# Evaluation of heavy metal removal from industrial wastewater using a new natural flocculant

Bahman Nazari, Saba Abdolalian, Mohsen Taghavijeloudar

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Bahman Nazari, Saba Abdolalian, Mohsen Taghavijeloudar. Evaluation of heavy metal removal from industrial wastewater using a new natural flocculant. 7th International Conference on Researches in Science & Engineering & 4th International Congress on Civil, Architecture and Urbanism in Asia, Feb 2023, Bangkok, Thailand. hal-04363030

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# Evaluation of heavy metal removal from industrial wastewater using a new natural flocculant

Bahman Nazari¹, Saba Abdolalian², Mohsen Taghavijeloudar*

1. Department of Chemical engineering, Babol Noshirvani university of Technology, Babol, Iran
Email: Bn.nazari1991@gmail.com

2. Department of Civil and Environmental engineering, Babol Noshirvani university of Technology, Babol, Iran

Email: Saba.abdolalian71@gmail.com

3. Department of Civil and environmental engineering, Seoul National University, Seoul, Korea

Email: Mohsen@SNU.ac.ir

## Abstract

Conventional flocculants bear environmental and health concerns which could be avoided by applying natural materials. In this research, performance of *Pistacia terebinthus*, as an eco-friendly coagulant for industrial wastewater treatment was evaluated. To do this, different dosages of *Pistacia terebinthus* (0.5, 1, 1.5, and 2 g/L) was applied to wastewater samples to remove heavy metals of Pb²⁺ and Cu²⁺. Additionally, the effect of various initial pH (3, 5, 7, 9, 11) on the flocculant performance was investigated. Moreover, scanning electron microscope (SEM) images and fourier-transform infrared spectroscopy (FTIR) spectra was conducted to find the morphology of flocs and the main mechanism of treatment. The results showed that in the optimal condition of NF dosage= 2 g/L and pH=11after 60 minutes of settling time, maximum removal efficiencies of 98% and 99% was obtained for Pb²⁺ and Cu²⁺, respectively. What is more, based on the results of this research, main mechanism of the *Pistacia terebinthus* as natural flocculant with pH adjustment for heavy metal removal is bridging combined with charge neutralization.

**Key words:** Wastewater treatment, Flocculation, Pulp and paper wastewater, Heavy metal removal
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# 1. Introduction

The pulp and paper manufactories are among the most important industries in the world, but also some of the biggest contaminating agents, discharging a variety of pollutants similar as gaseous, liquid and solid wastes into the environment [1]. Generally, pulp and paper wastewater (PPWW) contains organic and inorganic materials that are sometimes really poisonous such ingredients are colloids in solution, in suspense or in emulsion form. PPWW is among the most contaminating industries, which cause worldwide environmental damages. In fact, pulp and paper mill effluent is hugely poisonous and major source of aquatic pollution[2] [19] [20]. Due to high concentration of multiple harmful and serious pollutants, particularly heavy metals, industrial wastewater has become a major problem. Heavy metal pollution and its implications for human health and the environment have increased investigation in developing low cost and sustainable remediation technology [21] [22] [3]. The presence of heavy metals in aquatic bodies and organisms that are used as a source of food, is directly and indirectly correlated to public health issues ranging from poisoning causing cancer and even resulting in neurological diseases. Some of these metals, including Copper, Iron, Nickel, Chromium and magnesium also play an essential beneficial part in physiological and biochemical activities in numerous organisms. Still, increased doses of these heavy metals can cause acute and chronic toxicities in humans[4] [21].

Several methods have been proposed for PPWW treatment to diminishing heavy metals including physicochemical treatment methods[5] biological methods [6], Fenton process[7], nanotechnology [8] and coagulation/flocculation sedimentation [9], each of which has advantages and disadvantages. Wastewater treatment, coagulation/ flocculation can be utilized as pretreatment, post-treatment, or main treatment of wastewater. It has received broad interest at the industrial level because of its simple operation, high effectiveness and low cost. The general process of coagulation/flocculation includes destabilization, agglomeration of pollutants and the formation of flocs[10]. Although the coagulation efficiency of using these inorganic coagulants is well-proven, they pose detrimental effects on human health, produce large volume of sludge and are ineffective in low-temperature water[11].

The use of natural coagulants is being emphasized in recent years, as it has been well understood that these natural biocoagulants are environmentally and economically more adequate than chemical coagulants. Biocoagulants prepared from plants such as *Moringa Oleifera*, *Cocos nucifera* and *Jatropha curcas* were found more beneficial than chemical coagulants due to their low toxicity, biodegradability and lower production of sludge[12]. *Pistacia* species (Anacardiaceae family) have been widely distributed in the Middle East, Asian, European and American countries. It is a small tree widely growing in southern and western Turkey on dry rock slopes and hillsides or in pine forests[13].

The main objective of this research was to investigate the potential of using *Pistacia terebinthus* seeds as natural coagulant for removing heavy metals from pulp and paper wastewater treatment. To do this, the novel *Pistacia terebinthus* stock was prepared. Then the removal efficiencies of heavy metals (Pb²⁺ and Cu²⁺) using different dosage of *Pistacia*
terebinthus was investigated. Additionally, the effect of pH adjustment (Ranging 3 to 11) on the natural flocculants performance was evaluated. Optimum condition for obtaining maximum removal efficiencies of heavy metals were determined. Scanning electron microscope (SEM) images and Fourier-transform infrared spectroscopy (FTIR) spectra were used to characterize and analysis the underline mechanisms.

## 2. Materials and Methods

### 2-1- Wastewater sample and characterization

The wastewater samples used in the experiments were obtained from a local pulp and paper company (Pouya Ayesh Mazand) in Babol, Mazandaran, Iran. The samples were kept in a container and stored in a refrigerator. The wastewater samples were taken at the treatment plant, at different times. The samples characterization is represented in Table1.

<table><caption>Table 1: Characteristics of the pulp and paper wastewater sample in this study</caption><thead><tr><td>Parameter</td><td>Unit</td><td>Value</td></tr></thead><tbody><tr><td>pH</td><td>-</td><td>6.7</td></tr><tr><td>Dissolved oxygen (DO)</td><td>mg/L</td><td>1.52</td></tr><tr><td>Total suspended solid (TSS)</td><td>mg/L</td><td>2100</td></tr><tr><td>Chemical oxygen demand (COD)</td><td>mg/L</td><td>1250</td></tr><tr><td>Turbidity</td><td>NTU</td><td>530</td></tr><tr><td>Lead (Pb<sup>2+</sup>)</td><td>mg/L</td><td>48.52</td></tr><tr><td>Copper (Cu<sup>2+</sup>)</td><td>mg/L</td><td>5.86</td></tr><tr><td>Zeta potential</td><td>mV</td><td>-11.5</td></tr></tbody></table>

### 2-2-Prepration of *Pisacia terebinthus* flocculant

The *pistacia terebinthus* as natural flocculant were bought from a local market. The *pistacia terebinthus* were crushed and separated from the shell, then pulverized and powdered. To obtain stock soluble, 5 g of the obtained *Pistacia terebinthus* powder were mixed with 5.84 g of NaCl and solvate with 100 mL deionized water. Then uniform mixture was attained by exposing ultrasound radiation with power of 70% for 6 minute. The solution was filtered and the final solution was used as natural flocculants.

### 2-3-Coagulation-flocculation tests procedure

Jar tests were performed using flocculator to simulate the treatment coagulation-flocculation process. The flocculator comprises of 6 rotating impeller shaft which allows 6 samples to be run at the same time. Each of the 250 mL of the *Pistacia terebinthus*. The PPWW initial Pb²⁺ and Cu²⁺ were measured and recorded. Original pH of the PPWW was acclimated ranging from 3 to 11 using 1.0 M HCL and 1.0 M NaOH .Then, to evaluate the performance of natural flocculant, six different dosages of *Pistacia terebinthus* (0.5, 1, 1.5, and 2 g/L) were added to each beaker. Furthermore, the effect of pH on the flocculation of *Pistacia terebinthus* was
evaluated by adjusting the initial pH of wastewater (3, 5, 7, 9 and 11). Each beaker was agitated at 150 rpm for 5 minutes and 15 minutes of slow mixing with 25 rpm for flocculation mixing. The treated wastewater in each beaker was allowed to settle for a duration of 60 min. 20 mL of the supernatant was sampled from depth of 3 cm from the beaker for heavy metals measurement.

## 2-4- Analytical data

The concentration of heavy metal ions (Cu²⁺ and Pb²⁺) were measured using atomic absorption spectroscopic analysis of pulp and paper samples by acid digestion before and after treatment using an Atomic absorption spectrophotometer ELICO SL- 173[14]. The removal efficiencies were calculated using Eq. (1):

$$ Removal\ efficiency = \frac{(C_o - C_t)}{C_o} \times 100 \quad (1) $$

where, C₀ and Cₜ were the concentrations of the heavy metals (mg/L) in the wastewater before and after treatment, respectively.

The pH and dissolved oxygen (DO) of the samples were measured using pH and DO meter (WA-2017SD LUTRON, Japan). The morphology and flocculation shape were observed using a scanning electron microscope (SEM) (E-beam Pioneer, Tokyo, Japan) before and after the treatments. Fourier-Transform Infrared Spectroscopy (FTIR) (Nicolet FT-IR Avatar 360). All experiments were carried out in triplicates.

# 3. Results and discussion

## 3-1-Effect of *Pistacia terebinthus* as a natural flocculants for heavy metals removal

Performance of different dosages of *Pistacia terebinthus* as a natural flocculants for the removal of Pb²⁺ and Cu²⁺ from pulp and paper wastewater in pH of 7 is shown in Figure1(a&b). As can be seen from Figure1a, *Pistacia terebinthus* showed Cu²⁺removal efficiency of 71% (from 4.86 to 1.70 mg/L) at the optimum dosage of 2 g/L. Maximum Pb²⁺ removal of 75% (From 38 to 12.3 mg/L) was obtained by applying 2 g/L dosage of *Pistacia terebinthus*. Cu²⁺ and Pb²⁺removal is attributed to the settlement of cationic materials suspended in wastewater as results of coagulation-flocculation process. It can be concluded that the negatively charged surface of organic matters in untreated wastewater prevents particle aggregation due to repulsive forces. However, adding cationic natural polymer of *Pistacia terebinthus* in to wastewater can dramatically improve flocculation process through main mechanism of bridging. Similar results were observed for heavy metal removal by alum in previous reports [15].
<figure><img src="image_3.png" /><figcaption>Figure 1: Effect of Natural flocculant on a) Cu²⁺ and b) Pb²⁺ removal efficiency</figcaption></figure>

### 3-2-Effect of pH adjustment and *Pistacia terebinthus* in heavy metals removal

Figure 2 shows the interaction effect of pH adjustment and *Pistacia terebinthus* dosage on heavy metals (Cu²⁺ and Pb²⁺) removal efficiencies. According to Figure 2a and b, for heavy metals removal, the synergistic effects between pH adjustment and *Pistacia terebinthus* were observed under alkaline condition. According to Figure 2a and b, maximum removal of 98 % and 99 % were achieved for Cu²⁺ and Pb²⁺, respectively at dosage of 2 g/L and pH of 11. This high removal efficiency of heavy metal is attributed to the heavy metal oxidation under alkaline condition:

$$Cu^{2+} + 2OH^{-} = Cu(OH)_{2}$$

$$Pb^{2+} + 2OH^{-} = Pb(OH)_{2}$$

And better flocculation as a result of dual flocculation of sweeping mechanism (Pb(OH)₂ and Cu(OH)₂ precipitations) and particle-birding mechanism by the natural flocculation. The deterioration of heavy metal removal at acidic condition is related to the repulsive forces between positively charged *Pistacia terebinthus*, H⁺ and positively charged heavy metals. Under acidic condition (pH=3) the release of H⁺ ions enhance flocculation through charge neutralization and making the zeta potential less negative. Another phenomenon occurs under alkaline condition (pH=11) called sweeping mechanism as a results of precipitation of metal hydroxides (Pb(OH)₂ and Cu(OH)₂) that significantly improves flocculation process.
<figure><img src="image_4.png" /><figcaption>Figure 2: Effect of pH adjustment on (a) the removal efficiency of Cu²⁺ and (b) Pb²⁺</figcaption></figure>

3-3-Fourier transform infrared spectroscopy (FTIR) analysis

Figure3 shows FTIR analysis of the presence of active functional groups in the PPWW suspended solids without treatment as control (black line) and the flocs produced during to the individual treatment with *Pistacia terebinthus* at dosage of 1.5 g/l and pH=7 (green line) and flocs produced during the dual flocculation under the optimum condition of using 2 g/L of *Pistacia terebinthus* at pH = 3 (blue line) and pH = 9 (red line).

The peak positions between the wavelengths range of 3700 – 3000 cm⁻¹ are attributed to OH fictional groups [16]. Therefore, the strong peaks observed for individual and pH-assisted *Pistacia terebinthus* at 3282 cm⁻¹ are associated with the intermolecular hydrogen bonds and O-H stretching of polymeric compounds in *Pistacia terebinthus* macromolecules. On the contrary, in this spectral region no peak was observed in the case of PPWW (control) and acidic condition (pH = 3). While, a strong peak of 2926 and 2852 cm⁻¹ were observed in the case of individual and pH-assisted *Pistacia terebinthus* treatment within the wavelength between 2800 and 3000 cm⁻¹ which represent the stretching of asymmetric (C-H) and symmetric (CH₂), respectively[16],[17]. The observation of this peak is related to the presence of fatty acids and proteins in the *Pistacia terebinthus* which is not observed in the control case and pH adjustment without adding flocculant.
<figure><img src="image_5.png" /><figcaption>Figure 3: FTIR spectra of the PPWW suspended solids without treatment (Control) and the flocs produced during flocculation</figcaption></figure>

### 3-4-Morphological analysis of coagulations and flocs using SEM

SEM images of the flocs surface morphology of the untreated PPWW and treated PPWW without pH adjustment at optimum conditions of *Pistacia terebinthus* = 1.5 g/L and with pH adjustment at pH 3 and 11 were presented in Figure 4.

Figure 4a shows two negatively charged suspended particles in pulp and paper wastewater without any treatment (control) which are stand separately due to electro-repulsive force. However, after adding cationic polymers of *Pistacia terebinthus* to the wastewater sample, SEM images showed a network of filamentous polymers that small negatively charged particles are attached to them (Figure 4b). In the case of pH adjustment at lower pH 3 and high pH of 11 a synergistic effect was observed using both adding cationic polymers of *Pistacia terebinthus* and pH adjustment. It can be concluded that *Pistacia terebinthus* can be considered as a promising, sustainable and environmentally friendly approach for wastewater management and treatment which can effectively remove heavy metals (Pb²⁺ and Cu²⁺) from industrial pulp and paper wastewater to produce re-used water which is acceptable for agriculture purposes (Standard= Pb²⁺< 5 mg/L, Cu²⁺ < 0.2 mg/L).
<figure><img src="image_6.png" /><figcaption>Figure 4: SEM images of (a) untreated PPWW (b) NF=1.5 g/L, pH=7, (c) NF=2 g/L, pH=3, (d) NF=2 g/L, pH=11</figcaption></figure>

**4. Conclusions**

According to the findings of this research, *Pistacia terebinthus* has the potential to be used as new natural flocculent for sustainable industrial wastewater treatment. Findings concluded that the optimum conditions for the Cu²⁺ and Pb²⁺ removal efficiencies in wastewater, were at 2 g/L of *Pistacia terebinthus* dosage and pH of 11, and 60 min sedimentation time. The maximum removal efficiencies of 98% and 99% were observed for Cu²⁺ and Pb²⁺, respectively. Interaction is mainly due to formation of hydrogen bonds which is responsible for the coagulation and flocculation of the leachate. This study provides useful optimization result towards pulp and paper wastewater treatment technology. Similarly, effective heavy metal (Cu²⁺ and Pb²⁺) removal that reduces pollutant and toxicity of wastewater also proved to be the key point to facilitate better downstream processing treatment.
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