Burapha University Faculty of Engineering

Course: Physicochemical Process for Environmental Engineering

Submitted by: Mr. Piseth Som (ID:55910117) and Mr. Nopparat khopradit (ID:55920693)

ABSTRACT: Textile industries are one of the biggest users of water and complex chemicals during

textile processing at various processing stages. The unused materials from the processes are

discharged as wastewater that is high in color, suspended solid (SS) biochemical oxygen demand

(BOD), chemical oxygen demand (COD), pH, temperature, turbidity and toxic chemicals. Among

different physical, chemical, biological, and advanced chemical oxidation technologies, chemical

coagulation and flocculation is still a cost-comparative alternative for the treatment of industrial

textile wastewaters and is widely practiced by the small to large scale industries. Aluminum

sulfate (alum), ferrous sulfate, ferric chloride and ferric chloro-sulfate were commonly used as

coagulants. However, a possible link health hazard (Alzheimer’s disease), environmental concern,

sludge issue, and secondary effects associated with conventional aluminium-based coagulants

has become an issue in wastewater treatment. Hence, special attention has shift towards using

biodegradable polymer, chitosan in treatment, which are more environmental friendly.

Moreover, chitosan is natural organic polyelectrolyte of high molecular weight and high charge

density which obtained from deacetylation of chitin. Experiments were carried out on textile

industry wastewater by varying the operating parameters, which are chitosan dosage, pH and

mixing time in order to study their effect in flocculation process by using chitosan. The results

obtained proved that chitosan had successfully flocculated the anionic suspended particles and

reduce the levels of Chemical Oxygen Demand (COD) and turbidity in textile industry

wastewater. The optimum conditions for this study were at 30 mg/l of chitosan, pH 4 and 20

minutes of mixing time with 250 rpm of mixing rate for 1 minute, 30rpm of mixing rate for 20

minutes and 30 minutes of settling time. Moreover, chitosan showed the highest performance

under these conditions with 72.5% of COD reduction and 94.9% of turbidity reduction. In

conclusion, chitosan is an effective coagulant, which can reduce the level of COD and turbidity in

textile industry wastewater.

Key words: Textile wastewater, coagulation and flocculation, chitosan, biopolymer.

I. Introduction Textile industries are one of the biggest users of water and complex chemicals during

textile processing at various processing stages. The unused materials from the processes are

discharged as wastewater that is high in color, suspended solid (SS) biochemical oxygen demand

(BOD), chemical oxygen demand (COD), pH, temperature, turbidity and toxic chemicals. hough

effluent characteristics differ greatly even within the same process, some general values for

major processes in a textile mill(Eckenfelder, 2000; Hassan et al, 2009; Renault et al., 2009)

Strong colour is another important component of the textile wastewater which is very

difficult to deal with and colour is noticed in the wastewater effluent and the presence of small

concentrations of dyes in water is highly visible, and may affect their transparency and

aesthetics. The non-biodegradability of textile wastewater is due to the high content of dyestuffs,

surfactants and other additives, which are generally organic compounds of complex

structure(Eckenfelder, 2000).

Table 1 : typical charateristics of textile wastewater

Parameters Values

pH

Temperature (0 C)

Biochemical Oxygen Demand (mg/L)

Chemical Oxygen Demand (mg/L)

Total Suspended Solids (mg/L)

Total Dissolved Solids (mg/L)

Chloride (mg/L)

Total Alkalinity (mg/l)

Sodium (mg/l)

Total Kjeldahl Nitrogen (mg/L)

Colour (Pt-Co)

6.0– 10.0

35-45

100 – 4,000

150 – 10,000

100 – 5,000

1,800 -6,000

1,000 – 6,000

500 – 800

610 – 2,175

70 – 80

50-2500

Source: (Eckenfelder, 2000)

Dye wastewater from textile mills is a serious pollution problem because it is high in both

colour and organic content. A dye is a colored substance that can be applied in solution or

dispersion to a substrate in textile manufacturing, thus giving a color appearance to textile

materials. Discharging of dyes into water resources even in a small amount can affect the aquatic

life and food web. One of the main problem regarding textile waste-waters is the colored effluent.

The colored effluent contains visible pollutants. The primary concern about effluent color is not

only its toxicity but also its undesirable aesthetic impact on receiving waters. Non-biodegradable

nature of most of the dyes reducing aquatic diversity by blocking the passage of sunlight through

the water represents serious problems to the environment. In some cases, dyes in

lowconcentration are harmful to aquatic life. Since many dyes have adverse effect on human

beings, the removal of color from the effluent or process has appeared of importance for ensuring

healthy environment(Verma et al., 2012).

Besides, textile finishing’s wastewaters, especially dye-house effluents, contain different

classes of organic dyes, chemicals and auxiliaries. Thus they are coloured and have extreme pH,

COD and BOD values, and they contain different salts, surfactants, heavy metals, mineral oils and

others leading to higt terbility. Therefore, dye bath effluents have to be treated before being

discharged into the environment or municipal treatment plant. Textile dyes are structurally

different molecules themselves with low or no biodegradability. The removal of color is

associated with breakup of the conjugated unsaturated bonds in molecules. For this reason, many

chemical treatment processes have been used extensively to treat textile wastewaters. Most of

the studies, such as chemical precipitation, adsorption by activated carbon photocatalytic

oxidation, ozonation and Fenton’ oxidation focusing on color removal although effective, are

expensive or can cause further secondary pollution(Renault et al., 2009; Verma et al., 2012).

The available literature shows a large number of well established conventional

decolourisation methods involving physico-chemical, chemical and biological processes, as well

as some of new emerging techniques like sonochemical or advanced oxidationprocesses.

However, there is no single economically and technically viable method to solve this problem and

usually two or three methods have to be combined in order to achieve adequate level of

contamenants removal.

According to Verma et al., (2012), it was concluded that All decolourisation methods

described in this review have some advantages as well as some drawbacks, and their selection

will mostly governed by the textile wastewater characteristics like class and concentration of

dyes, pH, organic contents, heavy metals, etc. Among different physical, chemical, biological, and

advanced chemical oxidation technologies, chemical coagulation and floc-culation is still a cost-

comparative alternative for the treatment of industrial textile wastewaters and is widely

practiced by the small to large scale industries

Therefore, the objectives of this review are the analysis of application of Chitosan for textile

wastewater treatment, short description and critical treatment methods, comparison of its

relative advantages and disadvantages and propose for the effective and environmenal friendly

manner.

II. Coagulation and Flocculation Concept

2.1. Basic Theory Coagulation/flocculation is a frequently applied process in the primary purification of

industrial wastewater (and in some cases in secondary and tertiary treatment). Coagulation

using chemical coagulants consists of combining insoluble particles and/or dissolved organic

matter into large aggregates, thereby facilitating their removal in subsequent sedimentation,

floatation and filtration stages. It usually involves the dispersal of one or several chemical

reagents which destabilizes the colloidal particles, leading to the formation of micro-floc.

Bonding the micro-floc particles together by the addition of a flocculation additive forms larger,

denser flakes that are easier to separate. A simple separation step then eliminates the floc

(Verma et al., 2012; Renault et al., 2009; Hassan et al., 2009).

According to Renault et al (2009), there are two major classes of materials used in coagulation

and flocculation processes:

(1) Inorganic and organic coagulants including mineral additives (lime, calcium salts, etc.),

hydrolysing metal salts (aluminium sulphate, ferric chloride, ferric sulphate, etc.), pre-

hydrolysed metals (polyalu-minium chloride , polyaluminosilicate sulphate, etc.) and

polyelectrolytes (coagulant aids);

(2) Organic flocculants including cationic and anionic polyelectrolytes, non-ionic polymers,

amphoteric and hydrophobically modified polymers, and naturally occurring flocculants

(starch derivatives, guar gums, tannins, alginates, etc.)

Aluminum and iron salts are widely used as coagulants in water and wastewater treatment

for removing a broad range of impurities from effluent, including colloidal particles and dissolved

organic substances. Their mode of action is generally explained in terms of two distinct

mechanisms: charge neutralization in negatively charged colloids by cationic hydrolysis products

and incorporation of impurities in an amorphous hydroxide precipitate (sweep flocculation). The

relative importance of these mechanisms depends on pH and coagulant dose. Aluminium and

iron salts give cationic hydrolysis products that are strongly adsorbed on negative particles and

can give effective destabilization(Wang, Hung, & Shammas, 2005).

Several mechanisms such as polymer bridging, polymer adsorption and charge

neutralization (including electrostatic patch effects), depletion flocculation, displacement

flocculation, etc. have been proposed to explain the destabilization of colloids and suspensions by

polymers. Patch flocculation occurs when macromolecules with a high charge density adsorb to

particles and locally form positively and negatively charged areas on the particle surface (this

results in strong electrical attraction between particles). Polymer bridging occurs when long

chain polymers adsorb onto the surface of more than on particle, thereby forming strong

aggregates of large flocs. For the case where the polymer and the adsorption site are of opposite

signs, it is postulated that charge neutralization is the major mechanism(Renault et al., 2009).

Mechanisms of coagulation/flocculation involved in the removal of dissolved and

particulate contaminants using chitosan often cited are charge neutralization, adsorption (related

to protonated amine groups), precipitative coagulation, bridge formation (related to the high

molecular weight of biomacromolecules) and electrostatic patch. The mechanism is the

following: coagulation by charge neutralization destabilizes colloidal impurities and transfers

small particles into large aggregates (bridge formation) and adsorbs dissolved organic

substances onto the aggregates by an adsorption mechanism which can then be removed easily

by filtration and sedimentation(Hassan et al., 2009; Renault et al., 2009).

Over the usual range of water pH (5–9) particles nearly always carry a negative surface

charge and because of this, are often colloidally stable and resistant to aggregation. Coagulants

are then needed to destabilise the particles. Destabilization can be brought about by either

increasing the ionic strength (giving some reduction in the zeta potential and a decreased

thickness of the diffuse part of the electrical double layer) or specifically adsorbing counter-ions

to neutralize the particle charge. It is well known that bioflocculants can play these roles because

they have particular macromolecular structures with a variety of functional groups which can

interact with contaminants. Bioflocculation is a novel approach that is effective and competitive

(Renault et al., 2009) .

2.2. Motivation for Coagulant and Flocculent based on Biopolymers

As previously reported, the inorganic salt aluminium sulphate (alum) is one of the most

widely used coagulants in conventional water and wastewater treatments. The performance of

alum no longer needs to be proved and is appreciated for its low cost, ease of use and availability.

However, it produces abundant sludge that is difficult to dehydrate, its efficiency is entirely

dependent on the pH and when formed in cold water alum flocs are not very mechanically

resistant. In addition, the use of alum is a source of concern and the debate about its possible

toxicity is still open. Since high aluminum concentrations in water may have human health

implications, environmentally friendly coagulants will present an interesting alternative for the

purification of wastewaters(Verma et al., 2012).

It was also pointed out that the coagulants and flocculants frequently used are mineral

additives including metal salts such as polyaluminium chloride and synthetic polymers such as

polyacrylamide. Using these chemical substances may have several environmental consequences

(i) an increase in metal concentration in water (which may have human health implications); (ii)

production of large volumes of (toxic) sludge; (iii) dispersion of acrylamide oligomers which may

also be a health hazard. For these reasons, alternative coagulants and flocculants have been

considered for environmental applications. Biopolymers may be of great interest since they are

natural low-cost products, characterized by their environmentally friendly behavior. Among

these biopolymers, chitosan may be considered as one of the most promising

coagulation/flocculation materials(Renault et al., 2009).

According Hassan et al., (2009), it was confirmed that aluminum sulfate (alum), ferrous

sulfate, ferric chloride and ferric chloro sulfate were commonly used as coagulants . Additionally,

high COD removal capacities have been observed during the combined action of alum and lime

for the treatment of stabilized leachates. However, it has been stated out recently that there may

be a possibility for aluminium-based coagulants to link with Alzheimer’s disease. Hence, a special

attention has been given to the environmental friendly coagulant or flocculent, chitosan(Hassan

et al., 2009; Renault et al., 2009).

2.3. Chitosan as Bio-Coagulant and Flocculants Chitosan is a linear copolymer of D-glucosamine and N-acetyl-D-glucosamine produced by

the deacetylation of chitin, a natural polymer of major importance. Chitin is the second most

abundant biopolymer in the world, after cellulose. The main sources exploited are two marine

crustaceans, shrimps and crabs. Chitosan has unique properties among biopolymers especially

due to the presence of primary amino groups and it is a commercially interesting compound

because of its high nitrogen content in comparison to cellulose(Renault et al., 2009). Additionally,

chitosan is readily soluble in acidic solutions, which makes it more available for applications.

Chitosan is a biodegradable, non-toxic, linear cationic polymer of high molecular weight. Besides,

chitosan was an effective agent for coagulation of suspended solids from various food processing

wastes. Moreover, chitin extraction also does not cause any disturbance to the ecosystem, its

embraces all advantages provided by polysaccharides, considering it as the source of chitosan,

and both are biocompatible biopolymers for animal tissues with low toxicities and significant

biomedical applications. Chitosan coagulation produced flocs of better quality, namely larger

flocs and faster settling velocity. The effectiveness of chitosan for coagulating mineral

suspensions was improved due to the presence of inorganic solutes or due to addition of

materials extracted from soils at high pH(Hassan et al., 2009).

Chitosan is also widely applied in water and wastewater treatment because it can be

conditioned and used for pollutant complexation in different forms from water soluble to solid

form (table 2).

Table 2: Principle properties of chitosan to its use in water and wastewater treatment

application

Principle charateristics Potential application

- Non-toxic

- Biodegradable

- Renewable Resources

- Ecologically acceptable polymer

(eliminating synthetic polymers,

environmental friendly)

- Efficient against bacteria, viruses, Fungi

- Formation of salts with organic and

inorganic acids

- Ability to form hydrogen bonds

Intermolecularly

- Ability to encapsulate

- Removal of pollutants without

standingpollutant-binding capacity

- Flocculant to clarify water (drinking water,

pools)

- Reduction of turbidity in food processing

effluent

- Coagulation of suspended solids, mineral and

organic suspension

- Flocculation of bacterial suspensions

- Interactions with negatively charged

molecules

- Recovery of valuable products (proteins...)

- Chelation of metal ions

- Removal of dye molecules by adsorption

process

- Reduction of Odor

- Sludge Treatment

- Filtration and Separation

- Polymer Assisted Ultrafiltration

Chitosan has been used in the solid state for the chelation of metal ions near-neutral

solution, the complexation of metal anions in acidic solution and the dye complexation using

adsorption processes. Moreover, it also possesses several intrinsic characteristics that make it an

effective coagulant and/or flocculant for the removal of contaminants in the dissolved state. It

has characteristics of both coagulants and flocculants, i.e.,high cationic charge density, long

polymer chains, bridging of aggregates and precipitation (in neutral or alkaline pH conditions).

Its uses are justified by two important advantages: firstly, its non-toxicity and biodegradability;

secondly its outstanding chelation behavior(Renault et al., 2009; Verma et al., 2012).

The main reasons for the success of biopolymers such as chitosan in wastewater treatment

using coagulation/flocculation processes are: chitosan has the advantage of being a non-toxic

material, non corrosive and safe to handle well (non hazardous product, not irritating for skin

and eyes...) and chitosan-based material safe to animals and plants without causing

environmental pollution. In addition, chitosan is efficient in cold water and at much lower

concentrations than metal salts; it does not leave residual metals that can cause secondary

contamination problems; the low concentrations of polymers reduce the volume of sludge

produced compared to the sludge obtained with alum for example; chitosan considerably

increases the density of the sludge and facilitates its drying compared to the sludge produced

with metal salts; in addition, as biopolymers are biodegradable the sludge can be efficiently

degraded by micro-organisms; two studies reported that the sludge produced from the treatment

of milk processing plant wastewater and kaolinite suspensions was non-toxic and could be used

to stimulate growth in plants; chitosan does not add much to the salinity of the treated water and

is useable at alkaline pH(Renault et al., 2009).

III. Result and Discussion To verify the effectiveness and coagulation capacity of biopolymer Chitisan, this review is

mainly based on the experimental work of Hassan et al.,(2009) and relatively discussed with

other previous experimental work. Studies on the effects of chitosan dosage, pH and mixing time

were included in order to investigate the sorption capacity of chitosan in Coagulation and

flocculation process. Since the Chemical Oxygen Demand (COD) and Colour (dye) level in

wastewater from textile industry is considered as the most important parameter, so it has been

used as the indicator on the sorption capacity of chitosan in these experiments by supporting

with other parameter which is turbidity. The characteristics of the wastewater from textile

wastewater were as follow:

3.1. Effect of chitosan dosage Dosage was one of the most important parameters that been considered to determine the

optimum condition for the performance of chitosan in coagulation and flocculation. Basically,

insufficient dosage or overdosing would result in the poor performance in flocculation.

Therefore, it was crucial to determine the optimum dosage in order to minimize the dosing cost

and obtain the optimum performance in treatment(Ahmad et al., 2006).

According Hassan et al., (2009), the effect of dosage was analyzed at pH 4, 250 rpm of

mixing rate for 10 minute and 30 rpm of mixing rate for 20 minutes and 30 minutes of settling

time for a range of chitosan dosage which varied from 12 mg/l to 66 mg/l. Besides, the sample of

wastewater was adjusted from the initial pH of 12.99 to pH 4 due to chitosan was soluble in

acidic aqueous phases. Moreover, it was pointed out that there were 90 % of the functional group

of NH2 on chitosan surface has been protonated at pH 4. The pH was controlled by adding either

strong acid (HCl) or strong base (NaOH). The result has indicated that the optimum chitosan

dosage of 30 mg/l, chitosan recorded the highest reduction of parameters, which were the

reduction of 94.90% and 72.50 % for turbidity and COD respectively. Therefore, the optimum

chitosan dosage in the research was 30 mg/l as shown in figure 1(a) and 1(b). The possible

explanation was concluded that from the dosage 12 mg/l to 30 mg/l, the percentage of reduction

for COD and turbidity was increased. This phenomenon could be explained based on charge

density. If compared to the other coagulants, chitosan has a high charge density. Moreover, the

charge density of the polymer increased when polymer adsorption increased. Therefore, this

signifies the rapid destabilization of the particles. In other word, it can be defined as chitosan, a

coagulant which has a high charge density require less amount of the coagulant to destabilize the

particles.

In addition, a comparative study of Ahmad et al. (2006) , studying the removal of residual

oil in palm oil mill effluent by chitosan, showed that chitosan requires lower dosages to

destabilize the oil residue mainly by charge neutralization mechanisms, while the dosages

needed for alum and PAC were 10 times more than for chitosan. Chitosan also reacts faster to

residual oil compared to inorganic coagulants: the flocs produced by chitosan appear rapidly and

grow fast to form larger flocs which sediment easily. The mechanism are different: for chitosan,

the authors suggest that the biopolymer agglomerates the residual oil suspended in the effluent

(by a charge neutralization mechanism) and adsorbs it by an adsorption mechanism, while alum

and PAC just agglomerate and bridge the residual oil (they do not adsorb it). Indeed, The results

obtained proved that chitosan was comparatively more efficient and economical to alum and

PAC. At the defined optimum experimental conditions (dosage: 0.5g/l, contact time: 15min,

mixing rate: 100rpm, sedimentation time: 20min and pH 4) chitosan showed more than 95% of

suspended solid and residue oil removal. For alum and PAC the optimum dosages were 8.0 and

6.0g/l, respectively, 30min of mixing time at 100rpm, 50 and 60min of settling, respectively, and

pH of 4.5 to obtain the same percentage of removal as performed by chitosan

Figure 1: Effects of chitosan dosage on (a) COD level and the percentage of COD level reduction (b)

turbidity level and the percentage of turbidity level reduction by using chitosan. -■-, COD level; -♦-, % COD level reduction; -●-, turbidity level; -■-, % turbidity level reduction

In addition, there was a drastic drop for the percentage of reduction for COD and turbidity

when the chitosan dosage concentration was in the range of 30 mg/l to 66 mg/l. This poor

performance was due to the phenomenon of excess polymer is adsorbed on the colloidal surfaces

and producing restabilized colloids. Thus, there were no sites available on the particle surfaces

for the formation of interparticle bridges. The restabilized colloidal particles can become

positively charged and cause the electrostatic repulsion among the suspended solids.

3.2. Effect of pH The pH will not only affects the surface charge of coagulants and coagulant dosage, but also

affects the stabilization of the suspension. Besides, the solubility of chitosan in aqueous solution

is influenced by pH value. The efficiency of coagulation–flocculation with tap water was shown to

be highly dependent on the pH control and coagulant dose. At higher pH levels, larger amounts of

chitosan were required to reach the maximum removal of the treated solution. Therefore, the

study of pH was essential to determine the optimum pH condition of the treatment

system(Szyguła et al., 2009).

According Hassan et al., (2009), the effect of pH was analyzed at optimum dosage, 30 mg/l,

with 20 minutes of mixing time, 250 rpm of mixing rate for 10 minutes and 30 rpm of mixing rate

for 20 minutes and 30 minutes of settling time for a range of pH which varied from pH 2 to pH 10

in order to remove COD and turbidity from textile wastewater. The result have been indicated

that demonstrate that over 72.5 % COD reduction and 94.9 % turbidity reduction can be

achieved at pH 4. This result seems identical to the study by Ahmad et al. (2006). Therefore, the

optimum pH condition of the treatment system was pH 4 as represented in Figure 2(a) and 2(b).

Based on Hassan et al., (2009), the operating pH of 4.0 could influence the chitosan

behavior. In acidic solution, the amino groups of chitosan were protonated. Besides, chitosan

would be expected to exhibit behavior typical of a polyelectrolyte when under these conditions.

Polyelectrolyte act as coagulant aids in the treatment of water and wastewater; they may also be

used as primary coagulant for the same purpose. Many polyelectrolytes are advantageous over

chemical coagulants because they are safer to handle and are easily biodegraded. The removal of

COD and turbidity increased with increasing dose of polyelectrolyte . Moreover, the protonation

of amino groups of chitosan in solution makes chitosan positively charged which act as cationic

polyelectrolyte. Since the particles in textile suspension was negatively charged, chitosan was

very attractive as coagulant by allowing the molecule to bind to negatively charged surface via

ionic or hydrogen bonding. This will further reduce or neutralize the particles surface charge.

Therefore, the particles destabilization by chitosan could be explained by charge neutralization

mechanism.

The solubility of chitosan decreases as the pH varies towards the basic condition. Chitosan

dissolves in aqueous solution at pH less than 6.0. Over pH 6.0, it becomes insoluble in solution

and exists as solid particles. This statement was supporting the obtained results in this

experiment which the performance of chitosan in flocculation was worse in basic medium than

acidic medium. Besides, Ahmad et al., (2006) also proved that chitosan at alkaline pH shows very

low efficiency and required high concentration of chitosan to achieve the required treatment

levels. This confirmed that, at least partial, protonation of chitosan amino group was required to

achieve efficient coagulation of these organic suspensions.

According to another study conducted by Guilbal and Roussy (2007) on coagulation and

flocculation of dye-containing solutions using a biopolymer (Chitosan) also have revealed the

relationship between pH and chitosan dosage. The decreasing the initial pH resulted in a

decrease of the dosage of chitosan required for an efficient coagulation–flocculation. At

saturation of the polymer (corresponding to optimum dosage) and at initial pH 5 the molar ratio

between dye and amine groups (i.e. 1:4) respected the stoichiometry between sulfonic functions

and amine groups (i.e. 1:1). At pH 3 lower amounts of chitosan were required, probably due to

dye aggregation phenomenon. Dissolving chitosan allows increasing its reactivity for dye binding,

due to higher accessibility and better availability of amine groups.

Figure 2: Effects of pH on (a) COD level and the percentage of COD level (b) turbidity level and the percentage of turbidity level reduction by using chitosan. -■-, COD level; -♦-, % COD level reduction; -

●-, turbidity level; -■-, % turbidity level reduction

A possible explanation was pointed out that there are 90 % of the functional group of NH2

on chitosan surface has been protonated at pH 4, and gradually reduced to about 50% as pH

increased to 6. Therefore, the positive charges on the chitosan surface will significantly decrease

as solution pH increased, so the contribution by the charge neutralization of the chitosan to

destabilize the particles becomes less important as pH increased. The properties of chitosan,

including its cationic behavior and molecular weight, may be used both for charge neutralization

(coagulating effect for anionic compounds) and for particle entrapment (flocculating effect).

Moreover, based on observation, the floc produced by chitosan appears rapidly at pH 4 and form

a large size, which can be easily settled(Hassan et al., 2009; Szyguła et al., 2009).

3.3. Effect of mixing time

Besides the effect of chitosan dosage and pH, mixing time also play an important role on

flocs formation and growth in flocculation process. Polymeric flocculent disperses throughout the

medium and adsorbs on the colloidal particle surfaces for interparticle bridging or charge

neutralization during the mixing period. Besides, longer mixing time will lead to an increase in

flocs breakage. Hence, it decreases the flocculation rate. On the other hand, if the mixing time is

too short, the collisions between the flocculants and colloids are not efficient to precipitate

suspended solids in wastewater. Thus, the flocculation rate is not optimum under this condition.

In order to indicate the significance of the mixing time, Hassan et al., (2009) studied the

effect of mixing time was analyzed at optimum dosage, 30 mg/L and optimum pH, pH 4, 250 rpm

of mixing rate for 10 minutes and 30 rpm for 20 minutes and 30 minutes of settling time for a

range of mixing time which varied from 10 minutes to 30 minutes. The results are presented in

Figure 3(a) and 3(b) which shows the effects of dosage on the percentage of COD and turbidity

levels reduction by using chitosan in flocculation respectively. It was demonstrated that over

70.9 % COD reduction and 93.3 % turbidity reduction can be achieved at pH 4. Therefore, the

optimum mixing time condition of the treatment system is 20 minutes.

Mixing period is very crucial for polymeric flocculent on their performance in flocculation.

The trends that had been illustrated at the longer or shorter agitation time would result in the

poor performance of chitosan for binding and bridging. At lower agitation time (i.e. 10 minutes),

the collisions between the flocculants and suspended particles are low and lead to the lower

flocculation rate. On the other hand, if the mixing time is too long, the flocculate chains tend to

break and limiting the size of the flocs formed. The small size flocs are not dense to settle down in

wastewater and thus, indirectly cause the sample to be turbid again. This phenomenon was

observed in the Figure 3 which showed the lower percentage of reductions at longer mixing time

(i.e. 30 minutes).

Figure 3: Effects of mixing time on (a) COD level and the percentage of COD level reduction

(b) turbidity level and the percentage of turbidity level reduction by using chitosan. -■-, COD

level; -♦-, % COD level reduction; -●-, turbidity level; -■-, % turbidity level reduction

According to Ahmad et al. (2006), it was concluded that the flocs produced by chitosan

appear rapidly and grows very fast to form a larger size which can be easily sedimentated. The

effect of mixing time was conducted by varying the mixing time at 100rpm of mixing rate. The

sample was then let to settle for 1h. Dosage of chitosan, alum and PAC was fixed at their optimum

values which were analyzed to shows that the mixing time allocated to mix the chitosan, alum

and PAC with suspended solid in palm oil mill effluent. The result have shown that In order to

achieve 99% of suspended solid reduction from an influent with and 990mg/l of initial

suspended solid, the following optimum parameters should be considered: chitosan dosage of

0.5g/l, pH4, 15min of mixing at 100rpm and 20 min of settling. For alum and PAC the dosages are

8.0 and 6.0g/l, respectively, 30min of mixing time, 50min and 60min of settling at 100rpm and at

a pH of 4.5.

Furthermore, Ahmad et al. (2006) also investigated the effect of sedimentation as well. The

turbidity of the coagulated sample depends on the sedimentation effect. It was found that shows

that there is a drastic reduction in suspended solid reading once the sample is left to settle for

more than 1h. Chitosan shows the best and fastest sedimentation rate. It needs only about 20min

to reach the minimum suspended solid reading of 23mg/l. Alum and PAC needs about 50min to

achieve the minimum suspended solid values of107and70mg/l, respectively. Suspended solid

values gets lower as the bridged particles and flocs starts to settle to the bottom of the beaker

and this effect is mainly affected by the gravitational force. The flocs formed by chitosan are

larger and denser causing the suspended solid to settle faster.

IV. Conclusion

Chitosan could play an alternative role as a coagulant and flocculent for conventional

coagulants namely, aluminum sulfate (alum), ferrous sulfate, ferric chloride and ferric chloro-

sulfate which were commonly used as coagulants. Since, a possible link health hazard

(Alzheimer’s disease), environmental concern, sludge issue, and secondary effects associated

with conventional aluminium-based coagulants have become an issue in wastewater treatment.

Application of Chitosan as a coagulant in coagulation and flocculation process can functions

effectively in treating complex textile wastewater due to its effectiveness and environmental

friendly and eco-friendly nature. The effectiveness of the Chitosan in coagulation and flocculation

depend on dosage, pH value, mixing time, and wastewater type. It was proved that chitosan had

successfully flocculated the anionic suspended particles and reduce the levels of Chemical

Oxygen Demand (COD), color (dye) and turbidity in textile industry wastewater. The optimum

conditions for textile wastewater treatment acidic condition in pH value range from 3-5 with

mixing time for 20 min and settling time about 30 min for its capacity. Chitosan is an effective

coagulant, which can reduce the level of COD and turbidity in textile industry wastewater via

interparticle bridging or charge neutralization. Therefore, Chitosan could be comparative with

other iron salt bases coagulants.

References

Ahmad, A. L., Sumathi, S., & Hameed, B. H. (2006). Coagulation of residue oil and suspended solid

in palm oil mill effluent by chitosan, alum and PAC. Chemical Engineering Journal, 118(1–

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