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Application of Natural Coagulant Aids

Coagulation is chemical treatment process used to destabilize colloidal particlesIn coagulation, chemicals are added to waterThese chemicals are called Coagulants

Introduction

It is a chemical reagent having a binding property to bind the smaller size solids by neutralizing its charge into larger sizeCoagulant chemicals are either Metallic salts or Polymers

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• Good floc forming capacity• Readily dissolve in water• Form high quality of flocs in low quantity of doses• Not have any acute or chronical effects on health• Non toxic in nature• Cheap and readily available• Easy to transport • Not posses any sludge formation in water• Not affect any chemical parameters of water like

pH, hardness, turbidity etc• Not produce any color in to the water

Ideal Characteristics of Coagulants

Commonly used Coagulants

Coagulant aids are chemicals which add density to slow-settling flocs and add toughness to the flocs so that they will not break up during the mixing and settling processes

Coagulant aids are not always required and are generally used to reduce flocculation time

Coagulant aids may be :Weighing agentsInter particle bridging agents, orReaction enhancing agents

Coagulant Aids

  Activated Silica :   Increase the coagulation rate   Reduce the amount of coagulant needed       Widen the pH range for effective coagulation       Chief advantage-strengthens floc       Usually added after coagulant, never directly with alum

Weighting Agents :  Provide additional particles that can enhance floc formation Used to treat water that is high in color, low in turbidity and low in mineral content Different types include: Bentonite clay, powdered Limestone, and powdered Silicia

Types of Coagulant aids

Polyelectrolytes :Extremely large molecules which produce highly charged ions when dissolved in water.  These are also called polymers.

Types of Polyelectrolytes

Cationic (+)Have a positive (+) charge  Allows reduced coagulant doseFloc settles better Less sensitivity to pH Improved flocculation of organisms such as bacteria and algae

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Anionic (-)     Have a negative (-) charge     Used primarily as a coagulant aid

Increases floc size  Improve settling  Produce a stronger flocNot materially affected by pH, alkalinity, hardness, or turbidity

Nonionic  Balanced or neutral charge;Used as a primary coagulant or coagulant aid

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Recent studies have discovered a number of drawbacks of using traditional coagulants

Alum salts may cause human body disease and ferric salts may cause the unsightly brown staining of equipments

Therefore, it is necessary to decrease the dosage of traditional coagulants to reduce negative effects by using Coagulant aids

They also provide more rapidity to the slow forming flocs, improve sludge properties (density, strength, floc-size) and eases separation

Need for Coagulant Aids

1. Synthetic- organic coagulant aids2. Natural- organic coagulant aids

Synthetic- organic coagulant aidsPolyvinyl benzyl, tri methyl ammonium chloride ,

Polydimethyl aminomethyl polyacrylamide , polyacrylamide, Polyacrylic acid, Polystyrene sulfonate are some examples

For coagulation of heavy metal precipitates Commercially marketed in the form of dry powder,

granules, beads, aqueous solutions, aqueous gels, and oil-in-water emulsions

Promotes bridging and hence produce larger shear resistant

Classification

Natural- organic coagulant aidsSodium Alginate, chitosan, starch etc are some

examplesCoagulant aids derived from natural products

include starch, starch derivatives, proteins, and tannins.

Starch is the most widely usedMost suitable for use with ferric salts, but if used

properly can be effective when used with alum also Very effective for increasing settling velocity,

and reducing coagulant dosage.

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Synthetic polymers are the most common coagulant aids, which bind to particles much like coagulants whereas natural polymers, act as sites of nucleation to speed the formation of floc

It has been reported that synthetic polymers contain contaminants from the manufacturing process that may threaten human health

Synthetic polymers can also react with other chemicals added to the water treatment process to form undesirable secondary products

Why Natural Coagulant aids ?

Natural polymers, which are extracted from plant or animal life, can be workable alternatives to synthetic polymers

They are biodegradable and also have a wider effective dosage range of flocculation for various colloidal suspensions

Therefore, it is indispensable to develop high efficient and low cost natural polymers which were used as coagulant aids for water and wastewater treatment

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EFFECTIVENESS OF CHITOSAN AS NATURAL COAGULANT AID IN TREATING TURBID WATERSB. Bina,* M. H. Mehdinejad, M. Nikaeen, H. Movahedian AttarDepartment of Environmental Health Engineering, School of Public Health, Isfahan University of Medical Sciences, Isfahan, Iran

Case Study 1

Aim:

To investigate the effects of alum as coagulant in conjunction with chitosan as coagulant aid on the removal of turbidity, hardness and Escherichia coli from water

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Materials:

Synthetic water : Three groups of turbidities were considered, namely; low turbidity (10–20 NTU), medium turbidity (100–120 NTU) and high turbidity (200-220 NTU)

Alum solution : Prepared by dissolving 10g Alum (Al2(SO4)3.18H2O) in distilled water and the solution volume was increased to 1 L

Chitosan : Prepared from crab shells was obtained from GMA Chemical Company. It was in the form of a pale brown powder soluble in dilute acetic and hydrochloric acids

E coli : From A.T.T.C (American Type Culture Collection)

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Procedure:

A conventional jar test apparatus was employed for the testsThe optimum pH was observed between 7 to 7.5 for all turbidities

The optimum doses of alum and chitosan when used in conjunction, were 10mg/L and 1mg/L, 5mg/L and 0.5mg/L, and 5mg/L and 0.5mg/L in low, medium and high turbidities, respectively

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Results :

Residual Al+3 in treated water was less than 0.2 mg/L, meeting the international guidelines

The number of E coli decreased during 24 hr in all of turbidities. The removal efficiency of E coli were 99.8 , 99.9 and 99 % in low, medium and high turbid water after 1 hr( the end of jar test), respectively

Chitosan significantly reduced the required dosage of primary coagulant 50-87.5%

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The turbidity removal efficiency in low, medium and high turbidities were obtained about 74.3, 96 and 98.2 % respectively

The maximum of hardness removal was obtained as 84.3 % by chitosan in low turbid water with initial hardness about 204 mg/L as CaCO3

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Conclusion:

It was found that this method is an efficient approach for optimization of coagulation-flocculation process and appropriate for raw water treatment

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SNAIL SHELL AS COAGULANT AID IN THE ALUM PRECIPITATION OF MALACHITE GREEN FROM AQUA SYSTEMNurudeen A. Oladoja∗, Yekini D. AliuDepartment of Chemistry, Adekunle Ajasin University, Akungba-Akoko, Nigeria

Case Study 2

Aim:To investigate the ability of snail shell (SS) to act as coagulant aid in the alum precipitation of a basic dye (MG)

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Materials :SS preparation : The SS was obtained after the snail has been removed in boiled waterSnail shell was first washed with tap water then rinsed thoroughly with deionized waterIt was dried in the ovenSS was finally made into powder using laboratory grinding machine and sieved with a laboratory sieve of known mesh size

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Basic dye : The basic dye used in the present studies was malachite green (MG) [Chemical formula = C23H26ON2, nature = basic green]

Method :

The conventional jar test procedure with a six-unit multiple stirrer system was usedAlum, the coagulant was added to the samples of the synthetic MG-contaminated water and rapid mixing was performed at 200rpm for 2 minA flocculation time of 20min and then 30 min of settling time were allowed

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Varying dosages of the alum, ranging from 100 to 700 mg/l were added

The SS was added after the rapid mixing and the other procedures were followed accordingly

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Result :

Effect of alum as the primary coagulant:No variant in the dye concentrations after the addition of the coagulant

Effect of SS as the primary coagulant:The percentage of the dye removed increased with increase in the SS dosage for each dye concentration

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Effect of Alum/SS combination:

When the alum was used as a primary coagulant and the SS was used as the coagulant aid, the optimum percentages of dye removal obtained from the different initial dye concentrations of 5, 10, 20, 50, and 100mg/l are 50.32, 76.16, 85.56, 92.60, 94.00, respectively

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Conclusion :

The results obtained showed that alum alone could not decolorize the basic dye-contaminated water. The SS exhibited some potential in the color removal but this potential was enhanced when the SS was combined with alum

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Mohammad Hadi Mehdinejad ,Bijan Bina , Mahnaz Nikaeen and Hossein Movahedian Attar(2009) “Effectiveness of chitosan as natural coagulant aid in removal of turbidity and bacteria from turbid waters”, Journal of Food, Agriculture & Environment Vol.7 (3&4) : 8 4 5 - 8 5 0 .

Nurudeen A. Oladoja∗, Yekini D. Aliu “Snail shell as coagulant aid in the alum precipitation of malachite green from aqua system”, Journal of Hazardous Materials 164 (2009) 1496–1502

water.me.vccs.edu/exam_prep/coagulants.htm

en.wikipedia.org

References

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