Indi an Jou rnal of Chemical Technology VoL6, Jul y 1999,pp. 185- 193

Rheological properties of concentrated distillery spent wash and some metal corrosion studies

Jagdish Thampi & Aniruddha B Pandit"

Divi sion of Chemical Engineering, Department of Chemical Technology, University of Mumbai, Matunga, Mumbai 400019, India

Received 3 July 1998; accepted 14 June 1999

Spent wash generated by the alcohol distilleries is a major source of grou nd water pollution. Various treatment strategies. whi ch include aerobic, anaerabic digestion, thermal treatment and incineration have been adopted with reasonable success. For th e rigorous engi neering analysis of any of these processes, the information regarding the physico-chemical properties o f thi s eflluent such as density , surface tension and viscosity lire essenti al. The rheological properties of concentrated distillery wastes at room temperature and elevated temperatures were measured . The rheological properties have been co rre lated to solid concentration of the waste in the dissolved and suspended state at roo m temperature. For highly concentrated wastes (viz. 50 % and 60 % by weight of solid concentration) the vari ati on in rheological properties with temperature were also studied. A rheological model has been used to explain the observed results. The Bingham model was found suitab le to ex pl ai n the rheological properties of the concentrated di sti llery wastes at ambient temperature and elevated temperatures. The corrosion rates of different materials during evaporation of distillery waste were also measured in order to find out a sui tab le materi al of construction to handle distillery waste during concentration.

Spent wash originating from sugar cane molasses distillery is a maj or source of ground water pollution in tropical countries like India and Brazil where cane molasses is the main raw material for ethyl alcohol production . Various treatment strategies, which include aerobic, anaerobic digestion, thermal treatment and concentration/incineration have been adopted with reasonable success.

For the rigorous engineering analysis of any of these processes , the information regarding the physico-chemical properties of the effluent such as density , surface tension and viscosity are essential. For incineration of this waste (spent wash) it is necessary first to concentrate the waste, so that its ignition tS sustained and continuous. This concentration is usually carried out in multiple effect evaporators. Due to acidic pH and chloride contents of the spent wash, these multiple effect evaporators are prone to severe corrosion. Thus to design an effective incineration system including concentration, or for that matter any form of treatment the following information/characteristics of the effluent are required :

a) Boiling point and Ignition temperature i.e. flash point and fire point and so lid concentration relation to

'For cllrre~pondence

maintain the required furnace temperature. b) Rheological properties of the waste (spent wash)

at various solid concentrations and at different temperatures, required for an efficient atomizer and burner design to bum the concentrate in a suitably designed furnace. Also for the estimation of the heat transfer characteristics during evaporation! concen­tration.

c) Corrosion rates of various metals in the spent wash during the concentration of the same.

d) Density and surface tension to accurately estimate the expected heat transfer coefficients in the concentration/evaporation . This will allow the estimation of the required heat transfer area accurate I y.

The information regarding the rheological properties could also be effectively used for the design of aerobic, anaerobic treatment schemes as the rates of gas transfer, be it oxygen during aeration or methane and carbon dioxide during anaerobic digestion, are strongly influenced by the rheological properties of the liquid.

The distillery waste is a complex, structured fluid . Rheological analysis of this multiphase system can provide information auoll t each phase. as well as about the interaction between solid and liquid phases.

186 INDIAN J. CHEM. TECHNOL., JULY 1999

Rheology of flu ids

Rheology describes the deformation of a body under the influence of stresses. 'Bodies' in this context can be either solids, liquids or gases. The resistance of a fluid to shear is called viscosity. To maintain flow in a liquid, energy must be added continuously.

Various models have been used to describe these rheological properties of Newtonian and Non Newtonian fluids I. The relevant one for this paper is,

The Bingham Model

1=110 YHo if 111 >10'

y=0, if 111 <10' where

1=Shear stress, Pa; y=Shear rate, and is equivalent to Newtonian

10=Yield stress, Pa.

... (1)

· 1 . S ; 110 IS a constant viscosity, Pas, and

The substance remains rigid when the shear stress

is smaller in magnitude than the 'Yield stress' (10) . But flows somewhat like a Newtonian fluid when the

shear stress exceeds 10 , A subst~nce that follows thi s two parameter model is called a Bingham plastic.

When Lo=O, the equation reduces to Newton's law of viscosity,

L=~ Y

Viscoelastici ty of suspensions2

... (2)

Einsteen was the first to show the relationship

between viscosity 11 of the suspension and the volume

fraction 8 of spheres.

.. . (3)

where 11s is the viscosity of the continuous liquid phase. Many equations can be used fo r more concentrated suspensions . The one shown here is the Mooney equation, which takes into account particle shape Sand the morphology of the saturated suspensions. This parameter is K. The equation is, 'T1=t1

sS9/(1. K9) " - " ... (4)

Experimental Procedure Raw spent wash characteristics

The spent wash was obtained from a running d istillery based on semi-continuous fermentation using cane sugar molasses. The following charac­teristics were measured.

Colour Odour pH

Dark brown Molasses 4.14 at 30"C.

Boiling point Solid residue content Inorganic content of the solid residue '

I04"C 13% wt/wt

28.46% i.e. 3.69% wt/wl of the total liquid mass.

The solid content was found out by evaporation of the waste and drying the residue in an oven. The inorganic ash content was found out by incinerating the solid residue at 800°e.

Measurement of physico-chemical properties

The densities and surface tensions of raw and concentrated wastes were measured using specific gravity bottles and wire ten siometer respectively . For the measurement of surface tension, the concentrated wastes were filtered through Whatman 40 fi lter paper and then used for the measurement.

Concentration of the waste

The distillery waste was evaporated to different levels of concentrations viz. 20, 30, 40, 50 and 60% wUwt of solids in a glass beaker. The beaker was heated by means of a sand bath on an electric heater. A thermometer was immersed in the concentrating waste to measure the rise in boiling point with the concentration . During this concentration experiments metal strips of different materials viz. mjld steel (M.S), stainless steel- 316 (S.S-316), 316 L (S.S-316L), and 304 (S.S-304) were suspended in the waste. The meta l strips were cleaned with water and solvents and weighed prior to the studies. Only one inch each of the metal strips were immersed in the waste and this length was maintained th roughout the experiment. After each run of concentrations the metal strips were cleaned , dried in an oven and weighed accurately to measure the weight loss during the concentration/ evaporation of the spent wash. The process of concentration was monitored by observing the amount of water loss .

The concentrations in % wUwt were converted to weight fraction s for further calculations and the wastes were named as,

C 1=13 % Solid concentrated distillery spent wash,

Weight fraction, 0.13, C2=20% Solid concentrated distillery spent wash,

Weight fraction, 0.2,

C3=30% Solid concentrated distillery spent wash,

Weight fraction, 0.3, C4=40% Solid concentrated distillery spent wash,

Weight fraction , 0.4,

--4

THAMPI & PANDIT: RHEOLOGICAL PROPERTIES OF SPENT WASH AND CORROSION STUDIES 187

C5=SO% Solid concentrated distillery spent wash, Weight fraction, O.S,

C6=60% Solid concentrated distillery spent wash, Weight fraction, 0.6,

Measurement of rheological properties

The rheological properties of all the wastes were measured on HAAKE viscotester VT 500 with SVI stator.

Effect of concentration of so lids-The measure­ments at room temperature (30°C) were done for all the concentrated wastes including the original raw unconcentrated waste. The respective samples were filled in the stator and the values of viscosity (1') were noted down for different values of applied shear rate (y) by varying the rotor speed. Sufficient time was given to get a steady state reading. The shear stress ('t) values were calculated accordingly for the corresponding shear rate and viscosity. For 60% solid containing concentrated waste, the time taken to get steady state viscosity was significantly larger and hence was monitored separately against applied shear rates.

Effect of temperature-The -flash point and fire point of SO% concentrated waste are considerably high (l90-22SoC and 490-SlO°C)3. So it was thought to examine the variation of the rheological properties of highly concentrated wastes with temperature. The rheological properties at 40, SO and 60°C temperatures were measured only for C5 and C6. The procedure of measurement was akin to that at room temperature measurements, except with the use of hot water bath with HAAKE viscotester.

Effect of suspended solids-All the concentrated wastes as well as the original unconcentrated wastes were filtered using Whatman 40 filter paper and the rheological properties of the filtrate were again measured to observe the effect of suspended solids on the rheological properties .

Results and Correlations

Physico-chemical properties The densities and surface tension values of the raw

and concentrated spent wash are given in Table I. It can be seen from Table I that the density of the concentrated spent wash increased with an increase in the solid concentration as expected. The density variation with respect to the solid concentration has been correlated by the equation, PC=PW+KC ... (5)

Table I-Physical properties of distillery spent wash with different solid concentrations

Waste Density, Surface Boiling points, g/cm3 Tension, °C

at 30°C Dynes/cm

C) 1.05 49 104 C2 1.11 43 105 C3 1.17 40.3 105 C4 1.24 41.3 105 Cs 1.27 40 106 C6 1.29 42.5 109

wh~re pc=Densities of the wastes, kg/m3; pw=Density

of water, kg/m3; lC is a constant and C=concentration of

the wastes in weight fraction. The variation in the surface tension with respect to

the solid concentration also indicate some dependence but is not so strong. The surface tension of the raw spent wash C, ( solid concentration 13%) was 49 dynes/cm and decreased to 43 dynes/cm, when concentrated to 20% by weight of solid. Further concentration to 60%, did not change the surface tension values significantly and remained in the region of 42±2 dynes/cm.

Boiling points at different concentrations

It was observed that during the measurement of the boiling points, up to C5 there was not much increase in the boiling points while it increased considerably for C6. The boiling point values are given in Table 1.

Rheological properties Based on the experimental results the following

plots were drawn .

J. Viscosity (1') versus shear rate for different concentrations at room temperature (Fig. 1).

2. Shear stress ('t) versus shear rate (y) at room temperature for all the solid concentrations, (Fig. 2).

3. Shear stress ('t) versus shear rate (y) for C5 and C6

at different temperatures, (Figs 3 & 4) respectively and

4. Shear stress versus shear rate for the filtered wastes, (Fig. 5)

The general observations from these plots are, a) The viscosity (1') continuously decreased with

an increase in shear rate (y) indicating a shear thinning nature of all the wastes at all coricentrations and at all the temperatures studied in this work (Fig. 1).

188 INDIAN 1. CHEM. TECHNOL. , JULY 1999

6~-----------------------------' Solid conc.ntration wVtraction

-8- 0 ·13 -1- 0 ·30

-1- 0 '20 - - '0·40

5 -x- 0· 50 -¢-0·60

4

2

A

O~~~~~~ o 100 200 300 400 Shear rate. 1/s

Fi g. I- Viscosity versus shear rate at different concentrati ons at room temperatu re.

a CL

vi III • .. 1ft .. 2 L. (/)

l00r-------------------------------~

80

60

40

Solid concentration wt Ifraction

-0- 0 ·13

-.- 0·3 -x- 0 · 5

_--0·2 -~- 0 · 4 -0-0· 6

OL-~ __ ~ __ ~~~~~~~--~~~~ o 100 200 300 400

Shear' rote. Vs

Fig. 2- Shear stress versus shear rate at different concentrations.

b) The shear stress ('t) versus Shear rate (y) plots (Fig. 2) were all straight lines with +ve slopes and +ve 'y ' intercepts indicating the presence of ' yield stresses'. The 'yield stresses' were observed for C5

and C6 at elevated temperatures also (Figs 3 & 4) and even for filtered wastes (Fig. 5).

c) The 't versus y plots at room temperature (Fig. 2) were comparable up to a weight fraction of 0.4 (C4).

For C5, a little increase in viscosity was observed, while fo r C6 a marked increase in viscosity was observed as indicated by the slope of the straight lines.

d) On comparing Figs 2 and 5 it can be seen that the slope of the shear stress versus shear rate plot for C6 was very large compared to the fi ltered spent was h, but such a phenomenon was not observed for lower solid concentrations.

It was al so found that for C6, the values of vi scosity fluctuated in the beginning of the measurement and attained a more or less constant value after a certain time for a ll shear rates and this stab ili zat ion time reduced with an increase in the shear rate.

Rheological modeling of the concentrated distillery wasles-The fundamental objective of the rheological studies was to develop an equation which is able to describe dependence of the viscosity (11) on the shear rate (y) and on the solid concentration of the waste at different temperatures. An attempt was also made to correlate the rheological properties of the C5

and C6 with the variation in the temperature.

Observing the plots of 't versus y at room temperature for different concentrations (Fig. 2) and for C5 and C6 at e levated temperatures (Figs 3 and 4), It appears that ' Bingham model' (Eq. I) is a suitable representation of the flow properties of the di stillery wastes of different solid concentrations and at different temperatures .

In Fig. 2, the slopes are the 11<> values and the 'y' intercept are the 'to values of the different solutions/suspensions at room temperature and are plotted against solid concentrations in Figs 6 & 7 respectively. Figs. 8 & 9 are the plots of 11<> and 'to

against temperature for C5 and C6 . These are again the 'y' intercept and the slopes of the straight lines from Figs 3 and 4, respectively.

The further modeling procedure can be divided into several steps , the first concerning the choice of

~

THAMPI & PANDIT: RHtOLOGICAL PROPERTIES OF SPENT WASH AND CORROSION STUDIES 189

36

Temperature (oC )

34 -6- 30 -+- 40 -1- SO -/;0.- 60

32

~ iii 30 .. e It ... i s:. III

22~~ __ ~ __ ~ __ ~ __ ~~ __ ~ __ ~ __ ~ o 100 200 300 400

Shear rate,lIs

Fig. 3-Shear stress versus shear rate at different temperatures for

Cs·

Temperature (oC)

72 -0- 30 -+- 40 -1- SO -1:>.- 60

62

" Il.

vi III • 52 ... iii ... " • s:. III

42

Shear rate, 115

Fig. 4---Shear stress versus shear rate at different temperatures for Cfi ·

an adequate functional dependence of Jl<> and 'to on solid concentrat~on at room temperature.

Dependence of po on solid concentration at room temperature-From Fig. 6 it may be seen that in

Sold concentration wt . fradion

-0-0·13 -"-0 ·2 -1-0·3 -Ll.-0 ·4 , -x-o·s -<>-0 ·6

40

a Il.

.,; • e OJ ... 1 III 20

10

O~~ __ ~ ____ ~ __ ~ __ ~~ __ ~ __ ~ o 100 200 300 400

Sheaf rate , 115

Fig. 5-Shear stress versus shear rate for filtered concentrated distillery wastes .

general 110 increased exponentially with an increase in the solid concentration . Hence the dependence of Jl<> on concentration can be written as

... (6)

where C=concentration of the waste in weight fraction.

Dependence of yield stress ('to) on Solid Concentration at Room Temperature-From Fig. 7 it can be seen that the 'to values can be related to the solid concentration according to the quadratic equation,

... (7)

where, C=Solid concentration in weight fraction. The complete rheological model of distillery spent

wash for various concentrations at room temperature can be obtained by considering Eqs (1), (6) and (7) together. I.e. 't=27.52-32.89 Gt46.6 C2 +( 0.00 15 e63887 c) y

... (8)

Dependence of j.1,) and 'l'o on temperature for C5

From Fig. 8, it may be seen a linear relationship of Jl<> with temperature whose slope and 'y' intercept values are-4.44x I 0.4 kg/m.s.oC, 0.036 kg/m.s respec-

190 INDIAN J. CHEM. TECHNOL., JULY 1999

0 ·12 .

0 ·1

0·08

II

~ o· co

.JC

0 0 ·04 :l.

0·02

0 0 0 ·1 02 0 ·3 0·4 0 ·5 0 ·6 0 ·7

Solid concentration. wt. fraction

Fig. 6--~" versus solid concentration at room temperature.

26~------------------------------~

2

24

~ 023

.....

22

o 21

20'L-__ ~ __ ~ ____ ~ __ ~ __ .~ ____ ~~ o 0 ·1 0 ·2 0 ·3 0·4 O·S 0·6 0 ·7

Solid concentrations. wt. rr'lction

Fig. 7-1" versus solid concentration at room temperature.

tively. So the dependence of ~ on temperature (to C) IS,

~=0.036-4.44x I 0-4 t .. . (9)

Observing Fig. 9, the relationship of 'to with temperature (to C) can be written as, 'to=7.38+0.756 t-O.OO8 t2

. .. (10)

Considering Eqs (1), (9) and (10) together, the following comprehensive equation has been obtained, based on the assumption of Bingham model (Eq. 1) to explain the effect of the temperature for concentrated spent wash Cs

't=7.38+0.036y+(0.756-4.44xI0-4y) t-0.OO8 (2 .. . (II)

Dependence of j.1o and T" on temperature for C6-

From Fig. 8, it may be seen that for C6 also, ~ varied

0 ·14_------------------------, Said concentration. wt fradion

-0-0·5 -+-0·6

0·'

.. 0 ·08 ~.

~

:f 0 ·06 +

+

0·04

0 ·02

OL-__ ~~ __ ~~~~~~~~~ 20 30 40 50 60 70

Temperature.oC

Fig. 8-~" versus temperatu re.

linearly with temperature with slope and 'y' intercept values as-2.33x1O-3 kg/m. s.oC, 0.1782 kg/m.s respec­tively. So the dependence of ~ temperature (to C) can be written as ~=0. 13-2.33xIO-3 t ___ (12)

From Fig. 9, we can write the relationship of 'to with temperature (l C) for C6 as, 'to=18 .825+0.3025 t-0.OO37 t2

.. . (13)

Considering Eqs (I), (.12) and (13) together, it may similarly ,be written as, 't= 18.825+0. I 782y+(0.3025-2.33x I 0-3 y) t-0.OO37 t2

Discussion Rheological properties

... (14)

Distillery wastes of all concentrations studied, exhibited shear thinning characteristics with yield stress at all temperatures under study (Figs 1, 2, 3 & 4) . All the concentrated wastes and the original unconcentrated waste followed 'Bingham plastic' behaviouL The highly concentrated wastes, Cs and C6,

for which higher temperature studies were also conducted, also showed similar behaviour even at higher temperatures.

These wastes are mostly dispersions with solid particles, which when at rest can build up an inter

THAMPI & PANDIT: RHEOLOGICAL PROPERTIES OF SPENT WASH AND CORROSION STUDIES 191

e. ;,

~~------------------------------~

... 23

22 -x-CS -0-C6

21L-__ ~ ____ ~ __ ~ __ ~~ __ ~ __ ~ __ ~ o 10 20 30 40 SO 60 70

'-~ , ...... ..... -

'...::

Temperature. "t

Fig. 9-t" versus temperature.

-/

a 11k 11k a

h

Fig. l~Eledrostatic interaction between two charged particles.

molecular/inter particle network of binding forces (polar forces , Van der Walls forces etc). These forces restrict positional changes of volume elements and give the waste a SQlid character with an infinitely high viscosity below the critical shear rate. Forces acting from outside, if smaller than those forming the network, will deform the shape of this solid substance elastically. Only when the outside forces are strong enough to overcome the network forces -increase beyond the threshold shear stress called the ' yield stress' -does the network collapse. Volume elements can now change position irreversibly: the solid turns into a free flowing liquid.

It is reported4 that particle interactions 'and hydrodynamic coupling together with the Brownian motion and an imposed flow field lead to the special correlation between particles, which in tum determines the non-linear rheological behaviour of a suspension. While a repulsive interaction leads to an ordered liquid-like structure for sufficiently high particle concentrations, an attractive interaction may

lead to the formation of particle clusters and even in to a continuous network. The aggregation state of the dispersed phase is determined by a number of factors, essentially bound to the geometric and surface features of the particles (dimensions, shape, presence of charges or adsorbed compounds), to their density and to the specific field condition (temperature, hydrodynamic conditions, presence of other compo­nents in the fluid phase) . In the absence of an effective stabilizing action (of electrostatic and/or steric nature), particles do aggregate among themselves to an extent to which the rheological properties are affected substantially. This is mainly a function of the particle dimensions. Thus particle aggregation may lead to the formation of very large­particle clusters in colloidal systems. Even in coarse particle suspensions, a temporary aggregation can eventually be observed, depending on particle concentration and intensity of the applied field5

.

The structural alteration of particle aggregates accompanying the application of a stress field are the main factors responsible for the non-linear properties of aggregated dilute and concentrated suspensions. At rest, when particle concentration is sufficiently high, the aggregated dispersed phase may span the entire space from wall to wall, thus conferring to the system those mechanical characteristics, typical of a gel state, where as under flow conditions, it breaks down into smaller clusters, having shapes and dimensions which change from system to system and with the intensity of flow. Correspondingly the viscosity decreases with an increase in shear rate or shear stress, and this shear dependence is a function of the dispersed phase concentration.

The theory of Brownian movement can be well applicable to these wastes at lower concentrations as the general rheological bahaviour remained same even after filtration through Whatman-40 filter paper indicating that these wastes are micoemulsions of particles in a continuous media.

A useful approach in understanding the physicochemical relationship of colloids and lattices to their rheology is the two-body interaction potential modef. The flow unit that describes the viscoelastic nature of structured suspension is the elastic floc model6

. The distillery waste being an aqueous media is electrostaticaliy stabilized. The interaction of two charged particles is shown in Fig. 10. The intersurface distance is 11, the double layer parameter

192 INDIAN 1. CHEM. TECHNOL., JULY 1999

Table 2--Corrosion rates of various metals

Metal strips Weight (g) at different time (h) Corrosion rate, Oh 3h 6h

M.S 15.36 15.3 15.27

S.S-316 22.77 22.77 22.77

S.S-316L 30.81 30.8 30.8

S.S-304 40.55 40.54 40.54

is 11k, and the radius of the particle is a. The total interaction between the two particles is given by,

... (15)

where Ua11r is the attraction term and Urep is the repulsion term between the two particles, respectively. The repulsion potential to the surface potential <j>R, and the dimensions of k, a, and h may be related by

... (16)

where Er is the relative permittivity of the solution and f{) is that of free space. The attraction term is related to the composite Hamaker constant A. The attraction potential is now given by

Aa U --­

alrr- 12h .. . (17)

When the concentration increases, h decreases and from Eqs (16) and ( 17) it may be seen that the increase in Uattr will be more than that in Urep and this will hamper the electrostatic stabilization and which will result into cluster formation . The cluster formation and the Brownian movement act in the opposite direction to control the rheological beh,\vior of distillery waste . At low concentrations the Brownian movement of the particle are much higher, when an external shear force is applied. Due to which the yield stress ('to) is high . As the solid concentration goes on increasing the Brownian movement decreases due to the reduced amount of continuous phase and less flow area available for solid motion . So the stress ('to) starts decreasing. Beyond a certain critical concentration (0.33 weight fraction in this system) the cluster formation dominates over the decreasing Brownian movement and the particles start entangling into each other to form a network and the yield stress

('to) increases again (Fig. 7) . The relationship between Ilo and solid

concentration (Fig. 6) is in agreement with the observations of Heaton et aC for coal-water mixture.

8h II h glm2h

15 .26 15.22 17.768

22.77 22.77 0

30.8 30.8 0.9468

40.54 40.54 0.673

They observed that slight dilution of highly-loaded slurries causes viscosity to decrease drastically. In the case of distillery waste also the viscosity of the 60% concentrated waste is much higher than that of other concentrations.

The over all rheological properties of the filtered wastes a lso remained same after removing the suspended so lids. This clearly indicate that the over all rheological properties are more or lessdue to the characteristic of the di ssolved solids and the solvent phase. The dependence was more prominent at higher concentration , ie for C6. For the filtered C6 the slope of the shear stress versus shear rate plot was comparable with other concentrations. This was not the case with the unfiltered C6 (Figs 2 and 5) . In the case of filtered wastes the plots of shear stress versus shear rate were all almost parallel lines . This clearly indicates, the build up of shear stress is depended on the suspended solids and their inclination to form clusters. This can be attributed to the increased Newtonian characteristics of the filtered wastes. C6

ex perienced the maximum shear stress when it was not fi Itered.

Corrosion studies Weight loss due to corrosion-The weights of the

met~l strips at different time intervals of evaporation are tabulated in Table 2 from which the weight loss at each time interval can be calculated. From Table 2 it cim be observed that the weight of M.S . decreased continuously while that of S.S-316L and 304 decreased in the first three hours only. In the case of S.S-316 there was no weight loss during the experiment.

Mild steel exhibited a maximum corrosion in II h with a corrosion rate of 17.768 gmlm2h. There was no measurable corrosion during an evaporation period of II h in the case of S.S-316. In the case of S.S-316L and S.S-304, they corroded during the first three hours of evaporation on ly with a corrosion rate of 0 .9486 gmlm2 hand 0.673 gmlm2 h respectively and after­wards there was no additional corrosion. This is

THAMPJ & PANDIT: RHEOLOGICAL PROPERTIES OF SPENT WASH AND CORROSION STUDIES 193

probably due to the fonnation of a thin oxide film during the first few hours of evaporation which prevents further corrosion in the case of SS 316L and SS 304.

Conclusion The surface tensions of concentrated dist illery

wastes do not depend on the solid content of the wastes beyond a solid concentration of 20%, it remains more or less the same. The densities increase with an increase in solid concentration .

The general rheological behavior remains same i.e Bingham plasti c' , at different concentrat ions and

temperatures . The exact dependence on concentration of solids and temperature could be corre lated by a unifi ed equation. The rheological properties viz. viscosity are not changing sign ificantly with temperature for low solid concentrati on but change significantly for higher solid concentrati ons. The proposed equations (Eqs (4) to (14)) corre late the solid concentrat ions with rheological properties fo r all the wastes at ambient temperature, and fo r higher concentrated wastes it accounts fo r the effect of temperature also. The corre lations appear to be suitable to describe and predict the shear vi scosity -over a wide range of concentrations and temperature for di stillery wastes.

From the corrosion study, S.S-31 6 seems to be the best materia l of constructi on to process distillery waste ie evaporation and concentrat ion .. The studies

of the rheological properties and corrosion will help in the design of effective concentration and incineration system for the distillery waste .

[Note : Room temperature indicates a temperature of 30°C] .

Acknowledgment Prof. D.O. Kale, Head and Professor of Polymer

Tec hnology, Mr. Tipanna Mariappa, Plast ics and PPY divi s ion, Prof. S.G . Dixit , Head of the Chemistry di vision and Mr. Matha is Sequiera, Chemistry d iv ision, UDCT are being gratefully acknowledged for the ir co-operation during thi s research work.

References I Bird R B. Stewart. W E & Lightfoot E N, Transport

PhenolllelJa. John Wiley, ew York , ( 1960) 10. 2 Rohn C L. Analvtical Polymer Rheology, Structure·

Processillg ·Propertv Relationships (Hanser Publishers, Munich Vicn na New York), 1995 , 189.

3 Nishani H M. Chem Ellg Seminar, Universit y of Bombay, 1994.

4 LCl pas in R. Grossi M & Pricl S, Chelll Eng J, 64, (1996) 99.

5 Graham AI , Steele R D & Bird R B, In d Eng Chem Fundam, 23 (1984) 420.

6 Van De Van T G M & Hunter R J, Rheol Acta 16, (1977) 534.

7 Heaton H L & Me Hale E T, in Second European Confe rence on Coal Liquid Mixtures, EFCE Event Number 327, The Institution of Chemical Engineers, Symposium Series No. 95, 226.