**Abstract**

Application of biochar and ionic liquid-impregnated biochar was successfully tested for removal of nonbiodegradable polar halogenated aromatic contaminants (anti-inflammatory agents diclofenac and flufenamic acid and azo dye Mordant Blue 9) from contaminated aqueous solutions. The time dependence of removal efficiencies and adsorption isotherms were evaluated, and the effect of applied ionic liquids (quaternary ammonium salts) was considered. The determined removal efficiencies of the abovementioned contaminants based on the application of biochar or biochar combined with quaternary ammonium salts were compared with the action of commercially available active carbon and/or published results obtained by the action of additional low-cost sorbents. It was demonstrated that a more laborious two-step technique, based on the initial preparation of impregnated biochar by the action of R4NCl with subsequent application of this modified sorbent, is much less effective than simple mixing of biochar with R4NCl directly in the treated wastewater solution.

**Keywords:** drug, water treatment, sorption, diclofenac, flufenamic acid, anionic azo dye, mordant blue 9

## **1. Introduction**

An increase number of nonbiodegradable and often biologically active organic pollutants of anthropogenic origin, such as synthetic dyes and pharmaceuticals, have been detected in the natural environment and wastewaters. The occurrence of these artificial persistent or even biocidal pollutants in aqueous effluents of sewage treatment plants represents possible health hazard not only for the living aquatic organisms but also for terrestrial animals and people [1].

The representatives of these pollutants are polar and highly mobile halogenated aromatic carboxylic (e.g., diclofenac and flufenamic acid) or sulfonic acids and their salts (e.g., Mordant Blue 9 acid dye), respectively (**Table 1**). These ionizable polar compounds (their aqueous solubility strongly depends on the pH of the aqueous solution) are broadly used as remedies or colorants.

### **Table 1.**

*Structures of chlorinated aromatic acid salts.*

Specifically in the case of the painkiller diclofenac (DCF), studies have shown that conventional treatment processes are relatively ineffective in removing DCF from water sources and wastewater treatment plants [2]. Kasprzyk-Hordern et al. [2] observed no diclofenac removal in wastewater treatment using trickling filters and activated sludge. Rosal et al. in [3] reported only 5% of DCF removal after biological treatment of urban wastewater.

The concentration of ionizable contaminants, especially of alkaline salts of organic acids, in aqueous mother liquors from the production of these chemicals is frequently high, especially in the case of acid dyes (including Mordant Blue 9) isolated from the aqueous reaction medium by the so-called salting-out process [4]. Adsorption serves as the common and broadly used technique applicable for the treatment of water streams contaminated with these nonbiodegradable pollutants. The adsorption technique requires, however, high quantities of sorbent for effective water treatment which is accompanied by significant material costs. Therefore, carbonaceous rest, obtained by pyrolysis of waste biomass (biochar), potentially offers possible utilization in water treatment processes based on sorption as an alternative low-cost sorbent in comparison with activated carbon. For biochar, a porous structure with a sufficient specific area (above 400 m2 /g) is typical. Biochar poses polyaromatic systems substituted with some functional groups on its surface (COOH, OH, C=O) and even inorganic impurities (metal oxides) capable of engaging in **hydrogen-bonding or π-π** interactions with polar compounds.

Another notable attribute is biochar's affinity with the cationic surfactants (quaternary ammonium salts) [5].

This ability is of great interest for us due to the feasible utilization of cationic surfactants as liquid ion exchangers for chemisorption of the abovementioned chlorinated organic acid salts [6]. Ionizable halogenated contaminants produce ion pairs with only limited aqueous solubility and a good affinity with the biochar by the action of quaternary ammonium salts [7, 8].

The price of biochar is reasonably lower (around 1000 EURO/t) in comparison with active carbon (the cost of active carbon is approximately 2000 EUROs/t [9]).

**243**

**Figure 1.**

*Commercial twin-fire Gasifier [1].*

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated…*

Due to the abovementioned reasons, good cationic surfactant affinity of biochar seems to be very useful for uptake of ionizable contaminants using combined ion

Gasification is a thermochemical process that converts a (waste) woody biomass

Gasification is a complex process that can be divided into four basic stages. The first stage is drying. The second stage, taking place in the absence of oxygen and at temperatures above 250°C, is called pyrolysis. The waste woody biomass is converted into volatile matter and a carbonaceous residue (char) during the pyrolysis. The third stage is exothermic partial oxidation of the char and the volatile matter with an oxidizing agent (basically air). This exothermic process produces heat. The last (fourth) stage, called char gasification, is the sum of the endothermic reactions of char with CO2 and/or H2O driven by the heat from the third stage leading to the

The space separation of these four stages in a gasifier with proper process control can be used to optimize the outputs of the gasification process. The space separation and optimization of these four stages of the gasification process are the principle of the so-called multistage gasification. One concept used for multistage gasification is a twin-fire gasifier. The gas generator at the commercial heating plant (**Figure 1**)

into a producer gas and ash or carbonaceous residue (char). It can be used for combined heat and power production. The carbonaceous residue of the gasification process (called char) can match requirements classified as biochar [10]. The quality of both biochar and producer gas is highly dependent on the gasification technology

selected, most of all, on the design and operation parameters of the gasifier.

*DOI: http://dx.doi.org/10.5772/intechopen.92760*

**2. Origin of the tested biochar**

additional formation of H2 and CO.

exchange (chemisorption) and the sorption mechanism.

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated… DOI: http://dx.doi.org/10.5772/intechopen.92760*

Due to the abovementioned reasons, good cationic surfactant affinity of biochar seems to be very useful for uptake of ionizable contaminants using combined ion exchange (chemisorption) and the sorption mechanism.

### **2. Origin of the tested biochar**

*Applications of Biochar for Environmental Safety*

Diclofenac sodium salt (304.1)

Flufenamic acid sodium salt (303.2)

*Structures of chlorinated aromatic acid salts.*

Mordant Blue 9 (551.28)

**Table 1.**

**Applied contaminant (Mr [g/mol]) Chemical structure**

biological treatment of urban wastewater.

(quaternary ammonium salts) [5].

the action of quaternary ammonium salts [7, 8].

Specifically in the case of the painkiller diclofenac (DCF), studies have shown that conventional treatment processes are relatively ineffective in removing DCF from water sources and wastewater treatment plants [2]. Kasprzyk-Hordern et al. [2] observed no diclofenac removal in wastewater treatment using trickling filters and activated sludge. Rosal et al. in [3] reported only 5% of DCF removal after

The concentration of ionizable contaminants, especially of alkaline salts of organic acids, in aqueous mother liquors from the production of these chemicals is frequently high, especially in the case of acid dyes (including Mordant Blue 9) isolated from the aqueous reaction medium by the so-called salting-out process [4]. Adsorption serves as the common and broadly used technique applicable for the treatment of water streams contaminated with these nonbiodegradable pollutants. The adsorption technique requires, however, high quantities of sorbent for effective water treatment which is accompanied by significant material costs. Therefore, carbonaceous rest, obtained by pyrolysis of waste biomass (biochar), potentially offers possible utilization in water treatment processes based on sorption as an alternative low-cost sorbent in comparison with activated carbon. For biochar, a

poses polyaromatic systems substituted with some functional groups on its surface (COOH, OH, C=O) and even inorganic impurities (metal oxides) capable of engag-

Another notable attribute is biochar's affinity with the cationic surfactants

This ability is of great interest for us due to the feasible utilization of cationic surfactants as liquid ion exchangers for chemisorption of the abovementioned chlorinated organic acid salts [6]. Ionizable halogenated contaminants produce ion pairs with only limited aqueous solubility and a good affinity with the biochar by

The price of biochar is reasonably lower (around 1000 EURO/t) in comparison with active carbon (the cost of active carbon is approximately 2000 EUROs/t [9]).

/g) is typical. Biochar

porous structure with a sufficient specific area (above 400 m2

ing in **hydrogen-bonding or π-π** interactions with polar compounds.

**242**

Gasification is a thermochemical process that converts a (waste) woody biomass into a producer gas and ash or carbonaceous residue (char). It can be used for combined heat and power production. The carbonaceous residue of the gasification process (called char) can match requirements classified as biochar [10]. The quality of both biochar and producer gas is highly dependent on the gasification technology selected, most of all, on the design and operation parameters of the gasifier.

Gasification is a complex process that can be divided into four basic stages. The first stage is drying. The second stage, taking place in the absence of oxygen and at temperatures above 250°C, is called pyrolysis. The waste woody biomass is converted into volatile matter and a carbonaceous residue (char) during the pyrolysis. The third stage is exothermic partial oxidation of the char and the volatile matter with an oxidizing agent (basically air). This exothermic process produces heat. The last (fourth) stage, called char gasification, is the sum of the endothermic reactions of char with CO2 and/or H2O driven by the heat from the third stage leading to the additional formation of H2 and CO.

The space separation of these four stages in a gasifier with proper process control can be used to optimize the outputs of the gasification process. The space separation and optimization of these four stages of the gasification process are the principle of the so-called multistage gasification. One concept used for multistage gasification is a twin-fire gasifier. The gas generator at the commercial heating plant (**Figure 1**)

**Figure 1.** *Commercial twin-fire Gasifier [1].*

is built on this principle [11]. This type of gasifier is composed of two autothermic stages, each with a separate air intake, creating two separate "fires," therefore "twin-fire." The first air intake used for the partial combustion of the waste biomass is directed into the upper stage of the gasifier and produces the heat necessary for "autothermal" pyrolysis. The secondary air inlet, for partial oxidation of volatile matter, is directed to the top of the lower part of the gasifier, and the temperature of its "fire" exceeds 1200°C. Partial oxidation takes place in the free space above the char bed and produces heat for char gasification at the bottom of the second stage of the gasifier, reaching a temperature of approximately 950°C. The partial oxidation stage cracks down volatile matter into gases (i.e., CO, H2, CH4, CO2, and H2O) and thereby minimalizes the tar content. In the last stage, the hot products of the partial oxidation flow through the char bed and react with it, causing a temperature drop from 950 to 750°C due to the endothermic gasifying reactions. Optimization of this step can enhance the properties of the produced solid carbonaceous residue (biochar) by increasing its specific surface and due to its "activation" by the reactions with H2O and CO2. Moreover, the prolonged residence time (about 1 h) of the char at a high temperature of 750°C helps to achieve the stringent requirements on the content of polycyclic aromatic hydrocarbons in the produced biochar. For safety measures (to prevent producer gas leakage), the whole gasification unit and gas


**245**

**Table 3.**

by temperature above 700°C.

**ammonium chlorides in batch sorption**

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated…*

**Inorganic oxide Content of noncombustible part (wt. %)**

Al2O3 8.89 CaO 32.6 Fe2O3 6.74 K2O 6.69 MgO 5.78 MnO 1.20 Na2O 4.49 P2O5 2.21 SiO2 20.9 TiO2 2.93 Total amount 92.5

treatment line are operated at pressure slightly below atmospheric pressure (pressure difference—0.1–10 kPa) ensured by a fan (ventilator). The input material to the gasification generator is spruce wooden chips (waste biomass produced from spent packaging and pallets) with a water content max. 10 wt.%. The produced biochar (**Tables 2** and **3**) meet the European Biochar Certificate (EBC) standard of regulation (EU) 2019/1009 and the Central Institute for Supervising and Testing in Agriculture (Czech Certification Institute, the certification valid in the EU). The produced biochar can be grinded and is conveyed into a magnetic separator to eliminate any possible remaining metal particles. Lian and Xing published that increasing pyrolysis temperature above 700°C results in high aromaticity and porosity of obtained biochars structure, high carbon content, and progressive decreasing of nitrogen and oxygen content in produced biochar [12]. The described biochar produced in twin-fire gasifier is a typical high-temperature biochar with high carbon content, increased pH value, high porosity, increased ash content, and specific surface area (**Table 2**) [10]. As could be seen in **Tables 2** and **3**, elemental composition of produced highly porous biochar is mainly composed of C and very low contents of H, N, and O, with significant content of minerals. In comparison with starting wooden biomass, significant decrease in molar ratios of both H/C and O/C is observed in biochar due to the dehydration and thermolysis reactions caused

*Composition of noncombustible matter (ash) in the produced biochar according to XRF.*

**3. Preliminary experiments comparing sorption kinetics for removal of ionizable halogenated contaminants using biochar and quaternary** 

The above described biochar seems to be an interesting candidate for utilization in sorption processes due to the high porosity and specific surface comparable with active carbon (**Table 2**). This study is focused on the removal of ionizable organic compounds (halogenated organic acid salts) mentioned in the introduction chapter (**Table 1**). Due to the abovementioned high aqueous solubility of the studied sodium salts of chlorinated aromatic acids, the preliminary experiments were performed by the addition of high quantity (20 g/L) of the above-described

*DOI: http://dx.doi.org/10.5772/intechopen.92760*

### **Table 2.**

*Characteristics of the produced biochar.*

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated… DOI: http://dx.doi.org/10.5772/intechopen.92760*


### **Table 3.**

*Applications of Biochar for Environmental Safety*

Specific area, SBET (m2

Specific total pore volume, Vtot (mm3

Specific mesopore volume, Vmeso (m2

Specific micropore volume, Vmicro (mm3

is built on this principle [11]. This type of gasifier is composed of two autothermic stages, each with a separate air intake, creating two separate "fires," therefore "twin-fire." The first air intake used for the partial combustion of the waste biomass is directed into the upper stage of the gasifier and produces the heat necessary for "autothermal" pyrolysis. The secondary air inlet, for partial oxidation of volatile matter, is directed to the top of the lower part of the gasifier, and the temperature of its "fire" exceeds 1200°C. Partial oxidation takes place in the free space above the char bed and produces heat for char gasification at the bottom of the second stage of the gasifier, reaching a temperature of approximately 950°C. The partial oxidation stage cracks down volatile matter into gases (i.e., CO, H2, CH4, CO2, and H2O) and thereby minimalizes the tar content. In the last stage, the hot products of the partial oxidation flow through the char bed and react with it, causing a temperature drop from 950 to 750°C due to the endothermic gasifying reactions. Optimization of this step can enhance the properties of the produced solid carbonaceous residue (biochar) by increasing its specific surface and due to its "activation" by the reactions with H2O and CO2. Moreover, the prolonged residence time (about 1 h) of the char at a high temperature of 750°C helps to achieve the stringent requirements on the content of polycyclic aromatic hydrocarbons in the produced biochar. For safety measures (to prevent producer gas leakage), the whole gasification unit and gas

**Characteristics Value** Bulk density (g/mL) 166

pH 11.4 Electrical conductivity, EC (μS/cm) 1450 Ash (wt. %) 9.63 Carbon content, C (wt. %) 86.8 Organic carbon content, C (wt. %) 83.8 H/Corg ratio 0.0890 O/C ratio 0.0205 Sulfur content, S (wt. %) Less than 0.1 Content of combustible sulfur (mg/kg) 401 Chlorine content, Cl (mg/kg) 867 Fluorine content, F (mg/kg) 11.4 Content of P (g/kg) 0.65 Content of K (g/kg) 3.1 Content of Ca (g/kg) 15.7 Content of Mg (g/kg) 2.5 Sum PAH16 (mg/kg) Less than 0.5 Water content (wt. %) 1.18

/g) 444

liq/g) 293

/g) 142

liq/g) 157

**244**

**Table 2.**

*Characteristics of the produced biochar.*

*Composition of noncombustible matter (ash) in the produced biochar according to XRF.*

treatment line are operated at pressure slightly below atmospheric pressure (pressure difference—0.1–10 kPa) ensured by a fan (ventilator). The input material to the gasification generator is spruce wooden chips (waste biomass produced from spent packaging and pallets) with a water content max. 10 wt.%. The produced biochar (**Tables 2** and **3**) meet the European Biochar Certificate (EBC) standard of regulation (EU) 2019/1009 and the Central Institute for Supervising and Testing in Agriculture (Czech Certification Institute, the certification valid in the EU). The produced biochar can be grinded and is conveyed into a magnetic separator to eliminate any possible remaining metal particles. Lian and Xing published that increasing pyrolysis temperature above 700°C results in high aromaticity and porosity of obtained biochars structure, high carbon content, and progressive decreasing of nitrogen and oxygen content in produced biochar [12]. The described biochar produced in twin-fire gasifier is a typical high-temperature biochar with high carbon content, increased pH value, high porosity, increased ash content, and specific surface area (**Table 2**) [10]. As could be seen in **Tables 2** and **3**, elemental composition of produced highly porous biochar is mainly composed of C and very low contents of H, N, and O, with significant content of minerals. In comparison with starting wooden biomass, significant decrease in molar ratios of both H/C and O/C is observed in biochar due to the dehydration and thermolysis reactions caused by temperature above 700°C.

## **3. Preliminary experiments comparing sorption kinetics for removal of ionizable halogenated contaminants using biochar and quaternary ammonium chlorides in batch sorption**

The above described biochar seems to be an interesting candidate for utilization in sorption processes due to the high porosity and specific surface comparable with active carbon (**Table 2**). This study is focused on the removal of ionizable organic compounds (halogenated organic acid salts) mentioned in the introduction chapter (**Table 1**). Due to the abovementioned high aqueous solubility of the studied sodium salts of chlorinated aromatic acids, the preliminary experiments were performed by the addition of high quantity (20 g/L) of the above-described

biochar to the concentrated aqueous solutions of contaminants simulating effluents from industrial production sites. These preliminary experiments indicated that the maximum efficiency of contaminant removal was obtained after more or less than 90 minutes of biochar action in batch sorption under vigorous stirring (**Figure 2**). The removal efficiency for each contaminant reached more than 40% in all cases after 1 h of action. This means that these efficiencies are quite low even using this huge quantity of biochar. These results correspond with known high polarity of tested fully ionizated contaminants at pH above 8.5 and their low affinity to the low-polar surface of biochar. In contrast, however, it was published earlier that the addition of cationic surfactants to the wastewater contaminated with soluble organic acid salts can significantly improve removal efficiency due to the electrostatic attraction between negatively charged contaminant anions and positively charged cations of cationic surfactants [7, 8, 13].

Subsequently, possible enhancement of the removal efficiency of biochar caused by co-action with a cationic surfactant was tested. The sorption kinetics and removal efficiencies of the contaminant based on chlorinated carboxylic acid salts, biochar, and biochar in combined action with frequently used cationic surfactant quaternary ammonium salt (R4NCl) benzalkonium chloride (alkylbenzyldimethylammonium chloride, AlkBzMe2NCl) for removal of diclofenac sodium salt (NaDCF) and of flufenamic acid sodium salt (NaFLUFA) were compared.

The results for the removal rates of NaDCF and NaFLUFA are mentioned in **Figure 3**. As is apparent, after 30 min of action, the removal of NaDCF and NaFLUFA from aqueous solutions is completed. Whereas the application of sole biochar in quantity 20 g/L reduces the quantity of NaDCF (or NaFLUFA, respectively) with efficiency less than 45%, using a combination of cationic surfactant and biochar, the removal efficiency reaches over 65%. It should be said that the efficiency of NaDCF or NaFLUFA removal using sole cationic surfactant AlkBzMe2NCl without the addition of charcoal is much worse, below 34%. This observation could be explained by the known fact that NaDCF reacts smoothly with low-polar R4NCl

### **Figure 2.**

*Rate of removal of tested ionizable halogenated contaminants from 10 mM aqueous solutions (from 25 mM solution in case of NaDCF) using biochar in quantity 20 g/L.*

**247**

**Figure 3.**

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated…*

by ion exchange reaction producing high molecular (and less soluble) ion pairs R4N.

*Rate of NaDCF (25 mM aq. solution) and NaFLUFA (10 mM aq. solution) removal from aqueous solutions* 

Chemical structures of tested R4NCls are depicted in **Figure 4**. The effect of cation size of different cationic surfactants R4NCl (AlkBzMe2NCl, hexadecyltrimethylammonium chloride (AlkMe3NCl), and methyltrialkylammonium chloride, Aliquat 336) on removal efficiency of NaDCF and NaFLUFA is depicted in **Figures 5** and **6**. It is evident that the branched structure (quantity of long alkyl chains) of the used cationic surfactants and primarily the aqueous solubil-

important role in the removal efficiencies of the studied contaminants. This fact could be well described by comparison of the solubility of discussed pollutants and corresponding ion pairs in water and in low-polar solvent (octan-1-ol) using distribution coefficient between these two solvents (**Figure 7**, Eq. (1)). Octan-1-ol/ water distribution ratio is the most common way of expressing the lipophilicity of a compound, and it is defined as the ratio of the concentration of a solute in a watersaturated octanolic phase to its concentration in an octanol-saturated aqueous

log *Pow* = \_

The observed removal efficiencies of the co-action of different R4NCl with biochar (**Figure 5**) correspond well with the measured distribution coefficients between octan-1-ol and water of NaDCF and ion pairs R4N.DCF produced by the ion exchange of NaDCF with R4NCl, as could be demonstrated in **Figure 7**. The less hydrophobic quaternary cation produces less hydrophobic and more water soluble ion pair contaminant-COONR4 (with lower value of log POW,

*coctanol*

*caqueous phase* (1)

play an

ity of the produced ion pairs based on tetraalkylammonium salts R4N<sup>+</sup>

Contaminant-COONa + R4NCl ― > NaCl + Contaminant-COONR4 (ion-pair).

DCF (R4N.FLUFA, respectively) according to the scheme:

*using biochar (20 g/L) or a combination of AlkBzMe2NCl (1 g/L) with biochar (20 g/L).*

NaDCF + R4NCl ― > NaCl + R4N.DCF (ion pair). NaFLUFA + R4NCl ― > NaCl + R4N.FLUFA (ion pair).

phase. **P***ow* is defined as in Eq. (1) [14]:

*DOI: http://dx.doi.org/10.5772/intechopen.92760*

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated… DOI: http://dx.doi.org/10.5772/intechopen.92760*

### **Figure 3.**

*Applications of Biochar for Environmental Safety*

charged cations of cationic surfactants [7, 8, 13].

biochar to the concentrated aqueous solutions of contaminants simulating effluents from industrial production sites. These preliminary experiments indicated that the maximum efficiency of contaminant removal was obtained after more or less than 90 minutes of biochar action in batch sorption under vigorous stirring (**Figure 2**). The removal efficiency for each contaminant reached more than 40% in all cases after 1 h of action. This means that these efficiencies are quite low even using this huge quantity of biochar. These results correspond with known high polarity of tested fully ionizated contaminants at pH above 8.5 and their low affinity to the low-polar surface of biochar. In contrast, however, it was published earlier that the addition of cationic surfactants to the wastewater contaminated with soluble organic acid salts can significantly improve removal efficiency due to the electrostatic attraction between negatively charged contaminant anions and positively

Subsequently, possible enhancement of the removal efficiency of biochar caused by co-action with a cationic surfactant was tested. The sorption kinetics and removal efficiencies of the contaminant based on chlorinated carboxylic acid salts, biochar, and biochar in combined action with frequently used cationic surfactant quaternary ammonium salt (R4NCl) benzalkonium chloride (alkylbenzyldimethylammonium chloride, AlkBzMe2NCl) for removal of diclofenac sodium salt (NaDCF) and of flufenamic acid sodium salt (NaFLUFA) were compared. The results for the removal rates of NaDCF and NaFLUFA are mentioned in **Figure 3**. As is apparent, after 30 min of action, the removal of NaDCF and NaFLUFA from aqueous solutions is completed. Whereas the application of sole biochar in quantity 20 g/L reduces the quantity of NaDCF (or NaFLUFA, respectively) with efficiency less than 45%, using a combination of cationic surfactant and biochar, the removal efficiency reaches over 65%. It should be said that the efficiency of NaDCF or NaFLUFA removal using sole cationic surfactant AlkBzMe2NCl without the addition of charcoal is much worse, below 34%. This observation could be explained by the known fact that NaDCF reacts smoothly with low-polar R4NCl

*Rate of removal of tested ionizable halogenated contaminants from 10 mM aqueous solutions (from 25 mM* 

*solution in case of NaDCF) using biochar in quantity 20 g/L.*

**246**

**Figure 2.**

*Rate of NaDCF (25 mM aq. solution) and NaFLUFA (10 mM aq. solution) removal from aqueous solutions using biochar (20 g/L) or a combination of AlkBzMe2NCl (1 g/L) with biochar (20 g/L).*

by ion exchange reaction producing high molecular (and less soluble) ion pairs R4N. DCF (R4N.FLUFA, respectively) according to the scheme:

Contaminant-COONa + R4NCl ― > NaCl + Contaminant-COONR4 (ion-pair). NaDCF + R4NCl ― > NaCl + R4N.DCF (ion pair). NaFLUFA + R4NCl ― > NaCl + R4N.FLUFA (ion pair).

Chemical structures of tested R4NCls are depicted in **Figure 4**. The effect of cation size of different cationic surfactants R4NCl (AlkBzMe2NCl, hexadecyltrimethylammonium chloride (AlkMe3NCl), and methyltrialkylammonium chloride, Aliquat 336) on removal efficiency of NaDCF and NaFLUFA is depicted in **Figures 5** and **6**. It is evident that the branched structure (quantity of long alkyl chains) of the used cationic surfactants and primarily the aqueous solubility of the produced ion pairs based on tetraalkylammonium salts R4N<sup>+</sup> play an important role in the removal efficiencies of the studied contaminants. This fact could be well described by comparison of the solubility of discussed pollutants and corresponding ion pairs in water and in low-polar solvent (octan-1-ol) using distribution coefficient between these two solvents (**Figure 7**, Eq. (1)). Octan-1-ol/ water distribution ratio is the most common way of expressing the lipophilicity of a compound, and it is defined as the ratio of the concentration of a solute in a watersaturated octanolic phase to its concentration in an octanol-saturated aqueous phase. **P***ow* is defined as in Eq. (1) [14]: log *Pow* = \_

$$\log P\_{ow} = \frac{c\_{\text{actual}}}{c\_{\text{aquous phase}}} \tag{1}$$

The observed removal efficiencies of the co-action of different R4NCl with biochar (**Figure 5**) correspond well with the measured distribution coefficients between octan-1-ol and water of NaDCF and ion pairs R4N.DCF produced by the ion exchange of NaDCF with R4NCl, as could be demonstrated in **Figure 7**. The less hydrophobic quaternary cation produces less hydrophobic and more water soluble ion pair contaminant-COONR4 (with lower value of log POW,

**249**

**Figure 7.**

**Figure 6.**

*R4NCls (1 g/L) and biochar (20 g/L).*

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated…*

solubility is non-applicable for precise addition of appropriate quantity to treated wastewater. We tested, however, that A336 is well soluble in 50 wt.% aqueous AlkBzMe2NCl solution and the obtained mixture is less viscous and enables precise addition of R4NCls into the stirred aqueous solution. Due to these reasons, the mixtures of A336 and 50 wt.% aqueous AlkBzMe2NCl in two different weight ratios (2/3 or 3/2) were examined (see **Figures 5** and **6**). The low solubility of ion pairs A336.DCF produced by ion exchange reaction between A336 with NaDCF enables in particular extremely effective subsequent removal from the aqueous solution by

*Differences between the measured distribution coefficients log Pow between NaDCF and ion pairs produced by* 

*Rate of NaFLUFA removal from 10 mM aqueous solution using biochar (20 g/L) or a combination of different* 

*ion exchange of NaDCF with the corresponding R4NCl (R4N.DCF).*

*DOI: http://dx.doi.org/10.5772/intechopen.92760*

**Figure 4.**

*Chemical structures of tested cationic surfactants (quaternary ammonium chlorides, R4NCls) with different quantity of long alkyl chains (different cation size).*

**Figure 5.**

*Rate of NaDCF removal from 25 mM aq. Solution using biochar (20 g/L) or a combination of different R4NCls (1 g/L) and biochar (20 g/L).*

**Figure 5**). Benzalkonium chloride (AlkBzMe2NCl) which is readily soluble in water enables, for example, the worse removal of NaDCF in comparison with in-water insoluble Aliquat 336 (albeit the combination of the ion exchange with adsorption is still more effective in comparison with adsorption on sole biochar).

The highest value of log Pow was determined for low-polar and water immiscible ion pairs produced by the action of Aliquat 336 (A336). In contrast, A336 is extremely viscous (honey-like) material and together with its low aqueous

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated… DOI: http://dx.doi.org/10.5772/intechopen.92760*

### **Figure 6.**

*Applications of Biochar for Environmental Safety*

*quantity of long alkyl chains (different cation size).*

**248**

biochar).

**Figure 5.**

**Figure 4.**

*R4NCls (1 g/L) and biochar (20 g/L).*

**Figure 5**). Benzalkonium chloride (AlkBzMe2NCl) which is readily soluble in water enables, for example, the worse removal of NaDCF in comparison with in-water insoluble Aliquat 336 (albeit the combination of the ion exchange with adsorption is still more effective in comparison with adsorption on sole

*Rate of NaDCF removal from 25 mM aq. Solution using biochar (20 g/L) or a combination of different* 

*Chemical structures of tested cationic surfactants (quaternary ammonium chlorides, R4NCls) with different* 

The highest value of log Pow was determined for low-polar and water immiscible ion pairs produced by the action of Aliquat 336 (A336). In contrast, A336 is extremely viscous (honey-like) material and together with its low aqueous

*Rate of NaFLUFA removal from 10 mM aqueous solution using biochar (20 g/L) or a combination of different R4NCls (1 g/L) and biochar (20 g/L).*

**Figure 7.**

*Differences between the measured distribution coefficients log Pow between NaDCF and ion pairs produced by ion exchange of NaDCF with the corresponding R4NCl (R4N.DCF).*

solubility is non-applicable for precise addition of appropriate quantity to treated wastewater. We tested, however, that A336 is well soluble in 50 wt.% aqueous AlkBzMe2NCl solution and the obtained mixture is less viscous and enables precise addition of R4NCls into the stirred aqueous solution. Due to these reasons, the mixtures of A336 and 50 wt.% aqueous AlkBzMe2NCl in two different weight ratios (2/3 or 3/2) were examined (see **Figures 5** and **6**). The low solubility of ion pairs A336.DCF produced by ion exchange reaction between A336 with NaDCF enables in particular extremely effective subsequent removal from the aqueous solution by

### **Figure 8.**

*Rate of mordant blue 9 removal from 10 mM aqueous solution using biochar (20 g/L) or a combination of different R4NCls (1 g/L) and biochar (20 g/L).*

### **Figure 9.**

*Differences of measured distribution coefficients log Pow between commercial textile dye MB9 and ion pairs produced by ion exchange of MB9 with corresponding R4NCl.*

the addition of biochar. The surface of biochar sorbs produced A336.DCF better than AlkBzMe2N.DCF, as could be seen in **Figure 5**.

In accordance with the above described facts, the best removal efficiency of NaFLUFA was obtained using a combination of mixture of 3/2 (w/w) of A336 and 50% aq. AlkBzMe2NCl. The lowest effect of AlkMe3NCl on the removal of NaFLUFA corresponds, in contrast, with the least branched structure of AlkMe3N+ cation (**Figure 6**).

The same relationship between the structure of the used cationic surfactants and removal efficiency was observed in the case of the anionic textile dye Mordant

**251**

**Figure 10.**

*solution.*

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated…*

**4. A comparison of adsorption isotherms measured for removal** 

**carbon, biochar, and biochar in co-action with RNX**

Blue 9 (MB9). Subsequently, the measured log Pow values for MB9 and ion pairs R4N.MB9 are in good agreement once again with the measured removal efficiencies

**efficiencies of diclofenac or flufenamic acid sodium salts using active** 

The abovementioned differences in removal capacity of active carbons, biochar, modified biochar, and biochar in co-action of RNCls possessing quaternary cations with different bulkiness are illustrated in **Figure 10** for removal of NaDCF. The tested sorbents (active carbons or biochar) were used in quantity 10 g/L (with

**Figure 10** illustrates that the sorption capacity (*q*) showed the following behavior: PAC > [Biochar + AlkBzMe2NCl with Aliquat 336 (2:3)] > [Biochar + AlkBzMe2NCl with Aliquat 336 (3:2)] > [Biochar + AlkBzMe2NCl] > GAC > Biochar

*The dependence of sorption capacity of powdered (PAC) and granulated (GAC) active carbons, biochar, modified biochar and biochar in co-action with R4NCls on the equilibrium concentration of the NaDCF* 

The worst removal capacity poses modified biocharAlkBzMe2NCl prepared by mixing biochar with aqueous AlkBzMe2NCl solution, subsequent washing with water, and drying [15] (for more details see Experimental section) probably due to the low concentration of AlkBzMe2N-cations immobilized on surface of prepared modified biochar. **Figure 10** compared the effect of the addition of highly hydrophobic A336 added in different quantities to the hydrophilic 50% aq. AlkBzMe2NCl on the sorption capacity of biochar/ R4NCl mixture (which means sorption capacity of in situ-prepared biochar modified with added R4NCls). In agreement with the abovementioned effect of different R4NCls, using a higher quantity of A336 enables an increase of sorption capacity of biochar after the addition of R4NCls. In addition, the comparison of the effectiveness of traditional charcoal (granulated

*DOI: http://dx.doi.org/10.5772/intechopen.92760*

appropriate co-action of 1 g/L of R4NCl(s)).

> [Modified biochar AlkBzMe2NCl].

(**Figures 8** and **9**).

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated… DOI: http://dx.doi.org/10.5772/intechopen.92760*

Blue 9 (MB9). Subsequently, the measured log Pow values for MB9 and ion pairs R4N.MB9 are in good agreement once again with the measured removal efficiencies (**Figures 8** and **9**).

## **4. A comparison of adsorption isotherms measured for removal efficiencies of diclofenac or flufenamic acid sodium salts using active carbon, biochar, and biochar in co-action with RNX**

The abovementioned differences in removal capacity of active carbons, biochar, modified biochar, and biochar in co-action of RNCls possessing quaternary cations with different bulkiness are illustrated in **Figure 10** for removal of NaDCF. The tested sorbents (active carbons or biochar) were used in quantity 10 g/L (with appropriate co-action of 1 g/L of R4NCl(s)).

**Figure 10** illustrates that the sorption capacity (*q*) showed the following behavior: PAC > [Biochar + AlkBzMe2NCl with Aliquat 336 (2:3)] > [Biochar + AlkBzMe2NCl with Aliquat 336 (3:2)] > [Biochar + AlkBzMe2NCl] > GAC > Biochar > [Modified biochar AlkBzMe2NCl].

The worst removal capacity poses modified biocharAlkBzMe2NCl prepared by mixing biochar with aqueous AlkBzMe2NCl solution, subsequent washing with water, and drying [15] (for more details see Experimental section) probably due to the low concentration of AlkBzMe2N-cations immobilized on surface of prepared modified biochar. **Figure 10** compared the effect of the addition of highly hydrophobic A336 added in different quantities to the hydrophilic 50% aq. AlkBzMe2NCl on the sorption capacity of biochar/ R4NCl mixture (which means sorption capacity of in situ-prepared biochar modified with added R4NCls). In agreement with the abovementioned effect of different R4NCls, using a higher quantity of A336 enables an increase of sorption capacity of biochar after the addition of R4NCls. In addition, the comparison of the effectiveness of traditional charcoal (granulated

### **Figure 10.**

*The dependence of sorption capacity of powdered (PAC) and granulated (GAC) active carbons, biochar, modified biochar and biochar in co-action with R4NCls on the equilibrium concentration of the NaDCF solution.*

*Applications of Biochar for Environmental Safety*

*different R4NCls (1 g/L) and biochar (20 g/L).*

**250**

**Figure 9.**

**Figure 8.**

cation (**Figure 6**).

the addition of biochar. The surface of biochar sorbs produced A336.DCF better

*Differences of measured distribution coefficients log Pow between commercial textile dye MB9 and ion pairs* 

*Rate of mordant blue 9 removal from 10 mM aqueous solution using biochar (20 g/L) or a combination of* 

In accordance with the above described facts, the best removal efficiency of NaFLUFA was obtained using a combination of mixture of 3/2 (w/w) of A336 and 50% aq. AlkBzMe2NCl. The lowest effect of AlkMe3NCl on the removal of NaFLUFA corresponds, in contrast, with the least branched structure of AlkMe3N+

The same relationship between the structure of the used cationic surfactants and removal efficiency was observed in the case of the anionic textile dye Mordant

than AlkBzMe2N.DCF, as could be seen in **Figure 5**.

*produced by ion exchange of MB9 with corresponding R4NCl.*

Hydraffin CC8x30 GAC and powdered PAC Silcarbon CW20) and tested biochar and biochar with the co-action of the most effective mixture of cationic surfactants AlkBzMe2NCl with A336 is depicted in **Figure 10** using initial NaDCF concentration 0.25–8 g /L. It is evident that the combination of the aqueous surfactants mixture 50% aq. AlkBzMe2NCl and A336 in weight ratio 2/3 (used in quantity 1 g/L) with biochar (10 g/L) exhibits a similar sorption capacity as powdered active carbon Silcarbon CW20 (10 g/L) and a higher sorption capacity than granulated active carbon Hydraffin CC8x30 (10 g/L).

Similarly, studying removal efficiencies of NaFLUFA (initial concentration 0.25–7 g FLUFA/L) using active carbons (10 g/L), biochar (10 g/L), modified biochar (10 g/L), and biochar (10 g/L) with co-action of R4NCls (1 g/L), we observed that the activity of these sorbents was similar to the abovementioned removal of NaDCF (**Figure 11**). The sorption capacity has the rank order PAC mixture Aliquat 336 in 50% aq., AlkBzMe2NCl 3/2 with biochar mixture Aliquat 336 in 50% aq., and AlkBzMe2NCl 2/3 with biochar mixture of AlkBzMe2NCl with biochar AlkBzMe2NCl biochar. This similarity with NaDCF removal is not surprising; the chemical structures of both NaDCF and NaFLUFA are very similar (see **Table 1**). On the other hand, the sorption experiments using NaDCF and NaFLUFA were performed at different pH due to the low aqueous solubility of FLUFA at pH bellow 10. High removal efficiencies of A336/AlkBzMe2NCl mixtures with biochar even at high pH values are in agreement with our observation and the observation of Kosaiyakanon that the effect of pH is not crucial using separation method based on the formation of ion pairs [7, 8, 15]. q = \_(*c*0 − *c*).*V*

Sorption capacity q (mg/g) was calculated according to the following Eq. (2) [15]:

$$\mathbf{q} = \frac{(\mathbf{c}\_0 - \mathbf{c})\mathbf{\bar{v}}}{m} \tag{2}$$

**253**

**Table 4.**

Modified

Biochar + AlkBzMe2NCl

biocharAlkBzMe2NCl

Biochar +2/3 A336/ 50% aq. AlkBzMe2NCl

Biochar +3/2 A336/ 50% aq. AlkBzMe2NCl

*range 0.25–8 g/L) adsorbed by sorbents.*

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated…*

and Langmuir models are expressed in Eqs. (3) and (4), respectively:

Langmuir and Freundlich isotherm models were fitted to the data. The Langmuir model describes monolayer adsorption on a homogenous surface. The Freundlich model describes multilayer adsorption on a heterogeneous surface. The Freundlich

*q* = *kF c*1/*<sup>n</sup>* (3)

Here, *q* is the amount of adsorbed contaminant on the adsorbent at equilibrium (mg/g), *qmax* is the maximum adsorption of contaminant on the adsorbent (mg/g), *c* is the residual contaminant concentration at equilibrium (mg/L), *kL* is the Langmuir constant related to the energy of adsorption (L/mg), *kF* is the Freundlich constant indicating the adsorption capacity, and *n* is the Freundlich exponent accounting for the adsorption intensity or the energetic heterogeneity of the

The correlation coefficients suggest that the Freundlich model fits the data better than the Langmuir model (**Tables 4** and **5**). This can be an indication that NaDCF and NaFLUFA and/or ion pairs R4N.DCF (R4N. FLUFA, respectively) were

The maximum contaminant sorption capacities (qcont) of the biochar, both tested active carbons, and biochar with co-action of R4NCls at final pH of 8.7 were determined according to the Freundlich model (calculated for maximum applied concentration of contaminant using Eq. (3)). The differences in the action of sole biochar and biochar modified by different cationic surfactant(s) could be summa-

For the tested active carbons, the qcont values obtained by the same method were 661.6 mg NaDCF/g for granulated active carbon Hydraffin CC 8x30 and 742.3 mg

Interestingly, in all the cases, modified biochar prepared independently (ex situ) by impregnation of biochar with aqueous solution of R4NCls exhibited lower activity than the sequential addition of biochar and cationic surfactant(s) to the aqueous

PAC 2.14 1.03 0.954 833.3 0.0075 0.862 GAC 1.85 1.16 0.949 714.2 0.0034 0.811 Biochar 0.98 1.23 0.996 555.6 6.6 10<sup>−</sup><sup>4</sup> 0.886

*Identified parameters in Langmuir and Freundlich isotherm models for NaDCF (used in initial concentration* 

**Freundlich Langmuir**

1.95 0.73 0.975 400.0 5.3 10<sup>−</sup><sup>4</sup> 0.714

1.25 1.01 0.978 1250.0 0.0012 0.865

1.22 0.93 0.986 1428.6 5.7 10<sup>−</sup><sup>4</sup> 0.418

1.12 0.99 0.983 1111.1 0.0022 0.577

**(mg/g)**

**n R2 qmax**

adsorbed in multilayers into the active sites of the biochar surface.

rized by the ratio of increasing sorption capacity qcont/qcont\*

NaDCF/g for powdered active carbon Silcarbon CW20.

**(L/mg)1/n)**

**Sorbent kF (mg/g**

<sup>1</sup> <sup>+</sup>*kL <sup>c</sup>* (4)

[6] (**Table 6**).

**kL (L/mg)** **R2**

\_ *q qmax*= \_ *kL c*

*DOI: http://dx.doi.org/10.5772/intechopen.92760*

adsorbing surface [15].

where *c0* is the initial concentration (mg/L), *c* is the equilibrium concentration (mg/L), *m* is the mass of biochar (g), and *V* is the volume of treated model wastewater (L).

**Figure 11.**

*The dependence of sorption capacity of biochar, in-situ modified biochar two types of active carbons (powdered (PAC) Silcarbon CW20 and granulated (GAC) Hydraffin CC8x30 on the equilibrium concentration of the NaFLUFA solution).*

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated… DOI: http://dx.doi.org/10.5772/intechopen.92760*

Langmuir and Freundlich isotherm models were fitted to the data. The Langmuir model describes monolayer adsorption on a homogenous surface. The Freundlich model describes multilayer adsorption on a heterogeneous surface. The Freundlich and Langmuir models are expressed in Eqs. (3) and (4), respectively:

$$q = k\_F c^{1/n} \tag{3}$$

$$
\boldsymbol{q} = k\_F \boldsymbol{c}^{\dots, \dots} \tag{3}
$$

$$
\frac{\boldsymbol{q}}{\boldsymbol{q}\_{\text{max}}} = \frac{k\_L \boldsymbol{c}}{\mathbf{1} + k\_L \boldsymbol{c}} \tag{4}
$$

Here, *q* is the amount of adsorbed contaminant on the adsorbent at equilibrium (mg/g), *qmax* is the maximum adsorption of contaminant on the adsorbent (mg/g), *c* is the residual contaminant concentration at equilibrium (mg/L), *kL* is the Langmuir constant related to the energy of adsorption (L/mg), *kF* is the Freundlich constant indicating the adsorption capacity, and *n* is the Freundlich exponent accounting for the adsorption intensity or the energetic heterogeneity of the adsorbing surface [15].

The correlation coefficients suggest that the Freundlich model fits the data better than the Langmuir model (**Tables 4** and **5**). This can be an indication that NaDCF and NaFLUFA and/or ion pairs R4N.DCF (R4N. FLUFA, respectively) were adsorbed in multilayers into the active sites of the biochar surface.

The maximum contaminant sorption capacities (qcont) of the biochar, both tested active carbons, and biochar with co-action of R4NCls at final pH of 8.7 were determined according to the Freundlich model (calculated for maximum applied concentration of contaminant using Eq. (3)). The differences in the action of sole biochar and biochar modified by different cationic surfactant(s) could be summarized by the ratio of increasing sorption capacity qcont/qcont\* [6] (**Table 6**).

For the tested active carbons, the qcont values obtained by the same method were 661.6 mg NaDCF/g for granulated active carbon Hydraffin CC 8x30 and 742.3 mg NaDCF/g for powdered active carbon Silcarbon CW20.

Interestingly, in all the cases, modified biochar prepared independently (ex situ) by impregnation of biochar with aqueous solution of R4NCls exhibited lower activity than the sequential addition of biochar and cationic surfactant(s) to the aqueous


### **Table 4.**

*Applications of Biochar for Environmental Safety*

active carbon Hydraffin CC8x30 (10 g/L).

the formation of ion pairs [7, 8, 15].

water (L).

Hydraffin CC8x30 GAC and powdered PAC Silcarbon CW20) and tested biochar and biochar with the co-action of the most effective mixture of cationic surfactants AlkBzMe2NCl with A336 is depicted in **Figure 10** using initial NaDCF concentration 0.25–8 g /L. It is evident that the combination of the aqueous surfactants mixture 50% aq. AlkBzMe2NCl and A336 in weight ratio 2/3 (used in quantity 1 g/L) with biochar (10 g/L) exhibits a similar sorption capacity as powdered active carbon Silcarbon CW20 (10 g/L) and a higher sorption capacity than granulated

Similarly, studying removal efficiencies of NaFLUFA (initial concentration 0.25–7 g FLUFA/L) using active carbons (10 g/L), biochar (10 g/L), modified biochar (10 g/L), and biochar (10 g/L) with co-action of R4NCls (1 g/L), we observed that the activity of these sorbents was similar to the abovementioned removal of NaDCF (**Figure 11**). The sorption capacity has the rank order PAC mixture Aliquat 336 in 50% aq., AlkBzMe2NCl 3/2 with biochar mixture Aliquat 336 in 50% aq., and AlkBzMe2NCl 2/3 with biochar mixture of AlkBzMe2NCl with biochar AlkBzMe2NCl biochar. This similarity with NaDCF removal is not surprising; the chemical structures of both NaDCF and NaFLUFA are very similar (see **Table 1**). On the other hand, the sorption experiments using NaDCF and NaFLUFA were performed at different pH due to the low aqueous solubility of FLUFA at pH bellow 10. High removal efficiencies of A336/AlkBzMe2NCl mixtures with biochar even at high pH values are in agreement with our observation and the observation of Kosaiyakanon that the effect of pH is not crucial using separation method based on

Sorption capacity q (mg/g) was calculated according to the following Eq. (2) [15]: q = \_(*c*0 − *c*).*V*

where *c0* is the initial concentration (mg/L), *c* is the equilibrium concentration (mg/L), *m* is the mass of biochar (g), and *V* is the volume of treated model waste-

*The dependence of sorption capacity of biochar, in-situ modified biochar two types of active carbons (powdered (PAC) Silcarbon CW20 and granulated (GAC) Hydraffin CC8x30 on the equilibrium* 

*<sup>m</sup>* (2)

**252**

**Figure 11.**

*concentration of the NaFLUFA solution).*

*Identified parameters in Langmuir and Freundlich isotherm models for NaDCF (used in initial concentration range 0.25–8 g/L) adsorbed by sorbents.*


### **Table 5.**

*Identified parameters in Langmuir and Freundlich isotherm models for NaFLUFA (used in initial concentration range 0.25–7 g/L) adsorbed by sorbents.*


*\*Value of sorption capacity defined as qcont\**

### **Table 6.**

*A comparison of surface modification technique on increasing sorption capacity of chlorinated aromatic carboxylic acid sodium salts.*

solution contaminated with NaDCF (**Figure 10**). This could be explained by the possible parallel action of:


**255**

**Figure 12.**

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated…*

area (pH above zero point of charge of biochar [12, 16, 17])

biochar in **Tables 2** and **3**) (effect of the well-known insolubility of DCF salts

3.The effect of negative charge-assisted H-bonds which were published as the main mechanism for sorption of ionizable organic compounds at alkaline pH

4.Subsequently the high affinity of biochar to the produced ion pair R4N.DCF [15] (caused by decreasing of polarity of produced R4N.DCF ion pairs in comparison of NaDCF with subsequent increasing of their affinity to surface of

The abovementioned results demonstrated that using a two-step procedure to enhance the biochar's adsorption capacity using AlkBzMe2NCl as a modification agent is not effective and is more laborious in comparison with the addition of a sole

**5. A comparison of adsorption isotherms measured for removal efficiencies of textile dye mordant blue 9 using active carbons,** 

In order to test the removal potential of active carbons (10 g/L), biochar (10 g/L), and biochar (10 g/L) with co-action of R4NCls (1 g/L), broad concentrations (0.25–5.5 g/L) of MB9 in model aqueous solutions were chosen for the performed experiments, similar to the tested drugs. It is well-known that anionic dyes are efficiently removable from wastewater using adsorption on charcoal at low pH due to the suppression of their ionization. As the pH of the mixture increases,

*The dependence of sorption capacity of powdered (PAC) and granulated (GAC) active carbons, biochar, modified biochar and biochar in co-action with R4NCls on the equilibrium concentration of the MB9 solution.*

**biochar, and biochar in co-action with R4NX**

*DOI: http://dx.doi.org/10.5772/intechopen.92760*

tested biochar, as we were observed)

biochar.

with the mentioned polyvalent metal cations)

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated… DOI: http://dx.doi.org/10.5772/intechopen.92760*

biochar in **Tables 2** and **3**) (effect of the well-known insolubility of DCF salts with the mentioned polyvalent metal cations)


The abovementioned results demonstrated that using a two-step procedure to enhance the biochar's adsorption capacity using AlkBzMe2NCl as a modification agent is not effective and is more laborious in comparison with the addition of a sole biochar.

## **5. A comparison of adsorption isotherms measured for removal efficiencies of textile dye mordant blue 9 using active carbons, biochar, and biochar in co-action with R4NX**

In order to test the removal potential of active carbons (10 g/L), biochar (10 g/L), and biochar (10 g/L) with co-action of R4NCls (1 g/L), broad concentrations (0.25–5.5 g/L) of MB9 in model aqueous solutions were chosen for the performed experiments, similar to the tested drugs. It is well-known that anionic dyes are efficiently removable from wastewater using adsorption on charcoal at low pH due to the suppression of their ionization. As the pH of the mixture increases,

### **Figure 12.**

*Applications of Biochar for Environmental Safety*

**Sorbent kF (mg/g**

*concentration range 0.25–7 g/L) adsorbed by sorbents.*

Modified

AlkBzMe2NCl

AlkBzMe2NCl

**Table 5.**

biocharAlkBzMe2NCl

Biochar +2/3 A336/ 50% aq.

Biochar +3/2 A336/ 50% aq.

solution contaminated with NaDCF (**Figure 10**). This could be explained by the

*A comparison of surface modification technique on increasing sorption capacity of chlorinated aromatic* 

**Contaminant Sorbent qcont**

**(L/mg)1/n)**

PAC 2.06 0.77 0.949 1000.0 0.010 0.702 GAC 1.13 1.01 0.997 833.3 0.0029 0.634 Biochar 0.85 1.11 0.987 666.7 0.0018 0.766

Biochar + AlkBzMe2NCl 1.62 1.07 0.982 833.3 0.0027 0.770

NaDCF Biochar 539.5\* —

*Identified parameters in Langmuir and Freundlich isotherm models for NaFLUFA (used in initial* 

NaFLUFA Biochar 540.3\* —

**(mg/g)**

**Freundlich Langmuir**

0.95 1.07 0.996 714.3 0.0023 0.728

1.88 1.04 0.968 909.1 0.0032 0.748

1.84 0.97 0.969 909.1 0.0044 0.635

**(mg/g)**

**kL (L/mg)** **R2**

**n R2 qmax**

Modified biocharAlkBzMe2NCl 325.8 0.604 Biochar + AlkBzMe2NCl 682.2 1.264

Modified biocharAlkBzMe2NCl 514.6 0.952 Biochar + AlkBzMe2NCl 620.4 1.148

biochar+2/3 A336/50% aq. AlkBzMe2NCl 635.9 1.177 biochar +3/2 A336/50% aq. AlkBzMe2NCl 657.8 1.217

Biochar+2/3 A336/50% aq. AlkBzMe2NCl 628.5 1.165 Biochar +3/2 A336/50% aq. AlkBzMe2NCl 719.9 1.334

**Ratio of increasing capacity (qcont/qcont\***

**)**

1.Rapid ion exchange reaction between the added R4NCl and NaDCF accompanied by coagulation of the produced ion pairs R4N.DCF (this reaction was proved by isolation of mentioned R4N.DCF ion pairs by extraction and by

2.The effect of polyvalent metal cations from inorganic components of biochar on additional precipitation of insoluble DCF salts (with composition M+n. (DCF)n) [12] (M+n = CaII, MgII, AlIII, FeIII, etc., see the content of minerals in

**254**

**Table 6.**

possible parallel action of:

*carboxylic acid sodium salts.*

*\*Value of sorption capacity defined as qcont\**

subsequent NMR analysis)

*The dependence of sorption capacity of powdered (PAC) and granulated (GAC) active carbons, biochar, modified biochar and biochar in co-action with R4NCls on the equilibrium concentration of the MB9 solution.*


### **Table 7.**

*A comparison of surface modification technique on increasing sorption capacity of MB9.*


### **Table 8.**

*Identified parameters in Langmuir and Freundlich isotherm models for MB9 (used in initial concentration range 0.5–5.5 g/L) adsorbed by sorbents.*

the formation of negatively charged MB9 anions increases due to the ionization. The surface site of charcoal does not favor the adsorption of dye anions due to the electrostatic repulsion [18].

It has been observed, however, by Kosyiyakanon et al. that the addition of R4NCls to the biochar enables the high efficiency of acid dyes removal even in a broad pH area from 3 to 9 [15].

This fact could be explained by the formation of low-soluble high-molecular ion pairs (dye-SO3NR4) by the ion exchange reaction between the added R4NCl and -SO3Na groups bound in the structure of dye according to the scheme:

dye-SO3Na + R4NCl ― > NaCl + dye-SO3NR4 (ion-pair).

As could be seen in **Figure 12**, biochar is the worst sorbent; however, using R4NCls selected similarly to abovementioned separation of chlorinated aromatic carboxylic acids sodium salts, the sorption capacity rises efficiently.

**257**

*Application of Biochar for Treating the Water Contaminated with Polar Halogenated…*

were adsorbed in multilayers into the active sites of the biochar surface.

HSAB principle, cations of hard bases (AlkBzMe2N<sup>+</sup>

AlkBzMe2NCl) > PAC ~ (biochar+2/3 A336/50% aq.AlkBzMe2NCl) > GAC ~ (biochar + AlkBzMe2NCl) > (modified biocharAlkBzMe2NCl) > biochar, this indicated that the combined action of the sorted R4NCls mixture and biochar could specifically increase the sorption capacity for the used biochar above the adsorption capacity of commercial powdered active carbon Silcarbon CW20 (**Figure 12** and

Langmuir and Freundlich isotherm models were fitted to the data. Similarly, the correlation coefficients suggest that the Freundlich model fits the data better than the Langmuir model (**Table 8**). This indicates that MB9 and/or ion pairs R4N.MB9

<sup>−</sup>). Probably due to this reason, the observed removal efficiency

) prefer to bond to anions of

In case of the tested acid dye, the sorption capacity of the ex situ-prepared modified BiocharAlkBzMe2NCl is closer to the sorption capacity of in situ-mixed R4NCls with biochar (**Figure 12**). The observed higher sorption capacity of modified biocharAlkBzMe2NCl in comparison with biochar agrees with the published results by Mi et al. [13] and Kosaiyakanon [15]. This observation is in good agreement with hard and soft acids and bases (HSAB) theory [19]. According to the

of used modified biocharAlkBzMe2NCl is higher in case of MB9 removal than in the

Biochar obtained as a by-product in the gasification process of waste biomass was verified as a suitable sorbent for the removal of the three tested highly mobile, ionizable, and nonbiodegradable chlorinated aromatic acid sodium salts NaDCF, NaFLUFA, and MB9 from model wastewater solutions in a broad range of concentrations. For increasing biochar's removal efficiency, biochar was intentionally mixed with selected cationic surfactants to produce an in situ-modified sorbent designed for the effective removal of the abovementioned negatively charged pollutants even from alkaline aqueous solutions. The higher efficiency obtained using biochar mixed in situ with selected R4NCls in model wastewater could be explained by the multilayer adsorption of ion pairs (contaminant-COONR4 or contaminant-SO3NR4, respectively) on the heterogeneous biochar surface described

We demonstrated that a more laborious two-step technique, based on the initial preparation of impregnated biochar by the action of R4NCl with subsequent application of this modified sorbent, is much less effective than simple mixing of biochar with R4NCl directly in the treated wastewater solution. According to the performed experiments, cationic surfactants based on tetraalkylammonium chloride R4NXs

of NaDCF, NaFLUFA, and MB9 from aqueous solutions by the co-action of biochar. The most effective R4NX for the removal of these contaminants was verified Aliquat 336, which is, however, highly viscous and nonmiscible with water. Its dilution with an organic solvent is prohibited due to environmental reasons. From a practical point of view, we successfully tried and chose the application of the mixture containing three parts of A336 dissolved in two parts of 50 wt.% aqueous AlkBzMe2NCl, having acceptable removal efficiency for the studied contaminants and enabling the simple and precise addition of the most effective A336 cationic surfactant together with the tested biochar for effective wastewater treatment. This technique based on joint addition of selected R4NCls together with biochar enables attainment of removal

cations were verified as very effective for the uptake

application for removal of anions of soft carboxylic acids DCF and FLUFA.

*DOI: http://dx.doi.org/10.5772/intechopen.92760*

**Table 7**).

hard acids (dye-SO3

**6. Conclusions**

by Freundlich isotherms.

carrying highly branched R4N+

As the sorption capacities for the removal of chlorinated aromatic sulfonic acid sodium salt MB9 were (biochar +3/2 A336/50% aq. *Application of Biochar for Treating the Water Contaminated with Polar Halogenated… DOI: http://dx.doi.org/10.5772/intechopen.92760*

AlkBzMe2NCl) > PAC ~ (biochar+2/3 A336/50% aq.AlkBzMe2NCl) > GAC ~ (biochar + AlkBzMe2NCl) > (modified biocharAlkBzMe2NCl) > biochar, this indicated that the combined action of the sorted R4NCls mixture and biochar could specifically increase the sorption capacity for the used biochar above the adsorption capacity of commercial powdered active carbon Silcarbon CW20 (**Figure 12** and **Table 7**).

Langmuir and Freundlich isotherm models were fitted to the data. Similarly, the correlation coefficients suggest that the Freundlich model fits the data better than the Langmuir model (**Table 8**). This indicates that MB9 and/or ion pairs R4N.MB9 were adsorbed in multilayers into the active sites of the biochar surface.

In case of the tested acid dye, the sorption capacity of the ex situ-prepared modified BiocharAlkBzMe2NCl is closer to the sorption capacity of in situ-mixed R4NCls with biochar (**Figure 12**). The observed higher sorption capacity of modified biocharAlkBzMe2NCl in comparison with biochar agrees with the published results by Mi et al. [13] and Kosaiyakanon [15]. This observation is in good agreement with hard and soft acids and bases (HSAB) theory [19]. According to the HSAB principle, cations of hard bases (AlkBzMe2N<sup>+</sup> ) prefer to bond to anions of hard acids (dye-SO3 <sup>−</sup>). Probably due to this reason, the observed removal efficiency of used modified biocharAlkBzMe2NCl is higher in case of MB9 removal than in the application for removal of anions of soft carboxylic acids DCF and FLUFA.

### **6. Conclusions**

*Applications of Biochar for Environmental Safety*

**Sorbent kF (mg/g**

*\*Value of sorption capacity defined as qcont\**

Modified

**Table 7.**

Biochar + AlkBzMe2NCl

Biochar +2/3 A336/ 50% aq. AlkBzMe2NCl

Biochar +3/2 A336/ 50% aq. AlkBzMe2NCl

**Table 8.**

biocharAlkBzMe2NCl

**(L/mg)1/n)**

*A comparison of surface modification technique on increasing sorption capacity of MB9.*

**Contaminant Sorbent qcont**

MB9 Biochar 257.1\* —

the formation of negatively charged MB9 anions increases due to the ionization. The surface site of charcoal does not favor the adsorption of dye anions due to the

*Identified parameters in Langmuir and Freundlich isotherm models for MB9 (used in initial concentration* 

**Freundlich Langmuir**

0.90 1.24 0.995 357.1 0.0032 0.611

0.85 1.20 0.986 476.2 0.0014 0.550

0.88 1.09 0.985 500.0 0.0035 0.742

1.19 0.99 0.985 555.6 0.0058 0.768

**(mg/g)**

**(mg/g)**

**kL (L/mg)**

**Ratio of increasing capacity (qcont/qcont\***

**)**

**R2**

**n R2 qmax**

Modified biocharAlkBzMe2NCl 329.9 1.283 Biochar + AlkBzMe2NCl 369.6 1.437

biochar+2/3 A336/50% aq. AlkBzMe2NCl 411.2 1.599 biochar +3/2 A336/50% aq. AlkBzMe2NCl 448.2 1.743

PAC 0.91 1.08 0.984 500.0 0.0042 0.772 GAC 1.03 1.17 0.995 526.3 0.0015 0.611 Biochar 0.96 1.36 0.995 384.6 8.2 10<sup>−</sup><sup>4</sup> 0.739

It has been observed, however, by Kosyiyakanon et al. that the addition of R4NCls to the biochar enables the high efficiency of acid dyes removal even in a

This fact could be explained by the formation of low-soluble high-molecular ion pairs (dye-SO3NR4) by the ion exchange reaction between the added R4NCl and

As could be seen in **Figure 12**, biochar is the worst sorbent; however, using R4NCls selected similarly to abovementioned separation of chlorinated aromatic


dye-SO3Na + R4NCl ― > NaCl + dye-SO3NR4 (ion-pair).

carboxylic acids sodium salts, the sorption capacity rises efficiently. As the sorption capacities for the removal of chlorinated aromatic sulfonic acid sodium salt MB9 were (biochar +3/2 A336/50% aq.

**256**

electrostatic repulsion [18].

*range 0.5–5.5 g/L) adsorbed by sorbents.*

broad pH area from 3 to 9 [15].

Biochar obtained as a by-product in the gasification process of waste biomass was verified as a suitable sorbent for the removal of the three tested highly mobile, ionizable, and nonbiodegradable chlorinated aromatic acid sodium salts NaDCF, NaFLUFA, and MB9 from model wastewater solutions in a broad range of concentrations. For increasing biochar's removal efficiency, biochar was intentionally mixed with selected cationic surfactants to produce an in situ-modified sorbent designed for the effective removal of the abovementioned negatively charged pollutants even from alkaline aqueous solutions. The higher efficiency obtained using biochar mixed in situ with selected R4NCls in model wastewater could be explained by the multilayer adsorption of ion pairs (contaminant-COONR4 or contaminant-SO3NR4, respectively) on the heterogeneous biochar surface described by Freundlich isotherms.

We demonstrated that a more laborious two-step technique, based on the initial preparation of impregnated biochar by the action of R4NCl with subsequent application of this modified sorbent, is much less effective than simple mixing of biochar with R4NCl directly in the treated wastewater solution. According to the performed experiments, cationic surfactants based on tetraalkylammonium chloride R4NXs carrying highly branched R4N+ cations were verified as very effective for the uptake of NaDCF, NaFLUFA, and MB9 from aqueous solutions by the co-action of biochar. The most effective R4NX for the removal of these contaminants was verified Aliquat 336, which is, however, highly viscous and nonmiscible with water. Its dilution with an organic solvent is prohibited due to environmental reasons. From a practical point of view, we successfully tried and chose the application of the mixture containing three parts of A336 dissolved in two parts of 50 wt.% aqueous AlkBzMe2NCl, having acceptable removal efficiency for the studied contaminants and enabling the simple and precise addition of the most effective A336 cationic surfactant together with the tested biochar for effective wastewater treatment. This technique based on joint addition of selected R4NCls together with biochar enables attainment of removal

efficiency comparable with commercial active carbons containing at least twice higher specific area as biochar. These obtained results agree with the information by Xi et al. [20] which observed that the surface area of the used sorbent by the coaction of R4NX does not play a major role in sorption of anionic contaminants.
