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

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 p[r]

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

MASTER'S THESIS

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

HA THI DIEP ANH

THE BEHAVIOR OF HUMIC SUBSTANCE IN IRON ELECTROLYSIS PROCESS AND ITS INFLUENCE ON

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

Ha Thi Diep Anh

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

CHAPTER 3 RESULTS AND DISCUSSION 38

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

REFERENCES 53

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

Table 3.3 Effluent parameters after electrolysis performed in humic acid addition experiment 47

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 3.3 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

Figure 3.9 The new pathway model including ferrous compound coagulation 42

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

Figure 3.18 The effect of fulvic acid on iron electrolysis 51

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 Wastewater treatment plant

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)

Distinct mechanisms are involved in the removal of the various types of contaminants that exits in water and wastewater which include oxidation, reduction, coagulation, flotation, adsorption, precipitation, and others (Fayad, N (n.d.)., 2017)

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.).,

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

Mechanism of phosphorus removal by electrolysis method: By directing electric current through a pair of iron electrodes immersed in water At the Anode electrode oxidation occurs, iron is oxidized into Fe2+ ions and dissolved into solution

This Fe2+ ion will be oxidized with dissolved oxygen in the water to trivalent iron ion (Fe3+) Fe3+ will combine with PO43- 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

With the high potential in the handling and wide application mentioned above,

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:

(1) What is mechanism of DOC interference to phosphorus removal in iron electrolysis process used in Johkasou?

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

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

Conclusion

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

Conclusion

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

National technical regulation on the

effluent of aquatic Products Processing

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

Comparison between year 1971 and year 1991 is shown in Figure 1.1 below (Jenkins Ferguson Menar 1971, Sedlak 1991) It is visible how concentration

decreases and the structure changes in time

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 removal technologies

Electrolytical

method

Magnetic separation

Crystallization Adsorption Enhanced biological P

removal (EBPR)

Constructed wetland (CW) Precipitation

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:

Further findings were reported by Groterud i Smoczynski in 1991, who

experimented with two electrodes:

• 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+ + PO43- → AlPO4↓

Fe3+ + PO43-→ 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

secondary settling tanks This design is widely applied because of its good phosphorus removal effect

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

Influent

Primary clarifier

Aeration tank

Secondary clarifier

Influent

Primary clarifier

Aeration tank

Secondary clarifier

Effluent

Return Activated Sludge (RAS)

Waste Activated Sludge (WAS)

Chemical addition

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)

Although activated sludge has been used in wastewater treatment for a long time, this technology still reveals the disadvantages that need to be overcome such as the treatment efficiency is still unstable, especially the effectiveness of the treatment

of substances nutrition (nitrogen, phosphorus) and highly dependent on operational

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:

• Using activated algae: exposing algae culture environment to wastewater, can remove 90% of phosphorus (Rybicki, S M (n.d.)., 2004)

• 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

1970s- 1980s: that research on the application of EC for the treatment of various types of wastewater has generated significant interest The industrial development of EC process was, however, hampered by the cost deemed too high and by the competition of chemical treatment processes, without ruling out its us

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

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 = 𝐼 ×𝑡 ×𝑀

𝑧×𝐹 (g) Where:

• 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

• Electricity is not always easily available, and it is expensive in some regions

• 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

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

There are several sewage treatment systems that have been applied to domestic wastewater treatment in Japan Depending on the type of wastewater being treated, the size of the facility and the financial assistance of the major domestic wastewater treatment systems in Japan are classified as follows: urban drainage systems, rural drainage systems, and the Johkasou system (Ogawa, n.d.) Often centralized drainage systems will be built in large cities where densely populated areas, factories, and offices Wastewater will be collected through the pipeline system and treated in a concentrated manner at treatment plants However, in Japan, there are many places due to the terrain divided by rivers and mountains that cannot be connected to a centralized public sewage treatment plant Therefore, small-scale wastewater

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 free

space-• 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

Commonly used methods for phosphorus removal are chemical coagulation, electro-coagulation, and microbiological However, chemical precipitation methods

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

One of the technologies for removing and recovering phosphorus from other wastewater was applied in 30 Johkasou sites in Tsuchiura, Japan, and showed a 90%

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)

Another method that has been developed and introduced for "advanced Johkasou" to remove phosphorus is iron electrolysis Iron electrolysis is a type of electro-coagulation and has been used in wastewater treatment for a long time (Mollah et al 2001; Pulkka et al 2014) The iron electrolysis system consists of the power supply and two electrodes installed inside the aerobic tank Ferrous ions

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

Johkasou is an in-use wastewater treatment system that is used extensively in rural and sparsely populated areas With its clean design and automatic operation, the system stability requirements are extremely high In addition to issues related to the stability of the system such as no noise or solid structure to withstand earthquakes, the stability of treatment efficiency is also genuinely concerned Especially the issue regarding the stability of phosphorus removal Determining the exact conditions that affect the process of phosphorus removal by iron electrolysis can provide optimal