**3. Adsorption on rape waste biomass**

## **3.1 Adsorption/biosorption processes**

*Environmental Issues and Sustainable Development*

[33] and new polyurethane composites [23].

*Rape waste biomass as resourceful raw material in circular economy.*

level, and makes possible RSM use as feed additive or as a source for production of protein-rich ingredients with specific value and functionality [31]. The biotransformation of RSM using bacteria increases its nutritional value and enriches it with a variety of additives, including polymers, bio-surfactants and enzymes [32]. RSM has proved to be a plant-derived alternative for development of bio-plastic materials

The lignocellulosic biorefinery strategies integrate physical, chemical, thermophysical, thermochemical or biological processes for the pretreatment and conversion of biomass into bio-based products [34]. In the case of RS, these processes are adapted to the characteristic content of cellulose, hemicellulose and lignin that are the main components responsible for biorefinery. The use of the whole plant of RS for production of biodiesel, bioethanol and methane into the frame of biorefinery concept resulted in a 3 times increase of the efficiency of energy recovery as compared to conventional process of biodiesel production [35–37]. RS straws, containing >50% of carbohydrates, are an interesting source of biomass for biorefineries, by conversion into bioenergy and high-value chemicals. It is also an attractive source of fermentable sugars for bioethanol production [19]. More than 50% of RS

RS stalk and straw also present interest in pulping and papermaking industries [39–41]. The potential of RS straws as source of lignocellulosic fibers can also be valorized for the production of biocomposite materials [42, 43]. The beneficial effects of RS stalks use on the humus and nutrients content of some damaged soils have been pointed out [44, 45]. Polyphenols and proteins were extracted from rapeseed stems and leaves by pulse electric fields [46]. Another potential use for canola leaves is as annual forage for field-raised swine and poultry. RS leaves and hulls can be used in livestock (rabbits, swine, poultry, fish) feeding [17, 47], or substrate for fungi production [48]. RS shells can be used as precursors for activated carbon materials as cathode in lithium-sulfur batteries [49]. Other applications of RS wastes include the use as soil amendments for increasing crop growth, usually in

Another interesting possibility of recycled–value added application of RS wastes involves their ability to act as efficient biosorbent for the removal of heavy metals

straw could be recovered as xylan, lignin and nanocellulose [38].

**144**

**Figure 2.**

biochar form [8, 50, 51].

Among the numerous wastewater treatment processes, adsorption distinguishes by efficiency, design simplicity and flexibility, operation easiness, insensitivity to toxic pollutants and economic feasibility [52]. Adsorption refers to the retention of a chemical species (adsorbate) on the surface of a solid substance (adsorbent) by means of physical and chemical interactions. The existence of weak van der Waals interactions determines the fast kinetics, low heat, monolayer or multilayer coverage, non-selectivity and reversibility of the physical adsorption. A chemisorption mechanism reaches equilibrium slower due to creation of covalent bonds, which causes a high activation energy, monolayer coverage and irreversibility. The adsorption of inorganic and organic pollutants from wastewater is most often the result of both types of mechanisms overlapping. The significance of adsorption for wastewater treatment is highlighted by the increasing range of materials used as adsorbents. The materials that can act as adsorbents are remarkable by the variety of structures and properties. They can be raw and modified materials of mineral, organic or biological origin, natural materials, synthetic materials, industrial and agricultural wastes and biomasses [53].

The "green" subcategory of adsorption, biosorption, can be defined as the low-cost and low-tech concentration of pollutants from aqueous media on the solid surface of a biological matrix (biosorbent), achieved through a passive mechanism [54]. As a physico-chemical process, biosorption works by a combination of different interactions ranging from hydrogen forces to covalent bonds through which the targeted toxic species is retained on the biosorptive materials surface. The key concepts of biosorption have been fully decrypted by means of a large number of laboratory studies addressing issues of fundamental research (**Table 1**).

Due to its quasi-perfect framing into the sustainable development coordinates, biosorption has received considerable acceptance in removing heavy metals and organic pollutants from wastewater [54, 55]. Besides the ecologic and economic advantages, biosorption is also challenging by its applicability over a wide array of operational conditions, adaptability to varied designs of systems, possibility of sequential or simultaneous removal of pollutants from large volumes of wastewaters. Biosorption is a propriety characteristic to a broad spectrum of natural or waste bio-origin materials that are cheap, abundant, ready available, renewable, recyclable and versatile [55]. The biosorption potential of biomass is mainly due to their surface functional groups (hydroxyl, carboxyl, amino, sulfhydryl, carbonyl, phosphate) able to cope with the pollutants' toxicity. Due to the functional groups, these materials developed a wide range of uptake mechanisms (electrostatic interaction, ion exchange, precipitation, complexation, chelation, reduction) that ensure high pollutants removal efficiencies from aqueous media [13, 14, 56]. Various biological materials were tested for the development as biosorbents, including: microorganisms and algae, plant materials, agro-industrial wastes and other polysaccharides materials. These categories of green adsorbents have been almost exclusively investigated from the perspective of their application for removal of heavy metals and/or textile dyes from synthetic wastewaters. The promising results have opened the way to develop environmentally friendly technologies for removal – recovery – recycling of rare earths and precious metals [57, 58]. Biosorbents must


### **Table 1.**

*Description of biosorption process and its characteristics.*

exhibited high capacity and rate of biosorption, increased selectivity and multiple recyclability. Unlike algal biosorbents that have significant pollutant uptake capacity, fungi and some agricultural wastes show moderate capacity of biosorption [59]. Due to the adjustable surface chemistry of biomass, the essential features of biosorption materials can be significantly improved or tailored to practical applications by way of adequate chemical modification procedures [13, 14, 56, 60]. The stringent necessity for the near future is the transposition of biosorption processes performances to pilot and industrial scale.

#### **3.2 Characteristics of rape waste**

Rape waste biomass shows interesting properties that promote its biosorbent function for pollutants' removal, as another prospective way of waste reuse and recycling. The features of RS wastes are determined by factors correlated with the raw material (source, geographical region and environmental conditions), types of products and processes. RS wastes are vegetable materials with lignocellulosic composition of high degree of heterogeneity, as mentioned in Section 2.1. They have been assimilated with multi chromatographic systems carrying very different supports of polarity [61]. This heterogeneity is due to their complex structure and composition. For instance, the structure of the RSs encompasses three main structural components: (1) the embryo that in turn, is formed by cotyledon, hypocotyl and radicle; (2) the endosperm; (3) the coat of seed [62]. The seed flesh contains lipids (essentially residual oil) in the form of triacylglycerols and lipids associated with cell membranes, proteins (oleosins make up to 20% of total seed proteins) and fibers, composed from lignin and polysaccharides (cellulose, hemicellulose and pectin) [21]. The chemical composition of RS agro-wastes (stalk, straw, leaves) reveals a high content of carbon (457–465 mg/g) and nitrogen (1.9–6.7 mg/g), together with elements like Ca, Mg, K, Na and P [63, 64]. Deoiled CM contains

**147**

**Figure 3.**

*Valorization of Rapeseed Waste Biomass in Sorption Processes for Wastewater Treatment*

44.21% C, 6.3% H, 5.55% N and 0.37% S [25], while the following elemental analysis of RSC was reported: 77.82% C, 15.05% O, 5.48% N, 0.65% Ca, 0.48% S

The surface characteristics are of major importance for the biosorption potential of a material. One of them is the specific surface area assessed by Brunauer-Emmet-Teller (BET) method. For example, a BET area of 5.6 m<sup>2</sup>

determined for RSC by N2 adsorption analysis at 77 K [66]. The surface area of RS waste from a local unit of biodiesel production has been evaluated at 107.32 m<sup>2</sup>

by dynamic water vapor sorption [65]. A higher value was obtained for RS stalk -

The surface charge is expressed in terms of point of zero charge pH (pHPZC), representing the pH value at which the surface of biosorbent is neutral from electric point of view. The pHPZC of a RS waste has been reported as being 5 [68]. Thus, the surface of RS is positively charged at pH < 5 and favorable for anions biosorption. Meanwhile, for pH > 5, the surface of biosorbent is negatively charged and has affinity for cationic pollutants. More basic pHPZC values were obtained for canola stalk (5.7) [69], canola stalk and leaves (6.1) [63] and canola

The morphological features of the biosorbents are usually studied by means of scanning electron microscopy (SEM). From **Figure 3a**, it may be observed that rapeseed waste has an uneven and porous structure that seems to be very adequate for the biosorption of pollutants [71, 72]. RS stalk, straw and hull present a rough surface, with regular tunnel-like structure (remains of cell wall) [70, 73–75]. The small pores on the surface had an average pore diameter of

The Fourier transform infrared spectroscopy (FTIR) features are valuable source of information related to the functional groups playing a key role in the biosorption process. FTIR studies revealed that the surface of RS waste contains valuable functional groups playing a key role in the biosorption process, such as amino, hydroxyl and carbonyl groups [65, 70–72, 76, 77]. The main peaks in the

Thermal stability and degradation behavior of RS have been assessed by thermogravimetric analysis (TGA). Thermal decomposition of RS biomass has been described as a three stages process: moisture evaporation (up to 120°C), hemicellulose decomposition (200–250°C), degradation of cellulose and lignin (300–450°C) [25, 68]. The high thermal stability indicated by the TGA suggests that the RS biosorbents yielding as wastes from the treatment of wastewaters could be reused

FTIR spectrum of RS waste are presented in **Figure 3b**.

/g was

/g

*DOI: http://dx.doi.org/10.5772/intechopen.94942*

and 0.54% P [65].

/g [67].

43.21 m<sup>2</sup>

hull (7.0) [70].

1.09 ± 0.13 μm [73].

for energy recovery purposes.

*SEM image (a) and FTIR spectra (b) of RS waste.*

*Valorization of Rapeseed Waste Biomass in Sorption Processes for Wastewater Treatment DOI: http://dx.doi.org/10.5772/intechopen.94942*

44.21% C, 6.3% H, 5.55% N and 0.37% S [25], while the following elemental analysis of RSC was reported: 77.82% C, 15.05% O, 5.48% N, 0.65% Ca, 0.48% S and 0.54% P [65].

The surface characteristics are of major importance for the biosorption potential of a material. One of them is the specific surface area assessed by Brunauer-Emmet-Teller (BET) method. For example, a BET area of 5.6 m<sup>2</sup> /g was determined for RSC by N2 adsorption analysis at 77 K [66]. The surface area of RS waste from a local unit of biodiesel production has been evaluated at 107.32 m<sup>2</sup> /g by dynamic water vapor sorption [65]. A higher value was obtained for RS stalk - 43.21 m<sup>2</sup> /g [67].

The surface charge is expressed in terms of point of zero charge pH (pHPZC), representing the pH value at which the surface of biosorbent is neutral from electric point of view. The pHPZC of a RS waste has been reported as being 5 [68]. Thus, the surface of RS is positively charged at pH < 5 and favorable for anions biosorption. Meanwhile, for pH > 5, the surface of biosorbent is negatively charged and has affinity for cationic pollutants. More basic pHPZC values were obtained for canola stalk (5.7) [69], canola stalk and leaves (6.1) [63] and canola hull (7.0) [70].

The morphological features of the biosorbents are usually studied by means of scanning electron microscopy (SEM). From **Figure 3a**, it may be observed that rapeseed waste has an uneven and porous structure that seems to be very adequate for the biosorption of pollutants [71, 72]. RS stalk, straw and hull present a rough surface, with regular tunnel-like structure (remains of cell wall) [70, 73–75]. The small pores on the surface had an average pore diameter of 1.09 ± 0.13 μm [73].

The Fourier transform infrared spectroscopy (FTIR) features are valuable source of information related to the functional groups playing a key role in the biosorption process. FTIR studies revealed that the surface of RS waste contains valuable functional groups playing a key role in the biosorption process, such as amino, hydroxyl and carbonyl groups [65, 70–72, 76, 77]. The main peaks in the FTIR spectrum of RS waste are presented in **Figure 3b**.

Thermal stability and degradation behavior of RS have been assessed by thermogravimetric analysis (TGA). Thermal decomposition of RS biomass has been described as a three stages process: moisture evaporation (up to 120°C), hemicellulose decomposition (200–250°C), degradation of cellulose and lignin (300–450°C) [25, 68]. The high thermal stability indicated by the TGA suggests that the RS biosorbents yielding as wastes from the treatment of wastewaters could be reused for energy recovery purposes.

**Figure 3.** *SEM image (a) and FTIR spectra (b) of RS waste.*

*Environmental Issues and Sustainable Development*

Effect of experimental parameters: pH, initial pollutant concentration, biosorbent dose, contact time,

Radushkevich, Tempkin, Elovich etc.

Breakthrough curve and its modeling

Minimum number of reused cycles

Isotherm modeling: Langmuir, Freundlich, Dubinin-

Kinetics modeling: Lagergren (pseudo-first order), Ho (pseudo – second order); diffusion models -

Parameters process: initial concentration of adsorbate,

*Batch studies*

temperature

intraparticle, film

*Desorption studies* Desorption agent

**Table 1.**

*Fixed – bed column studies*

pH, flow rate, bed height

**Targeted issues Relevance**

Thermodynamic parameters Biosorption energy (heat)

performances to pilot and industrial scale.

*Description of biosorption process and its characteristics.*

**3.2 Characteristics of rape waste**

exhibited high capacity and rate of biosorption, increased selectivity and multiple recyclability. Unlike algal biosorbents that have significant pollutant uptake capacity, fungi and some agricultural wastes show moderate capacity of biosorption [59]. Due to the adjustable surface chemistry of biomass, the essential features of biosorption materials can be significantly improved or tailored to practical applications by way of adequate chemical modification procedures [13, 14, 56, 60]. The stringent necessity for the near future is the transposition of biosorption processes

Optimization of the biosorption process

the maximum biosorption capacity

conditions

Quantification of the interactions. Evaluation of

Determination of uptake rate. Insights into the mechanism of biosorption reactions

Valuable information for design of wastewater treatment for continuous operation in real

Biosorbent regeneration and recyclability

Rape waste biomass shows interesting properties that promote its biosorbent function for pollutants' removal, as another prospective way of waste reuse and recycling. The features of RS wastes are determined by factors correlated with the raw material (source, geographical region and environmental conditions), types of products and processes. RS wastes are vegetable materials with lignocellulosic composition of high degree of heterogeneity, as mentioned in Section 2.1. They have been assimilated with multi chromatographic systems carrying very different supports of polarity [61]. This heterogeneity is due to their complex structure and composition. For instance, the structure of the RSs encompasses three main structural components: (1) the embryo that in turn, is formed by cotyledon, hypocotyl and radicle; (2) the endosperm; (3) the coat of seed [62]. The seed flesh contains lipids (essentially residual oil) in the form of triacylglycerols and lipids associated with cell membranes, proteins (oleosins make up to 20% of total seed proteins) and fibers, composed from lignin and polysaccharides (cellulose, hemicellulose and pectin) [21]. The chemical composition of RS agro-wastes (stalk, straw, leaves) reveals a high content of carbon (457–465 mg/g) and nitrogen (1.9–6.7 mg/g), together with elements like Ca, Mg, K, Na and P [63, 64]. Deoiled CM contains

**146**
