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ARRAAvailable online 25 December 2008

BiopolymerChitosanCoagulation

, oenology, food processing and nutrition. This amino-biopolymer hasat deal of attention in the last decades in water treatment processes

the area of water and wastewater treatment. Their coagulation and occulation properties

. . . . .

. . . . .ts bacess. . . .

domestic, industrial and agricultural, and is not only dueto petroleum, minerals, sewage treatment sludge or persis-tent organic pollutants produced by the incineration of

The best purication approach are sought to reach thedecontamination objectives required by law. The literaturereports a multitude of processes for the decontaminationof contaminated water and wastewater such as coagula-tion, precipitation, extraction, evaporation, adsorption onactivated carbon, ion-exchange, oxidation and advanced

0014-3057/$ - see front matter 2008 Elsevier Ltd. All rights reserved.

* Corresponding author. Tel.: +33 3 81 66 57 01; fax: +33 3 81 66 57 97.E-mail address: gregorio.crini@univ-fcomte.fr (G. Crini).

European Polymer Journal 45 (2009) 13371348

Contents lists available at ScienceDirect

European Poly

elsedoi:10.1016/j.eurpolymj.2008.12.0274. Mechanisms of coagulation/flocculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 005. Chitosan for coagulation and flocculation a review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 006. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

1. Introduction

Water pollution results from all Human activities:

waste, but also to synthetic substances produced by chem-istry (dyes, fertilisers, pesticides, and so on) [1]. Whenwater is polluted, decontamination becomes necessary.FlocculationWastewater treatmentBioocculant

Contents

1. Introduction . . . . . . . . . . . . . . . . .2. Categories of materials . . . . . . . .3. Why use coagulants and flocculan

3.1. Coagulation/flocculation pro3.2. Chitosan as bioflocculant . .can be used to remove particulate inorganic or organic suspensions, and also dissolvedorganic substances. This paper gives an overview of the main results obtained in the treat-ment of various suspensions and solutions. The effects of the characteristics of the chitosanused and the conditions in solution on the coagulation/occulation performance are alsodiscussed.

2008 Elsevier Ltd. All rights reserved.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00sed on biopolymers? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00Keywords:for the removal of particulate and dissolved contaminants. In particular, the developmentof chitosan-based materials as useful coagulants and occulants is an expanding eld inagriculture, textilesalso received a grerticle history:eceived 30 October 2008eceived in revised form 11 December 2008ccepted 17 December 2008

Chitosan is a partially deacetylated polymer obtained from the alkaline deacetylation ofchitin, a biopolymer extracted from shellsh sources. Chitosan exhibits a variety of phys-ico-chemical and biological properties resulting in numerous applications in elds suchas cosmetics, biomedical engineering, pharmaceuticals, ophthalmology, biotechnology,i c l e i n f o a b s t r a c tniversit de Franche-Comt, Laboratoire Chrono-environnement, UMR 6249 UFC/CNRS usc INRA, Place Leclerc 25030 Besanon cedex, France

r tF. Renault, B. Sancey, P.-M. Badot, G. Crini *Review article

Chitosan for coagulation/occulation

journal homepage: www.ocesses An eco-friendly approach

mer Journal

vier .com/locate /europol j

1338 F. Renault et al. / European Polymer Journal 45 (2009) 13371348usually involves the dispersal of one or several chemicalreagents which destabilises the colloidal particles, leadingto the formation of micro-oc. Bonding the micro-oc par-ticles together by the addition of a occulation additiveforms larger, denser akes that are easier to separate. Asimple separation step then eliminates the oc. The coagu-lants and occulants frequently used are mineral additivesincluding metal salts such as polyaluminium chloride andsynthetic polymers such as polyacrylamide. Using thesechemical substances may have several environmental con-sequences (i) an increase in metal concentration in water(which may have human health implications); (ii) produc-tion of large volumes of (toxic) sludge; (iii) dispersion ofacrylamide oligomers which may also be a health hazard.For these reasons, alternative coagulants and occulantshave been considered for environmental applications[1622]. Biopolymers may be of great interest since theyare natural low-cost products, characterized by their envi-ronmentally friendly behaviour. Among these biopolymers,chitosan may be considered as one of the most promisingcoagulation/occulation materials [17].oxidation, incineration, electrooatation, electrochemicaltreatment, biodegradation and membrane ltration [27].However, many of the available processes proposed cannotbe used on an industrial scale for technological and espe-cially economic reasons. Complete treatment will clearlyrequire several steps and it is often appropriate to combineseveral methods of purication before maximal efciencyis obtained, knowing that each method has its advantagesand its disadvantages. An industrial efuent treatmentprocess line must also be designed according to the qualityobjectives: for instance lowering the levels of pollution, re-turn to a watercourse or recycling.

A general scheme of industrial water treatment involvesthree main stages [1]:

a primary treatment or pre-treatment step usingmechanical, physical and chemical methods;

a secondary treatment or purication step using chemi-cal or biological methods;

and treatment of the sludge formed (incineration forexample).

In certain cases, a tertiary treatment of the water canalso be required to remove the remaining pollutants orthe molecules produced during the secondary purication(e.g., the removal of salts produced by the mineralisation oforganic matter). Primary treatment only concerns hetero-geneous efuent, i.e., efuent containing suspended solidsor immiscible liquids, and eliminates the solid particlesand suspended substances (colloids or dispersions) fromthe efuent. This pre-treatment stage is mandatory beforesecondary treatment because otherwise particulate pollu-tion would hinder later treatment, make it less efcientor damage the purication equipment.

Coagulation/occulation is a frequently applied processin the primary purication of industrial wastewater (and insome cases in secondary and tertiary treatment) [815].Coagulation using chemical coagulants consists of combin-ing insoluble particles and/or dissolved organic matter intolarge aggregates, thereby facilitating their removal in sub-sequent sedimentation, oatation and ltration stages. It2. Categories of materials

The use of organic polyelectrolytes in water treatmentwas recently reviewed by Bolto and Gregory [16], withemphasis on the types of polymers commonly availableand the nature of the impurities to be removed. Polyelec-trolyte applications in industrial wastewater treatmenthave been reviewed by Bratby [17] and Trkman [22].Examples include efuents from the dye, textile and milkindustries.

There are two major classes of materials used in coagu-lation/occulation processes [11,17]:

(1) inorganic and organic coagulants including mineraladditives (lime, calcium salts, etc.), hydrolysingmetal salts (aluminium sulphate, ferric chloride, fer-ric sulphate, etc.), pre-hydrolysed metals (polyalu-minium chloride, polyaluminosilicate sulphate,etc.) and polyelectrolytes (coagulant aids);

(2) and organic occulants including cationic and anio-nic polyelectrolytes, non-ionic polymers, ampho-teric and hydrophobically modied polymers, andnaturally occurring occulants (starch derivatives,guar gums, tannins, alginates, etc.).

Coagulation is mainly induced by inorganic metal salts,e.g., aluminium and ferric sulphates and chlorides. Themost common additives are aluminium sulphate (gener-ally known as alum), ferric chloride and ferric sulphate[11,17]. The addition of these cations results in colloidaldestabilization, as they specically interact with and neu-tralise the negatively charged colloids. For example, oncethe Fe(III) coagulant has been added to the solution to betreated, the Fe(III) ions hydrolyse rapidly in an uncontrol-lable manner, forming a range of hydrolysis species whichplay an essential role in the coagulation process. Metalspeciation in solution has been well documented [11,17].In wastewater treatment using inorganic coagulants, anoptimum pH range in which metal hydroxide precipitatesoccur, should be determined. The addition of metals de-presses the wastewater pH to a lower value. In general,decreasing the pH from the alkaline levels to near neutrallevels has a strong positive effect on the reduction of tur-bidity, suspended solids (SS) and chemical oxygen demand(COD). However, the signicant disadvantage of these con-ventional coagulants is the inability to control the natureof the hydrolysis species formed when the coagulant isintroduced in the solution [17]. As a result, their perfor-mance is dependent not only on the pH of the water andtheir concentration, but also on the temperature and nat-ure of the solution. Therefore, new types of reagents havebeen developed [11,23]. Alternative coagulants based onpre-hydrolysed forms of aluminium (such as polyalumini-um chloride or PAC) and iron (polyferric sulfate or PFS) aremore effective than the traditional additives. Their signi-cant advantage is that their hydrolysis occurs under spe-cic experimental conditions during the preparationstage of the coagulants, and not after their addition tothe raw solution. This results in a much tighter control ofthe procedure. It is known that PAC-based products pro-vide better coagulation than alum at low temperatures

bridges, high removal efciency can be achieved even witha small amount of occulant, which generates a small vol-ume of sludge [11]. Furthermore, the polymer performanceis less dependent on pH (for example polyamines are effec-tive over a wide range of pH). There are no residuals ormetals added such as Al(III) and Fe(III), and the alkalinityis maintained. The occulation performance primarily de-pends on the type of occulant used, how much is used,its molecular weight, ionic nature, the type of material insuspension wastewater and the type of wastewater[11,1522]. Table 1 shows some examples of commercialpolymeric occulants. For example, poly(acrylamide)(PAM) is a commonly used organic polymeric occulant be-cause it is possible to synthesize polymers with variousfunctions (positive, negative or neutral charge) which canbe used to produce a good settling performance at relativelylow cost. Although extensive work has been done, futureresearch needs to look into how molecular weight andcharge density distribution affect the occulation perfor-mance to produce a better choice of occulants for specicindustrial applications [11,17,22].

F. Renault et al. / European Polymer Journal 45 (2009) 13371348 1339and also produce lower volumes of sludge. Because theyare already partially neutralised, they have less effect onthe pH of the water and so reduce the need for pH correc-tion. However, a detailed understanding of the occulationmechanisms (in particular the mode of action) of thesecoagulants is still lacking [11,16,17,22].

The coagulation process is not always perfect as it mayresult in small ocs when coagulation takes place at lowtemperatures or produce fragile ocs which break up whensubjected to physical forces. It is not only necessary toovercome these problems but also to improve the processto obtain good quality efuent and rapid sedimentation ofthe ocs formed. To do so, several products known as coag-ulant aids or polymeric additives can be used to bringtogether and agglomerate the ocs formed by the coagu-lant [11,17]. These water-soluble polymers, regularly usedin water treatment, are mainly synthetic, although a fewnatural products may be of interest [16,20,21]. The poly-meric additives are broadly characterized by their ionicstructure: cationic, anionic and non-ionic [20,21]. Ionicpolymers or polyelectrolytes of various structures areusually used as coagulant aids to enhance the formationof larger oc in order to improve the rate of sedimentation[17,22]. Coagulant aids can act either by polymer bridgingor by charge neutralization [11,17,20,21].

Flocculants are used in fast solidliquid separationsinvolving the aggregation of particles. Flocculating agentsare classied into inorganic and polymeric materials[11,17]. Inorganic occulants have almost been abandonedbecause they had numerous disadvantages such as the largeamounts required for efcient occulation and subse-quently the large volume of sludge produced. They are alsohighly sensitive to pH, inefcient towards very ne parti-cles, and applicable only to a few disperse systems [17,22].As mentioned, inorganic polymeric occulants such aspre-hydrolysed PFS or polyferric chloride (PFC) have beenrecently proposed. These materials contain complex poly-nuclear ions formed by OH bridging having high molecularweight and high cationic charge. These compounds becomemore effective at a comparatively lower dose than the con-ventionally applied reagents. They can be used over a widerange of pH and temperature due to their high level ofhydrolysis.

Technological progress in polymer chemistry has alsoimproved occulant technology to provide organic poly-mers and polyelectrolytes with greater purication ef-ciency [16,24,25]. Commercial organic occulants arebasically of two types: synthetic materials based on variousmonomers (acrylamide, acrylic acid, diallyldimethylammo-nium chloride, etc.) and natural organic materials based onpolysaccharides or natural polymers (starch, cellulose,alginate, natural gums, etc.) [2628]. The advantage of poly-meric occulants is their ability to produce large, dense,compact ocs that are stronger and have good settling char-acteristics compared to those obtained by coagulation.Polymeric occulants are easy to handle and immediatelysoluble in aqueous systems. They can also reduce the sludgevolume. Because cationic polymeric occulants destabilizeparticles and colouring matter through the compression ofelectrical double layers, charge neutralization, adsorptionand subsequent formation of particlepolymerparticle3. Why use coagulants and occulants based onbiopolymers?

3.1. Coagulation/occulation process

As previously reported, the inorganic salt aluminiumsulphate (alum) is one of the most widely used coagulantsin conventional water and wastewater treatments. Theperformance of alum no longer needs to be proved and isappreciated for its low cost, ease of use and availability.However, it produces abundant sludge that is difcult todehydrate, its efciency is entirely dependent on the pHand when formed in cold water alum ocs are not verymechanically resistant. In addition, the use of alum is asource of concern and the debate about its possible toxicityis still open. Since high aluminium concentrations in watermay have human health implications, environmentally

Table 1Examples of polymeric occulants used in water and wastewatertreatment.

Cationic polyelectrolytes Poly(diallyldimethyl ammonium chloride) Epichlorohydrin/dimethylamine polymers Cationic polyacrylamides Poly(alkylamines) [poly(ethyleneimine), poly(vinylamine)] Poly(styrene) derivatives Ionenes Sulphonium polymers Natural cationic polymers (chitosan, cationic starches)Anionic polyelectrolytes Anionic polyacrylamides Carboxylic acid polymers Phosphonic acid polymers Sulphonic acid polymers Natural anionic polymers (sulphated polysaccharides, modied

lignin sulphonates)

Non-ionic polymers Polyacrylamide Natural non-ionic polymers (starch, cellulose derivatives)

the zeta potential and a decreased thickness of the diffusepart of the electrical double layer) or specically adsorbingcounterions to neutralise the particle charge. It is wellknown that bioocculants can play these roles becausethey have particular macromolecular structures with avariety of functional groups which can interact with con-taminants [30,31]. Bioocculation is a novel approach thatis effective and competitive. In particular, chitosan is apromising bioocculant for environmental and puricationpurposes, as reported in recent patents [3942].

3.2. Chitosan as bioocculant

Chitosan is a linear copolymer of D-glucosamine and N-acetyl-D-glucosamine produced by the deacetylation ofchitin, a natural polymer of major importance [43,44]. Chi-tin is the second most abundant biopolymer in the world,after cellulose. The main sources exploited are two marinecrustaceans, shrimps and crabs. Chitosan has unique prop-erties among biopolymers especially due to the presence ofprimary amino groups and it is a commercially interestingcompound because of its high nitrogen content in compar-ison to cellulose [43]. The main parameters inuencing the

1340 F. Renault et al. / European Polymer Journal 45 (2009) 13371348friendly coagulants will present an interesting alternativefor the purication of wastewaters [17]. The use of inor-ganic polymeric coagulants has been also questioned.

Increasing use is also being made of synthetic coagu-lants of organic polymeric origin. Commercial syntheticpolymers have been utilised in coagulation/occulationprocesses for water purication for at least four decades[11,16,17]. In comparison with alum, some of the advanta-ges of these polymers are: lower coagulant dose require-ments, increase in the rate of separating the solid andwater phases arising from larger agglomerate sizes, ef-ciency at low temperatures (hydrolysing metal coagulantsperform less well at low temperatures), a smaller volumeof sludge, a smaller increase in the ionic load of the treatedwater, a less pH-dependent process and a reduced level ofaluminium in the treated water. Polymer-based productsalso improve settleability and increase the oc toughness.However, although synthetic water-soluble polymers nda wide range of applications as coagulants and occulants,the potential problems associated with their use are highcost, lack of biodegradability and polymer toxicity. It isimportant to note that the use of polyelectrolytes is alsoa source of debate. Contaminants of synthetic polymersused in water and wastewater treatment generally arisefrom residual unreacted monomers (such as acrylamide,ethyleneimine, and trimethylolmelamine), unreactedchemicals used to produce the monomer units (such asepichlorohydrin, formaldehyde and dimethylamine) andreaction by-products of the polymers in water [11,16,17].For example, acrylamide is extremely toxic producing se-vere neurotoxic effects [17]. Commercial forms of syn-thetic organic occulants may also contain toxic productsfrom the additives. Bolto and Gregory [16] reported thatthe normally used anionic and non-ionic polymers are gen-erally of low toxicity, but cationic polyelectrolytes aremore toxic, especially to aquatic organisms. The majorityof commercial polymers are also derived from petro-leum-based raw materials using processing chemistry thatis not always safe or environmentally friendly. Today, thereis growing interest in developing natural low-cost alterna-tives to synthetic polyelectrolytes [2931]. Numerousbiological products have recently been proposed and stud-ied as effective coagulants and occulants for replacingconventional materials [3236]. Some of the reportedproducts named bioocculants include biopolymers(starches, chitosan, alginates) and microbial materials pro-duced by micro-organisms including bacteria, fungi andyeast [37]. Compared with conventional chemical occu-lants, bioocculants are safe and biodegradable polymers,and produce no secondary pollution [17,30,31,38,39]. Theymay potentially be applied not only in food and fermenta-tion processes, downstream processing but also in waterand wastewater treatment. Because of the above concernson polyelectrolyte toxicity, it is believed that the use ofbioocculants will increase [17,30,39].

Over the usual range of water pH (59) particlesnearly always carry a negative surface charge and becauseof this, are often colloidally stable and resistant to aggrega-tion. Coagulants are then needed to destabilise the parti-cles. Destabilisation can be brought about by eitherincreasing the ionic strength (giving some reduction incharacteristics and properties of chitosan are its molecularweight (MW), degree of deacetylation (DD), representingthe molar fraction of deacetylated units, and crystallinity.These parameters are determined by the conditions setduring preparation [44,45].

The potential industrial use of chitosan is widely recog-nized. This versatile material is used in biomedicalengineering, pharmacy, dentistry, ophthalmology, biotech-nology, chemistry, cosmetics, textile, pulp and paper,oenology, food industry, agriculture and photography[4652]. Chitosan is also widely applied in water andwastewater treatment (Table 2) because it can be condi-tioned and used for pollutant complexation in differentforms, fromwater soluble forms to solid forms (gels, beads,

Table 2Principal properties of chitosan in relation to its use in water and wastetreatment application.

Principal characteristics Potential applications

Non-toxic Flocculant to clarify water(drinking water, pools)

Biodegradable Reduction of turbidity in foodprocessing efuents

Renewable resource Coagulation of suspended solids,mineral and organic suspensions

Ecologically acceptable polymer(eliminating synthetic polymers,environmentally friendly)

Flocculation of bacterialsuspensions

Efcient against bacteria, viruses,fungi

Interactions with negativelycharged molecules

Formation of salts with organicand inorganic acids

Recovery of valuable products(proteins. . .)

Ability to form hydrogen bondsintermolecularly

Chelation of metal ions

Ability to encapsulate Removal of dye molecules byadsorption processes

Removal of pollutants withoutstanding pollutant-bindingcapacities

Reduction of odours Sludge treatment Filtration and separation Polymer assisted ultraltration

membranes, bers, etc.). Chitosan has been used in the so-lid state for the chelation of metal ions in near-neutralsolution, the complexation of metal anions in acidic solu-tion and the dye complexation using adsorption processes[5357]. This biopolymer has been used in gel-bead formfor adsorption in batch or xed-bed column systems,deposited on a suitable support (e.g., ceramic), or in awater soluble form in polymer-enhanced ultraltrationprocesses and solvent extraction processes [5762].

Chitosan also possesses several intrinsic characteristicsthat make it an effective coagulant and/or occulant for theremoval of contaminants in the dissolved state [57,59]. Ithas characteristics of both coagulants and occulants, i.e.,high cationic charge density, long polymer chains, bridgingof aggregates and precipitation (in neutral or alkaline pHconditions). Its uses are justied by two important advan-tages: rstly, its non-toxicity and biodegradability [17];secondly its outstanding chelation behaviour [53,55,56].Its unique physico-chemical properties render it very ef-

F. Renault et al. / European Polymer Journal 45 (2009) 13371348 1341cient in interactions with various contaminants includingboth particulate and dissolved substances. These proper-ties have been exploited for the design of coagulation/oc-culation processes applied to the treatment of variousefuents (see Table 3). For example, chitosan has been suc-cessfully used, for precipitative occulation at pH abovethe pKa of the macromolecule, in the treatment of mineraland organic suspensions [7375] and the coagulation ofnegatively charged contaminants in acidic solutions con-taining dyes [85] or humic acid [82,83]. Other examplescan be found in the review of No and Meyers [57].

The main reasons for the success of biopolymers such aschitosan in wastewater treatment using coagulation/oc-culation processes are: chitosan has the advantage of beinga non-toxic material, non corrosive and safe to handle well(non hazardous product, not irritating for skin and eyes. . .)[16,17]; Hirohara et al. patented a chitosan-based materialsafe to animals and plants without causing environmentalpollution [39]; chitosan is efcient in cold water and atmuch lower concentrations than metal salts; it does notleave residual metals that can cause secondary contamina-tion problems; the low concentrations of polymers reduce

Table 3Examples of efuents treated by coagulation/occulation using chitosan.

Efuent Reference(s)

Food, seafood and sh processing wastes [6368]Wastewater from milk processing plant [69]Brewery wastewater [70]Surimi wash water [71,72]Inorganic suspensions (bentonite, kaolinite) [7378]Bacterial suspensions [7981]Efuents containing humic substances [82,83]Efuents containing dyes [84,85]Pulp and paper mill wastewater [8690]Olive oil wastewater [9193]Oil-in-water emulsions [94]Aquaculture wastewater [95]Efuent containing metal ions [9698]Efuent containing phenol derivatives [99]Partially puried sewage [100]Brackish water [101]Raw drinking water [102]the volume of sludge produced compared to the sludge ob-tained with alum for example; chitosan considerably in-creases the density of the sludge and facilitates its dryingcompared to the sludge produced with metal salts; in addi-tion, as biopolymers are biodegradable the sludge can beefciently degraded by micro-organisms; two studies re-ported that the sludge produced from the treatment ofmilk processing plant wastewater [69] and kaolinite sus-pensions [77] was non-toxic and could be used to stimu-late growth in plants; chitosan does not add much to thesalinity of the treated water and is useable at alkaline pH.

In the coagulation/occulation process, the settlingspeed of the ocs formed is also important since it inu-ences the overall cost and efciency [17]. It is known thatthe addition of occulant has a signicant effect on the set-tling time when alum and/or PAC are used as coagulants. Inthe case of chitosan, the increase of oc size favours theoc settling speed and therefore reduces the settling time.

There are, of course, disadvantages which must be bal-anced against the benets: chitosan is only efcient over alimited pH range and when present in excess, has a nega-tive effect on performance (overdosing can restabilize adispersion and affect other process aspects); the coagula-tion/occulation properties depend on the differentsources of chitin/chitosan (the quality of commercial chitinavailable is not uniform); another important criterion to betaken into account concerns the variability and heteroge-neity of the biopolymer chitosan: changes in the specica-tions of the macromolecule may change coagulationproperties; each chitosan must be characterized in termsof fraction of deacetylation, polymer weight and crystallin-ity because these parameters signicantly inuence itsphysico-chemical properties (solubility, viscosity); thereis a need for a better standardization of the production pro-cess to be able to prepare biopolymers having the samecharacteristics. These problems can rebut industrial users[55].

The main parameter which must be taken into accountfor the design of the experimental mode is solubility. How-ever, the solubility is a very difcult parameter to control[45]. Chitosan is a linear hydrophilic copolymer with a ri-gid structure containing both glucosamine and acetylglu-cosamine units. It is insoluble in either water or organicsolvents. However, in dilute organic acids such as aceticacid and formic acid and inorganic acids (with the remark-able exception of sulphuric acid), the free amino groups areprotonated and the biopolymer becomes fully soluble. ThepKa of the amino group of glucosamine residues is about6.3 and, at acidic pH (below pH 5), chitosan becomes asoluble cationic polymer with high charge density[44,45]. So, treatment of chitosan with acids produces pro-tonated amine groups along the chain and this facilitateselectrostatic interactions between polymer chains andthe negatively charged contaminants (metal anions, dyes,organic compounds, etc.). However, its solubility dependson several parameters such as the DD and MW of the poly-mer, the distribution of acetyl groups along the macromo-lecular chain, the type and concentration of the acid usedfor dissolving the polymer, the polymer concentration,and the ionic strength. It is important to note that the DDaffects the apparent pKa and thus charge, viscosity and

particle, thereby forming strong aggregates of large ocs.

1342 F. Renault et al. / European Polymer Journal 45 (2009) 13371348For the case where the polymer and the adsorption siteare of opposite signs, it is postulated that charge neutral-ization is the major mechanism. Mechanisms of coagula-tion/occulation involved in the removal of dissolved andparticulate contaminants using chitosan often cited arecharge neutralization, adsorption (related to protonatedamine groups), precipitative coagulation, bridge formationsolubility. Other important parameters for the design ofcoagulation/occulation procedures using chitosan are re-lated to the intrinsic physical and chemical characteristicsof themacromolecule (i.e., crystallinity, purity, hydrophilic-ity, charge density). All these characteristics may affect theperformance of chitosan. Several examples are given in part5 concerning the impact of chitosans characteristics.

4. Mechanisms of coagulation/occulation

As already mentioned, aluminium and iron salts arewidely used as coagulants in water and wastewater treat-ment for removing a broad range of impurities from efu-ent, including colloidal particles and dissolved organicsubstances. Their mode of action is generally explained interms of two distinct mechanisms: charge neutralizationin negatively charged colloids by cationic hydrolysis prod-ucts and incorporation of impurities in an amorphoushydroxide precipitate (sweep occulation). The relativeimportance of these mechanisms depends on pH and coag-ulant dose. Aluminium and iron salts give cationic hydroly-sis products that are strongly adsorbed on negativeparticles and can give effective destabilisation. The princi-ples governing the action of hydrolysing coagulants arewell understood [11,17,103106]. For simple metal saltsat low dosages, it is well established that charge neutral-ization can be an effective means of destabilising colloidalparticles. At higher coagulant dosages bulk precipitationof metal oxide hydroxide occurs. Pre-hydrolysed coagu-lants are often more effective than simple metal salts[11,15,17]. The improved performance of these materialsis probably due to the different nature of the precipitateformed, although more detailed studies are needed [29].Polymeric additives can also be used to cause aggregationof particles and may act either by polymer bridging orcharge neutralization (electrostatic patch effects). The ac-tion of hydrolysing metal coagulants can involve similarmechanisms. Readers interested in a detailed discussionof coagulation by hydrolysing metal salts and the mecha-nisms involved should refer to the comprehensive reviewsof Duan and Gregory [105], and Bratby [17].

Several mechanisms such as polymer bridging, polymeradsorption and charge neutralization (including electro-static patch effects), depletion occulation, displacementocculation, etc. have been proposed to explain the desta-bilisation of colloids and suspensions by polymers[11,16,17,35]. Patch occulation occurs when macromole-cules with a high charge density adsorb to particles and lo-cally form positively and negatively charged areas on theparticle surface (this results in strong electrical attractionbetween particles). Polymer bridging occurs when long-chain polymers adsorb onto the surface of more than onization, patch occulation, and/or polymer bridging. Thechitosan characteristics that are important for occulationare therefore charge density (related to its DD), molecularweight (MW) and molecular structure. Literature datashow that the type of mechanism also depends on differentfactors such as pH, ionic strength of the solution, and coag-ulant concentration. For example, the main mechanism fordye coagulation with chitosan appears to be charge neu-tralization at acidic pH [85] and increasing chitosan dosageincreases dye removal up to a concentration resulting incomplete neutralization of anionic charges. Above that con-centration, the excess of cationic charges leads to suspen-sion re-stabilization. Numerous works claim that chitosanis involved in a dual mechanism including coagulation bycharge neutralization and occulation by bridging mecha-nisms [57,85]. It should be also noted that one of the great-est differences between metal salts and cationic polymersconcerns their hydrolysis. Aluminium sulphate hydrolysesimmediately on contact with water giving rapid adsorptionreactions while chitosan is not hydrolysed [17]. A mecha-nism of action of polymeric occulating agents was de-scribed in detail by OMelia [106].

5. Chitosan for coagulation and occulation a review

Different reviews of chitosan-based materials have ap-peared concerning separation and complexation, includingmembrane ltration [50] and adsorption [5356,59]. Obvi-ously, chitosan has also been investigated as a coagulantfor the capture of contaminants from aqueous solutionsin numerous articles [57,107]. However, the studies mainlyfocused on the recovery of suspended solids (SS) and col-loids; in the case of dissolved contaminants there are manyfewer studies [84].

In 19751978, extensive studies by Bough and co-workers [63,64,108115] demonstrated the effectivenessof chitosan for coagulation and recovery of SS in processingwastes from a variety of food processing industries includ-ing poultry, eggs, cheese, meat, fruit cakes, seafood andvegetables. These studies indicated that chitosan can re-duce the SS of such processing waste by as much as 65%(related to the high molecular weight of biomacromole-cules) and electrostatic patch. The mechanism is the fol-lowing: coagulation by charge neutralization destabilizescolloidal impurities and transfers small particles into largeaggregates (bridge formation) and adsorbs dissolved or-ganic substances onto the aggregates by an adsorptionmechanism which can then be removed easily by ltrationand sedimentation. For example, cationic chitosan deriva-tives can be easily adsorbed onto the colloid surface of an-ionic inorganic (bentonite) suspensions due to electrostaticattraction. Adsorbed macromolecules tend to form loopsand extend some distance from the particle surface intothe aqueous phase. Their ends also dangle and get adsorbedby another particle forming a bridge between particles. Foreffective bridging occur, the length of the biopolymerchains should be sufcient to extend from one particle sur-face to another. Hence a polymer with longer chains shouldbe more effective than one with shorter chains. Here, oc-culation is interpreted as being a result of charge neutral-

F. Renault et al. / European Polymer Journal 45 (2009) 13371348 1343to 99% and good results were also obtained for the reduc-tion of turbidity (TB) and chemical oxygen demand(COD). In some instances, chitosan can be used as a coagu-lant aid in conjunction with a synthetic polyelectrolyte oran inorganic salt to increase treatment performance. Amechanism of action of chitosan as occulating agentwas described by which the polymer destabilizes the col-loidal suspension by adsorption of particles with subse-quent formation of particlepolymerparticle bridges.

The effectiveness of chitosan as coagulant has also beenreported by Johnson and Gallanger [116], Senstad andAlmas [117], Moore et al. [118], No et al. [57,65,119], andSievers et al. [120]. These authors clearly demonstratedthat chitosan has an intrinsic capacity to be used as a coag-ulant to reduce SS, TB and COD. These works also reportedthat positively charged cationic macromolecules can desta-bilize the negative colloidal suspension by charge neutral-ization as well as by bridge formation. In addition, anotherimportant advantage must be cited: after being used thesludge may be disposed of with a lower environmentalimpact than common metal- and synthetic polymer-basedsystems [69,70,77,122]. Chi and Cheng [69] reported thatthe sludge from one coagulation process could be used di-rectly as a feed supplement. Divakaran and Pillai [77] sug-gested that the sludge produced during the occulation ofkaolinite suspensions could be safely disposed off in land-lls. However, such re-use needs to be carefully assessedand its harmlessness must be checked.

There is recent literature concerning the evaluation ofthe coagulation/occulation performance of chitosan. Thisbiopolymer has an extremely high afnity for many classesof contaminants: it has demonstrated outstanding removalproperties for natural organic matter [123], humic sub-stances [82,124,125], inorganic suspensions [74,75], dyemolecules [84,85], metal cations [97,98], proteins [70],phenolic and aromatic derivatives [99], oil and grease[9194], bacterial [81,126] and algal [127] suspensions.For humic materials, Guibal et al. [84] showed that chito-san can be used as a primary coagulant or as a occulantafter coagulation: it has characteristics of both coagulantsand occulants. Ahmad et al. [91] demonstrated it was avery effective coagulant to remove the residual oil contentfrom palm oil mill efuent compared to alum and PAC.Divakaran and Pillai [127] showed that chitosan reducedalgal contents effectively by occulation and settling. How-ever, they noted that the occulation was very sensitive topH. Chitosan can be used not only as a coagulant and/orocculant but also as a bactericide. For example, Chung[95] showed that this biopolymer was useful not only forthe removal of SS, organic and inorganic compounds, TB,and COD, but also for the removal of pathogens. Huangand co-workers [121,122] showed that chitosan could bea promising substitute for alum and PAC in the coagulationof colloidal particles because of its suitability for coagula-tion without posing any health threats as residual alumin-ium and other synthetic polymers do. To reach the samelevel of turbidity removal, the required amount of chitosanis only half that of PAC. Chitosan coagulants also producedlarger ocs of better quality and faster settling velocity[122]. They also indicated that replacing PAC with chitosanin the water treatment process can be cost effective.Coagulation/occulation processes have been widelyused as pre-treatments to remove suspended particlesand colouring materials in primary treatment prior to bio-logical treatment. However, dye molecules, in particularreactive dyes [89], cannot be easily removed by conven-tional coagulants. Guibals group [7375,84,85,128130]published a series of papers on the ability of chitosan toact as an effective coagulant to treat not only particulatesuspensions but also dissolved substances. In particular,they showed that colour can be removed either by adsorp-tion onto solid-state chitosan or by coagulation/occula-tion using dissolved-state chitosan. The reactivity ofamine groups was signicantly increased when dissolvedbiopolymer was used [84]. The authors explained their re-sults by the fact that using chitosan in the dissolved stateimproves the accessibility and availability of reactive sitescompared to the solid state [85]. Comparison of saturationvalues for adsorption and coagulation/occulation provedthat the molar ratio between the amine groups of the bio-polymer and the sulfonic groups of the dye molecules wasmuch greater when using chitosan in the dissolved state(coagulation/occulation) than in the solid state (adsorp-tion). The conformation of polymer chains also seems tobe the key parameter in the comparison of removal perfor-mance [84]. All these works showed that the coagulation/occulation process involved several mechanisms such ascharge neutralization, precipitative coagulation, bridging,electrostatic patch and aggregation phenomenon. In gen-eral, a charge neutralization associated to bridging effectis sufcient to explain the results [130]. However, the typeof mechanism depends mainly on coagulant dosage andpH. They observed that an excess of cationic charge con-tributes to re-stabilising the suspension and reducing theefciency of the process. The authors also noted that theoptimum dosage correlated well with the initial concentra-tion of the pollutant indicating that the addition of the bio-polymer could be easily monitored by determining thepollutant concentration in the solution. The effect of pHcan be attributed to differences in the protonation of thebiopolymer amine groups, changes in the conformationof the macromolecule chain (chain repulsion) and thestructure of the ocs. In neutral solutions, because of themore coiled structure, the biopolymer is able to producelarger and denser ocs. In acidic solutions, chitosan be-comes a more extended chain (more charged) and there-fore produces smaller, looser ocs, conrming theprevious results reported by Huang et al. [121]. Theseauthors showed that when the positive charge of chitosanis neutralised by the negative ion in acid solution, the con-formation of the biopolymer changes. Huang et al. [121]also indicated that the chitosan becomes more compactin more acidic solution and therefore lowers the viscosityof the solution. The length of polymer chains (related tothe MW of the biopolymer) is also an important parameterto be considered for optimising the use of chitosan in coag-ulation/occulation. However, the results and their inter-pretation also depend on the type of contaminant. Guibalet al. [84] showed that the MW of chitosan did not affectthe coagulation/occulation of humic acid (HA). They as-sumed that the more complex and exible structure ofHA may limit the inuence of MW. In the case of bentonite

suspensions, they noted that the performance decreasedwith decreasing MW while for kaolinite suspensions theimpact of MW was not very marked. Increasing the bio-polymer concentration reduced the impact of MW. Guibaland co-workers [73,84,128] concluded that chitosan offersa promising alternative to the use of mineral reagents(alum or ferric salts) or synthetic polymers as coagulantsor coagulant aids.

Other studies of dye-chitosan interactions have beencarried out. Sanghi and Bhattacharya [89] showed thatchitosan, as coagulant aid, is very effective for decolouringacidic and direct dyes. They also reported that reactive dyeswith anthraquinone groupswere themost difcult to decol-our. Gandjidoust et al. [90] reported that the natural coagu-lant chitosan resulted in the highest removal in both colourand TOC as compared to synthetic polymers (poly(acryl-mide) or PAM, poly(ethyleneimine) or PEI) and a chemicalcoagulant (alum). Similar conclusions were reported byRodrigues et al. [86] and Wang et al. [87] for the treatmentof paper pulp and papermillwastewater. Our grouphas alsoproposed modied chitosan-based biopolymers as adsor-bents and/or coagulants for the removal of SS; DCO and col-our from pulp and paper mill efuent [53,136138] (Fig. 1).Overall, these studies report that the bindingmechanism ofdyes by polymers can be described as adsorption, hydrogen

of the coagulant, the type of acid used to dissolvethe chitosan, the reaction time, the rate of rotationand the speed gradient;

(iii) the chemistry of the pollutants (type of pollutantsand their physico-chemical properties such as polar-ity and hydrophobicity);

(iv) and nally the solution conditions referring to itspH, the ionic strength, the zeta potential, the colour,the concentration of the colloidal particles, the pres-ence of impurities (i.e., dissolved salts or trace ele-ments such as ions and chemicals) and temperature.

It is generally expected, and often found, that the coag-ulationocculation efciency of chitosan is proportionalto its charge and consequently highly N-deacetylated sam-ples are usually applied as coagulant and occulant mate-rials. However, it is important to note that severalcontradictory observations have been reported and thereader is encouraged to refer to the original papers forcomplete information on experimental conditions in thecoagulation studies used.

Chitosan can dissolve in carboxylic acid solutions or ininorganic solutions. Acetic acid is a common solvent forthis biomacromolecule. However, Huang et al. [121] re-ported that this organic solvent increased the organic con-

) rawre obt

1344 F. Renault et al. / European Polymer Journal 45 (2009) 13371348bonding, hydrophobic or electrostatic interaction.The data from the literature show that the control of the

performance of chitosan in coagulation/occulation pro-cess depends on the following factors:

(i) the origin and the nature of the chitosan (i.e., itsintrinsic characteristics such as DD and MW, andthe activation conditions of the raw biopolymer);

(ii) the inuence of process variables such as the equip-ment installed, the addition of reagents, the dosage

Fig. 1. Photograph of samples analysed (a) efuent after PAC treatment; (bwere performed using a Jar-Test equipment; DCO and turbidity values wetent of suspensions. They suggested using hydrochloricacid as an alternative solvent. In addition, they also indi-cated that it was important to search for the optimal acidconcentrations since the viscosity of dissolved chitosancoagulants decreases with increasing concentrations ofacid. In another work [122], the authors conrmed thatthe performances of chitosan depend on the process vari-ables such as the dosage of chitosan, the speed of mixingand pH. The optimum chitosan dosage was smaller inacidic solutions, although smaller ocs were produced,

efuent; (c) efuent after chitosan-based material treatment (experimentsained after a 2-min settling time).

F. Renault et al. / European Polymer Journal 45 (2009) 13371348 1345and increasing the speed during rapid mixing can also re-duce the optimum dosage. The authors supposed thatdestabilization of particles was enhanced by the increasein charged groups (in acidic solutions, there is an increasein the number of protonated amine groups on chitosan)followed by charge neutralization, resulting in a decreasein optimum dosage. The authors also found a linear rela-tionship between the DD and the optimal chitosan dosage,which indicates that amino groups of macromolecules arethe active site for coagulation [121]. There is a relationshipbetween the DD and the treatment time. The speed of mix-ing may affect the coagulation only before the optimal dos-age is reached. Huang and co-workers [121,122] concludedthat the optimal pre-treatment condition to prepare chito-san coagulant and its dosage were the key parameters toevaluate the coagulation performance.

Guibal et al. [84,129] showed the characteristics ofchitosan (mainly DD and MW) slightly affected the coagu-lationocculation performance. The DD had more effecton bentonite suspensions and dye solutions than on kaolinand humic acid suspensions. Very low doses of biopolymerwere required for the treatment of concentrated suspen-sions of bentonite; sedimentation was fast and very lowturbidity was obtained within a few minutes settling time;the doses were signicantly lower when the pH of the sus-pension was less than the intrinsic pKa of chitosan. In con-trast to the ndings of Guibal and co-workers, Chung [95],studying the removal of SS, COD, TB and organic com-pounds from aquaculture wastewater by chitosan, ob-served that the treatment efciency of chitosan washighly dependent on its DD and on the pH of the solution.A high DD and low pH value improved the performance ofthe coagulation process. Huang et al. [121] also showedthat the charge density of chitosan, and its coagulation per-formance, was directly proportional to the DD.

Wibowo et al. [71] studied the inuence of the MW andDD of chitosan on the removal efciency of proteins. Theyconcluded that the difference in MW and DD values be-tween samples could not explain the signicant differencesin protein recovery. No meaningful correlation was appar-ent. Kvinnesland and degaard [124], studying the effectsof polymer characteristics on separation in humic sub-stance removal by cationic polymer coagulation, showedthat polyelectrolyte MW did not show any signicant ef-fect on the coagulation of humic substances. Chen et al.[135] reported that the DD of chitosan had limited effecton the occulation performance while its MW played akey role. The higher the MW, the better the occulation.Large differences were found by Strand et al. [80,81,126]in the efciency of chitosan materials to occulate bacte-rial suspensions, both regarding the effective biopolymerconcentrations and the type of chitosan giving the bestperformance. In particular, the effect of MW on occula-tion performance was found to be of importance. Thechoice of the optimal chitosan type for a given applicationis a tricky task [126].

The interaction between chitosan and mineral colloids(bentonite) has been investigated by Roussy et al. [75].They showed that it was not necessary to add largeamounts of chitosan: doses as low as 0.20.5 mg/L weresufcient to achieve the complete coagulationocculationof the solutions in a very short time (a few minutes weresufcient). With optimised selection of polymer character-istics, the required dosage can be decreased to 0.1 mg/L orbelow depending on the biopolymer. Their investigationsclearly indicated that chitosan had a natural selectivityfor mineral colloids. However, they reported that the DDof chitosan inuences the coagulation and its MW the oc-culation mechanism. Similar conclusions were reported byHuang and Chen [76] for the removal of bentonite. Theyindicated that the coagulation behaviour of chitosan withrespect to kaolinite was different from that with bentonite.Chitosan failed to form a good aggregate with kaolinite.However, in contrast to this, Divakaran and Pillai [77] con-cluded that chitosan was a useful occulant for kaolinitesuspensions in water.

Ahmad et al. [91], studying the removal of residual oil inpalm oil mill efuent by chitosan, showed that chitosan re-quires lower dosages to destabilize the oil residue mainlyby charge neutralization mechanisms, while the dosagesneeded for alum and PAC were 10 times more than forchitosan. Chitosan also reacts faster to residual oil com-pared to inorganic coagulants: the ocs produced by chito-san appear rapidly and grow fast to form larger ocs whichsediment easily. The mechanism are different: for chitosan,the authors suggest that the biopolymer agglomerates theresidual oil suspended in the efuent (by a charge neutral-ization mechanism) and adsorbs it by an adsorption mech-anism, while alum and PAC just agglomerate and bridgethe residual oil (they do not adsorb it). In another work,Ahmad et al. [92] conrmed that chitosan derivatives pos-sess a number of functional groups responsible for thebinding of pollutants either by chemical and/or physicaladsorption. The results can be mainly explained on the ba-sis of the higher charge density of chitosan requiring lowerdoses to destabilize the solution. The charge mechanismwas also introduced by Huang and Chen [76] and Panet al. [122] in the removal of colloidal particles by chitosan,and Bolto et al [123] and Szygula et al. [130] in the removalof natural organic matter and dyes. Different conclusionshave been reported by Strand et al. [81], and Meyssamiand Kasaeian [93]. Strand et al. [81], applying chitosan toocculate bacterial suspensions, pointed out the predomi-nant role of bridging in the occulation mechanism.Meyssami and Kasaeian [93], studying the treatment ofan olive oil water suspension by chitosan, noted that thepresence of sodium chloride in the solution aids the coag-ulation phenomenon and they concluded that the majormechanism is chemical bridging rather than charge neu-tralization. Wu et al. [98] investigated the use of chitosanas occulant for coprecipitation of Mn(II) and removal ofSS, and reported that charge neutralization, occulationand adsorption occur simultaneously.

Several workers have suggested that although chitosanas such is very useful as a coagulant, it may be advanta-geous to chemicallymodify the biopolymer, e.g., by graftingreactions. These modications can improve the removalperformance of the chitosan as patented by Laue and Hun-keler [42] and also reported by Wang et al. [131], Mishraet al. [132], Wang et al. [133], Chavasit and Antonio Torres[134], and Crini et al. [136]. For example, Mishra et al. [132]reported that chitosan-g-N-vinyl formamide showed better

1346 F. Renault et al. / European Polymer Journal 45 (2009) 13371348results formetal ion adsorption and occulation than chito-san. The grafted copolymers generally possess the mainproperties of both initial components, and they are chemi-cally stable and usually biodegradable [131].

6. Conclusions

Chitosan possesses several intrinsic properties such asits non-toxicity, its biodegradability and its outstandingchelation behaviour that make it an effective coagulantand/or occulant for the removal of contaminants in thedissolved state. It has the physico-chemical characteristicsof both coagulants and occulants, i.e., high cationic chargedensity and long polymer chains, leading to bridging ofaggregates and precipitation. Numerous works have dem-onstrated that chitosan and its derivatives (in particulargrafted biopolymers) can be a potential substitute formetallic salts and synthetic polyelectrolytes in the treat-ment of wastewater for the removal of both particulateand dissolved substances. However, more studies are re-quired to rene the optimisation of the properties of chito-san such as the degree of deacetylation which caninuence coagulation and the molecular weight whichaffects occulation.

Acknowledgements

Authors thank OSEO ANVAR (Besanon, France) andINRA Transfert (Dpartement Valorisation, Paris, France)for nancial support (Programme Chitodex Project Devel-opment of biocoagulants). The research grants given bythe French Ministry of Research and Education, the CNRSand the Rgion of Franche-Comt which provide nancialsupport for the Ph.D. students F. Renault and B. Sanceyare gratefully acknowledged. Thanks are due to the threegroups involved in our research program on pollutant com-plexation by chitosan-based materials: that of Dr. Giangia-como Torri from G. Ronzoni Institute (Milan, Italy), of Prof.Bernard Martel from University of Lille (France) and ofProf. Yayha Lekchiri from University of Oujda (Morocco).We acknowledge the constant contribution of Dr. NadiaMorin-Crini (Chrono-environment Laboratory, Besanon,France) to this research program. The authors also thankDr. Peter Winterton (University of Toulouse, France) forits critical reading of this review, G. Ronzoni Institute(Milan, Italy) for providing of chitosan samples, and Mr.Jean-Claude Jeune (ARIST, Besanon, France) for providingof patents.

References

[1] Crini G, Badot PM. Traitement et puration des eaux industriellespollues (in French). Besanon, France: PUFC Press; 2007.

[2] Mondal S. Methods of dye removal from dye house efuentanoverview. Environ Eng Sci 2008;25:38396.

[3] Moo-Young HK. Pulp and paper efuent management. WaterEnviron Res 2007;79:173341.

[4] Lefebvre O, Moletta R. Treatment of organic pollution in industrialsaline wastewater: a literature review. Water Res2006;40:367182.

[5] Swami D, Buddhi D. Removal of contaminants from industrialwastewater through various non-conventional technologies: areview. Int J Environ Pollut 2006;27:32446.[6] Dabrowski A, Podkoscielny P, Hubicki Z, Barczak M. Adsorption ofphenolic compounds by activated carbona critical review.Chemosphere 2005;58:104970.

[7] Matsumoto MR, Jensen JN, Reed BE, Lin W. Physicochemicalprocesses. Water Environ Res 1996;68:43150.

[8] Manu B. Physico-chemical treatment of indigo dye wastewater.Coloration Technol 2007;123:197202.

[9] Moreno CHA, Cocke DL, Gomes JAG, Morkovsky P, Parga JR.Electrocoagulation mechanism for metal removal. ECS Trans2007;2:5170.

[10] Grenoble Z, Zhang C, Ahmed S, Jeffcoat SB, Karanl T, Selbes M, et al.Physico-chemical processes. Water Environ Res 2007;79:122896.

[11] Stechemesser H, Dobi B. Coagulation and occulation. Surfactantscience series, vol. 126. 2nd ed. CRC Press; 2005.

[12] Kulkarni AG, Tandon R, Mathur RM. Some chemical aspects of colorremoval from efuents of paper industry. IPPTA Quart J Indian PulpPaper Tech Assoc 2006;18:5561.

[13] Aboulhassan MA, Souabi S, Yaacoubi A, Baudu M. Improvement ofpaint efuents coagulation using natural and synthetic coagulantsaids. J Hazmat Mat 2006;138:405.

[14] Dovletoglou O, Philippopoulos C, Grigoropoulou H. Coagulation fortreatment of paint industry wastewater. J Environ Sci Health A Tox/Hazard Subst Environ Eng 2002;37:136177.

[15] Jiang JQ, Graham NJD. Pre-polymerized inorganic coagulants andphosphorus removal by coagulation a review. Water SA1998;24:23744.

[16] Bolto B, Gregory J. Organic polyelectrolytes in water treatment.Water Res 2007;41:230124.

[17] Bratby J. Coagulation and occulation in water and wastewatertreatment. 2nd ed. IWA Publishing; 2007.

[18] Mukherjee M, Swami A, Ramteke DS, Moghe CA, Sarin R. Role ofconventional and non-conventional coagulants with and withoutpolyelectrolyte in treatment of renery wastewater. Pollut Res2004;23:41726.

[19] Bolto B, Dixon D, Eldridge R, King SJ. The use of cationic polymers asprimary coagulants in water treatment. In: Hahn HH, Hoffmann E,Odegaard H, editors. Proceeding of the fth gothenburgsymposium. Chemical water and wastewater treatment. Berlin:Springer; 1998. p. 17382.

[20] Bolto B. Soluble polymers in water purication. Prog Polym Sci1995;20:9871041.

[21] Levine NM. Natural polymer sources. In: Schwoyer WLK, editor.Polyelectrolytes for water and wastewater treatment. Boca Raton,FL: CRC Press; 1981. p. 4760.

[22] Trkman A. In: Trkman A, Uslu O, editors. New developments inindustrial wastewater treatment. Dordrecht: Kluwer; 1991.

[23] Cheul YB. Polyaluminium hydroxy chlorosulfate as coagulant forsettling wastewater by coagulating suspended particles inwastewater, thereby forming oc, and method for preparing thesame. Korean Patent KR2005000511 (2003).

[24] Wu F, Zhao M, Chen J, Tang L, Fang X, Yu X. Coagulation decolourantfor printing and dyeing waste water. Chinese Patent CN101215029(2007).

[25] Takashi A, Tomonori E. Organic coagulant. Japanese PatentJP2007289928 (2007).

[26] Aesoy A, Haraldesen K. Product for the treatment of water andwastewater and a process for producing said product. EuropeanPatent EP1558528; WO2004041732 (2003).

[27] Ylikangas AM, Larsen CK. Method for removal of materials from aliquid stream. United States Patent US2007235391; WO200711747(2007).

[28] Takeda K, Adachi K, Tsuzuki T, Mori Y. Process for producing water-soluble polymer. European Patent EP1693391; WO2004JP17936(2004).

[29] Vijayaraghavan K, Yun YS. Bacterial biosorbents and biosorption.Biotechnol Adv 2008;26:26691.

[30] Sharma BR, Dhuldhoya NC, Merchant UC. Flocculants-anecofriendly approach. J Polym Environ 2006;14:195202.

[31] Crini G. Recent developments in polysaccharide-based materialsused as adsorbents in wastewater treatment. Prog Polym Sci2005;30:3870.

[32] Maximova N, Dahl O. Environmental implications of aggregationphenomena: current understanding. Curr Opin Colloid Int Sci2006;11:24666.

[33] Deng S, Yu G, Ting YP. Production of a bioocculant by Aspergillusparasiticus and its application in dye removal. Colloids Surf BBiointerfaces 2005;44:17986.

[34] Chen Y, Lian B. Progress of microbial occulant study and itsapplication. Bull Mineral Petrol Geochem 2004;23:839.

F. Renault et al. / European Polymer Journal 45 (2009) 13371348 1347[35] Jiang JQ. Development of coagulation theory and new coagulantsfor water treatment: its past, current and future trend. WaterSupply 2001;1:5764.

[36] Salehizadeh H, Shojaosadati SA. Extracellular biopolymericocculantsrecent trend and biotechnological importance.Biotechnol Adv 2001;19:37185.

[37] Wang HC, Li MH, Tsang HW, Wu MM, Lin HPP. Novel biologicalocculants and production methods. United States PatentUS20070062865 (2007).

[38] Arevalo NK, Galan Wong LJ, Hernandez Luna CE, Salazar AlpucheRY. Method of removing heavy metals and solids by complexingbiodegradable polyelectrolytes (pectin and chitosan). MexicanPatent MX2002NL00016; WO03099729 (2002).

[39] Hirohara H, Takehara M, Fukita A, Kansai KKK, Hirohara H.Flocculant and sludge treatment method. Japanese PatentJP2001129310 (1999).

[40] Ren Q, Song X, Li J, Ma R, Mei Z, Ma X. A heavy metal chelatecomposition containing chitosan derivatives and uses thereof.European Patent EP1553135; WO2003CN00589 (2003).

[41] Jang SH, Kim JG, Yoon YM. Method for extracting humic acid fromlivestock manure using chitosan as coagulant. Korean PatentKR20040032503 (2002).

[42] Laue C, Hunkeler D. Polymer occulants and preparation thereof.European Patent EP1236748 (2001).

[43] Roberts GAF. Chitin chemistry. London: MacMillan; 1992.[44] Kurita K. Chitin and chitosan: functional biopolymers from marine

crustaceans. Mar Biotechnol 2006;8:2036.[45] Rinaudo M. Chitin and chitosan: properties and applications. Prog

Polym Sci 2006;31:60332.[46] Harish Prashanth KV, Tharanathan RN. Chitin/chitosan:

modications and their unlimited applicationan overview.Trends Food Sci Technol 2007;18:11731.

[47] Kashyap N, Kumar N, Ravi Kumar MNV. Hydrogels forpharmaceutical and biomedical applications. Crit Rev Ther DrugCarrier Syst 2005;22:10750.

[48] Prabaharan M, Mano JF. Chitosan-based particles as controlled drugdelivery systems. Drug Deliv 2005;12:4157.

[49] Ravi Kumar MNV, Muzzarelli RAA, Muzzarelli C, Sashiwa H, DombAJ. Chitosan chemistry and pharmaceutical perspectives. Chem Rev2004;104:601784.

[50] Krajewska B. Membrane-based processes performed with use ofchitin/chitosan materials. Sep Purif Technol 2005;41:30512.

[51] Giri Dev VR, Neelakandan R, Sudha S, Shamugasundram OL, NadarajRN. Chitosana polymer with wider applications. Text Mag2005;46:836.

[52] Struszczyk MH. Chitin and chitosan. Part II. Applications ofchitosan. Polimery 2002;47:396403.

[53] Crini G, Badot PM. Application of chitosan, a naturalaminopolysaccharide, for dye removal from aqueous solutions byadsorption processes using batch studies: a review of recentliterature. Prog Polym Sci 2008;33:399447.

[54] Grente C, Lee VKC, Le Cloirec P, McKay G. Application of chitosanfor the removal of metals from wastewaters by adsorptionmechanisms and model review. Crit Rev Environ Sci Technol2007;37:41127.

[55] Guibal E. Interactions of metal ions with chitosan-based sorbents: areview. Sep Purif Technol 2004;38:4374.

[56] Varma AJ, Deshpande SV, Kennedy JF. Metal complexation bychitosan and its derivatives: a review. Carbohydr Polym2004;55:7793.

[57] No HK, Meyers SP. Application of chitosan for treatment ofwastewaters. Rev Environ Contam Toxicol 2000;163:128.

[58] Ravi Kumar MNV. A review of chitin and chitosan applications.React Funct Polym 2000;46:127.

[59] Wase DAJ, Forster CF. Biosorbents for metal ions. CRC Press; 1997.[60] Peter MG. Applications and environmental aspects of chitin and

chitosan. JMS Pure Appl Chem 1995;A32:62940.[61] Skjak-Braek G, Anthonsen T, Standford P. Chitin and chitosan. New

York: Elsevier Applied Science; 1989.[62] Muzzarelli RAA. Natural chelatin polymers: alginic acid, chitin and

chitosan. New York: Pergamon; 1974.[63] Bough WA. Coagulation with chitosanan aid to recovery of by-

products from egg breaking wastes. Poult Sci 1975;54:190412.[64] Bough WA. Chitosana polymer from seafood wastes, for use in

treatment of food processing wastes and activated sludge. ProcessBiochem 1976;11:136.

[65] No HK, Meyers SP. Crawsh chitosan as a coagulant in recovery oforganic compounds from processing streams. J Agric Food Chem1989;37:5803.[66] Guerrero L, Omil F, Mndez R, Lema JM. Protein recovery during theoverall treatment of wastewaters from sh-meal factories.Bioresour Technol 1998;63:2219.

[67] Savant VD, Torres JA. Chitosan-based coagulating agents fortreatment of Cheddar cheese whey. Biotechnol Prog2000;16:10917.

[68] Fernandez M, Fox PF. Fractionation of cheese nitrogen usingchitosan. Food Chem 1997;58:31922.

[69] Chi FH, Cheng WP. Use of chitosan as coagulant to treatwastewater from milk processing plant. J Polym Environ2006;14:4117.

[70] Cheng WP, Chi FH, Yu RF, Lee YC. Using chitosan as a coagulant inrecovery of organic matters from the mash and lauter wastewaterof brewery. J Polym Environ 2005;13:3838.

[71] Wibowo S, Velazquez G, Savant V, Antonio Torres J. Effect ofchitosan on protein and water recovery efciency from surimi washwater treated with chitosanalginate complexes. Bioresour Technol2007;98:53945.

[72] Savant VD, Torres JA. Fourier transform infrared analysis of chitosanbased coagulating agents for treatment of surimi waste water. JFood Technol 2003;1:238.

[73] Roussy J, Van Vooren M, Dempsey BA, Guibal E. Inuence ofchitosan characteristics on the coagulation and theocculation of bentonite suspensions. Water Res2005;39:324758.

[74] Roussy J, Van Vooren M, Guibal E. Inuence of chitosancharacteristics on coagulation and occulation of organicsuspensions. J Appl Polym Sci 2005;98:20709.

[75] Roussy J, Van Vooren M, Guibal E. Chitosan for the coagulation andocculation of mineral colloids. J Dispersion Sci Technol2004;25:66377.

[76] Huang C, Chen Y. Coagulation of colloidal particles in water bychitosan. J Chem Technol Biotechnol 1996;66:22732.

[77] Divakaran R, Pillai VNS. Flocculation of kaolinite suspensions inwater by chitosan. Water Res 2001;35:39048.

[78] Divakaran R, Pillai VNS. Mechanism of kaolinite and titaniumdioxide occulation using chitosan-assistance by fulvic acids?Water Res 2004;38:213543.

[79] Xie W, Xu P, Wang W, Liu Q. Preparation and antibacterial activityof a water-soluble chitosan derivative. Carbohydr Polym2002;50:3540.

[80] Strand SP, Vandvik MS, Vrum KM, stgaard K. Screening ofchitosan and conditions for bacterial occulation.Biomacromolecules 2001;2:12133.

[81] Strand SP, Vrum KM, stgaard K. Interactions between chitosanand bacterial suspension-adsorption and occulation. Colloid Surf B2003;27:7181.

[82] Bratskaya SY, Avramenko VA, Sukhoverkhov SV, Schwarz S.Flocculation of humic substances and their derivatives withchitosan. Colloid J 2002;64:75661.

[83] Bratskaya SY, Schwarz S, Chervonetsky D. Comparative study ofhumic acids occulation with chitosan hydrochloride and chitosanglutamate. Water Res 2004;38:295561.

[84] Guibal E, Van Vooren M, Dempsey BA, Roussy J. A review of the useof chitosan for the removal of particulate and dissolvedcontaminants. Sep Sci Technol 2006;41:2487514.

[85] Guibal E, Roussy J. Coagulation and occulation of dye-containingsolutions using a biopolymer (chitosan). React Funct Polym2007;67:3342.

[86] Rodrigues AC, Boroski M, Shimada NS, Garcia JC, Nozaki J, Hioka N.Treatment of paper pulp mill wastewater by coagulationocculation followed by heterogenous photocatalysis. JPhotochem Photobiol A Chem 2008;194:110.

[87] Wang JP, Chen YZ, Ge XW, Yu HQ. Optimization of coagulationocculation process for a paper-recycling wastewater treatmentusing response surface methodology. Colloids Surf A PhysicochemEng Aspects 2007;302:20410.

[88] Chen X, Sun HL, Pan JH. Decolorization of dyeing wastewater withuse of chitosan materials. Ocean Sci J 2006;41:2216.

[89] Sanghi R, Bhattacharya B. Comparative evaluation of naturalpolyelectrolytes psyllium and chitosan as coagulant aids fordecolourization of dye solutions. Water Qual Res J Can2005;40:97101.

[90] Ganjidoust H, Tatsumi K, Yamagishi T, Gholian RN. Effect ofsynthetic and natural coagulant on lignin removal from pulp andpaper wastewater. Wat Sci Technol 1997;35:2916.

[91] Ahmad AL, Sumathi S, Hameed BH. Coagulation of residue oil andsuspended solid in palm oil mill efuent by chitosan, alum and PAC.Chem Eng J 2006;118:99105.

[92] Ahmad AL, Sumathi S, Hameed BH. Chitosan: a natural biopolymerfor the adsorption of residue oil from oily wastewater. AdsorptionSci Technol 2004;22:7588.

[93] Meyssami B, Kasaeian AB. Use of coagulants in treatment of oliveoil wastewater model solutions by induced air otation. BioresourTechnol 2005;96:3037.

[94] Bratskaya SY, Avramenko VA, Schwarz S, Philippova I. Enhanced

[115] Wu ACM, Bough WA. A study of variables in the chitosanmanufacturing process in relation to molecular-weightdistribution, chemical characteristics and waste-treatmenteffectiveness. In: Muzzarelli RAA, Pariser ER, editors. Proceedingsof the rst international conference on chitin/chitosan. MIT SeaGrant Program, Cambridge, MA; 1978. p. 88102.

1348 F. Renault et al. / European Polymer Journal 45 (2009) 13371348occulation of oil-in-water emulsions by hydrophobically modiedchitosan derivatives. Colloid Surf A Physicochem Eng Aspects2006;275:16876.

[95] Chung YC. Improvement of aquaculture wastewater using chitosanof different degrees of deacetylation. Environ Technol2006;27:1199208.

[96] Gamage A, Shahidi F. Use of chitosan for the removal of metal ioncontaminants and proteins from water. Food Chem2007;104:98996.

[97] Assaad E, Azzouz A, Nistor D, Ursu AV, Sajin T, Miron DN, et al.Metal removal through synergic coagulationocculation using anoptimised chitosan-montmorillonite system. Appl Clay Sci2007;37:25874.

[98] Wu ZB, Ni WM, Guan BH. Application of chitosan as occulant forcoprecipitation of Mn(II) and suspended solids from dual-alkaliFGD regenerating process. J Hazard Mat 2008;152:75764.

[99] Wada S, Ichikawa H, Tatsumi K. Removal of phenols and aromaticamines from wastewater by a combination treatment withtyrosinase and a coagulant. Biotechnol Bioeng 1995;45:3049.

[100] Zeng D, Wu J, Kennedy JF. Application of a chitosan occulant towater treatment. Carbohydr Polym 2008;71:1359.

[101] Divakaran R, Pillai VNS. Flocculation of river silt using chitosan.Water Res 2002;36:24148.

[102] Rizzo L, Di Gennaro A, Gallo M, Belgiorno V. Coagulation/chlorination of surface water: a comparison between chitosanand metal salts. Sep Purif Technol 2008;62:7885.

[103] Grifths S. Flocculation: a new design procedure. Water2003;30:4454.

[104] Thomas DN, Judd SJ, Fawcett N. Flocculation modelling: a review.Water Res 1999;33:157992.

[105] Duan J, Gregory J. Coagulation by hydrolysing metal salts. AdvColloid Int Sci 2003;100102:475502.

[106] OMelia CA. Coagulation and occulation. In: Weber WJ, editor.Physicochemical processes for water quality control. NewYork: Wiley; 1972. p. 61109.

[107] Choi KH, Choi DM, Kim DS. Preparation method of chitosan-basedcoagulant for wastewater treatment. Korean PatentKR200000052018 (1999).

[108] Bough WA. Reduction of suspended solids in vegetable canningwaste efuents by coagulation with chitosan. J Food Sci1975;40:297301.

[109] Bough WA, Shewfelt AL, Salter WL. Use of chitosan for thereduction and recovery of solids in poultry processing wasteefuents. Poult Sci 1975;54:9921000.

[110] Bough WA, Landes DR. Recovery and nutritional evaluation ofproteinaceous solids separated from whey by coagulation withchitosan. J Dairy Sci 1976;59:187480.

[111] Bough WA, Landes DR. Treatment of food-processing waste withchitosan and nutritional evaluation of coagulated by-products. In:Muzzarelli RAA, Pariser ER, editors. Proceedings of the rstinternational conference on chitin/chitosan. MIT Sea GrantProgram, Cambridge, MA; 1978. p. 21830.

[112] Bough WA, Salter WL, Wu ACM, Perkins BE. Inuence ofmanufacturing variables on the characteristics and effectivenessof chitosan products. I. Chemical composition, viscosity, andmolecular-weight distribution of chitosan products. BiotechnolBioeng 1978;20:193143.

[113] Bough WA, Wu ACM, Campbell TE, Holmes MR, Perkins BE.Inuence of manufacturing variables on the characteristics andeffectiveness of chitosan products. II. Coagulation of activatedsludge suspensions. Biotechnol Bioeng 1978;20:194555.

[114] Wu ACM, Bough WA, Holmes MR, Perkins BE. Inuence ofmanufacturing variables on the characteristics and effectivenessof chitosan products. III. Coagulation of cheese whey solids.Biotechnol Bioeng 1978;20:195766.[116] Johnson RA, Gallanger SM. Use of coagulants to treat seafoodprocessing wastewaters. J Water Pollut Control Fed1984;56:9706.

[117] Senstad C, Almas KA. Use of chitosan in the recovery of protein fromshrimp processing wastewater. In: Muzzarelli RAA, Jeuniaux C,Gooday GW, editors. Proceedings of the third internationalconference on chitin and chitosan. Senigallia, Italy; 1986. p. 56870.

[118] Moore KJ, Johnson MG, Sistrunk WA. Effect of polyelectrolytetreatments on waste strength of snap and dry bean wastewater. JFood Sci 1987;52:4912.

[119] Jun HK, Kim JS, No HK, Meyers SP. Chitosan as a coagulant forrecovery of proteinaceous solids from tofu wastewater. J Agric FoodChem 1994;42:18348.

[120] Sievers DM, Jenner MW, Hanna M. Treatment of dilute manurewastewaters by chemical coagulation. Trans ASAE1994;37:597601.

[121] Huang C, Chen S, Pan JR. Optimal condition for modication ofchitosan: a biopolymer for coagulation of colloidal particles. WaterRes 2000;34:105762.

[122] Pan JR, Huang C, Chen S, Chung YC. Evaluation of a modiedchitosan biopolymer for coagulation of colloidal particles. ColloidSurf A Physicochem Eng Aspects 1999;147:35964.

[123] Bolto B, Dixon D, Eldridge R. Ion exchange for the removal ofnatural organic matter. React Funct Polym 2004;60:17182.

[124] Kvinnesland T, Odegaard H. The effects of polymer characteristicson nano particle separation in humic substances removal bycationic polymer coagulation. Water Sci Technol 2004;50:18591.

[125] Vogelsang C, Andersen DO, Hey A, Hakonsen T, Jantsch TG, MllerED, et al. Removal of humic substances by chitosan. Water SciTechnol Water Supply 2004;4:1219.

[126] Strand SP, Nordengen T, stgaard K. Efciency of chitosans appliedfor occulation of different bacteria. Water Res 2002;36:474552.

[127] Divakaran R, Pillai VNS. Flocculation of algae using chitosan. J ApplPhycol 2002;14:41822.

[128] Roussy J, Chastellan P, Van Vooren M, Guibal E. Treatment of ink-containing wastewater by coagulation/occulation usingbiopolymers. Water SA 2005;31:36976.

[129] Guibal E, Touraud E, Roussy J. Chitosan interactions with metal ionsand dyes: dissolved-state versus solid-state application. World JMicrob Biotechnol 2005;21:91320.

[130] Szygula A, Guibal E, Ruiz M, Sastre AM. The removal of sulphonatedazo-dyes by coagulation with chitosan. Colloids Surf APhysicochem Eng Aspects 2008;21:18.

[131] Wang JP, Chen YZ, Zhang SJ, Yu HQ. A chitosan-based occulantprepared with gamma-irradiation-induced grafting. BioresourTechnol 2008;99:3397402.

[132] Mishra DK, Tripathy J, Srivastava A, Mishra MM, Behari K. Graftcopolymer (chitosan-g-N-vinyl formamide): synthesis and study ofits properties like swelling, metal ion uptake and occulation.Carbohydr Polym 2008;74:6329.

[133] Wang YN, Cui L, Xu TK. Applications of modied chitosan occulantto dyeing wastewater. Wool Text J 2008;5:1820.

[134] Chavasit V, Antonio Torres J. Chitosan-poly(acrylic acid):mechanism of complex formation and potential industrialapplications. Biotechnol Prog 1990;6:26.

[135] Chen L, Chen D, Wu C. A new approach for the occulationmechanism of chitosan. J Polym Environ 2003;11:8792.

[136] Crini G, Martel B, Torri G. Adsorption of C. I. Basic Blue 9 onchitosan-based materials. Int J Environ Pollut 2008;34:45165.

[137] Crini G, Gimbert F, Robert C, Martel B, Adam O, Morin-Crini N, et al.The removal of basic Blue 3 from aqueous solutions by chitosan-based materials. J Hazard Mat 2008;153:96106.

[138] Crini G, Torri G, Weltrowski M, Martel B, Morcellet M, Cosentino C.Synthesis, NMR study and preliminary sorption properties of twoN-benzyl sulfonated chitosan derivatives. J Carbohydr Chem1997;16:6819.

Chitosan for coagulation/flocculation processes An eco-friendly approachIntroductionCategories of materialsWhy use coagulants and flocculants based on biopolymers?Coagulation/flocculation processChitosan as bioflocculant

Mechanisms of coagulation/flocculationChitosan for coagulation and flocculation a reviewConclusionsAcknowledgementsReferences