Biochar derived from fruit by-products using pyrolysis process for the elimination of Pb(II) ion: An updated review
Graphical abstract
Introduction
The global human population is set to overshoot to 9.9 billion people by 2050 from the current living 7.8 billion people (PRB, 2020). The growing human population and increased development would not only boost the demand for food but also lead to serious food wastages (Baig et al., 2019). The United Nations Food and Agriculture Organization (FAO) reported that a billion tonnes of food are wasted every year of which 60% is contributed from solid food waste, including fruit and vegetable by-products comprising peeled skin, seeds, and stones, which ultimately pose a serious waste disposal problem (FAO, 2020b; Sagar et al., 2018). For instance, in Malaysia, approximately 20–50% of fruits and vegetables are usually discarded, indicating that almost half of the agricultural yields are lost during the process of food management (Sulaiman and Ahmad, 2018). These food residues are usually placed in a bin, thrown down the drain, or fed to animals. In fact, the significant contribution of fruit and vegetable wastes in municipal solid waste has become the biggest challenge to local authorities and city councils in developing countries to handle the issue of solid waste management.
Furthermore, the rising volume of food waste has afflicted increasing burden on environmental issues. Inappropriate management of landfill waste would result in the release of methane and carbon dioxide as well as the increasing cost of the municipal budget for waste management (Deng et al., 2012; Lipiński et al., 2018; Lopez Barrera and Hertel, 2021). In addition, the huge amount of waste generated from fruit and vegetable could severely impact the climate, water bodies, land, and overall biodiversity. Although many efforts have been implemented by various governments and international bodies through the setting up of waste management policies and aggressive awareness campaigns to educate the community, the outcome is still far from expected as the problem is complicated, especially in the context of agriculture waste management (Jayashree et al., 2012).
In order to promote a zero-waste strategy, the conversion of fruit waste into value-added products is one of the alternative solutions to minimise the waste generation issue (Sirohi and Pandey, 2019). Based on the findings from past researches, it was concluded that certain fruit wastes possess great potential to be transformed into other useful products, such as biochar that can be utilised as an adsorbent to adsorb metal ions from water or wastewater. Fruit waste has been proven to be a good adsorbent due to the high content of functional groups, such as carboxylic acid and hydroxyl groups, on the surface of the fruit peel. These functional groups aid in the elimination of heavy metal ions using ion-exchange or complexation, thus, increasing the adsorption capacity (Chao et al., 2014; Saini et al., 2020). The advantages of fruit waste as low-cost adsorbents have been reported in previous studies, including cost-effective and environmentally friendly material, widely available, requires minimal treatment, and is highly efficient (Chao et al., 2014; Kumar et al., 2019). Since the properties of adsorbents serve as a crucial factor for the adsorption of metal ions; hence, research on the development of low-cost and effective adsorbents for heavy metal removal is of great significance. To date, the global scientific community have put in a lot of effort in search of effective alternative adsorbents from cheap raw materials. The persistent effort can be measured by analysing the database in ScienceDirect by entering the keywords “fruit waste as an adsorbent for heavy metal ion removal”. The search retrieved 16 research articles published in 2000 and approximately 409 research articles as of July 2021. The increasing trend of published articles indicates the deep interest among many researchers on this topic. The introduction of fruit waste-based adsorbent is beneficial to the economy and is capable to provide competitive performance with commercial activated carbon. It can also be used in many applications, including gas adsorption and recovery of metals present in the wastewater (Deng et al., 2012).
According to the Agency for Toxic Substances and Disease Registry, lead (Pb) ranked second (after arsenic) as the most toxic element among the hazardous metals (ATSDR, 2020). It has been considered one of the most toxic heavy metals in the ecosystem. Therefore, cost-effective methods and high adsorption capacity performance are needed for Pb(II) ion removal. This review provides a solid foundation on the utilisation of fruit wastes for heavy metals removal and adds significant insights into the importance of creating sustainable solutions that can minimise waste generation. To the best of our knowledge, a systematic and comprehensive review on the conversion of fruit waste as biochar using the pyrolysis method, a detailed description of the preparation of biochar, and the relationship between adsorption mechanisms and adsorption capacity of biochar emphasising on Pb(II) removal has not yet been reported to this day. Hence, this review attempts to address the aforementioned research gap by setting up the review paper as follows: the introductory section provides an overview of the overwhelming fruit waste issue and the solution to tackle the problem. The second section describes a full detail of the review methodology that was carried out in the study to collect data from the selected database. Next, a detailed explanation of Pb(II) properties based on their chemical, physical, and mechanical properties is given, followed by a discussion on the effect of Pb(II) on humans. A more in-depth discussion on the variety of low-cost materials derived from fruit waste residue is presented, which focused on the preparation step of biochar using pyrolysis and other conversion method as well as the possible mechanism during the reaction process. Finally, this paper concludes with an overview of the main findings and several suggestions for future studies on the potential treatment technologies using fruit waste-based adsorbents.
The specific objectives of this review are as follows:
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To summarise the scientific inventions and reviews on various types of fruit waste as an effective adsorbent for the adsorption of Pb(II) ions from synthetic and real wastewater.
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To provide detailed information on the preparation step of biochar using pyrolysis and other conversion method as well as the possible mechanisms associated with these materials.
This paper would provide greater understanding to new researchers regarding the preparation of biochar from fruit waste through the pyrolysis technique as well as offering fresh and innovative ideas from the current research that can be applied in their research work. This information is very useful for researchers that aim to venture into this field. For experienced researchers, this paper would fulfil the role as a central referral point to dissect recent progress on fruit waste-based adsorbents and the adsorption mechanism in proposing future research directions. Overall, this review paper would be considered a significant point of reference for future studies.
In 1999, Moher et al. (1999) developed a standard checklist item for the preparation of a meta-analyses report on the randomised clinical controlled trials using the Quality of Reporting of Meta-analyses (QUOROM) statement. Moher et al. (2009) also published an article to introduce a standardised methodology and a flow diagram to report systematic reviews, which is known as the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The PRISMA systematic review was used primarily to provide supporting reports on medical studies for well-informed decision-making in the health sector. Since then, the application of systematic review methodology has spread beyond the medical fields, including in software engineering, education, social welfare and international development, and the public and environmental health sector. PRISMA is now widely used by a range of journals as a pre-submission checklist, specifically for review articles. Given that PRISMA was developed for systematic reviews in the healthcare sector, it has limited applicability for reviews in other scientific fields, such as engineering and environmental management.
The PRISMA is a standard guideline for conducting systematic reviews to guide researchers to improve the reporting of systematic reviews and produce high-quality literature review with complete information (Ahn and Kang, 2018). The methodology also provides an item checklist for researchers to examine their reports, such as the value of their systematic review to users and improving the objective and outcomes of the report, completely and accurately. The standard flow diagrams for the original and updated reviews as well as the checklist are available on the PRISMA statement website (PRISMA, 2021). In the present review study, the PRISMA method was employed based on the standard guidelines, including literature search for a specific topic, choosing the suitable published papers, extraction of data, and summarising (see Fig. S1 in the Supplementary file). Thus far, there is no systematic review article has been published on the potential of fruit waste as an adsorbent to eliminate Pb(II) ions using the PRISMA method.
The keyword-based search for this review as demonstrated in the Supplementary file (Table S1) was conducted based on the PRISMA guidelines. Currently, there is limited information on the potential use of fruit waste as an effective adsorbent to eliminate Pb(II) ions. Most of the top-tier databases (such as Web of Science or Scopus), only listed few studies related to this field, while many of the research focused on other types of raw material (waste material) or adsorbents. The total of publications related to this topic based on the Web of Science database is 340 articles and 447 articles from the Scopus database. The number of publications was highest in 2020 and the lowest was in 2008 and 2009. The highest number of published articles were from India followed by China and Brazil.
In this review, all the scientific information was compiled from the database following the PRISMA method. Firstly, a literature search was carried out using the combined search results from multiple databases, including Scopus, Web of Science and ScienceDirect. The language used for the title, abstract, and full article was selected based on the articles published in the English language only. In order to include as many literature reports as possible, the keywords were emphasised on fruit waste materials that are commonly found in developing countries. In addition, a suitable keyword to search for research and review articles was based on the relevant literature and summarised publications on the elimination of Pb(II) via adsorption. The search strategy was based on the selected keywords and a combination of the keywords such as “fruit waste AND adsorption AND Pb(II)” OR “fruit waste AND adsorption AND lead” OR “fruit waste AND adsorption AND heavy metal” OR “fruit waste AND pyrolysis AND Pb(II)” OR “fruit waste AND pyrolysis AND lead” OR “fruit waste AND pyrolysis AND heavy metal”. These keywords were chosen to search for better input and suitable information regarding the preparation step of biochar, possible mechanisms associated with these materials, and regeneration studies on the adsorption of Pb(II) using fruit waste as adsorbents.
The second step of the PRISMA method involved the classifying of the published articles and filtering of unrelated data using Microsoft Excel 2019 (Microsoft, USA). The collected data were screened by analysing the title, abstract, and full articles. Any unrelated articles from the scope of the study were removed and the data published from 2000 to 2021 was compiled.
In the final reviewing stage, the content of each published article was evaluated and valuable information from the articles was extracted.
Section snippets
Overview of Pb
Pb is one of the metal elements that have been extensively used in various applications since ancient times (Holland et al., 2003; Nriagu, 1983). They were used by the Egyptians and the Romans for glazing pottery, constructing water pipes and plumbing, and a component in cosmetics (Ghazi and Millette, 1964). Pb is also known as one of the seven metals of antiquity due to its unique properties, such as soft texture, very malleable, ductile, low melting point, a poor conductor of electricity or
Carbon-based adsorbents derived from fruit waste
The advanced development of low-cost materials as effective adsorbents from agricultural wastes to treat wastewater has attracted the interest of researchers in the field of heavy metal, particularly the use of adsorption techniques. This is due to the easily available, cheap, eco-friendly material, and low processing requirement to setup the adsorption process (Abegunde et al., 2020; Malik et al., 2017).
Fruit waste makes a suitable candidate as an adsorbent as it contains lignin,
Summary and prospects of fruit waste adsorbents
This review has presented an overview of the past and current development of Pb(II) removal using low-cost biochar from published articles between 2000 and the present, focusing on the conversion of fruit waste materials into biochar for the adsorption of Pb(II). This study provided an up to date scientific inventions and reviews on the various type of fruit by-products for effective adsorption of Pb(II) ions from water and wastewater. This study also presented detailed information on the
Credit author contribution statement
Farihahusnah Hussin: Writing - original draft, collecting and analysis journal articles. Mohamed Kheireddine Aroua: Reviewing & Editing, Supervision. Małgorzata Szlachta: Reviewing & Editing final version of manuscript and provide resources to address reviewer comments.
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.
Acknowledgements
The author would like to thank Sunway University and Research Service for the research funding provided (grant no. GRTIN-IRG-33-2021).
References (248)
- et al.
Removal of Pb(II) from aqueous solution by using biochars derived from sugar cane bagasse and orange peel
J. Taiwan Institut. Chem. Eng.
(2016) - et al.
Effective carbonaceous desiccated coconut waste adsorbent for application of heavy metal uptakes by adsorption: equilibrium, kinetic and thermodynamics analysis
Biomass Bioenergy
(2020) Chapter 13 - lead
- et al.
Recent trends of heavy metal removal from water/wastewater by membrane technologies
J. Ind. Eng. Chem.
(2019) - et al.
A review on the influence of chemical modification on the performance of adsorbents
Resourc. Environ. Sustain.
(2020) - et al.
Biosorptive removal of Pb2+ and Cd2+ onto novel biosorbent: defatted Carica papaya seeds
Biomass Bioenergy
(2011) - et al.
Facile one pot green synthesis of Chitosan-Iron oxide (CS-Fe2O3) nanocomposite: removal of Pb(II) and Cd(II) from synthetic and industrial wastewater
J. Clean. Prod.
(2018) - et al.
Removal of Cu(II), Cd(II) and Pb(II) ions from aqueous solutions by biochars derived from potassium-rich biomass
J. Clean. Prod.
(2018) - et al.
Enhanced adsorption of aqueous Pb(II) by modified biochar produced through pyrolysis of watermelon seeds
Sci. Total Environ.
(2021) - et al.
Adsorption studies on citrus reticulata (fruit peel of orange): removal and recovery of Ni(II) from electroplating wastewater
J. Hazard Mater.
(2000)