simultaneous removal of arsenic and ammonia from groundwater by phytofiltration with cattails (typha spp.) cultivation

LIST OF FIGURES Figure 1.1 Tentative risk map of arsenic concentrations in groundwater of the Red River Delta 13 Figure 1.2 Expressions of the black foot disease 15 Figure 1.3 Situatio

1.2.1 Arsenic Contamination of Groundwater: 11

1.2.2 Ammonia Contamination of Groundwater: 16

1.3.2 Ammonia Removal from Groundwater 19

1.4.1 Characteristics of Phytofiltration Systems 21

1.4.2 Principles of Phytofiltration Systems 23

2.3 Setup and Operation of Phytofiltration Systems: 29

ABBREVIATION

APHA American Public Health Association

ATSDR Agency for Toxic Substances and Disease Registry

CETASD Center for Environmental Technology and Sustainable Development

FAO Food and Agriculture Organization

HUS Hanoi University of Science

MCL Maximum Concentration Limit

MONRE Ministry of Natural Resource and Environment

NRC National Research Council

TCVN The Vietnamese Standard

US EPA The United Stated Environmental Protection Agency

WEPA Water Environment Partnership in Asia

WHO World Health Organization

LIST OF FIGURES

Figure 1.1 Tentative risk map of arsenic concentrations in groundwater of

the Red River Delta

13

Figure 1.2 Expressions of the black foot disease 15 Figure 1.3 Situation of ammonia contamination of groundwater in Hanoi City 16 Figure 1.4 Arsenic Removal Mechanisms in a Phytofiltration System 25

Figure 2.2 Cross section of an phytofiltration system with cattails (Typha

spp.) cultivation

30

Figure 3.1 Biomass accretion of cattails after periods of transplanting time 40 Figure 3.2 Root accretion of cattails after periods of transplanting time 41

Figure 3.4 [As] in outflows after periods of treatment time 43

Figure 3.6 [NH4+-N] in inflows and outflows after periods of treatment time 47 Figure 3.7 [NO2--N] in outflows after periods of treatment time 49 Figure 3.8 [NO3--N] in outflows after periods of treatment time 50 Figure 5.1 Sequentially assembled phytofiltration systems with cattails

(Typha spp.) cultivation

54

Figure 8.1 Distribution of documented world problems with arsenic in

groundwater in major aquifers as well as water and environmental problems related to mining and geothermal sources

61

Figure 8.2 Evaluation of simultaneous removal of arsenic and ammonia via 64

LIST OF TABLES

Table 1.1 MCL values for arsenic in drinking water 10 Table 1.2 Average arsenic concentrations and ranges in sample collected in

rural districts in the Red River Delta in 2001 13

Table 1.3 Average arsenic concentrations and ranges in sample collected in

the Mekong Delta on July, 2004 (n = 112) 14

Table 1.4 Average NH4+-N and NO2--N concentrations and ranges in

samples collected in 2004 in the Mekong River Delta 17

Table 1.5 The seven states of oxidation in which nitrogen can exist 19 Table 2.1 Initial concentrations of ammonia and arsenic in inflows 31 Table 2.2 Daily-taken volumes of outflow samples 31 Table 3.1 Front accretion of cattails after periods of transplanting time

Table 8.4 Values of Ka (Ionization constant in the ammonia and

ammonium equilibrium) dependent on Temperature 33

Table 8.5 Loading rates on arsenic and ammonia of some plants

transplanted hydroponically in arsenic- and

ammonia-contaminated water

64

LIST OF DIAGRAMS / FLOWCHARTS

Flowchart 5.1 Potential applications of phytofiltration for

arsenic-contaminated soil and water

55

INTRODUCTION

Groundwater in Vietnam is abundant; however, it is often polluted by different contaminants, especially by arsenic and ammonia [WB, 2002] The frequency of ammonia-contaminated groundwater demonstration in the Red River Delta areas is approximately 80% - 90% with average ammonia concentrations ranging from 10 mg/L – 30 mg/L [Le Van Cat, Tran Mai Phuong, 2005] In the Mekong River Delta, ammonia contamination of groundwater is also alarming with average ammonia concentrations ranging from 0.1 - 35 mg/L [M Berg, 2006] Ammonia does not directly cause poisoning, but unfortunately, its transformed products (such as nitrite

NO2-, nitrate NO3- ) can cause health risks to human beings [US EPA, 2000] Besides, groundwater in Vietnam is significantly polluted by arsenic [WB, 2002] The levels of arsenic contamination were examined and varied from 1 µg/L to 3050 µg/L (48% above 50 µg/L and 20% above 150 µg/L) in groundwater samples from domestic shallow tube-wells in rural areas in the Red River Delta Particularly, of which, the groundwater used directly as drinking water source had an average concentration of 430 µg/L in several highly affected rural areas [Tran Hong Con, 2006] In the Mekong River Delta, arsenic concentrations in groundwater are also high in range from 1 µg/L to 845 µg/L [M Berg et al., 2006]

Actually, such high arsenic- and ammonia-contaminated groundwater indicates that millions of people, especially who are living in the Red River Delta and in the Mekong River Delta daily consuming untreated groundwater, might be at high considerable health risks of poisoning caused by such contaminated groundwater Treatment technologies for arsenic and/or ammonia removal from contaminated groundwater have been paid much attention and concern There are several current treatment technologies for ammonia removal from groundwater such as Breakpoint Chlorination, Ion Exchange by Clinoptilolite, Air-stripping [Le Van Cat, 2007]

Exchange by Activated γ-Al2O3 [US EPA, 2000] However, selection of an optimal treatment technology depends on both objective and subjective factors, for example, contaminant contents, economic conditions, treatment scales, availability While precipitation is the most common among such methods, the disadvantage is that it only reduces the dissolved metal concentration to the solubility product level, which is frequently out of compliance with rigorous discharge permit standards and thus requires additional cleaning stages

These aforementioned techniques are all generally expensive and might possibly generate by-products dangerous to human health [US EPA, 2000] Regarding to rural areas conditions, the priority factors which should be much taken into account are costs and treatment scales Applications of these technologies for small-scale treatments are certainly more difficult in comparison to those for large-scales in point of views of financial problems, operation and maintenance conditions

In Vietnam, several studies on removal of arsenic and ammonia from contaminated groundwater have been researched and implemented in recent years However, applications of the above-mentioned technologies often faces difficulties and disadvantages such as high costs, complicated operation and maintenance skills In addition, each of these treatment technologies can be compatible for partially removing one contaminant Thus, simultaneous removal of contaminants requires a series of sophisticatedly combined treatment systems An optimal treatment technology which can be broadly applied in rural areas must be considered in terms

of low cost, small-scale treatment, simple operation and maintenance Moreover, requirements of simultaneous removal of both arsenic and ammonia should necessarily be taken into account

Phytofiltration system, a plant-based technology for the removal of toxic contaminants from soil and water, has been receiving renewed attention A great deal of research in decades that plants have the genetic potential to remove many toxic contaminants from water and soil [R.L Chaney et al., 2000] Plants can

uptake nutrients for their biomass development and growth Moreover, plants can transport oxygen from the air through their leaves, their shoots and finally to their root-zones for aerobic microorganisms to carry out nitrification and denitrification, with presence of ammonia as a preferable nutrient source Ammonia will be transformed to gaseous nitrogen (non-toxic) and to escape to the air In addition, plants have metals-accumulating ability to build their own cellular matters via uptake process Consequently, arsenic and ammonia will be removed from groundwater after periods of time

Phytofiltration has been proposed as a cost-effective, environmental-friendly alternative technology A number of plants have been identified for the phytofiltration, and some have been used in practical applications In this study,

cattails (Typha spp.) were chosen as a model plant for the phytofiltration systems

because of its high arsenic-accumulating ability coupled with its rapid growth and generation of high biomass yields This finding may open a door for phytofiltration

of ammonia and arsenic-contaminated groundwater in Vietnam

This study aims at:

1 Examining simultaneous removal ability of ammonia and arsenic from contaminated water by three pilot phytofiltration systems with cattails

(Typha spp.) cultivation;

2 Constructing and developing an optimal treatment technology for simultaneous removal of ammonia and arsenic (and other contaminants) from groundwater for drinking uses

1.1.2 Groundwater Quality Requirements for Drinking Purpose

a/ Arsenic MCL Standard for Drinking Water:

The MCL for arsenic in drinking water according to several standards are shown in

Table 1.1:

Table 1.1 - MCL values for arsenic in drinking water [J Matschullat, 2000]

▪ WHO: World Health Organization, drinking water guidelines for arsenic;

▪ EU: European Union;

▪ NL: Dutch drinking water guidelines for arsenic (the first numbers refer to reference values, the second to maximum permissible levels);

▪ TVO-D: German drinking water standards for arsenic;

▪ DVGW: German surface water (raw water) guidelines (for ranges see NL);

▪ TCVN: Vietnamese Standards

b/ Ammonia MCL Standard for Drinking Water:

Ammonia MCL standards for drinking water in somewhere around the world are different The WHO and EU standards for ammonia MCL in drinking water is of 0.5 mg/L Whereas, Vietnamese standard has set a limit for ammonia-nitrogen MCL

in drinking water is 3 mg/L according to new TCVN 5520-2003 [TCVN, 2003]

1.2 Current Status of Ammonia and Arsenic Contamination of Groundwater

1.2.1 Arsenic Contamination of Groundwater:

a/ Arsenic Contamination:

Arsenic, a significant contaminant of groundwater, has been found in many regions around the world [P.L Smedley and D.G Kinniburgh, 2002] Arsenic is widely known for its adverse effects on human health, affecting millions of people High concentrations of arsenic (above 50 g/L) in groundwater used as drinking water source have been reported in several countries such as Bangladesh, India, China, Mexico, Nepal, Taiwan, Vietnam…

In some Asian countries, arsenic in groundwater is a major health concern and the risks from using shallow tube-wells (STWs) for drinking water are well-known As part of the green revolution, millions of STWs have been installed throughout Asia over the last three decades This has resulted in a sharp increase of groundwater extraction for irrigation The direct consumption of groundwater through tube-wells

in an attempt to replace polluted surface water supplies has resulted in widespread arsenic poisoning

a1/ Sources of arsenic contamination:

Arsenic is one of the most toxic elements encountered in the environment Arsenic

anthropogenic activities The primary anthropogenic contributions of arsenic to groundwater are from application of arsenical pesticides, irrigation, mining and smelting of arsenic-containing ores, combustion of fossil fuels (especially coal), land filling of industrial wastes, release or disposal of chemical warfare agents [K.H Goh and T.T Lim, 2005], manufacturing of metals and alloys, petroleum refining, and pharmaceutical manufacturing [R.Y Ning, 2002] Another potential contributing source of arsenic in groundwater is the current use of chromated copper arsenate (CCA) as wood preservative Organic arsenic is also a constituent

of feed additives for poultry and swine for the control of coccidian intestinal parasites and to improve feed efficiency, and appears to concentrate in the resultant animal wastes There is a significant use of arsenic in the production of lead-acid batteries, while small amounts of very pure arsenic are used to produce gallium arsenide, which is a semi-conductor used in computers and other electronic applications [R.Y Ning, 2002] Even though industrial use of arsenic has decreased

in recent years, it remains a significant arsenic contamination source of groundwater for some human health problems [M Karim, 2000]

a2/ Arsenic contamination of groundwater in Vietnam:

Groundwater in the two large alluvial deltas of Mekong River and Red River has been exploited for domestic uses by private tube-wells [M Berg et al., 2006] M Berg et al., (2006) found that the arsenic concentrations in groundwater somewhere

in the Mekong River Delta and Red River Delta range from 1 to 845 µg/L and from

1 to 3050 µg/L, respectively Whereas, Trang et al., (2006) found elevated arsenic concentrations in areas of the Mekong Delta, where 405 (40%) of the tube-wells had arsenic levels higher than 100 µg/L

A tentative risk map of arsenic being higher than 50 µg/L in groundwater of the Red River Delta is presented in Figure 1.1 This map was established from geological raster information, climate and land use

Figure 1.1 - Tentative risk map of arsenic concentrations in groundwater of the

Red River Delta [FAO, 2007]

Table 1.2 - Average arsenic concentrations and ranges in sample collected in rural districts in the Red River Delta in 2001 [M Berg et al., 2006]

Rural Districts n Average (µg/L) Range (µg/L)

Table 1.3 - Average arsenic concentrations and ranges in sample collected in

the Mekong Delta on July, 2004 (n = 112) [M Berg et al., 2006]

Arsenic concentratioin (µg/L)

In Vietnam, the aquifers under the large deltas of Mekong River and Red River are now widely exploited for drinking water and for agricultural uses These above-presented data are demonstrating that people living in the two deltas are chronically exposed to elevated arsenic levels in groundwater used as their drinking water source via broadly-distributed tube-well system and at high risk of arsenic contamination The total number of tube-wells in the two regions is unknown but could be over one million [P.L Smedley and D.G Kinniburgh, 2002] It means that millions of people in Vietnam are likely to be affected by using contaminated groundwater from tube-wells and through consumption of contaminated foods Unfortunately, symptoms of chronic arsenic poisoning usually take more time than ten years to develop and appear, the number of future arsenic related ailments in Vietnam, therefore, is likely to increase Urgently, early mitigation measures should

As (III) are the most abundant [M.B Hossain, 2005]

b2/ Arsenicosis:

Arsenic contamination of water supplies poses serious risks to human health because inorganic arsenic is a known carcinogen and mutagen, and is detrimental to the human immune system [NRC, 2001] Drinking water and/or obtaining foods rich in arsenic over a long period lead to arsenicosis Chronic levels of 50 µg/L of arsenic can cause health problems after 10 to 15 years of exposure The development of symptoms of arsenicosis is strongly dependent on exposure time and the resulting accumulation in the body The various stages of arsenicosis are characterized by skin pigmentation, keratosis, skin cancer, effects on the cardiovascular and nervous system, and increased risk of lung, kidney and bladder cancer [H.M Anawar et al., 2002]

In China, exposure to arsenic via drinking-water has been shown to cause a severe disease of the blood vessels known as “black foot disease” [M.M Wu, 1989]

Figure 1.2 - Expressions of the black foot disease (WHO 00229, 2007)

b3/ Arsenicosis causes:

Arsenicosis is caused by the chemical arsenic, especially inorganic arsenic Arsenic

is a toxic element that has no apparent beneficial health effects for humans

concentrations in drinking water Besides, it may also be due to intake of arsenic via food or air The multiple routes of arsenic exposure contribute to chronic poisoning [WHO, 2001]

1.2.2 Ammonia Contamination of Groundwater:

a/ Ammonia Contamination:

Researches on ammonia contamination of groundwater, especially in the Red River Delta, have been paid much attention [WB, 2002] A few initial results have been achieved to evidently demonstrate and alarm such high ammonia contamination of groundwater in Vietnam

As shown in Figure 1.3 it is the situation of ammonia contamination of groundwater

in several sites of Hanoi City:

Figure 1.3 - Situation of ammonia contamination of groundwater in Hanoi City

PV: Phap Van TM: Tuong Mai YP: Yen Phu

As presented, groundwater in several sites of Hanoi City is strongly affected with high ammonia concentrations, especially in Ha Dinh and Phap Van areas with ammonia concentrations of higher 10 mg/L (shown in red color)

In the Mekong River Delta, ammonia contamination of groundwater is also alarming M Berg et al., 2006 researched and found demonstrations of ammonia contaminations of groundwater as shown in Table 1.4 below:

Table 1.4 - Average NH 4 + -N and NO 2 - -N concentrations and ranges in samples

collected in 2004 in the Mekong River Delta [M Berg et al., 2006]

NH 4 + -N concentration (mg/L) 5.0 0.1 - 35

NO 2 - -N concentratioin (mg/L) 0.25 0.25 – 4.4

*/ Ammonia contamination sources of groundwater can be from both natural and

anthropogenic sources Natural sources include biological fixation of atmospheric nitrogen which serves as a significant source of natural nitrogen input to water Anthropogenic sources include uses of chemical fertilizers, pesticides, run-off,

industrial discharges, etc [ATSDR, 2004]

b/ Ammonia Toxicity:

There has no scientific report told that ammonia affects directly to human health but transformed products made from ammonia like nitrite, nitrate via nitrification and denitrification are very dangerous [ATSDR, 2004] Nitrite can combine with secondary amines in the digestive tract to produce N-nitrosamine which is carcinogenic And, nitrate is agent created bluish coloration of the skin

NH 4 + → NO 2 - → NO 3 - (a)

1.3 Treatment Technologies

1.3.1 Arsenic Removal Treatment:

The most common water treatment technologies for arsenic-contaminated water include the following:

a/ Coagulation/Filtration:

Coagulation/filtration removes arsenic by co-precipitation with iron oxide [US EPA, 2002] Coagulation/filtration using alum is already used by some utilities to remove suspended solids, and may be adjusted to remove arsenic Iron oxide adsorption filters the water through a granular medium containing ferric oxide Ferric oxide has a high affinity for adsorbing dissolved metals such as arsenic [US EPA, 2002] The iron oxide medium eventually becomes saturated, and must be replaced

This treatment method is effective for removal of As(V) according to lab- and plant tests However, it is generally unable to successfully remove arsenic in large-scale system to lower levels due to the affinity and solubility limitation of the resultant products [US EPA, 2002] The procedures are also time-consuming and expensive, and not cost-effective And another disadvantage of this method is the generation of large volumes of arsenic-contaminated coagulation sludge [US EPA, 2002] The disposal of such contaminant wastes may be a concern, especially if nearby landfills are unwilling to accept such sludge

3 Wherein substantially no ferric ions are added to the aqueous medium; and whereby dissolved arsenic in the aqueous medium is reduced to a lower level than possible if only the step of adding lime were performed

1.3.2 Ammonia Removal from Groundwater

a/ Biological-nitrogen species:

In nature, nitrogen-compounds can be existed in many states of oxidation, ranging from reduced ammonia – nitrogen (NH3-N)/ammonium – nitrogen (NH4+-N) to highly oxidized nitrates-nitrogen (NO3--N) In all, nitrogen can exist in seven states

of oxidation, as shown in Table 1.5:

Table 1.5 – The seven states of oxidation in which nitrogen can exist

[Le Van Cat, 2007)

b/ Ammonia Removal from Groundwater:

In water, ammonia/ammonium and nitrate are more abundant than nitrite and other organic nitrogen-compounds At aim of an achievement of the most effective ammonia removal technology from groundwater, such technology should be a

complete transformation of the nitrogen-compounds finally into gaseous nitrogen, which is inert and does not pollute environment

Based on this principle, physiochemical and/or biological treatments can be applied for removal of nitrogen-compounds from groundwater as follows:

b1/ Transformation of the nitrogen-compounds finally into gaseous nitrogen which then releases to the air This method is due to the following processes:

 Biological processes (Nitrification and Denitrification);

o Nitrification: Ammonium is converted into nitrite, and finally to nitrate The bacteria involved are autotrophic and use oxygen as their electron acceptor, whereas ammonium is used as their substrate The conversion

to nitrite is performed by Nitrosomonas sp; and the conversion to nitrate

by Nitrobacter sp These bacteria are obligate aerobes, meaning that they

can grow only in the environment in which dissolved oxygen (DO) is present If the absence of DO for prolonged periods, however, is not lethal to those microorganisms [H.A Painter, 1970]

o Denitrification: In the absence of dissolved oxygen, bacteria will use nitrate as a terminal electron acceptor and convert nitrate to nitrogen gas

 Anamox process (Oxidation/Reduction of ammonia via microorganism activities);

 Direct oxidation of ammonia to form gaseous nitrogen;

b2/ Transformation of the nitrogen-compounds into cellular components (biomass

of plants and microorganisms)

 These transformations are involved in biochemical reactions occurring in plant cells (via photosynthesis reactions) and microorganism cells (via assimilation reactions) These processes exist in nature

b3/ Volatilization of ammonia into the air

Treatment cost-effectiveness these methods are certainly different An optimal selection of treatment technology should be based on cost-effectiveness (low operation and maintenance cost, simple handling ) and treatability (long-life, maximum elimination of not only ammonia but other contaminants )

b/ Main Components of Phytofiltration Systems: The three main components of

a phytofiltration system are hydrology, soils/sediments, and vegetation The interactions of these components dictate the overall contaminant removal efficiency

of the phytofiltration systems

1 Hydrology: Hydrologic regime is the major regulating factor of all phytofiltration systems used for water treatment Hydrologic characteristics depend on configuration or geometry of phytofiltration systems, water loading rate, and water depth

2 Soil substrate for rooting media: The type and textile of soil affect physical, chemical, and biological mechanisms regulating the removal of contaminants from water Soil characteristics which should be taken into account are soil pH, soil penetrability, and soil thickness Of which, soil penetrability, soil thickness are important factors in soil selection Soil vertical penetrability is dependent on the type and textile of soil Sandy soil has high spongy textile which is supportive for penetration

In many phytofiltration systems, the soil layer is upper-lain by a small pebble layer to prevent water sampling from being blocked

3 Vegetation: The following factors should be taken into account in the plant selection:

▪ High capability of nutrient storage and uptake;

▪ High capability of transporting oxygen from the air to the rhizosphere;

▪ High resistibility to water and climatic conditions;

▪ Low sensitivity to various chemical components in soil and water;

▪ High growth rate and multiplication (high biomass production)

Herbaceous emergent macrophytes have been demonstrated and applied in many phytofiltration systems because many of these plants are perennial and have a high capacity of biomass production and contaminant storage [R.R Brooks, 1998] They are widely distributed on the shorelines of lakes and streams and in wetland ecosystems The emergent macrophytes most typically used in phytofiltration

systems include cattails (Typha spp.), reeds (Phragmites sp.), and bulrush (Scirpus spp.) [R.R Brooks, 1998] These emergent macrophytes, especially cattails (Typha

spp.), are potentially available in Vietnam

c/ Physicochemical Characteristics of Phytofiltration Systems:

Emergent macrophytes can easily transport oxygen through their stems and leaves into their root zone Oxygen not used during root respiration may leak into the adjacent soil, creating an aerobic zone around the roots The excess oxygen in rhizosphere may be significant in the aerobic oxidation of soluble organic compounds and nitrification of ammonia-nitrogen/ammonium-nitrogen Field studies with and without plants give the most reliable estimates of oxygen available

to bacteria in the rhizosphere Although there is clear evidence of oxygen transport into the roots by diffusion and mass flow, at times oxygen transport may be

insufficient to meet plant metabolic requirements, implying that there is no enough oxygen to significantly affect water treatment processes

1.4.2/ Principles of Phytofiltration Systems

a/ Nutrient Storage and Uptake Capacity of Plants:

The nutrient removal capacity of an phytofiltration system is dependent on plant growth rates, contaminant content and bioavailability, sediment characteristics, oxygen transfer capacity of the plants into the root-zone, biochemical and physiochemical processes functioning at the root-water-sediment interface, plant density per unit area, plant harvesting, and climatic conditions

Nutrient uptake rates and maximum growth rates define the nutrient storage capacity of the plant The potential rate of nutrient uptake by a plant is limited by its net productivity (growth rate) and the concentration of nutrients in the plant tissues Nutrient storage is dependent on plant tissue nutrient concentrations and on the potential for biomass accumulation (that is, the maximum standing crop - biomass per unit area) Maximum growth typically is attained at the lower range of nutrient supply, whereas maximum nutrient uptake rate is reached at much higher levels of nutrients

b/ Mechanisms of Arsenic Uptake and Accumulation in Plants

- / Arsenic speciation and distribution can provide important information helpful to understanding the mechanisms for arsenic accumulation, translocation, and transformation in plants The two most important forms, As(V) and As(III), are taken up to plants by completely different mechanisms Uptake, accumulation and toxicity vary within and between plant species In general, more arsenic in the soil and water leads to higher concentrations in plants, but this depends on many other factors

Arsenic is a nonessential element for plant growth At higher concentrations, arsenic

death However, during evolution plants have developed two strategies that enable them to survive and reproduce in arsenic enriched environment: arsenic exclusion and arsenic accumulation [H Dahmani-Muller et al., 2000]

Successful application of phytofiltration systems to arsenic-contaminated soils and water depends on many factors, among which are plant biomass and arsenic concentrations Plants must be able to produce sufficient biomass while accumulating a high concentration of arsenic In addition, plant species should be responsive to agricultural practices designed to enhance arsenic accumulation and to allow repeated planting and harvesting of arsenic-rich biomass Furthermore, it is important to understand the availability and phytotoxicity of arsenic to the plant itself

-/ Uptake: Arsenic in soil and water is found to be predominantly as inorganic species It was hypothesized that the plant uptakes arsenic as arsenate As(V) and then arsenate is converted to arsenite As(III) within the plant [W Zhang et al., 2002] Arsenate and arsenite are taken up by different mechanisms Abedin et al., (2002) suggested that the plants were effectively exposed to As(III) and not to As(V) because of the reducing soil conditions The uptake mechanism of organic arsenic is largely unclear so far

-/ Translocation and accumulation: Organic arsenic is more readily translocated but

the uptake is much lower compared to inorganic arsenic For example, in pot experiments with rice plants exposed to arsenic added via arsenate in irrigation water, rice plant parts were ranked according to the arsenic concentrations as follows: root > straw > husk > grain [Carbonell et al., 1998] Concentrations in all plant parts increased with the exposure concentration This is a common observation for other plants as well [B.M Bleeker, 2003]

-/ Metabolism: After uptake, arsenate is rapidly reduced to arsenite, causing oxidative stress This induces the formation of certain anti-oxidants This is regarded as a detoxification mechanism [A.A Meharg and J Harley-Whitaker,

2002] In spite of the rapid reduction of arsenate to arsenite, high levels of arsenate have also been found in plant material Abedin et al., (2002) reported that more than

70 percent of the arsenic in the straw of rice was present as arsenate Schmidt et al., (2004) found arsenate in plants that were only exposed to arsenite, showing that oxidation of arsenite in plants also took place Many organic arsenic species have been found in plants as well, but only in minor amounts [V.M Dembitsky and T Rezanka, 2003]

c/ Mechanisms of Ammonia Uptake and Accumulation in Plants

Nitrogen-compound removal processes in phytofiltration systems include nitrification and denitrification, ammonia volatilization (little) and plant uptake

Figure 1.4 – Arsenic Removal Mechanisms in a Phytofiltration System

Uptake by plants (predominantly in roots)

Precipitation (as effect of microbial transformations)

column Whereas, a significant portion of dissolved organic nitrogen is returned to water column during breakdown of detrital plant tissue or soil organic matter Effluent leaving phytofiltration systems may therefore contain elevated levels of inorganic nitrogen The potential export of organic nitrogen will, however, depend

on the environmental conditions present in the water and soil Depending on the metabolic activity of the bacteria, organic bound nitrogen can be mineralized to ammonium-nitrogen Mineralization also occurs in the underlying soil, and the ammonium-nitrogen formed can be subsequently released into the overlying water Plant uptake of nitrogen is one of the main processes involved in the removal of ammonia from water Removal of nitrogen through plant uptake will depend on the growth rate of the plant, culture density, and environmental parameters such as solar radiation and temperature Aquatic plants are capable of assimilating both ammonium and nitrate However, many aquatic plants prefer ammonium to nitrate, even when both ions are present in the water at the same time because ammonium is one of the essential nutrients and the most important chemical components for protein synthesis of plant cells

In all, nitrogen-compounds uptake and accumulation of aquatic plants involved to ammonia elimination in phytofiltration systems are summarized as follows:

1 The plants shall uptake nitrogen-compounds for their cell synthesis, especially ammonium because ammonium is the most preferable nutrient proteins and one

of the most important chemical components for cell synthesis in comparison to other elements

2 In phytofiltration systems, herbaceous emergent plants have have capability of transport oxygen to the root zone and create oxidizing rhizosphere for aerobic microorganism activities and development Such aerobic microorganisms living near the plant root system shall oxidize ammonia to form nitrite, and finally nitrate via nitrification In the further areas around the plant root zone, oxygen concentration is lower There, with presence of nitrate, nitrate is gradually

reduced to gaseous products such as nitrous oxide and nitrogen gas The aerobic rhizosphere (the nearer root-zone) of aquatic plants has been shown to support nitrification, whereas the anaerobic rhizosphere (the further adjacent root-zone) supports denitrification

The bacteria involved in nitrification are autotrophic and use oxygen as their electron acceptor, whereas ammonium is used as their substrate The conversion to

nitrite is performed by Nitrosomonas sp; and the conversion to nitrate by Nitrobacter sp Most denitrifiers in denitrification are facultative, meaning that they can use either oxygen (aerobic respiration) or nitrate (anoxic respiration) as the

terminal electron acceptor in respiration These microorganisms use similar

metabolic pathways The only difference between aerobic respiration and anoxic

respiration is the enzyme catalyzing the final electron transfer occurring in the electron transport chain If both oxygen and nitrate are present, microorganisms will preferentially use oxygen as the terminal electron acceptor This is because denitrification yields less energy than aerobic respiration

CHAPTER 2 - MATERIALS AND METHODS

2.1 Plant Selection:

Phytofiltration, a plant-based technology for the removal of contaminants from soil and water, has been receiving renewed attention The prerequisite for successful phytofiltration systems is the existence of suitable plants The ideal plant species for phytofiltration systems should have high capability of substrate uptake, fast growth rate and high biomass production, high oxygen transport from the air to the rhizosphere as well as high resistibility to humid soil and climatic conditions, especially compatible with conditions of tropical climate in Vietnam

In the first experiments, 6 selected kinds of plants including cattails (Typha spp.), umbrella plant (Vyperus Alterisolius), elephant plant (Pennicetum sp.), canna (Cannas spp.), elephant ear (Colocacia esculenta) and dasheen were hydroponically

transplanted in solutions of arsenic- and ammonia contaminated water Based on the

previous experimental results (see Figure 8.2 and Table 8.5), cattails (Typha spp.)

demonstrated as the most feasible plant and chosen for evaluation of its removal capacity to arsenic and ammonia from contaminated water in the phytofiltration systems in this study

Figure 2.1 - Cattails (Typha spp.)

2.2 Soil Selection for Rooting Media:

Soil substrate for rooting media plays an important role in phytofiltration systems because the type and textile of soil affect physical, chemical, and biological mechanisms regulating the removal of contaminants from water and soil

Sandy soil, which has high spongy textile and supports for penetration, was selected

to apply in this phytofiltration system The sandy soil was washed by running water several times before being used for rooting media in the phytofiltration systems The soil layer was upper-lain by a small pebble layer to prevent sampling outflow

from being blocked by fine sands

2.3 Setup and Operation of Phytofiltration Systems:

2.3.1 Plant Cultivation:

Cattails (Typha spp.) were collected in nature Then, the cattails were washed in

running-tap water to remove medium from the root zones and immediately transplanted into three identical 80-litter volumetric PVC plastic pots, surface area

of each pot was at 0.16 m2 Each pot consisted of four healthy cattails, which were evenly positioned 10 cm deep under the surface of the sandy soil layer

After cultivation, the plants were given several days to grow under flooded conditions for primary biomass production as well as acclimatization to the moist conditions The planted pots were placed in natural open-air conditions Over this period, the daily overall temperature fluctuation ranged from 28oC to 29.5oC (average 28.4oC) When fronds of the cattails reached 0.8-1.0 m high (equivalent to 0.2-0.3 kg/cattail body), the cattails were ready to be used for phytofiltration evaluation of these pilot systems

2.3.2 Operation:

The three phytofiltration systems were fed with tap water pickled with 30 mg/L of ammonia and 300 µg/L of arsenic (initial concentrations) (see Table 2.1) Volumes

increased as shown in Table 2.2 The three phytofiltration systems were separately installed to perform different functions for investigation described as follows:

1 Pot A was used to treat arsenite and ammonia, simultaneously;

2 Pot B was used to treat arsenate and ammonia, simultaneously;

3 Pot C was used to treat mixture of 50% arsenate + 50% arsenite and ammonia, simultaneously

Open air (3-4 cm)

Water layer (3-5 cm)

Sandy soil layer (35-40 cm)

Small pebble layer (6-8 cm)

Tap volume control

Cattails (Typha spp.)

Outflow Inflow

Figure 2.2 - Cross section of an phytofiltration system with cattails

(Typha spp.) cultivation

2.3.3 Preparation of Ammonia and Arsenic Solutions

Ammonia was supplied as a solution of NH4Cl in running-tap water to produce initial ammonia concentration of 30 mg/L; whereas, arsenite and arsenate were supplied as solutions of As2O3 and of Na3AsO4, respectively, in running-tap water

to produce the same initial concentrations of 300 µg/L This initial ammonia and arsenic concentrations were chosen to encompass their high concentration levels occurring in groundwater of contaminated areas in the Red River Delta and in the Mekong River Delta

Table 2.1 - Initial concentrations of ammonia and arsenic in inflows Ammonia Arsenite (As(III)) Arsenate (As(V))

2.4 Sampling:

Inflows and outflows of the three systems were daily sampled for chemical analysis

in parallel All samples were immediately analyzed after sampling

Table 2.2 – Daily-taken volumes of outflow samples

outflows/day

(L/d)

2.5 Chemical analysis of samples [APHS, 1970]:

Chemical analysis of samples (both inflows and outflows) included:

2.5.1 pH-value measurement

In this study, the pH-values of samples were determined by the pH meter METTLER TOLEDO MP 200

Principle: Alkalinity is significant in many uses and treatments of waters

Alkalinity of a water is the capacity of that water to accept protons Alkalinity is usually imparted by the bicarbonate (HCO3-), carbonate (CO32-) and hydroxide ion (OH-) of a natural or treated water supply If pH is lower than 8.2, alkalinity results from only bicarbonate (HCO3-)

Alkalinity is determined by titration with a standard solution of a strong mineral acid to the successive bicarbonate, carbonic acid equivalence points, and indicated

by means of color

Reagents:

1 In this study, standard 0.02N HCl acid solution was used as a titrant solution

2 Methyl orange indicator solution: Dissolve 0.5 g of methyl orange to 100 mL distilled water

Procedure:

+/ Total-alkalinity of samples was determined by methyl orange indicator method:

 Use 25 ml of a sample and put it into an erlenmayer flask

 Add 0.05 mL (equivalent to 1 drop) of methyl orange indicator solution into the erlenmayer flask

 Titrate over with HCl 0.02N standard acid solution to the proper equivalence point (The indicator changes the coloration from orange at pH 4.6 to pink at pH 4.0

+/ Alkalinity calculation:

V HCl x 0.02 x 50,000 Total – Alkalinity = - = 20 x V HCl (mg CaCO 3 /L) (i)

25 mL of sample

2.5.3 Ammonia-nitrogen analysis

Principle: Ammonia-nitrogen is present in many surface and ground waters A