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

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 SW

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

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

ACKNOWLEDGMENTS

First of all, I would like to express the sincere gratitude to my principal supervisor, Dr Nguyen Thi An Hang at VNU Vietnam Japan University, for accepting me as her master student and continuous teaching and supporting me in the process of doing experiments as well as writing essays and making presentations She always encourages and is willing to help me when I have difficulties 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 to Assoc 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 my deepest thanks to Dr Nguyen Thi Hoang Ha She gave me valuable supports in developing research methods, and enthusiastically guided me to fullfil

my thesis I always 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 Jun Nakajima for supporting not only me but also all of memerbers in my class during Master 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, for always supporting me in conducting experiments as well as analyzing environmental parameters

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

2018 Asean Research Center (ARC) research grant of Vietnam National University, 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 unconditional helps with plant sampling, the love and encouragement

Hanoi, June 9th, 2019

Vu Thi Thom

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

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

LIST OF ABBREVIATIONS

COD Chemical oxygen demand

CW Constructed Wetland BOD Biological oxygen demand EBPR Enhanced biological phosphorus removal EPA Environmental Protection Agency

HF Horizontal flow HLR Hydraulic loading rate HRT Hydraulic retention time SSF Subsurface water flow

SF Surface flow

TN Total nitrogen

TP Total phosphorus TSS Total suspended solids

VF Vertical flow WHC White hard clam

INTRODUCTION

Background

In Vietnam, in recent years, pig breeding industry has developed rapidly Since most of pig farms have not designed and operated appropriately, wastewater from pig farms cause serious environmental pollution, which poses a high risk to public health and surrounding ecosystems Therefore, the proper treatment of swine wastewater is urgent and necessary At present, swine wastewater in Vietnam is normally treated

by biogas technology However, the concentration of pollutants in the effluent is still high, exceeding national discharge standards (QCVN 01-79: 2011/BNNPTNT) Thus, further processing after biogas treatment of swine wastewater is mandatory Constructed wetlands (CWs) is a promising technology, which possesses many advantages, 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 wide application of CWs is limited by intensive land requirement, long-term unsustainability (Bunce et al., 2018) Especially, although CWs can achieve high removal efficiency with TSS, COD, BOD, it is demonstrated to be inefficient in nutrient 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 via substrate 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 receives the great interests of scientists in the world So far, a numerous number of studies on successful phytoremediation of wastewater polluted by phosphorus The most common types 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 by Persicaria hydropiper, representing 97.63% (Zheng et al., 2013) However, these are wildlife grass type with no or less economic value There is still lack of information about potential plants with high economic value for phytoremediation and CWs to treat P- rich water and wastewater Also, very few studies on factors influencing the growth and utapke of phosphorus by plants

The objectives of this study comprise (1) to search for potential plants for phosphorus 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 each chapter 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, roles and 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 up experiments 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

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 future research 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 and consumes livestock products the most Like other countries in the region, Vietnam needs to maintain high growth level to meet the demand of domestic consumption and 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 (%)

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 farms throughout 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 land use The fast population growth and urbanization have resulted in a reduction of agricultural land In order to ensure food security, Vietnam has no choice but

implementation of intensive animal husbandry Of which, pig raising plays an important 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) to 38% (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 high content of organic matter, TSS, N, P, and pathogen According to the report to assess 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

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 technical standards for breeding facilities Therefore, breeding productivity is usually low and the surrounding environment is seriously polluted The wastewater from pig farms includes urine, wastewater from pig bathing and facilities cleaning A majority of pig farms discharge directly the wastewater into surrounding water bodies, causing unpleasant smells (H2S and NH3) especially in the hot and sunny days The ineffective 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 is estimated 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 for long distances for purposes of agriculture and aquaculture development

Table 1.3 Methods for handing and using liquids at systems

Discharge into 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-chemical treatment method, and (3) Biological treatment method Of which, biological treatment 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, anaerobic biological trickling filtration, upflow anaerobic slug blanket (UASB), expanded granular sludge bed (EGSB) The commonly used aerobic processes are aerotank, aerobic biological filtration, biological lagoon, algae, aquatic plants In order to cut down the price of pig breeding, farm owners in Vietnam tend to simply apply biogas instead of combining various technologies The commonly used treatment train is: Swine wastewater => Biogas tank => Lagoon => Environment Consequently, the effluent after biogas treatment is heavily polluted, and far above the discharge standard (QCVN 40:2011/BTNMT)

Table 1.4 3 main parameters of swine wastewater after biogas treatment

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, the excessive 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 water quality 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 anaerobic decomposition of organic matter, producing foul smell (H2S, NH3, CH4) (Thongtha

et al., 2014) Phosphorus in water and wastewater may come from natural or artificial

activities Natural activities include earthquake, soil erosion, etc Human activities can release phosphorus into aquatic medium, such as agriculture, wastewater, storm water, etc The contribution of domestic sewage, agriculture and industry to the global phosphorous load is 54, 38, and 8% respectively The phosphorus load from agriculture 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, magnetic separation, 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 chemical precipitation is widely used for phosphorus treatment, because it is flexible, easy to install, high P removal, less space requirement However, its application is limited due to high chemical demand, chemical sludge generation, effluent neutralization requirement, difficult to identify optimal dosing conditions, low bioavailability of end-products, unsuitable for wastewater with low P levels Another method for phosphorus removal is adsorption This method is favored because of simple operation, less chemicals use, no sludge formation, suitability for P-poor wastewater Nevertheless, limitations of this method are high cost, disposal problems after use, etc In a study conducted by Gustafsson et al (2008) using naturally occurring materials, the phosphorus removal efficiency reached 95% In another study, Seo et

al (2013) reported that phosphorus could be removed up to 90% In recent years, phosphorus removal using enhanced biological methods has received great interests

of scientists in the world, due to the dominant advantages of modest cost, minimal sludge formation or ability 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 membrane bioreactor integrated into a continuous flow EBPR Besides

to advantages, this method has some constraints, including external carbon source

requirement, complex configuration and operating regimes, more energy and space requirement (Nguyen et al., 2015) The utilization of biological process is not only limited to EBPR but also using algal or aquatic plants Sukacova et al (2015) stated that fixed growth algal bioreactor could eliminate up to 97% phosphorus in wastewater The ability of macrophyte in phosphorus decontamination from wastewater 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, low energy consumption, does not require high operational and environmentally friendly techniques (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 area for construction of artificial wetlands is relatively large, which is an obstacle to the selection of this treatment method, so artificial wetlands are suitable for crowded areas with wide and unfocused land area

b Advantages and limitations

CWs are inexpensive (building, maintenance), simple operation, tolerant to various flow, 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 affected external environmental conditions such as rainfall, droughts, seasons, sensitive to toxic chemicals (Davis, 1995)

c Classification

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 into categories: 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 lower than the substrate surface in the SSF system (Davis, 1995)

Based on the flow direction of water, SSF is divided into 2 types of horizontal flow (HF) and vertical flow (VF) Water in HFCWs flooded the substrate in the system before exiting through water level control While water in the VFCWs system drains with 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 is removed 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, and removed from the system through the plants harvested Secondly, phosphorus is necessary to microbial, phosphorus bacteria converted poorly soluble organic phosphorus and phosphorus to dissolved inorganic phosphorus which is conducive to absorption by plants Finally, phosphorusis removed by adsorption of media or ion exchange, the iron, aluminum, calcium compounds will affect the adsorption capacity

of the media, and PAOs excess polyphosphate phosphorus also has a certain role to removal phosphorus Since the constructed wetland have a special aerobic and anaerobic conditions, PAOs can be adsorbed an excess of phosphorus in the aerobic state, and released excess phosphorus in anaerobic conditions, some of phosphorus will spread with the water transport, other will adsorption by the medium, because of the release of phosphorus, adsorption by media in favor of phosphorus 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 of organic phosphorus, but the absorption of plant is given priority to remove inorganic phosphorus, which may be related to the large plants, like reed plants, need for inorganic phosphorus with a longterm growth.( LI jianbo, 2008) considered that: the adsorption by plants is a major way when at a low concentration of phosphorus, and the absorption 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 after reaching 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 successful movement of wastewater (Kadlec and Wallace, 2009) Moreover, substrate sorption may 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 wastewater treatment is an important issue The selection of substrates is determined

in terms of the hydraulic permeability and the capacity of absorbing pollutants Poor

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

HRT (Hydraulic retention time)

HRT determines the average contact time of microbial communities with pollutants (Lee et al., 2009) Furthermore, the effect of HRT may differ between CWs depending on the dominant plant species and temperature, as those factors can affect the hydraulic efficiency of wetlands

HLR (Hydrologic loading rate)

HLR is defined as following formular:

𝑞 = 𝑄/𝐴100Where q is defined as the volume per time per unit area (cm day -1); A is the wetland surface area (m2), Q is the flow rate (m3 day-1) Avila et al (2014) also studied the feasibility of hybrid CW systems used for removing emerging organic contaminants, and demonstrated that the removal efficiency for most compounds decreased 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 the performance of a wetland system (Zhang et al., 2012) Wetlands can be fed in continuous, batch, and intermittent modes These modes affect the oxidation and reduction conditions as well as the oxygen to be transferred and diffused in the system resulting in treatment efficiency modification

b P removal efficiency

Table 1.5 P removal by Constructed Wetland

Types of plants Environments Types of

wastewater

Initial concentration (mgP/L)

Removal (%)

Synthetic strom water 4.51 mg/l

6-36

Typha

Lockport dolomite

Sewage wastewater

189 (mg/m2/d) 18 Queenston

shale

400-700 (mg/m2/d) 17-28 Fonthill

sand

105-331 (mg m−2day−1)

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

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 an environment for microorganisms to attach and release oxygen from the root system which affect removal efficiency of plants (Jethwa and Bajpai, 2016) Using green plants to reduce pollutant concentration in soil and water was defined as phytoremediation (“Phyto” meaning plants, “remediation” meaning to restore and clean) (Cunningham et al., 1997)

Phytoremediation is more attractive than other technologies thanks to low maintenance, far-reaching, reducing pollution emissions, dust and by-products, preventing soil erosion, surface water flow, permeability, noise reduction, and increased aesthetics, carbon dioxide absorption, improved soil supply after treatment (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 floating macrophytes 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 of these 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

frequently used submerged plants are Hydrilla verticillata, Ceratophyllum demersum, Vallisneria natans, Myriophyllum verticillatum and Potamogeton crispus The floating leaved plants are mainly Nymphaea tetragona, Nymphoides peltata, Trapa bispinosa and Marsilea quadrifolia The free-floating plants are Eichhornia crassipes, Salvinia natans, 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 are Cyperus papyrus L., P australis and Typha domingensis, Schoenoplectus tabernaemontani In Central and South Americas, Oceania, Palla was recored the most popular wetland plants Regarding types of the wetland plants used subsurface wetland, 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

Species Common name Science name Submerged plant

Hydrilla Hydrilla verticilata

Water milfoil Myriophyllum spicatum

Blyxa Blyxa aubertii

Free floating plants

Water hyacinth Eichhornia crassipes

Rootless duckweed Wolfia arrhiga

Water lettuce Pistia stratiotes

Water fern Salvinia spp

Emergent plant Cattails Typha spp

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 Other changes take place in rhizosphere affecting plant P uptake The roots secrete organic acids (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 various removal effects For immature CWs, the role of plants in eliminating P will not be clearly shown However, the P removal efficiency of the system can still be enhanced by plants through its indirect impact on the treatment conditions of the system (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)

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

Phragmites australis 34.19 1st year

unharvested Zheng et al (2015)

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

Phragmites australis 35.93 2nd year

unharvested Zheng et al (2015)

VSSF

Typha latifolia 35.53 Tang et al (2008)

Typha latifolia 42.54 Tang et al (2008)

Typha latifolia 74.87 Tang et al (2008)

Typha orientalis 14.31 Tang et al (2008)

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

Iris sibirica 13.19

Phragmites Australis 22

Sara G

Abdelhakeem , Samir A Aboulroos

HSSF

Canna indica 0.7 Cui et al (2015)

Canna indica 0.43 Cui et al (2015)

Phragmites australis 0.56 Meng et al (2014)

Arundo donax 0.36 Meng et al (2014)

Typha latifolia 0.06 Meng et al (2014)

SSF

Arachis duranensis 10.4 Van et al (2015)

Cyperus alternifolius 29.8 Van et al (2015) Philodendron

Phalaris arundinacea 45.9 Lower input

Březinová and Vymazal (2015)

Phalaris arundinacea 3.1 Higher input

Březinová and Vymazal (2015)

b Plant selection criteria

Factors affecting the removal efficiency of plants include differences in

species, growth conditions, root surface area, oxidizing supply capacity, type of waste 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, they uptake a significant amounts of nutrient during the period of their growth Harvesting their 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 well developed root system, the tolerance ability to flood affects the nutrient removal efficiency by plants (Almuktar, 2018)

Tolerant to contaminant

Plants can be affected by environment stresses because many pollutants are present in CWs The concentration of influences in wastewater is too high to exceed the capacity of plants which reduces the growth and survival of plants (Surrency, 1993) In addition, high levels of pollutants directly affect the ecosystem of CWs causing inhibition of plant growth, even causing the disappearences of plants (Wu et al., 2015)

The high concentration of pollutants in water resulting in disadvantage of both treatment efficiency and plant survival Plant tolerance to the high concentration of pollutants is another important factor which is considered when selecting 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 removal efficiency (Wu et al., 2015)

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

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 were implemented at lab-scale The former was done at the laboratory of Master’s Program

in Environmental Engineering (MEE), VNU Vietnam Japan University (VJU), whereas the latter was located on the roof of a residential building in Yen Hoa, Cau Giay, Hanoi

Concerning wastewater quality, this study focused on the removal of ortho phosphate (P-PO43-) of investigated plants Besides, other environmental parameters, such as TSS, pH, BOD5, COD, TN, N-NH4+, TP, P-PO43- were measured 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 as main indicator

2.2 Materials, chemicals and equipment

2.2.1 Materials

a Plants

The investigated plant Ubon paspalum was collected in a home garden in Dong Phong commune, Tien Hai district, Thai Binh province whereas Colocasia gigantean, Piper lolot, Sauropus androgynous, and Cymbopogon citrate were gathered in Quang

Bi commune, Chuong My district, Hanoi City Depending on the purpose 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 Bi commune, Thinh Da hamlet, Chuong

My district, Hanoi cityPiper lolot Piper sarmentosum

Giant elephant Colocasia gigantea

Star gooseberry Sauropus androgynus

Ubon paspalum Ubon paspalum

Dong Phong commune, Tien Hai Distric, Thai Binh province

b Synthetic wastewater

Synthetic wastewater was prepared accordingly the composition and characteristics the real swine wastewater collected from a pig farm, which was located 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 purchased from 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 in phytoremediation or CWs to eliminate phosphorus All investigated plants were grown in the soil They were harvested for determination of phosphorus content at the mature age In this experiment, phosphorus content and biomass growth rate were used for comparison purpose

b Investigating influential factors

All experiments were implemented with simulated swine wastewater First, the stock phosphorus solution (1000 mg P/L) was prepared by dissolving 4.39 g KH2PO4 into 1L of distilled water Then, the P stock solution was diluted 20 times to prepare

P working solution (50 mg P/ L) After that, the certain amount of NH4Cl was added

to make the nutrient solution A (50 mg P/ L and 500 mg N/ L) Finally, the A solution was 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 varying the influential factors while using the same background nutrient solution (except the experiment to investigate effect of initial P concentration)

Effect of initial phosphorus concentration: This experiment was designed to investigate how the plant can grow and uptake phosphorus in the solutions of different phosphorus concentrations This experiment was conducted with synthetic wastewater, 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 almost removed Cymbopogon citrate and 1.5-month Ubon paspalum were utilized for comparison 45

g of each plant was cultivated in a beaker containing 200 mL of nutrient solution The water sampling was done at the beginning of the experiment and after every 2 days for determination of phosphorus concentration First, the water volume was measured Next, tape water was added for compensation of vaporization After that,

7 mL of water was sampled for P analysis

Effect of pH: This experiment was to evaluate the influence of pH on phosphorus uptake and growth of two plants, namely Cymbopogon citrate and Ubon paspalum 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 using H2SO4 and NaOH of various concentrations to ensure that the change in volume of the solution was negligible 2-week Cymbopogon citrate and 3-month Ubon paspalum 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 was collected for P concentration and pH analysis Before sampling, the water volume left in the beaker was measured The status of plant was also recorded

Effect of plant age: The purpose of this test was to identify at which growth period, the plant is most efficient in phosphorus removal from wastewater This experiment was implemented with the background nutrient solution Ubon paspalum

of 3 kinds of age (1, 1.5, and 3 months) and Cymbopogon citrate of 2 kinds of age (baby and mature) were used This experiment lasted for 7 turns (2 days/ turn) The water sampling was implemented the same as that for experiment to investigate the effect of pH

Effect of plant density: The experiment was to determine the best plant density for plant growth and phosphorus accumulation This experiment was carried out in both soil and auqeous solutions For hydroponic experiments, three kinds of plant density, such as 1, 3, and 5 plant(s)/ beaker were applied The water sampling was done in a similar procedure to that of experiments for pH and plant age For soil experiment, it was conducted only with Ubon paspalum with 3 types of plant density (1, 3, and 5 plants/ trough) The soil was fertilized 3 times/ week, 2 months after planting, the Ubon paspalum was harvested for determination of both P content and biomass growth

Effect of water level: This experiment was to evaluate the ability of plant to adapt with different water levels It was done with 3 kinds of water levels (2, 5, and

8 cm) The water sampling frequency was the same as that of the experiment on pH, plant age, and density

c Trial application of the selected plant in CWs

CWs experiment setting up: The experiment was designed to include 4 treatment systems in parallel In the systems 1&3, the horizontal flow constructed wetland was followed by the adsorption unit The wastewater was stored in a big sink, then pumped into the CWs using 4 peristaltic pump (HV-77200-50, Masterflex Cole-Parmer, USA) To ensure that the effluent quality meets the requirement of discharge standard, after going through CWs, the wastewater was pumped into adsorption unit The systems 2&4 did not include adsorption units and used as the control systems

Figure 2.1 Scheme of horizontal constructed wetland

(at the start of experiment) Dimension and filter materials: The four CWs tanks were made of stainless steel, in rectangle shape and have the same dimension (L x W x H = 68.5 cm x 33

cm x 42 cm The efficient volume of each tank was 0.095 m3

The filter media including sand, WHC, yellow sand, and gravel were arranged into 3 layers with descending particle size from bottom to top of the tank The bottom layer, which was made of 5-10 mm gravel, had the height of 1.5 cm The upper layer, which was made of 0.25-0.5 mm sand, had the length of 13 cm For the treatment systems 1&2, the middle layer, which was 27.5 cm in height, was made of 2 particle sizes (1.4 -2.0 mm and 2.0 - 4.0 mm) For the systems 3&4, the filter material in the middle layer was made of yellow sand 0.5-0.85 mm rather than WHC

Tank 1+ Tank 2 Tank 3+ Tank 4 Adsorption unit

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

Plants

The plant used in the CWs experiment was Ubon paspalum This plant was

selected because of high biomass, fast growth, deep roots, good tolerance to flooding, high uptake of nutrient, high economic value To the best of our knowledge, this is the first time this plant has been used in CWs for phosphorous decontamination

The plant was grown in soil of a home garden It was cut off leaves to mitigate the water evaporation The stem with the height of 25 cm was put into a bucket of tap water for 1 week in the cool place with daylight When the new leaves reached the height of 10 cm, the water in the bucket was replaced by the background nutrient solution and kept for another 1 week for adaptation After that, the plants were transferred into CWs It took around 2 weeks for CWs plants to stabilize and grow well

Wastewater characteristics

This experiment used the background nutrient solution, which simulated 25% real swine wastewater in terms of P and N contents (12.5 mg P/ L, and 125 mg N/ L) Every two days, waster sampling was implemented at the inlet and the outlet of all four CWs and after two adsorption units for P and pH measurement

Operational parameters

The treatment systems were operated with hydraulic loading rate (HLR) of 0.032 and 0.027 m3/m2/d for the treatment systems 1&2 and the treatment system 3&4, respectively The hydraulic retention time (HRT) of the CWs, adsorption unit 1 and adsorption unit 3 was 5.4, 0.16 and 0.19 d, respectively The HRT of the hybrid treatment system 1 (CW1 + adsorption unit 1) and the hybrid treatment system 2 (CW3 + adsorption unit 2) was 5.5 and 5.59 d, respectively

2.2.3 Plant sample preparation and P analysis

Figure 2.3 Plant sample preparation and analysis

Plant sample preparation: First, plant samples were well rinsed with double distilled water, dried in the room with the air conditioner (27 0C and high fan speed) for 15 min Next, the plant was cut into different parts (stem, leaves, and roots) and then measured the fresh weight Then, the cut plants were placed in the Thermo Scientific oven at 70 0C for 48 h, and cooled down to the room temperature After that, the dried plant samples were measured to determine the dry weight The dried samples were ground into powder using the plant crusher and coffee grinder The powdered plants were kept in a tight glass bottle for P analysis

Plant sample digestion: The plant samples were digested according to Vietnam Standard TCVN 8551:2010 using heating digester (DK6) Accordingly, 0.5 g of the plant sample was mixed with 10 mL of the mixture of HClO4: HNO3 (1: 2 in volume), kept overnight and then digested in DK6 for 5 h at different temperatures

P analysis: The wastewater and plant samples (after digestion) were measured

to identify the concentration of phosphorus according to Method 365.3 of EPA, using UV-VIS S2150 Spectrophotometer