Treatment of Wastewater from Pulp and Paper Mill using Coagulation and Flocculation

Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 158-163

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

https://doi.org/10.47277/JETT/9(1)163

Treatment of Wastewater from Pulp and Paper Mill

using Coagulation and Flocculation

Balpreet Kaur *, Rajeev Kumar Garg , Anirudh Pratap Singh

Department of Chemical Engineering, ShaheedBhagat Singh State Technical Campus, Ferozepur, Punjab, India

Dean, Punjab Technical University, Jalandhar, Punjab, India

Received: 10/06/2020

Accepted: 21/10/2020

Published: 20/03/2021

Abstract

In this work, an effluent sample from a local medium-scale paper mill has been treated using alum as a coagulant and chitosan (natural

polymer) as a flocculant. Initially, the dose of alum has been optimized by adjusting the zeta potential to near zero for best coagulation

results. The dose of 0.04 g/L was able to merely coagulate and unable to cause sweep flocculation of impurities. Then, at the optimised

dose of 0.04 g/L various concentrations of chitosan in the range of 0.1-0.5 g/L were investigated for obtaining maximum flocculation of the

suspended impurities. The physico-chemical parameters like pH, total suspended solids (TSS), chemical oxygen demand (COD),

absorbance, and zeta potential were studied for comprehending the flocculation behavior. The observed results exhibited that the maximum

flocculation was achieved at the chitosan concentration of 0.3 g/L. At the flocculant concentration of 0.3 g/L, 81% TSS removal and

maximum 78% COD were reduced. Moreover, zeta potential value of the collected supernatant was close to zero (–1.49 mV) which

showed larger floc formation and easy settleability of the impurities. In all, it can be said that the utilization of chitosan along with alum

may be a better option for the treatment of pulp and paper wastewater as well as other similar types of wastewater.

Keywords: Pulp and paper mill waste water; coagulation-flocculation; chitosan; zeta potential; COD

life of aquatic beings like zooplankton and fish is adversely

affected due to release of toxic chemicals.

Introduction

The environmental pollution due to the activities of small

The use of cleaner technologies and incorporating

modifications in the process design can potentially reduce the

pollutant load from industrial wastewater. Nevertheless, waste

generation cannot be completely eliminated. Therefore,

alternative techniques need to be introduced which can meet the

prescribed discharge limits for most affec ting pollutants like

COD, BOD, AOX, color, turbidity, etc. [9, 10]. In this respect,

chemical coagulation and flocculation offer a promising solution

to waste water treatment facilities [11]. In this technique salts of

selective metals are added to wastewater which initially

neutralize the charge on impurities and subsequently

agglomerate them into larger flocs which can be easily removed

by settling. The factors affecting the effectiveness of these

techniques are the nature of coagulating agent, dose of

coagulant, pH of solution, concentration, and nature of

impurities present in wastewater. Generally, the pulp and paper

mill effluents consist of many non-biodegradable, hydrophobic,

and polar compounds specifically phenols, lignin, long-chain

fatty acids, resinous acids, and aromatic compounds [12].

Almost all of these toxic compounds can be effectively removed

through coagulation followed by flocculation.

and medium-scale pulp and paper industries is

multidimensional, causing serious problems not only to land

fertility but also to the natural flora fauna as well as aquatic

environment. The pulp and paper industry generates about 70-

20 m of wastewater per metric ton of paper produced [1, 2].

Pulping is the initial step in paper making involving mechanical

or chemical treatment of raw material. It is widely used for the

separation of cellulose/hemi-cellulose ﬁbers for attaining

improvement in its papermaking properties [3]. Further,

bleaching is carried out in multistage processes to remove the

residual lignin and hence achieve whiteness and brightness in

the pulp [4]. Both these steps are highly energy-intensive

consuming enormous volumes of freshwater and involving

usage of large quantities of chemicals which consequently affect

the properties of discharged effluents [5]. Various studies

authenticate the harmful and undesirable impacts of these

chemicals [6-8]. These effluents have been responsible for

generating color problems, algal growth, and scum formation

which hamperthe aesthetic looks of the environment.Also the

In the past, many synthetic flocculants e.g. (PAM, HE, PEI)

for precipitation of suspended impurities of paper mill waste

water have been used [13]. The precipitated products obtained

after the application of these flocculants have not been fully

analyzed for degradation. It is expected that the precipitates are

Corresponding author: Balpreet Kaur, Department of

Chemical Engineering, Shaheed Bhagat Singh State Technical

Campus, Ferozepur, Punjab, India. Email:

balpreet_kaur@yahoo.com

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Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 158-163

difficult to biodegrade as most of the flocculants are inorganic in

nature or synthetic or polymeric materials which are itself

difficult to biodegrade [14]. Chitosan a natural polymer obtained

after partial deacetylation of chitin (biopolymer) has immense

potential as a flocculant for wastewater treatment and sludge

dewatering, as it is non-toxic, biodegradable, biocompatible and

environment friendly [15-19]. Renault et al. [20] examined the

flocculation behavior of cardboard mill wastewater collected

after biological treatment with aerated lagoons using

polyaluminium chloride (PAC) and chitosan solution.

Flocculation tests indicated a drop of about 45% in COD and

Table 1: Chemical Characteristics of the wastewater collected

from the paper mill

Parameters

COD (mg/L)

Value

2816

6.51

TSS (mg/L)

2029

-40

0.8

Zeta Potential (mV)

Dissolved Oxygen (ppm)

.1.1 Preparation of chitosan (bio-flocculant) solution

Chitosan powder (0.125 g) was accurately weighed in a 250

ml volumetric flask and mixed thoroughly with 12.5 ml HCL

0.1M) solution and kept for one hour. The dissolution was slow

and some amount of chitosan remained in the form of a thin gel.

It was then diluted to 250 ml with water to obtain a 0.5 g/L

chitosan (CH) solution. After further dilutions five different

concentrations (0.1, 0.2, 0.3, 0.4 and 0.5 g/L) of chitosan

solution were prepared. The solutions were freshly prepared

before each set of experiments.

65% in turbidity with PAC flocculant. On the other hand,

flocculation using chitosan dissolved in acetic acid displayed a

comparatively higher drop in COD (~80%) and turbidity

(

~85%). Picos-Corrales et al. [21] studied the effect of chitosan

and bean straw flour as bio-flocculants in the treatment of

agricultural wastewater. Results from jar tests confirmed the

higher efficiency of chitosan in the removal of pollutants and

reducing the concentration of undesirable metals like manganese

and iron from wastewater. However, both the materials

performed better than the commercially available

polyaluminium chloride coagulant. Altaher et al. [22] studied the

effect of chitosan as a supporting coagulant along with

conventional alum for sea water treatment. The combination of

both (chitosan 5 mg/L and alum 13.5 mg/L) was effective in

.2 Analytical methods

COD tests were conducted on the supernatant collected after

treatment of water sample with chitosan solution of various

concentrations using closed reflux titrimetric method based on

the APHA manual. To measure the charge on colloidal particles

in waste water solutions NICOMP 380 ZLS (NICOMP Zeta

potential/Particle Sizer, Santa Barbara, CA, USA) was used.

The absorbance of various samples was recorded on UV-Vis

double beam spectrophotometer (UV 5704SS), by Electronics

Corporation of India. Samples were filtered with a glass filter

before analysis using a quartz cuvette. pH meter (Eutech,

Singapore) was used to measure the pH of all solutions. pH

meter was calibrated with buffer solutions of pH 4, pH 7, and

pH 9 before actual measurements. Magnetic stirrer model Remi,

India was used for proper mixing of solutions. The total

suspended solids (TSS) were evaluated with the use of standard

filter paper (Whatman 42) and the residue retained on the filter

was dried to a constant weight at 103 to 105 °C for 1 hr. The

increase in weight of the filter represented the total suspended

solids.

reducing the turbidity from 1×10 to 10 NTU. Meraz et al. [23]

investigated the behavior of two different molecular weights of

chitosan on the coagulation-flocculation efficiency of tortilla

industry waste water. Both the variants with dose less than 3 g/L

were successful in lowering the turbidity of water by 80% with

pH of 5.5 maintained in the solution.

In the present study, chitosan is being used as a flocculant

along with alum as a coagulant for the removal of suspended

impurities from pulp and paper mill waste water. For a particular

dose of alum, varying concentrations of bio-flocculant chitosan

were examined for maximum removal of suspended and

colloidal impurities from wastewater. Zeta potential of the

supernatant before and after treatment with alum/chitosan was

used as

a yardstick for evaluating each procedure and

understanding the colloidal behavior of suspended particles

there in. Further, the reduction in the COD of waste water with

addition of different concentrations of chitosan was determined.

Also, the TSS, absorbance and pH of each solution before and

post treatment with chitosan solution was investigated.

Experimental section

Five conical flasks of 250 ml capacity with 100 ml of

wastewater sample in each were arranged for experimental

study. Alum dose of 0.04 g/L was added to each flask. To ensure

uniform mixing the mixtures were stirred at 140 rpm for 2

minutes. Then, 100 ml of chitosan solution of different

concentrations (0.1, 0.2, 0.3, 0.4, and 0.5 g/L) was respectively

added to five flasks and stirred thoroughly for 30 minutes at 40

rpm. It was kept undisturbed for half an hour for the settling of

flocs. The pH was determined at this stage for each treated water

sample. The supernatant was analyzed for investigating the

various physico-chemical characteristics such as pH, COD, zeta

potential, absorbance, and TSS.

Materials and methods

.1 Materials

Wastewater was collected from the water treatment plant of

a medium scale, agro residue, and recycle based paper mill in

Punjab, India (details are not given due to confidentiality) with a

production capacity of 200 tons/day. The major products

produced by the mill are mechanical pulp, paper and board. The

waste water samples collected were characterized and the results

are given in Table 1. The measurement of these parameters was

based on Standard Methods for the Examination of Water and

Wastewater

AlK(SO .12H

[24]. sulfate

Aluminum

potassium

)

(purity 99.9%, AR grade), used as

Results and discussion

The mechanism involved in coagulation by alum follows

coagulant in the study was purchased from CDH Pvt Ltd., India.

Chitosan powderwas sourced from India Sea Foods, Cochin

with ash content of 0.05%.

two steps. Firstly, the positively charged hydroxyl groups

attached to aluminum neutralize negatively charged particles

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Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 158-163

present as impurities in waste water via adsorption and also

affect their zeta potential. Besides, they also lower or remove the

DLVO (Derjaguin, Landau, Verwey, and Overbeek) energy

barrier. However, this step depends upon the dose of alum and

the pH of the solution. In the second step, when the alum dose

exceeds 0.03 g/L, the sweep flocculation starts predominating.

Though there is no specific value for zeta potential that ensures

effective coagulation for any waste water treatment plant, still

value lying between -4 and +3 mV offers an optimum range for

efficient coagulation [25]. For determining of the optimum dose

of alum for coagulation of colloids of present water sample

following experimentation was done.

4.2 Effect of chitosan concentration on zeta potential

Zeta potentials of the supernatants obtained from various

samples after treatment with different concentrations of chitosan

(0.1-0.5 g/L) were recorded and the results are summed in Table

Table 3: Variation in zeta potential of waste water with

variation in chitosan concentration

CH concentration (g/L)

Zeta potential (mV)

.0(only alum)

-8

-12

0.2

-7.26

-1.49

+3.45

+5.16

0.3

.1 Effect of alum dose on zeta potential

00 ml of waste water sample was individually filled in four

conical flasks. Different amount of alum dose such as 0.02 g/L,

.03 g/L, 0.04 g/L, and 0.05 g/L was added to each flask. The

0.4

0.5

solutions were stirred at 140 rpm for 2 min. Thereafter, the zeta

potential of each solution was measured. The values obtained

are presented in Table 2 and the observed results are shown in

Fig. 1.

Table 2: Variation in zeta potential of waste water samples with

variation in alum dose

Alum dose (g/L)

Zeta potential (mV)

.02

.03

.04

.05

-31.82

-19.49

-3.72

+15.23

Figure 2: Effect of chitosan concentration on zeta potential

From this table, it can be observed that the addition of alum

of 0.04 g/L of water sample led to the decrease in value of its

zeta potential to -3.72 mV and it is expected that at this

concentration the maximum coagulation must have occurred.

Various reports available in literature corroborate the fact that at

maximum coagulation occurred at zeta potential ranging from -4

to +3 mV [25-27].

Fig. 2 shows the effect of various doses of chitosan on zeta

potential of water sample. It was noticed that with increasing

dose of chitosan, the zeta potential of the wastewater gradually

changed from more negative to less negative and then shifted to

a positive value. Analyzing the flocculation behavior of the

samples it was observed that maximum flocculation occurred

when the value of zeta potential was almost near to zero (-1.49

mV) and the corresponding CH concentration was 0.3 g/L.

Further increase in CH concentration enhanced the zeta potential

which may be attributed to excess adsorption of chitosan on the

colloidal impurities leading to charge reversal. Similar results

have been reported in the literature [28, 29].

.3 Effect of chitosan concentration on pH

pH was monitored for all samples and the results are

presented in Table 4. It has been observed that as the

concentration of chitosan increases, the pH of the solution shows

a dropping trend but not in a much wide range. This may be due

to preparation of CH solution in acidic medium in which

chitosan acts a cationic bio-polymer owing to the presence of

plentiful amine groups. The pK

which depends upon its degree of deacetylation. In general,

when pH of solution exceeds pK (chitosan) it does not dissolve

in water and if pH value is less than pK (chitosan), amine

, subsequently increasing

for chitosan is typically ~6.5,

Figure 1: Variation in zeta potential of waste water with variation in

alum dose

groups get protonated to form -NH

attraction toward s negatively charged impurities present in

waste water [30, 31]. Further, at higher alkalinity, there is a

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2021, Volume 9, Issue 1, Pages: 158-163

reasonable tendency of deprotonation of the hydroxyl groups to

generate negatively charged species. Thus, the pH for all the

samples was maintained below 6.5. Fig. 3 depicts the decline in

pH with CH concentration. The values signify that all the CH

concentrations possess the capability to bridge with the

impurities and the typical value of pH for optimum CH

concentration is 0.3 g/L is 6.08.

flocculant are phenol (~220 nm), aromatic compounds (254 nm),

and compounds derived from lignin (~280 nm) [32]. The highest

absorbance was exhibited by the sample with 0.3 g/L chitosan

concentration.

Table 5: Variation in COD of water samples with addition of

different concentrations of chitosan

CH concentration

g/L)

untreated waste water 2816

COD value

COD reduction

(%)

---

63.8

68.5

71.7

Table 4: Variation in pH of the water samples with variation in

chitosan concentration

(

(mg O /L)

CH concentration (g/L)

pH of solution

0.0 (only alum)

1019

6.47

6.37

6.08

0.1

0.2

885

795

0.3

0.4

0.5

616

684

951

78.1

75.7

66.2

5.96

5.89

Figure 4: Percentage reduction in COD with varying chitosan

concentration

Figure 3: Variation in the pH of the solutions with variation in chitosan

concentration

.4 Effect of chitosan concentration on COD

The COD values of the untreated and treated effluents

(

water samples) were determined as per the methodology

mentioned in section 2.2.1. The untreated effluent has a COD

value of 2816 mg of O /L and the COD values and

corresponding reduction after treatment with varying

concentrations of chitosan are presented in Table 5. Fig. 4 shows

the trend in COD reduction post chitosan treatment. The

treatment with CH solution (0.1 g/L) reduces the COD by 68.5%

and a further increase in CH concentration enhances COD

reduction up to CH concentration of 0.3 g/L [29].

.5 Effect of chitosan concentration on absorbance

UV-Visible absorption spectra of the chitosan treated

effluent samples analyzed in the region of 200-600 nm are

shown in Fig. 5. A noticeable reduction in absorbance in the

region of 250-300 nm is observed by all the samples, indicating

the presence of lignin-based compounds responsible for

imparting dark color to the liquid effluent which gets adsorbed

in this region. The major compounds absorbed by the bio-

Figure 5: UV-Vis spectrum of wastewater with varying concentrations of

chitosan

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2021, Volume 9, Issue 1, Pages: 158-163

.6 Effect of chitosan concentration on TSS

it led to reduction in removal percentage of TSS. This behavior

may be attributed to the reversal of surface charge leading to

restabilization of the coagulated particles. This may be further

explained due to the unavailability of sites for bridge formation by

polymers, resulting in steric repulsion [34].

Suspended impurities not only hamper the color and brightness

of processed water but also affect its texture and promote the

growth of slime. For this reason, the waste water sample after

treatment with chitosan was analyzed for TSS removal. The TSS

values thus obtained and their corresponding removal percentage

are presented in Table 6. It can be noticed that as the chitosan

concentration is increased, the total suspended particle removal

rate also improves, but after a certain dose of chitosan (0.3 g/L) the

TSS removal rate drops.

Conclusions

The treatment of pulp and paper mill waste water has been

attempted with conventional coagulant alum and a natural

biodegradable polymeric flocculant, chitosan. The alum dose was

optimized through zeta potential measurement which was found to

be 0.04 g/L. Maximum reduction in COD was obtained at chitosan

concentration of 0.3 g/L and a further increase in dose did not

improve the reduction efficiency. Also, a decrease in absorbance

was observed in the UV-Vis spectra in the range of 200-300 nm for

all the samples indicating the absorption of phenolics, lignin, and

other aromatics in this wavelength region. Further, the TSS was

reduced when the chitosan dose was increased stepwise. The

maximum removal efficiency was exhibited at CH concentration of

Table 6: Variation in the TSS of water sample with variation in

chitosan concentration

CH concentration (g/L) ) TSS

TSS removal (%)

(

mg/L)

515

627

1635

1587

1550

0.3 g/L in the solution. Besides, with the increasing dose of

chitosan (0.1 to 0.5 g/L), the zeta potential of the sample gradually

changed from negative to near zero and then shifted to positive. At

high doses of chitosan, the sign of zeta potential is reversed due to

excess adsorption of chitosan on the negatively charged colloidal

impurities. At the flocculant concentration of 0.3 g/L, maximum

81% TSS and maximum 78% COD were reduced. Overall it can be

said that the utilization of chitosan along with alum may be a better

option for the treatment of pulp and paper wastewater as well as

other similar types of wastewater.

Acknowledgments

The authors want to acknowledge ShaheedBhagat Singh State

technical campus, Ferozepur for providing instrumental

facilities.

Ethical issue

Authors are aware of, and comply with, best practice in

publication ethics specifically with regard to authorship

(

avoidance of guest authorship), dual submission, manipulation

of figures, competing interests and compliance with policies on

research ethics. Authors adhere to publication requirements that

submitted work is original and has not been published elsewhere

in any language.

Figure 6: Percentage TSS removal with varying concentration of

chitosan

Fig. 6 shows that the removal efficiencies of TSS with chitosan

Competing interests

The authors declare that there is no conflict of interest that

would prejudice the impartiality of this scientific work.

flocculant are attained upto 81%. The removal rate of contaminant

particles from waste water is proportional to the number of

particles (N), time (t), and the fraction of successful collisions

(



). It can be determined from the following equation:

Authors’ contribution

All authors of this study have a complete contribution for

data collection, data analyses and manuscript writing.



  K  (N)

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coagulant and/or flocculant and suspended particles better would

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concentration of 0.3 g/L in the TSS removal may be due to the high

collision frequency between the chitosan and suspended solid

particles [33]. However, as the chitosan dose was further increased,

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