Nutrient Removal from Industrial Wastewater Systems Using
Controlled Activated Sludge Treatment
1ILIRJAN MALOLLARI, 2*REDI BUZO, 1ANNA TAKA
1Group of Chemical Process Engineering, Department of Industrial Chemistry,
Faculty of Natural Sciences,
University of Tirana, ALBANIA
2*Department of Biochemistry,
Faculty of Natural Sciences,
University "F.S.Noli", Korça, ALBANIA
Abstract: Biological treatment with activated sludge as an alternative treatment was studied, and
nitrogen and phosphorus were monitored. This scheme involves modifying the treatment tank by
dividing it into anoxic and aerobic sections. According to this scheme, the process simulation was
performed using Hydromantis' GPS-X 7.0 computer software. Wastewater discharges are usually
generated by various industrial activities such as the milk (dairy) processing industry, petroleum
processing refineries and slaughterhouses, which were studied in detail. The economic evaluation
(cost estimation) of removing nutrients has been done using the CapdetWorks 4.0 computer
simulation software. A cost sensitivity analysis has also been performed for the variable influent
flows, altering the alpha factor for oxygen transfer during the aeration process and serving as a
typical variable. The simulation procedure and economic evaluation have been carried out for a
complete wastewater treatment plant, including both treatment lines (the water line and the sludge
line simultaneously), and the derived results have been represented through illustrated graphs,
tables, and meaningful diagrams.
Keywords: industrial wastewater, biological treatment, nutrient removal, activated sludge,
simulation, economic evaluation
Received: February 4, 2023. Revised: November 19, 2023. Accepted: December 22, 2023. Published: March 4, 2024.
1. Introduction
Wastewater results from both human
activities and various industrial processes, as
well. It is well-known that these discharges
contain pollutants of multiple natures that
significantly impact the environment, human
beings, and other living organisms. This is why
they must be treated before their release into
receiving waters [1-3].
Wastewater Treatment Plants are the structures
set up for this purpose. In these plants, a series
of chemical, physical and biological processes
are carried out, which aim at removing
pollutants and bringing the values of the
characteristic parameters of waters back within
the allowed values so that they do not threaten
the environment and the living organisms. The
purpose of this paper is to study the biological
treatment of wastewater using the activated
sludge process. If the conventional natural
treatment scheme is modified, this is a very
efficient treatment process for removing
organic matter and nutrients, such as nitrogen
and phosphorus, from wastewater [4-6].
Using simulation methods, results have been
obtained for the treatment process in two
different configurations: a configuration that
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includes only the biological treatment process
for nutrient removal and a design that provides
for all the treatment processes that take place
in a typical wastewater treatment plant, where
activated sludge is used as a biological
treatment. The economic evaluation for these
two configurations has also been carried out,
and results have been obtained from a cost-
sensitivity analysis of parameters such as the
influent flow or the value of the alpha factor
for oxygen transfer during the aeration process
[7-10].
1.1 Wastewater characteristics
Total water discharges include urban
discharges, industrial discharges and
infiltrations. The characteristics of water
discharges are divided into three categories:
- Physical characteristics (Total Solids,
temperature, colour, turbidity, smell and
odour).
- Chemical characteristics (pH, fat, oil and
grease FOG, nutrients, chemical and
biochemical oxygen demand COD and BOD,
dissolved oxygen DO, chloride content,
metals, etc.).
- Biological characteristics (bacteria, viruses
and protozoa)
The following material describes the
biological method for nutrient removal.
1.2 Biological nutrient removal
Two common nutrients in water discharges are
nitrogen (N) and phosphorus (P). Those two
compounds have to be removed from the
wastewater since they are responsible for the
eutrophication of receiving waters [11-12].
1.3 Nitrogen biological removal
Different forms of nitrogen can be found in
wastewater, and natural degradation can be
performed under other conditions and by
different organisms. Organic nitrogen consists
of a complex mixture of compounds, including
amino acids, sugars and proteins. This form of
nitrogen is usually neglected in wastewater
treatment because it undergoes a biological
process, ammonification, in the sewer system
and is converted to ammonia before arriving at
Wastewater Treatment Plants [1].
There are two different processes for
biological nitrogen removal: nitrification and
denitrification [2]. Oxidation in nitrite is
performed by specific bacteria called
Nitrosomonas, while further oxidation in
nitrate is performed by bacteria called
Nitrobacteria. Both these steps are carried out
under aerobic conditions. During the
denitrification process, nitrates are converted
to nitrogen gas. This process occurs under
anoxic conditions and requires a carbon source
such as methanol [3].
1.4 Phosphorus biological removal
Total phosphorus in wastewater consists of
different forms of phosphorus, such as organic
phosphorus in orthophosphates and
phosphorus in polyphosphates, which undergo
hydrolysis and turn into orthophosphate.
Phosphorus biological removal processes are
related to the alternating exposure of
microorganisms to aerobic and anaerobic
conditions. Phosphorus is used for the growth
of the microbial colony, its maintenance and
energy transport, and is also stored by the
microorganisms for further use. Thus,
phosphorus is also removed with the removal
of microorganisms [4-6]. During anaerobic
conditions, these microorganisms assimilate
the fermentation products of biodegradable
organic matter and produce
PolyHydroxyButyrate (PHB) using the
accumulated polyphosphates as an energy
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source, a process that is accompanied by the
release of orthophosphates. Thus, in the
cellular biomass during anaerobic conditions,
the concentration of PHB increases and that of
polyphosphates decreases [7, 8]. During the
aerobic phase, the PHB is an energy source for
new cell growth. The energy released by the
oxidation of PHB is used to absorb phosphorus
in the cells of microorganisms, thus reducing
its concentration in water discharges. Finally,
the phosphorus-rich sludge is separated from
the treated water [9-12].
1.5 Wastewater Treatment Plants
Wastewater generated by industrial processes
and urban discharges, or municipal
wastewater, must be treated before its final
discharge to receiving waters; for this purpose,
the Wastewater Treatment Plants have been set
up. These plants consist of two treatment lines:
- The first treatment line, also known as the
water line, includes the treatment of water
discharges for pollutant removal [13].
- The second treatment line, also known as the
sludge line, includes the treatment of the
sludge generated from the first line processes
and its final disposal.
The first treatment line includes the following
processes: Pretreatment, Primary treatment,
Secondary treatment, Tertiary treatment, and
Disinfection.
The second treatment line consists of the
following processes: Thickening, Digestion,
Dewatering, and Final disposal.
1.6 Biological Treatment using Activated
Sludge Process
The activated sludge biological treatment
mainly consists of four components: an
aeration tank, a secondary sedimentation tank,
a pump for sludge recycling and distributors
for oxygen supply, as shown in Fig. 1.
Microorganisms come into contact with the
organic matter dissolved in polluted water and
use the energy of chemical bonds between C,
H and other elements as food and for the
growth of the microbial colony.
Fig. 1. Conventional activated sludge process
treatment (source: https://h2omspl.com/activated-
sludge-process-asp/)
Thus, the organic material is broken down into
CO2, H2O, other compounds and more
microorganisms. After the biological reactions
are carried out for a certain amount of time in
the aeration tank, the mixed liquid, ML (the
mass of microorganisms mixed with the
polluted water in the presence of oxygen), is
sent to the secondary clarifier where the solids,
MLSS, are separated from the water
(settling). One part of the sludge is recycled
into the aeration tank, and the remaining is
removed as waste and sent to the second
treatment line. Nutrients such as N and P can
also be removed through biological treatment
by modifying the aeration tank and dividing it
into three sections: anaerobic, anoxic, and
aerobic [14-16].
2. Materials and Methods
For nutrient removal, a process simulation for
a modified activated sludge process treatment
scheme was applied using a GPS-X simulator
by Hydromantis. Samples from different
industries in Albania have been tested
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according to the following order: A specific
library of simulators called "Petrochemical
Wastewater Library (mantisiwlib)" has been
used to simulate the petroleum processing
industry's discharge treatment process [17-18].
The "Comprehensive – Carbon, Nitrogen,
Phosphorus, pH (mantis2lib)" library has been
used for the remaining types of water
discharges, then studies water discharges
generated by slaughterhouses before and after
treatment, followed by water discharges
outflow from the milk processing industry, and
finally water samples coming out from a
petroleum processing industry—the economic
evaluation of those two schemes using
CapdetWorks software, also by Hydromantis.
3. Results and Discussion
Our study was started by constructing a
process diagram (Fig.2) for a modified
activated sludge process treatment scheme for
nutrient removal. Then, the protocol of process
simulation is applied using the GPS-X
simulator issued by Hydromantis Co. The
calculations for the petroleum processing
industry discharge treatment process have
obtained the results.
Fig. 2: Simulation diagram of the treatment
process
Properties of the wastewater from the
petroleum industry are shown in Fig. 3:
3.1. Case of discharges generated by
slaughterhouses
Properties of the wastewater outflow from
slaughterhouses before and after treatment are
shown in Fig.4: Numerical results have been
disciplined in Tables 1 and 2, respectively, for
slaughterhouse wastewater properties before
and after treatment.
Fig. 3: Characteristics of water discharges
generated by the petroleum processing industry
before and after treatment
Fig. 4: Characteristics of water discharges
generated by slaughterhouses before and after
treatment
Table 1. Wastewater parameters before treatment
Water
parameter
Slaughter
houses
Milk
processing
industry
TSS
(mg/l)
1189
730
BOD5
(mg/l)
2454
773.6
COD
(mg/l)
4221
1500
TN
(mg/l)
427
40
TP (mg/l)
50
10
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Table 2. Wastewater parameters after treatment
Water
parameter
Slaughter
houses
Milk
processing
industry
Petroleum
processing
industry
TSS (mg/l)
10.43
5.50
2.73
BOD5 (mg/l)
11.56
11.20
2.39
COD (mg/l)
362.1
93.79
15.72
TN (mg/l)
329.3
3.69
13.84
TP (mg/l)
11.38
6.02
2.01
3.3 The case of properties parameters of
wastewater discharged by a milk processing
industry
The protocols for this case have been applied
as for the previous case studies, and the results
have been presented in Fig.5.
Fig. 5: Characteristics of water discharges
generated by the milk processing industry before
and after treatment
3.4 A sensitivity analysis has been
performed, and the following results
presented in Fig.6 have been obtained:
Figure 6: Nutrients, in mg/L profile variation from
the airflow (in m3/d) into the air tank.
3.4 Economic evaluation
Economic evaluation [9] was performed for
the previewed treatment plant using
CapdetWorks software by Hydromantis. A
process flow diagram is shown in Fig.7
Fig. 7: Process Flow Diagram
Fig. 8: Dependence of the Present worth value and
project cost from the type of treatment plant for
Milk, Slaughterhouse, and Petroleum wastewater,
respectively
A cost estimation procedure has been carried
out for the previewed wastewater treatment
plant design, and the f results are graphically
presented in Fig.8 and Fig.9:
Fig. 9: Dependence of the Annual cost from the
type of wastewater treatment plant for Milk,
Slaughterhouse, and Petroleum wastewater,
respectively
4. Discussions:
Considering the graphs and the table, the cost
values are higher for the water discharges
generated by slaughterhouse treatment. This is
also related to the relatively higher values of
the characteristic parameters of this discharge
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compared to the other types of discharges that
have been studied.
Cost sensitivity analysis showed that the
average influent flow and the alpha factor for
oxygen transfer during the aeration process
were variables.
On the other hand, water discharges from the
milk processing industry showed variations in
Fig. 10. The rest of the water discharges
studied follow the same trend.
Fig. 10: Variation of the project cost vs. average
flow (m3/d).
5. SIMULATION FOR A COMPLETE
WASTEWATER TREATMENT PLANT
A complete plant simulation was then
performed using a GPS-X computer simulator,
and the following results have been obtained.
The whole plant flow diagram was firstly
constructed for the complete treatment
processes (shown in Fig.11) for the influent
wastewater characteristics, which, as can be
seen, are of an approximate value to typical
ones found in real applications.
Fig. 11: Simulation diagram of the treatment process
Fig. 12. Characteristics of water discharges before
and after treatment
Total Wastewater discharges' parameters
before and after treatment:
A dissolved oxygen (DO) profile.
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This was monitored, calculated through a
simulation process, and presented graphically
(Fig.13).
Fig. 13: Dissolved Oxygen profile
Economic evaluation for the entire
treatment plant
Later, an economic assessment for the partial
and total project was carried out (Fig 14, 15)
using Capdet Works software, and the
following results have been obtained:
Fig.14: Partly Process Flow Diagram
Fig. 15. Sankey Diagram regarding the plant
capacity.
A sensitivity analysis has been performed, and
the relevant results have been obtained:
Fig. 16: Illustrative Diagram of the total
energetic expenditures
Last consideration for the entire project
The objective of this paper was to study the
biological treatment of wastewater using the
activated sludge process (Fig.17). Focusing on
nutrient removal, a modified treatment scheme
was reviewed, which consisted of two divided
treatment zones with different aeration
conditions, an anoxic zone and an aerobic one
(Fig 18).
Fig. 17: Schematic presentation of the biological
treatment of wastewater using the activated sludge
process.
6. Experimentation in the Pilot Plant
To study the biological treatment process of
water discharges with activated sludge,
experimentation can be carried out in the
activated sludge treatment pilot plant
"PPFAC" monitored and computer-controlled
by SCADA software from EDIBON Ltd
(Spain). The main parts of the pilot plant and
the working principle are described below.
6.1. Description of the pilot plant and the
treatment process
The activated sludge treatment process
consists of three main components:
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the biological treatment tank, where the
polluted water is brought into contact with
microorganisms,
clarifying container for separating sludge
from treated water,
Active sludge recycling system from the
clarification vessel to the biological treatment
tank.
The pilot plant for computer-controlled
activated sludge treatment, or otherwise
Computer Controlled Activated Sludge
Process Unit, "PPFAC", is designed to treat
water discharges using activated sludge. The
main parts of the planned plant are also
described here, as well as the treatment
process.
Fig. 18: Total Process Flow Diagram constructed
with computer software CapdetWorks.
As a result of the simulation, the modified
scheme was highly effective, as the values of
the water parameters were significantly
reduced. However, the nutrient values could
have been further reduced, and a way to
achieve that could be by adding an anaerobic
tank in the treatment process. A complete
wastewater treatment plant scheme with the
activated sludge process was also studied
(Fig.18). This scheme led to biogas
production. Adding a two-stage anaerobic
digestion process can enrich this product in
methane. Illustrative drawings and
accompanying figures show the pilot plant's
main parts below.
7. Conclusions. In this paper, the biological
treatment of water discharges using activated
sludge was studied based on a modified
scheme, which, in addition to the removal of
organic matter, also removes nutrients. Water
discharges generated by the milk processing
industry, petroleum processing industry and
slaughterhouses were studied, and the
reduction rate of water parameters after
treatment are shown in the table below:
Table 3. Decreasing rate of water parameters after
treatment
The reduction rate of water parameters
after treatment (%)
Wastewater type
TSS
BOD
5
COD
TN
TP
Slaughterhouses
99.12
99.53
91.42
22.88
77.2
Milk processing
industry
99.25
98.55
93.75
90.77
39.8
Petroleum
process industry
96.48
97.99
92.51
68.60
79.9
Using simulation methods, a sensitivity
analysis of the nutrient profile was carried out,
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with the airflow into the aeration tank as a
variable, and it turned out that with the
increase of the airflow, the nutrient
concentrations decreased. The economic
evaluation was carried out, and a cost
sensitivity analysis was performed with the
average influent flow and the alpha factor for
oxygen transfer during the aeration process as
variables. It resulted in an increase in the
influent flow, which increased the cost values.
In contrast, with the rise of the alpha factor's
value, the cost values decrease because the
aeration process is carried out more efficiently.
Also, the simulation and economic evaluation
of a complete wastewater treatment plant that
includes both the water and the sludge lines
was carried out. After treatment, the values of
the characteristic parameters of water
discharges were reduced by 87% for TSS, 93%
for BOD5, 88% for COD and 31% for total
nitrogen and total phosphorus. As a result of
anaerobic digestion, biogas is produced, a
mixture of mainly CH4 and CO2 gases, in
fractions of 54% and 45%, respectively. This
biogas can generate electricity for the
treatment plant or distribution to the network.
From cost sensitivity analysis, it turned out that
with the increase in the influent flow, the cost
values increase. In this work, the biological
treatment of water discharges using activated
sludge was studied, and the modified scheme
was treated, which, in addition to the removal
of organic matter, also removes nutrients such
as nitrogen and phosphorus. The process
simulation was carried out based on the pilot
plant "PPFAC" configuration, which includes
modifying the treatment tank to remove
nutrients employing the GPS-X 7.0 simulator
from Hydromantis. The simulation showed
that the treatment process with activated
sludge is efficient, leading to a decrease in the
values of parameters such as BOD5, COD,
TSS, nitrogen and total phosphorus and an
increase in the concentration of dissolved
oxygen in the water. The central part of the
energy costs in the plant is related to the
aerobic treatment process. The central part of
operational costs in the plant is also related to
the aerobic treatment process.
Then, the economic evaluation of this
treatment process was carried out using
CapdetWorks 4.0 software from Hydromantis.
From the economic evaluation, some results
were obtained with corresponding values for
different cost items for the main processes of
the plant, where an essential part of the values
was related to the aerobic and anaerobic
treatment process. An analysis of the
sensitivity of different cost items was carried
out about the flow at the plant entrance, from
which it was found that with the increase in the
flow of water discharges to be treated, the
operational cost, maintenance and energy cost
values increase. The analysis of the sensitivity
of different cost items to the value of the alpha
factor for the transfer of oxygen during the
aeration process was also carried out. With the
increase in the value of this factor, the
operational cost, maintenance and energy cost
values decrease after the ventilation process is
carried out with higher efficiency. Also, the
simulation and economic evaluation of a
complete water discharge treatment plant was
carried out, including both treatment lines, the
treatment of the water mass and the treatment
of the sludge. The simulation showed that the
complete treatment process was very efficient
as treated water was obtained with low values
of the relevant parameters. This was also
noticed by the results of a sensitivity analysis
that was carried out for several parameters,
from the airflow to the aeration tank. As
expected, operational and energy costs for this
plant were higher than in the treatment process
based on the pilot plant configuration.
However, their central part was related to the
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aerobic treatment process. However, a
significant amount was related to the anaerobic
treatment and anaerobic digestion. Due to
anaerobic digestion, biogas is also obtained, a
mixture of mainly CH4 and CO2 gases in 54%
and 45% fractions. This biogas can generate
electricity for the treatment plant or
distribution to the network.
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