Results in Engineering 24 (2024) 103052
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Case report
Microalgae cultivation for dairy wastewater treatment: Insight from recent
research and bibliometric analysis
Motasem Y.D. Alazaiza a,* , Tharaa M. Alzghoul b,c, Salem S. Abu Amr d ,
Madhusudhan Banglore Ramu a
a
Department of Civil and Environmental Engineering, College of Engineering, A’Sharqiyah University, 400, Ibra, Oman
Department of Civil Engineering, Faculty of Engineering, Tafila Technical University, Tafila, 66110, Jordan
Department of Civil Engineering, School of Engineering, The University of Jordan, Amman, 11942, Jordan
d
International College of Engineering and Management, P.O.Box2511, C.P.O Seeb, P.C. 111, Oman
b
c
A R T I C L E I N F O
A B S T R A C T
Keywords:
Bibliometric analysis
Bioenergy
Biofertilizers
Biomass
Dairy wastewater
Microalgae
Nutrient removal
Research trends
VOSviewer
With the continuous increase in dairy production, large amounts of wastewater containing organic matter and
nutrients are generated. Finding effective methods for treating dairy wastewater (DWW) is vital for protecting
the environment and water resources. In this context, microalgae cultivation emerges as a promising technology
for treating DWW and producing biofuel at the same time. This bibliometric study aims to analyze the published
research on the use of microalgae in treating DWW. The primary research trends and specific challenges and
opportunities in this field will be explored. A bibliometric analysis of 126 articles and review articles in this field
from the Scopus database was conducted. The analysis also shows that slightly over 69 % of the publications
were published in the last five years, implying growing concern about the cultivation of microalgae to treat
DWW. As per the findings of the conducted research, the three most important journals in this field include
Bioresource Technology, Environmental Science and Pollution Research, and Algal Research. Significant con­
tributors to the research were India, China, the US, Iran, Italy, South Korea, Taiwan, and Greece with Tunghai
University and National Cheng Kung University. The primary research direction in this field is properly indicated
by the frequently used keywords related to microalgae cultivation in DWW that were identified, including
"Microalgae," "Dairy Wastewater," "Wastewater Treatment," "Nutrient Removal," "Biomass," and "Biodiesel."
Chlorella vulgaris, Cyanobacteria, and Scenedesmus obliquus are common species of microalgae used to treat
DWW.
1. Introduction
cleaning, washing, sterilization, and floor washing, thus contributing to
the release of a relatively large amount of wastewater [8]. Dairy
wastewater (DWW) includes detergents used in washing, materials used
for sterilization, fats, lactose, acetate, lactate, nutrients, wasted milk,
and soluble proteins [9]. In this sector, according to Shete and Shinkar
[10], Boguniewicz-Zablocka et al. [8], and Labbé et al. [11], about 10
m3 of total water is consumed per 1 m3 of milk, thus between 0.2 and 10
L of DWW is produced for each 1 L of milk.
Due to the difference in season and system of milking, the charac­
terization of DWW is highly fluctuating, including biological oxygen
demand (BOD) 40-48,000 mg/L, chemical oxygen demand (COD) 8095,000 mg/L, total nitrogen (TN) 14-830 mg/L, total phosphorus (TP)
9-280 mg/L, total dissolve solid (TDS) 50-25000 mg/L, and total
Today the world faces constant growth and increase of populations
and urbanization leading to high pressure on water, its availability and
quality [1]. It is apparent that clean water needs are not only confined to
the developing countries but also in the developed ones, whereby water
shortages have become almost permanent owing to pollution from ur­
banization and industry [2,3]. Some of the industrial sectors that cause
the highest demands of water include petroleum refining [4], carwash
[5], textile manufacturing [6], pharmaceuticals [7], and dairy industry
[3]. Thus, it results in the generation of large amounts of different kinds
of wastewater. The dairy industry is one of the world’s largest food in­
dustries, and on a daily basis they use a substantial volume of water in
* Corresponding author.
E-mail addresses: my.azaiza@gmail.com (M.Y.D. Alazaiza), tharaaalzghoul@gmail.com (T.M. Alzghoul), s.abuamr@hotmail.com (S.S. Abu Amr), madhusudhan.
ramu@asu.edu.om (M.B. Ramu).
https://doi.org/10.1016/j.rineng.2024.103052
Received 28 August 2024; Received in revised form 17 September 2024; Accepted 2 October 2024
Available online 3 October 2024
2590-1230/© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/bync/4.0/).
M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
suspended solid (TSS) 10-23000 mg/L [12–15]. Macronutrients and
some micronutrients are also more or less prominent in DWW, with the
presence of Ni, Co, Fe, Na, K, Cl, and Mg at some levels [16]. This
wastewater, when discharged directly into water bodies without the
necessary treatment, poses severe environmental and health issues such
as polluting water bodies and harming aquatics and the sustainability of
the scarce water resource [17,18], affecting lands and the environment
[10,19], and its effects resulting in oxygen decrease because of fuel algal
blooms caused by excess nutrients, N and P, which highlights the process
of biofermentation of the natural water bodies and creates imbalance in
the environment [10,20,21]. Hence, proper treatment before its
discharge into the environment is required to mitigate environmental
threats [8]. However, this effluent, which contains N and P, could be a
rich source of nutrients that can be utilized for the growth of microalgae
[22–24].
Several authors have investigated the role of microalgae in the
removal of various pollutants from wastewater during the last decades
and have received great attention due to their advantages [25,26].
Moreover, the application of microalgae leads to a combination between
DWW treatment and the production of valuable compounds [27]. One
benefit of cultivating microalgae in DWW is the production of biomass
utilizing minerals, N, P, and carbon without the need of additional nu­
trients [11,28,29]. The production of algal lipid, which may comprise
about 70 % of the dry cell weight and is easily transformed into bio­
diesel, which is currently utilized as a fossil fuel substitute, has drawn
particular attention [30,31]. Existing natural resources are being
consumed more quickly than they are replenished due to the depletion
of fossil fuel supplies and the growing shortage of water and food [21,26,
32]. The generation of raw materials for different applications using
microalgae is limited by the high cost of synthetic medium [13]. As a
result, using wastewater for microalgae cultivation has emerged as a
substitute to lower processing costs and produce biomass from micro­
algae that has a variety of uses [33]. Using microalgae cultivation in
wastewater has several benefits, including lowering the effluent’s COD
and BOD levels [11,34], eliminating P and N from wastewater utilizing
only solar energy, producing biomass [34,35], bioremediating DWW at
a low cost [11], and potentially extracting high-value products like
carbohydrates and lipids for use in the chemical industries, nutraceuti­
cal, and pharmaceuticals [11].
Many previous studies have focused on the efficiency of microalgae
cultivation processes in removing pollutants from DWW [21,36],
nutrient recovery and by-product production of biofuels through
microalgae cultivation processes [22], and focusing on the microalgae
products, species, biomass market, and pretreatment processes used for
extraction [37]. Despite all these aspects, more comprehensive studies
are still needed to understand other aspects of using microalgae in DWW
treatment. Therefore, developing a thorough grasp of the research
environment and spotting emerging tendencies and directions in this
field will be essential for developing practical and economical applica­
tions of this process in the future.
Nevertheless, the use of bibliometric analysis, which is involved in
the use of statistical and mathematical techniques, is deemed vital in as
much as the ability to forecast future research advancement within a
certain area of specialization [38,39]. One of the most effective methods
for both qualitative and quantitative analyses of scientific endeavors is
bibliometric analysis [40,41]. Co-citation analysis is the study of citation
relationships among documents; bibliometrics deals with the quantity of
documents as well as their external attributes like books, articles, pat­
ents, and their references [40,42]. This allows the researcher to define
and subsequently analyze quantitative relationships within a particular
research field, making new research directions apparent [43,44]. In
assessing the extent of the study output of countries, organizations, and
individuals in a given specialization area, then bibliometric data that
can be obtained from bibliographic analyses contain useful information
that gives a general overview of research and helps to locate new fronts
for research [43,45]. Thus, bibliometric analysis helps researchers to
obtain an improved understanding of the current knowledge, the iden­
tification of significant publications, and the assessment of the trends in
a particular scientific field, which indicates the directions for further
research. These analyses offer information about the focal concepts as
well as the dynamic processes of a particular field of study [40,46,47].
In this framework, our research intends to conduct temporal bib­
liometric analysis of the review articles and articles on cultivation
microalgae in DWW, specifically to quantitatively investigate the char­
acteristics such as number of publications, subject area, top production
of journals, most active authors and countries, co-authorship between
countries, and finally to identify the new thematic areas and research
gaps related in this field. Therefore, to complement the previously
mentioned in previous research. This study applied bibliometric analysis
to both quantitatively and qualitatively assess the publications outlining
cultivation microalgae in DWW between 2010 and 2024. The papers for
analysis have been retrieved from the Scopus databases, concentrating
on the research articles and review articles only.
2. Materials and methods
2.1.1. Data source and search strategy
In this research, the methodology applied to review the literature
was done using the PRISMA checklist [42]. As for the type of
meta-analysis, we followed PRISMA guidelines while not including
meta-analysis techniques into the analysis. In systematic literature re­
views, bibliometric analysis is one of the valuable procedures for accu­
mulating the large and replicable database [42]. While doing
bibliometric analysis, one should distinguish very well the objectives of
the study and give detailed accounts of how the materials that are
pertinent to the study were identified. The expansiveness in the accep­
tance and success of bibliometric analysis could be said to be because of
its ability to offer an integrated outline of the research sector, outputs,
organizations, and trends [45,48]. They can be used on a large scale for
the review and assessment of immense scholarly data to understand the
association between journal citations and offer an outlook on the
existing or emergent area of study [49]. Strengthening of further
research and development could be served by bibliometric analysis and
its implications stated by researchers [44]. Because of these character­
istics, bibliometric techniques are applied in many and various sciences
[50,51].
As to track the directions and developments of cultivation micro­
algae in DWW treatment studies, this paper employed bibliometric
analysis. Publication analysis was carried out using the Scopus database
for the period 2010 to July 2024. The choice of the Scopus database was
made because of the database’s inclusion of all fields of study and
richness in published articles in the literature field [46–48]. The
following query string and the given keywords were utilized to do a
literature search: "(TITLE-ABS-KEY (("Wastewater treatment") AND
("Microalgae" OR "Algae" OR "Micro algae") AND ("Dairy" OR "Dairy
effluent" OR "DWW") AND ("Biodiesel" OR "Bioenergy" OR "Biomass" OR
"Biofertilizer" OR "Biogas")) AND PUBYEAR >2009 AND PUBYEAR
<2025 AND (LIMIT-TO (SRCTYPE,"j")) AND (LIMIT-TO (LANGUAGE,
"English"))). The methodology of searching is illustrated in the following
Fig. 1.
As depicted in Fig. 1, based on the keywords, our first search yielded
a total of 146 publications that are in the form of articles, conference
articles, review articles, and book chapters. After then, we proceeded to
filter this corpus down to only consist of journal articles and review
articles in the English language only. After this filtering process, 126
publications were selected.
2.2.2. Data extraction and filtering
After extracting data and arranging it in the Scopus database, the
Comma-Separated Values (CSV) files were created. In the process of
2
M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
Fig. 1. Research methodology.
selecting the sources, several procedures of filtering were applied to
ensure the reliability and accuracy of the data. In these phases, such
processes were implemented like removing the redundancy and
applying inclusion and exclusion criteria based on language, document
type, and source. Once records were segmented and searched, each year,
the name of the source, authors, and their affiliations were studied
meticulously. In addition, it was considered the quality of the found
documents in the title of the document, abstracts, and keywords sec­
tions. Unfortunately, any incomplete or erroneous records had to be
properly expelled based on the data filterization process to bring the
data set into better shape before subjecting it to other forms of analysis.
results and get acquainted with the outlines of bibliometric results, we
downloaded the data for VOSviewer 1.6.20 software processing. VOS­
viewer 1.6.20 software, which is an open-source, easy-to-use program, is
used for networking and visualization of bibliometric data [42]. It dif­
fers from other software applications, CiteSpace, SciMAT, Gephi, and
Bib Excel, in some ways [52,53]. Data processing and analysis were done
utilizing VOSviewer 1.6.20 software because it can handle networks of
highly sizeable dimensions and also possesses text-mining capabilities
[50]. Concerning the identification of relations, trends, and patterns in
the literature, bibliometric maps were generated with VOSviewer 1.6.20
software, where the connections between the selected articles are
visualized [54]. One of the strengths of the program encompasses the
fact that the program can dynamically change the labels in use and
thereby suits the purpose of the algorithm to display co-occurrences
[54].
Three primary areas of focus for the analysis were the nations of
origin, the author keywords used in the papers and journals where the
articles have been published, and the article database. These
2.3.3. Data analysis
In the bibliometric studies, the habit of constructing, illustrating, and
displaying the bibliometric maps for readability. The work with litera­
ture and recognition of relations between certain sources seems to be
less complicated due to this approach. Since we were to analyze the
3
Results in Engineering 24 (2024) 103052
M.Y.D. Alazaiza et al.
components offer a comprehensive overview of the condition of the
research, which makes them essential for bibliometric investigations
[55,56]. Total link strength (TLS), average normalized citations, and
publications were all taken into account while choosing the parameters
for the analysis. These measurements are useful in determining the ar­
ticle’s visibility and impact [57].
Upon conducting the search, a total of 126 documents were
retrieved, comprising 113 journal articles and 13 review articles. These
documents were obtained from 53 unique publication sources or venues.
An extensive pool of 544 authors contributed to the literature on the
subject, representing 331 different institutions worldwide. Geographi­
cally, authors from 38 countries made significant contributions to the
literature. The cumulative impact of these 126 documents was evi­
denced by a total of 4621 citations, underscoring their influence within
the academic community. Further insight into the research focus of the
literature was gleaned from the analysis of author-supplied keywords,
revealing a rich tapestry of 431 unique terms. Table 1 succinctly sum­
marizes the key bibliometric findings derived from the examination of
the literature on cultivation microalgae in DWW treatment.
By examining the distribution of publications on DWW treatment,
this study provides trends in the production of microalgae in DWW
research. An examination of the major research subjects during the
previous several decades is presented in Fig. 3. The use of microalgae
cultivation in the management of DWW is a multidisciplinary subject
with intimate ties to several scientific domains.
First, the category of “environmental sciences” (35.63 %) plays a
major role in this topic, as it includes the study of the impact of DWW on
the environment and the technologies used to treat it in an environ­
mentally friendly way. Environmental sciences are concerned with un­
derstanding and evaluating the environmental impacts of DWW and
developing sustainable bioremediation technologies using microalgae.
The category of “energy” (17.24 %) is also closely related, as microalgae
can be utilized as a source of renewable energy and the production of
biofuels from DWW.
Second, the category “Chemical Engineering” (16.48 %) contributes
to the design, development, and optimization of methods necessary for
the treatment of DWW using microalgae. The categories of “Agricultural
and Biological Sciences” (6.9 %) and “Microbiology and Immunology”
(1.92 %) provide the scientific and technical basis for the cultivation and
development of microalgae suitable for DWW treatment, while the
microbiology and immunology study the behavior and interactions of
microorganisms involved in biological water treatment processes using
microalgae.
Third, the categories of “Biochemistry, Genetics, and Molecular
Biology“ (5.75 %), “Engineering” (4.21 %), and other categories such as
“Medicine“ (2.68 %), “Social Sciences“ (2.5 %), and “Chemistry“ (2.3 %)
contribute to the development of practical, economic, and social appli­
cations for the application of microalgae in the treatment of DWW.
Overall, it is clear that the treatment of DWW using microalgae
cultivation is a multidisciplinary topic that combines environmental,
engineering, biological, and social sciences, emphasizing the importance
of integration between these fields to develop effective and compre­
hensive solutions to this important environmental problem. With this
integration between these diverse scientific fields, integrated and
effective solutions can be developed for the treatment of DWW using
microalgae cultivation.
3. Results and discussion
3.1.1. Trend of annual publications
The changes in the number of published articles on cultivation
microalgae in DWW and six main Scopus subject categories are illus­
trated in Fig. 2a. The Scopus database search outcomes of research
documents in this field, published between 2010 and July 2024, were
126 documents. The most common type among them is "articles," which
makes up 113 articles, or 77.4 % of all publications. "review articles"
(8.9 %), "conference articles" (4.8 %), and others (such as "book chap­
ters" and "not journal") make up the remaining publication categories.
Since “articles” and “review articles” accounted for the largest part of
publications, the other categories were not considered any further.
Concerning the trend of annual publications, their representation in
the context of cultivating microalgae in DWW treatment shown in
Fig. 2b reflects evolutionary changes and dynamics of the research ac­
tivity over the last decade, with a total of 126 articles before July 2024.
Starting in 2010, the number of publications steadily increased over the
years, with a notable acceleration in the rate of publication from 2020
onwards. In particular, there is a significant spike in 2023, where the
number of publications reaches its peak at 23. This surge suggests a
heightened interest and emphasis on cultivation microalgae in DWW
treatment during that year, likely to be driven by the growing interest in
using a low-cost, environmentally sustainable treatment method and its
potential as a renewable energy source through conversion to biofuel,
making it a valuable by-product for DWW treatment. Regarding 2024,
it’s important to note that the data only covers the period until July 31,
2024. Up to that point, there have been 14 publications recorded for the
year, indicating a continuation of research activity in the field. While
this number may represent a decrease compared to the peak observed in
2023, it’s essential to consider that the year is not yet complete and
other publications may still be on the way. Thus, the number may
potentially be higher in the final count for 2024 regarding the publi­
cations at the moment.
3.2.2. Leading journals for studies on the use of microalgae to treat DWW
Table 2 offers an overview of the top 19 sources that have been
prolific in publishing literature focused on the DWW treatment by
microalgae, which also includes information on each source’s total ci­
tations, TLS, h-index, and SCImago Journal Rank (SJR). The publica­
tions on the treatment of DWW by microalgae are primarily
concentrated in several high-impact scientific journals. Leading the list
are "Bioresource Technology" and "Science of the Total Environment,"
with 25 and 8 publications, respectively, and 1613 and 998 total cita­
tions, respectively, indicating the substantial contributions to the
dissemination of research in this field. Closely following are "Environ­
mental Science and Pollution Research," "Algal Research," "Journal of
Environmental Chemical Engineering," and "Journal of Environmental
Management," each with 7, 7, 6, and 5 publications, respectively, and
301, 361, 233, and 141 total citations, respectively. These journals have
played a significant role in publishing scholarly work on the DWW
treatment by microalgae.
Other notable sources include "Biomass Conversion and Biorefinery,"
"Journal of Applied Phycology," "Sustainability (Switzerland)," "Envi­
ronmental Research," "Scientific Reports," and "Journal of Cleaner Pro­
duction," each with 3 publications, each with 34, 16, 18, 133, and 475
total citations, respectively. These journals further underscore the
breadth and depth of research published on this topic.
Additionally, "Water Research," "Biochemical Engineering Journal,"
"Chemosphere," "Environmental Technology (United Kingdom)," "Fron­
tiers in Bioengineering and Biotechnology," "Journal of Environmental
Health Science and Engineering," and "Water Science and Technology"
Table 1
Summary of key bibliometric results.
Description
Results
Publications (113 journal articles and 13 review articles)
Total Citations
Authors
Author Keywords
Publication venues
Authors’ Affiliations
Countries
126
4621
544
431
53
331
38
4
M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
Fig. 2. (a) The proportion of document type reports for cultivation microalgae in DWW research; (b) annual publications related to cultivation microalgae in DWW
research, as determined by the Scopus database until July 2024 (n = 126).
have also significantly contributed to the scholarly discourse, each with
2 publications and 130, 54, 43, 14, 7, 29, 3, and 31 of total citations,
respectively.
The primary sources were determined to be journals with two or
more publications published in this field of study between 2010 and
2024. Fig. 4 shows that 19 of the sources that were located met these
criteria. The main sources of information for research on DWW treat­
ment by microalgae are these 19 journals, which are also crucial to the
field’s advancement.
Overall, these top sources represent important platforms for re­
searchers to disseminate their findings, contribute to the advancement
of knowledge, and foster dialogue within the scientific community
regarding cultivation of microalgae in DWW for treatment. Their
consistent publication output underscores their commitment to facili­
tating the exchange of ideas and driving innovation in this critical area
of environmental science.
3.3.3. Country collaboration network related cultivation microalgae in
DWW
The present bibliometric analysis provides an overview of the lead­
ing countries in terms of their contributions to publications within the
field of DWW treatment by microalgae. Table 3 summarizes the key
statistics, including the number of publications and corresponding
citation counts for the top contributing nations. India emerges as the
global leader in this research area, with 38 published documents and a
total of 1536 citations. China, the United States, and Iran follow closely,
contributing 19, 14, and 10 publications, respectively. While China’s
total citation count stands at 1,081, the United States has a higher
impact with 1339 citations. Iran’s publications have garnered 513
5
M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
Fig. 3. Scopus publications categorized by subject.
citations in total. Italy presents a significant contribution of 9 docu­
ments, with a substantial impact reflected in 342 total citations. South
Korea, Taiwan, and Greece each contribute 8 publications, with citation
counts of 498, 81, and 350, respectively. Malaysia’s 7 documents have
accumulated 491 citations, while Brazil’s 6 publications have 180 ci­
tations. Australia and Hong Kong also demonstrate notable involvement,
each contributing 5 publications. These documents have received 305
and 87 citations, respectively, underscoring the substantial impact of
their research efforts in the field of DWW treatment by microalgae.
Overall, this analysis highlights the global distribution of research ac­
tivities and the varying degrees of impact achieved by different coun­
tries in this emerging scientific domain.
The treatment of DWW through the cultivation of microalgae has
emerged as a global research focus, given the high treatment efficiency
of this approach [21]. To gain a comprehensive understanding of the
current state of research in this field, a bibliometric analysis of the
published literature is warranted.
Research collaboration, defined as the joint production of scientific
knowledge, is a prevalent model in this domain [58]. Collaborations can
occur at various levels, including between individual authors, in­
stitutions, and countries [58]. To examine the network of international
collaborations, a network diagram was constructed using VOSviewer
1.6.20 software. In this diagram, the participating countries are repre­
sented as labeled nodes, and the lines that link the nodes show how
much each nation contributed to the overall work. The size of the nodes
represents the quantity of citations that the publications from each
nation have earned, while the thickness of the lines represents the
strength of the collaborative links [59].
The network analysis revealed that 12 countries have demonstrated a
significant interest in researching DWW treatment through microalgae
cultivation, as illustrated in Fig. 5. The countries with the most promi­
nent roles, as evidenced by the larger node sizes and thicker connecting
links, are likely to be at the forefront of this field of research. This in­
formation can serve as a valuable indicator of the global landscape of
research activities and the influential players driving the advancement
of DWW treatment processes using microalgae.
Table 2
The top 19 sources by citation count for DWW treatment by microalgae research.
Source Journal
TLS
Total Number
of Documents
Total
Citations
Hindex
SJR
Bioresource Technology
Environmental Science
and Pollution
Research
Algal Research
Science of the Total
Environment
Water Research
Biomass Conversion and
Biorefinery
Journal of Applied
Phycology
Journal of
Environmental
Management
Biochemical
Engineering Journal
Chemosphere
Environmental
Technology (United
Kingdom)
Frontiers in
Bioengineering and
biotechnology
Journal of
Environmental
Chemical Engineering
Sustainability
(Switzerland)
Environmental Research
Journal of
Environmental Health
Science and
Engineering
Scientific Reports
Water Science and
Technology
Journal of Cleaner
Production
57
24
25
7
1613
301
364
154
2.576
0.944
13
12
7
8
361
998
100
353
0.954
1.998
12
8
2
3
130
34
354
45
3.338
0.595
6
3
16
137
0.605
6
5
141
218
1.678
4
2
54
143
0.718
4
4
2
2
43
14
311
84
1.806
0.546
3
2
7
101
0.893
3
6
233
127
1.355
3
3
18
169
0.672
2
2
3
2
133
29
179
63
1.679
0.673
2
2
2
2
3
31
315
153
0.900
0.548
1
3
475
309
2.058
6
M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
Fig. 4. Co-occurrence map of journals published in 2010–2024 that have more than two publications pertaining to the use of microalgae to treat DWW.
literature [48]. This method facilitates the identification of researches
that are frequently cited together, thereby revealing the underlying
conceptual frameworks and thematic connections within a research
domain. In the present study, we conducted a comprehensive co-citation
network analysis utilizing the VOSviewer 1.6.20 software. This analyt­
ical approach allowed us to obtain valuable insights into the groups and
interrelationships among the publications in the field of interest. Table 4
presents the results of this thorough examination, providing a detailed
understanding of the current state of the article in this area. The authors
identified through this co-citation network analysis have demonstrated
remarkable dedication and expertise in advancing the scholarly work
within this domain, as evidenced by their prolific publication outputs.
This information serves to highlight the influential figures and seminal
works that have shaped the conceptual foundations and intellectual
discourse surrounding the topic under investigation.
The dataset under analysis comprises 126 articles, representing the
contributions of 544 unique authors. Interestingly, a few authors have
contributed to several publications, demonstrating a special interest in
this field of study. The pertinent data pertaining to the most prominent
authors is shown in Table 4, together with the quantity of publications
and citations their writing has accumulated. It is crucial to recognize
Table 3
Leading 12 nations through publishing on the use of microalgae to treat DWW
from 2010 to 2024 (ranked by TLS).
Country
TLS
Number of publications
Total Citations
India
China
South Korea
United States
Italy
Taiwan
Malaysia
Greece
Iran
Australia
Brazil
Hong Kong
3175
2425
1410
1369
1210
1120
1100
674
652
489
484
482
38
19
8
14
9
8
7
8
10
5
6
5
1536
1081
498
1339
342
81
491
350
513
305
180
87
3.4.4. Co-citation authors network in DWW treatment by cultivation
microalgae study
Co-citation author network analysis is a well-established biblio­
metric technique that enables the systematic mapping of the existing
Fig. 5. A network visualization displaying the primary nations taking part in the research examining the utilization cultivation of microalgae to treat DWW.
7
M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
microalgae. The study began with the isolation of environmental algal
strains stored DWW tanks (treated) and DWW tanks (untreated) in a
dairy farm (Perlis, Malaysia). A group of environmental strains suitable
for use was then selected based on analysis of cellular lipid content using
Nile red (NR) staining to form consortium members. Afterwards, pre­
liminary studies were conducted on culturing two groups of commercial
and environmental strains in DWW, and the cultivation of the environ­
mental strain was shown to be successful. The ability of a consortium of
native strains set of 10 strains to remove more than 98 % of nutrients
from the treated DWW was tested. The lipid content and biomass pro­
duction of the consortium cultivated in the treated DWW were
measured, which were 29.47 thousand L/ha/year (16.89 %) and 153.54
t/ha/year, respectively. It was found that 72.7 % of the algal oils pro­
duced could be converted into biofuel. In conclusion, this study
demonstrated that DWW can support the growth of a group of local
environmental algae and produce biodiesel with high efficiency, with
the ability to effectively remove nutrients and organic matter from
treated DWW [61].
The study that is second most referenced on the list has 161 citations.
The scholarly essay named "Sequential cultivation of microalgae in raw
and recycled dairy wastewater: Microalgal growth, wastewater treat­
ment, and biochemical composition" was authored by Ref. [12] and
appeared in Bioresource Technology in 2019. This study investigated
the reuse of DWW in two successive microalgae culture cycles. In the
first step, the one cycle of heterotrophic and two cycles of mixotrophic
cultivation of freshwater Scenedesmus quadricauda and marine (Tet­
raselmis suecica (Ts) microalgae in DWW was studied. After the first
12-day cultivation cycle, the microalgae biomass was harvested by
centrifugation, and the DWW was collected for reuse in the second cycle.
The cultivation of microalgae, lipid profile, pollutant removal efficiency,
and pigment content were evaluated in both cultivation cycles. The
study’s findings demonstrated that Ts and Sq developed throughout the
first and second cycles of mixotrophic culture in DWW, registering
growth rates of 0.61 and 0.43 g/L and 0.65 and 0.36 g/L, respectively.
Efficient removal of pollutants by Sq was achieved after the two cycles of
culture. The fatty acid composition was different depending on the type
of marine or freshwater algae, the culture cycle (first and second), and
the culture mode (heterotrophic and mixotrophic). The outcomes indi­
cated that reusing DWW in two consecutive cycles of microalgae culture
could lead to higher pollutant removal efficiency and higher algal
biomass production. The Sq demonstrated high removal efficiencies for
100 % of sulfate (1), 100 % of phosphate (PO3−
4 ), 92.15 % of total ni­
trogen (TN), and 76.77 % of TOC over the two cycles. The dominant
fatty acids also differed between the 1st and 2nd cycles, as well as be­
tween the freshwater and marine microalgae species [12].
The third top-cited study by Daneshvar E., published in the journal
Bioresource Technology, which has 160 citations, has the title "Versatile
applications of freshwater and marine water microalgae in dairy
wastewater treatment, lipid extraction and tetracycline biosorption"
[62]. This study differs from the previous study by the same researcher
[12] in that it dealt with the cultivation of two species of algae, fresh­
water (Sq) and marine (Ts), under heterotrophic and mixotrophic con­
ditions in DWW. The results showed good growth of both algae species
in DWW without adding N and P, with the maximum biomass produc­
tion reaching 0.61 g/L for the marine algae Ts after 12 days and 0.47 g/L
for the freshwater algae Sq after 8 days. In terms of pollutant removal
efficiency, Sq algae achieved high removal efficiency of 70 % sulfate, 85
% PO3−
4 , 80 % TOC, and 90 % TN from DWW. Furthermore, the fatty
acid composition of algae grown in artificial culture medium and DWW
was analyzed, and differences in the relative composition of fatty acids
were shown. The potential of using the remaining biomass after lipid
extraction to remove tetracycline (TC) antibiotic from water was also
investigated, with the maximum adsorption capacity reaching 295.34
and 56.25 mg/g for Sq and Ts algae, respectively [62].
There are differences between the two studies presented by the same
author. The first study [12] aimed to study the potential of reusing DWW
Table 4
Co-occurrence map 2010-2024 researcher collaboration.
Author
No. of Publications
Author
Total Citation
Chang, jo-shu
Venkata Mohan, S.
Kusmayadi, A.
Leong, Y.K.
Mohanty, K.
Wang, Z.
Feng, P.
Huang, C.Y.
Lee, D.J.
Qin, L.
Ravi Kiran, B.
Yen, H.W.
7
7
5
5
5
5
4
4
4
4
4
4
Hena, S.
Daneshvar, E.
Chokshi, K.
Hemalatha, M.
Gentili, F.G.
Qin, L.
Lu, Q.
Choi, H.J.
Biswas, T.
Zkeri, E.
Kusmayadi, A.
Chandra, R.
182
161
147
143
120
119
98
76
67
53
43
37
that while this system rewards authors with a larger amount of articles,
it inadvertently intensifies the Matthew Effect. In this particular context,
our analysis reveals 12 primary authors who have authored at least four
publications in this particular field of study.
Among them, at the top of the list are Chang, jo-shu., and Venkata
Mohan, S., each with seven publications attributed to their name, indi­
cating a substantial body of research output in the use of microalgae for
treating DWW. It’s interesting to note that none of the papers that were
chosen had these authors identified as highly cited. Following closely
are Kusmayadi, A., Leong, Y.K., Mohanty, K., and Wang, Z., each with
five published, further underscoring their influential roles in the schol­
arly discourse surrounding this domain. Additionally, the presence of
Feng, P., Huang, C.Y., Lee, D.J., Qin, L., Ravi Kiran, B., and Yen, H.W.,
each with four published, highlights a cohort of authors who have
consistently contributed to the understanding of using microalgae
cultivation in DWW applications enriching our knowledge of the chal­
lenges and optimization processes within the wastewater treatment
sector.
Hena, S., has received the most number of citations (182), making
them the most referenced author. Daneshvar, E., has received 161 ci­
tations, followed closely by Chokshi, K., with 147 citations, Hemalatha,
M., with 143 citations, and Gentili, F.G., with 120 citations. Notably,
Kusmayadi, A., and Qin, L., are the only researchers mentioned in both
the list of the highest number of published research papers and the list of
the highest cited in this field, underscoring their exceptional produc­
tivity and influence within the research community. These results point
to a multi-author and collaborative approach in the discipline; however,
certain authors have taken on more prominent roles in terms of influ­
ence on citations and publication output.
3.5.5. Top cited publications of cultivation microalgae in DWW
An essential technique for determining the intellectual connections
between publications, especially when one study is mentioned in
another, is the scientific mapping of citation analysis [48]. This method
helps identify the most important research articles within a certain ac­
ademic topic and makes it easier to analyze citation trends and patterns
[60]. To this end, the research examined the papers published using
citation analysis. According to the Scopus database, the top 37 papers
with the most citations are shown in Table 5. The only factor used to
determine these articles’ ranking is adherence to the Scopus database.
This citation analysis provides valuable insights into the most impactful
and influential publications within the research domain of cultivating
microalgae in DWW treatment.
The top five publications, as identified through a search of the Scopus
database and with over 140 citations, are summarized in the following
data: ’’Cultivation of algae consortium in a dairy farm wastewater for
biodiesel production.’’ With 182 citations, the most referenced publi­
cation. This article was published in 2015 in the Water Resources and
Industry journal by Hena et al. This study investigated the potential of
using DWW as a potential source for biofuel production from
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M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
Table 5
The top 37 most-cited articles.
First Author
Year
Document Title
Journal
Citations
Ref.
Hena, S.
Daneshvar, E.
2015
2019
Water Resources and Industry
Bioresource technology
182
161
[61]
[12]
Daneshvar, E.
2018
Bioresource technology
160
[62]
Chokshi, K.
2016
Bioresource technology
147
[16]
Hemalatha, M.
2019
Bioresource technology
143
[63]
Gentili, F.G.
2014
Bioresource technology
120
[64]
Qin, L.
2016
[22]
2016
2018
2016
98
88
76
[65]
[66]
[25]
Biswas, T.
2021
67
[67]
Zkeri, E.
2021
Environmental science and
pollution research
Bioresource technology
Water Research
Environmental Engineering
Research
Journal of Environmental
Management
Bioresource Technology
119
Lu, Q.
Hena, S.
Choi, H.J.
Cultivation of algae consortium in a dairy farm wastewater for biodiesel production
Sequential cultivation of microalgae in raw and recycled dairy wastewater: Microalgal
growth, wastewater treatment and biochemical composition
Versatile applications of freshwater and marine water microalgae in dairy wastewater
treatment, lipid extraction and tetracycline biosorption
Microalgal biomass generation by phycoremediation of dairy industry wastewater: An
integrated approach towards sustainable biofuel production
Microalgae-biorefinery with cascading resource recovery design associated to dairy
wastewater treatment
Microalgal biomass and lipid production in mixed municipal, dairy, pulp and paper
wastewater together with added flue gases
Microalgae consortia cultivation in dairy wastewater to improve the potential of nutrient
removal and biodiesel feedstock production
Mitigating ammonia nitrogen deficiency in dairy wastewaters for algae cultivation
Dairy farm wastewater treatment and lipid accumulation by Arthrospira platensis
Dairy wastewater treatment using microalgae for potential biodiesel application
53
[68]
Kusmayadi, A.
2022
Chemosphere,
43
[24]
Hena, S.
2015
Water research
42
[69]
Chandra, R.
2021
37
[70]
Kiran, B. R.
2021
Journal of Environmental
Management
Bioresource Technology
37
[71]
Labbé, J.I.
2017
34
[11]
Swain, P.
2020
Journal of Environmental
Chemical Engineering
Biomass and Bioenergy
30
[72]
Higgins, B.T.
2012
Journal of Industrial Ecology
28
[73]
Asadi, P.
2020
27
[74]
Khalaji, M.
2021
22
[28]
Tricolici, O.
2014
Journal of Environmental Health
Science and Engineering
Biomass Conversion and
Biorefinery
Water Science and Technology
21
[75]
Mehrotra, S.
2021
21
[9]
Kiran, B.R.
2022
Sustainable Energy Technologies
and Assessments,
Bioresource Technology
19
[76]
Verma, R.
2022
Science of The Total Environment
16
[77]
Ma, M.
2023
Journal of Cleaner Production
16
[78]
Kuravi, S.D.
2022
Bioresource Technology
16
[79]
Kusmayadi, A.
2023
Bioresource technology
16
[80]
Audu, M.
2021
Algal Research
15
[81]
Chang, Y.L.
2023
Chemical Engineering Journal
12
[82]
Dudek, M.
2022
Sustainability
11
[83]
Gatamaneni, L.
B.
Iliopoulou, A.
2021
Environmental Technology
11
[84]
11
[85]
Barsanti, L.
Singh, P.
2021
2023
Journal of Chemical Technology &
Biotechnology
Journal of Applied Phycology
Bioresource Technology
8
7
[86]
[87]
Kumari, S.
2022
Environmental Science and
Pollution Research
7
[88]
Kusmayadi, A.
2022
Algal Research
5
[89]
2022
An eco-friendly strategy for dairy wastewater remediation with high lipid microalgaebacterial biomass production
Comparing the use of a two-stage MBBR system with a methanogenic MBBR coupled with a
microalgae reactor for medium-strength dairy wastewater treatment
Integrating anaerobic digestion and microalgae cultivation for dairy wastewater treatment
and potential biochemicals production from the harvested microalgal biomass
Three stage cultivation process of facultative strain of Chlorella sorokiniana for treating dairy
farm effluent and lipid enhancement
An approach for dairy wastewater remediation using mixture of microalgae and biodiesel
production for sustainable transportation
Photosynthetic transients in Chlorella sorokiniana during phycoremediation of dairy
wastewater under distinct light intensities
Microalgae growth in polluted effluents from the dairy industry for biomass production and
phytoremediation
Enhanced lipid production in Tetraselmis sp. by two stage process optimization using
simulated dairy wastewater as feedstock
Life Cycle Environmental and Cost Impacts of Using an Algal Turf Scrubber to Treat Dairy
Wastewater
Lipid and biodiesel production by cultivation isolated strain Chlorella sorokiniana pa.91 and
Chlorella vulgaris in dairy wastewater treatment plant effluents
Treatment of dairy wastewater by microalgae Chlorella vulgaris for biofuels production
Dairy wastewater treatment using an activated sludge-microalgae system at different light
intensities
Bioelectrogenesis from ceramic membrane-based algal-microbial fuel cells treating dairy
industry wastewater
Phycoremediation potential of Tetradesmus sp. SVMIICT4 in treating dairy wastewater using
Flat-Panel photobioreactor
Phycoremediation of milk processing wastewater and lipid-rich biomass production using
Chlorella vulgaris under continuous batch system
Alga-based dairy wastewater treatment scheme: Candidates screening, process advancement,
and economic analysis
Mixotrophic cultivation of Monoraphidium sp. In dairy wastewater using Flat-Panel
photobioreactor and photosynthetic performance
Integration of microalgae cultivation and anaerobic co-digestion with dairy wastewater to
enhance bioenergy and biochemicals production
Ash-pretreatment and hydrothermal liquefaction of filamentous algae grown on dairy
wastewater
Microalgae-bacteria consortia for the treatment of raw dairy manure wastewater using a
novel two-stage process: Process optimization and bacterial community analysis
The Cultivation of Biohydrogen-Producing Tetraselmis subcordiformis Microalgae as the
Third Stage of Dairy Wastewater Aerobic Treatment System
Phycoremediation and valorization of synthetic dairy wastewater using microalgal consortia
of Chlorella variabilis and Scenedesmus obliquus
Treatment of different dairy wastewater with Chlorella sorokiniana: removal of pollutants
and biomass characterization
Remediation of dairy wastewater by Euglena gracilis WZSL mutant and β-glucan production
Dairy wastewater treatment using Monoraphidium sp. KMC4 and its potential as
hydrothermal liquefaction feedstock
Experimental and optimization studies on phycoremediation of dairy wastewater and
biomass production efficiency of Chlorella vulgaris isolated from Ganga River, Haridwar,
India
Simultaneous nutrients removal and bio-compounds production by cultivating Chlorella
sorokiniana SU-1 with unsterilized anaerobic digestate of dairy wastewater
9
M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
in two consecutive cycles of microalgae cultivation. The growth of two
microalgae species, the removal efficiency of pollutants, and the
chemical composition of algae were studied in both cycles. The second
study [62] aimed to study the potential of using freshwater and salt­
water microalgae in DWW treatment, lipid extraction, and antibiotic
adsorption. The main difference between the two studies is that the first
one focused on reusing DWW in two consecutive cycles of microalgae
cultivation, while the second one was more comprehensive in using
algae for DWW treatment and other applications.
The fourth most-cited published has received 147 citations. The
research titled "Microalgal biomass generation by phycoremediation of
dairy industry wastewater: An integrated approach towards sustainable
biofuel production," authored by Chokshi et al. [16], published in Bio­
resource Technology in 2016 [16]. This study aimed to use DWW as a
growth medium (without any pretreatment) for culturing Acutodesmus
dimorphus. The results showed that Acutodesmus dimorphus cells
effectively consumed (N and P) from DWW. After 4 days of cultivation,
the COD level was reduced by more than 90 %, and after 6 days, the
ammoniacal nitrogen (277.4 ± 10.75 mg/L) was completely consumed.
After 8 and 4 days of cultivation, respectively, dry biomass of 790 and
840 mg/L was found; this is around 5-6 times the amount of dry biomass
obtained from BG-11 cultivation (149 mg/L after 8 days). About 25 % of
this biomass is made up of lipids, which may be turned into bioethanol
and biodiesel, respectively, while 30 % is made up of carbohydrates.
According to theoretical calculations, 1 kg of Acutodesmus dimorphus
biomass could provide 273 g of biofuel, or roughly 78 g of bioethanol
and 195 g of biodiesel. amounting to 273 g of biofuel. Microalgae
cultivation in DWW without any pretreatment benefits wastewater
disposal while producing large amounts of biomass in a sustainable
manner [16].
The study titled "Microalgae-biorefinery with cascading resource
recovery design associated to dairy wastewater treatment," authored by
Hemalatha et al. [63], published in Bioresource Technology, has been
cited 143 times. This study investigated the integration of fermentation
and photosynthesis processes to utilize microalgal biomass for treating
DWW and producing value-added bioproducts, such as bioethanol. The
cultivated microalgae had a biomolecular composition of 22 % lipids,
15 % proteins, and 38 % carbohydrates, indicating a higher fraction of
carbohydrates and lipids compared to proteins. The microalgae treat­
ment of DWW achieved 90 % TOC removal with a maximum biomass
concentration of 1.4 g/L. Acid hydrolysis of the defatted microalgae
biomass produced 30 % reducing sugars, which were then fermented by
Saccharomyces cerevisiae to produce 116 mg/g of bioethanol. The
reducing sugars from the microalgae predominantly consisted of 54.12
% glucose. This study demonstrates the potential of using microalgae
biomass for the production of various bio-based products through an
integrated biorefinery approach, facilitating closed-loop resource re­
covery and minimizing waste generation.
These top-cited published studies highlight the use and cultivation of
microalgae in treating DWW in different methods, as illustrated in
Table 4. Although traditionally focused on the use of biological, phys­
ical, and chemical methods, there is a growing interest in using micro­
algae as an effective and environmentally friendly tool for treating DWW
and using it in the production of biochemical compounds [63,64]. Most
of the studies mentioned in Table 4 focused on integrated processes that
include pre- or post-treatment of wastewater before microalgae culti­
vation to improve treatment efficiency [24,68,81]. A Study conducted
by Kusmayadi et al. [80] focused on integrating anaerobic co-digestion
and microalgae cultivation of DWW to improve biochemical and bio­
energy production [80]. The studies show that microalgae such as
Chlorella sorokiniana [70,74], Tetradesmus sp. [72,76], Chlorella vul­
garis [74,88], Monoraphidium sp. [79,87], and Scenedesmus obliquus
[84] derived from different natural environments were able to adapt to
DWW and achieve effective removal of contaminants such as N and P
and organic matter [70–72,87,88]. The focus was also on improving the
treatment methods using different light intensity conditions and
different operating methods [75]. These studies have also shown the
potential for achieving added value by using biomass rich in useful
biocomponents such as lipids, hydrocarbons, and proteins in the fields of
bioenergy and biochemistry [63,68,80]. Therefore, a crucial component
of creating novel and efficient DWW management methods is the com­
bination of wastewater treatment with the use of the biomass that is
produced as a consequence.
3.6.6. Primary research topics of DWW treatment by cultivation
microalgae
Biberci [45] pointed out that co-occurrence analysis can play an
important role for the identification of the research topics and the
assessment of the dynamics of research fronts in a given field of
knowledge. When applying the obtained data of Scopus in our analysis
with the help of VOSviewer 1.6.20 software, the minimum count of
keywords was set at 3. Therefore, out of 431 author keywords, 39 strings
were obtained through this stage. In this context, the following is a
network diagram depicted in Fig. 6 in order to expose the co-occurrences
of keywords in the context of the research articles related to the appli­
cation of cultivation microalgae in the treatment of DWW.
In the diagram shown below in Fig. 6, the nodes represent the ele­
ments, and the shape as well as position of the node illustrate the
probability of co-occurrence of elements. Exploring the keyword cooccurrence network map, it is possible to distinguish seven isolated
clusters of various colors, which means they represent different topics
within the studied subject area. The different colored nodes in the figure
are each a cluster of the latter, and each cluster examines a different
discipline in the application of cultivation microalgae in DWW. The size
of the nodes in the diagram means occurrence frequency; the thickness
of the links between the entities means the strength of a connection.
Table 6 provides a list of keywords that met or exceeded the study’s
specified threshold. It is worth noting that this study focused on the
authors’ keywords rather than the index keywords. Table 6 lists the top
39 keywords according to their TLS, arranged in descending order. A
thorough scientific analysis was utilized to calculate the ranking of these
keywords, accounting for variables such as cumulative link strength, the
quantity of links pointing to each keyword, and the frequency of their
occurrence.
The results of the keyword overlap analysis indicate that the most
commonly used terms in the field of using microalgae cultivation in
DWW research are "microalgae", "dairy wastewater", and "wastewater
treatment." These results confirm the central role played by microalgae
cultivation in the field of DWW treatment. The most prominent key­
words related to microalgae cultivation in DWW were identified,
including "nutrient removal," "biomass," "biodiesel," "biofuel," "lipids,"
"Chlorella vulgaris," "biorefinery," and "Chlorella," all of which were in
the top 14 keywords. By analyzing the TLS values, "microalgae" had the
highest value of 79, followed by "dairy wastewater" with 52, "waste­
water treatment" with 44, and "nutrient removal" with 32. These results
reflect the relative importance of these key concepts in the field of
microalgae cultivation for DWW treatment.
Fig. 6 and Table 6 show the top 39 keywords in the Scopus database.
The keywords used in the field of using microalgae cultivation to treat
DWW reflect many promising and interconnected areas: First, "dairy
wastewater" and "DWW" refer to the main source of polluted water that
can be treated using microalgae. Secondly, "wastewater treatment,"
"lipids," and "nutrient removal" refer to the main goal of using micro­
algae, which is to clean the polluted water by absorbing the harmful
chemicals. Thirdly, "microalgae," "Chlorella Vulgaris," and "Chlorella"
refer to the main types of microalgae used in this process. Fourthly,
"biomass," "biodiesel," "biofuel," and "biorefinery" refer to the byprod­
ucts that can be obtained from cultivating algae, which can be used for
commercial and industrial purposes. Finally, "phycoremediation,"
"anaerobic digestion," and "bioremediation" describe the biological
processes used in employing algae to treat DWW. Overall, these
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M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
Fig. 6. Co-occurrence clustering of author keyword in a network visualization.
network diagram, which is highlighted in red, represents "utilizing
microalgae for wastewater treatment." The second cluster of greencolored keywords highlights "the potential of microalgae-based tech­
nologies to enable a circular economy approach for DWW treatment and
biofuel production." The third cluster of keywords, colored in blue,
represents a "scientific approach to utilizing microalgae, particularly the
Chlorella species, for the treatment of DWW and the production of
biofuels within an integrated biorefinery system." The fourth cluster of
keywords, denoted by the color yellow, presents a "holistic approach to
DWW management that integrates anaerobic digestion, algae-based
technologies, and microbial fuel cells." The fifth cluster of keywords,
represented by the color purple, focuses on "the utilization of the
microalgal species Chlorella vulgaris for nutrient removal and the pro­
duction of valuable biomass and lipids." The sixth cluster of keywords,
represented in light blue, focuses on "the integration of nutrient
removal, phosphorus recovery, and hydrothermal liquefaction (HTL)
technologies." The seventh cluster of keywords, represented by the color
orange, focuses on "the use of phycoremediation and cyanobacteria for
environmental remediation and resource recovery.";
Among these sets, the first cluster focuses on the utilization of
microalgae in wastewater treatment. The keywords that make up this
group are: "Microalgae," "Wastewater Treatment," "Photobioreactor,"
"biohydrogen," "lipid productivity," "biomass production," "biofuels,"
"mixotrophic cultivation," and "Scenedesmus Obliquus," which repre­
sents the key focus areas in utilizing microalgae for wastewater reme­
diation and biofuel production. These terms indicate the use of specific
microalgal species, such as Scenedesmus obliquus, cultivated in photo­
bioreactors to treat polluted wastewater through various biological
processes [79,90]. The goals include enhancing lipid productivity and
overall biomass production to generate valuable biofuels and other
co-products. Mixotrophic cultivation techniques, which combine auto­
trophic and heterotrophic growth modes, are also highlighted as a
means to optimize microalgal performance and productivity. Addition­
ally, the generation of biohydrogen is noted as a potential energy-rich
byproduct from the microalgal cultivation system. Overall, these key­
words point to the multifaceted approach of leveraging
microalgae-based processes for sustainable biofuel development and
wastewater treatment.
In the second cluster, this cluster focuses on the utilization of
microalgae in the treatment of DWW by removing nutrients and pol­
lutants and extracting fats and fatty acids from them, which can be used
in the production of biodiesel. At the core of this cluster are terms such
as "biodiesel," "lipid," and "fatty acid," indicating the focus on converting
Table 6
Top 39 keywords from the studies published on cultivation microalgae for DWW
treatment.
Keywords
Cluster
TLS
Occurrence
% Occurrence
Microalgae
Dairy Wastewater
Wastewater Treatment
Nutrient Removal
DWW
Biomass
Biodiesel
Phycoremediation
Bioremediation
Biofuel
Lipids
Chlorella Vulgaris
Biorefinery
Chlorella
Anaerobic Digestion
Algae
Bioenergy
Circular Economy
Nutrients Removal
Photobioreactor
Biohydrogen
Lipid
Lipid Productivity
Nutrient Recovery
Biomass Production
Fatty Acid
Biofuels
Cyanobacteria
Effluent
Remediation
Renewable Energy
Resource Recovery
Anaerobic Digestate
Dairy Wastewater Treatment
Phosphorus
Microbial Fuel Cell
Mixotrophic Cultivation
Hydrothermal Liquefaction
Scenedesmus Obliquus
1
3
1
5
4
5
2
7
2
3
5
5
3
3
4
4
4
2
2
1
1
2
1
6
1
2
1
7
3
3
3
4
2
2
6
4
1
6
1
79
52
44
32
27
24
22
19
17
16
16
15
14
11
10
9
9
9
9
9
8
8
8
8
7
7
6
6
6
6
6
6
5
5
5
4
4
3
3
43
27
25
16
14
9
11
9
10
6
6
7
5
5
3
5
4
5
4
4
4
3
3
5
4
3
4
6
3
3
3
3
3
4
3
3
3
3
3
15.14
9.51
8.80
5.63
4.93
3.17
3.87
3.17
3.52
2.11
2.11
2.46
1.76
1.76
1.06
1.76
1.41
1.76
1.41
1.41
1.41
1.06
1.06
1.76
1.41
1.06
1.41
2.11
1.06
1.06
1.06
1.06
1.06
1.41
1.06
1.06
1.06
1.06
1.06
keywords reflect the wide potential of using microalgae cultivation to
treat DWW and convert it into value-added products.
Seven large groups are visible on the network map used in this study,
as shown in Fig. 6. In other words, the first cluster in this study’s
11
M.Y.D. Alazaiza et al.
Results in Engineering 24 (2024) 103052
microalgal species is to remove nutrients, such as N and P, from
wastewater or other aquatic environments. By doing so, the Chlorella
vulgaris biomass is produced as a byproduct of this nutrient removal
method. The inclusion of the keyword "lipids" suggests that the Chlorella
vulgaris biomass is further processed to extract and concentrate the lipid
content. Lipids are valuable components of microalgal biomass, as they
can be converted into biofuels or other high-value lipid-based products.
Overall, this approach aligns with the broader goals of resource recov­
ery, sustainability, and the development of integrated biorefinery sys­
tems, as evidenced by the connections to the other keyword clusters.
The sixth cluster of keywords focuses on the integration of nutrient
removal, phosphorus recovery, and hydrothermal liquefaction (HTL)
technologies. At the center of this cluster is the keyword "nutrient
removal," which, similar to the previous cluster, indicates the impor­
tance of removing nutrients, such as P and N, from wastewater or other
aquatic environments. This nutrient removal process is a crucial step in
resource recovery and water treatment. Closely connected to the
"nutrient removal" keyword is the specific focus on "phosphorus." This
suggests that the recovery and reuse of phosphorus, a critical and finite
nutrient, is a key objective within this cluster. Phosphorus is an essential
element for agricultural production and plant growth, and its efficient
recovery from wastewater can contribute to a more sustainable and
circular phosphorus economy. The inclusion of the term "hydrothermal
liquefaction" (HTL) introduces a specific technological approach to
processing the nutrient-rich biomass generated during the nutrient
removal process. HTL is a thermochemical conversion technique that
can effectively transform the biomass into a biocrude oil, which can then
be further refined and utilized as a renewable transportation fuel or for
other energy-related applications [94]. By integrating the concepts of
nutrient removal, phosphorus recovery, and hydrothermal liquefaction,
this cluster represents a comprehensive strategy for addressing the
challenges of wastewater management, nutrient recycling, and the
production of renewable energy and fuels. This approach aligns with the
broader goals of sustainable resource utilization and the development of
integrated biorefinery systems.
Finally, the seventh cluster of keywords focuses on the use of phy­
coremediation and cyanobacteria for environmental remediation and
resource recovery. The central keywords in this cluster are "phycor­
emediation" and "cyanobacteria." Phycoremediation refers to the use of
algae and other photosynthetic microorganisms, such as cyanobacteria,
to remove or transform contaminants from various environmental
matrices, such as wastewater, soil, or water bodies [95,96]. Cyanobac­
teria, also known as blue-green algae, are a diverse group of photosyn­
thetic prokaryotic organisms that are often employed in
phycoremediation processes due to their ability to thrive in a variety of
environmental conditions and their capacity to accumulate or degrade
various pollutants [97–99]. The inclusion of these keywords suggests a
focus on leveraging the natural capabilities of cyanobacteria and other
microalgal species to remediate contaminated environments, such as
treating wastewater, removing heavy metals, or mitigating eutrophica­
tion in water bodies. This cluster aligns with the broader themes of
environmental sustainability and resource recovery, as the phycor­
emediation processes can not only remove contaminants but also
potentially recover valuable resources, such as nutrients or biomass,
which can be further utilized in different applications, such as bioenergy
production or agricultural fertilizers. By integrating phycoremediation
and cyanobacteria-based technologies, this cluster represents a
nature-inspired approach to addressing environmental challenges and
promoting a more circular and sustainable utilization of resources.
the biomass generated from microalgae cultivation into sustainable
biofuel, particularly biodiesel. Equally important are the keywords
"bioremediation" and "nutrient removal," which emphasize the ability of
microalgae to treat DWW by effectively absorbing and removing
harmful nutrients and pollutants. The concept of a "circular economy"
further suggests a holistic, closed-loop system where the byproducts and
waste streams, such as "anaerobic digestate," are reintegrated and uti­
lized, minimizing environmental impact [91,92]. By specifically tar­
geting "dairy wastewater treatment," this cluster of keywords highlights
the application of this integrated microalgae-based technology to
address a significant environmental challenge within the dairy industry.
Overall, this set of keywords represents a comprehensive, sustainable
approach to leveraging microalgae for the dual purposes of wastewater
remediation and biofuel production, creating a circular economy that
maximizes resource efficiency and minimizes waste.
The third cluster of keywords suggests a "scientific approach to uti­
lizing microalgae, particularly the Chlorella species, for the treatment of
DWW and the production of biofuels within an integrated biorefinery
system." At the center of this cluster is the term "dairy wastewater,"
highlighting the specific environmental challenge that is being
addressed through the application of this technology. The keywords
"remediation" and "effluent" indicate the ability of microalgae to remove
contaminants from the DWW, effectively treating this problematic waste
stream. Closely linked to this is the term "biofuel," which points to the
potential of converting the microalgal biomass generated during the
wastewater treatment process into a sustainable source of renewable
energy. The inclusion of the "biorefinery" concept suggests a holistic
approach where the DWW treatment, bioremediation, and biofuel pro­
duction are seamlessly integrated into a single, efficient system. This
biorefinery integration allows for the maximization of resource utiliza­
tion and the production of multiple valuable products, such as biofuels
and other co-products, as indicated by the "renewable energy" keyword.
These microalgae can be used in the establishment of an integrated
biorefinery to produce biofuels and other products.
The fourth cluster of keywords presents a holistic approach to DWW
management that integrates anaerobic digestion, microalgae-based
technologies, and microbial fuel cells. At the core of this cluster is the
term "dairy wastewater," which once again highlights the specific
environmental challenge of treating DWW. The inclusion of "anaerobic
digestion" suggests the use of an anaerobic biological process to break
down the organic matter in the DWW, generating biogas as a byproduct.
Complementing this, the keyword "algae" indicates the utilization of
algal species, either as a standalone solution or in combination with
other technologies, for the treatment and processing of DWW. This in­
tegrated approach allows for the conversion of the biogas and algal
biomass into valuable forms of "bioenergy," contributing to the pro­
duction of renewable energy. Underpinning this entire system is the
focus on "resource recovery," which emphasizes the extraction and reuse
of the valuable resources, such as nutrients and energy, present in DWW
and its byproducts. Finally, the term "microbial fuel cell" suggests the
integration of this technology, which uses microorganisms to generate
electricity directly from organic matter, as part of the overall dairy
wastewater treatment and resource recovery system. By leveraging this
interconnected set of technologies and processes, this cluster represents
a holistic and sustainable approach to DWW management, promoting a
circular bioeconomy through efficient wastewater treatment, bioenergy
production, and the recovery of valuable resources.
The fifth cluster of keywords focuses on "the utilization of the
microalgal species Chlorella vulgaris for nutrient removal and the pro­
duction of valuable biomass and lipids." At the center of this cluster is
the keyword "Chlorella vulgaris," which highlights the specific micro­
algal strain that is being leveraged in this approach. Chlorella vulgaris is
a well-studied and widely used microalgal species known for its versa­
tility and effectiveness in various applications [93]. Closely linked to the
Chlorella vulgaris keyword are the terms "nutrient removal" and
"biomass." This indicates that the primary objective of using this
4. Conclusion
This research conducted a bibliometric analysis of research on DWW
treatment through the cultivation of microalgae. The VOSviewer 1.6.20
software was utilized to perform bibliometric analysis of 126 articles
and review articles obtained from the Scopus database after filtering.
12
Results in Engineering 24 (2024) 103052
M.Y.D. Alazaiza et al.
Important new trends in this field were revealed.
From the bibliometric analysis, it can be concluded that over 69 % of
the studies on cultivation microalgae to treat DWW have been published
in the last five years. Specifically, the trends from the analysis show an
increase in interest in DWW treatment by cultivating microalgae in the
last five years, which peaks in 2023, where there were 23 reported
publications. Based on the findings of the present research, the three topranking academic journals covering the cultivation of microalgae for
treating DWW are Bioresource Technology, Environmental Science and
Pollution Research, and Algal Research. Most research is conducted in
fairly common areas in concentrations related to environmental science,
energy, and others: 35.63 %, 17.24 %, and 23.75, respectively.
India, China, the US, and Iran presented the largest input concerning
the cultivation of microalgae to treat DWW, contributing to 30.16 %,
15.08 %, 11.11 %, and 7.9 %, respectively. Tunghai University and
National Cheng Kung University made significant contributions in this
field with 5 papers each. Keywords of the DWW treatment by microalgae
cultivation were analyzed with the help of co-occurrence and clustering.
The author’s keywords used, which proved effective in detecting new,
urgent topics, and comprehensive study tendencies. The most frequently
used words are "microalgae," "dairy wastewater," "wastewater treat­
ment," "nutrient removal," and "biomass." The chosen keywords define
the main subject of investigation in this field properly. Some of the
microalgae species used to treat DWW include Chlorella vulgaris, Cya­
nobacteria, and Scenedesmus obliquus. This study also aims at
employing microalgae for justified treatment of DWW by eliminating
nutrients (N and P) and pollutants from them in addition to extracting
fats and fatty acids that can be utilized for biodiesel production.
[5] M.Y. Alazaiza, T.M. Alzghoul, S.A. Amr, M. Bangalore Ramu, D.E. Nassani,
Bibliometric insights into car wash wastewater treatment research: trends and
perspectives, Water 16 (14) (2024) 2034. .
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[7] Z. Al-Qodah, T.M. Al-Zghoul, A. Jamrah, The performance of pharmaceutical
wastewater treatment system of electrocoagulation assisted adsorption using
perforated electrodes to reduce passivation, Environ. Sci. Pollut. Control Ser. 31
(13) (2024) 20434–20448. .
[8] J. Boguniewicz-Zablocka, I. Klosok-Bazan, V. Naddeo, Water quality and resource
management in the Dairy Industry, Environ. Sci. Pollut. Control Ser. 26 (2) (2017)
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wastewater, Sustain. Energy Technol. Assessments 48 (2021) 101653. .
[10] B.S. Shete, N.P. Shinkar, Dairy industry wastewater sources, characteristics & its
effects on environment, International Journal of Current Engineering and
Technology 3 (5) (2013) 1611–1615. .
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[18] R. Abrane, S. Hazourli, A. Eulmi, Comparative study between electrocoagulation
and adsorption on the Opuntia Ficus indica powder for industrial dairy wastewater
treatment, Desalination Water Treat. 228 (2021) 153–164.
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Management in India: Status and Future Prospects for Environmental
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[20] M. Nayak, A. Karemore, R. Sen, Performance evaluation of microalgae for
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[23] A.L. Gonçalves, J.C. Pires, M. Simões, A review on the use of microalgal consortia
for wastewater treatment, Algal Res. 24 (2017) 403–415. .
[24] A. Kusmayadi, P.H. Lu, C.Y. Huang, Y.K. Leong, H.W. Yen, J.S. Chang, Integrating
anaerobic digestion and microalgae cultivation for dairy wastewater treatment and
potential biochemicals production from the harvested microalgal biomass,
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application, Environmental Engineering Research 21 (4) (2016) 393–400. .
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productivities of Scenedesmus sp. cultivated in the wastewater of the dairy
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(2018) 265–269. .
[28] M. Khalaji, S.A. Hosseini, R. Ghorbani, N. Agh, H. Rezaei, M. Kornaros, E. Koutra,
Treatment of dairy wastewater by microalgae Chlorella vulgaris for biofuels
production, Biomass Conversion and Biorefinery (2021) 1–7. .
[29] J.M. Melo, M.R. Ribeiro, T.S. Telles, H.F. Amaral, D.S. Andrade, Microalgae
cultivation in wastewater from agricultural industries to benefit next generation of
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(2022) 22708–22720. .
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and sustainable energy reviews 14 (2) (2010) 557–577. .
[31] L. Wang, M. Min, Y. Li, P. Chen, Y. Chen, Y. Liu, R. Ruan, Cultivation of green algae
Chlorella sp. in different wastewaters from municipal wastewater treatment plant,
Applied biochemistry and biotechnology 162 (2010) 1174–1186.
Funding
This research was funded by A’Sharqiyah University, grant number
ASU/IRG/23/34/01.
CRediT authorship contribution statement
Motasem Y.D. Alazaiza: Writing – original draft, Visualization,
Validation, Supervision, Resources, Funding acquisition. Tharaa M.
Alzghoul: Writing – original draft, Software, Resources, Methodology,
Data curation. Salem S. Abu Amr: Supervision, Resources, Investiga­
tion. Madhusudhan Banglore Ramu: Visualization, Validation,
Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Data availability
No data was used for the research described in the article.
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