus papyrus L., P australis and Typha domingensis, Schoenoplectustabernaemontani In Central and South Americas, Oceania, Palla was recored themost popular wetland plants Regarding types of the wetland plants used subsurfacewetland, the second most common plant is Typha spp which is found in Australia,

East Asia, North America, Africa In addition, P.australis is the most popular

species globally (IWA Specialist Group 2000; Scholz 2006; Vymazal 2014)

Common species used in HFCWs are Scirpus (lacustri, acutus, californicus

and validus) Typha (domingensis, glauca, orientalis, latifolia and angustifolia),

Bulrush and comment reeds Phragmites spp is the most popular (Vymazal, 2011).And most of them are herbaceous plants (Vymazal, 2011; Jethwa and Bajpai, 2016)

Table 1.6 Plant species are used to treat swine wastewater

Hydrilla Hydrilla verticilata

Submerged plant Water milfoil Myriophyllum spicatum

Blyxa Blyxa aubertii

Water hyacinth Eichhornia crassipes

Rootless duckweed Wolfia arrhiga

Free floating plants

Water lettuce Pistia stratiotes

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1.4.2 Removal P mechanisms by plants

a Removal P mechanisms and P removal efficiency of plants

The roots use energy to get P into the tree through the cell membrane Otherchanges take place in rhizosphere affecting plant P uptake The roots secrete organicacids (citrate and oxalate) which increase the availability of P availability Amount

of excreted organic acid, mycorrhizal fungi, root-zone microorganisms allow a plant

to uptake P more from soil P is removed from the system by harvesting the plants(Brix 1997; Ma et al 2016)

In fact, the CWs with plants are more effective (Vymazal, 2011; Tanner,2001) Depending on the stage of the system, plants will contribute to variousremoval effects For immature CWs, the role of plants in eliminating P will not beclearly shown However, the P removal efficiency of the system can still beenhanced by plants through its indirect impact on the treatment conditions of thesystem (Tanner, 2001)

In addition, phytoremediation (phytoremediation) is economically viable.According to Champagne (2007), this method is at least 40% cheaper than other on-site processing methods and 90% less than ex situ technologies

The removal efficiency of P of Typha latifolia, Canna indica, Phragmites

australisdao is 0.06 -74.87%, 0.43 - 4.17, 0.56 - 36.7%, respectively under different

conditions In the same research conditions, the efficiency of removing P of

Cladium mariscus and Iris pseudacorus is 10% and 18% (Jesus et al., 2017) The

treatment efficiency of the dominant species is 37, 53, 61% for Phragmites, Typha,

Scirpus respectively (Vymazal, 2011).

Table 1.7 P removal efficiency by plants in CW (Jesus et al., 2017)

CW

Phragmites australis 36.71 1st year harvested Zheng et al (2015)

Phragmites australis 34.19 1st year Zheng et al (2015)

Phragmites australis 32.02 2nd year harvested Zheng et al (2015)

Phragmites australis 35.93 2nd year Zheng et al (2015)

unharvested

VSSF Phragmites australis 10.76

Scirpus validus 32.27

Iris pseudacorus 34.17 High nutrient

Iris sibirica 13.19 Medium nutrient

Iris sibirica 13.19 Low nutrient

alternifolius Philodendron

b Plant selection criteria

Factors affecting the removal efficiency of plants include differences in

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species, growth conditions, root surface area, oxidizing supply capacity, type ofwaste water and rate of loading, ability to withstand, absorb pollutants, be resistant

to flooding, huge biomass (Jesus et al., 2017)

Fast growth

The rapid growth of plants corresponded with high level of P Therefore, theyuptake a significant amounts of nutrient during the period of their growth Harvestingtheir above parts is the way to remove nutrients from wastewater (Vymazal, 2007)

Tolerant to continuous flooding

Beside the requirement of wetland plants with huge biomass and welldeveloped root system, the tolerance ability to flood affects the nutrient removalefficiency by plants (Almuktar, 2018)

Tolerant to contaminant

Plants can be affected by environment stresses because many pollutants arepresent in CWs The concentration of influences in wastewater is too high to exceedthe capacity of plants which reduces the growth and survival of plants (Surrency,1993) In addition, high levels of pollutants directly affect the ecosystem of CWscausing inhibition of plant growth, even causing the disappearences of plants (Wu

et al., 2015)

The high concentration of pollutants in water resulting in disadvantage ofboth treatment efficiency and plant survival Plant tolerance to the highconcentration of pollutants is another important factor which is considered whenselecting them for CWs (Almuktar, 2018)

Ability to accumulate contaminant

Wetlands plants are recognized as an important factor affecting water quality

in CWs Absorption capacity of pollutants of plants contributes to CWs removalefficiency (Wu et al., 2015)

Most common plants used in CWs are weedy plants, which do not bring

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economic value This study was conducted to find out whether the plants are both economically valuable and treat environmental pollution.

CHAPTER 2: MATERIALS AND RESEARCH METHODOLOGY 2.1 Research object, scale, and scope

2.1.1 Research objects

In this research, experiments to investigate influential factors on P removal

by selected plants and those with CWs were conducted with synthetic wastewater.The experiments to search for potential plants were carried out with soil

This study investigated 05 types of plants, including Colocasia gigantean,

Piper lolot, Sauropus androgynous, Cymbopogon citratu, and Ubon paspalum.

2.1.2 Research scale & scope

The experiments to evaluate influential factors and those with CWs wereimplemented at lab-scale The former was done at the laboratory of Master’sProgram in Environmental Engineering (MEE), VNU Vietnam Japan University(VJU), whereas the latter was located on the roof of a residential building in YenHoa, Cau Giay, Hanoi

Concerning wastewater quality, this study focused on the removal of orthophosphate (P-PO43-) of investigated plants Besides, other environmentalparameters, such as TSS, pH, BOD5, COD, TN, N-NH4 +

, TP, P-PO4

weremeasured to evaluate the composition of real swine wastewater

In relation to plants, in the experiment to screen plants, the attention was paid

to the content of phosphorus in the whole plant as well as in different parts of plants

In experiments to explore influential factors, phosphorus removal rate was used asmain indicator

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2.2. Materials, chemicals and equipment

2.2.1 Materials

a Plants

The investigated plant Ubon paspalum was collected in a home garden inDong Phong commune, Tien Hai district, Thai Binh province whereas Colocasiagigantean, Piper lolot, Sauropus androgynous, and Cymbopogon citrate weregathered in Quang Bi commune, Chuong My district, Hanoi City Depending on thepurpose of experiments, the plants of different ages were utilized

Table 2.1 The list of investigated plants

Common name Science name Picture Location

Lemongrass Cymbopogon citratus

Quang Bicommune,Piper lolot Piper sarmentosum Thinh Da

hamlet, Chuong

My district,Hanoicity

Giant elephant Colocasia gigantea

Star gooseberry Sauropus androgynus

Dong Phongcommune,

Distric, ThaiBinh province

b Synthetic wastewater

Synthetic wastewater was prepared accordingly the composition andcharacteristics the real swine wastewater collected from a pig farm, which waslocated in Luong Xa village, Nam Dien commune, Chuong My district, Ha Noi

c Chemicals

KH2PO4, NH4Cl used in this study were of analytical grade and purchasedfrom ESQ Co., Ltd (Ba Dinh, Hanoi)

2.2.2 Experimental design

a Screening potential plants

This experiment was to search for plants, which have potential for used inphytoremediation or CWs to eliminate phosphorus All investigated plants weregrown in the soil They were harvested for determination of phosphorus content atthe mature age In this experiment, phosphorus content and biomass growth ratewere used for comparison purpose

b Investigating influential factors

All experiments were implemented with simulated swine wastewater First, thestock phosphorus solution (1000 mg P/L) was prepared by dissolving 4.39 g KH2PO4into 1L of distilled water Then, the P stock solution was diluted 20 times to prepare

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P working solution (50 mg P/ L) After that, the certain amount of NH4Cl was added tomake the nutrient solution A (50 mg P/ L and 500 mg N/ L) Finally, the A solutionwas diluted four times to get the background nutrient solution B (12.5 mg P/ L and 125

mg N/ L) The experiments to investigate influential factors were carried out by varyingthe influential factors while using the same background nutrient solution (except theexperiment to investigate effect of initial P concentration)

Effect of initial phosphorus concentration: This experiment was designed toinvestigate how the plant can grow and uptake phosphorus in the solutions ofdifferent phosphorus concentrations This experiment was conducted with syntheticwastewater, which simulated 100%, 50 and 25% of real swine wastewater (P-PO4

50 mg/L, N-NH4-500 mg/L), in term of P and N This experiment included 3 turns,each turn lasted for 9 days, when the phosphorus in the solution was almostremoved Cymbopogon citrate and 1.5-month Ubon paspalum were utilized forcomparison 45 g of each plant was cultivated in a beaker containing 200 mL ofnutrient solution The water sampling was done at the beginning of the experimentand after every 2 days for determination of phosphorus concentration First, thewater volume was measured Next, tape water was added for compensation ofvaporization After that, 7 mL of water was sampled for P analysis

Effect of pH: This experiment was to evaluate the influence of pH onphosphorus uptake and growth of two plants, namely Cymbopogon citrate and Ubonpaspalum It was conducted with aqueous solutions of different pH values (3, 5, 7,

9, and 11) The pH value of the background nutrient solution was adjusted usingH2SO4 and NaOH of various concentrations to ensure that the change in volume ofthe solution was negligible 2-week Cymbopogon citrate and 3-month Ubonpaspalum were utilized The plant (60 g) was placed into a beaker containing 200

mL of the background nutrient solution This experiment comprised 7 turns (2 days/turn) At the start of experiment and after every 2 days, water sample of 7 mL wascollected for P concentration and pH analysis Before sampling, the water volumeleft in the beaker was measured The status of plant was also recorded