The behavior of humic Substance in iron electrolysis Process and its influence on Phosphorus removal

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VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

HA THI DIEP ANH

THE BEHAVIOR OF HUMIC

SUBSTANCE IN IRON ELECTROLYSIS

PROCESS AND ITS INFLUENCE ON

PHOSPHORUS REMOVAL

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VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

HA THI DIEP ANH

THE BEHAVIOR OF HUMIC

SUBSTANCE IN IRON ELECTROLYSIS

PROCESS AND ITS INFLUENCE ON

PHOSPHORUS REMOVAL

MAJOR: ENVIRONMENTAL ENGINEERING

CODE: 8520320.01

RESEARCH SUPERVISOR:

Prof. Dr. JUN NAKAJIMA

Associate Prof. Dr. LE VAN CHIEU

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ACKNOWLEDGMENT

First and foremost, I would like to sincerely thank my instructor, Prof. Jun
Nakajima for helping and always encouraging me, because of his patience,
motivation, and immense knowledge. His generosity and devoted guidance
contributed greatly to my dissertation completion and developed myself. There is no
unmatched honor to work with him.

Second, I would like to thank my co-supervisor, Associate Prof. Dr. Le Van
Chieu a lot because of his thoughtfulness and kindness. He is always enthusiastic
about reading and revising my research carefully.

Third, I would like to express my sincere thanks to all MEE Department for
your valuable support in the process of implementing the thesis as well as my stay at
VJU. And I would also like to thank JICA for its support. Thanks for all that we have
been through together.

I would like to express my appreciation to all Ritsumeikan University
professors, staff, and doctors, for their warm and enthusiastic welcome during my
internship. They gave me access to labs and research facilities. Without their valuable
support, it would not be possible to do this research.

Finally, I would like to thank my family and friends who have supported me
spiritually throughout the process of writing this thesis in particular, and my life in
general.

Hanoi, August 7th, 2020

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TABLE OF CONTENT

ACKNOWLEDGMENT... i

INTRODUCTION ... 1

1. Background ... 1

2. Objectives ... 3

3. Structure of thesis ... 5

CHAPTER 1. LITERATURE REVIEW ... 7

1.1. Phosphorus removal technologies ... 7

1.1.1. Phosphorus (P) pollution. ... 7

1.1.2. Phosphorus removal technologies. ... 8

1.2. Electrocoagulation/Iron electrolysis. ... 15

1.2.1. Definition. ... 16

1.2.2. Advantages and drawbacks of EC ... 17

1.2.3. The principle of electrocoagulation ... 18

1.3.4. Application of EC ... 19

1.3. Iron electrolysis application for phosphorus removal in Johkasou systems. ... 19

1.3.1. Johkasou systems for decentralized domestic wastewater treatment. ... 19

1.3.2. Phosphorus removal in Johkasou and application of iron electrolysis ... 20

1.3.3. Interference of phosphorus removal using iron electrolysis. ... 23

1.4. Humic substance. ... 24

1.4.1. General description ... 24

1.4.2. Chemical characteristic ... 26

CHAPTER 2. MATERIALS AND METHODOLOGY ... 28

2.1. Materials ... 28

2.1.1. Synthetic test liquor (phosphate solution) ... 28

2.1.2. Humic substance sample liquor. ... 28

2.1.3. Humic acid sample liquor ... 29

2.2. Iron electrolysis experiment set-up. ... 30

2.3. Operational condition of experiment. ... 31

2.3.1. Iron electrolysis with or without oxygen supply. ... 31

2.3.2. Iron electrolysis with HS addition ... 32

2.3.3. Iron electrolysis with humic acid addition. ... 33

2.4. Chemical analysis. ... 34

2.4.1. Suspended solid (SS)... 34

2.4.2. Iron analysis. ... 35

2.4.3. Phosphorus analysis. (PO4-P)... 36

2.5. Fluorescence spectroscopy analyses by three-dimensional excitation-emission
matrix. ... 36

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3.1.1. Iron electrolysis with aeration. ... 38

3.1.2. Iron electrolysis without aeration. ... 39

3.1.3. Discussion ... 41

3.2. The effect of humic substance on iron electrolysis ... 43

3.2.1. Iron coagulation decrease by humic substance addition ... 43

3.2.2. Decrease of phosphorus insolubilization by iron coagulation decrease ... 44

3.2.3. Discussion. ... 45

3.3. The effect of fulvic acid to iron electrolysis ... 47

3.3.1. Iron electrolysis with humic acid addition ... 47

3.3.3. Discussion ... 50

CONCLUSION ... 52

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LIST OF TABLES

Table 1.1. Vietnam national technical regulations on effluent discharge ... 7

Table 2.1. Preparation of synthetic test liquor ... 28

Table 2.2. Operational experiment condition. ... 32

Table 2.3. Preparation chemicals to iron analysis ... 35

Table 2.4. Preparation chemicals to phosphorus analysis ... 36

Table 3.1. Effluent parameters after electrolysis performed in aeration condition .. 38

Table 3.2. Effluent parameters after electrolysis performed in humic substance 
addition experiment ... 43

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LIST OF FIGUREURES

Figure 1. Iron electrolysis reactor (Fayad, N. (n.d.)., 2017) ... 2

Figure 2. Structure of thesis ... 6

Figure 1.1. Changes in structure of phosphorus compounds in municipal wastewater 
between year 1971 and 1991 (Rybicki, n.d.). ... 9

Figure 1.2. Phosphorus removal technologies ... 9

Figure 1.3. One – point chemical addition ... 10

Figure 1.4. Two – point chemical addition... 10

Figure 1.5. Metabolic pathway of PAO under aerobic and anaerobic conditions 
(Bunce et al., 2018) ... 14

Figure 1.6. Iron electrolysis principle ... 18

Figure 1.7. Combination process of BOD and nitrogen removal type Johkasou and 
phosphorus adsorption column (Ebie et al., 2008)... 22

Figure 1.8. Johkasou for phosphorus – BOD – Nitrogen removal. (Kumokawa, n.d.)
 ... 23

Figure 1.9. Hypothetical humic acid structure according to Stevenson (1982) ... 26

Figure 1.10. The hypothetical model structure of fulvic acid (Buffle's model) ... 26

Figure 1.11. Chelation of Cu and Zn in top 2 examples with simple complexation of 
Zn by an amino acid (Hd, n.d.). ... 27

Figure 2.1. The map of Hanoi and Nam Son landfill ... 29

Figure 2.2. Humic acid, Nacalai Tesque, Japan. ... 29

Figure 2.3. Schematic diagram of the laboratory-scale experiment. ... 30

Figure 2.4. The types of equipment used to set-up experiments ... 30

Figure 2.5. Synthetic test wastewater preparation ... 31

Figure 2.6. Set – up experiments ... 32

Figure 2.7. Humic substance experiment set-up. ... 33

Figure 2.8. Humic acids addition experiment set-up ... 34

Figure 2.9. Procedure iron calculate. ... 34

Figure 2. 10. Fluorescence Spectrophotometer F-7000 (Hitachi, Tokyo, Japan) .... 37

Figure 3.1. Phosphorus insolubilization ... 39

Figure 3.2. Iron coagulation ... ………..39

Figure 3.3. Iron coagulation (without aeration) ... 39

Figure 3.4. Iron coagulation (N2 gas bubbling) ... 39

Figure 3.5. Iron coagulation under aerobic condition (a) and anaerobic condition 
(b)………..37

Figure 3.6. Phosphorus insolubilization (without aeration)………..41

Figure 3.7. Phosphorus insolubilization (N2 gas bubbling) ... 41

Figure 3.8. The existing pathway models. ... 41

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Figure 3.10. Iron coagulation (Humic substance addition) ... 44

Figure 3.11. Phosphorus insolubilization (HS addition) ... 45

Figure 3.12. Molar ratio of ΔFe / ΔP ... 46

Figure 3.13. Soluble complex formation of ferrous ion and HS ... 47

Figure 3.14. Iron coagulation (Humic acid addition) ... 48

Figure 3.15. Phosphorus insolubilization (HA addition) ... 49

Figure 3.16. EEMs Fluorescence spectra of humic substance sample (leachate 
sample) ... 49

Figure 3.17. EEMs Fluorescence spectra of humic acid sample. ... 50

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LIST OF ABBREVIATIONS

BOD
DC
DOC
EBPR
EC
EEM
FDOM

HA
HS
MBR
PAO
SBR
SWTPs
SS
TDS
WWTP

Biochemical oxygen demand
Direct current

Dissolved organic carbon

Enhanced biological phosphorus removal
Electrocoagulation

Excitation emission matrix

Fluorescent dissolved organic matter
Humic acid

Humic substance
Membrane bioreactor

Phosphorus accumulation organisms
Small-scale wastewater treatment plants
Sequencing batch reactor

Suspended solids
Total dissolved solid

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INTRODUCTION

1.

Background

Some serious environmental problems such as eutrophication are due to the
direct discharge of phosphorus into the water source. The abundance of these
nutrients will spur the development of algae, mosses, and mollusks in the water and
will ultimately affect the biological balance of water. In addition, phosphorus is also
a limited resource, so we need to remove and recover P effectively from wastewater
before discharging it into the water source.

In order to remove phosphorus from wastewater sources, there are several
methods being applied, including adsorption, chemical precipitation (using metal
salts), biological processes, and ion-exchange methods ion (Omwene et al., 2018).
Among the methods in the two most used methods are chemical precipitation and
biological processes. Chemical precipitation and adsorption are currently the best
methods for efficiency. By adding metal salts (aluminum salts or iron salts) most of
the phosphorus is removed. Biological methods can also eliminate up to 90% of total
phosphorus but this method is only suitable for wastewater with low phosphorus
concentrations. And when there is a change in the chemical composition, high
phosphorus concentration, and changes in the temperature of the wastewater, the
treatment efficiency is not high. Moreover, many of the above methods have long
operating times, eliminating ineffective and costly (Wysocka and Sokolowska, 2016).
Therefore, electrocoagulation (EC) to remove phosphorus has been used as an
alternative process (especially chemical precipitation). Electrochemical (electrolysis
+ coagulation) combining coagulation, flotation, and electrolysis is a process of
destabilizing suspended pollutants or dissolving in water environments using electric

current (Fayad, N. (n.d.)., 2017).

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their removal is mainly accomplished by destabilization and adsorption”.
Coagulation is a traditional physicochemical treatment via phase separation for the
decontamination of wastewaters before discharge to the environment. EC is causally
related to the conventional coagulation process, which has been used as a method for
water clarification and stabilization, and nowadays, it is still extensively used
(Garcia-Segura et al., 2017).

Moreover, this technique has the advantages to be able to overcome the
drawbacks of the above methods such as simple equipment, easy operation, and only
use electric current so there is no need to add chemicals and reduce time retention
time, settling speed is also faster and creates less sludge (Moussa et al., 2017).

In addition, the EC does not use chemicals, so it does not raise water or aquatic
organisms. The EC only uses electricity for operation without adding any chemical,
so it is suitable for domestic scale facilities. EC applied in small-scale wastewater
treatment Johkasou (domestic, small-scale, on-site, decentralized) (Fayad, N. (n.d.).,
2017).

EC can be applied to treat wastewater containing heavy metals, organic
substances, and other ions such as PO43- and AsO2-, ...

EC reactor is composed of an electrolytic cell and connected externally to a
direct current power supply.

Figure 1. Iron electrolysis reactor (Fayad, N. (n.d.)., 2017)

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This Fe2+ ion will be oxidized with dissolved oxygen in the water to trivalent iron ion
(Fe3+). Fe3+ will combine with PO

43- in water to form a precipitate and settle to the

bottom of the device (Morrizumi et al., 1999). This precipitate can be removed by
pumping out of the system or by using the flotation method to remove the sludge.

EC has been applied to industrial wastewater treatment plants or small
wastewater treatment models. The small-scale wastewater treatment plants (SWTPs)
are called Johkasou and this model treats domestic wastewater on-site for about 10
households, so it is widely applied in Japan. But it is difficult to remove phosphorus
by the activated sludge method because it is dependent on the input parameters.
Therefore iron-electrolysis was developed and used in this model to remove
phosphorus more effectively. According to previous studies, it has achieved good
performance although some examples showed a slightly lower phosphorus removal
(Mishima et al., 2017).

A study on the effects of calcium in increasing phosphorus removal efficiency
has been conducted and results of countermeasures have been reported.

In addition, testing of such cases shows that the DOC (humic substances are
imported from sewage or produced in Johkasou tanks), causing low performance.
Regarding the effect of humic substances, a hypothesis has been obtained that it forms
a chelate compound with iron ions provided by iron electrolysis (Mishima et al.,
2018).

Testing to verify this idea has been started but has not ended. Previous research
using EDTA, a typical chelate-making material, shows the potential for interfering
with phosphorus removal by forming a chelate with supplied iron. The mechanism of
the effects of humic compounds on phosphorus removal is still unclear, especially the
sequencing batch reactor activated sludge processes, which are still poorly

understood. Next, a test using humic substances is needed to clarify this mechanism
of intervention.

2. Objectives

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treatment Johkasou. However, there are still problems remain that affecting the
removal of phosphorus. There have been many previous studies on factors affecting
the phosphorus removal process, such as the influence of electric current, the effect
of initial pH, the effect of initial phosphorus concentration. No research has been
done to study influence the DOC co-substance or co-ions present in wastewater on
phosphorus removal. It is very necessary to improve this method to clear the
interference problem. Because in real sewage not only phosphorus but also many
other compounds such as DOC coexist under some condition. It may increase or
decrease processing efficiency.

Therefore, the action of phosphorus, iron, and organic substances coexisting
in wastewater must be thoroughly investigated to clarify the factors that influence the
phosphorus removal process. Moreover, it is also necessary to determine the optimal
and stable reaction conditions in the actual model.

Based on this study focused on investigating the impact of a high molecular
organic compound capable of complexing with Fe, particularly humic substance
(HS). However, humic substances including humic acid (HA), fulvic acid, and humin,
can also affect the removal of phosphorus by electrolysis of iron. Therefore, in this
study, the effect of HA is the main object of study, by adding HA to the electrolysis
process and conducting related analyzes to evaluate the effect. This study focuses on
clarifying the mechanism of the phenomenon occurring during electrolysis under the
presence of HS and developing a model describing this process.

To achieve the above objective, I operated a laboratory scale batch

experiments with simulated wastewater and prepared HA (commercial humic acid or
humic acid from humic substance sample) was operated.

Summary of research object and scope:
Research question:

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(2) What is main DOC factor that interferes phosphorus removal in iron
electrolysis process?

Research objective:

(1) To clear the mechanism of phenomena occurring in iron electrolysis
process under the condition of abundant of DOC.

(2) To clarify specific factor in DOC that interferes phosphorus removal in
iron electrolysis process used in Johkasou.

3. Structure of thesis

The structure of this thesis is shown in the Figure 2. This thesis contains of 3
chapters. The main content of each chapter is presented as follows:

Introduction: Introduction Briefly summarize the foundational knowledge 
causally related to the research and identify the main research subjects and tasks.

Chapter 1: Literature review provide background knowledge of phosphorus 
pollution and its consequences, history of phosphorus removal technologies. Focus
on EC's role in phosphorus removal.

Chapter 2: Material and Methodology Describe materials, equipment, and

methods used in the study. Detailed description set-up experiments. Analytical
methods as well as equipment were also introduced.

Chapter 3: Results and discussion

3.1. Iron electrolysis without oxygen supply.

3.2. The effect of Humic substance to iron electrolysis.
3.3. The effect of Fulvic acid to ion electrolysis

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Figure 2. Structure of thesis 
Introduction

Briefly summarize the foundational knowledge
causally related to the research and identify the
main research subjects and tasks.

Chapter 1: Literature review

Provide background knowledge of
phosphorus pollution and its consequences,
history of phosphorus removal technologies.

Chapter 2: Material and methodology

Describe materials, equipment, and methods
used in the study. Detailed description Set-up
experiments. Analytical methods as well as
equipment were also introduced.

Chapter 3: Results and discussion.

3.1. Iron electrolysis without oxygen
supply.

3.2. The effect of Humic substance
to iron electrolysis.

3.3. The effect of Fulvic

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CHAPTER 1: LITERATURE REVIEW

1.1. Phosphorus removal technologies

1.1.1. Phosphorus (P) pollution.

Phosphorus and nitrogen are crucial nutrient that extremely needed for growth
of plant and animals (Yan et al., 2015). In addition, phosphorus plays an important
role in several industries (e.g. fertilizers, detergents, paint ...). Increasing input of
nitrogen and phosphorus compounds to receiving surface waters, especially to lakes
and artificial reservoirs lead to increase of primary production of water born
organisms and finally its consequence is lack of oxygen in waters. The removal of
phosphorus from domestic wastewater is primarily to reduce the potential for
eutrophication (Dunne et al., 2015).

The excessive amounts of phosphorus in the aquatic environment due to
human activity can negatively affect aquatic ecosystems. Therefore, several technical
standards for the quality of wastewater effluent have been made public to control
phosphorus pollution.

To minimize surface water pollution and to control pollution sources, each
country has issued its own standards on effluent standards. The following are some
of Vietnam's effluent discharge standards that specify a limit for phosphorus
effluence.

Table 1.1. Vietnam national technical regulations on effluent discharge for 
Phosphorus.

No. Regulations Unit Maximum value allowed

QCVN 40:2011/BTNMT

National technical regulation on 
Industrial wastewater

mg/L 4 - 6

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National technical regulation on the 
effluent of aquatic Products Processing 
industry

QCVN 14-MT:2015/BTNMT

National technical regulation on domestic 
wastewater

mg/L 6 - 15

QCVN 08-MT:2015/BTNMT

National technical regulation on surface 
water quality

mg/L – 0.5

1.1.2. Phosphorus removal technologies.

Phosphorus enters water derived from urban sewage, chemical fertilizers,
washed away from the soil, rainwater, or phosphorus sediments dissolved again.
Phosphorus in water usually exists in the form of orthophosphate (PO43-, HPO42-,

H2PO4-, H3PO4) or polyphosphates [Na3(PO3)6] and organic phosphates.

Phosphorus exists in wastewater soluble form. That is why most of the applied
methods based on a general principle of converting phosphorus compounds from
soluble to insoluble. The basic principle for removing phosphorus in water is to
convert phosphorus from soluble form to insoluble form by precipitating with ions of
aluminum, iron, calcium, or forming biomass by chemical methods. There are many
methods of handling phosphorus but can be classified into two main groups:
physical-chemical method and biological method.

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Figure 1.1. Changes in structure of phosphorus compounds in municipal 
wastewater between year 1971 and 1991 (Rybicki, S. M. (n.d.)., 2004).

Figure 1.2. Phosphorus removal technologies

Physical-chemical technologies.

Physical and chemical processes have been applied to remove and control
phosphorus for many years. This method clearly shows the processing efficiency, but
they still have some limitations. Physical-chemical treatment of phosphorus removal
involves the addition of trivalent metal salts to react with dissolved phosphates and
remove by sedimentation or filtration. Metal salts are commonly used in the form of

Phosphorus removaltechnologies

Physical – chemical Biological

Electrolytical
method

Magnetic
separation

Crystallization Adsorption Enhanced biological P 
removal (EBPR)

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alum and the most common is salt of iron or aluminum. Depending on the dosage
point, this method can be used in various technology schemes (Graziani et al., 2006):
• primary precipitation in mechanical wastewater treatment plants (older
constructions).

• primary precipitation before further biological treatment.

• simultaneous precipitation (adding chemicals to final zones of activated
sludge reactor).

• final precipitation.

Because the amount of precipitate produced is causally related to the amount
of phosphorus removed, hence study to find the quantitative optimization point is
extremely important in chemical treatment. Contact filtration is also a widely
integrated method with physical-chemical methods to ensure a stable phosphorus
output. Investigations on other physical-chemical methods containing many
processes most will be described in the following processes:

• Electrolytical method
• Precipitation

• Crystallization
• Magnetic separation
• Adsorption

Electrolytical method.

Electricity has been used for water treatment for a long time, around the 1860s
electricity was used to treat sewage in England. Development of the direct use of
electricity for treatment is carried out in subsequent years. The basic principle of the
process is that the chemical precipitation of iron compounds is formed on an
electrode. Operation of the plant showed positive results. In the following years, the
technology continued to be researched and developed, and until 1950 the first
experiments on electrolyte treatment were directed at removing nutrients. During this
process, the phosphorus content was reduced to 1.0 mgP/L.

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• Aluminum electrode for phosphorus removal.
• Carbon electrodes for electrochemical.

For decades, this technology has been increasingly used to treat industrial
wastewater containing metals. It is also used to treat pulp and paper industry
wastewater, metal processing, and mining. EC is also applied to treat many types of
wastewater containing food waste, dyes, organic matter from leachate. Studies are
often carried out on the EC to optimize key operational parameters such as amperage,
effluent flux (Fayad, N. (n.d.)., 2017).

Precipitation

Chemical methods have been widely used in phosphorus removal. This
method removes phosphorus by adding metal salts to the wastewater so that it reacts
with the phosphorus in a soluble form. The produced precipitate will then be removed
by sedimentation or filtration. The most used metal salts are trivalent metal salts (iron,
aluminum): aluminum sulfate, ferric chloride, ferric sulfate, ferrous sulfate, and
ferrous chloride. These chemicals combine with phosphorus as shown by the
following reactions (Graziani et al., 2006).

Al3+ + PO

43- → AlPO4↓

Fe3+ + PO

43-→ FePO4↓

Depending on the design of each specific treatment plant, the chemical
addition point is designed differently. But there are two main scenarios for chemical

additions:

Effluent polishing in the secondary process. Chemicals added right before the

secondary settling tanks

Two – point chemical addition. Chemicals are added in both primary and

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Figure 1.3. One – point chemical addition Figure 1.4. Two – point chemical addition

Crystallization

This method has been developed and applied for phosphorus removal since
the 1980s. This method was specifically presented by Joko, who showed the
long-term operation of the installation to remove phosphorus. The phosphorus from
wastewater is biologically treated by crystallizing hydroxyapathyte Ca5(OH)(PO4)3.

This method also shows relatively good handling efficiency. Joko completed
tests on Yamato (Japan) WWTP, which confirmed the decrease of P level from 1-4
mgP/L in biologically treated wastewater down to 0.3 - 1.0 mgP/L after
crystallization.

This method has the advantage that the product after crystallization can be
used for fertilizer production, but this method is not widely applied because it is quite
complex and high processing cost (Rybicki, S. M. (n.d.)., 2004)

Magnetic separation.

In the 1970s, magnetic separation technology was investigated by De Latour 
and reported that it was an effective method if applied after adding iron or aluminum

salts. This method can remove most of the phosphorus in the water, the amount of

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phosphorus in the output can reach 0.1 - 0.5mgP/L compared to other methods with
equivalent costs (Velsen et al.1991).

The principle of this method is to separate particles that are removed by a
magnetic field. Therefore, it can remove all impurities

Adsorption

Around the 1970s there were trials of phosphorus adsorption using fly ash.
The phosphorus in the wastewater will be attracted to the molecular binding force
and trapped on the adsorbent surface. This method is widely used for both high and
low concentrations of phosphorus (Rybicki, S. M. (n.d.)., 2004)

Adsorbents are the most important factor affecting phosphorus removal
efficiency. In the past, activated carbon was the most widely used adsorbent, but it
also revealed some disadvantages such as regeneration and high cost. Therefore, a lot
of research has been done to reduce the production costs of these adsorbents, and
there are several solutions that are proposed to use by-products in agriculture and
industry.

Biological technologies.

Biological methods for handling phosphorus have been studied and applied
for a long time. This method is associated with the use of activated sludge to remove
pollutants in the water environment, which proved to be quite effective with organic
pollutants. Current biological methods are developing in two directions:

• Optimizing wastewater treatment plants using activated sludge technology.

• Dealing with pollutants by constructed wetlands

Enhanced biological phosphorus removal (EBPR)

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skills, making it difficult to control the process (Seviour et al., 2003). This is a 
technological barrier when applied to decentralized treatment facilities (Brown and
Shilton, 2014). However, the understanding of biochemical mechanisms involved in
P uptake is increasing. The phosphorus uptake process is dependent on phosphorus
accumulation organisms (PAO) for EBPR. The application of this method is subject
to strict operating conditions for carbon source, glycogen, and electron acceptor.
When good operating conditions can be assured, 80% of the phosphorus can be
removed from the wastewater by this method (Bunce et al., 2018)

Figure 1.5. Metabolic pathway of PAO under aerobic and anaerobic 
conditions (Bunce et al., 2018)

This method can be used in different designs for each type of wastewater plant.
Recent EBPR applications include a combination of a membrane bioreactor (MBR),
a sequencing batch reactor (SBR), and an activated sludge reactor. This combination
has been shown to be effective in removing phosphorus from municipal sewage,
particularly the MBR proving highly effective in capturing suspended solids in the
tank.

Constructed wetland

Using natural cycles to remove phosphorus is particularly suitable for small
communities and local systems because it is easy to operate and the cost is quite
cheap:

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• Using artificial and natural wetlands can apply treatment without the use of

chemicals.

An artificial wetland is an engineering system comprising of filter materials,
plants, and microorganisms. Phosphorus will be removed by decomposing
organisms, plants that absorb, settle, or adsorb on filter materials. Microorganisms in
the system also have the role of metabolizing phosphorus from the form of poorly
soluble organic to dissolved inorganic phosphorus which plants can easily to absorb
(Vymazal., 2007).

1.2. Electrocoagulation/Iron electrolysis.

Electrocoagulation (EC) is a technique that has been used and successfully for
treating various types of wastewater. The technology uses direct current between a
pair of metal electrodes submerged in water. Metal ions at the right pH will produce
precipitates and metal hydroxides. The resulting precipitate will destabilize and
synthesize particles or adsorb dissolved pollutants. This method was also started to
apply in the late 19th century:

1880: in US – first document on the use of EC for the treatment of effluents.
1880: in UK, WWTP apply this patent to treat sewage.

1930: due to high operating costs and replace by chemical coagulant.

1947: small size installations, EC is more competitive than conventional
process.

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1.2.1. Definition.

Electrolysis process in which current is passed between 2 electrodes through
an ionized solution (electrolyte) to deposit positive ions on the negative electrode

(cathode) and negative ions on the positive electrode (anode) (Yousuf et al., 2001).

Electrolyte:

• positive ions → move to cathode (occurring oxidation process).
• negative ions → move to anode (occurring reduction process).

EC is a process of destabilizing suspended emulsified or dissolved
contaminants in an aqueous medium.

Connected externally to a direct current power supply (DC)
Electrochemical dissolution of the sacrificial anode (+)

The dissociation of the ions from the anode follows Faraday ‘s law

𝑚 =

ì ì

ì (g)
Where:

ã I: current (A)

• t: time of operation (s)
Coagulating ions

Coagulant

Metallic
hydroxide

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• M: molecular weight of the anode material (g/mol)

• F: Faraday’s constant (96,500 C/mol)

• Z: number of electrons involved in the reaction.
• m: mass of anode dissolved (g)

1.2.2. Advantages and drawbacks of EC

Advantages of EC.

• Requires simple equipment and is easy to operate

• EC cell has no moving parts and requires little maintenance as the electrolytic
processes are controlled electrically.

• The treated solution gives palatable, pleasant, clear, colorless, and odorless
water.

• The formed sludge is mainly composed of metallic oxides/hydroxides, so it
is readily settable and easy to de-water.

• The formed flocs are much larger than those produced by chemical
coagulation, contain less bound water and are acid-resistant and more stable.
• Does not require the use of chemicals, so there will be less risk of secondary
pollution, contrary to chemical coagulation. Where chemical substances are
added at high concentrations.

• The bubbles generated during electrolysis result in the flotation of the
pollutants, and consequently their separation is facilitated.

• EC produces effluent with less total dissolved solids (TDS) content as

compared with chemical treatments. If this water is reused, the low TDS level
contributes to a lower water recovery cost.

• Even the smallest colloidal particles are removed by EC since the applied
electric current makes collision faster and facilitates coagulation.

Drawbacks of EC.

• Gelatinous hydroxides may solubilize.

• Sacrificial anodes, which are oxidized should be replaced regularly.

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• An impermeable oxide film may be formed on the cathode leading to loss of
efficiency of the EC unit (Yousuf et al., 2001)

1.2.3. The principle of electrocoagulation.

The EC theory has been discussed by several authors and it has been agreed
that the EC process consists of three consecutive stages: (1) formation of flocculation
by electrolytic oxidation of sacrificial electrodes; (2) destabilize contaminants,
suspension particles and break emulsions; (3) synthesize destabilized phases to form
flocs (Yousuf et al., 2001). The mechanism of emulsification and instability of
pollutants has been described as follows:

• Double-layer compression diffuses around charged particles, achieved by the
interaction of ions generated by the dissolution of the sacrificial electrode due
to the current flowing through the solution.

• Neutralizing the charge of various ions in solution. These reactions will
reduce the repulsive force between electric particles enough for Van der

Waals to prevail, thus causing precipitation.

• Floc formation and floc are formed because of the coagulation process
creating a layer of sludge.

The mechanism of the EC is highly dependent on the chemistry of the water
environment, especially the conductivity. In addition, other characteristics such as
pH, particle size, and metal that make up the electrode also affect the EC process.
The mechanisms for removing ions by EC will be explained in detail by the example
regarding the removal of phosphorus by EC using an iron electrode.

Figure 1.6. Iron electrolysis principle

At the Anode

Fe → Fe2+ → Fe3+
Fe3+ + PO43- → FePO4

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1.3.4. Application of EC

EC has been widely used in the field of wastewater treatment in recent years.
EC can eliminate non-metallic inorganic, heavy metals, organic substances, and
actual industrial wastewater (Garcia-Segura et al., 2017). Therefore, EC is applied for
wastewater treatment of almost industries such as tannery and textile industry
wastewater, food processing industry wastewater, paper industry wastewater, etc.
However, the EC is still limited in removing certain compounds such as ammonium
ions and it has not been able to remove dissolved substances such as glucose and
volatile fatty acid. Therefore, in many cases optimization is needed to improve the
removal efficiency of pollutants. In some cases, it is necessary to combine with one
or two other methods to increase the efficiency of wastewater treatment, i.e. hybrid

process, to ensure the effluent quality (Yousuf et al., 2001). EC can be designed in
combination with membrane separation, reverse osmosis, electro filtration, sludge
dewatering, and other conventional technologies in wastewater treatment systems to
improve the efficiency of pollutant removal. In addition, studies on the removal of
color-induced dye materials have been reported by (Lin et al., 1996). In addition, the
combination of EC with activated sludge and dissolved air flotation has also been
applied in textile and municipal wastewater treatment (Yousuf et al., 2001)

1.3. Iron electrolysis application for phosphorus removal in Johkasou systems.

1.3.1. Johkasou systems for decentralized domestic wastewater treatment.

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treatment plants (SWTP), called Johkasou, are widely used in decentralized domestic
wastewater treatment for sparsely populated areas in Japan (Kumokawa, n.d.).

Johkasou systems are designed to be suitable for the treatment of domestic
wastewater of individual households or a population cluster of fewer than 10
households. Depending on the scale, Johkasou can be classified into the small scale
and medium/large scale Johkasou. In terms of small Johkasou, they can be
mass-produced, easily installed with little topography restriction and the treated water can
be discharged directly into the environment (Ogawa, n.d.).

Because small-scale Johkasou can be installed at the household level and
locally discharged, they have outstanding advantages in terms of environmental
protection and cost effectiveness:

• Advanced technology, high processing efficiency, long-term stability

• The quality of treated water can be used for other purposes such as watering
plants, washing cars.

• Does not cause unpleasant odors.

• Long service life can withstand seismic tremors, easy to install, and
space-free.

• There are many options suitable for all processing power and easy to move
without affecting the equipment inside.

• Reasonable investment and operating costs. Operation, maintenance,
dredging is easy.

The Johkasou system plays an important role in reducing pollution from
domestic wastewater. The conventional Johkasou system possesses anaerobic,
anoxic, and aerobic tanks. The microorganisms attached to the material are used to
remove organic matter. The removal rate of organic pollutant discharge load in
wastewater of this model is about 95% and the total nitrogen is in the range of 65 to
80%. Meanwhile, phosphorus removal efficiency is still low (Fujimura et al., 2019).

1.3.2. Phosphorus removal in Johkasou and application of iron electrolysis

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and microbiological methods are rarely applied in phosphorus removal by Johkasou.
The chemical precipitation method requires a large amount of precipitate, sludge
disposal is difficult and requires a strict experimental operation. The process of
removing phosphorus by microbial activity takes a long time, the amount of sludge
generated should accumulate about 1 year inside the tank and require strict
biochemical environment, and human activities (Jing et al., 2020). Phosphorus
treatment results are usually 30% lower. Recently, functions to remove both nitrogen
and phosphorus have been developed. Johkasou that can remove both phosphorus and
nitrogen is called an "advanced treatment type" (Fujimura et al., 2019). Many

methods have been studied to improve the removal efficiency of pollutants. Methods
developed and introduced into Johkasou for phosphorus treatment are Iron
electrolysis, Adsorption/desorption by zirconium, using pellet to remove phosphorus.
The effect of phosphorus removal pellets in wastewater was examined in
Johkasou's operation by (Fujimura et al., 2019). This phosphorus removal tablet was
developed by Sugawara and is manufactured by Nikka Maintenance Co., Ltd., Japan.
The main component of the tablet is Potassium aluminum sulfate and a small amount
of auxiliary. The tablets are cylindrical in shape, weighing 200g and having a
diameter of 6.0 cm and a height of 4.5 cm. Unlike conventional aluminum sulfate
potassium powder, which dissolves immediately in water and flows out of the
reaction tank in Johkasou, the pellets dissolve slowly but completely and
effectively-being maintained over a long period of time. The pellets will be placed in a mesh bag
and fixed in the tank. Phosphorus removal tablets will be put into Johkasou's aerobic
or raw water compartment. Phosphorus in wastewater will combine with aluminum
ions released from the pellets. Removing this precipitate in the form of sludge can
remove phosphorus from wastewater. Yoko Fujimura reported the results of a
phosphorus elimination efficiency survey conducted in Sakura City (Chiba, Japan)
showing that most of the phosphorus in the outlet effluent decreased after 1 week
when the pellets were removed. was placed in Johkasou.

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phosphorus from domestic wastewater. The phosphorus adsorbent used is zirconium

(provided by Japan EnviroChemicals, Ltd). The principle of adsorption is ion

exchange, although it is possible to adsorb different anions the ability to adsorb
phosphorus is quite high. The phosphorus adsorption process is designed as the next
stage of BOD and nitrogen removal. Adsorption columns are installed in the reaction
tank and part of the wastewater is used for backwashing, as shown Figure 2.7 (Ebie
et al., 2008). After the concentration of phosphorus in the output exceeds 1 mg/L, the
material will be released. The collected adsorbent will be soaked in an alkaline

solution (sodium hydroxide) to remove the phosphorus. The adsorbent will be
reactivated by soaking in acid solution (sulfuric acid). The phosphorus released from
the desorption process is recovered with a high crystallinity equal to trisodium
phosphate by crystallizing at low temperatures in a vacuum. This method is a new
method for decentralized wastewater treatment, but it shows good treatment results.
The phosphorus concentration in the outlet effluent is less than 1 mg/L and the
recovered phosphorus is also of high purity. This recovered phosphorus can be used
in agricultural production as a fertilizer.

Figure 1.7. Combination process of BOD and nitrogen removal type 
Johkasou and phosphorus adsorption column (Ebie et al., 2008).

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released from the electrode are oxidized by dissolved water in water to become ferric
ions. These iron ions combine with the phosphate in the wastewater and easily settle
to the bottom of the tank from which the sludge needs to be removed (Morrizumi et
al., 1999). In addition, during electrolysis, it does not affect the respiration process of
microorganisms in the tank. In this method, the iron released from the electrode acts
as a precipitant, so the molar ratio between iron and phosphorus determines the
removal efficiency of phosphorus. Iron supplementation by adjusting the amperage
or reaction time ensures that the molar ratio of Fe/P is 2.0 to ensure that the
phosphorus concentration after treatment is less than 1.0mg/L. This technology is
very suitable for SWTP because the entire device is compactly designed and fully
automatic and connected to the controller.

Figure 1.8. Johkasou for phosphorus – BOD – Nitrogen removal. (Kumokawa, 
n.d.)

1.3.3. Interference of phosphorus removal using iron electrolysis.

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In the process of electrolysis of iron, iron ions from the anode will dissolve

into the solution and combine with the phosphate in the solution to precipitate and
settle to the bottom of the tank. However, this process also produces iron oxides,
which will stick to the anode surface and prevent iron from dissolving into the
solution. This leads to a reduction in phosphorus removal efficiency. But this problem
has been solved by swapping the cathode and anode after a period of operation. In
addition, there have been several cases that have been reported as reducing
phosphorus removal performance due to calcium deficiency in water. And to
overcome this situation, a recommendation has been made by (Mishima et al., 2017)
to maintain calcium levels in the water between 20mg / L and 25mg/L.

However, in some schools, despite the above situation, the reduction of
phosphorus was observed. Mishima et al., 2017 conducted a long-term investigation
of phosphorus removal by iron electrolysis in Johkasou tanks. Based on the data
obtained, Mishima et al. showed that DOC can inhibit phosphorus removal by iron
electrolysis (Mishima et al., 2017). Specifically, phosphorus was removed almost
completely when the DOC was low. In this study, the average DOC was 8.2 mg/L,
but there were times when high DOC values were reached, up to a maximum of 20
mg/L. Therefore, DOC may interfere with phosphorus removal. Iron can form a
complex with HS, which are the components of DOC in wastewater. This competition
reduces the amount of iron in combination with the phosphates in the water resulting
in reduced phosphorus removal efficiency. Another evidence that DOC has inhibited
phosphorus removal is that despite the posting of molar Fe/P, no improvement was
observed in the high DOC concentration (Mishima et al., 2017). Accordingly, the
inhibition of DOC on the phosphorus removal process by iron electrolysis is
completely clear.

1.4. Humic substance.

1.4.1. General description

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molecular weight, Fulvic acids 800 A and < 3,500 Da) (Becket Tet al, 1987 and
Muscolo et al, 2007).

HS in soil and sediment can be divided into three main groups: Humic acids
(HA), Fulvic acids (FA), and Humin. HS are highly chemically reactions but are
considered difficult to biodegrade. Aquatic HS contains only HA and FA and these
components are generally removed from water by lower the pH to 2 and adsorbing
both components on a suitable resin column. HA is the main component of HS. It can
form complexes with metal ions commonly found in the environment, Fulvic acids
are like HA. However, there are some differences in carbon and oxygen content,
acidity of the degree of polymerization, molecular weight, and color.

Humic acid (HA) is the main component of humic substances, the main
organic component of soil (humus), peat, and coal. It is produced by biodegradation
of dead organic matter. It is not a single acid; rather, it is a complex mixture of
different acids containing carboxyl and phenolate groups so that the mixture acts as
a dibasic acid or, sometimes, as a tribasic acid. HA can form complexes with ions
commonly found in humic colloidal media. HA is insoluble in water at acidic pH,
while fulvic acid is also derived from humic substances but soluble in water
throughout the pH range. HA and FA are often used as a soil supplement in
agriculture.

Fulvic acid (FA) is a family of organic acids, natural compounds, and humus
components (part of soil organic matter). They are like HA, with differences in carbon
and oxygen content, acidity, degree of polymerization, molecular weight, and color.
Fulvic acid remains in the solution after removing HA from humin by acidification.
Fulvic acid has a relatively low molecular weight and is more bioactive than HA.

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Figure 2.9. Hypothetical humic acid structure according to Stevenson (1982)

Figure 2.10. The hypothetical model structure of fulvic acid (Buffle's model)

1.4.2. Chemical characteristic

Humic acids and fulvic acids are aromatic polymer molecules that vary in size
and molecular weight. The size of humic acid allows these macromolecules to be
rolled up to form particles or rings that at a certain pH (acid) will precipitate while
the fulvic acids are too small to go through a processed analog and therefore still in
the same process solution.

The presence of carboxylate and phenolate groups gives the humic acids the
ability to form complexes with ions such as Mg2+, Ca2+, Fe2+, and Fe3+. Many humic

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Figure 2.11. Chelation of Cu and Zn in top 2 examples with simple 
complexation of Zn by an amino acid.

The HA and FA are extracted from soil and other solid phase sources using a
strong base (NaOH or KOH) (Weber et al., 2018); they are:

Fulvic acid: soluble at all pH values.

Humic acid: insoluble under acidic conditions (pH<2) but soluble in solution
of higher pH values.

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CHAPTER 2: MATERIALS AND METHODOLOGY

2.1. Materials

2.1.1. Synthetic test liquor (phosphate solution)

Synthetic test liquor is prepared to simulate the real domestic effluent input of
the Johkasou system. For iron electrolyte experiments, the test effluent consists of
phosphorus (phosphate solution), Chloride, and Calcium. The concentration of
phosphorus and calcium in the experimental wastewater is nearly the average value
of the real wastewater in Johkasou. Chloride is added to ensure electrical conductivity
for the solution. Phosphorus was prepared by completely dissolving Potassium
dihydrogen phosphate (KH2PO4) salt in pure water. Chloride and Calcium solutions

were also prepared by dissolving sodium chloride (NaCl) and Calcium chloride
(CaCl2.2H2O) salts, respectively. The concentration of stock solutions and the

concentration of components in the synthetic wastewater are presented in Table 2.1. 
Table 2.1. Preparation of synthetic test liquor

No. Solution Chemicals Mass (g) Volume 
(ml)

Stock 
solution 
(mg/L)

Working 
solution 
(mg/L)

1. Cl- NaCl 1.50 1000 900 ≈ 91

2. Ca2+ CaCl

2.2H2O 2.93 1000 800 20

3. PO4-P KH2PO4 2.20 1000 500 5

Stock solutions were stored in glass bottle and stored for 1 month while
working solutions are prepared daily.

2.1.2. Humic substance sample liquor.

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sampling landfill is 21 years old and is in the stabilized phase of methanogenic.
Leachate has been filtered through filter paper (pore size: 10µm-20µm) to remove
suspended solids and store in the refrigerator.

Figure 2.1. The map of Hanoi and Nam Son landfill

2.1.3. Humic acid sample liquor

The Humic acid solution is prepared from commercial humic acid (powder
form; Nacalai Tesque, Japan). Humic acid is exceedingly difficult to dissolve under
normal conditions so to be able to completely dissolve humic acid we must prepare
alkaline (pH ≥ 10). And to make sure humic acids are completely dissolved they
should be kept for 12 hours. The solution is then filtered through a 1µm filter paper.
The concentration of the stock solution is 1000mg/L.

Figure 2.2. Humic acid, Nacalai Tesque, Japan.

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2.2. Iron electrolysis experiment set-up.

The iron electrolysis experiments are set - up according to the batch reactor
model. The combined wastewater (prepared daily in 3.1.1) is placed in a 200ml high
beaker and two iron electrodes (120mm × 20mm × 2mm) are installed above the

beaker. The two electrodes are connected to direct current (PMC35-1A; Kikusui
Electronics Corp) 0.014A. Aeration machine is installed and performs air blowing
from the bottom of the beaker. Electric current is controlled by multimeter, as shown
in Figure 2.3. The duration of the experiment was calculated based on Faraday's law, 
this calculation to ensure the molar ratio between Fe / P = 2 or 4.

Figure 2.3. Schematic diagram of the laboratory-scale experiment.

Figure 2.4. The types of equipment used to set-up experiments 
Aeration machine Power supply

(PMC35-1A; Kikusui
Electronics Corp)

Iron
electrode

Multimeter

+

-

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2.3. Operational condition of experiment.

2.3.1. Iron electrolysis with or without oxygen supply.

To determine the effect of oxygen on iron electrolysis experiments under
different conditions were arranged.

• The first test is performed under aerobic conditions (using aeration machine).
• The second experiment is to allow the process of electrolysis to occur
naturally.

• The third experiment was performed under anaerobic conditions, an inert gas
supply device N2 was used to eliminate oxygen in the water to ensure anaerobic

conditions completely.

In addition to the current was measured in multimeter, DO (HACH, HQ11d)
and pH (S220-Kit, Metter Toledo) were also measured to ensure that the experiment
takes place under the right conditions. The synthetic wastewater of all three
experiments was prepared in the same way as in Figure 2.5. The concentration of 
components in the simulated wastewater is the same as the concentration of these
components measured and reported in the Johkasou system. The specific arrangement
of the experiments is shown in Figure 2.6 and Table 2.2.

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Table 2.2. Operational experiment condition.

Figure 2.6. Set – up experiments

Under these three different conditions, the DO is tightly controlled using
HACH's sensors (HACH, HQ11d). DO is measured at the following every 15
minutes. In addition, parameters such as amperage or electrolysis time are calculated
according to Faraday's law to estimate the molar ratio Fe/P as 2 and 4.

Aeration Without

aeration Supply N2 gas

Fe/P molar ratio 2 & 4 2 & 4 2 & 4

Current (A) 0.014 0.014 0.014

Electrolysis time

(mins) 15& 30 15& 30 15& 30

pH 5.5 ~ 6.5 5.5 ~ 6.5 5.5 ~ 6.5

DO (mgO2/L) 8 ~ 9 Not control < 0.1

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2.3.2. Iron electrolysis with HS addition

The iron electrolysis with HS is performed under aerobic conditions and the
electrolysis time is 15 minutes. The whole experiment set-up is like the experimental
set-up with aeration in section 2.3.1. The HS is added to the synthetic wastewater
before starting the experiment in the following order: 0ml 20ml 50ml 100ml
-150ml, details were shown in Figure 2.7

Figure 2.7. Humic substance experiment set-up.

2.3.3. Iron electrolysis with humic acid addition.

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Figure 2.8. Humic acids addition experiment set-up 
2.4. Chemical analysis.

2.4.1. Suspended solid (SS)

The method chosen for SS analysis is the Determination suspended solids by

filtration through glass-fiber filters (ISO 11923: 1997) – TCVN 6625:200.

Principle of this method:

• Washing filter paper (3 times) by pure water.
• Drying at 105oC with oven (3 hours)

• Cooling to normal temperature with desiccator (1 hour)
• Weigh the filter paper (W1 - mg)

• Carry out sample filtering (Vsample = 50ml)

• Drying at 105oC with oven (3 hours)

• Cooling to normal temperature with desiccator (1 hour)
• Weigh the filter paper (W2 - mg)

Calculate the results:

SS (mg/L)

=

(𝑊1 −𝑊2)×1000

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2.4.2. Iron analysis.

In this iron electrolysis experiment, total iron (TFe); Dissolved inorganic iron
(D-Fe), and D-Fe2+ were measured. The method used is the Determination of iron -

Spectrometric method using 1.10- phenanthroline (ISO 6332: 1988) – TCVN 
6177:1996. The principle of this method is that when adding the 1,10 - phenanthroline

reagent solution to a sample containing iron will produce an orange-red complex and

measure the absorbance of this complex at a wavelength of 510 nm. If you want to
determine TFe and S-Fe, add hydroxyl ammonium chloride to reduce Fe2+ to Fe3+.

Calibration curves are based on known iron content and their absorbance is measured
by UV-VIS Diode Array Spectrophotome (S2100, Unico). By using the calibration
curve, the unknown iron concentrations were calculated.

Preparation chemicals

Table 2.3. Preparation chemicals to iron analysis

No. Regents Preparation

1. Hydroxyl ammonium Chloride
(HClNH2OH) – 10% (w/v)

Dissolve 10g HClNH2OH in 100ml

2. 1,10 phenanthrolinium Dissolve 0.13g in 100ml DW

Ammonium acetate – acetate
buffer

Dissolve 250g CH3COONH4 in

120ml DW + 700ml CH3COOH and

make up to 1000ml by DW

Procedure iron calculate.

TFe = D-Fe + P-Fe
D-Fe = D-Fe2+ + D-Fe3+

Total inorganic
iron (TFe)

Dissolved
iron (D-Fe)

Insoluble
iron (P-Fe)

D-Fe2+

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2.4.3. Phosphorus analysis. (PO4-P)

The concentration of orthophosphate is determined by the spectrometric
method of ammonium molybdate reagent (Ammonium molybdate spectrometric

method - ISO 6878: 2004) – TCVN 6202:2008. The principle of this method is based

on the reaction between orthophosphate ions and the acid solution of molybdate and
antimony ions to form an antimony phosphomolybdate complex. The reduction of
this compound with ascorbic acid forms a dark green molybdenum complex. Measure
the adsorption of this complex at the most sensitive wavelength of 880 nm (if lower

sensitivity is accepted, it can be measured at 700 nm wavelength). Calibration curves
are based on known phosphorus content and their absorbance is measured by
UV-VIS Diode Array Spectrophotome (S2100, Unico). By using the calibration curve,
the unknown phosphorus concentrations were calculated.

Preparation chemicals

Table 2.4. Preparation chemicals to phosphorus analysis

No. Regents Preparation

1. Ammonium
molybdate

Dissolve 6g (NH4) Mo7O24.4H2O + 0.24g

Potasium antimony (III) tartrate in 300ml DW.
Add 120 ml H2SO4: H2O (v/v: 2/1)

Add 5g ammonium amidosulfate
Make up to 500ml by DW

2. L – ascorbic Dissolve 7.2g L-ascorbic in 100ml DW

2.5. Fluorescence spectroscopy analyses by three-dimensional 
excitation-emission matrix.

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fluorescence detection are scanned from 200nm to 600nm with 30000nm / min. A
1cm cuvette was used.

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CHAPTER 3: RESULTS AND DISCUSSION

3.1. Iron electrolysis without oxygen supply.

3.1.1. Iron electrolysis with aeration.

Table 3.1. Effluent parameters after electrolysis performed in aeration experiment 
(n=3)

Parameter (mg)

Fe/P molar ratio

2 4

D-Fe2+ 0 ± 0.13 0 ± 0.13

D-Fe3+ 0.23 <0.01

D-Fe 0.23 ± 0.14 0 ± 0.14

P-Fe 2.5 4.52

TFe 2.73 ± 0.06 4.52 ± 0.06

PO4-P 0.01 ± 0.0048 0 ± 0.004

SS 8.4 ± 0.2 13.7 ± 0.7

The experiments with aeration were carried out 3 times to determine the mean.

Table 3.1 shows the average value of the effluent quality after the electrolysis of iron. 
The remaining dissolved iron in wastewater is mainly in the form of iron ions III.
Phosphorus is well removed under aerobic conditions because the average value of
residual phosphorus was low, about 0.01mg. A trend of decreased PO4-P has been

observed with an increasing molar Fe/P ratio. Along with the decrease in PO4-P, an

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Figure 3.2 illustrates the result obtained after calculating the ratio between the 
existing forms of Fe in the solution after electrolysis. At a molar ratio of 2, we
observed that over 90% of iron exists in an insoluble form. And this also corresponds
to the removal efficiency of phosphorus proving that the amount of iron added from
the electrode is sufficient to reduce the phosphorus concentration below 1.0mg/L.

3.1.2. Iron electrolysis without aeration.

As mentioned above, for without aeration experiment I set up two
experiments: no aeration and N2 blowing.

0%

20%

40%

60%

80%

100%

1

2

Pho
sp

ho
rus
i
ns
ol
ub
il
iz
at
ion
(%
)

insoluble

soluble

Fe / P

2

4 0%

20%

40%

60%

80%

100%

1

2

Ir
on
coa
g
ul
at
ion

(%
)

insoluble

Fe / P

2

4 0%

20%

40%

60%

80%

100%

1

2

Ir
on
coa
g
ul
at
ion
(%
)

insoluble

soluble

Fe / P

2

4 0%

20%

40%

60%

80%

100%

1

2

Ir
on
coa
g
ul
at
ion
(%
)

insoluble

soluble

Fe / P

2

Figure 3.2. Iron coagulation 
Figure 3.1. Phosphorus insolubilization

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Figures 3.3 and 3.4 show the percent of insoluble iron and iron in solution. It
is clear that the difference between the two existing forms of iron is quite obvious.
This proves that in the absence of aeration, the precipitation process still occurs but
the difference in the color of the precipitate has been noted. While the color of
precipitate in aeration medium is orange - brown, the precipitate, in this case, is green.
This suggests that the difference in the composition of flocculation and the form of
iron ions in the precipitate. The color of the sediment was greenish showing ferrous
salts. Therefore, it can be concluded that although oxygen is not supplied, the iron
coagulation and sedimentation proceeded.

(a) (b)

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3.1.3. Discussion

It has always been known that the process of removing phosphorus by iron
electrolysis takes place in the order that iron ions are supplied from the anode and
then oxidized by dissolved oxygen in the wastewater and becoming ferric ions. These
ferric ions combine with phosphate in wastewater to precipitate and settle to the
bottom of the tank, as shown in Figure 3.8.

Figure 3.8. The existing pathway models

0%

20%

40%

60%

80%

100%

1

2

Pho
sp
ho
rus
i
ns
ol
ub
il
iz
at
ion
(

%
)

insoluble

soluble

0%

20%

40%

60%

80%

100%

1

2

Phosphor
us
insol
ubi
li
zat
ion
(%
)

insoluble

soluble

Fe / P

2

4

Figure 3.6. Phosphorus 
insolubilization (without aeration)

Figure 3.7. Phosphorus 
insolubilization (N2 gas bubbling)

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However, another way of removing phosphorus by iron electrolysis has been

found. Based on the results presented above, we can clearly see that the precipitation
and deposition process still take place in a different way. This pathway is summarized
as follows: ferrous ions liberate anodes that can precipitate Fe2(PO4)3 _ iron (II)

phosphate and can settle to the bottom of the tank in the anaerobic condition. In
addition, one hypothesis is also given that the released ferrous ion will precipitate,
and this precipitate continues to be oxidized by dissolved oxygen in the wastewater
and takes place at the same time as ferrous oxidation into ferric ions.

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3.2. The effect of humic substance on iron electrolysis

3.2.1. Iron coagulation decrease by humic substance addition

Table 3.2. Effluent parameters after electrolysis performed in humic substance 
addition experiment (n=3).

Parameter 
(mg)

Humic substance addition (ml)

0 20 50 100 150

D-Fe2+ 0.064 ± 0.001 0.07 ±0.003 0.41 ± 0.03 0.66 ± 0.03 0.94 ± 0.03

D-Fe 0.072 ± 0.01 0.08 ± 0.07 0.43 ± 0.003 0.64 ± 0.08 0.93 ± 0.01

D-Fe3+ <0.01 <0.01 <0.01 <0.01 <0.01

P-Fe 3.088 2.55 1.61 2.05 1.64

TFe 3.16 ± 0.17 2.62 ± 0.18 2.02 ± 0.03 2.69 ± 0.42 2.57 ± 0.21

PO4-P 0.01 ± 0.001 0.3 ± 0.002 0.52 ± 0.006 0.64 ± 0.003 0.74 ± 0.014

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Figure 3.10. Iron coagulation (Humic substance addition)

3.2.2. Decrease of phosphorus insolubilization by iron coagulation decrease

Compared with the absence of HS, it is clear that HS interfered with the
reaction that produced precipitation during iron electrolysis. It interferes with the
process of iron ions combined with phosphate in the wastewater, resulting in less
precipitation. Therefore, the amount of free phosphate in the wastewater remains and
increases gradually according to the concentration of the HS in the wastewater, as
shown in Figure 4.11. It can be easily seen from Figure 4.11 that the ratio of 
insoluble phosphorus accounts for the majority in the case. High HS concentrations
mean that the process of phosphorus removal by iron electrolysis has been inhibited
by HS. Thus, it can be considered that the inhibition of HS elimination by reducing
the amount of iron combined with phosphorus.

0%

20%

40%

60%

80%

100%

0

20

50

100

150

Iron

coagulation(

HS addition (ml)

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Figure 3.11. Phosphorus insolubilization (HS addition)

3.2.3. Discussion.

HS supplementation has significantly inhibited the elimination of phosphorus
by iron electrolysis. After adding HS, the remaining phosphorus increases and is
proportional to the amount of HS added. These results show that the presence of HS
prevents iron ions from being released from the anodes and phosphate in the
wastewater due to the formation of complexes between iron and HS (Figure 3.11). 
HS has also been shown to compete with PO4-P in combination with iron-on goethite,

thereby reducing the adsorption of PO4-P (Sibanda and Young, 1986; Hawke et al.,

1989; Antelo et al., 2007).

0%

20%

40%

60%

80%

100%

0

20

50

100

150

Phosphor

insolubil

ization

(%)

HS addition (ml)

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Figure 3.12. Molar ratio of ΔFe / ΔP

The molar ratio of ΔFe / ΔP line incline was almost 1.0 and MP/MFe = 31/56 ≈

0.554 nearly incline: 0.536. This suggests that the same mole of P as Fe combined in
the complex was soluble (Figure 3.13). This means that the number of moles of P in 
the soluble form is equal to the number of moles of Fe combined in the complex and
soluble phosphorus was kept to be PO4-P because it cannot be combined with Fe. The

significance of the same number of moles in P and Fe would be that Fe and P are
combined using a monodentate or bidentate ligand without humic substances. This
phenomenon can be explained by the fact that PO4-P can form complexes with

hydroxyls in water in a pH range of 4.5 to 7. This can occur in the environment around
the anode where Fe and P will be start reaction.

There is also a hypothesis that the addition of HS creates a negative

electrostatic field around the surface of the colloidal particles that will lead to a
significant reduction of the Zeta electrodynamic potential. Thereby reducing the
possibility of collisions of charged particles in the solution resulting in the reduction
of phosphorus. In addition, in the high pH environment PO43- subjected to the high

competition of OH- as well as electrostatic repulsion (Fu et al., 2013).

y = 0.536x + 0.280

R² = 0.988

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1 Δ Fe (mg/200mL)

Δ P

(mg/

20

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Figure 3.13. Soluble complex formation of ferrous ion and HS 
3.3. The effect of fulvic acid to iron electrolysis

3.3.1. Iron electrolysis with humic acid addition

Table 3.3. Effluent parameters after electrolysis performed in humic acid 
addition experiment (n=3)

Parameter 
(mg)

Humic acid addition (ml)

0 20 40 50

D-Fe2+ 0.064 ± 0.001 0.13 ±0.06 0 ± 0.03 0 ± 0.03
D-Fe 0.072 ± 0.01 0.12 ± 0.016 0.07 ± 0.01 0.03 ± 0.003

D-Fe3+ <0.01 <0.01 0.07 0.03

P-Fe 3.09 3.1 3.54 3.57

TFe 3.16 ± 0.17 3.22 ± 0.08 3.61 ± 0.03 3.60 ± 0.06
PO4-P 0.01 ± 0.001 0.01 ± 0.002 0.01 ± 0.002 0.02 ± 0.002

Fe

insoluble

coagulated Fe

(decrease)

soluble complex of

Fe–humic substance

(increase)

insoluble P

(decrease)

soluble P (increase)

ΔFe

ΔP

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Figure 3.14. Iron coagulation (Humic acid addition)

Figure 3.14 and Table 3.3 illustrates the result obtained after calculating the 
ratio between the existing forms of Fe in the solution after electrolysis. It is clearly
visible from Table 3.3 and Figure 3.14 that most of the iron supplied from the anode 
has precipitated. Although, under conditions of humic acid addition, the precipitation
process is still the same as in the absence of humic acid. No obstruction to the process
is observed. This suggests that humic acid may not inhibit precipitation. This is also
evident in Figure 3.15, where one can clearly see that most of the dissolved 
phosphorus in PO43- form is almost removal. Instead, phosphorus is insoluble in the

form of precipitation with iron ions released from the anode. This proves that the
removal of phosphorus by iron electrolysis has occurred under this condition.

0%

20%

40%

60%

80%

100%

0

20

40

50

Ir

on

coagulation(

%)

HA addition (ml)

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Figure 3.15. Phosphorus insolubilization (HA addition)

3.3.2. EEM of the used humic substance and humic acid sample

Figure 3.16. EEMs Fluorescence spectra of humic substance sample 
(leachate sample)

0%

20%

40%

60%

80%

100%

0

20

40

50

Phosphorus

insolubl

e

(%

)

HA addition (ml)

insoluble

soluble

fulvic acid like
peak

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Figure 3.17. EEMs Fluorescence spectra of humic acid sample

In Figure 3.16, it is clear that the leachate shows the presence of humic and 
fulvic acids. Specifically, the fluorescence peak is considered to be fulvic acid λEx
around 300nm and λEm from 400 - 450 nm. This result is also reported by previous
studies, Baker et al. (2004) reported with λEx = 320 - 360 and λEm = 400 - 470nm, 
it came from the fulvic acid-like peak. Another peak is also found at λEx around

250nm and λEm between 400-500nm, which was considered humic acid. Whereas
for humic acid samples, the observed results were λEx around 250nm and λEm
between 400-500nm.

3.3.3. Discussion

The two peaks of humic acid and fulvic acid were detected in the fluorescence
excitation-emission matrix (EEM) of the used humic substance sample. While only
one peak of humic acid was detected in the EEM of the used humic acid sample. This
led to a new hypothesis that fulvic acid in humic substance samples appears to reduce
iron coagulation during iron electrolysis. This theory is described in detail in Figure
3.18, in this new hypothesis, fulvic acid will complex with iron and reduce the amount
of iron combined with phosphate in water, thereby inhibiting the process of removing
phosphorus by iron electrolysis. This may account for the fact that although adding
HA to the wastewater does not impede the phosphorus removal process by binding
competition. This contrasts with the previously reported assumptions about the

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adsorption of iron oxides of HA by complexing with iron (Tipping, 1981; Gerke,
1993).

It may also explain that HA does not interfere with phosphorus removal as
follows: Humic acid is known to be insolubilized in low pH conditions. Therefore, it
seems that humic acid will be insolubilized in high H+ conditions near anode in

electrolysis and then would be coagulated together with FeOOH as well as insoluble
P. On the contrary, fulvic acid will be kept soluble even near anode and cathode in
electrolysis. It would then form a soluble complex with Fe.

Figure 3.18. The effect of fulvic acid on iron electrolysis. 
fulvic acid

humic acid

Fe

insoluble
coagulated Fe

soluble complex of

Fe and fulvic acid insoluble P

Fe

fulvic acid

interference

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CONCLUSION

The current research has identified specific factor of DOC that interferes the
phosphorus removal by iron electrolysis process in Johkasou. The main findings from
this study are summarized as follows:

1) Iron coagulation proceeds not only under aerobic condition by forming
ferric floc but also under anaerobic conditions by forming ferrous floc, showing a
new pathway of phosphorus insolubilization using ferrous floc in iron electrolysis
process.

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</div>

The behavior of humic Substance in iron electrolysis Process and its influence on Phosphorus removal

VIETNAM NATIONAL UNIVERSITY, HANOI

<b>VIETNAM JAPAN UNIVERSITY </b>

<b>HA THI DIEP ANH </b>

<b>THE BEHAVIOR OF HUMIC </b>

<b>SUBSTANCE IN IRON ELECTROLYSIS </b>

<b>PROCESS AND ITS INFLUENCE ON </b>

<b>PHOSPHORUS REMOVAL </b>

VIETNAM NATIONAL UNIVERSITY, HANOI

<b>VIETNAM JAPAN UNIVERSITY </b>

<b>HA THI DIEP ANH </b>

<b>THE BEHAVIOR OF HUMIC </b>

<b>SUBSTANCE IN IRON ELECTROLYSIS </b>

<b>PROCESS AND ITS INFLUENCE ON </b>

<b>PHOSPHORUS REMOVAL </b>

<b>MAJOR: ENVIRONMENTAL ENGINEERING </b>

<b>CODE: 8520320.01 </b>

<b>RESEARCH SUPERVISOR: </b>

<b>Prof. Dr. JUN NAKAJIMA </b>

<b>Associate Prof. Dr. LE VAN CHIEU </b>

<b>ACKNOWLEDGMENT </b>

<b>TABLE OF CONTENT </b>

<b>LIST OF TABLES </b>

<b>LIST OF FIGUREURES </b>

<b>LIST OF ABBREVIATIONS </b>

<b>INTRODUCTION </b>

<b>1. </b>

<b>CHAPTER 1: LITERATURE REVIEW </b>

𝑚 =

<b>CHAPTER 2: MATERIALS AND METHODOLOGY </b>

<b>+ </b>

<b>+ </b>

<b>- </b>

=

<b>CHAPTER 3: RESULTS AND DISCUSSION </b>

0%

20%

40%

60%

80%

100%

1

2

insoluble

soluble

Fe / P

2

4

0%

20%

40%

60%

80%

100%

1

2

insoluble

Fe / P

2

4

0%

20%

40%

60%

80%

100%

1

2

insoluble

soluble

Fe / P

2

4

0%

20%

40%

60%

80%

100%

1