Intensified phosphorus removal from synthetic wastewater by lab scale horizontal sub surface flow constructed wetlands using a mixture of coal slag and calcined ferralsols as substrate

VIETNAM NATIONAL UNIVERSITY, HANOIVIETNAM JAPAN UNIVERSITY LE THI VAN INTENSIFIED PHOSPHORUS REMOVAL FROM SYNTHETIC WASTEWATER BY LAB-SCALE HORIZONTAL SUB-SURFACE FLOW CONSTRUCTED WETLAN

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

LE THI VAN

INTENSIFIED PHOSPHORUS REMOVAL FROM SYNTHETIC WASTEWATER BY LAB-SCALE HORIZONTAL SUB-SURFACE FLOW CONSTRUCTED WETLANDS USING

A MIXTURE OF COAL SLAG AND

CALCINED FERRALSOLS AS SUBSTRATE

MASTER'S THESIS

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

LE THI VAN

INTENSIFIED PHOSPHORUS REMOVAL FROM SYNTHETIC WASTEWATER BY LAB-SCALE HORIZONTAL SUB-SURFACE FLOW CONSTRUCTED WETLANDS USING

A MIXTURE OF COAL SLAG AND

CALCINED FERRALSOLS AS SUBSTRATE

MAJOR: ENVIRONMENTAL ENGINEERING

CODE: 8520320.01

SUPERVISORS:

Principal Supervisor: Dr NGUYEN THI AN HANG

Co-Supervisor: Assoc Prof Dr SATO KEISUKE

Hanoi, 2020

I extend my sincere thanks to Assoc Prof Dr Sato Keisuke, my Co-supervisor, who gave

me practical advices on the feasibility and applicability of my research It was very kind of him to give me opportunities to learn about Japanese culture and people, which will definitely be useful for my future.

My gratitude is also gone to Dr Vu Ngoc Duy for his extraordinary supports I was

immensely benefited from his continuous assistance in constructed wetlands setting up and experimental data processing.

My special thanks go to B.Sc Nguyen Thi Xuyen, the project assistant, for her helps with

taking care of CWs system during the global COVID-19 pandemic period For me, she is a sincere friend and I have learnt a lot from her.

I would like to acknowledge VNU Vietnam Japan University (VJU), Ritsumeikan University (RITs), and Hiyoshi Corporation for providing me the best conditions to study

and have internship in Vietnam and Japan Especially, I am so grateful to Prof Jun Nakajima and Prof Soda Satoshi for teaching me at VJU and supporting me during my

internship in Japan.

This research was completed in the laboratory of the Master’s Program in Environmental Engineering (MEE), VNU Vietnam Japan University (VNU-VJU) I would like to acknowledge Vietnam National Foundation for Science and Technology Development (NAFOSTED) [grant number 105.99-2018.13, 2018], and Asia Research Center, Vietnam National University, Hanoi (ARC-VNU) and Korea Foundation for Advanced Studies (KFAS) [grant number CA.18.11A, 2018] for financial supports.

Lastly, I would like to express my deep gratitudes to my parents for raising me with a love

of science and supporting me in all my pursuits My heartfelt thanks go to Son-san for his

love, accompanying, and comments on my thesis research Thank you all my friends, who

were MEE Batch 3 students, for unforgettable memories.

Hanoi, June 14 th 2020

Le Thi Van

TABLE OF CONTENTS

ACKNOWLEDGEMENTS i

TABLE OF CONTENTS iii

LIST OF TABLES vi

LIST OF FIGURES vii

LIST OF ABBREVIATIONS x

INTRODUCTION 1

CHAPTER 1: LITERATURE REVIEW 4

1.1 Pig farming in Vietnam 4

1.1.1 Pig farming development in Vietnam 4

1.1.2 Environmental concerns of anaerobically treated swine wastewater 5

1.2 Phosphorus pollution and remedy technologies 8

1.2.1 Phosphorus significance and environmental concern 8

1.2.2 Technologies for phosphorus decontamination of anaerobically treated swine wastewater (ATSWW) 10

1.3 Constructed wetlands 11

1.3.1 Definition 11

1.3.2 Classification of constructed wetlands (CWs) 12

1.3.3 Phosphorus removal by different components in CWs 14

1.3.4 Advantages and disadvantages of CWs in P removal from wastewater 21

1.4 Study subjects 22

1.4.1 Filter materials 22

1.4.2 Plants 26

CHAPTER 2: MATERIALS AND METHODS 28

2.1 Materials 28

2.1.2 Wetland plants 31

2.2 Experimental set-up 33

2.2.1 Ferralsols calcination 33

2.2.2 Adsorption tests 34

2.2.3 Constructed wetlands design and operation 36

2.3 Analytical methods and equipment 38

2.3.1 Substrate characterization 38

2.3.2 Environmental parameters analysis 41

2.4 Calculation and statistical analysis 44

2.4.1 Calculation 44

2.4.2 Statistical analysis 44

CHAPTER 3: RESULTS AND DISCUSSION 45

3.1 Ferrasols calcination for P removal enhancement 45

3.1.1 Lab-scale Ferralsols calcination 45

3.1.2 Large-scale Ferralsols calcination 46

3.2 Adsorptive behaviours of calcined Ferrasols 46

3.2.1 Factors influencing P adsorption 46

3.2.2 Adsorption isotherms 50

3.2.3 Adsorption kinetics 55

3.3 Characterization of the filter materials 57

3.3.1 Characterization of natural and calcined Ferralsols 57

3.3.2 Characterization of coal slag 64

3.4 Applicability of the investigated filter materials 66

3.5 Treatment performance of sub-surface horizontal flow constructed wetlands 67

3.5.1 P treatment performance 67

3.5.2 Side-effects of filter materials on HSSF-CWs effluents 69

CHAPTER 4: CONCLUSIONS AND RECOMMENDATIONS 73

4.1 Conclusions 73

4.2 Recommendations 73

REFERENCES 75

APPENDICES 89

LIST OF TABLES

Table 1.1 Treatment efficiency of piggery wastewater by anaerobically treatment in

Thua Thien Hue 7

Table 1.2 P removal mechanisms of CWs components 14

Table 1.3 Effect of nutrient uptake by plants on removal of nitrogen and phosphorus (%) in different CWs simulated scenarios 19

Table 2.1 Parameters of real post-anarobically swine wastewater in Hanoi 33

Table 3.1 Comparison of P adsorption capacity of investigated filter materials 45

Table 3.2 Coparing CF500 produced in lab-scale and large-scale 46

Table 3.3 Langmuir and Freundlich adsorption isotherm constants 53

Table 3.4 P adsortion capacity of different materials 54

Table 3.5 Kinetic constants 57

Table 3.6 Mineral composition of NF and CF500 samples 60

Table 3.7 Main chemical compositions of NF, CF500 and CS 60

Table 3.8 Types of vibration peak in NF and CF500 62

Table 3.9 The chemical compositions in CF500 and NF 62

Table 3.10 Hydraulic properties of CF500 compared with other materials 64

Table 3.11 The chemical compositions in CS 65

Table 3.12 Physical properties of CS compared with other materials 65

Table 3.13 Selection the mixing ratio of CF500 and CS 66

Table 3.14 The concentration of 6 heavy metals in post-adsorption solutions 71

LIST OF FIGURES

Figure 1.1 Distribution of pig production in Vietnam by ecological regions 5

Figure 1.2 Swine wastewater 6

Figure 1.3 P is an important and essential nutrient for plants 8

Figure 1.4 HABs are triggered by nutrient enrichment 9

Figure 1.5 Stabilization lagoon 11

Figure 1.6 Classification of CWs 12

Figure 1.7 The diagram of VSSF-CWs 13

Figure 1.8 HSSF-CWs 14

Figure 1.9 P adsorption mechanism on material surface 16

Figure 1.10 Phytoremediation Using Aquatic Plants 17

Figure 1.11 Rhizosphere in CWs plants 18

Figure 1.12 Phosphorus cycle in constructed wetland 18

Figure 1.13 Source structure of the national electricity system by primary energy 22 Figure 2.1 Pha Lai Thermal Power Joint Stock Company 28

Figure 2.2 Principle diagram of electricity production technology 29

Figure 2.3 Sampling location of Ferralsols in Dak Nong Province 30

Figure 2.4 Stone placed at the bottom of CW units 31

Figure 2.5 Sand added on the top of CWs units 31

Figure 2.6 Aquatica ipomoea planted from seeds on the soil before being transferred into CW units 32

Figure 2.7 Cymbopogon citratus kept alive in the tap water before being transferred into CW units 32

Figure 2.8 Aquatica ipomoea at the time being tranferred into CWs 32

Figure 2.9 Carbolite furnace 33

Figure 2.10 Preparing NF for calcination with the commcerical furnace 34

Figure 2.11 Layers structure of tanks in CWs 37

Figure 2.12 Nutrient solution storage tank 38

Figure 2.13 The HSSF-CWs system planted with water spinach and lemongrass 38

Figure 2.14 AMRAY Model 1830 Scanning Electron Microscope 40

Figure 2.15 Empyrean equipment 40

Figure 2.16 X-ray fluorescence spectrometer 41

Figure 2.17 FTIR Spectrometer 41

Figure 2.18 Shaker 42

Figure 2.19 UV/Vis Diode Array Spectrophotometer 42

Figure 2.20 The pH meter 42

Figure 2.21 The SensION + EC5, Hach, China 43

Figure 2.22 Atomic absorption spectrophotometer 43

Figure 3.1 Effect of pH of NF and CF500 on P removal 47

Figure 3.2 Effect of dosage of NF and CF500 on P removal 49

Figure 3.3 Effect of temperature of CF500 on P removal 50

Figure 3.4 The fitting Langmuir and Freundlich isotherm models 51

for P adsorption by CF500 51

Figure 3.5 The fitting Langmuir and Freundlich isotherm models for P adsorption by NF 51

Figure 3.6 The fitting Langmuir and Freundlich isotherm modelts for P adsorption by CS 52

Figure 3.7 Linear form of adsorption isortherms: a) Langmuir model and b) Freundlich model of CF500 52

Figure 3.8 Linear form of adsorption isortherm following a) Langmuir model and b) Freundlich model of NF 53

Figure 3.9 Linear forms of adsorption isortherms: a) Langmuir model and b) Freundlich model of CS 53

Figure 3.10 Kinetic curve of CF500 55

Figure 3.11 Kinetic curve of NF 56

Figure 3.12 Kinetic curve of of CS 56

Figure 3.13 SEM observation for a) NF and b) CF500 58

Figure 3.14 XRD spectrum of NF 59

Figure 3.16 FTIR analysis for NF and CF500 61

Figure 3.17 The P removal efficiency of 4 units of CWs 67

Figure 3.18 The change of P concentration in the effluent over the time 68

Figure 3.19 pH of post-adsorption solutions 70

Figure 3.20 EC of post-adsorption solutions 71

PhosphorusRibonucleic acidSub-surface flow constructed wetlandsSuspended solid

Total Kjeldahl nitrogenTotal phosphate

Vertical sub-surface flow constructed wetlands

According to the Food and Agriculture Organization (FAO), Asia is one of thelargest producers and consumers of livestock products (Vu, 2019) The pig breedingindustry in Asia develops at a very fast pace but it is mainly spontaneous and hasnot yet met the technical standards of breeding facilities and breeding techniques(Le, 2014) Therefore, the swine wasteawter normally contains high levels ofpathogens, nirogen (N), and phosphorus (P) (Vietnam National Environment Report,2014) Nowadays, there are variable technologies for treating livestock wastewatersuch as: The upflow sludge blanket filteration, USBF (Truong, 2010); stabilizationlakes (Nguyen, 2011); upflow anaerobic sludge blanket, UASB (Rodrigues, 2010),anaerobic reactor of expanded granular sludge bed - EGSB (Lee, 2012) In Vietnam,anaerobic treatment is considered an appropriate solution to treat wastewaterscontaining high contents of organic matter and suspended solids such as swinewastewater However, this technology is not the final stage in the treatement system

to ensure the criteria for safe discharge into the environment (Nguyen, 2012).Therefore, it is necessary to implement additional treatment to swine wastwaterafter anaerobic treatment before discharging it into the environment

Phosphorus is an important element in all known life forms Inorganic P in the form

PO43-plays an important role in biological molecules such as Deoxyribonucleic acid(DNA) and Acid ribonucleic (RNA) On the other side, P at high concentration isone of the causes of water pollution with phenomena known as eutrophication andtoxic algae According to QCVN 40: 2011/BTNMT (column B), the discharge limitfor P in the industrial wastewater is 6 mg/L

Constructed wetland (CW) is one of technologies for wasteawter treatment, which

is based on the natural functions of filter materials, platns and microorganisms(Vymazal, 2007) CWs have many advantages, namely simple operation, lessmaintaining demand, low energy requirement, green teachnology, and especially aresuitable for small communities as a decentralized technology (Wu, 2015)

In the CWs, P can be removed from wastewater via several pathways, such assorption onto filter materials, plant uptake and microbial assimilation (Vymazal,2008) Of which, the role of filter materials is domninant, with the removalmechanisms as follows: adsorption, precipitation, settling, etc (Wu et al., 2015).Regarding the P treatment performance, the horizontal subsurface flow CWs(HSSF-CWs) were found to be more efficient than other types of CWs, such asvertical subsurface flow CWs (VSSF-CWs), free water surface CWs (FWS-CWs)(Arun,2019) Even in the HSSF-CWs, their P removal ability is usually low andunstable To overcome this challenge, this study aims at enhancing the P removalefficiency of HSSF-CWs by utilizing a mixture of an industrial by-product (coalslag) and a natural material (Ferralsols) as the filter materials and accumulating

plants, namely water spinach (Aquatica ipomoea) and lemongrass (Cymbopogon

citratus) To achieve this ultimate goal, a research titled “Intensified phosphorus

removal from synthetic wastewater by lab-scale horizontal sub-surface flow constructed wetlands using a mixture of coal slag and calcined ferralsols as substrate” was carried out with the specific objectives as follows: (i) Improve P

sorption capacity of raw ferralsols (NF) by calcination, (ii) Investigate theadsorption behaviors, (iii) Evaluate the P treatment performance of the HSSF-CWsusing mixture of filter materials and acumulating plants, and (iv) Elucidate possibleside-effects of using the selected media in HSSF-CWs

This thesis comprises of 4 main Chapters with the following major contents:

Introduction: This part gave the research background, objectives, scope and scale,

and research significance

Chapter 1 Literature review: This Chapter provided overall information about

environmental problems related to P pollution, the discharge standsards for Pcontaining wastwater, numerous technologies for P decontamination fromwastewater In addition, the composition of swine wastwater after anaerobictreatment was investigated Especially, this chapter focuses on the CWs,

Chapter 2 Materials and methods: This Chapter introduced materials, methods

and equipments used for this research Also, the experimental set-up was described

in details

Chapter 3 Result and discussion: This Chapter referred the results on calcination

of Ferralsols for strengthenning its P removal ability, characterization of raw andcalcined materials, adsorption behaviors, and treatment perfomance of theHSSF-CWs using the selected filter materials and plants, and side-effects of usingmaterials in HSSF-CWs

Chapter 4 Conclusions and recommendations: This Chapter provided the key

findings obtained from this results as well as suggestions for future research

Appendices This part consisted of pictures of research activities of this work.

CHAPTER 1: LITERATURE REVIEW

1.1 Pig farming in Vietnam

1.1.1 Pig farming development in Vietnam

According to the Food and Agriculture Organization (FAO), Asia will become thelargest producer and consumer of livestock products (Vu, 2019) Therefore,Vietnam's livestock needs to maintain a high growth rate to meet the domesticconsumption demand and to serve the export According to the Ministry ofAgriculture and Rural Development (MARD), the annual growth rate of thelivestock in the period of 2008-2019 was relatively high and stable, representing5-6% In the draft Strategy for livestock development (Ministry of Industry andTrade, 2019) from 2020 to 2030, the average annual growth rate for the periods of2020-2025 and 2025-2030 were predicted to be 4-5% and 3-4%, respectively

Livestock in general and pig production contribute significantly to Vietnam's GDPgrowth According to the Global Environmental Strategy Institute, agriculture sectoraccounted for 25% of the country's GDP in 2014 In particular, the pig industryrepresented 71% of the GDP of the entire agriculture sector (Pham, 2017) Thenumber of pig farming households with a scale of 100 pig heads or more was30,926, accounting for 1.04% of the total pig breeding households throughout thecountry [1] However, small-scale animal husbandry still dominates due to theconditions in Vietnam Pig production is concentrated mainly in areas Red RiverDelta and Northem Uplands according to the result presented in Figure 1.1

Figure 1.1 Distribution of pig production in Vietnam by ecological regions

(Nguyen, 2017a)

1.1.2 Environmental concerns of anaerobically treated swine wastewater

According to the study of Le (2014), the pig breeding industry develops at a veryfast pace but it is mainly spontaneous and has not yet met the technical standards ofbreeding facilities and breeding techniques Pollution caused by pig breedingincludes solid waste, air pollution and water pollution One pig emits 1.5 kg ofmanure daily and gradually increases with body weight Livestock solid wastecontains large amounts of organic matter from manure, uneaten food, straw, etc Itcontains many pathogenic microorganisms and high nitrogen (N), phosphorus (P)content (National Environment Report 2014) On the other hand, livestock andslaughtering contribute up to 26% of greenhouse gas emissions (GHGs) in the totalemissions caused by animals (Tambone, 2015) In addition, odor is also a cause ofair pollution in the livestock sector However, livestock wastewater is the mostsignificant source of pollution This is a type of wastewater generated fromlivestock activities including urine, rinse water, and bathing water for cattle andmay contain part or all of animal manure Wastewater accounts for the majority oflivestock wastes because 1 kg of livestock solid waste can be mixed with 20 to 49

kg of water (Nguyen, 2011b)

Figure 1.2 Swine wastewater (Nguyen, 2019a)Nowadays, there are various technologies for treating livestock wastewater such asThe Upflow Sludge Blanket filtration, USBF (Truong, 2010); Stabilization lakes(Nguyen, 2011); Upflow anaerobic sludge blanket, UASB (Rodrigues, 2010),Anaerobic reactor of expanded granular sludge bed - EGSB (Lee, 2012) However,the most common technology in livestock wastewater treatment is anaerobicallydigestion According to Cu (2012), biogas technology is commonly used to produceelectricity and heat in the developing countries Anaerobically digestion have ability

to reduce emissions GHGs from manure and generating renewable energy (Møller,2004; Sommer, 2004) There are millions of biogas tanks overworld, in which,roughly 3.8 million are located in India, about 60,000 tanks in Bangladesh andabout 30 million tanks were built in China (Cu, 2012) In Vietnam, Biogas isconsidered an appropriate solution to treat wastes contain high concentrations oforganic matter and solids such as pig wastewater However, the biogas systems arenot the final treatment system to ensure the criteria for safe discharge into theenvironment (Nguyen, 2012)

According to previous studies, the parameters of wastewater after the anaerobicallydigestion exceeded the permitted standard many times

Table 1.1 Treatment efficiency of piggery wastewater by anaerobically treatment

in Thua Thien Hue (Nguyen, 2012)

TT Parameter Unit

Inffluentconcentration( TB±s )

Effluentconcentration( TB±s )

Efficiency(%)

QCVN 40:2011/BTNMT(column B)

-Accordingly, despite the high treatment efficiency of over 70% for manyparameters, the quality of water after the anaerobically treatment is still not reachedthe standard to be discharged into the environment In detail, BOD5 is 6 timeshigher, COD is 3 times, TKN is 13 times, and TP is 57 times higher than thestandard This result has also been supported by other studies (Ho, 2016; Le, 2017)

In addition, the low treatment efficiency of nutrients (N, P) will create a burden onthe receiving source Therefore, it is necessary to take additional steps to treatwastewater after anaerobically treatment before discharging into the environment.Thus, it can be concluded that pigs breeding is an industry that can bring hugeeconomic benefits but also certain environmental risks In particular, the negativeeffects caused by livestock wastewater are the most significant Therefore it isnecessary to study and select appropriate and effective technologies to treat in order

to prevent negative impacts from livestock wastewater

1.2 Phosphorus pollution and remedy technologies

1.2.1 Phosphorus significance and environmental concern

On the one side, P is an important element in all known life forms Inorganic P inthe form PO43- plays an important role in biological molecules such as DNA andRNA Living cells also use P to transport cellular energy through ATP Almostprocess in the cell that uses energy has P in its ATP form Despite being the 11thmost abundant element on earth, P in nature exists only in the form of P ore and this

is an almost unrecoverable resource (when it takes 10-15 million years to recover)(Do, 2008) In agriculture, P is an important and essential nutrient for plants, Pdeficiency is one of the causes of crop productivity decline (Ryan, 2012)

Figure 1.3 P is an important and essential nutrient for plants (Pennsylvania's

Nutrient Management Act Program, 2005)

On the other side, P is one of the causes of water pollution in the presenceexceeding concentrations The recognizable manifestation of P pollution areeutrophication leading to algal blooms An excessive increase in nutrients,especially P in surface water, leads to low DO levels, killing fish and aquaticorganisms (Iodache, 2014) Various species of algae (such as microsystis) canproduce dangerous toxins during their life cycle, which are the causes of fishes andaquatic plants death, destroying ecological balance (Sathasivan, 2009) In addition,

the increase of algae also indicates the occurrence of other pathogenicmicroorganisms such as Pfisteria (Sathasivan, 2008) However, chemicals used toremove algea react with organic matter in the water and create disinfectionby-products (DBPs), in which, the most dangerous compound are Trihalomethanes(THMs) and Haloacetic acids because of their carcinogenic potential (Nguyen,

Figure 1.4 HABs are triggered by nutrient enrichment (Munn, 2018)

In Vietnam, the highest discharge threshold for P in industrial wastewater is 6mg/L(QCVN 40: 2011/BTNMT, column B), this number is 1mg/L in Canada (Guidelines

on wastewater quality and wastewater treatment at federal facilities, 1976), and 0.5mg/L in China (China National Standard, 2006, Level A)

1.2.2 Technologies for phosphorus decontamination of anaerobically treated swine wastewater (ATSWW)

The concentration of P after the anaerobically treatment in pig wastewater exceedsthe standard many times Therefore, various technologies have been used to treat P

in wastewater after anaerobically treatment such as: stabilization lagoon, tricklingfilter, AAO Technology

Stabilization lagoon after anaerobically treatment are popular in rural areas wherethere is a large land fund P removal in stabilization lagoon is associated with itsuptake by algal biomass, precipitation and sedimentation (Kayombo, 2004).However, wastewater contain high nutrient concentration as water afteranaerobically treatment, Stabilization lagoon do not completely eliminate N and P,leading to pollution of wastewater receiving areas In addition, the low controloptions and more dependant on climatic conditions are disadvantages of thistechnology (State of Michigan Department of Natural Resources and Environment,2010) Similarly, trickling filter used for livestock wastewater after anaerobicallytreatment was presented in Nguyen's research (2016) However, the nutrientremoval especially for P treating was limitation Nguyen (2017b) reported in herresearch the possibility of treating contaminants in livestock wastewater afteranaerobically treatment using AAO technology combined with coconut fiber media.Accordingly, TP have significantly decreased but still have not reached thedischarge standard In addition, the operation of AAO require high technicalcontrolling, difficulting mud control, lacking of carbon sources (Zhang, 2018)leading to that using AAO to treat livestock wastewater after anaerobicallytreatment is unpopular

Figure 1.5 Stabilization lagoon

Thus, P has important roles to humans, creatures and ecosystems but P also hascertain negative effects Also, it is a non-renewable resource and will be exhausted

in the future Therefore, the key requirements are removal and recovery P fromwastewater Currently, there are various technologies used to treat livestockwastewater but the most common is anaerobically treatment technology Treatmentefficiency of anaerobically treatment for the main parameters such as BOD, COD,

SS, and VSS is over 75% However, the concentration of these parameters are stillnot enough quality to discharge directly into the environment Therefore, thewastewater after anaerobically treatment needs to be further treated to reach thedischarge standards It can be seen that, although various technologies have beenused to treat livestock wastewater after the anaerobically treatment, thesetechnologies show many weaknesses in treatment efficiency or technicalrequirements

1.3 Constructed wetlands

1.3.1 Definition

CWs are engineered systems that have been designed and constructed to utilize thenatural processes involving wetland vegetation, soils, and the associated microbialassemblages to assist in treating wastewaters (Vymazal, 2010)

CWs have been applied to treat wide range of wastewater types such as domesticwastewater, municipal sewage, leachate, industrial wastewater and rainwater(Vymazal, 2010).

According to Wu (2015), CWs are a technology that uses plants to treat differentwaste CWs is required large building area, low operating energy, and suitable forsmall communities or decentralized sources CWs are a natural treatment systemwhere physical, chemical and biological processes occur when water, soil, plantsand microorganisms interact together It is considered a natural ecosystem designed

to take advantage of natural processes to treat wastewater (Qasaimeh, 2015)

1.3.2 Classification of constructed wetlands (CWs)

There are many ways to classify wetland systems depending on the structure,substrate, or kind of plants in the system By the flow model, CWs can be classifiedinto two types: Free water surface constructed wetlands (FWS-CWs) andsub-surface flow constructed wetlands (SSF-CWs) (Vu, 2012) In addition, there iscombining basic systems to form a hybrid treatment system

Figure 1.6 Classification of CWs (Herath, 2015)

FWS-CWs have a low P removal ability because of limited contact of water withsoil particles which adsorb and/or precipitate phosphorus (Vymazal, 2010) Thisidea was agreed in the White's study (2011), that the P-removal ability ofFWS-CWs is low The removal of P by FWS-CWs stay in range between 30 to 50%

in the long term (Economopoulou, 2004) In addition, FWS-CWs have manydisadvantages such as easily causing odors due to regular anaerobic condition, goodconditions for mosquitoes and insects living

Based on the flow directions, SSF-CWs can be divided into two categories in thedirection of flow: Subsurface flow vertical flow constructed wetlands (VSSF-CWs)and subsurface flow horizontal flow (HSSF-CWs)

Overall, P removal by VSSF-CWs is normally low Abdelhakeemre (2016) reportedthat, the P eliminating is 22% in VSSF-CWs with plant and 17% VSSF-CWswithout plant Due to the water supply, the conditions in the FWS-CWs changefrom aerobic to anaerobic and vice versa, which affects the P removal ability ofVSSF-CWs Anaerobic soils releasemore phosphate to soil solutions low inphosphate andsorbed more phosphate from soil solutions high in sol-uble phosphatethan do aerobic soils (Vymazal, 2007) This phenomenon can be explained thatorganic structural phosphorus can become soluble phosphorus when the organicmatter was oxidized Insoluble P form can re-dissolve under altered conditions(Kadlec, 2008)

HSSF has the ability to remove a variety of pollutants such as COD, SS, N, P.According to Volker (2001), HSSF has a better ability to eliminate P than VSSFdue to its ability to accumulate in P humic of P This result agrees with Arun's study(2019) when showing that P removal ability of HSSF is higher than VSSF.

Figure 1.8 HSSF-CWs (White, 2013)

1.3.3 Phosphorus removal by different components in CWs

The P elimination pathway in CWs system consists of: P removal by filter media,plants, microorganisms and other factors In particular, removal of P by filter mediaand plants are two removing P sustainability processes (Wu, 2013) When hydraulicretention time is long and the soil has a fine structure, the process of P removal ismainly adsorption and precipitation in the substrate, because this condition provides

a good opportunity for P adsorption and reaction (Nguyen, 2015a; Qin, 2016)

Table 1.2 P removal mechanisms of CWs components (Nguyen, 2019)

The substrates Adsorption

Chemical bonding of P to iron,aluminum, and calcium on soilparticle exchange sites

Precipitation P binds to dissolved iron, aluminum,

and calcium to form a solid orsemi-solid

Sedimentation Particulate phosphorus settles out of

the water column

Vegetation

OrthoP and some organic P taken up

by plants and algae

The microbes Immobilization

Plant available and some organicforms of P are consumed bymicrobial communities and stored intheir tissues

a The wetland substrates

Metabolism of P between materials and wastewater in CWs is very diverseincluding: adsorption - desorption, precipitation and dissolution, fragment and leach,mineralize, and settle (Vymazal, 2008) Filter materials in CWs play a importantrole in P eliminating through two pathways: adsorption, precipitation (Wu, 2015;Qin, 2016)

Regarding P sorption mechanisms in CWs involves the movement of dissolvedinorganic P from soil, wastewater to the surface of materials, where it onlyaccumulates on the surface without penetrating the interior The balance betweenadsorption and desorption maintains the equilibrium between the solid phase and P

in water in the pores of the material This phenomenon is defined as the phosphatebuffering capacity similar to the pH buffering capacity of the soil (Dunne, 2006)

P is adsorbed on the substrate based on presence of Al, Fe, Ca, and Mg ions, whereability to eliminate P of these ions depends on the pH of the system and the amount

of ions exist in the system In acidic condition, inorganic P is adsorbed on theoxides of iron and aluminum while compounds of calcium and magnesium areusually produced at higher pH

Figure 1.9 P adsorption mechanism on material surface (Ramesh, 2008)

The adsorption capacity of materials is usually determined through the Langmuirmodel The other commonly used models are Freundlich and Tempkin (Hongling,2017) The adsorption isotherms illustrate the balance between amount ofadsorption and solubility under certain conditions

P removal by chemical precipitation mechanism include the reaction betweenphosphate ions with metal cations such as calcium, aluminum, iron, magnesium toform amorphous crystalline salts The following chemical reaction showsimmobilization P with silicate clay:

Al3++ H2PO4-+2H2O = 2H++ Al(OH)2H2PO4(Variscite)

Al2SiO5(OH)4 + 2H2PO4- = 2Al(OH)2H2PO4+Si2O

52-Similar precipitation reactions occur with iron ions under acid conditions, or withcalcium and magnesium under neutral conditions (Ramesh, 2008)

Al3++ PO43-→ AlPO4↓

Fe3++ PO43-→ FePO4↓

5Ca2++ 3 PO43-+ OH-→ Ca5(PO4)3(OH)↓

In case wastewater have acid conditions, Fe and Al content may be more importantbecause precipitation reactions with these ions are preferred at lower pH levels(Arias, 2001)

The P dominant removal mechanism depends on the physical and chemicalproperties of the filter material In addition, P removal capacity also depends on thecontent of calcium, iron, aluminum and their oxides and hydroxides (Yang, 2018).There are many ways to classify filter materials based on usage history, sources ofsubstrates or removal mechanism Regarding the sources of substrates, they can beclassified into three types: natural natural materials, industrial by-products andman-made artificial products (Cucarella, 2009).

b The wetland plants

Plants is a necessary part of CWs that plays an important role in pollutant removal.The contribution of wetland vegetation to pollutant removal through filtration andsedimentation, stabilization of the wetland surface, light attenuation, and additionalsurface area for the attachment of microorganisms (Shan, 2011) The active reactionzone of constructed wetlands is the root zone (or rhizosphere) This is wherephysicochemical and biological processes take place that are induced by theinteraction of plants, microorganisms, the soil and pollutants (Stottmeister, 2003).This is where the most intensive interaction between the plant and microorganisms

is to be expected The roots releases organic acids (oftenly citrate and oxalate)which rising the availability of P availability Amount of excreted organic acid,mycorrhizal fungi, root-zone microorganisms allow a plant to uptake P more fromsoil (Nguyen, 2019b)

Figure 1.10 Phytoremediation Using Aquatic Plants (Fletcher, 2020)

Figure 1.11 Rhizosphere in CWs plants (Ghimire, 2019)

The removal abbility of pollutants differed from plant species, whichmay be related to plant tolerance to pollutants, redox conditions inroot zone or microbial activities Aquatic plants can not only absorbed P fromwater though leaves, stems and roots, but also affected the oxygen content insediments by photosynthesis That would lead to differences in P absorption byplant species

Figure 1.12 Phosphorus cycle in constructed wetland (Nguyen, 2019a)

There are various species of plants that can be used in the CWs It can be classified

as submerged vegetation, floating aquatic plants, semi-submerged aquatic plants

Many specific plants have been used in the study such as Vetiveria Zizanioides (Bwire, 2011; Abolfazl, 2014), Polygonum hydropiper (Bui, 2014), Cyperus

involucratus (Nguyen, 2015b)

Table 1.3 Effect of nutrient uptake by plants on removal of nitrogen and

phosphorus (%) in different CWs simulated scenarios (Jesus, 2018)

Plant

species CW type

N uptake(%)

(Zheng et al.2015)

Phragmites

australis FWS 17.04 34.19

1st yearunharvested

(Zheng et al.2015)

Arundo

donax HSSF 7.49 0.36

-(Meng et al.2014)

Typha

latifolia HSSF 1.73 0.06

-(Meng et al.2014)

Iris sibirica VSSF 19.86 13.19 High nutrient (Gao et al.

2014)

Iris sibirica VSSF 23.9 14.23 Medium

nutrient

(Gao et al.2014)

Iris sibirica VSSF 50.19 22.32 Low nutrient (Gao et al.

2014)

P can be completely and permanently removed from wastewater at harvest Premoval capacity depends on the type of used plant and the concentration of P in thewastewater Nutrients eliminating is generally higher when the plants in CWs areharvested (38.1% TP) than they have not been harvested (29.1% TP) The harvested

plants in the first year of removal are larger than the second year (3.7 g P/m2 and 3.2

g P/m2) (Zheng, 2015)

However, the effect of plants and associated rhizosphere on CWs removalefficiency was found not to be always significant P removal seems to be one factorthat is less likely to be positively affected by the presence of plants, may be due tohigh substrate adsorption In fact, in a large portion of the studies having statisticalanalysis, no significant differences between planted and unplanted controls werefound (67% of the cases for total phosphorus) (Jesus, 2018)

The plants used in the CWs are those that are able to withstand pollution, able toabsorb pollutants, easy to find, have good ability to grow in water and adapt well toenvironment (Nguyen, 2015b) High levels of pollution directly affect the CWsecosystem, inhibiting plant growth and even causing plant death (Wu, 2015) A highconcentration of pollutants in water leads to disadvantages in both treatmentefficiency and survival Plant tolerance to high levels of pollutants is anotherimportant factor to consider when selecting them for CWs (Almuktar, 2018) Theability to absorb pollutants of plants contributes to the pollution eliminating inwastewater, improving the treatment efficiency of CWs (Wu, 2015)

c The microbes

In CWs, the conversion and mineralization of pollutants and nutrients are carriedout by microorganisms (Zhu, 2013) In SF-CWs, the aerobic process only takesplace near the roots and on its surface Anaerobic processes including nitrification,sulfate reduction or CH4 generation are more intense at other areas (Stottmeister,2003) Treatment of pollutants, especially organic compounds, by microorganismsdepends on many factors and it is difficult to clearly explain the mechanisms (Li,2014) However, the ability to handle P of microorganisms in the CWs has beenshown to be ineffective by Huang (2012) The P uptake by microorganisms occursvery quickly, but the intensity is very low (low storage volume) (Vymazal, 2007).Microorganisms also play a large role in P mineralization Therefore, P removal

ability by microorganisms is temporary, since when they die, they release the Pback to the environment.

There are certain relationships among the main components of CWs.Microorganisms can promote plant growth (Gerhardt, 2009) thanks to the ability tochange the form of P which plant can use (Thongtha,v2014) Thongtha's study alsoshows that microorganisms contributes about 8 percent in the P removal whentreating domestic wastewater

Thus, despite the diversity of microorganisms in the CWs, their ability to remove P

is the lowest compared with other components in the CWs

1.3.4 Advantages and disadvantages of CWs in P removal from wastewater

Constructed wetlands (CWs) are affordable and reliable green technologies for thetreatment many kinds of wastewater Compared to conventional treatment systems,CWs are low cost, have fewer operational and maintenance requirements, and have

a high potential for being applied in developing countries; particularly in small ruralcommunities (Gorgoglione, 2018)

However, Vymazal (2010) has shown that CWs are ineffective in removingnutrients from wastewater, especially for P, unless appropriate materials areselected In CWs, two main components that play crucial role in eliminating Ppollution are the filtering material and the plants Using filter media that is both Peliminating, anti-clogging for the system and reusing waste is a solution to the goal

of removing P from wastewater In addition, selecting plants with good P uptakecapacity is good way to completely remove P permanent from wastewater

Another disadvantage of CWs is that it requires a large area of construction.However, comparing with other technologies to treat livestock wastewater afterbiogas treating such as stable lakes, trickling filters or AAO, CWs shows betterabout safety, no smell or mosquito and simpler technical requirements

1.4 Study subjects

1.4.1 Filter materials

Although CWs show good removal abilities for main pollutant parameters such asBOD, COD, SS, TSS, their ability to retain P is very low For P elimination, theselection of filter media is extremely important In addition, the P removal capacity

of HSSF system is higher than that of VSSF system (Arun, 2019) Since this studyaims at enhancing the P removal from pig wastewater after anaerobic treatment, theHSSF-CWs system were selected for investigation

a Coal slag

According to Vietnam Energy Association's report (2015), 35% of electricity wasgenerated from thermal power plants In Vietnam, most coal-thermal power plantsare located in the North, where the coal sources are closely located (Nguyen,

2015a)

Figure 1.13 Source structure of the national electricity system by primary energy

(Vietnam Energy Association's report, 2015)The the quality of raw coal used for thermal power plant is usually low Depending

on production technologies of the thermal power plants, the amounts andcharacteristics of coal slag can vary significantly According to a survey by theJapan Bank for International Cooperation (2003), the amount of slag discharged

from five thermal power plants of in the north of Vietnam was 673,600 tonsannually In the future, when the demand for electricity increases and the thermalpower plants keep working, the amount of coal slag is expected to be increasedsubstantially.

In Vietnam, coal slag is currently considered as an industrial waste Normally, coalslag is not disposed but utilized to produce construction materials

Many studies have shown that coal slag is capable of removing dyes such as azo,Tryphenylmethane and Brilliant Blue FCP (Gupta, 2006), Vertigo Blue 49 (Nguyen,

2015a) and reducing COD in the wastewater from the paper mill up to 40% (Pierre,2002)

Nguyen (2020) reported that the coal slag under optimal conditions could remove P

up to 21.63 mgP/g in the P concentration range of 0-30 mg/L A great potential ofthe coal sal for removing P was also reported by Safaa (2013) Accordingly, withthe increase of the initial concentration of phosphate from 0.1 to 25 mg/L, thepercentage removal for the slag increases from 76% to 99% The effective Premoval of coal slags could be explained by the presence of SiO2, Al2O3, and Fe2O3

in their compositions (Kieu, 2011)

On the other hand, Phan (2008) pointed in his study that coal slag of the thermalpower plants hardly reacted directly with water Nguyen (2015a) presented the goodwater conductivity of coal slag This characteristic is extremely important in theapplication of materials in CWs because it helps to minimize the possibility ofclogging

However, a controversial issue regarding to the application of coal slag is thepossible release of heavy metals into the aquatic environment (Li, 2016) Therefore,further studies are needed to identify effects of coal slag before applying them asCWs substrates on a large scale

Thus, in order to make use of industrial waste, coal slag is a potential material for

b Ferralsols

According to the Soil Map of the World (FAO, 2005), Ferralsols can be subdividedinto 6 groups: Plinthic Ferralsols (Fp), Humic Ferralsols (Fh), Acric Ferralsols (Fa),Rhodic Ferralsols (Fr), Xanthic Ferralsols (Fx), Orthic Ferralsols (Fo)

Ferralsols consist mainly of quartz, kaolinite, oxides, and organic matter (Eswaran,2005) Ferralsols composed primarily of base cation-poor minerals such as 1:1phyllosilicates (e.g., kaolinite) and sesquioxides (Tabor, 2017) Ferralsols are one ofthe major soil groups in Siaya County in western Kenya with low available P This

is one of the factors limiting crop production in western Kenya (Owino, 2015).The worldwide extent of Ferralsols is estimated at some 750 million hectares,almost exclusively distributed in the humid tropics on the continental shields ofSouth America and Africa (Rattan, 2016) In Southeast Asia, about 4 percent of theland area is covered by Ferralsols, located mainly in Vietnam, Thailand andCambodia (USAID, 1980)

Feralsols group dominates in the land distribution of Vietnam (with about 65.2% ofthe whole territory), in which the most common is red and brown feralite soil (Ton,2000) According to the Vietnam Association of Land, ferralsols is diverselydistributed in many provinces and cities of Vietnam such as the Northeast region(Phu Tho, Ha Giang, Tuyen Quang, Yen Bai and Bac Kan), Northwestern region(Lang Son, Hoa Binh and Cao Bang) and the Central Highlands region In general,the soil is less porous (about 40% porosity); acid condition (pHKCl 4.0 - 4.5); Pcontent ranges from 1 to 5 mg P2O5/100 grams of soil The P content in ferralsols isvery low and difficult to use for cultivation unless there are solutions to improve thesoil or apply additional fertilizers (Owino, 2015)

The Central Highlands is a region with a high area of ferralsols in Vietnam Theboundary of the Central Highlands region almost coincides with the administrativeboundaries of 5 provinces of Kon Tum, Gia Lai, Dak Lak, Dak Nong and LamDong province (Nguyen, 2015c) The natural area of the Central Highlands is

5,646,127 ha including 10 soil groups Of which, Ferralsols group has the largestarea (3,556,336 ha), accounting for 69.2 percent of the total regional area.

In the Central Highlands, ferralsols group is mainly used for agroforestryproduction In the field of environmental treatment, ferralsols has been used as apotential adsorbent to remove many heavy metals such as arsenic (Kassenga, 2008),chromium, copper, zinc, lead (Ntambi, 2020) or organic toxins such as Bisphenol S(BPs) (Shiqiu, 2019) Muindi (2015) showed a great potential of natural ferralsols inKenya in removing P

Explaining the P-removal ability of ferralsols, Tabor (2017) has shown that themain components of ferralsols are basic cation-poor minerals such as phyllosilicatesand sesquioxides This was also presented in USDA Soil Taxonomy that yellow-redsoil contained some amorphous, aluminum-iron mineral components that wereeasily converted into crystal minerals such as kaolinite, goethite, hematite orgibbsite These components are capable of removing P by adsorption, precipitation,and ion exchange mechanisms

Thus, ferralsols is a natural material, with a huge reserve worldwide and widelydistributed in Vietnam In addition, it has a great potential in removing P Therefore,this study focuses on the use of ferralsols as the wetland substrates for eliminating Pfrom wastewater

c Sand

According to the General Department of Geology and Minerals of Vietnam (2017),sand is widely distributed in 09 coastal provinces in the North and Central Vietnam.The total reserves of 13 mines, which have been explored, is 123 million tons andthe forecast resource is about 3 billion tons Sand is used extensively in humanactivities, especially construction In environmental treatment, sand has beenstudied as an adsorbent for removing heavy metals (Pb, Cr, Cu, Zn) and organicmatter (Awan, 2003) Many studies also showed the ability to remove P of sand.However, P removal capacity of sand compared to other natural materials such as

1.4.2 Plants

a Water spinach (Aquatica ipomoea)

Aquatica ipomoea (commonly known as water spinach) orginates from Central Asia,

South and Southeast Asia, tropical Africa, South America and Oceania Currently,water spinach is grown in many countries, such as Vietnam, Laos, Cambodia,

Thailand, Philippines and China (Tran, 2017) Aquatica ipomoea can grown in different medium including land, water fields, and lakes Aquatica ipomoea is easy

to grow by sowing or cuttings, they grow very fast and strong (Nguyen, 2011a;

Truong, 2012) Moreover, Aquatica ipomoea has a very short regeneration cycle time (about 4 weeks) Aquatica ipomoea also shows good adaptability and growth

under experimental conditions (Le, 2010)

Aquatica ipomoea has been popularly used for environmental treatment, such as

heavy metals, N and organic pollution treatment In addition, it is reported thatwater spinach demonstrated a great potential in removing P from wastewater Liu

(2013) reported that Aquatica ipomoea in the CWs could remove N and generate power Aquatica ipomoea also shows potential in treating organic and N pollution

(Endut, 2016; Liu, 2018) In addition, it also shows the ability to accumulate heavy

metals in its bodies (Milla, 2014; Saat, 2017) Studies on Aquatica ipomoea have

also been conducted, indicating that this plant had a good ability to accumulate P intheir bodies (Haq, 2018)

Osman (2014) used Aquatica ipomoea in HSSF-CWs system to treat domestic

wastewater The results showed that, with the TP influent concentration range of1.303 - 1.474 mg/L, the TP removal efficiency was 72.8%

In summary, Aquatica ipomoea is a common plant species in Vietnam It is widely

distributed, easy to grow and adapt with different environments, as well as have

short life cycles Aquatica ipomoea is capable of eliminating a variety of pollutants from wastewater, especially for P These are advantages of Aquatica ipomoea when

being selected for use as a wetland plant

b Lemongrass (Cymbopogon citratus)

Lemongrass is a native aromatic tall sedge, which grows in many areas of tropicaland sub-tropical South East Asia and Africa (Gagan, 2011) Lemongrass

(Cymbopogon citratus) is easy to grow, which requires warm, humid conditions,

full sunlight and plenty of moisture (Terra, 2009)

Recently, lemongrass has been studied and applied in the synthesis of compositematerials (Bekele, 2017), production of silica (Firdaus, 2015) In fact, lemongrass isthe most widely used in medicine and cuisine Lemongrass oil is widely used inAsian and African countries In the field of environmental treatment, lemongrasshas been used to adsorb heavy metals such as copper, nickel, lead and cadmium(Hassan, 2016) and dye colors (Singh, 2014; Ahmad, 2019)

Anand's research (2017) reported that lemongrass demonstrated positive effects onthe P removal via adsorbing P from the roots and enhancing stability of CWs

Thus, similar to Aquatica ipomoea, lemongrass is a widely distributed plant species

in Vietnam It is easy to grow and adapt to diverse natural conditions It also has ashort life time and high economic value Lemongrass is capable of removing manypollutants, including P Therefore, it is of high potential to use lemongrass in CWsfor P decontamination from livestock wastewater

CHAPTER 2: MATERIALS AND METHODS

Figure 2.1 Pha Lai Thermal Power Joint Stock Company

Pha Lai Thermal Power Joint Stock Company has 02 power generation plants Theconstruction of plant 1 was started in 1980 and completed in 1986 Plant 1 has amaximum capacity of 440MW including 4 power generation sets Plant 2 was built

in 1998 and completed in 2002 It have a maximum capacity of 600MW includingtwo power generation sets Currently, the maximum power output of Pha LaiThermal Power Joint Stock Company is 6.54 billion kWh/year Of which, the power