possibility of reuse of waste water in dairys
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Desalination 195 (2006) 141–152
0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved
*Corresponding author.
Wastewater treatment in dairy industries — possibility of reuse
Baisali Sarkar, P.P. Chakrabarti, A. Vijaykumar, Vijay Kale*
Lipid Science and Technology Division, Indian Institute of Chemical Technology, Hyderabad 500007, India
Tel. +91 (40) 2719-3370; Fax +91 (40) 2719-3370; email: vijay_kale1@rediffmail.com
Received 30 June 2005; accepted 7 November 2005
Abstract
The reuse of wastewater from the dairy industry was investigated using coagulation, adsorption and membrane
separation. Dairy industry was chosen as it requires huge volume of water. In recent times, development of newer
membranes with high flux/rejection characteristics have increased the probability of water reuse and recycling up
to a greater extent. In this investigation thorough pretreatment studies were done using different types of coagulants
categorized as inorganic, polymeric, and organic having biological origins. The coagulant treatment was performed
at various pH using different dosages and it was followed by activated charcoal treatment. The combined effects of these two pretreatment methodologies were evaluated. The color and the odor were removed completely and
permanently after charcoal treatment. The pretreated water was passed through a cross flow reverse osmosis
membrane system and the permeate water was found to have very good quality. This was compared to the process
water used by the dairy farm and was found that the water can be recycled or reused.
Keywords: Dairy wastewater; Coagulants; Powdered activated charcoal (PAC); TDS; COD; Membrane processes
1. Introduction
Ever increasing industrialization and rapid
urbanization have considerably increased the rateof water pollution. The dwindling supplies of natural resources of water have made this a serious
constraint for industrial growth and for a reason-able standard of urban living. The environmental
pro-tection agencies have imposed more stringentregulatory prohibitions and they have started more
strict vigil along with some non governmental
organizations to protect the environment. This hasmade the water treatment more expensive and to
comply with the discharge quality standard itself,
is becoming a huge burden for the industries. Itwas therefore felt that the possibilities of reuse of
the wastewater for various purposes should beinvestigated. The recycling or reuse of water for similar duties mainly depends on availability of suitable process technology for water purification.
Due to wide fluctuations in industrial effluentquality, this becomes more challenging. With theadvent of membrane technology and significant
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142 B. Sarkar et al. / Desalination 195 (2006) 141–152
improvements in efficiency and cost effectiveness,the competitiveness of recycling over discharge
has greatly increased.
In dairy industries, water has been a key pro-
cessing medium. Water is used throughout all steps
of the dairy industry including cleaning, sanitiza-
tion, heating, cooling and floor washing — andnaturally the requirement of water is huge. Dairy
wastewater is distinguished by the high BOD and
COD contents, high levels of dissolved or sus- pended solids including fats, oils and grease, nutri-
ents such as ammonia or minerals and phosphatesand therefore require proper attention before dis- posal.
In recent times, researchers have shifted their
interests in possibilities of reuse or recycling of industrial wastewaters — dairy industries are no
exceptions [1,2]. Dairy wastewater generally does
not contain conventional toxic chemicals likethose listed under EPA’s Toxic Release Inventory.
However, it has high concentration of dissolved
organic components like whey proteins, lactose,fat and minerals [3] and it is also malodorous
because of the decomposition of some of the con-taminants causing discomfort to the surrounding population. To comply with the discharge stan-
dard, the dairy industries are practicing an elabo-
rate effluent treatment protocol which is affectingthe overall economy of the plant. The need of the
hour is a suitable technology for recycling or reuse
at least a reasonable quantity of the wastewater produced in the plant.
Recent studies revealed that membrane sepa-
rations may help in solving problem of attaining
a quality of water that can be recycled back to the
process and it was tested for various chemical
industries and in some food processing industries
also [4–7]. Even the dairy industry effluent was
also treated by membrane process and possibility
of reuse was reviewed [1,8]. However the protein-
ous materials of the dairy wastewater were found
to be severe foulant for the existing membrane
materials [9]. With the advent of the newer mem-
brane materials which are less prone to fouling,
the research thrust in this area has increased tre-mendously. To control the fouling and to improve
the productivity and life of membranes, use of
coagulant and adsorbent before membrane ap-
plication were done in primary and secondary
effluent treatment and in sewage effluent treatment
[10–12]. In the present investigation, thorough
pretreatment studies were performed using con-
ventional coagulants and a few newer coagulants
to evaluate their suitability for treatment of dairy
effluent. The effectiveness of use of Na-CMC and
chitosan as coagulant in the treatment of somefood processing industry wastewater such as inegg processing plant and in fish meal factories
had been reported [13,14]. Not much literature is
available on another polysaccharide — alginicacid as coagulant in the treatment of wastewater.
Activated charcoal treatment was done after
coagulation as it is known to remove the color and odor of the surface water and improve the
taste of drinking water combined with some other
treatment options [15,16]. To optimize the con-ditions for chemical pretreatment of dairy waste-
water, studies were undertaken to evaluate theeffects of dosages of coagulants and adsorbents, pH, contact time, settling time etc. before the
membrane processing. Preliminary results of each
chemical pretreatment were evaluated with respectto percent reduction of total dissolved solids (TDS)
and chemical oxygen demand (COD) of treated
water. Membrane separation studies were per-formed in both the dead end system (for labora-
tory-scale studies) and cross flow system (for
pilot-scale studies) and the water quality obtainedafter membrane separations were compared to the
process water actually used by some dairy indus-
tries.
2. Experimental
2.1. Materials
Raw wastewater was collected from A.P. Dairy,
Hyderabad, India at an interval of 15 days and
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B. Sarkar et al. / Desalination 195 (2006) 141–152 143
stored in the refrigerator, if required to be usedfor long periods.
2.1.1. Reagents
For the pretreatment studies before membrane
processing different types of coagulants like in-
organic (alum and ferric chloride), polymeric(polyaluminium chloride) and natural organic
(sodium carboxymethyl cellulose commonly
known as Na-CMC, alginic acid, and chitosan)were tested. Alum was purchased from local mar-
ket. Ferric chloride LR grade was procured fromS.D. Fine Chem Ltd., Mumbai whereas poly-aluminium chloride was obtained from Permionics
Pvt. Ltd., Vadodara, Gujarat, India. Alginic acid
(LR grade) was obtained from Loba Chemie Pvt.Ltd., Mumbai, India. Chitosan and Na-CMC were
purchased from Sigma Aldrich Inc., St. Louis,
USA. Powdered activated charcoal (LR grade)was obtained from S.D. Fine Chem Ltd., Mumbai,
India. Commonly used chemicals to maintain the
pH of the medium NaOH and HCl both LR grade
were procured from S.D Fine Chem Ltd, Mumbai
and Ranbaxy Fine Chemicals Ltd, New Delhi,
India respectively.
2.1.2. Membranes
Cellulose acetate flat sheet membranes of 44 cm2 surface area having 10,000 Da and 1,000 Da
molecular weight cut off were supplied by Milli-
pore Corporation, MA, USA. Permionics Pvt.Ltd., Vadodara, India had supplied nanofiltration
membrane of 300 Da molecular weight cut off
(MWCO) and RO flat sheet membrane as com- plimentary samples. The membranes are poly-
amide on non oven polyester. The ceramic micro-
filtration membrane having 0.45 micron pore sizeused in pilot plant was purchased from Orelis,
France. It is having tubular configuration with 19
channels and 0.167 m2 surface area. Spiral woundRO membrane with 2 m2 surface area was pro-
cured from Osmonics, USA. The membrane is
made up of cellulose acetate and having more than99% NaCl rejection.
2.1.3. Membrane units
The ultrafiltration experiments were performed
in a dead-end test cell supplied by Millipore Cor-
poration, MA, USA. The nanofiltration/reverseosmosis experiments were done in a stainless steel
test cell of dead-end type having maximum pres-
sure limit of 50 bar. This test cell was supplied bySnowtech Pvt. Ltd., Mumbai, India. Both the test
cells were fitted with magnetic stirrer. The trans-
membrane pressure (TMP) was generated bynitrogen gas. Pilot scale cross flow membrane unit
had a feed tank of 50 L capacity and was supplied by Nishotech Systems Pvt. Ltd., Mumbai. Themembranes used in pilot scale studies were housed
in stainless steel casing.
2.2. Analytical methods
Wastewater samples and various water samples
after treatment were analyzed for suspended solid,
total dissolved solid content (TDS), chloride, sul-fate, hardness, oil and grease content (FOG), and
phosphorus content according to the standard
method [17]. pH and conductivity were measuredwith the help of digital pH meter (model: DI 707),
supplied by Digisun Electronics, Secunderabad,India and digital conductivity meter (DCM 900)
supplied by Global Electronics, Hyderabad, India
respectively. Turbidity measurement was donewith Digital Nephelo-Turbiditymeter 132. For
COD estimation the digestion of the sample was
done in a COD reactor, supplied by HACH,Colorado, USA followed by titration with standard
ferrous ammonium sulfate. 5 day 20°C BOD
values were estimated using YSI5100 dissolvedoxygen meter, supplied by YSI Incorporated,
Ohio, USA.
2.3. Experimental procedure
2.3.1. Chemical pretreatment of dairy waste-
water
Wastewater sample collected from dairy farm
was filtered and the filtered water samples were
then subjected to coagulant and PAC treatment.
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144 B. Sarkar et al. / Desalination 195 (2006) 141–152
400 ml of filtered wastewater was taken in 500ml beaker.
a.Optimization of the coagulant dosages:
Coagulant dosages were varied from 100 to
1000 mg/L. Addition of coagulant was followed
by stirring for 5 min on magnetic stirrer and settl-
ing for 120 min. Depending on the analytical re-sults the dosages were further reduced to 10–
100 mg/L in case of chitosan.
b.Optimization of pH for an individual co-agulant : pHs selected were 4.0, 6.5 and 8.0. pH
of the wastewater was maintained with the helpof 1:1 HCl and 0.1N NaOH, whenever required.c. Optimization of settling time after coagula-
tion: The settling time intervals were varied be-
tween 30–150 min to get the best possible results.d. Studies on powdered activated charcoal
treatment: Variable dosages (0.5–2.0 g/L) of PAC
were added to the wastewater sample and stirredon magnetic stirrer for 90 min. The pH of the
wastewater was also varied in the same manner
as mentioned in the coagulant treatment. Thestirring time was varied from 30 to 120 min. The
optimum conditions of PAC treatment wereselected depending on TDS and COD values of the treated water.
2.3.2. Selection of pretreatment sequence
The effects of coagulant treatment followed
by the PAC treatment were evaluated and the
sequence of operation was finalized based on the
percent reduction of TDS and COD.
2.3.3. Membrane processing of pretreated
water
After coagulant and PAC treatment the pH of
the water was adjusted to 6.5, and was passedthrough UF and RO membranes separately in the
test cells and checked for TDS and COD reduc-
tion. For UF treatment the pressure was main-tained at 3–3.5 bar. For RO experiments as high
as 35 bar transmembrane (TMP) pressure was
created to get a reasonably good flux.
In the pilot unit, the wastewater sample after chemical pretreatment and pH adjustment was first
passed through a tubular ceramic microfiltration
membrane having 0.45 micron pore size. Trans-
membrane pressure of 1.75–2 bar was maintained.
The permeate of the MF membrane was then
passed through a spiral wound RO membranewhere the TMP was maintained at 18–20 bar.
3. Results and discussion
The quality of raw dairy wastewater collectedfrom A.P. Dairy, Hyderabad, India varied batch-
wise according to the production of the dairy farm.
Generally it had bad smell and was light greenishin color. Water pH was in the neutral to slight
alkaline range. The high BOD and COD values
indicated that it is heavily contaminated withorganic matter.
The quality of raw dairy wastewater is given
in Table 1.
3.1. Coagulant treatment
Coagulation–flocculation is one of the mostimportant physicochemical treatment steps in in-
dustrial wastewater treatment to reduce the sus-
pended and colloidal materials responsible for turbidity of the wastewater and also for the
reduction of organic matters which contributes to
the BOD and COD content of the wastewater [18,19]. Addition of coagulants involves destabili-
zation of the particulate matters present in the
wastewater, followed by particle collision and flocformation which results in the sedimentation or
Table 1
Characteristics of raw dairy wastewater
pH 5.5–7.5
TSS, mg/L 250–600
Turbidity, NTU 15–30
TDS, mg/L 800–1200
COD, mg/L 1500–3000
BOD, mg/L 350–600
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B. Sarkar et al. / Desalination 195 (2006) 141–152 145
flotation. The performance of a particular coagu-lant depends upon the quality of the wastewater.
Different types of coagulants were selected in the
present study to observe their effects on dairy
effluent. Performance of coagulants was primarily
based on pH, conductivity, TDS and COD values
of treated water.
3.1.1. Effects of inorganic coagulants
Alum was found to be effective coagulant inreducing solids, organics and nutrients in the dairy
industry effluent to reuse it in irrigation [2]. Re-moval of 99% suspended solids with appreciableremoval of COD and turbidity were achieved
when slaughterhouse wastewater was treated with
alum in the range of 100–1000 mg/L and pH inthe range of 4–9 [19]. Ferric chloride had shown
better results than alum in the removal of COD
and suspended solid and in the reduction of color in a cost effective way for the clarification of tan-
nery wastewater. The performance of the coagu-
lants was highly dependent on pH and dosages
[20].
The most commonly used inorganic coagulants
in wastewater treatment; alum and ferric chloride
were therefore tried in initial experiments. As the
dosages of the coagulants were increasing, the
formation of floc followed by settling was appre-
ciable in both the cases at pH 6.5 and 8.0. No co-
agulation was observed at pH 4.0 for ferric
chloride which is reflected in Fig. 1a. At 500 mg/L
dosage of ferric chloride the TDS is showing mini-
Fig 1a. Variation of TDS with ferric chloride dosage. Fig. 1b. Variation of TDS with alum dosage.
mum when the starting pH is in the range of 6.5– 8.0. Alum also showed the same trend and at
500 mg/L dosage and at pH 6.5–8, TDS was found
to be minimum (Fig. 1b). Hydrolysis of Al2(SO
4)
3
and FeCl3in the alkaline medium at that particular
dosage results in the formation of corresponding
gel like hydroxides and some positively chargedmononuclear and polynuclear species. These posi-
tively charged compounds combine with nega-
tively charged colloidal particles present in thewastewater by charge neutralization mechanism
and at the time of settling under gravity these hyd-roxides and complexed hydroxides sweep awayremaining uncharged/ charged colloidal particles
of the wastewater with them and precipitates out
[21]. The increase of TDS after that particular dosage may attribute to the optimum hydrolysis
of the coagulants at that particular dosage. The
hydrolysis of these coagulants results in the forma-tion of strong acids which enhances the ionic
strength of the medium.
As a result, pH of the medium was found todecrease and conductivity was found to increase
with coagulant dosages as shown in Figs. 2a and2b. Use of ferric chloride at higher dosages pro-duces orange colored water. These results prompt-
ed us to search for other coagulants.
3.1.2. Effect of polymeric coagulant
Coagulation using inorganic coagulants may
result in the production of huge volume of sludge
and aluminium or iron salts may be retained in
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146 B. Sarkar et al. / Desalination 195 (2006) 141–152
Fig. 2a. Effect of coagulant dosages on the pH of the
medium.
the treated water. It is well known that uptake of
aluminium is associated with Alzheimer’s diseases
[22] and blood cancer. Synthetic polymeric co-
agulants were known to have some advantages
over these inorganic coagulants. Polyaluminium
chloride (PACl) is one of the most commonly used polymeric coagulants used in wastewater treat-
ment. Treatment of secondary effluent from con-
ventional wastewater treatment plant with poly-
aluminium chloride at pH 6.0 resulted in removalof 95% turbidity as compared to alum and ferric
chloride [23]. In our study we observed that, incontrast to alum, poly aluminium chloride kept
the pH of the medium very stable with increase
in dosages and it did not have any significant effecton the reduction of solid content in case of dairy
wastewater.
3.1.3. Study on natural organic coagulants
Polymeric coagulants involve in the produc-
tion of lower volume of sludge and its effective-ness is not very much dependent on the pH of the
water. However, use of these coagulants are re-
stricted because of the production of chlorinated
and several other by-products in water which have
adverse impact on human health [24]. Natural
organic materials are biodegradable and mostly
non toxic in nature and less polluting to environ-
ment. Na-CMC and alginic acid — two members
Fig. 2b. Effect of coagulant dosages on the conductivity
of the medium.
in that category had been reported as coagulant
in treatment of dairy wastewater [25,26]. In this
study, therefore, these two coagulants were also
tried for their effectiveness. However no floc
formation was found in the entire pH range. After
analysis it was observed that although the pH of
the treated water did not change much with
dosages as happened with inorganic coagulants,
the TDS was found to increase with dosages as
shown in Figs. 3a and 3b. Being high molecular weight compounds, Na-CMC and alginic acid
instead of performing as coagulant may lead to
increase the TDS with dosages. The higher rate
of increase of TDS after alginic acid treatmentconfirms the higher average molecular weight of
alginic acid compared to Na-CMC. It was there-
fore decided not to use these coagulants for further studies.
Chitosan is another high molecular weight
organic compound obtained from natural sourcelike shells of shrimp, crab, and lobster and also
biodegradable and non toxic in nature and it hasvery high affinity to proteins [25,27]. 100– 700 mg/L dosages of chitosan had been used in
the treatment of pulp and paper mill wastewater
and 2–15 g/L was applied in distillery wastewater treatment [28,29]. Only 26–28% reduction in total
solid was observed in fisheries wastewater when
treated with chitosan at an optimal 60 mg/L dosageat pH 5.5 [30].
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B. Sarkar et al. / Desalination 195 (2006) 141–152 147
Fig. 3a. Effect of Na-CMC dosages on TDS at different
pHs.
Fig.3b. Effect of alginic acid dosages on TDS at differ-
ent pHs.
Therefore it was decided to check its suitability
for the pretreatment of dairy wastewater and it
was observed that the conductivity and pH of the
medium were appreciably constant with dosages
of chitosan.
The dairy wastewater when treated with
chitosan at a dosage of 100 mg/L had resulted in
TDS values of the wastewater 440–540 mg/L in
the pH range of 4.0–6.5 as shown in Fig. 4a. In
Fig. 4b the change of COD of the wastewater with
dosages of chitosan is observed and at 100 mg/Lof chitosan dosage the COD is in the range of
450–680 mg/L when the pH is in the range of 4.0– 6.5.
Since chitosan is a costly coagulant compared
to other coagulants it was decided to check theeffect of lesser dosages. Dosages were again
varied between 10–100mg/L at pH 6.5 and 4.
A maximum of 22% reduction in TDS and 20%decrease in COD was observed at pH 6.5 when
Fig. 4a. Effect of chitosan dosages on TDS at different
pHs.
Fig. 4b. Effect of chitosan dosages on COD at different
pHs.
treated with chitosan in the dosage range below
100 mg/L. At pH 4.0 these reductions were 48%
in TDS and 57% in COD at 10–50 mg/L chitosan
dosage. To make the treatment protocol cost effec-
tive for industry 10 mg/L dosage was selected at
pH 4.0. Chitosan contains two highly polar –OH
and –NH2
groups and have pK avalue nearly 6.5.
In the acidic medium, i.e. at pH less than 6.5 it is
cationic in nature and forms –NH3
+ group and at-
tracts the negatively charged protein molecules
present in dairy wastewater and reduces the solidcontent appreciably [27].
Once the coagulant and its dosages were select-ed the settling time for coagulation was varied
between 30–150 min at a particular coagulant do-
sage and at a particular pH. After 60 min settlingtime no more further reduction in TDS and COD
was observed with time. Fig. 5 shows approx. 44%
TDS and 40% COD reduction after 60 min settlingtime when treated with 10 mg/L chitosan at pH 4.
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148 B. Sarkar et al. / Desalination 195 (2006) 141–152
Chitosan was found to have significant effectas coagulant for the dairy wastewater taken for
treatment in the present investigation. It had
lowered the TDS and COD values considerablyat very low dosage as compared to the common
coagulants. Since the required dosage was very
less, it might be used commercially as a coagulantin the pretreatment of dairy wastewater. The con-
ductivity did not increase after chitosan treatment
which may help in designing the final reverse os-
mosis step. However odor was still persistent after
treatment with chitosan.
3.2. PAC treatment on raw wastewater
Powdered activated charcoal (PAC) had been
used as adsorbent in various industrial wastewater treatments. Olive mill effluent with high COD,
BOD and phenolic content when treated with PAC
had shown 94% removal of phenols with 83% re-moval of other organic matter at an optimum con-
centration of PAC [31]. Removal of phthalate fromwastewater was done by modified activatedcarbon, performance of which was pH dependent
[32]. Treatment of dairy wastewater with some
low cost adsorbents and PAC had shown that PACwas better in lowering TDS than other pretreated
adsorbents like bagasse, straw dust, saw dust,
coconut coir and fly ash [33]. In our present work,an adsorption study with PAC was done on filtered
Fig. 5. Percent reduction of TDS and COD with coagula-
tion settling time after 10 mg/L chitosan dosage at pH = 4.
raw wastewater to optimize pH, dosage, and con-tact time of PAC.
Fig. 6 shows the effect of pH of the wastewater
on the adsorption properties of PAC. A Maximum
of 40% and 62% reduction of TDS and COD
respectively were observed at pH 4. This may be
due to the generation of positive charge on thesurface of charcoal particles in the acidic pH which
attract negatively charged organic molecules
abundantly present in the wastewater and remove by charge neutralization.
Varied dosages of PAC were added to thewastewater having 730 mg/L and 1532 mg/L TDSand COD respectively at pH 4. Stirring time was
fixed at 90 minutes. Optimum dosage of PAC was
found to be 1.5 g/L as shown in Fig. 7 and the re-duction of TDS and COD were 44% and 60%
Fig. 6. % removal of COD and TDS after 1.5 g/L char-
coal treatment at different pHs.
Fig. 7. Variation of TDS and COD with PAC dosages at
pH 4.0.
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B. Sarkar et al. / Desalination 195 (2006) 141–152 149
respectively. With further increase of PAC dosagethere was no appreciable reduction of TDS and
COD.
The variation of TDS and COD with time using
1.5 g/L PAC at pH 4 is shown in Fig. 8. With in-
creasing time the TDS and COD values were de-
creasing and at 90 min of time maximum removalof 44% and 68% of TDS and COD respectively
were observed.
From the above experiments it may be con-cluded that after treatment of filtered raw dairy
wastewater with 1.5g/L PAC at pH 4 and 90 minstirring time, the reduction of TDS was 40–44%and COD was 60–68%. The color and odor had
been eliminated also. This optimized PAC treat-
ment protocol was tried after coagulant treatedwastewater.
3.3. Optimization of pretreatment protocol
After 10 mg/L chitosan treatment at pH 4.0
the filtered water was treated with already opti-
mized 1.5 g/L dosage of PAC at the same pH and
stirred on magnetic stirrer for 90 min and then
again filtered. Results show 57% reduction in TDS
along with 62% reduction in COD as shown in
Fig. 9. No change in conductivity was observed.
Color and odor were removed completely. The
quality of the treated water was found to be
reasonably good for further processing through
membranes.
Fig. 8. Variation of TDS and COD with stirring time af-
ter 1.5 g/L PAC treatment at pH 4.
3.4. Membrane processing in test cells
The chemically pretreated wastewater was
passed through 10,000 Da followed by 1,000 Da,
and reverse osmosis membranes separately in adead end test cell. Appreciable reduction in TDS
and COD was not seen after UF. After passing
through RO membrane a complete water analysiswas done on the permeate and results obtained
are given in Table 2.
3.5. Pilot-scale membrane separation studies
To reduce the fouling of spiral-wound RO
membrane, a MF pretreatment was given before
reverse osmosis to arrest the charcoal particles,fat molecules having bigger sizes and the micro-
organisms present in the wastewater. 71% FOG
along with 81% BOD reduction was observedafter MF run. Raw water turbidity reduction was
observed 88% only after pH adjustment to 4.0.
This may be due to the coagulation and agglo-meration followed by precipitation of milk protein
particularly casein molecules in acidic pH. Coagu-
lant treatment further removed suspended andcolloidal materials lowering further turbidity. PAC
treatment after coagulant treatment significantlychanged the appearance of the wastewater — it
became clear and odorless. COD in RO feed after
MF came down to 197 mg/L. Reverse osmosistreatment reduced 98% COD from original. BOD
Fig. 9. Treatment of dairy wastewater with 10mg/L
chitosan followed by 1.5g/L charcoal at pH 4.
0
500
1000
1500
2000
2500
0 50 100 150
Stirring time (min)
T D S a n d C O D
( m g / L )
TDS(mg/L)
COD(mg/L)
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150 B. Sarkar et al. / Desalination 195 (2006) 141–152
and COD values of the wastewater came down to
8 mg/L and 16.5 mg/L respectively after reverse
osmosis treatment. Drastic reduction in waste-
water conductivity after RO (96% from the pre-
vious step) signifies the rejection of ionic species
only by reverse osmosis and the results are tabu-
lated in Table 3.
Table 2
Analysis of dairy wastewater after pretreatment and membrane processing in test cell unit
Raw filtered dairy
wastewater
Wastewater
at pH 4
After 10 mg/L
chitosan treatment
After 1.5 g/L PAC
treatment
After RO
processing
pH 5.84–6.71 — 4.09–4.25 4.38–4.71 6.15–6.43
Conductivity, µS/cm 556–880 616 –920 638–797 646– 803 47–111
Turbidity, NTU 15–30 8.4 3.6–3.8 0.3–0.1 0–0.06
TDS, mg/L 696–980 350–950 260–440 100–200 57–90
Hardness, mg/L 150–200 150–200 150–200 150–200 19–28
Chloride, mg/L 58–71 209–264 209 204–209 58–60
Sulphate, mg/L 25–131 84 62–81 50–82 17–30
Phosphorus, mg/L 0–1.64 0–1.68 0–1.64 nil nilCOD, mg/L 405–1308 405–1165 203–583 203–388 81–117
Fat oil and grease, mg/L 86–252 182 83 60 nil
Color White White Turbid Clear Clear
Odor Bad smell Bad smell Reduced Absent Absent
Table 3
Analytical results of dairy wastewater after pretreatment and membrane processing in pilot plant unit
Filtered raw
dairy wastewater
Wastewater
at pH 4
After 10mg/L
chitosan treatment
After 1.5g/L
PAC treatment
MF permeate RO permeate
pH 6.61 4.06 4.21 5.16 6.53 6.55Conductivity, µS/cm 923 920 933 987 1057 40
Turbidity, NTU 16 2.1 1.9 0.3 0.1 0
TDS, mg/L 780 920 470 360 300 33
TSS, mg/L 216 nil nil nil nil nil
Hardness, mg/L 125 125 125 125 125 3
Chloride, mg/L 70.4 309 307 289 260 16
Phosphorous, mg/L 1.5 1.5 1.5 nil nil nil
COD, mg/L 1080.5 884 295 197 197 16.5
FOG, mg/L 216 156 56 50 14 nil
BOD, mg/L 540 540 520 440 85 8
Color White White Turbid Clear Clear Clear
Odor Bad smell Bad smell Reduced Absent No smell No smell
3.6. Comparison of dairy process water with ROwater
The process water sample used in some localdairy industries was collected. These samples wereanalyzed and compared with the permeate of re-verse osmosis studies done earlier. The results areshown in Table 4.
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B. Sarkar et al. / Desalination 195 (2006) 141–152 151
4. Conclusion
Chitosan at very low dosage, 10 mg/L was found
to be a better coagulant compared to inorganic
and organic coagulants. PAC treatment after chito-
san was found to be useful in complete removal
of color and odor of the wastewater before mem-
brane processing. Performance of chitosan and
PAC is pH dependent. Chitosan and PAC work
efficiently at the same pH 4.0 and comprise the
RO pretreatment step suitable for dairy waste-
water. Pilot scale experiment using spiral woundRO membrane yields better water quality com-
pared to flat sheet membranes used in bench scale
experiments. The quality of water after reverseosmosis was found to be comparable to that of
process water used in the Dairy and can be re-
cycled back.
Acknowledgement
B.S. and A.V. acknowledge the Council of Sci-entific and Industrial Research (CSIR), India for
awarding senior research fellowship and junior
research fellowship respectively. The authors arethankful to A.P. Dairy, Hyderabad, India for their
cooperation in supplying wastewater during the
course of this study. The authors wish to thank Permionics, Vadodara, India for giving polyalumi-
nium chloride and RO flat sheet membrane used
in the experiment as a complimentary sample.
Table 4
Comparison of RO water with dairy process water
Process water RO permeate
pH 7.3 6.5
Conductivity, µS/cm 242 40
Turbidity, NTU 0.2 0.0
TDS, mg/L 128 33Hardness, mg/L 88 3
FOG, mg/L Nil Nil
Chloride, mg/L 58 16COD, mg/L 24.7 16.5
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