Excessive release of organic and inorganic pollutants, due
to urbanization and industrialization is a critical environmental
problem worldwide [1]. In fact, discharge of wastewater from
industrial activities releases effluents particularly rich in toxic
and carcinogenic pollutants. In the last few years, environmental
remediation was focused on the use of low cost adsorbents for the
removal of metals and metalloids from wastewater.
There are several physic-chemical methods to remove elements
from wastewater (chemical precipitation, solvent extraction,
reverse osmosis, adsorption, ion exchange and chemical reduction)
[1,2]. Adsorption is recognized as an effective and economic
method because it offers high efficiency and flexibility in operation
[3]. The adsorption phenomenon, in which the transfer of matter is
provided from a gas, liquid or dissolved solid phase (adsorbate) to
a solid biological adsorbent surface (biosorbent) in contact with it,
can be called: “biosorption”.
Different biomaterials with high specific surface areas like
activated carbons, resins and zeolites have been widely used for
heavy metal wastewater treatment. However, to minimize the
cost, alternative approaches have been developed using low cost
materials such as agricultural waste by-products [4]. These include
the use of modified clay [5,6], soil [7], seed powder [8], sugar cane
bagasse [9], coffee and tea waste [10,11], neem bark [12] maize
tassels [13], modified coconut fiber [14], coconut husk [15], rice
husk [16], oil palm shell [17], fly ash, lime, agricultural ash and saw
dust [18,19].
Among these low-cost materials, food waste adsorbents compete
favourably in terms of cost, efficiency and ease of operation [20].
Moreover, with the aim of sustainable development, recycling food
waste, which amounts to US $680 billion in industrialized countries
and US $310 billion in developing countries [21], is beneficial. Food
waste adsorbents do not require modification reaction like other
materials used in adsorption processes [22]; technical applicability
and cost advantages are two key factors for the selection of food
waste as low-cost adsorbents for treating wastewater.
In recent studies, the adsorption capacity of several food waste
materials (banana peel [22], apple peel [23], eggplant peel [24],
potato peel [25], orange peel [26], lemon peel [27,28], watermelon
peel [29,30], tomato peel [31], coffee waste [10,11,32,33] decaf
coffee waste, carob peel and grape waste [34,35]) has been assessed
by performing adsorption experiments in heterogeneous operating
conditions (Figure 1).
Figure 1: Food waste materials’ processing [36].
In a latest study [37], the efficiency of such food waste materials
for the removal of metals and metalloids from complex multielement
solutions was evaluated in homogeneous experimental
conditions, which allowed comparing the adsorption capacities
of the individual adsorbents. The pH selected for the adsorption
experiments were pH 2.0 and pH 5.5. The removal efficiency of the
food waste adsorbents was also verified on a real polluted matrix;
coffee waste and decaf coffee waste resulted the most efficient
food waste adsorbents for the removal of Cu, watermelon peel for
Pb and grape waste for Ni and Zn. This data confirmed the results
obtained by the adsorption experiments performed in synthetic
multi-element solutions. Banana peel, watermelon peel and grape
waste resulted the most efficient and the least selective adsorbents
for the removal of most of the metals and metalloids. Furthermore,
the adsorbent surfaces of the food waste materials were analysed
by FTIR spectroscopy and showed different types and amounts of
functional groups, which demonstrated to act as adsorption active
sites for various elements [37].
Considering the high efficiency of the examined low-cost
adsorbents for the removal of inorganic pollutants, preliminary
studies were conducted in our lab for assessing the potential of
the investigated food waste materials to adsorb volatile organic
compounds from a real polluted matrix of leachate. Some recent
studies have shown the efficiency of low cost materials for the
removal of industrial organic dyes [33,38,39], polycyclic aromatic
hydrocarbons [40] and phenolic compounds [41]. However, the
food waste adsorbents’ efficiency for the removal of volatile organic
compounds was not investigated.
Our preliminary studies showed good adsorption capacities
of the examined food waste materials for aliphatic and aromatic
hydrocarbons. Therefore, it is worth to carry out further studies
about volatile organic compounds’ removal by food waste
adsorbents.
Professor, Chief Doctor, Director of Department of Pediatric Surgery, Associate Director of Department of Surgery, Doctoral Supervisor Tongji hospital, Tongji medical college, Huazhong University of Science and Technology
Senior Research Engineer and Professor, Center for Refining and Petrochemicals, Research Institute, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia
Interim Dean, College of Education and Health Sciences, Director of Biomechanics Laboratory, Sport Science Innovation Program, Bridgewater State University