Abstract
Over the past decade, biochar (BC) has received significant attention in many environmental applications, including water purification, since it is available as a low-cost by-product of the energetic valorisation of biomass. Biochar has many intrinsic characteristics, including its porous structure, which is similar to that of activated carbon (AC), which is the most widely used sorbent in water treatment. The physicochemical and performance characteristics of BCs are usually non-homogenously investigated, with several studies only evaluating limited parameters, depending on the individual perspective of the author. Within this review, we have taken an innovative approach to critically survey the methodologies that are generally used to characterize BCs and ACs to propose a comprehensive and ready-to-use database of protocols. Discussion about the parameters of chars that are usually correlated with adsorption performance in water purification is proposed, and we will also consider the physicochemical properties of pollutants (i.e., Kow). Uniquely, an adsorption efficiency index BC/AC is presented and discussed, which is accompanied by an economic perspective. According to our survey, non-homogeneous characterization approaches limit the understanding of the correlations between the pollutants to be removed and the physicochemical features of BCs. Moreover, the investigations of BC as an adsorption medium necessitate dedicated parallel studies to compare BC characteristics and performances with those of ACs.
Highlights
Biochar (BC) is a low-cost solid by-product of the thermal conversion of feedstocks of a different nature, such as agricultural [1], wood residues [2], manure [3], and sludge [4].The thermal conversion procedures available at this time to obtain biochar can be grouped into the following technologies, according to the processing parameters: fast [5]and slow pyrolysis [6], gasification [7], hydrothermal [8], and flash carbonization [9].Biochar production mainly relies on the first two technologies
This approach would ensure the coherence of the results presented in the literature and the straightforward comparison among the biochars produced and a comparison between biochar and activated carbon
Van Krevelen plots, which were previously discussed in the activated carbon section, are extensively employed in biochar characterization to define biochar composition as a function of the thermal conditions used for biochar production [70,84,85]
Summary
Biochar (BC) is a low-cost solid by-product of the thermal conversion of feedstocks of a different nature, such as agricultural [1], wood residues [2], manure [3], and sludge [4]. The concept of exploiting biochar for water treatment as a potential surrogate of activated carbon (AC), the commercial adsorbent that is the most widely used in the refining tertiary stage of water treatment technologies, has escalated the need to improve the sorption characteristics of biochar These efforts are clearly highlighted by the literature and reviews that analyse strategies for the surface modification of biochar [24] or the production of biochar with the addition of nanoscale metals [25] to the biomass before thermal conversion. Despite authors studying the removal of compounds by BCs agree with the fact that physicochemical and performance characterization is of paramount importance to understand pollutant–BC interactions [26,27], a lack of homogenous scientific approaches is observed in the current literature due to the absence of any standardization On this premise, it becomes relevant to compare biochar and activated carbon as adsorbents for organic micropollutants in water purification. To the best of our knowledge, all of these aspects are innovatively investigated in this review
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