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Cellulose (2021) 28:9857–9871
countries, although Spanish and Finnish authors also stand out on the European continent that deserve special attention when establishing new scientific collaborations in this area. In this field, high-level journals stand out, including Carbohydrate Polymers , Journal of Applied Polymer Science and Cellulose , which gives an idea of the impact of the research. The analysis of the keywords establishes several scientific communities that indicate the main areas of research being conducted: (1) fabrication of cellu- lose-based membranes, hydrogels and materials for decontamination; (2) chemical modification of cellu- lose towards bioflocculants; (3) control and monitoring of wastewater treatment. The extraction of biological macromolecules and applications on nanotechnology account for minor contributions. Moreover, this analysis also reflects some gaps that must be overcome and that can point out for the scientific community which areas need greater efforts to be focused on, such as evaluating in each case the biodegradability of cellulose derivatives instead of taking it for granted. Also, the high functionality of cellulose allows for its modification towards promis- ing, and fortunately trendy as of today, stimuli- responsive polymers. Despite the usefulness of such polymers in solid–liquid systems, including floccula- tion (e.g., for reversible aggregation as a function of temperature or pH), the lack of those terms shows that researchers have not taken that opportunity yet. One opportunity that is being tackled and that will probably constitute a major research trend in the short term, is the use of bioflocculants to harvest microal- gae biomass, particularly as feedstock for biofuel generation. Most water treatment documents focus on the study of environmentally concerning parameters of quantitative nature, such as chemical oxygen demand, total suspended solids, turbidity and color. However, it is necessary to make efforts to study the effectiveness of this type of compounds in eliminat- ing PhEPs in order to meet the environmental legislation before the wastewater is discharged. In many articles a high-cost effectiveness and low cost of cellulose derivatives is assumed due to the great availability of the biopolymer. Nonetheless, there are no studies detailing the total cost of treatment to make it comparable with existing data in the literature on conventional coagulants/flocculants. Although laboratory-scale studies carried out with cellulosic
which ones deserve special attention. For example, stimuli-responsive polymers or “smart polymers” are macromolecules that are sensitive to a variety of signals, including temperature, pH, light, electrical or magnetic fields, chemicals, etc. In spite of being widely studied in the last decade, they do not appear in any of the clusters in Fig. 5. They have been used in medical applications and they show convincing potential for flocculation processes (Mac´czak et al. 2020). Oechsle et al. (2018) prepared a CO 2 -switch- able hydrogel from a suspension of cellulose nanocrystals (CNCs) and its properties make it a promising candidate to be used as flocculant in water treatment (Oechsle et al. 2018). However, much remains to be investigated in this field, which rises as an alternative way to obtain novel cellulose-derived bio-flocculants. Bioflocculants of cellulosic origin have been used in a wide variety of systems, including turbidity removal from drinking water and municipal wastew- ater treatment plants, water decolorization in textile industry effluent treatment, flocculation in pulp slurries, treatment of water contaminated by oil spills, etc. (Mac´czak et al. 2020). However, in coagulation-flocculation processes in wastewater, there is a lack of pilot plant experiments and techno-economic assessments with coagulants/floc- culants from cellulose, as evidenced by the absence of keywords like cost , economic , feasibility or pilot plant . Those studies are necessary to address the (sometimes unpredictable) problems associated with upscaling. In parallel, pilot plant assays allow the accomplishment of a reliable economic analysis of the process. In this sense, the authors believe that future studies should be accompanied by an economic study on the viability of the process, detailing the cost of treatment per cubic meter as a function of the application of the treated water.
Conclusions
The results of this bibliometric study show that cellulose-based agents for flocculation-coagulation processes is a research area of growing interest with a multidisciplinary approach. There is a wide variety of applications for cellulosic flocculants, but the main one by use and interest is the treatment of wastewater. China, Japan, and the US are the most prolific
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