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\DOI{10.5802/crchim.392}
\datereceived{2025-03-05}
\dateaccepted{2025-03-05}
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%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{Materials and Energy Valorization of Biomass and Waste : The Path for Sustainability and Circular Economy Promotion}
%\def\cdr@specialtitle@french{Valorisation \'energ\'etique et mati\`ere de la biomasse et des d\'echets : la voie de la durabilit\'e et de la promotion de l'\'economie circulaire}
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\dateposted{2025-03-17}
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\title{Foreword to Special Issue ``Valorization of biomass and waste:
the path for sustainability and circular economy promotion''}

\alttitle{Avant-propos du num\'ero sp\'ecial \og Valorisation \'energ\'etique et mati\`ere de la biomasse et des d\'echets : la voie de la durabilit\'e et de la promotion de l'\'economie circulaire \fg{}}

\author{\firstname{Salah} \lastname{Jellali}\CDRorcid{0000-0002-4095-4154}}
\address{Centre for Environmental Studies and Research, Sultan Qaboos
University, Muscat, Al-Khoud 123, Oman}
\email[S. Jellali]{s.jelali@squ.edu.om}

\author{\firstname{Mejdi} \lastname{Jeguirim}\CDRorcid{0000-0003-2401-5824}\IsCorresp}
\address{The Institute of Materials Science of Mulhouse (IS2M),
University of Haute Alsace, University of Strasbourg, CNRS, UMR 7361,
F-68100 Mulhouse, France}
\email[M. Jeguirim]{mejdi.jeguirim@uha.fr}

\keywords{\kwd{Solid wastes}
\kwd{Management}
\kwd{Biomaterials}
\kwd{Adsorbents}
\kwd{Catalysts}
\kwd{Energy recovery and storage}}

\altkeywords{\kwd{D\'echets solides}\kwd{Gestion}\kwd{Biomat\'eriaux}\kwd{Adsorbants}\kwd{Catalyseurs}\kwd{R\'ecup\'eration et stockage d'\'energie}}

\begin{abstract}
Biomass and wastes are produced in huge amounts all over the world.
Even if they have high potential to be valorized in various sectors
including energy, agriculture, and environment, a big fraction
continues to be considered as a serious burden. This situation is
worsened by the global climate change due to important emission of
greenhouse gases (GHGs) generated by the consumption of considerable
amounts of fossil fuels and also by the mismanagement of the produced
biomass and wastes. The sustainable valorization of these biomass and
wastes for energy recovery, synthesis of new materials for use in
industry, in agriculture, and in environment, will decrease GHG
emission, boost the circular economy, and preserve the environment. The
current special issue published in Comptes Rendus Chimie (CRC) reviews
recent advancements in biomass and waste valorization for the promotion
of circular economy and sustainability concepts. 
\end{abstract}

\begin{altabstract}
Les d\'{e}chets solides incluant la biomasse sont produits en grandes
quantit\'{e}s dans le monde. M\^{e}me si ces d\'{e}chets ont un
potentiel \'{e}lev\'{e} de valorisation dans divers secteurs
(\'{e}nerg\'{e}tique, agriculture et environnement), une grande partie
continue d'\^{e}tre consid\'{e}r\'{e}e comme un fardeau dans plusieurs
pays. Cette situation est aggrav\'{e}e par le changement climatique en
raison des importantes \'{e}missions de gaz \`{a} effet de serre (GES)
dues \`{a} la consommation de quantit\'{e}s consid\'{e}rables de
combustibles fossiles et \'{e}galement \`{a} la mauvaise gestion de ces
d\'{e}chets. La valorisation durable de ces d\'{e}chets pour la
production d'\'{e}nergie renouvelable, la synth\`{e}se de nouveaux
mat\'{e}riaux destin\'{e}s \`{a} \^{e}tre utilis\'{e}s dans
l'industrie, l'agriculture et l'environnement, diminuera les
\'{e}missions de GES, stimulera l'\'{e}conomie circulaire et
pr\'{e}servera l'environnement. L'\'{e}dition sp\'{e}ciale actuelle
publi\'{e}e dans Comptes Rendus Chimie (CRC) examine les avanc\'{e}es
r\'{e}centes en mati\`{e}re de valorisation de la biomasse et des
d\'{e}chets pour la promotion de l'\'{e}conomie circulaire et de
durabilit\'{e}.
\end{altabstract}

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\section{Introduction} \label{sec1}

Consumption of resources and production are continuously increasing in
the world. This is mainly caused by the high rate of population growth,
urbanization, and industrialization. This has ultimately induced the
production of huge amounts of waste. Waste can be liquid or solid.
Solid wastes are usually classified according to their source. They
include household waste, institutional waste, industrial waste, medical
waste, agricultural waste, and municipal waste. Biomass is an important
part of this waste. It is defined as renewable organic materials
originating from plants and animals and represents an important
fraction of municipal solid wastes.

According to the latest report of the United Nations Environment
Program (UNEP 2024), municipal solid waste produced globally was
evaluated to 2.1 billion tons. This amount will reach more than 3.7
billion tons by 2050. In 2020, only 13\% of this amount was valorized
for energetic purposes. In developing countries, direct incineration
and landfilling are generally used for the management of wastes, which
result in negative effects onto the environment and \mbox{human}
health. The same report of UNEP \mbox{indicates} that, in comparison with 2020
and for a waste management scenario as usual, by 2050 there will be a
91\% increase in GHG emission, a 84\% increase in loss of natural
species, and a 87\% increase in negative impact on human health.

Valorization of waste, and particularly biomass has become a promising
alternative option to incineration and landfilling. Waste valorization
consists in the application of the 4Rs principle: Reduce, Recycle,
Reuse, and Recovery. The last option permits the conversion of wastes
into valuable materials that can be used in various sectors such as
energy, agriculture, and environment. Indeed, renewable energy can be
recovered from this waste through various mastered technologies
including anaerobic digestion, gasification, and pyrolysis. This energy
can partially replace the one generated from fossil fuel combustion and
consequently reduces atmospheric pollution as well as GHG emission.
This will in turn facilitate the transition to sustainable energy that
is regarded as a focal point in the United Nations Sustainable
Development Goals and also the Paris Agreement on climate change.
Besides renewable energy production systems, an intensive research work
is being deployed for its tailored storage. In this context, the
synthesis of specific materials is considered an important challenge to
advance the transition to sustainable and renewable energy. Moreover,
new valuable materials can be also derived from this waste. For
instance, organic wastes may be transformed into an eco-friendly
compost (through composting technology) that can be used instead of
synthetic fertilizers in agriculture. This operation will boost the
circular economy concept and reduces farmersâ€™ expenses. Besides that,
this waste may be converted into a valuable biochar through the
pyrolysis process. This biochar, in raw or modified form, may be used
for the treatment of industrial/urban wastewater. Moreover, it can be
used for nutrient recovery from actual wastewater for further use in
agriculture. These nutrients-loaded biochars, when used to amend
agricultural soils, usually allow soils to improve their water holding
capacity and microbiological activity. Furthermore, it can act as
slow-release fertilizer which offers cultivated plants the required
nutrients during a long period and at the same time reduces the
pollution risk to the underlying groundwater. Likewise, using biochar
instead of activated carbons for the treatment of wastewater and in
substitution of synthetic fertilizers promotes the circular economy and
sustainability concepts, reduces GHG emission, protects the groundwater
against pollution, and offers a high economic added value to farmers.
\looseness=-1

The present special issue in the journal ``Comptes Rendus Chimie'', is
entitled: ``Valorization of biomass and waste: the path for
sustainability and circular economy promotion''. It provides an
interesting update on the conversion of wastes, in general and biomass
in particular into high added-value by-products by using advanced and
eco-friendly technologies. These by-products are intended to contribute
to the promotion of circular economy and sustainability. Moreover, this
special issue aims to fulfill national and international requirements
regarding sustainable development and climate change adaptation and
mitigation.

\section{Outcomes} 

The current special issue contains 12 papers that have undergone a peer
review process by at least two skilled reviewers. Published papers
address several subtopics, including: (i) direct valorization of waste
in several domains including concrete, cellulose and biomaterials
extraction, (ii) biomass turned into adsorbents for removal of
pollutants from wastewater, (iii) use of catalysts to improve the
quality of biomass conversion by-products, (iv) application of
hydrothermal carbonization as an innovative option for waste
management, and (v) test of new materials for solar energy storage.

The first part of this special issue addresses the challenges of waste
management, direct reuse, and the extraction of valuable
biomaterials~\cite{1,2,3,4,5}. For instance, Chaouch et~al.~\cite{1}
investigated the use of
recycled Polyvinyl chloride (PVC) powder as a substitute for
conventional PVC resin in the expanded layer of floorcoverings. They
showed that mixing recycled PVC with PVC resin up to 33\% did not
affect its mechanical characteristics (i.e., break strength, elongation
at rupture, and tear resistance). Moreover, with finer recycled PVC
particles (size lower than 200~${\upmu}$m), this percentage can be
pushed further to 86\%. In another study, in order to reduce the cost
of air condition in arid areas, Siddique et~al.~\cite{2} tested the use
of four types of recycled plastics: low-density polyethylene (LDPE),
\mbox{polypropylene (PP),} polyester, and \mbox{high-density} polyethylene (HDPE), as
partial sand substitutes in concrete for roofing applications. Their
results show that LDPE exhibited the most significant economic and
environmental benefits. In the case of New Delhi, a LDPE percentage of
30\% leads to an annual saving of around 1~\dollar/m\tsup{2}
and a reduction in carbon emissions of 18~kg/kWh. The third study, by
Ben Ali et~al.~\cite{3}, showed that cellulose can be extracted in an
eco-friendly way from prickly pear seeds. The cellulose extraction
yield was 39.3\% by maceration and 23.2\% when using the Soxhlet
extraction method. Moreover, characterization of the extracted
cellulose showed that it was exceptionally strong and light, allowing
its possible use for the production of carbon fibers for reinforcing
composite materials used in the aerospace, automotive, shipbuilding,
and other industries. In the fourth study, Mestour et~al.~\cite{4}
examined the optimization of using supercritical CO\tsub{2}
for the extraction of bioactive substances from onion waste. They
reported that the optimal oil extraction yield (24.4\%) was achieved
for a pressure, temperature, particle size, and CO\tsub{2}
mass flowrate of 250~bar, 57~\textdegree C, 0.25~mm, and 50~g
CO\tsub{2}/min, respectively. The analysis of the oil
produced by gas chromatography showed that it contained the four
following fatty acids: 9,12-octadecadienoic acid, methyl ester;
9,12-octadecadienoic acid (Z,Z)-, methyl ester; 9-octadecadienoic acid
(Z)-, methyl ester; and hexadecanoic acid, methyl ester. Finally,
Deffar et~al.~\cite{5} studied the extraction of bioethanol from a
pre-treated water hyacinth biomass, a free-floating perennial plant.
Bioethanol extraction was carried out through a fermentation process by
using a locally isolated thermophilic consortium in a partially
consolidated bioprocessing process. They showed that the maximum
experimental yield (7.7~g/L) was achieved at 50~\textdegree C, 72~h of
fermentation time, and an inoculum dose of 6.64\% ($v/v$). 

The second part of this special issue is about biomass transformation
into valuable by-products including biochar, bio-oil and
biogas~\cite{6,7,8,9,10,11,12}. In this context, Jellali et
al.~\cite{6} synthesized three Mg-, Al-, and Mg/Al-modified biochars
from date palm wastes and valorized them for the recovery of phosphorus
from aqueous solutions under a wide range of experimental conditions.
Their ultimate aim is to use the phosphorus-loaded biochar in
agriculture as a \mbox{slow-release} fertilizer. They showed that the biochar
modified using a Mg/Al mixture solution exhibited the best
physico-chemical properties and consequently the highest P recovery
efficiency (14.1~mg/g). Moreover, the P recovery process involved both
physical and chemical mechanisms. They conclude that the P-loaded
Mg/Al-modified biochar has a good potential to be used as an attractive
slow-release fertilizer instead of the costly commercial ones. In
another study, Alfares et~al.~\cite{7} examined the valorization of an
abundant plant waste in Iraq: pinecones. They pyrolyzed different
particle sizes (0.26--0.841~mm) of this waste at numerous temperatures
(400--600~\textdegree C) for diverse residence times (30--120 min) and
various heating rates (10--50~\textdegree C/min). They showed that the
highest pyrolytic oil yield production (42.1\%) was obtained for a
particle size of 0.4~mm, a pyrolysis temperature of 500~\textdegree C,
a residence time of 1~h, and a heating rate of 30~\textdegree C/min.
The bio-oil characterization indicated that it can be considered as a
high energy fuel since its higher calorific value was evaluated to be
around 27.0 MJ/kg. Moreover, the activation of the corresponding
biochar with K\tsub{2}CO\tsub{3} at 750~\textdegree C led to the
formation of a highly porous material. This activated biochar exhibited
a large Cr(VI) removal capacity under a wide range of experimental
conditions. For their part, Audu et~al.~\cite{8} studied the effect of
a new catalyst, synthesized by incorporating mesoporous iron oxide
(FeO) into alumina (Al\tsub{2}O\tsub{3}), on the quality of the biogas
formed from the pyrolysis of polyethylene terephthalate (PET). They
showed that, in comparison with a blank test, use of this catalyst at a
5\% load decreases oxygen content in the biogas from 23.3\% to 5.3\%.
Moreover, the presence of this catalyst significantly improved the
contents in H\tsub{2} and CH\tsub{4} gases. The highest H\tsub{2} and
CH\tsub{4} contents were evaluated to 17.1\%, and 16.2\%, respectively.
These yields were obtained for catalyst doses of 5 and 3\%,
respectively. In another study, Zheng et~al.~\cite{9} synthesized a
novel hierarchical calcium-based catalyst CaO(S) through
sol--gel-biotemplate method using calcium nitrate-ethanol-citric acid
as precursor and rape pollen as biotemplate. Then, they used it to
catalyze oil/methyl acetate/methanol for no-glycerol biodiesel
production. They showed a relatively high yield of no-glycerol
biodiesel (96.6\%) for the following optimal parameters: a temperature
of 65~\textdegree C, a catalyst dosage of 10\%, and an oil/methyl
acetate/methanol ratio of 1/1/8. Furthermore, the \mbox{regeneration} study
showed a significant catalytic stability with a yield of 91.4\% after
three cycles. Besides that, hydrothermal carbonization (HTC) of biomass
was studied in this special issue~\cite{10,11}. In this context, Zhang
et~al.~\cite{10} studied the effect of the HTC experimental conditions
on the yield and quality of the hydrochars produced from sludge. They
showed that the organic matter and ash content in the sludge as well as
the HTC temperature highly affect the fuel properties of hydrochars.
However, the solid loading had no significant effect on hydrochar
quality but did affect energy consumption by the HTC process itself.
The former lack of effect was confirmed by Bedoui et~al.~\cite{11} when
studying the HTC of date pits and pine nut shells at 250~\textdegree C
for 1~h. These authors also showed that the hydrochar with the largest
higher heating value (29.7 MJ/kg) was observed for date pits and a
solid/water ratio of 1:48. Moreover, steam activation of the hydrochar
for 1~h at 850~\textdegree C highly improved its physicochemical
properties, especially its porosity and surface area. 

In a last but not least contribution, Sharma et~al. \cite{12},
studied the effect on freshwater production of incorporating sensible
heat storage materials (i.e., bricks, paper napkins wrapped around the
brick, sand bed) in a triangular solar still. They showed that adding a
sand bed reduced the cost of freshwater generation by around 43\%, and
the payback \mbox{period} by 44\%.

\section*{Declaration of interests}

The authors do not work for, advise, own shares in, or receive funds
from any organization that could \mbox{benefit} from this article, and have
declared no affiliations other than their research organizations.

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