ijciet 06 09_002

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 6, Issue 9, Sep 2015, pp. 08-19, Article ID: IJCIET_06_09_002

Available online at

http://www.iaeme.com/IJCIET/issues.asp?JTypeIJCIET&VType=6&IType=9

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication

___________________________________________________________________________

COLUMN STUDY OF THE ADSORPTION OF

PHOSPHATE BY USING DRINKING WATER

TREATMENT SLUDGE AND RED MUD

Prof. Dr. Alaa Hussein Al-Fatlawi

College of Engineering / Babylon University/Iraq

Mena Muwafaq Neamah

College of Engineering / Babylon University/Iraq

ABSTRACT

The present study investigates the efficiency of phosphate removal from

wastewater by the Drinking Water Treatment Sludge (DWTS), and Red Mud

(RM) sorbent. Wastewater was taken from the effluent channel of Almuamirah

wastewater treatment plantin at Al-Hilla city/Iraq. Drinking Water Treatment

Sludge (DWTS), was taken from the sedimentation tanks of Al-Tayara drinking

water treatment plant, in the same city.

Column experiment was carried out to study the adsorption isotherm of

phosphorus at 25±1⁰C and solution of different pH and adsorbent dosages.

The effects of (DWTS) dose, bed height (H), contact time (T), agitation speed

(S), hydrogen ion concentration (pH), (DWTS –RM) ratio, were studied.

All continuous experiments were conducted at constant conditions, bed

depths 25 cm, initial phosphate concentration 4 mg/L, flow rate 5 mL/min,

particle size (1mm) for (DWTS), and (0.425mm) for (RM) and solution pH of

4.

The results show that the use of (RM) reduces the operating time by about

21% compared to the use of (DWTS).Increasing (RM) ratio increasing the

removal efficiency and decreasing the equilibrium time in about 57% and 38%

for 50% and 33% (RM) ratio respectively.

At the highest phosphate concentration of 4 mg/l, the (DWTS) bed was

exhausted in the shortest time of less than 9 hours leading to the earliest

breakthrough. Percent of phosphate removal decreased with the increase in

initial concentration. Both the breakthrough and exhaustion time increased

with increasing the bed height.

The results show that a significant increase in the operating time is

achieved by adding different ratios of (RM) to (DWTS). Adding 33%, and 50

% (RM) weight ratios to the (DWTS) bed decreases the operating time by

about 18%, and 30% respectively.

Column Study of The Adsorption of Phosphate by Using Drinking Water Treatment Sludge

and Red Mud


Key words: Column Study, Adsorption, Drinking Water Treatment Sludge

(DWTS), and Red Mud (RM), phosphate.

Cite this Article: Prof. Dr. Alaa Hussein Al-Fatlawi and Mena Muwafaq

Neamah. Investigating Column Study of The Adsorption of Phosphate by

Using Drinking Water Treatment Sludge and Red Mud. International Journal

of Civil Engineering and Technology, 6(9), 2015, pp. 08-19.

http://www.iaeme.com/IJCIET/issues.asp?JTypeIJCIET&VType=6&IType=9

1. INTRODUCTION

Phosphorus (P) is an essential nutrient for the growth of organisms in most

ecosystems, but superfluous phosphorus can also cause eutrophication and hence

deteriorate water quality. Phosphorus is released into aquatic environments in many

ways, of which the most significant are human industrial, agricultural, and mining

activities. Although phosphorus removal is required before discharging wastewater

into bodies of water, phosphorus pollution is nevertheless increasing. Therefore, there

is currently an urgent demand for improved phosphorus removal methods which can

be applied before wastewater discharge. In wastewater treatment, enhanced biological

phosphorus removal (EBPR) is becoming an increasingly popular alternative to

chemical precipitation (CP) because of its lower costs and reduced sludge production.

Much water treatment sludge is produced in the production of service water and

drinking water. It is impossible to prevent the production of water treatment sludge.

The water treatment sludge is liquid and solid and is regarded as a waste.

Consequently, the water treatment sludge must be handled in accordance with

regulations in forces. The quantity of the water treatment sludge is rather high. The

water treatment sludge is placed mostly in landfills. In some countries, for instance in

the Netherlands, about 25 per cent of the produced water treatment sludge is re-used,

(Miroslav, 2008).

It is still an issue to choose a disposal or liquidation method for the water

treatment sludge that would be reasonable in terms of technology and economy.

According to environment protection regulations it is required to minimise the

quantity of wastes produced. If possible, the wastes should be re-used or processed as

secondary raw materials as much as possible. If this is not possible, the solid wastes

should be put back in the environment where the space occupied should be as little as

possible and minimum costs should be incurred, (Moldan et al., 1990).

Phosphorus removal from wastewater has been widely investigated and several

techniques have been developed including adsorption methods, physical processes

(settling, filtration), chemical precipitation (with aluminum, iron and calcium salts),

and biological processes that rely on biomass growth (bacteria, algae, plants) or

intracellular bacterial polyphosphates accumulation (de-Bashan et al., 2004).

Recently, the removal of phosphate from aqueous solutions via adsorption has

attracted much attention. The key problem for many phosphorus adsorption methods,

however, is finding an efficient adsorbent. Several low-cost or easily available clays,

waste materials and by-products.

Prof. Dr. Alaa Hussein Al-Fatlawi and Mena Muwafaq Neamah


2. MATERIAL AND METHODS

2.1 Adsorbate

Phosphate was selected as a representative of a contaminant because the it is the main

nutrient for the growth of aquatic microorganisms like algae but the excess content of

phosphorus in receiving waters leads to extensive algae growth (eutrophication).

The samples was collected from the effluent channel of Almuamirah wastewater

treatment plant in Al-Hilla city, Iraq. These samples were immediately transported to

the laboratory for processing. The total amount of plant nutrients and other pollutants

present in a sewage plant effluent is subjected to seasonal, daily, and hourly variation.

Table 1 summarizes the composition and variability of the effluent under study. The

wastewater sample was used as stock solution to provide the specific value of

phosphate concentration. Where necessary, pH adjustment was made on each sample

by addition of 0.1 M HNO3 and NaOH solutions using a HACH-pH meter.

Table 1 Physico-chemical analysis of secondary wastewater effluent sample, (Almuamirah

wastewater treatment plant, 2014)

parameters Quantitative composition

E.C, µs/cm 3.5

T.D.S, mg/L 1288

Salinity, mg/L 2.18

Total hardness, as CaCo3, mg/L 1200

pH 7.9

Mg, mg/L 232.8

Ca, mg/L 160.3

So4, mg/L 769.4

Cl, mg/L 289.9

Po4, mg/L 2.7

No3, mg/L 0.46

T.S.S, mg/L 40

BOD5, mg/L 32

COD, mg/L 54

DO, mg/L 2.3

Fecal coliform, mpn/100 ml 120000

Total coliform, mpn/100 ml 128000

2.2 Adsorbent

Two types of adsorbent were used in the present study for adsorption of phosphate

from secondary effluents of wastewater treatment plant they are:

1. Drinking Water Treatment Sludge (DWTS),

2. Red Mud (RM).

2.2.1. Drinking Water Treatment Sludge (DWTS)

The composition and properties of the water treatment sludge depends typically on the

quality of treated water as well as on types and doses of chemicals used during the


and Red Mud


water treatment. Depending on the quality of the treated water, the water treatment

sludge contains suspensions of inorganic and organic substances.

The (DWTS) used in this study was taken from the sedimentation tanks of Al-

Tayara drinking water treatment plant, in Al-Hilla city, Iraq. This sludge was dried at

atmospheric temperature for 5 days, and then sieved on 2 mm mesh to achieve

satisfactory uniformity. The sludge had a particle size distribution ranged from 150

μm to 10 mm (Fig. 1) with an effective grain size, d10, of 250 μm, a median grain size,

d50, of 460 μm and a uniformity coefficient, Cu= d60/d10, of 2.24.

Figure 1 Gradation curve for (DWTS) used in the present study.

The geometric mean diameter (1.19) is given by where d1 is the

diameter of lower sieve on which the particles are retained and d2 is the diameter of

the upper sieve through which the particles pass (Alexander and Zayas, 1989). Table

2 presents the physical and chemical characteristics of this (DWTS).

Table 2 Physical and chemical characteristics of DWTS

Element Quantitative composition

T.O.C, mg/L 4.29

E.C, µs/cm 620

T.D.S, mg/L 312

Salinity, mg/L 0.2

pH 8.1

L.O.I, mg/L 15.76

Fe2O3, mg/L 3.6

CaO, mg/L 15.32

SO3, mg/L 0.63

MgO, mg/L 3.66

Al2O3, mg/L 11.56

R2O3, mg/L 15.16

SiO2, mg/L 45

2.2.2. Red Mud (RM)

The Red Mud (RM) used in this study was supplied by the Iraqi commercial markets.

It is a solid waste produced in the process of alumina production from bauxite

following the Bayer process. Red mud, as the name suggests, is brick—red in colour

and slimy, having an average particle size of <10μm. A few particles greater than

0

20

40

60

80

100

120

0.1 1 10

% o

f cu

mu

lati

ve p

assi

ng

Partical size (diameter , mm)



20μm are also available [Liu et al., 2011].The mesh size of red mud used in the study

was of 1mm. This size was obtained by sieving analysis using the American Sieve

Standards in the building of Materials Engineering laboratory at the University of

Babylon. Its composition, property and phase vary with the type of the bauxite and the

alumina production process, and also change over time. The chemical composition of

the red mud is given in Table 3.

As a pre-treatment, (RM) was crushed and sieved to get granular (RM)with

particle size of 0.425 mm to be used in present experiments as shown in Fig. 2.The

granular (RM) was firstly washed with distilled water and then dried in an electric

oven at 120⁰C, overnight. This time was usually enough to remove any undesired

moisture within the particles. It was then placed in desiccators for cooling.

Figure 2 Gradation curve for (RM) used in the present study.

Table 3 The main chemical constituents of (RM), (Ping and Dong, 2012)

Chemical constituent Quantitative composition, %

Fe2O3 26.41

Al2O3 18.94

SiO2 8.52

CaO 21.84

Na2O 4.75

TiO2 7.40

K2O 0.068

Sc2O3 0.76

V2O5 0.34

Nb2O5 0.008

TREO 0.012

Loss 9.71

0

20

40

60

80

100

120

0.1 1 10

% o

f cu

mu

lati

ve p

assi

ng

Partical size (diameter , mm)


and Red Mud


3. PREPARATION OF SAMPLES WITH DIFFERENT (DWTS)

AND (RM) RATIOS

Two different (DWTS) and (RM) weight and ratios of (DWTS) to (RM) were used

starting with 0%, 33% and then 50%. The added (DWTS) was with a size of 1mm

while the size of (RM) was of 0.425mm. Each sample was mixed by shaking using a

shaker for 1 hour. The 0% ratio was first prepared and used in the experiments. When

an increase in the operating time was achieved, the addition ratio was raised to 50%.

4. EXPERIMENTAL PROCEDURES

The reactor setup (Fig. 3) used in the present study is constructed of pyrex glass tube

of (100 cm) height, and (7.5 cm) internal diameter. The column was made in a

methacrylate cylinder, thus allowing for visual examination of the progress of the

wetting front and detection of preferential flow channels along the column walls. The

column dimensions were defined to minimize the occurrence of channeling by

making the column diameter at least 30 times the maximum particle size found in the

material used. The column dimensions also met the minimum length-to-diameter

requirement (Relyea, 1982). This means the column length (100 cm) must be four

times greater than its diameter (7.5 cm). Attached to the lower part of the column was

a plastic funnel, inside which a perforated fiberglass plate was installed to support the

column’s methacrylate structure. The plate was covered by a mesh to act as a filter

and to retain the porous medium. The entire device was mounted on top of a metal

structure that allowed its height above the surface and the verticality of the column to

be regulated (Fig. 3). The column was packed with (DWTS) and (RM) in different

ratios as filter. Fluid entered the column, previously saturated with the wastewater.

Contaminant up gradient wastewater (Table 1) was used to flow through the layer of

packed materials. A constant-head reservoir of 50 liter volume polyethylene container

was used to deliver influent wastewater at a flow rate of 5 mL/min. The sample was

collected as a function of time at the bottom of the column through a 30 liter

polyethylene container to collect the effluent solution. Two valves were used to

control the desired flow rate through the adsorption column. The first sample,

corresponding to time 0, was taken when water started to flow from the lower part of

the column. Samples were filtered through 0.45µm cellulose acetate filters.

Figure 3 Experimental set-up of column test used in the present study.

Monitoring of phosphate concentrations in the effluent was conducted for a period

of 120 hr. Samples were taken regularly (after different periods) from the effluent.

The water samples were immediately introduced in glass vials and then analyzed by

AAS.



The filling material in the column was assumed to be homogeneous and

incompressible, and constant over time for water-filled porosity. The volumetric water

discharge through the column cross section was constant over time and set as the

experimental values. The pollutant inlet concentration was set constant. All tubing

and fitting for the influent and effluent lines should be composed of an inert material.

Information from the column study can be used along with the site characterization

and modeling to help in designs the field-scale (DWTS).

5. RESULTS AND DISCUSSIONS

The adsorption experiments were carried out in columns that were equipped with a

stopper for controlling the column flow rate. This experiment is useful in

understanding and predicting the behavior of the process. The sample solution was

passed through the adsorption column with a known amount of (DWTS) at a flow rate

of 5mL/min by gravity. The flow rate was kept constant by controlling the stopper

valve. The concentration of phosphate residual in the sorption medium was

determined using fully automated PC-controlled true double-beam AAS with fast

sequential operation (Varian AA50 FS, Australia) for fast multielement flame AA

determinations with features 4 lamp positions and automatic lamp selection.

The results of phosphate adsorption onto different adsorption fixed beds using a

continuous system were presented in the form of breakthrough curves which showed

the loading behaviors of phosphate to be adsorbed from the solution expressed in

terms of relative concentration defined as the ratio of the outlet phosphate

concentration to the inlet phosphate concentration as a function of time (Ce/C₀ vs.

time).

5.2. Breakthrough Curves of the Different Adsorbents

Two continuous flow adsorption experiments were conducted to study the adsorption

behavior of fixed beds of (DWTS), and (RM). All the experiments were conducted at

constant conditions, bed depths 25 cm, initial phosphate concentration 4 mg/L, flow

rate 5 mL/min, particle size (1mm) for (DWTS), and (0.425mm) for (RM) and

solution pH of 4. The breakthrough curves of the experiments are presented in Fig. 4

in terms of Ce/C₀ versus time in minutes.

Figure 4 Experimental breakthrough curves for adsorption of phosphate onto DWTS and RM

at C₀=4 mg/L, pH=4, Temp. = 25 ⁰C, H= 25 cm.

0

0.2

0.4

0.6

0.8

1

1.2

0 1000 2000 3000 4000

Ce

/C

₀

Time, min.

DWTS

RM


and Red Mud


Fig. 4 shows that the two adsorbents used in present study are efficient in the

removal of phosphate. The use of (RM) reduces the operating time by about 21%

compared to the use of (DWTS). It is obvious from this figure that the breakthrough

curves for the two adsorbents used are of S shape.

5.2. Effect of Initial phosphate Concentration

The effect of changing of phosphate concentration from 2.7 mg/l to 4 mg/l with

constant bed height of (DWTS) of 25 cm, flow rate of 5 mL/min, and solution pH of 4

is shown by the breakthrough curves presented in Fig. 5. At the highest phosphate

concentration of 4 mg/l, the (DWTS) bed was exhausted in the shortest time of less

than 9 hours while its 50 hours for (RM).Leading to the earliest breakthrough. The

breakpoint time decreased with increasing the initial concentration as the binding sites

became more quickly saturated in the column. This indicated that an increase in the

concentration could modify the adsorption rate through the bed. A decrease in the

phosphate concentration gave an extended breakthrough curve indicating that a higher

volume of the solution could be treated. This was due to the fact that a lower

concentration gradient caused a slower transport due to a decrease in the diffusion

coefficient or mass transfer coefficient.

The effect of initial phosphate concentration onto (DWTS) and (RM) are shown

here (Fig. 5 and 6). It could be seen that the percent of phosphate removal decreased

with the increase in initial concentration. This means that the amount of these

phosphate sorbed per unit mass of sorbent increased with the increase in initial

concentration. This plateau represents saturation of the active sites available on the

(DWTS) samples for interaction with contaminants, indicating that less favorable sites

became involved in the process with increasing concentration.

Figure 5 Experimental breakthrough curves for adsorption of phosphorus onto DWTS at

different initial concentrations, pH=4, H=25 cm, Temp.=25 ⁰C.

0

0.2

0.4

0.6

0.8

1

0 1000 2000 3000 4000

Cₑ

/C₀

Time, min.

C=2.7 mg/L

C=4 mg/L



Figure 6 Experimental breakthrough curves for adsorption of phosphorus onto RM at

different initial concentrations, pH=4, H=25 cm, Temp.=25 ⁰C.

5.3. Effect of Adsorbent Bed Height

The effect of bed height was investigated for phosphorus adsorption onto (DWTS);

the experimental breakthrough curves are presented in Fig. 7. This Fig. shows the

breakthrough curves obtained for phosphate adsorption on the (DWTS) for five

different bed heights of (5, 10, 15, 20, and 25 cm), at a constant flow rate of 5

mL/min, phosphate initial concentration of 4 mg/L, and solution pH of 4.It is clear

that the increase in bed depth increases the breakthrough time and the residence time

of the solute in the column.

Both the breakthrough and exhaustion time increased with increasing the bed

height. A higher phosphate uptake was also expected at a higher bed height due to the

increase in the specific surface of the (DWTS) which provides more fixation binding

sites for the phosphate to adsorb. The increase in the adsorbent mass in a higher bed

provided a greater service area which would lead to an increase in the volume of the

solution treated. (Gupta et al., 2001) reported in their works that when the bed height

is reduced, axial dispersion phenomena predominates in the mass transfer and reduces

the diffusion of the solute, and therefore, the solute has not enough time to diffuse

into the whole of the adsorbent mass.

The effect of bed depth on the adsorption capacity of (DWTS) was shown in

Fig.8, by plotting the capacity versus different bed depth. This Fig. shows that

increasing bed depth would increase the capacity because additional spaces will be

available for the wastewater molecules to be adsorbed on these unoccupied areas.

Furthermore, increasing bed depth will give a sufficient contact time for these

molecules to be adsorbed on the (DWTS) surface.

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600

Cₑ/

C₀

Time, min.

C=2.7 mg/L

C=4 mg/L


and Red Mud


Figure 7 Experimental breakthrough curves for adsorption of phosphorus onto DWTS at

different bed thickness C₀=4 mg/L, pH=4, Temp.=25 ⁰C.

Figure 8 Effect of different bed depth on the adsorption capacity of DWTS (Q=5 mL/min,

C₀=4 mg/L, pH=4, Temp=25 ⁰C).

5.4. Effect of Different (DWTS) – (RM) Ratios

The effect of different (DWTS) – (RM) weight ratios were investigated for phosphate

adsorption onto (DWTS) by adding different weight ratios of (0.425mm particle size)

(RM) to the (DWTS) bed which was of (1 mm particle size). Three experiments were

conducted using different weight ratios of (DWTS) – (RM) (0%, 33%, and 50%). All

experiments were carried out at constant conditions, flow rate of 5 mL/min, initial

phosphate concentration of 4 mg/L, (DWTS) bed height of 25 cm, and solution pH of

4. The experimental breakthrough curves are presented in Fig. 9.

This Fig. shows that a significant decrease in the operating time is achieved by

adding different ratios of (RM) to (DWTS). Adding 33%, and 50 % (RM) weight

ratios to the (DWTS) bed decreases the operating time by about 18%, and 30%

respectively. In the packed bed of the (DWTS) column, the contact points between the

0

0.2

0.4

0.6

0.8

1

1.2

0 1000 2000 3000 4000

Cₑ

/C₀

Time, min.

H=25 cm

H=20 cm

H=15 cm

H=10 cm

H=5 cm

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 5 10 15 20 25 30

Ad

orp

tio

n c

apac

ity,

mg/

g.

Bed depth, cm.



(DWTS) particles represent dead zones because they don’t contribute in the

adsorption process. So, adding a specific ratio of (RM) to the bed with a smaller

particle size fills the dead zones between the particles and increases the total specific

surface area of the bed leading an increase in the adsorption capacity and the

operating time.

Increasing the (RM) ratio to 50% caused the operating time to decrease as

compared to 33% ratio, but the bed was still achieving slightly higher operating time

and removal efficiency than the pure (0% ratio) (DWTS) bed. In fact, the (RM) has

higher adsorption capacity and higher porosity than (DWTS). Therefore; increasing

the (RM) ratio to 50% causes an increase in the available adsorption sites and the total

adsorption capacity of the bed, and this leads to a decrease in the operating time.

Figure.9 Experimental breakthrough curves for adsorption of phosphate onto different (RM)

ratios, (C₀ =4 mg/L, pH=4, H=25 cm, Temp=25 ⁰C).

6. CONCLUSIONS

The following Conclusions were obtain from this study:-

(DWTS) seems suitable for use as filler for remediation of wastewater

contaminated by phosphate. The laboratory column experiment show the

possibility decrease of contaminants in treated wastewater.

The use of (DWTS) as a reactive medium for the treatment of wastewater ensures

that significant rates of reduction of phosphate are achieved, particularly in cases

in which there is initially a high concentration.

Results from the column study showed that higher initial concentration resulted

in shorter column saturation.

(DWTS) is environment friendly, cost- effective, and locally available adsorbent

for the adsorption of phosphate ions from secondary wastewater effluents.

The effect of different (DWTS) – (RM) weight ratios shows that a significant

decrease in the operating time is achieved by adding different ratios of (RM) to

(DWTS). Adding 33 %, and 50 % (RM) weight ratios to the (DWTS) bed

decreases the operating time by about 18%, and 30% respectively. Increasing the

(RM) ratio to 50% caused the operating time to decrease as compared to 33%

ratio.

Increasing (RM) ratio increasing the removal efficiency and decreasing the

equilibrium time in about 57% and 38% for 50% and 33% (RM) ratio

respectively.

0

0.2

0.4

0.6

0.8

1

1.2

0 1000 2000 3000 4000

Cₑ/

C₀

Time, min.

DWTS

33% RM

50% RM


and Red Mud


One of the important aspects of the present study is represented by considering

the (DWTS) as reactive medium, i.e. not inert. The utilization of these conditions

is logic because the (DWTS) and (RM) may be worked together under the same

field conditions of the continuous flow.

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