**4. Pollutants removal and system configuration**

#### **4.1 Types of pollutants adsorbed and wastewater characteristics**

A systematic adsorption investigation starts at laboratory scale, when the interaction between a single target pollutant and the adsorbent is studied. This fundamental set-up is called a mono-component system, consisting from a single pollutant-model (usually, its salt form) dissolved in high-grade purified water. The complexity of the system will grow with two or more target pollutants to be removed from the same aqueous media. The multi-component system study is necessary in order to see the possible effects (competitive or synergic) generated by the presence of another compound (possible interference) on the uptake by the adsorbent. The ultimate goal is to test the adsorbent in a real aqueous media, i.e. wastewater, which is a more complex system, containing many dissolved (and in many cases, not individually known) compounds.

To the authors' best knowledge, the first studies using RS biomass-based adsorbents, i.e. canola meal, were reported over two decades ago by Al-Asheh and Duvnjak [24, 78, 79]. After 2010 (**Figure 4a**), RS waste has again attracted attention in the research community, as a result of worldwide increased production of rape cultures and waste management regulatory pressures.

#### *4.1.1 Mono-component systems: inorganics adsorption*

**Figure 4b** presents the distribution of model pollutants reported in literature, by the number of RS-derived adsorbents investigated for the individual uptake of a certain pollutant (i.e., in mono-component system). Among inorganic compounds, the prevalence of heavy metals removal from wastewater is justified by their high occurrence, persistence in the environment and high toxicity. Numerous articles have reported the use of RS-based adsorbents for the abatement of Pb and Cd removal, followed by Cu, Ni and Zn (**Figure 4b**). It is interesting that most fractions of rape biomass were studied for Cu adsorption, in natural or modified state (**Table 2**): from sprouts to stalks and leaves resulted from harvesting and finally, to rapeseed press-cake. A quite similar variability can be observed for cadmium. An

#### **Figure 4.**

*Distribution of adsorption studies using rapeseed biomass per years (a) and tested RS-based adsorbents (except the 22 cases of 1 adsorbent per pollutant) on different wastewater contaminants (b).*

**149**

RSM, i.e. 15.43 mg/g [77].

**\****Langmuir maximum sorption capacity.*

size and preparation conditions vary.

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

**Adsorbent Efficiency Adsorbent Efficiency** Canola meal [24] 36.747 mg Cu/g\* RSC [68] 13.858 mg Zn/g\*

RSM [71] 18.35–22.70 mg Pb/g\* Canola straw [char] [64] 30.50–37.49 mg

Canola residues [81] 90–99% Cd Canola shoot [char] [80] 4.14 mg Cd/g,

, 17.1 mg

*Brassica* straw [char, magnetic-gelatin] [85]

Canola stalk and leaves

40% Cu RS oil cake [char] [87] 129.87 mg Pb/g\*

[75]

Cr\*

char

62.5 mg Fe/g\*

40.0 mg Mn/g\*

41.7 mg Zn/g\*

20.8 mg Ni/g\*

35.7 mg Cu/g\*

71.4 mg Cd/g\*

133.33 mg Ni/g\*

15.52 mg Cu/g

Cd\* : 10.93– 25.19 mg/g stalks; 18.15–27.40 mg/g fermentation residues

: 84–108 mg/g char; 72–195 mg/g steam-AC

Cu/g\*

Deoiled RSM [88] 97.09 mg Pb/g\*

Canola straw [char] [84] Pb\*

Cr Expired rapeseeds [89] 4.65–45.38 mg Hg/g

RS stalk from 2 cultivars [NaOH, enzymatic hydrolysis] [67]

: 35.1971 mg/g char; 434.85 mg/g magnetic-gelatin

,

,

,

,

,

,

, 89.6%

Cd, 67.2% Cu, 40.3% Ni, 92.3% Pb

: 13.4 mg/g RSC; 36.6 mg/g husk; 8.6 mg/g WS; 10.7 mg

,

40% Ni, 98% Pb, 91.8%

Cu\*

Cu/g seeds

21.72 mg Cd/g\*

26.9 mg Ag/g\*

*Efficiency of RS-based adsorbents for heavy metals removal from liquid phase.*

Cu/g\*

Cr

AC prepared from canola shoot showed maximum sorption capacities of 15.52 mg Cu/g and 4.14 mg Cd/g [80]. Similar efficiency for Cu adsorption was observed for

*Notes: "[X]" indicates that the native biomass has undergone significant structure modification, while X can be the chemical agent used, the final adsorbent or other mixture component; char – carbonized material (e.g. biochar).*

The sorptive potential of RS agro-wastes was commonly assessed (**Table 2**). In many cases, the residues were used after minimal pre-treatment, which usually involves the removal of impurities by several washings and drying for a certain period of time, at room temperature, in sunlight or in an oven. Washed and dried canola agro-residues from Iran were used for adsorption of cadmium ions from aqueous solution [81], whilst a mixture of stalk and leaves was used for the removal of several metals in the sequence of sorption capacities: Cd > Fe > Zn > Mn > Cu > Ni [75]. Untreated stalks have been investigated in the adsorption process of Cr, Cd, Ni and Pb [82]. Reference [67] used several cultivars of RS to assess the ethanol production after a mild alkali pretreatment (1% NaOH, 50°C). The solid residues obtained after yeast fermentation exhibited higher Cd adsorption capacities than the raw stalks (**Table 2**). In the last years, RS straw was used as feedstock for biochar production at laboratory scale [64, 83–85]. Although the adsorption capacities of these materials are usually higher than the precursors (**Table 2**), the feedstock particles

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

Canola meal [78] 22.69 mg Zn/g\*

RSM [77] 15.43 mg Cu/g\*

Canola straw [char] [83] 14.56 mg/g\*

RSC, husks, WS, ground seeds [21]

RS pellet cellulose [citric

*Brassica campestris* waste

RS pomace [sunflower husks, char] [90]

acid] [86]

stem [82]

**Table 2.**

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


*Notes: "[X]" indicates that the native biomass has undergone significant structure modification, while X can be the chemical agent used, the final adsorbent or other mixture component; char – carbonized material (e.g. biochar).* **\****Langmuir maximum sorption capacity.*

#### **Table 2.**

*Environmental Issues and Sustainable Development*

**4. Pollutants removal and system configuration**

many cases, not individually known) compounds.

cultures and waste management regulatory pressures.

*4.1.1 Mono-component systems: inorganics adsorption*

**4.1 Types of pollutants adsorbed and wastewater characteristics**

A systematic adsorption investigation starts at laboratory scale, when the interaction between a single target pollutant and the adsorbent is studied. This fundamental set-up is called a mono-component system, consisting from a single pollutant-model (usually, its salt form) dissolved in high-grade purified water. The complexity of the system will grow with two or more target pollutants to be removed from the same aqueous media. The multi-component system study is necessary in order to see the possible effects (competitive or synergic) generated by the presence of another compound (possible interference) on the uptake by the adsorbent. The ultimate goal is to test the adsorbent in a real aqueous media, i.e. wastewater, which is a more complex system, containing many dissolved (and in

To the authors' best knowledge, the first studies using RS biomass-based adsorbents, i.e. canola meal, were reported over two decades ago by Al-Asheh and Duvnjak [24, 78, 79]. After 2010 (**Figure 4a**), RS waste has again attracted attention in the research community, as a result of worldwide increased production of rape

**Figure 4b** presents the distribution of model pollutants reported in literature, by the number of RS-derived adsorbents investigated for the individual uptake of a certain pollutant (i.e., in mono-component system). Among inorganic compounds, the prevalence of heavy metals removal from wastewater is justified by their high occurrence, persistence in the environment and high toxicity. Numerous articles have reported the use of RS-based adsorbents for the abatement of Pb and Cd removal, followed by Cu, Ni and Zn (**Figure 4b**). It is interesting that most fractions of rape biomass were studied for Cu adsorption, in natural or modified state (**Table 2**): from sprouts to stalks and leaves resulted from harvesting and finally, to rapeseed press-cake. A quite similar variability can be observed for cadmium. An

*Distribution of adsorption studies using rapeseed biomass per years (a) and tested RS-based adsorbents (except* 

*the 22 cases of 1 adsorbent per pollutant) on different wastewater contaminants (b).*

**148**

**Figure 4.**

*Efficiency of RS-based adsorbents for heavy metals removal from liquid phase.*

AC prepared from canola shoot showed maximum sorption capacities of 15.52 mg Cu/g and 4.14 mg Cd/g [80]. Similar efficiency for Cu adsorption was observed for RSM, i.e. 15.43 mg/g [77].

The sorptive potential of RS agro-wastes was commonly assessed (**Table 2**). In many cases, the residues were used after minimal pre-treatment, which usually involves the removal of impurities by several washings and drying for a certain period of time, at room temperature, in sunlight or in an oven. Washed and dried canola agro-residues from Iran were used for adsorption of cadmium ions from aqueous solution [81], whilst a mixture of stalk and leaves was used for the removal of several metals in the sequence of sorption capacities: Cd > Fe > Zn > Mn > Cu > Ni [75]. Untreated stalks have been investigated in the adsorption process of Cr, Cd, Ni and Pb [82]. Reference [67] used several cultivars of RS to assess the ethanol production after a mild alkali pretreatment (1% NaOH, 50°C). The solid residues obtained after yeast fermentation exhibited higher Cd adsorption capacities than the raw stalks (**Table 2**). In the last years, RS straw was used as feedstock for biochar production at laboratory scale [64, 83–85]. Although the adsorption capacities of these materials are usually higher than the precursors (**Table 2**), the feedstock particles size and preparation conditions vary.

According to **Table 2**, the most popular bio-material for heavy metals adsorption is RS meal (or cake, press-cake). This complex lignocellulosic material is comprised of a water-soluble fraction (e.g., phytic acid, proteins, glucosinolates etc.) and a solid fraction, formed from husks (hulls) and the flesh of seeds. Authors [21] made a systematic research regarding the component of RSC responsible for metal binding. By comparing the adsorption capacity of Cu for press-cake, husks, white sediment (WS, i.e. flesh of seeds) and ground seeds, under the same experimental conditions, they observed that husks are the most efficient fraction. Based on the removal efficiency, RSC presents higher affinity for Pb, followed by Cd, Cu and Ni [78]. The values of metal biosorption capacity reported in literature aren't higher than 40 mg/g. Meanwhile, the ACs obtained from RSM can easily achieve adsorption capacities of around 130 mg/g (**Table 2**), by creating a microporous structure and a high surface area.

Nutrients were also under investigation for adsorption on agricultural RS residues. Native and modified canola stalks and leaves were used for the removal of phosphorus from aqueous solutions [63]. According to Langmuir sorption capacity (*q*L), sorbents efficiency followed the sequence: *native* (4.3 mg/g) < *modified by CaCl*2 (6.6 mg/g) < *modified by urea* (8.5 mg/g) < *modified by FeCl*3 (9.0 mg/g). A biochar prepared from RS leaves and stems was combined with Mg-Al layered double oxides and tested for the adsorption of phosphate from water [91]. The phosphate removal efficiency remained above 92% at a pH range of 2–10, for an initial pollutant concentration (*C*i) of 50 mg/L, while *q*L reached a value of 132.8 mg/g. Adsorption of ammonium nitrogen from diluted aqueous solutions was studied using natural mineral and organic adsorbents [76]. The authors observed that the canola agro-residues presented an adsorption capacity comparable to that of zeolite and bentonite. The organic spent adsorbent can be safely used afterwards as soil fertilizer. *q*L of ammonium ion for several ACs from CM varied between 17.9 and 148.9 mg/g [92]. The low cost of the KOH treated AC was determined.

A single study was found with regards to the adsorption of fluoride using canola stalk treated with bicarbonate, reporting a removal efficiency of 79% for *C*<sup>i</sup> of 10 mg F/L [93].

#### *4.1.2 Mono-component systems: organics adsorption*

To the authors' knowledge, adsorption/biosorption studies using rape-derived sorbents involved the following categories of organic compounds: textile dyes, phenolic compounds, organochloride compounds, pesticides and herbicides. Phenolic compounds and textile dyes were the organic pollutants with the highest interest for removal from aqueous phase by RS biomass (**Figure 4b**).

Various dyestuffs, including acid, basic, direct and reactive, were used as model pollutants in the adsorption experiments. From **Table 3**, higher sorption capacities for cationic dyes (13.22–836.2 mg/g) were observed, when compared to those for anionic dyes (2.01–11.81 mg/g). This is mainly because of the different treatments (chemical or thermal) applied to the rape biomass. Among the various dyes, malachite green (MG) and methylene blue (MB) are preferred as model contaminants. Extensive research was done using stalk adsorbents, in different forms: native, chemically treated, biochar or activated form (**Table 3**).

Other studies involving RS meal adsorbents (**Table 3**) deal with the removal of chloroform and dichloromethane, atrazine, phenolic compounds and dyes. In addition, there is a study from Canada reporting acyclovir adsorption on powdered AC prepared from deoiled CM with a removal efficiency of 39.5% at Ci = 400 mg/L [25]. RS cake was used many times as precursor for AC production, which was then used

**151**

*\**

**Table 3.**

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

Defatted seeds [95]

Waste of RS after microbial culture medium [48]

Laccase immobilized with RS press cake [98]

Canola stalk [101]

[AC] [102]

RSC [AC] [104]

Canola hull [105]

Swede rape straw native, [tartaric acid] [74]

[char] [107]

residue [108]

Swede rape hull [microwave] [109]

[AC] [111]

71.9% chloroform, 69% dichloromethane, 46.8% benzene

74% Amaranth, 81% Acid Orange 7, 50% Acid Blue 113, 83% Trypan Blue, 57% Sunset Yellow FCF

6.73 mg Methylene blue/g\*\*

332 mg phenol/g, 482 mg p-cholorophenol/g

Phenol: 88 mg/g steam-AC,

63% Reactive Red 198, 70% Reactive Blue 19, 80% Direct Red

: 128.2 mg/g native, 246.4 mg/g modified

2,4-dichlorophenoxyacetic acid/g

79, 81% Direct Red 80

MB\*

93.4 mg MB/g

Acid Orange 7

272 mg MB/g\*

135.8 mg

68 mg/g CO2-AC

17.857 mg MG/g\*

**Adsorbent Efficiency Adsorbent Efficiency**

68.6% chloroform, 70.4% dichloromethane, 78.6% trichloroethylene

: 836.2 mg/g RS-magnetic NPs, 93.3 mg/g

2.15 mg Reactive Yellow

Atrazine: 70% for beads form; 96% for rods form

49.01 mg Basic Red 46/g\*

25.0 mg Basic Violet 16/g\*

: 143 mg/g native, 432 mg/g modified

Canola stalk [69] 32.8 mg Remazol Black B/g\* Canola

32.79 mg Remazol Black 5/g

*Efficiency of RS-based adsorbents for organics removal from liquid phase.*

RS meal [72] 11.81 mg Reactive Blue 19/g\* RSC

0.079 mg bromopropylate/g\*

90–100%

Canola hull [70] 67.56 mg Basic Blue 41/g\*

MB\*

Canola stalk [20] 25.06 mg Acid Orange 7/g\*

RSM [110] 78 mg MG/g\*

*Langmuir sorption capacity. \*\*Sips sorption capacity.*

, 4.78 mg Reactive

, 26.41 mg Basic

, 27.19 mg Basic

;

,

,

102 mg Methyl violet/g Canola stalk

,

, 122 mg MB/g\* Canola stalk

*Notes: "[X]" indicates that the native biomass has undergone significant structure modification, while X can be the chemical agent used, the final adsorbent or other mixture component; char – carbonized material (e.g. biochar).*

RSC [61] 58.2% atrazine RS [AC] [99] 70–95% phenol

RS-polypyrrole

for phenolic compounds abatement (**Table 3**). Moreover, pesticides of moderately to highly hydrophobic nature, like atrazine, have shown fairly good removal efficiencies when RS cake was used (yet, mainly due to the absorption in the oil droplets that remain trapped in the matrix after seed pressing) [61]. Higher efficiencies than powdered AC were obtained for volatile organic compounds, where some intracellular fat particles named spherosomes are responsible for their uptake [94, 95].

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

MG\*

84/g\*

Black 5/g\*

Green 4/g\*

Violet 10/g\*

Defatted seeds [94]

RSM [magnetic NPs, polypyrrole] [96]

RS straw-based compost [97]

RSC [alginate] [100]

Swede rape straw native, [oxalic acid] [73]

Canola straw [char] [106]

RS stalk [AC] [103]


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

*Notes: "[X]" indicates that the native biomass has undergone significant structure modification, while X can be the chemical agent used, the final adsorbent or other mixture component; char – carbonized material (e.g. biochar). \* Langmuir sorption capacity.*

*\*\*Sips sorption capacity.*

#### **Table 3.**

*Environmental Issues and Sustainable Development*

and a high surface area.

of 10 mg F/L [93].

According to **Table 2**, the most popular bio-material for heavy metals adsorption is RS meal (or cake, press-cake). This complex lignocellulosic material is comprised of a water-soluble fraction (e.g., phytic acid, proteins, glucosinolates etc.) and a solid fraction, formed from husks (hulls) and the flesh of seeds. Authors [21] made a systematic research regarding the component of RSC responsible for metal binding. By comparing the adsorption capacity of Cu for press-cake, husks, white sediment (WS, i.e. flesh of seeds) and ground seeds, under the same experimental conditions, they observed that husks are the most efficient fraction. Based on the removal efficiency, RSC presents higher affinity for Pb, followed by Cd, Cu and Ni [78]. The values of metal biosorption capacity reported in literature aren't higher than 40 mg/g. Meanwhile, the ACs obtained from RSM can easily achieve adsorption capacities of around 130 mg/g (**Table 2**), by creating a microporous structure

Nutrients were also under investigation for adsorption on agricultural RS residues. Native and modified canola stalks and leaves were used for the removal of phosphorus from aqueous solutions [63]. According to Langmuir sorption capacity (*q*L), sorbents efficiency followed the sequence: *native* (4.3 mg/g) < *modified by CaCl*2 (6.6 mg/g) < *modified by urea* (8.5 mg/g) < *modified by FeCl*3 (9.0 mg/g). A biochar prepared from RS leaves and stems was combined with Mg-Al layered double oxides and tested for the adsorption of phosphate from water [91]. The phosphate removal efficiency remained above 92% at a pH range of 2–10, for an initial pollutant concentration (*C*i) of 50 mg/L, while *q*L reached a value of 132.8 mg/g. Adsorption of ammonium nitrogen from diluted aqueous solutions was studied using natural mineral and organic adsorbents [76]. The authors observed that the canola agro-residues presented an adsorption capacity comparable to that of zeolite and bentonite. The organic spent adsorbent can be safely used afterwards as soil fertilizer. *q*L of ammonium ion for several ACs from CM varied between 17.9

and 148.9 mg/g [92]. The low cost of the KOH treated AC was determined. A single study was found with regards to the adsorption of fluoride using canola stalk treated with bicarbonate, reporting a removal efficiency of 79% for *C*<sup>i</sup>

To the authors' knowledge, adsorption/biosorption studies using rape-derived sorbents involved the following categories of organic compounds: textile dyes, phenolic compounds, organochloride compounds, pesticides and herbicides. Phenolic compounds and textile dyes were the organic pollutants with the highest interest for

Various dyestuffs, including acid, basic, direct and reactive, were used as model pollutants in the adsorption experiments. From **Table 3**, higher sorption capacities for cationic dyes (13.22–836.2 mg/g) were observed, when compared to those for anionic dyes (2.01–11.81 mg/g). This is mainly because of the different treatments (chemical or thermal) applied to the rape biomass. Among the various dyes, malachite green (MG) and methylene blue (MB) are preferred as model contaminants. Extensive research was done using stalk adsorbents, in different forms: native,

Other studies involving RS meal adsorbents (**Table 3**) deal with the removal of chloroform and dichloromethane, atrazine, phenolic compounds and dyes. In addition, there is a study from Canada reporting acyclovir adsorption on powdered AC prepared from deoiled CM with a removal efficiency of 39.5% at Ci = 400 mg/L [25]. RS cake was used many times as precursor for AC production, which was then used

*4.1.2 Mono-component systems: organics adsorption*

removal from aqueous phase by RS biomass (**Figure 4b**).

chemically treated, biochar or activated form (**Table 3**).

**150**

*Efficiency of RS-based adsorbents for organics removal from liquid phase.*

for phenolic compounds abatement (**Table 3**). Moreover, pesticides of moderately to highly hydrophobic nature, like atrazine, have shown fairly good removal efficiencies when RS cake was used (yet, mainly due to the absorption in the oil droplets that remain trapped in the matrix after seed pressing) [61]. Higher efficiencies than powdered AC were obtained for volatile organic compounds, where some intracellular fat particles named spherosomes are responsible for their uptake [94, 95].

#### *4.1.3 Multi-component systems*

There are few studies involving RS sorbents that report simultaneous adsorption experiments. Firstly, Al-Asheh et al. [24, 78] investigated the single, binary, ternary and quaternary adsorption of some heavy metals using CM. They observed the same succession in single system and mixture based on the molar sorption capacities for: Zn > Cu > Cd [24]. In a later study, the same authors noticed Ni was strongly inhibited by the presence of Cu and Pb in the same solution [78]. In binary and tertiary metal systems, inhibition of Pb was manifested by Cu, Cd and/or Ni, whereas Cd uptake was higher in binary mixture with Ni or Pb. Copper biosorption was restricted by Pb only in binary mixtures, while in any other combination with Cd and Ni, it was promoted. In all cases, copper exhibited the highest molar biosorption capacity, followed by Cd, Ni and then Pb in mono-, bi- and tri-component systems. In a quaternary mixture, the following order (molar basis) was obtained: Cu > Cd > Pb > Ni.

The efficiency of canola residues (stalk and leaves) in the competitive biosorption of Cd, Cu, Ni, Zn, Fe and Mn was investigated by means of equilibrium isotherms [75]. The authors mention that: "The sorption isotherm of heavy metals in single and competitive systems were studied using batch technique. Sorbents were allowed to equilibrate with solutions at different initial metal concentrations (0, 5, 10, 30, 50, 100, 150, 200, and 300 mg/L)." However, it is not clearly stated for competitive systems if the mentioned initial concentrations are for each metal (and the highest total *C*i would be 300 mg/L times 6 metals = 2400 mg/L) or the values are cumulated (the highest *C*i of each metal would be 300 mg/L divided by 6 metals = 50 mg/L). In any case, the biosorption capacities of all metals have decreased in multi-component systems with more than 67% as compared to the individual biosorption (**Table 2**), in the following order of metal sorption: Ni (6.6 mg/g) < Zn (9.4 mg/g) < Fe (10.7 mg/g) < Mn (10.2 mg/g) < Cu (11.6 mg/g) < Cd (14.7 mg/g).

To the authors' knowledge, the only article reporting simultaneous biosorption of pollutants of different type, i.e. Pb and Reactive blue 19 (Rb19) dye, is reference [112]. In the absence of a rigorous experimental framework for multi-component biosorption study, the authors have tried multiple strategies to study the biosorption of binary system using RS meal. These involved: (i) influence of Pb:Rb19 molar ratio (range of 0.8–6.0), (ii) equilibrium studies by varying the initial concentration of one pollutant (15–150 mg/L), while maintaining a fixed *C*i (50 mg/L) of the second contaminant, (iii) kinetics modeling at various pollutant molar ratios, and (iv) selectivity tests. The biosorption profile of the binary system was found to be versatile. At low *C*i, dye biosorption was promoted by the presence of metal ions. However, at high *C*i of dye, lead uptake was inhibited.

Studies on sorption processes with rape biomass involving real effluents were reported by few authors [71, 80, 94, 98, 111]. Heavy metals have been successfully removed from industrial effluents: Cu from smelting wastewater in Canada using CM [78], Pb from spiked industrial wastewater in Romania (94% efficiency in biosorption column with RS meal) [71] and Cd (20% reduction) and Cu (95% removal) from acid mine water in Australia by using biochar obtained from canola shoot [80]. Dichloromethane was removed (90%) from chemical wastewater on defatted seeds from oil extraction in Japan, while total elimination of an herbicide from drainage water from sugarcane fields in Iran using canola stalk-based AC was obtained [111].

#### **4.2 Batch and dynamic process operation**

Current research regarding adsorption as a wastewater treatment technology is focused on trials of a large and diverse range of materials that could become

**153**

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

suitable adsorbents for different pollutants. This could be easily done at laboratory scale by using batch testing. The batch operation is also favored for obtaining fundamental information about the adsorption process, like the adsorption capacity in optimum working conditions. A summary of the best adsorption conditions by using RS biomass is presented in **Table 4**. Among the factors influencing the sorption process, solution acidity affects the pollutant speciation, the charge of functional groups on the sorbents surface and the ions competition for the binding sites. As **Table 4** shows, metals usually adsorb at acidic pH (precipitation of metal hydroxides at pH > 6 is also avoided). Organic contaminants, like volatile compounds or phenols, mostly favor neutral to alkaline conditions. On the other hand, pH values of 6–8 are optimal for cationic dyes, while acidic medium is best for anionic dyes. The amount of available sorption sites is directly dependent on the amount of adsorbent used and its granulometry. Native biosorbents, which have low specific area, impose the use of a higher dose, whereas a lower dosage is necessary for chemically modified or pyrolised adsorbents. However, a too high dose may lead to particle agglomeration and low access to the sorbent. The rapidity with which the sorption equilibrium is reached depends on the contact time and agitation speed. The average time when using RS adsorbents was reported to be a few hours (**Table 4**). Temperature influences the sorption capacity and biosorbent structural stability. An endothermal process is favored at high temperatures, involving heating costs and a possible biosorbent structural damage. However, many studies have reported high adsorption capacities close to room temperature

The biosorption equilibrium can be modeled by using equilibrium and kinetics experimental data. The most frequently used isotherms are Langmuir and Freundlich. The wide applicability of Langmuir isotherm model in case of heavy metals on native RS biosorbents and dyestuffs (**Table 4**) indicates the monolayer uptake on a homogenous surface without interaction between adsorbed molecules [48]. When using ACs, the metals sorption conformed to the assumptions of the Freundlich model – multilayer uptake occurring on a heterogeneous surface [85]. Phenol and organochloride compounds adsorption also follow the Freundlich model. In some cases, Freundlich and Langmuir models were both good models to describe the system at equilibrium conditions, indicating the complexity of the process. Kinetics of adsorption using RS biomass widely conforms to the pseudosecond order model (**Table 4**), implying that the rate-limiting step is a chemical

Because it is inconvenient to have a one-time use sorbent, regeneration of the spent sorbent by means of desorption is necessary. The eluents used for desorption of metal and dyes can be either acids, alkalis or some other chemical compounds (**Table 4**). The observed trend is that the pH can act like a switch for the selective desorption of pollutants (acidic medium for metals, basic medium for dyes). After desorption, the recovered rape-based adsorbent can be re-used in a new sorption process. The number of cycles of sorption–desorption indicate the reusability adsorbent potential (**Table 4**). Some sorbents, including untreated RS meal, maintain a decent sorption efficiency after several cycles of adsorption–desorption. After 3 cycles, the drop in efficiency was between <5% and 22.5% [48, 88]. Some studies reported up to 5–6 cycles of biosorbent reuse, and the decrease in the removal efficiency was found between 16.2% and 43% [85, 111]. Another practical aspect of the type of eluent used is the indication about the sorption mechanism. For example, a pH-dependent desorption suggests the involvement of electrostatic interactions in the sorption process. Or if water is a successful eluent, then the pollutant uptake is predominantly based on physisorption [21]. Several researchers have made efforts to elucidate the main sorption mechanism(s) (**Table 4**). Nevertheless, the adsorption

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

(**Table 4**), which is important for practical reasons.

sorption between the adsorbent and pollutant [73].

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

suitable adsorbents for different pollutants. This could be easily done at laboratory scale by using batch testing. The batch operation is also favored for obtaining fundamental information about the adsorption process, like the adsorption capacity in optimum working conditions. A summary of the best adsorption conditions by using RS biomass is presented in **Table 4**. Among the factors influencing the sorption process, solution acidity affects the pollutant speciation, the charge of functional groups on the sorbents surface and the ions competition for the binding sites. As **Table 4** shows, metals usually adsorb at acidic pH (precipitation of metal hydroxides at pH > 6 is also avoided). Organic contaminants, like volatile compounds or phenols, mostly favor neutral to alkaline conditions. On the other hand, pH values of 6–8 are optimal for cationic dyes, while acidic medium is best for anionic dyes. The amount of available sorption sites is directly dependent on the amount of adsorbent used and its granulometry. Native biosorbents, which have low specific area, impose the use of a higher dose, whereas a lower dosage is necessary for chemically modified or pyrolised adsorbents. However, a too high dose may lead to particle agglomeration and low access to the sorbent. The rapidity with which the sorption equilibrium is reached depends on the contact time and agitation speed. The average time when using RS adsorbents was reported to be a few hours (**Table 4**). Temperature influences the sorption capacity and biosorbent structural stability. An endothermal process is favored at high temperatures, involving heating costs and a possible biosorbent structural damage. However, many studies have reported high adsorption capacities close to room temperature (**Table 4**), which is important for practical reasons.

The biosorption equilibrium can be modeled by using equilibrium and kinetics experimental data. The most frequently used isotherms are Langmuir and Freundlich. The wide applicability of Langmuir isotherm model in case of heavy metals on native RS biosorbents and dyestuffs (**Table 4**) indicates the monolayer uptake on a homogenous surface without interaction between adsorbed molecules [48]. When using ACs, the metals sorption conformed to the assumptions of the Freundlich model – multilayer uptake occurring on a heterogeneous surface [85]. Phenol and organochloride compounds adsorption also follow the Freundlich model. In some cases, Freundlich and Langmuir models were both good models to describe the system at equilibrium conditions, indicating the complexity of the process. Kinetics of adsorption using RS biomass widely conforms to the pseudosecond order model (**Table 4**), implying that the rate-limiting step is a chemical sorption between the adsorbent and pollutant [73].

Because it is inconvenient to have a one-time use sorbent, regeneration of the spent sorbent by means of desorption is necessary. The eluents used for desorption of metal and dyes can be either acids, alkalis or some other chemical compounds (**Table 4**). The observed trend is that the pH can act like a switch for the selective desorption of pollutants (acidic medium for metals, basic medium for dyes). After desorption, the recovered rape-based adsorbent can be re-used in a new sorption process. The number of cycles of sorption–desorption indicate the reusability adsorbent potential (**Table 4**). Some sorbents, including untreated RS meal, maintain a decent sorption efficiency after several cycles of adsorption–desorption. After 3 cycles, the drop in efficiency was between <5% and 22.5% [48, 88]. Some studies reported up to 5–6 cycles of biosorbent reuse, and the decrease in the removal efficiency was found between 16.2% and 43% [85, 111]. Another practical aspect of the type of eluent used is the indication about the sorption mechanism. For example, a pH-dependent desorption suggests the involvement of electrostatic interactions in the sorption process. Or if water is a successful eluent, then the pollutant uptake is predominantly based on physisorption [21]. Several researchers have made efforts to elucidate the main sorption mechanism(s) (**Table 4**). Nevertheless, the adsorption

*Environmental Issues and Sustainable Development*

However, at high *C*i of dye, lead uptake was inhibited.

**4.2 Batch and dynamic process operation**

Studies on sorption processes with rape biomass involving real effluents were reported by few authors [71, 80, 94, 98, 111]. Heavy metals have been successfully removed from industrial effluents: Cu from smelting wastewater in Canada using CM [78], Pb from spiked industrial wastewater in Romania (94% efficiency in biosorption column with RS meal) [71] and Cd (20% reduction) and Cu (95% removal) from acid mine water in Australia by using biochar obtained from canola shoot [80]. Dichloromethane was removed (90%) from chemical wastewater on defatted seeds from oil extraction in Japan, while total elimination of an herbicide from drainage water from sugarcane fields in Iran using canola stalk-based AC was

Current research regarding adsorption as a wastewater treatment technology is focused on trials of a large and diverse range of materials that could become

There are few studies involving RS sorbents that report simultaneous adsorption experiments. Firstly, Al-Asheh et al. [24, 78] investigated the single, binary, ternary and quaternary adsorption of some heavy metals using CM. They observed the same succession in single system and mixture based on the molar sorption capacities for: Zn > Cu > Cd [24]. In a later study, the same authors noticed Ni was strongly inhibited by the presence of Cu and Pb in the same solution [78]. In binary and tertiary metal systems, inhibition of Pb was manifested by Cu, Cd and/or Ni, whereas Cd uptake was higher in binary mixture with Ni or Pb. Copper biosorption was restricted by Pb only in binary mixtures, while in any other combination with Cd and Ni, it was promoted. In all cases, copper exhibited the highest molar biosorption capacity, followed by Cd, Ni and then Pb in mono-, bi- and tri-component systems. In a quaternary mixture, the following order (molar basis) was obtained: Cu > Cd > Pb > Ni. The efficiency of canola residues (stalk and leaves) in the competitive biosorption of Cd, Cu, Ni, Zn, Fe and Mn was investigated by means of equilibrium isotherms [75]. The authors mention that: "The sorption isotherm of heavy metals in single and competitive systems were studied using batch technique. Sorbents were allowed to equilibrate with solutions at different initial metal concentrations (0, 5, 10, 30, 50, 100, 150, 200, and 300 mg/L)." However, it is not clearly stated for competitive systems if the mentioned initial concentrations are for each metal (and the highest total *C*i would be 300 mg/L times 6 metals = 2400 mg/L) or the values are cumulated (the highest *C*i of each metal would be 300 mg/L divided by 6 metals = 50 mg/L). In any case, the biosorption capacities of all metals have decreased in multi-component systems with more than 67% as compared to the individual biosorption (**Table 2**), in the following order of metal sorption: Ni (6.6 mg/g) < Zn (9.4 mg/g) < Fe (10.7 mg/g) < Mn (10.2 mg/g) < Cu (11.6 mg/g) < Cd (14.7 mg/g). To the authors' knowledge, the only article reporting simultaneous biosorption of pollutants of different type, i.e. Pb and Reactive blue 19 (Rb19) dye, is reference [112]. In the absence of a rigorous experimental framework for multi-component biosorption study, the authors have tried multiple strategies to study the biosorption of binary system using RS meal. These involved: (i) influence of Pb:Rb19 molar ratio (range of 0.8–6.0), (ii) equilibrium studies by varying the initial concentration of one pollutant (15–150 mg/L), while maintaining a fixed *C*i (50 mg/L) of the second contaminant, (iii) kinetics modeling at various pollutant molar ratios, and (iv) selectivity tests. The biosorption profile of the binary system was found to be versatile. At low *C*i, dye biosorption was promoted by the presence of metal ions.

*4.1.3 Multi-component systems*

**152**

obtained [111].


**155**

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

PSO, IPD Acetone; 83.79%

F; PSO; endothermal

**Best fit model Desorption Proposed** 

2,4-dichlorophenoxyacetic acid adsorption efficiency

NaOH 1 M; Cr: 57% sorption capacity after 6 cycles

after 5 cycles

L, F; PSO - Phosphate "Memory effect,"

**mechanism**

electrostatic attraction, surface complexation, anion

exchange

Aromatic ring interaction

Electrostatic interaction, redox reaction, surface complexation

mechanism is characterized by a high degree of complexity, especially when natural

*Optimum conditions of adsorption/desorption for pollutant uptake on RS-based adsorbents.*

*Notes: Adsorbents corresponding to each reference can be found in Tables 2 and 3; L (Langmuir), F (Freundlich), L-F (Langmuir–Freundlich), S (Sips), T (Tempkin) isotherm models; PFO (pseudo-first order), PSO (pseudosecond order), IPD (intraparticle diffusion), SD (surface diffusion) kinetics models; ANN – artificial neural* 

In a single biosorption run, it is quite often that the sorbent does not reach the maximum sorption capacity (e.g., given by the Langmuir isotherm model) for a certain pollutant. Nevertheless, there will not be any further noticeable uptake of the respective pollutant even if the contact time is prolonged. Then, the spent sorbent is not sent to regeneration, but instead to a new sorption run involving a different target pollutant. And then in a third run of adsorption and so on. This concept is called an alternating or sequencing sorption. The main idea is to load the biosorbent as much as possible before its disposal, which could be practical for a low capacity biosorbent. This concept was studied by Morosanu et al. [65, 114] using RS meal as adsorbent and they have achieved 4 sequential adsorptions. The research was done considering two directions: (a) the biosorption of Rb19 dye followed by lead ions - RS-Rb19/Pb biosorption system, and (b) the biosorption of Pb followed by Rb19 dye - RS-Pb/Rb19 system. The authors observed that: (i); Pb uptake at higher concentrations is impeded by the presence of Rb19 on RS; (ii) dye sorption is favored by Pb presence; (iii) for the system RS-Rb19/Pb, pollutant desorption is selective, as a function of pH (**Table 4**); (iv) desorption was <7% in case of RS-Pb/Rb19 system. The experimental data suggests that the succession of pollutant biosorption matters. However, the biosorbent reuse in a new sorption cycle in order to determine the

At larger scale, continuous sorption processes are preferred. However, we have found only two studies using RS adsorbents in column tests. Amiri et al. [111], using a fixed-bed column (30 cm length, 2.5 cm inlet diameter) filled with canola stalkderived AC (height of 20 cm) to adsorb 2,4-dichlorophenoxyacetic acid, obtained maximum sorption capacities comparable with the batch data. The intraparticle diffusion coefficient from batch experiments was used for column modeling. Lead uptake in a fixed-bed column with RS meal (bed height 6 cm) was reported [71]. A faster column saturation was observed at higher pollutant concentration, while the maximum sorption capacities were higher than the one provided by Langmuir

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

**Ref. Optimum** 

[91] pH 2, dose 2.5 g/L, 30 min, 200 rpm

[111] pH 2, dose 0.33 g/L, 25°C, 45–60 min, 120 rpm

[85] pH 1, dose

*network.*

**Table 4.**

1 g/L, 25°C, 12 h, 160 rpm

**parameters**

lignocellulosic biosorbents are involved.

pollutants' uptake was not done.

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


*Notes: Adsorbents corresponding to each reference can be found in Tables 2 and 3; L (Langmuir), F (Freundlich), L-F (Langmuir–Freundlich), S (Sips), T (Tempkin) isotherm models; PFO (pseudo-first order), PSO (pseudosecond order), IPD (intraparticle diffusion), SD (surface diffusion) kinetics models; ANN – artificial neural network.*

#### **Table 4.**

*Environmental Issues and Sustainable Development*

**Best fit model Desorption Proposed** 

dichloromethane, benzene

L HCl 0.1 M; 102.6% Cu Proton & Ca

F - Phenol π–π dispersion

RB19, 91% DR79, and 95%

L; PSO HCl 0.01 M; 91.01% MB Electrostatic

SRS and 12.4% for SRSOA

NaOH 0.1 M; 94.5% MG; 95% of MG uptake capacity in the next adsorption cycle was

F, L - Cr Formation of

NaCl 0.05 M at pH 3; MG: 93% (RM-MNs) - 71% (RM-PPy); 3 reuse cycles with 22.5% decrease of dye removal for RM-MNs and 11.2% for

min. 3 reuse cycles with <5% decrease of biosorption


F - Chloroform,

T; PSO H2SO4; 88% RR198, 86%

L NaNO3 1 M; 45.7% Cu @ pH 3.5

L; PSO - Acid orange 7, Remazol black 5

L; PSO HCl 0.01 M; 68.6% MB for

achieved

RM-PPy

L; PSO HNO3 0.1 M; 98.2% Pb;

efficiency

L; PSO; endothermal

S; SD (RM-MNs), ANN (RM-PPy); endothermal

L; PSO; endothermal DR80 at pH 12

**mechanism**

Uptake by spherosomes

exchange, chemisorption

interaction, electrostatic interaction

Electrostatic interaction

Electrostatic interaction, formation of surface complexes

Electrostatic attraction, chemisorption

attraction, chemisorption, particle diffusion

Electrostatic attraction, chemisorption, diffusion

Electrostatic attraction

surface complexes, hydrolysis reactions

Electrostatic interactions; more complex mechanism for RM-PPy

interaction, complexation reaction, ion-exchange

Ion-exchange

**Ref. Optimum** 

[95] pH 7, dose

[21] pH 5, dose

[99] pH 7.5, dose

[113] pH 2.5, dose 1 (RR198, RB19) - 2 (DR79, DR80) g/L, 60 min, 200 rpm

[64] pH 4.5–5, dose 8 g/L, 25°C, 2 h

[20] pH 2.5, dose

[74] pH 8, dose 1 g/L, 40–60 min

[73] pH 8, dose 1 g/L, 60–180 min

[48] pH 6.5, dose 2.5 g/L, 180 min, 120 rpm

[83] pH 4, dose

[96] pH 6, dose

[71] pH 5.2, dose

3 h

[88] pH 5.5, dose

4 g/L, 25°C, 2 h

1 g/L, 25°C, 120 min (RM-MNs) - 150 min (RM-PPy)

10 g/L, 20 °C,

8 g/L, 22 °C, 30 min

7.5 g/L, 25°C, 120min, 100 rpm

**parameters**

10 g/L, 6 h

10 g/L, 1 h, 120rpm

1 g/L, 7 days, 25°C

**154**

*Optimum conditions of adsorption/desorption for pollutant uptake on RS-based adsorbents.*

mechanism is characterized by a high degree of complexity, especially when natural lignocellulosic biosorbents are involved.

In a single biosorption run, it is quite often that the sorbent does not reach the maximum sorption capacity (e.g., given by the Langmuir isotherm model) for a certain pollutant. Nevertheless, there will not be any further noticeable uptake of the respective pollutant even if the contact time is prolonged. Then, the spent sorbent is not sent to regeneration, but instead to a new sorption run involving a different target pollutant. And then in a third run of adsorption and so on. This concept is called an alternating or sequencing sorption. The main idea is to load the biosorbent as much as possible before its disposal, which could be practical for a low capacity biosorbent. This concept was studied by Morosanu et al. [65, 114] using RS meal as adsorbent and they have achieved 4 sequential adsorptions. The research was done considering two directions: (a) the biosorption of Rb19 dye followed by lead ions - RS-Rb19/Pb biosorption system, and (b) the biosorption of Pb followed by Rb19 dye - RS-Pb/Rb19 system. The authors observed that: (i); Pb uptake at higher concentrations is impeded by the presence of Rb19 on RS; (ii) dye sorption is favored by Pb presence; (iii) for the system RS-Rb19/Pb, pollutant desorption is selective, as a function of pH (**Table 4**); (iv) desorption was <7% in case of RS-Pb/Rb19 system. The experimental data suggests that the succession of pollutant biosorption matters. However, the biosorbent reuse in a new sorption cycle in order to determine the pollutants' uptake was not done.

At larger scale, continuous sorption processes are preferred. However, we have found only two studies using RS adsorbents in column tests. Amiri et al. [111], using a fixed-bed column (30 cm length, 2.5 cm inlet diameter) filled with canola stalkderived AC (height of 20 cm) to adsorb 2,4-dichlorophenoxyacetic acid, obtained maximum sorption capacities comparable with the batch data. The intraparticle diffusion coefficient from batch experiments was used for column modeling. Lead uptake in a fixed-bed column with RS meal (bed height 6 cm) was reported [71]. A faster column saturation was observed at higher pollutant concentration, while the maximum sorption capacities were higher than the one provided by Langmuir

model. The authors also tested an industrial wastewater containing lead ions in column configuration.

Considering the adsorbent's life cycle, when its regeneration is not economical anymore or it's not possible due to a previous chemisorption mechanism, the sorbent must be disposed of in such a manner that secondary pollution is avoided. In this sense, several authors proposed that exhausted RS meal could be used as a substrate for microbial colonization [48, 61]. Other practices involved biochar production from dye-loaded rape straw (modified with oxalic acid) [73], soil fertilizer [76] and using depleted biochars as biofuel [106]. To avoid leaching, a metal contaminated CM biochar was stabilized using phosphate binders [115]. Recovery of heavy metals from RS biomass can be done by electrochemical methods [116].
