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Cellulose (2021) 28:9857–9871
by many microorganisms, granting cellulose versa- tility and biodegradability. An in-depth bibliometric analysis will allow us to estimate the extent of interest in cellulose derivatives in wastewater treatments. This valuable tool, which has proved its usefulness in the context of coagula- tion-flocculation processes and other water remediation techniques (Zhang et al. 2020; Demir and Sharma 2021), helps researchers in relating scientific production and industrial development, evaluating the main trends in the generation of knowledge, and identifying the main contributors (Zhang et al. 2020). While the timely bibliometric study by Zhang et al. (2020) on agents for sludge removal mentions polysaccharides such as starch and chitosan (Zhang et al. 2020), cellulose is left out the picture and, for that matter, the vast literature on cellulose-based agents for coagulation-flocculation is yet to be analysed. We aim to provide researchers and manufacturers with a thorough and systematic analysis of the scientific production on cellulose and its derivatives in wastewater treatments, particularly for particle aggregation purposes. In order to show the growing interest in this topic, trends of cellulosic coagulants, flocculants and/or adjuvants are analysed. More specifically, the methodology encompasses Scopus- indexed publications (studying both journals and papers therein), books or book chapters and confer- ences, if they are accessible through the keywords that define the scope of this article. This paper seeks to assess the evolution of the scientific production on the topic, to classify it by type of publication and subject area, and to identify the main authors and institutions involved. These tasks manifest the poten- tial of the knowledge gathered to evaluate and improve the current industrial processes, their envi- ronmental impact, and the social perception thereof.
carbon, filtration, and chemical oxidation. Usually, none of such methods can offer a stand-alone solution and they need to be continuously revised, comple- mented and improved to address the new emerging contaminants (Verma et al. 2012; Teles et al. 2020). Undoubtedly, coagulation-flocculation is one of the most widely used wastewater treatment tech- niques, aiming to reduce turbidity, colour and organic matter levels by aggregation of small or colloidal particles (Matilainen et al. 2010). These terms, coagulation and flocculation are sometimes used interchangeably and/or ambiguously (Xiao et al. 2015). For the sake of accuracy and in agreement with other authors (Al-Risheq et al. 2021) we henceforth define coagulation as the destabilization of a suspension of particles, whereas flocculation is the aggregation of destabilized particles. By reducing the electrostatic repulsion between microparticles, their size geometrically increases, and thus sediment with ease or become readily treatable by other kinds of solid–liquid separation (Matilainen et al. 2010). Depending on the nature of the agent, this loss of electrostatic repulsion can be attained by chemical or organic coagulation. Chemical coagulation, based on the use of inorganic compounds, strongly depends on many variables such as the dosing time, the pH, and the concentration of the inorganic salts (Li et al. 2021). Hence, it is difficult to predict the behaviour of a certain chemical coagulant in real complex environments. Organic flocculation, on the other hand, usually involves biomolecules of natural origin and attains denser and bigger flocs, which may imply a more cost-effective solution (Renault et al. 2009). Besides improving the coagulation process in itself, some other advantages include more biodegradability and less toxicity to the environment (Bolto and Gregory 2007). It is easy to see why, among the biological macromolecules that can be used as main agents or at least as adjuvants in coagulation-flocculation pro- cesses, cellulose derivatives play a major role. Firstly, cellulose is highly available, being the most abundant biopolymer on Earth (Peng et al. 2020). Secondly, like any other hydroxy polymer, it can be chemically modified towards different functional groups, cationic or anionic, hydrophilic or hydrophobic, etc. (Moral et al. 2015; Aguado et al. 2019). Thirdly, their glycosidic bonds are chemically stable, but cleavable
Methodology
Searching process
The strategy chosen to develop this bibliometric analysis involves the search engine of Elsevier’s database Scopus, as chosen elsewhere (Mongeon and Paul-Hus 2016), given that it encompasses more publications than ISI Web of Knowledge and, at the
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