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Ci. e Nat., Santa Maria v.42, e27, 2020

DOI:10.5902/2179460X41226

ISSN 2179-460X

Received 19/11/19   Accepted: 15/01/20  Published:24/06/20

 

 

 

Environment

 

Scientometric analysis applied to the water treatment with activated carbon

 

Análise cientométrica aplicada ao tratamento de água com carvão ativado

 


Kelly Kathleen Almeida HeylmannI

Bruno Vasconcellos LopesI

Carolina Faccio DemarcoIII

Thays França AfonsoIV

Tito Roberto Sant'Anna Cadaval JúniorV

Andrei Vallerão IgansiVI

Maurizio Silveira QuadroVII

Robson AndreazzaVIII

 

I    Universidade Federal de Pelotas, RS, Brasil - kellyheylmann@hotmail.com

II    Universidade Federal de Pelotas, RS, Brasil -lopesbruno13@gmail.com

III   Universidade Federal de Pelotas, RS, Brasil -carol_demarco@hotmail.com

IV   Universidade Federal de Pelotas, RS, Brasil -thaysafonso@hotmail.com

V   Universidade Federal do Rio Grande, RS, Brasil -titoeq@gmail.com

VI   Universidade Federal do Rio Grande, RS, Brasil -andreivallerao@gmail.com

VII  Universidade Federal de Pelotas, RS, Brasil -mausq@hotmail.com

VIII Universidade Federal de Pelotas, RS, Brasil -robsonandreazza@yahoo.com.br

 

 

ABSTRACT

 The current moment requires the development of new technologies that can provide alternatives to conventional treatment and that efficiently remove pollutants that are difficult to treat. Activated carbon has been highlighted as low cost material that can be used as adsorbents for the removal of contaminants. Thus, the aim of the present study was to analyse the relevant literature related to the production of activated carbon for the treatment of water. For the study, there were found 4,182 relevant studies in the database of the Web of Science and from these restrictions and readings were obtained 27 articles. The information obtained was: i - temporal evolution of publications, ii - distribution of articles by periodicals, iii - spatial distribution, iv - precursor material, v - activation technology, vi - pollutants and vii - treatment efficiency. Results show that the activated carbon produced from corn and industrial ash residues are good adsorbents. Dyes, heavy metals and phenols were the most studied pollutants, and had the higher treatment efficiency values. The approach of the present study allows to identify the main points of this new technology and it helps to support new researches and applications.

Keywords: Scientometry. Biomaterials. Wastewater. Waste.

 

 

RESUMO

O momento atual requer o desenvolvimento de novas tecnologias que possam fornecer alternativas ao tratamento convencional e que removam eficientemente poluentes de difícil tratamento. Com o crescente interesse em materiais de baixo custo que possam ser empregados como adsorventes para a remoção de contaminantes, o carvão ativado tem se destacado. Deste modo, o objetivo do presente estudo foi analisar a literatura relevante relacionada à produção de carvão ativado para o tratamento de água. Para o estudo, foram encontrados 4.182 estudos relevantes na base de dadosdo Web of Science e destes, a partir de restrições e leituras, obtiveram-se 27 artigos. As informações obtidas foram: (i) evolução temporal das publicações, (ii) distribuição dos artigos por periódicos, (iii) distribuição espacial, (iv) material precursor, (v) tecnologia de ativação, (vi) modelos ajustados, (vii) poluentes e (viii) eficiência de tratamento. Os resultados demonstram que o carvão ativado produzido a partir de resíduos da produção de milho e cinzas industriais apresenta-se como bons adsorventes. Os corantes, metais pesados e fenóis foram os poluentes mais estudados e que também possuem maiores valores de eficiência de tratamento. A abordagem do presente estudo permite identificar os principais pontos desta nova tecnologia de uma forma capaz de produz resultados que ajudarão a apoiar novas pesquisas e aplicações.

 

Palavras-chave: Cientometria. Biomaterial. Águas residuárias. Resíduos.

 


1 Introduction

 

In recent decades, water treatment and supply systems have withstood high pressure from industrial segments and the growing population. Water quality criteria may become unreachable for certain structures and values. In recent years, under a scenario of high environmental pollution, there has been a gradual interest in the use of activated charcoal for water and wastewater treatment systems (WONG et al., 2018). Thus, activated charcoal has great utility in pollution control.

However, the use of commercial activated charcoal becomes costly for the removal of large-scale contaminants, making more economical alternative materials and methods to be sought for its production (PALLARÉS; GONZÁLEZ-CENCERRADO; ARAUZO, 2018). The studies seek to find low cost and high efficiency carbonaceous materials, as well as to understand the adsorptive processes of these new coals from their characterization and the study to the fit of models (PRADEEP et al., 2016).

In this context, it is highlighted the studies with proposals for the use of waste as a raw material to obtain coal, because in this way, it is promoted the reuse of a solid waste. Solid waste processing for the production of activated charcoal can reduce its management and disposal problems, as well as reducing production costs (AKPA; NMEGBU, 2014).

Activated carbon has excelled in the processes of adsorption, purification, filtration, deodorization and separation. Adsorption provides some advantages over classic water and wastewater treatment methods such as low waste generation, efficient substance removal, simplicity of operation, easy metal recovery and the possibility of reuse of the adsorbent (HETTIARACHCHI et al., 2016). The ability to remove a wide variety of compounds in contaminated waters has increased the demand for activated charcoal in recent years (CRINI; LICHTFOUSE, 2018). Activated charcoal applications are numerous and its properties will depend on the reaction conditions, carbonization method and activation employed and essentially on the nature of the precursor material (KOSHELEVA; MITROPOULOS; KYZAS, 2018).

The present study aimed to analyze the relevant literature related to the production of activated charcoal for water treatment through a scientometric analysis. The study determined the temporal evolution of publications, the distribution of articles by journals and country, the activation technology, the main precursor materials used, the best-adjusted kinetic and isothermal models, the pollutants removed and the efficiency of treatment with the activated carbon produced.

2 Materials and Methods

Data were obtained from the Web of Science (WoS) database for the years 1987-2017, totaling a 30-year search period. Data collection was performed from four WoS research fields, each field being directed to a research interest. Operators were employed to produce a detailed search and generate subject queries with some variations. The proposed research fields were: a) Object of interest of the study: activatedcharcoal$ OR activatedcarbon$; b) Application of activated charcoal: watertreat* OR waterremov* OR wateradsorpt* OR wateradsorbent*; c) Reusable or waste-activated activated carbon: renew* coal$ OR reus* coal$ OR waste$; d) Cost of production and/or obtaining: lowcostadsorbent$ OR lowcostcoal$.

The studies obtained for the initial search were 4,182 studies. After using some restrictions in the search field, a total of 27 articles were obtained. The search field selection and restriction procedures are described in the flowchart proposed in Figure 1.

Figure 1 - Flowchart of the data collection process from the inserted search field and restrictions applied for the systematic review. Source: Authors.

 

The articles found were reevaluated for their relevance to the topic of interest through readings of titles and abstracts. Thus, some publications may have been withdrawn if they were not related to the proposal of the work. From the final number of articles, after all screening and restrictions, information was extracted from each article for data collection. The extracted information and its importance are described below:

a) Year: The analysis of the temporal distribution of this study is given by collecting the years of publication;

b) Journal: The determination of the distribution of articles by journal was determined according to the number of articles about the published subject and the impact factor of this in the academic scope;

c) Country: The analysis of the spatial distribution of this study is performed by collecting the countries of each publication. The country chosen refers to the first author's address, and this one directly relates to the research investment and his interest in the new technology. It should be noted that there were works in which the precursor material is from a different location from the country of authorship of the publication;

d) Raw material used: The precursor materials used for the production of activated charcoal were collected from each publication to identify the most used materials;

e) Temperature: The carbonization or pyrolysis process consists of burning the raw material used. The study of the employed temperature is very important to determine the amount of final carbon present as well as the porous arrangement;

f) Activation technology: The activation process consists of unclogging the pores and increasing the surface area. The importance of this process is in its relationship with the adsorptive capacity presented by coal and its surface functional groups. In the study, articles were classified into chemical or physical activation;

g) Adjusted models: The behavior of the coals can be understood by adjusting to kinetic and isothermal models. This process is of great importance in designing a water and wastewater treatment system as well as in achieving efficiency control throughout the process. The best fit kinetic and adsorption isotherm models were collected;

h) Pollutant removed: The analysis of the main pollutants removed by the activated charcoal produced sought to identify the main contaminants, its problem in water treatment and their interaction with the coal surface functional groups.

i) Treatment efficiency: Treatment efficiency and production data were observed. When comparing the efficiency values ​​the amount of adsorbent added as well as its specific porosity must be taken into account. However, it is important to highlight that many studies do not characterize the material and do not describe the amounts of adsorbent used, thus presenting only the initial and final pollutant concentration values ​​and the adjustment parameters of the models.

The results were analyzed by descriptive statistics with the aid of RStudio software only for understanding their dispersion and obtaining mean values, variances and deviations. The use of graphical analysis demonstrates the trends, outliers and data organization for the study.

3 Results and Discussion

Data obtained from the WoS database for the years 1987 to 2017 totaled a 30-year search period; however, all studies meeting the search criteria were published after 2000 (Figure 2). The low occurrence of studies in the past may be related to the low cost of obtaining and producing activated charcoal as well as the low demand for its large-scale use. The results showed a low relationship between the journals with the largest number of publications on the subject and the impact factor values found, respectively.

 


 

 

 

 

 

 


Figure 2 - Distribution of articles found by journal related to their impact factor and year of publication: a) Environmental Technology; b) Journal of Cleaner Production; c) Environmental Science and Technology; d) Waste biomass valorization; e) Environmental Science and Pollution; f) Journal of Environmental Engineering; g) Water air soil pollut. Journal; h) Journal of Environmental Science and Health; i) Water Science and Technology Water Supply; j) Clean Technologies and Environmental Policy; k) Water Research; l) Journal of Hazardous Materials; m) Toxicological & Environmental Chemistry; n) Waste Management; o) Wiley Interdisciplinary. Source: Authors.


A study conducted by MERCURI et al., (2016) found no relationship between the impact factor and relative frequency of studies per journal calculated for their area of study, thus demonstrating that the impact factor should not be considered isolated.

The years of 2006 and 2008 did not present results for the research. The largest number of studies found was conducted from 2013 to 2016, with 46.2% of the total number of articles found. The year of 2013 was found with the largest number of studies on the subject. The largest number of publications in the area were found for Environmental Technology Reviews and the highest impact factor observed for Water Research. It is important to note that for 2017 only articles published until April were considered. Further research may be conducted later this year for further understanding of the study.

The spatial distribution of articles is concentrated on the Asian continent (Figure 3). The countries with the most research in the area were India and China respectively. Only these two countries accounted for almost 50% of publications in the area.

 

Figure 3 - Spatial distribution of studies. Source: Authors.

 

The results suggest a strong Asian interest in the use of activated charcoal for water treatment. However, the analysis performed for the application scale of the activated charcoal produced showed that all studies performed were laboratory scale, and of these, only 7% presented proposals for future large-scale applications. The result obtained for application scale may be related to the lack of interest of large public and private sector companies in the application of this technology. It is important to highlight that the application scale is directly related to the cost of obtaining and that it depends on the precursor material chosen. The precursor materials for activated carbon production found in the present study can be seen in Figure 4.

Figure 4 - Raw material used in the activated carbon production process found for the literature approached. Source: Authors.

The most used materials in the coal production process were the ashes of the industrial burning process and the residues from the corn production. Considering that the carbonization process is essential for the production of activated charcoal (TOVAR et al., 2019), the predominance of the use of materials from the burning process was already expected. The results also suggest that large-scale production processes, which consequently generate a large volume of waste, are one of the criteria for choosing the precursor material.

The choice of raw material becomes a determining factor for achieving high yield in the activated carbon production process. Many materials have adsorption capacity, however, few materials perform this function with high efficiency, causing the demand for new materials (GODIYA et al., 2019). Thus, the nature of the precursor material, carbonization process temperature and activation method are critical to achieving the expected efficiency.

In the carbonization or pyrolysis process the precursor material is subjected to high temperatures where volatile chemical compounds (H, N and O) and light gases (CO2, H2, CO and CH4) are removed forming a fixed primary porous carbon mass (PEDROZA et al., 2019). The study of the temperature employed in this process is necessary to understand its properties and the adsorptive process. In the analysis of the literature found, different temperature values were observed for the precursor materials (Figure 5).

 

Figure 5 - Temperature values found in the carbonization process of the raw material for the production of activated charcoal. Source: Authors.

 

It is evident that light and moist materials require lower temperatures in the process. The highest temperature found in the studies was 1260ºC for feldspar material, and similarly, the lowest temperature recorded was 350ºC for residues from corn production. The average temperature value found was 765.2ºC.

In this context, the burnt material is fundamentally microporous, but this porosity may be filled or partially blocked by the decomposition and burning products. Therefore, activation is required to unblock and enlarge the pores formed in this process (CASTRO et al., 2018).

The activation process aims to remove the organic compounds present such as tar, creosote and naphtha, as well as other residues that may clog the pores. The studies were classified according to the possible activation nature, which may be chemical or physical (MAMANÍ et al., 2019). For the chemical activation process there are 92.6% of the chosen works. The high use of the chemical activation process in relation to the physical process may be related to ease of operation, low process cost as well as high efficiency after application of the method.

It is important to remember that chemical activation is driven by the impregnation of a dehydrating or oxidizing chemical on the precursor material, while physical activation involves the exposure of activated carbon to vapors and oxygen-containing gases (LIEW et al., 2018).

The chemical and physical activation agents found in the literature are presented in Figure 6.

Figure 6 - Chemical and physical agents used in the activation process of the charcoal produced. Source: Authors.

 

After the production of activated carbon, it is necessary to study its characteristics and adsorptive capacity. The use of methodologies to determine their characteristics may be necessary. In the present study, it was decided to determine the adsorptive capacity in relation to the adjustment of these coals to kinetic and isothermal models. Methods of determining physical and chemical characteristics may differ greatly and depend greatly on laboratory conditions and experimental errors.

The study of adsorption kinetics is essential because it provides information on the speed at which reactions occur, the factors that influence adsorption, and the interactions that occur at the adsorbate-adsorbent interface. Adsorption kinetics also allow the determination of the amount of solute that is removed from a solution over time, being of great importance in the design of an effluent treatment system and also for obtaining process efficiency control (KAUSAR et al., 2018). Adsorption isotherms, which take into consideration the study of equilibrium, can provide important information for the evaluation of affinity or adsorption capacity, being an excellent selection criterion. It can determine the surface area of ​​the adsorbent, the pore volume and the statistical distribution as well as the determination of the optimum heat at adsorption. Isotherms characterize the equilibrium of total solute concentration over adsorbed concentration and solution concentration (KOOPAL; TAN; AVENA, 2019).

The models found for kinetic adjustment were Pseudo First Order, Pseudo Second Order, Elovich and Interparticle Diffusion. To adjust the isotherms, the equations of Langmuir, Freundlich, Tempkin and Dubinin – Radushkevich and Redlich-peterson were found. The adjusted work numbers for each model are shown in Figure 7.

Figure 7 - Kinetic model and adsorption isotherm adjusted for each study conducted with the activated carbon produced. Source: Authors.

 

The results show that the Pseudo First Order kinetic model (55.6%) and the Langmuir equation (66.7%) were better adjusted to the activated charcoal studies. This result implies the determination of the adsorptive behavior of this material.

To understand the results, it is worth remembering that the Pseudo First Order model assumes that adsorption occurs as a result of a concentration gradient and the Langmuir equation suggests that every adsorbed species interacts only with a defined site, each active site accommodates only one molecule, there are no interactions between neighboring site molecules and the adsorption energy of each site is equal (SONG et al., 2018). The models fitted together suggest that the molecules are adsorbed due to concentration gradient and that they adhere to the surface of activated carbon at well-defined and localized active sites.

It is important to highlight the main difference between the most widely used isotherms is that Freundlich does not predict adsorbent saturation, unlike Langmuir. These two equations fit most systems employed with activated charcoal, but Freundlich is supposed to better represent systems with real effluents. The isotherm models of the Langmuir and Freundlich equations are the most used.

The study of the adsorbable molecules is then employed. Different toxic compounds difficult to remove by conventional treatment are studied. The pollutants found can be observed in Figure 8.

Figure 8 - Pollutant removed by treatment with activated charcoal produced from alternative precursor material according to the literature. Source: Authors.

The main pollutants studied were arsenic, dyes and phenol. The percentage of these studies was 41.7%. The spatial distribution of the studies compared to the pollutant group demonstrates a global interest in removing these pollutants, as studies in South Africa, China, Spain, India, England, Iran, Mexico and Senegal were conducted for this purpose.

Another important factor that should be considered in the analysis of the pollutants studied is the temporal variability. The group of the main compounds studied is present during the research period, thus demonstrating that these are substances that are difficult to treat and require studies with proven efficiency in the field.

The specificity between adsorbate and adsorbent leads to the need to expand studies in the area. The use of activated carbon adsorption as a method of water and wastewater treatment has been of interest to different researchers (HAGEMANN et al., 2018).

The efficiencies found by all studies were gathered into similar or similarly toxic chemical compounds and their averages were calculated. The efficiency classes are shown in Figure 9.

Figure 9 - Pollutant removal efficiency. Source: Authors.

 

The results demonstrate a high efficiency in the treatment of dyes and heavy metals. Most commercially used dyes and metals are resistant to biodegradation, photodegradation and oxidizing agent treatment processes. Proper treatment of these is necessary, because when discharged without proper treatment in water bodies are responsible for serious damage to biological systems and human health (AFROZE; SEN, 2018). The adsorption of inorganic compounds by activated carbon has been widely studied, and its purpose is to remove pollutant metals from liquid discharges and to recover certain valuable metals.

Polyurethane treatment was the least efficient treatment followed by pesticides and organic compounds treatment. These may be related to pore arrangement, exposure time to carbonization and activation processes, specific affinity between adsorbate and adsorbent, molecule size and concentration of the pollutant under study. Importantly, low-efficiency coals can be extremely microporous, while the molecules of these pollutants are larger than the size of their pores. Dyes and heavy metals are smaller molecules, and therefore easier to be adsorbed on small sites compared to other types of pollutants.

Several studies corroborate the results found. A study conducted by GOLIN (2007) describes in its review that precursor materials such as tires, pits, wood scraps and ashes have good removal efficiency of adsorbents such as cadmium, cobalt, copper, lead, mercury, nickel and zinc. SOARES (1998) observed a removal efficiency of over 95% for the activated carbon monoclotriazine yellow and red by activated carbon dyes from mining. CLAUDINO (2003) investigating the production of activated charcoal from agricultural waste from southern Santa Catarina State found high phenol removal.

The removal efficiency values may vary according to different factors such as process time, pollutant concentration, amount of adsorbent and pH. DA SILVA et al., (2016) found removal efficiency between 76 and 93% for three different activated carbons.

The results demonstrate that most of the precursor materials used were good adsorbents. Changes in production processes such as variations in temperature and time of exposure to burning, as well as the activating agent chosen may be responsible for the increased adsorptive capacity.  In addition, modifications in the adsorption process such as pH and temperature control, variation in agitator speed and form of column organization may be responsible for the increase of efficiency.

 

4 Conclusions

The study showed that activated charcoal is an important tool to control environmental pollution and is even more employed when produced from waste. The precursor materials as well as the carbonization and activation methods were relatively well suited for most of the verified studies.

The results show that in the last 30 years, the 2000 year has been an initial start in the production of papers regarding alternative materials for the production of activated charcoal. It is evident that other studies were produced before this year, but these did not come under the desired initial conditions or were not in the Environmental Sciences category. The spatial distribution of the articles showed that India and China have a great interest in this subject.

The interest of the study in promoting the knowledge of the main materials and pollutants studied, as well as the production methods were addressed. The gaps are mainly related to the limited number of large or medium scale studies. Many interesting studies with large-scale application focus on commercial activated carbon. However, the increasing number of publications on the subject in recent years may be an indication that there is a scientific effort to promote the combination between laboratory studies and the market.

The results showed that there are a wide variety of precursor materials capable of becoming good adsorbents and that their application in water treatment can be very successful. Activated carbon produced from alternative materials presents good removal efficiency for most of the studied compounds.

The study approach has identified the main strengths and weaknesses of this new technology in a way that can produce good results that will help support new research and applications in this field from a global perspective.

Ackowledgments

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.