VIETNAM MINISTRY OF EDUCATION AND TRAINING
HANOI UNIVERSITY OF CIVIL ENGINEERING

TRAN HOAI SON

STUDY ON WASTEWATER TREATMENT BY ADVANCED
FILTRATION SYSTEM USING RECYCLED MATERIAL FROM
CONSTRUCTION SOLID WASTE
Major: Environmental Engineering – Water and wastewater
environmental technology
Code: 62520320-2

SUMMARY OF DOCTORAL DISSERTATION

Hanoi, 2023


The dissertation was completed at Hanoi University of Civil
Engineering.
Academic Advisor 1: Assoc. Prof. Tran Thi Viet Nga
Academic Advisor 2: Prof. Ken Kawamoto
Peer reviewer 1: Assoc. Prof. Nguyen Ngoc Dung

Peer reviewer 2: Assoc. Prof. Nguyen Manh Khai

Peer reviewer 3: Assoc. Prof. Do Khac Uan

The doctoral dissertation will be defended at the level of the
University Council of Dissertation Assessment’s meeting at Hanoi
University of Civil Engineering
At ..... hour ....., day ..... month ..... year 20….

The dissertation could be found at the National Library of Vietnam
and the Library of Hanoi University of Civil Engineering.


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INTRODUCTION
1. Research rationale
The current status of wastewater treatment (WWT) in Vietnam has
improved significantly, but the rate of treated wastewater is still low,
reaching only 14% in urban areas, 16.1% in craft villages, and only
<10% in rural areas. Untreated wastewater is the direct cause for
environmental pollution and adversely affects the landscape and
people's health.
Decentralized wastewater management using low-cost wastewater
treatment technology such as construction wetland and soil filtration
has shown high treatment efficiency and meets environmental
protection requirements. These technologies often need to use a
substantial amount of filter material. To replicate these models, it is
necessary to research suitable filter materials that are abundant at low
cost and meet wastewater treatment requirements.
Construction solid waste is being increasingly generated, it has
exceeded 3000 tons/day in Hanoi. The low rate of reuse and recycling
and most of the construction waste being buried cause severe
environmental consequences. Therefore, it is necessary to carry out
studies on the reuse of construction waste in wastewater treatment.
Autoclaved aerated concrete (AAC) is gradually being used to replace
concrete and traditional calcined materials with many outstanding
technical advantages such as lightweight, sound, and heat insulation,...

The capacity of AAC production plants has reached 1,95 million m3
per year and increasing quickly, leading to an increase in the
generation of construction waste, AAC concrete. With a high
chemical composition of metals (Ca, Fe, Al, Mg, K, ...), high porosity,
and large contact area, AAC waste has both potential as an adsorbent
and bio-filtration material in wastewater treatment plants such as
constructed wetlands or biological filtration tanks.
In Vietnam, studies on the reuse of construction waste, especially
AAC concrete in wastewater treatment are very few, and there is no
methodical application research in wastewater treatment. Therefore,
research on wastewater treatment using AAC waste is very necessary,
contributing to thorough dealing with environmental problems, taking
advantage of construction waste to help reduce costs, reduce resource


2

exploitation, contribute to environmental protection, and incentivize
the development of a circular economy.
2. Aims of the dissertation
The objective of the dissertation is to demonstrate the applicability
of AAC waste in wastewater treatment, including:
[1] Evaluation of AAC's ability to remove pollutants such as heavy
metals (Pb, Cd, As), and nutrients (phosphates) in wastewater by
adsorption method, including assessment of adsorption capacity,
adsorption mechanism, and effecting factors of the adsorption process.
[2] Evaluation of the effectiveness of wastewater treatment through
the use of the advanced biological filtration system using AAC waste
as a microbial carrier, adsorbent, and affecting factors the treatment
process.

[3] Evaluate the possibility of reuse of AAC in wastewater treatment,
and propose models of wastewater treatment using construction waste.
3. Object and scope of research of the dissertation
- Research object: The research objects are AAC autoclaved aerated
concrete, the ability to treat wastewater using AAC, domestic
wastewater, wastewater containing heavy metals, and wastewater with
high phosphorus content.
- Scope of the study: The scope of the research is to treat heavy metals
(Pb, Cd, As), organic substances, and nutrients in wastewater using
AAC autoclaved aerated concrete.
4. The scientific basis
The scientific basis of the dissertation is based on two main methods:
Adsorption method to treat heavy metals and phosphorus in
wastewater based on the technical characteristics of AAC which is an
alkaline material, rich metals containing, porous hollow material, and
with a large surface area; The biological treatment method uses an
adherent microbial film for wastewater treatment based on the
characteristics of AAC as a porous material with a large surface area
which is convenient for the development of microbial films to adhere
to the material, and based on the phosphate adsorption capacity of
AAC.
5. Research content
[1] Overview of composition, properties, and technical characteristics


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of construction waste, autoclaved aerated concrete. Overview of
research on wastewater treatment using AAC. Overview of pollutants
in wastewater that can be treated with AAC, wastewater construction

that can use AAC materials.
[2] Evaluate the adsorption capacity and the adsorption mechanism of
heavy metals (Pb, Cd, As) and phosphorus of AAC waste.
[3] Evaluate the microbial carrying capacity and wastewater treatment
of AAC waste.
[4] Evaluate the effectiveness of wastewater treatment of bio-filtration
systems using AAC.
[5] Study to evaluate the potential of phosphorus recovery from
wastewater by using AAC waste for wastewater treatment.
[6] Research and propose a wastewater treatment line using AAC
waste.
6. Research methods
Methods used: literature review; field survey; in-field
experiment; data processing; consulting with experts.
7. Scientific and practical contributions of the dissertation
a. Scientific contribution
- Determine the technical characteristics of some types of construction
waste (AAC) suitable for the treatment and removal of some
pollutants in wastewater.
- Determine the adsorption capacity, and adsorption mechanism of
some heavy metals (Pb, Cd, ...) and phosphate of AAC concrete.
- Evaluate the effectiveness of wastewater treatment of the model of
an improved biological filtration system using AAC materials
according to the following parameters: COD, N-NH4, TN, TP, ....
- Evaluation of the potential for phosphorus recovery from wastewater
using AAC.
b. Practical contribution
- Proposing the treatment lines of heavy metals, phosphorus in
wastewater, and domestic wastewater treatment lines by the advanced
biological filtration system using AAC.

- The results of the dissertation have important implications in
improving the reusability of construction waste in wastewater
treatment, opening a new approach to sustainable wastewater


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treatment using recycled and low-cost materials from construction
waste.
- The results of the dissertation are sources of scientific data for
training and scientific research in the field of environmental
engineering.
8. New findings of the dissertation
a. Determine the characteristics and reuse potential of AAC waste
concrete in wastewater treatment.
b. Evaluating the adsorption capacity of KLN (Pb, Cd, As) and
phosphate of AAC through the determination of adsorption kinetic
parameters, isotherm model, adsorption process mechanism, and
influencing factors.
c. Assessing the wastewater treatment capacity of the bio-filtration
system using AAC waste including treatment efficiency, optimal
operating mode, analysis of treatment process mechanism, and
practical application directions in wastewater treatment.
9. Dissertation structure
The dissertation consists of 130 pages typed A4, specifically
numbered as follows: Introduction (9 pages); Chapter 1: Overview of
research issues (27 pages); Chapter 2: Scientific basis of wastewater
treatment with AAC waste concrete (18 pages); Chapter 3: Research
Methods (13 pages); Chapter 4: Results and discussion (47 pages);
Conclusion and recommendations (3 pages); List of published works

(1 page); References (9 pages); In addition, the dissertation has a
number of unnumbered parts, including dissertation cover (2 pages);
Commitment (1 page); Table of Contents (3 pages); List of symbols
and abbreviations (2 pages); Table list (2 pages); List of drawings (2
pages) and Appendix (25 pages). The dissertation has 40 tables and 55
figures.
CHAPTER 1. OVERVIEW OF RESEARCH ISSUES
1.1. Overview of construction solid waste and AAC
1.1.1. Overview of construction solid waste (CSW) in Vietnam
Construction waste is generally increasing, accounting for 10-15% of
urban solid waste. In Hanoi, construction waste has generated around
3000 tons/day. The most common construction waste treatment
method today is waste dumping and burying, which takes up a lot of


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space and waste resources. The percentage of concrete in construction
waste is about 23% to 32%. Construction waste has great value in
being reused and recycled into other materials, however, construction
waste recycling plants are not yet well developed in Vietnam, leading
to low rates of recycling and reuse. The national strategy on integrated
solid waste management sets a target that by 2025, 90% of total
construction waste generated in urban areas will be collected and
treated, of which 60% will be reused or recycled.
1.1.2. Overview of autoclaved aerated concrete
There are 12 AAC factories with a total design capacity of 1.95 million
m³/year in Vietnam. AAC is manufactured from cement, lime,
gypsum, finely ground sand, water, and gaseous agent. It is estimated
that the amount of AAC waste generated is up to 0.04 - 0.1 million

m³/year. In the future, when the demand for AAC increases, the
amount of AAC waste generated will also increase.
1.1.3. Physical and chemical properties of AAC
The composition of AAC includes: SiO2=44,8-57,0%; CaO=24,927,6%; Al2O3=1,95-16,06%; Fe2O3=1,0-4,2%; MgO=0,5-0,65%;
K2O=0-0,7%. AAC has a large surface area > 20 m2/g. The total
porosity of AAC is around 77-80%, whereas the macroporous porosity
is up to 37-46%, and the ratio of pore with r ≥10 μm occupied up to
70-80%.
1.2. Overview of wastewater treatment using CSW
1.2.1. Removal of heavy metals in wastewater by using CSW
Construction solid waste, especially the property of concrete waste is
similar to calcium silicate materials, it has a metal-rich chemical
composition, large surface area, and great potential for usage as a
heavy metal adsorbent. The main materials studied and researched
include Marble powder, laterite, concrete powder, concrete waste,
autoclaved aerated concrete,... Almost all of the research use synthetic
wastewater with common non-metallic metals. : Pb, Cd, Cr, Cu, Ni,...
The adsorption capacity of heavy metals in concrete waste and AAC
waste fluctuates widely depending on each metal, in which Pb and Cd
are suitable for removal by using concrete waste, AAC waste. The
adsorption capacity is up to 20-300 mg/g, the treatment efficiency
reaches > 90%.


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1.2.2. Wastewater treatment using CSW
a. Wastewater treatment using CSW
Dong et al (2016) used AAC waste to replace microbial carrier
materials in biological filter tanks for wastewater treatment, the COD

and TP removal efficiency was from 60,2 to 84,6%, and 75,8-91,3%
respectively. The microorganisms grow well on the surface of AAC
substrates. Li et al (2021) reported the filter column using waste
concrete has the highest TP removal efficiency up to 87,1%, which is
explained by the chemical composition containing Ca, Fe, Al ions
which participate in ion exchange reactions and precipitates with
phosphates. The study by Bao et al (2019) showed that the biological
filtration model using AAC had better performance than the model
using commercial Caramite substrates (TN removal rate was 45,96%
> 15,64%, the removal rate of PO43- was 72,45% > 33,97%,
respectively). With the large porosity, interconnected pore network,
large surface area, and rough surface of AAC, it is believed to be
suitable and support the growth of microbial biofilms. The growth of
voids inside the AAC promotes phosphorus and nitrogen removal.
b. Removal Phosphorus in wastewater using CSW
The studies evaluating the P adsorption capacity of construction waste
and AAC were carried out through static and dynamic adsorption
studies. Chemical adsorption is the dominant process, including ion
exchange reactions to precipitate phosphates such as Ca3(PO4)2,
AlPO4.2H20, MgHPO4.3H20) and HAP(Ca5(OH)(PO4)3) precipitation
on the surface of the adsorbent.
1.2.3. Advance filtration system for domestic wastewater treatment
Advanced filtration systems in decentralized domestic wastewater
treatment which combined with biological filter tanks, filter trenches,
and constructed wetlands using porous and P-adsorbent materials
(Filtralite P) to increase the efficiency of wastewater treatment, have
been developed and widely used in developed countries. These
biological filter systems got removal efficiency of BOD > 80%, TP >
94%, TN: 32-64%, and wastewater after treatment met environmental
protection requirements. AAC is a porous material and rich in Ca, so

this material has great potential as a P adsorbent as well as a microbial
carrier in advanced biological filtration systems for wastewater


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treatment.
1.3. Potential applications of AAC in wastewater treatment
1.3.1. Pollutants in wastewater can be treated with AAC
a. Heavy metals: detected in many types of wastewater from different
fields such as mining wastewater, plating industry wastewater,
wastewater from metal recycling craft villages, leachate, etc. Common
heavy metals in wastewater such as Pb, Cd, As,...
b. Municipal wastewater: classified as low-strength wastewater,
characterized by low organic matter content. The concentrations of
pollutants in MWW in Hanoi are relatively low: COD < 300 mg/L,
NH4-N: 5-25 mg/L, TN: 5-55 mg/L, TP: 1,3-21,5 mg/L.
c. Phosphorus-concentrated wastewater: Phosphate in wastewater
exists in the form of organic P, soluble monophosphate, phosphate
condensates, phosphates salts, and phosphates in biomass cells. TP
content in bioreactors ranges from 1.3-21.5 mg/L, in wastewater from
4.3-25 mg/L, and in wastewater from food processing plants (dairy)
from 6-500 mg/l.
1.3.2. The Potential applications of AAC in decentralized domestic
wastewater treatment
Popular decentralized domestic wastewater treatment: Advanced
septic tank with anaerobic filter compartment; Baffled anaerobic
reactor; Anaerobic filter tank; Biological filter tank; Construction
wetland. Which can be combined to form wastewater treatment
systems working in natural conditions. Construction waste such as

AAC waste can be used as filter material, and microbial carrier in
these works.
1.4. Research orientation
The research orientation of the dissertation is to demonstrate the ability
to treat contaminated objects in wastewater when using AAC
materials, including the ability to act as adsorbents and treat some
heavy metals (Pb, Cd, As). ), phosphate; AAC's ability as a microbial
carrier in biological filtration systems for bioreactor treatment. From
there, the research elaborates on directions for applying AAC waste in
low-cost wastewater treatment systems.
CHAPTER 2. SCIENTIFIC BASIS OF WATER TREATMENT
PROCESS BY AAC WASTE


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2.1. Theoretical basis of the adsorption process
Adsorption is the accumulation of substances on the phase interface.
In wastewater treatment, when talking about the adsorption method, it
is talking about the adsorption of dissolved pollutants at the interface
between the liquid and solid phases. Pollutants in water are under the
influence of two forces. A bond develops from the adsorption of
adhesive molecules on the substrate and the resulting attractive forces,
usually designated as secondary or van der Waals forces.
2.1.1. The concepts of the adsorption process
a. Adsorption capacity is the amount of adsorbent retained per unit
(𝐶 − 𝐶 ).𝑉
mass of material: q= 𝑜 𝑐𝑏
(2.1)
𝑚

b. Adsorption efficiency is the ratio between the concentration of the
equilibrium solution and the initial concentration of the solution:
(𝐶 − 𝐶 )
𝐸 = 0 𝑐𝑏 × 100
(2.2)
𝐶0

c. Langmuir model
The equation expresses the Langmuir model:
𝐶𝑐𝑏
1
1
= 𝑏𝑞 + 𝑞 𝐶𝑐𝑏
𝑞
𝑚

𝑚

(2.3)

d. Freundlich model
The equation expresses the non-linear equation of the Freundlich
1/𝑛
isotherm model: qe = Kf.𝐶𝑒 , (n>1)
(2.4)
1
And the formula of the graph form: Logqe = logK f + logCe
(2.5)
𝑛
2.1.2. Adsorption kinetics

a. The Pseudo–first-order
(2.6)
b. The Pseudo–second-order
(2.7)
2.1.3. The effect factors on the adsorption process in wastewater
treatment
The ratio between the concentration of the adsorbent solution and the
adsorbent; Temperature; Adsorbent and adsorbed nature; pH.
2.2. Scientific basis for adsorption/removal of heavy metals and
phosphates by AAC


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2.2.1. Characteristics of AAC
AAC has total porosity of 77-80%, many interconnected pore
networks, macro porosity of 37-46%, and surface area BET > 20 m2/g,
AAC has the characteristics of calcium silicate materials, exhibits
alkalinity, can release OH- radicals, thereby participating in
precipitation reactions with heavy metal ions. The composition of
metals such as Ca, Al, and Fe facilitates ion exchange reactions, and
forms complexes with heavy metal ions and phosphates in wastewater
to form precipitates or complexes on the surface.
2.2.2. Main mechanisms of heavy metal adsorption by AAC
The mechanism of heavy metal removal by calcium silicate materials
is mainly regulated by three- step or five-step mechanisms, such as
hydrolysis, hydration, ion exchange, surface complexation, and
surface precipitation.
2.2.3. The mechanisms of phosphate adsorption by AAC
The removal of P by AAC is a simultaneous process of Ca/alkali

dissolution, metal ions, surface adsorption, and chemical precipitation,
the main products are Ca3(PO4)2, Ca5(OH)(PO4)3, MgHPO4, and
AlPO4.
2.3. Scientific basis for wastewater treatment by biological
filtration using AAC
2.3.1. Mechanism of wastewater treatment process by biofilm
Bacteria can grow to adhere to almost any surface, forming
architecturally complex communities known as biofilms. Biofilms
include bacteria, fungi, algae, protozoa and other organisms. The
treatment mechanism is the filtration-absorption process thanks to the
biofilm on the filter material and media.
2.3.2. Mechanism of wastewater treatment in biological contact filter
tanks
a. Mechanism for the treatment of biodegradable organic matter
Biodegradation (aerobic and anaerobic) plays the largest role in the
removal of soluble, colloidal organic substances in wastewater;
Sedimentation and filtration.
b. Mechanism of removal of nitrogen compounds
The evaporation of ammonia; nitrification/denitrification and some
other mechanisms.


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c. Mechanism of removal of phosphorus compounds
Adsorption and precipitation on the surface of the filter media, storage
in biomass, and accumulation in the sediment.
d. Mechanism of bacteria and viruses treatment
Physical processes such as agglomeration and deposition, filtration,
adsorption; unfavorable environmental conditions (pH, temperature,

solar radiation, lack of nutrients).
e. Mechanism of removal of TSS: The process of filtration,
sedimentation, and biodegradation, adsorption, adsorption on filter
media, supporting materials by van der Waals gravity, Brown motion.
2.3.3. The effect factors on wastewater treatment by biological
contact filter tanks
a. Filter material properties
The influencing parameters of materials include: material size, the
surface area of the material, chemical composition, and porosity of the
material.
b. Effect of temperature
Temperature affects the rate of chemical reactions, adsorption,
metabolism, and growth of biofilm.
c. Effect of pH: The pH of wastewater is an influence on chemical
metabolism, adsorption and biochemistry taking place in the work.
d. Hydraulic loading rate and hydraulic retention time
The hydraulic loading rate (HLR) is small, and the hydraulic retention
time (HRT) will be long, which will facilitate the adsorption process,
and the settling process and thereby increase the treatment efficiency.
e. Recirculation flow: The flow recirculation increases nitrification
and can improve denitrification by increasing exposure time and
providing additional organic matter.
CHAPTER 3. RESEARCH METHODS
3.1. Research object and content


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Figure 3.1. Research Diagram
3.2. Experimental planning

3.2.1. Material preparation and physicochemical characterization
a. Material Origin
AAC waste is collected from the Viglacera Yen Phong factory, Bac
Ninh province, Vietnam.
b. Prepare materials for experiments
Large blocks of AAC are pounded and sieved to obtain sizes from 3050 mm, 5-10 mm, and 3-5 mm. The adsorption experiment used 3-5
mm and 5-10 mm AAC particles. Experimental wastewater treatment
by advanced biological filtration system: 30-50 mm AAC was used as
a microbiological substrate, and 3-5 mm particles were used as
adsorbent.
c. Investigation of the point of zero charge of materials
The zero charge point of the surface of a substance is the pH value at
which the surface of the material is electrically neutral (pHpzc). The
potentiometric titration technique is used to determine the zero charge
point of a material.
3.2.2. Study on static adsorption capacity


12

Batch adsorption experiments (according to OECD standard methods)
were performed to evaluate the adsorption capacity, adsorption
kinetic, and factors affecting the adsorption process. Experiment using
synthetic wastewater. H3AsO4, PbCl2,, Pb(NO3)2, CdCl2, KH2PO4 are
used to make synthetic wastewater solutions containing objects to be
adsorbed.
a. Effect of adsorption/reaction time
Experimental conditions for static adsorption, investigating the effect
of adsorption time are shown in Table 3.1. Each experiment was
repeated 2 times.

Table 3.1. The input data studied the effect of time on the adsorption
efficiency of heavy metal ions and phosphates of AAC.
Adsorbed AAC size
Co
m (g) V (ml)
T (min)
substance
(mm)
(mg/L)
Cd
10
100
30, 60, 120,
500
240, 480,
Pb
10
100
500
3-5
960, 1440
As
10
100
500
5 - 10
(10’ và 20’
P
2
50

18
for Pb)
b. Effect of adsorbent concentration
The conditions of the adsorption experiment to investigate the effect
of adsorbent concentration are shown in Table 3.2. Each experiment
was repeated 2 times.
Table 3.2. The input data studied the effect of concentration on the
adsorption efficiency of heavy metals and phosphates of AAC.
Adsorbed AAC size
Co
m (g)
V (ml)
T (h)
substance
(mm)
(mg/L)
Cd
10
100
24
0-5000
0-5000
Pb
10 (1)
100
24
3-5
(25000)
5 - 10
As

10
100
24
0-5000
P
2
50
24
0-70
3.2.3. Experimental wastewater treatment by advanced biological
filtration system using AAC
The laboratory wastewater treatment system consists of a vertical
dripped filtration tank → a horizontal filtration tank → a reactive bed


13

filter tank as shown in Figure 3.2.

Figure 3.2. Experimental diagram of municipal wastewater treatment
by the biological filtration system
The experiment operation process is described in Table 3.3. Inlet and
outlet wastewater samples of the tanks are taken weekly and measured
parameters COD, TP, NH4-N, parameters DO, pH, and temperature
are measured daily.
Table 3.3. Experimental parameters of wastewater treatment
Q
HRT
Recirculation flow
Time (day)

(L/day)
(h)
(L/day)
Phase 1
0-65
15
26-27
0
Phase 2
65-110
10
39-40
13 (130% Q)
110-155
15
26-27
13 (86% Q)
Phase 3
155-200
20
19-20
13 (64% Q)
3.3. Methods of analysis and evaluation in the dissertation
3.3.1. The methods of evaluation of composition, surface
morphology of materials
The chemical composition of AAC was analyzed by X-ray diffraction
(XRD) and X-ray scattering spectroscopy (EDX/EDS) analysis
performed at the laboratory of Saitama University, Japan, and VNU



14

University of Science. The scanning electron microscopy (SEM)
method helps to observe images of surface and material structure.
3.3.2. The methods of assessment of water quality indicators
Analytical methods for heavy metals: The parameters As, Cd, Pb
were analyzed according to the wastewater analysis standard
SMEWW 3125 (2012) by the atomic absorption spectroscopy (AAS)
method.
Analytical methods for COD, TP, TN, NH4-N: These criteria are
analyzed according to equivalent Vietnamese and international
standards, including SMEWW 5220C: (2012), TCVN 6179–1 (1996),
TCVN 6638 (2000), TCVN 6202 (2008). The sampling of water to
analyze these parameters is done once a week, measured by
colorimeter HACH DR/890.
Method of measuring pH, DO: According to TCVN 6492 (2011),
TCVN 7325 (2004), using a handheld meter of Horiba PC110, Japan.
Calculation: Treatment efficiency (E%), adsorption capacity at time t
(Qt, mg/g), and adsorption capacity at equilibrium (Qe, mg/g), were
𝐶 −𝐶
calculated from the following equations:: 𝐸 = 𝑜𝐶 𝑒 × 100 (3.1);
𝑄𝑡 =

𝐶𝑜 −𝐶𝑡
𝑚𝑠

× 𝑉 (3.2); 𝑄𝑒 =

𝐶𝑜 −𝐶𝑒
𝑚𝑠


𝑜

(3.3). Where Co and Ce (mg/L)

being the initial and final concentrations of the ions in the solution,
then Ct (mg/L) is the concentration at time t. V is the solution volume
(L) and ms is the mass of adsorbent powder used (g). Qt (mg/g) is the
adsorption capacity at time t (min). Qe (mg/g) is the adsorption
capacity at equilibrium corresponding to the Ce concentration (mg/L).
CHAPTER 4. RESULTS AND DISCUSSION
4.1. Properties of the adsorbent
4.1.1. The chemical composition of the material
AAC has the content of SiO2: 55,18%, CaO: 28,89% Al2O3: 2,76%,
Fe2O3: 1,72%, K2O: 0,87%, MgO: 0,63%. It is shown as an alkaline
material, AAC can neutralize acidic wastewater during adsorption.
The high content of metals in AAC indicates the ability of ion
exchange reaction with heavy metals, and surface adsorption with
pollutants.
4.1.2. The point of zero charge (pHpzc)
The point of zero charge of AAC is around pH 5. When the pH of the


15

solution is < pHpzc (pH<5), AAC has a positive charge (+) and will
adsorb anion (-) better. When the pH of the solution is > pHpzc (pH>5),
AAC has a negative charge (-) that will adsorb cation (+) better.
4.1.3. Other material specifications
AAC has a volumetric weight from 550-750 kg/m3, average

compressive strength 2,5-5 Mpa, total porosity 77-80%, macroporosity 37-46%, the surface area (BET) 21 -24 (m2/g).
4.2.
Evaluation of heavy metal adsorption efficiency and
influencing factors
4.2.1. Adsorption capacity of some metals of AAC
a. Effect of the contact time on adsorption capacity
The adsorption capacity Qt (mg/g) of AAC is directly proportional to
the adsorption contact time. Under the same experimental conditions,
the adsorption equilibrium time with Cd(II) and As(V) was 16-24
hours, and Pb(II) was after 0.5 hours. Pb removal efficiency after 30
minutes reached > 90%. The Cd removal efficiency is from 21-99%,
and the As treatment efficiency increases from 6-17% when the
reaction time is increased from 0,5-24 hours.
b. Effect of pH on treatment efficiency
The pH of the solution increases with the reaction time, and the pH of
all adsorbed solutions is >7, based on the pHpzc of AAC is about pH 5,
AAC has a negative potential value of ζ (-) so cation Pb2+, Cd2+… can
be adsorbed by the negative (-) charged surface AAC through the
formation of stable chemical bonds on the surface. Therefore, the
efficiency of Pb and Cd adsorption is increased when the pH is
increased. Arsenic exists mainly in the form of anion (AsO43-) so it is
difficult to fix on AAC, so the adsorption efficiency is lower than that
of Pb, Cd.
c. The maximum adsorption capacity of AAC according to the
concentration experimental solution
At the same experimental conditions with the concentration of the
solutions ranging from 0-5000 mg/L, the maximum Cd adsorption
capacity was about 9,0-9,2 mg/g and the equilibrium point was
reached at the Ci range of 2000 mg/L, the maximum adsorption
capacity of As reached 2,0-2,2 mg/g, the equilibrium point at around

Ci of 2000 mg/L. The Pb adsorption capacity of AAC reached about


16

50 mg/g and did not reach the equilibrium value when investigating
the Ci of 5000 mg/l. When changing the investigation ratio of
adsorbent (gram)/solution (ml) to 1/100, the obtained results show that
the maximum adsorption capacity of Pb(II) is up to 250 mg/g.
Table 4.1. Summary of batch adsorption test results of AAC
Heavy
S/L ratio (g/mL)
equilibrium
Qm (mg/g)
metal
time (h)
As
1/10
16-24
2,0-2,2
Cd
1/10
16-24
9-9,2
Pb
1/100
0,5
230 -250
4.2.2. Evaluation of the heavy metal adsorption isotherms of AAC
The results show that both Langmuir and Freundlich isotherm models

are suitable to describe the adsorption process of Cd and Pb, As (R2>
0,89).
Table 4.2. Parameters of the adsorption isotherm of AAC
Langmuir
Fruendlich
AAC S/L Metal b
Qm
R²
Kf
1/n
R²
L/mg mg/g
mg/g
3-5
0,2700 9,26 0,999 1,507 0,282 0,887
1:10 Cd
5-10
0,0641 8,96 0,999 1,222 0,296 0,892
3-5
0,0018 2,35 0,972 0,022 0,591 0,964
1:10 As
5-10
0,0016 2,13 0,963 0,013 0,653 0,945
3-5
0,0034 256,41 0,998 16,99 0,305 0,951
1:100 Pb
5-10
0,0022 232,56 0,997 11,96 0,327 0,941
Effect of grain size: The calculation results show that the AAC
material with a smaller size will have a higher adsorption capacity due

to its larger surface area.
4.2.3. Evaluation of the heavy metal adsorption kinetic
The results of the heavy metal adsorption kinetics on AAC are shown
in Table 4.3.
Table 4.3. Kinetics of heavy metal adsorption on AAC
qe
The Pseudo–secondThe Pseudo–first-order
experi
order
AAC Metal
ment
q
qe
K1
R²
e
K2
R²
-1
mg/g mg/g g/mg.min
mg/g
min


17

qe
The Pseudo–secondexperi
order
AAC Metal

ment
q
qe
K1
R²
K2
R²
e
-1
mg/g mg/g g/mg.min
mg/g
min
3-5
0,0076 0,956 4,20 4,90 0,0028 0,998 5,18
Cd
5-10
0,0035 0,953 3,39 4,52 0,0016 0,997 4,99
3-5
0,00253 0,833 0,38 0,93 0,0254 0,998 0,95
As
5-10
0,00207 0,832 0,13 0,75 0,0922 0,997 0,76
3-5
0,991 0,999 4,68
0,1716 0,902 2,21 4,69
Pb
1,94
4,69
5-10
0,802 0,999 4,68

0,1769 0,901
The Pseudo-second-order model well captured the measured data, the
measured maximum adsorption capacity (Qm) and estimated
equilibrium adsorption capacity (Qe) became almost identical, and the
correlation coefficient R2 >0,99.
4.2.4. Competitive Metal Adsorption
When simultaneously treating Pb and Cd, the adsorption capacity and
removal efficiency of Pb(II) are both higher than that of Cd(II), the
hydrated radius of Pb(II) is 4.01 Å smaller than that of Cd(II). Cd(II)
is 4.26 Å, so Pb(II) exerts a greater affinity for adsorbents. Besides, Pb
can precipitate at lower pH conditions (pH > 7) than Cd (pH > 9).
Table 4.4. Results of simultaneous Pb and Cd adsorption of AAC.
m
V
Ci
Ce
Qe
E
AAC Metal
(g)
(ml)
(mg/l) (mg/l) (mg/g) (%)
Cd
10,06 100,00 508,14 108,00 3,98 78,75
3-5
Pb
4,96 99,00
10,06 100,00 504,08 5,03
Cd
100,00

508,14
171,00
3,37 66,35
10,01
5-10
Pb
4,98 98,82
10,01 100,00 504,08 5,93
4.2.5. Mechanism of heavy metals adsorption and removal of AAC
a. Mechanism of adsorption and removal of Pb and Cd
AAC is characteristic of calcium silicate materials, so heavy metals
(HMs) removal is mainly regulated by a five-step mechanism of
hydrolysis, hydration, ion exchange, surface complexation, and
surface precipitation. Ca2+ ion exchange, surface complexation, and
precipitation are the main adsorption mechanisms of HMs for AAC;
The Pseudo–first-order


18

that is, the reaction of calcium silicate materials with water produces
calcium silicate hydrates (C-S-H) and calcium hydroxide (CH) due to
the hydration, and those substances function as adsorption sites of
HMs. The hydration reactions [equation (4.1)] might have formed CaOH functional groups on the edges of tobermorite. Then, hydrolyzed
HM ions [equation (4.2)] in reaction with those functional groups
might be contributed to the HM adsorption process. This could be also
supported by the measured negative ζ-potentials for the AAC.
[1] Hydration of the adsorbent surface:
(X, Si – O)2−Ca2+ + 2H2O → 2(X, Si − O) −H+ + Ca2+ + 2OH(4.1)
[2] Hydrolysis of metal ions:

M2+ + 2(OH)− → M(OH)2
(4.2)
The result of analyzing the Ca2+ concentration before and after the
experiment showed the relationships between the released Ca2+
amount and adsorbed metal amount in the, the Ca2+ was released
linearly along with the metal adsorption (R2> 0,97). This suggests that
chemical adsorption by ion exchange (between Ca2+ and Cd2+, Pb2+) n
the hydrated adsorbent surface is the dominant adsorption
mechanism of HM adsorption for tested AAC fines (equation (4.3)
and (4.4)).
[3] Ion exchange on the adsorbent surface:
(X, Si – O) 2− Ca2+ + M2+ → (X, Si – O) 2− M2+ + Ca2+
(4.3)
(X, Si – O) 2− Ca2+ + 2M(OH)+ → 2(X, Si – O)− M(OH)+ + Ca2+ (4.4)
In addition, the surface precipitation of HMs can be due to the
solution pH [equation (4.5)]. Cd(II) and Pb(II) have the potential to
precipitate as metal hydroxides when the solution pH reaches 9 for
Cd(II) and 7 for Pb(II). It is important that the pH after adsorption
became greater than pH = 8 for Cd(II) and pH = 7 for Pb(II), at Ci <
2000 mg/L. This implies that the surface precipitation of HMs
contributed partially to HM removal in water along with the ion
exchange.
[4] Surface precipitation of metals:
M2+ + 2(OH)− → M(OH)2
(4.5)
At very high initial HM concentrations (Ci ≥ 2.000 mg/L), the
previous reaction would not be possible because of the lower pH. The
adsorption shifted to multilayer-type adsorption at higher Ci> 2.000



19

mg/L. With increasing Ci and metal adsorption, the pH after
adsorption decreased continuously < 5. This can be caused by high
deprotonation from the calcium silicate surface, which is a result of
the surface complexation formation on AAC (equation (4.6)), the
dissipation of OH− due to surface precipitation might contribute to the
increase in adsorption and decrease in pH after the adsorption.
[5] Formation of surface complexation on AAC:
2(X, Si – O) − H+ + M2+ → (X, Si – O) 2−M2+ + 2H+
(4.6)
(M = Cd, Pb)
b. Mechanism of adsorption and removal Asen
In the synthetic wastewater solution (H3AsO4), exists mainly as an
anion AsO43-. In an alkaline solution, AAC has also a negative charge
(-) too, so AsO43- hard to adsorb on AAC. As the adsorption
mechanism takes place mainly in the early stage, when the hydrolysis
of concrete has not yet taken place, at this time the solution (H3AsO4 )
has pH< 3, which is under pHpzc (pH 5) of AAC. Then, AAC has a
positive charge (+) and attracts anions AsO43-, the cation sites of Fe
and Al are suitable sites for arsenic adsorption on the surface AAC.
As the contact time increases, the pH of the solution increases,
creating an alkaline environment due to the hydrolysis of AAC. At
this time, AAC becomes negatively charged (-), and no longer attracts
anion AsO43-, besides, Fe and Al adsorption nuclei are also limited due
to iron oxide (Fe2O3: 1,72%) and Aluminum oxide (Al2O3: 2,76%)
composition in AAC is low, so the As adsorption efficiency of AAC is
not high.
c. SEM and EDX analysis results
The analytical results show that in the presence of heavy metals in the

composition of AAC, the percentage of Pb is greater than the
percentage of Cd and the percentage of As. This proves that there is a
process of adsorption of these HMs on AAC.
d. Evaluation of the ability to wash away and treat materials after
heavy metal adsorption
The heavy metals are mostly removed in the form of hydroxide
precipitates on the surface of the material, so in the alkaline
environment created by AAC, the precipitates are stable, and very
difficult to dissolve in water. Further evaluation studies on reuse and


20

possible conditions of heavy metal leakage are needed to recommend
reuse operations.
4.3. Evaluation of phosphate adsorption capacity by AAC
4.3.1. Investigate the effect of reaction time
The adsorption capacity P of AAC increased rapidly between 0 and
480 min and slowly increased to saturation from 480 min to 1440 min.
TP removal efficiency reaches 91%-100% respectively after 1440
minutes.
4.3.2. Effect of the phosphorus concentration
P removal efficiency is best when the test solution was 3-30 mg/L
with a treatment efficiency of 96-100%. At the equilibrium
concentration of 70 mg/L, the adsorption capacity was achieved at 1,0
-1,1 mg P/g, and at this experimental concentration point, the P
removal efficiency only reached 60-62%.
4.3.3. Evaluation of the phosphorus adsorption isotherms and
adsorption kinetic of AAC
a. Evaluation of the phosphorus adsorption isotherms

The Langmuir model is more suitable than the Freundlich model with
the correlation coefficient R2 = 0,9996 and 0,9991 compared to 0,6166
and 0,6096 respectively, that is monolayer adsorption dominates.
Maximum adsorption capacity (Qm, mg/g): 1,06- 1,1 mg P/g,
Langmuir adsorption constant (b, L/mg): 2,81- 4,88 L/mg. Freundlich
adsorption constant (Kf, L/mg): 0,612- 0,702 L/mg; 1/n from 0,220 to
0,225 (0,1 <1/n <0,5) favorable for adsorption, confirming the
suitability of AAC for P removal.
b. SEM and EDX analysis results
The analysis results show that there is P in the chemical composition
of the AAC material after adsorption, which proves the phosphate
adsorption capacity of AAC.
c. Evaluation of the phosphorus adsorption kinetic
The Pseudo-second-order model captured well the measured data, the
measured maximum adsorption capacity (Qm) and estimated
equilibrium adsorption capacity (Qe) became almost identical, and the
correlation coefficient R2 > 0,99.
Table 4.5. Kinetics of phosphorus adsorption on AAC
AAC The Pseudo–first-order
qe
The Pseudo–second-order


21
K1
R²
qe
experiment
K2
R²

qe
min-1
mg/g
mg/g
g/mg.min
mg/g
3-5 0,0051 0,954 0,22
0,45
0,0863
0,999 0,457
5-10 0,0042 0,965 0,26
0,44
0,0548
0,999 0,453
d. Mechanism of adsorption and removal phosphorus of AAC
The phosphorus removal mechanisms by AAC are a simultaneous
process of Ca/alkali dissolution, surface adsorption, and chemical
precipitation, with weakly adsorbed phosphorus and Ca-P
precipitation as the major products. The adsorption process can be
written as the following equations:
Ca2+ + PO43- → Ca3(PO4)2 
(4.7)
2+
2Ca + 4OH + 3HPO4 → Ca5(OH)(PO4)3  +3H2O
(4.8)
Al3+ + PO43- + 2H20 → AlPO4. 2H20 
(4.9)
AAC material maintains environmental pH from 8-10 to help release
more Ca2+ and OH-, These ions react with PO43- to make the final
product Ca5(OH)(PO4)3 and this keeps the P removal efficiency high.

4.4. Experimental results of wastewater treatment by advanced
biological filtration system using AAC
4.4.1. Evaluation of COD removal efficiency
COD removal efficiency is from 60-95%. The COD output is < 30
mg/L. The removal efficiency increased with increasing retention time
and recirculation ratio (Figure 4.1)

b)
Figure 4.1. COD index before, after treatment (a) and treatment
efficiency (b)
4.4.2. Evaluation of the removal efficiency of Nitrogen Ammonium
(N-NH4)
N-NH4 treatment efficiency is about 50%-90%. Treatment efficiency
increased with increasing retention time (20h→40h) and circulation
rate (0%→130%). AAC has improved the pH condition of the
a)


22

treatment system to remain stable in the range of 8-8.5 to increase the
efficiency of the nitrification process.

b)
a)
Figure 4.2. N-NH4 concentration before, and after treatment (a) and
treatment efficiency (b)
4.4.3. Evaluation of total nitrogen removal efficiency (TN)
TN removal efficiency was 30-80%. Treatment efficiency increased
with increasing retention time (20h→40h) and circulation rate

(0%→130%). AAC has improved the pH condition and added an
alkaline source for the treatment (the pH of the system was stable in
the range of 8-8.5), which increases the efficiency of TN removal.

a)
b)
Figure 4.3. TN concentration before and after treatment (a) and
treatment efficiency (b)
4.4.4. Evaluation of total phosphorus removal efficiency
TP removal efficiency is stable from 73-100%. TP concentration of
the outlet wastewater is less than 2 mg/L


23

a)

b)

Figure 4.4. TP concentration before and after treatment (a) and
treatment efficiency (b)
The mechanism of P removal from wastewater can be explained by
the adsorption of P on AAC particles and the formation of a biofilm
containing organic substances and nutrients (N and P) on the surface
of the material. AAC. After 195 days of operation, the system was
stable, there was no blockage, and the P content retained in the system
was 0,7 g/kg AAC.
4.4.5. Evaluate other parameters
a. pH
The influent has a pH in the range of 6,5-7,9, the wastewater after the

treatment stages has a pH higher than 8, and the pH of the output
wastewater is in the range of 8-8,5. AAC is alkaline, capable of
applying this material to neutralize and treat low pH wastewater and
simultaneously create stable pH conditions to support nitrification and
denitrification.
b. Turbidity and total subbed solids
The effluent is colorless, odorless, and has very low turbidity. The
average output residue content is 5-10 mg/L, with turbidity < 5NTU,
which shows that the treated water has the potential to be reused for
different purposes.
4.4.6. AAC material is suitable for biofilm systems. AAC facilitates
biofilm formation, and sustainable growth on the surface, with no
signs of clogging or disintegration. AAC creates an alkaline
environment with a stable pH (8-8,5) which supports the treatment
process (nitrification and denitrification) to take place smoothly,
minimizing the use of chemicals to raise pH, thereby saving money.
expense.