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CHAPTER 3

EXPERIMENTAL INVESTIGATIONS 3.1 GENERAL Basis of selection of the wastewaters namely pharmaceutical and surfactant

wastewaters and two soils and their characteristics, details of the chosen experimental

set-up and the experimental scheme adopted for the study are presented and discussed

in detail in this chapter.

3.2 WASTE WATER SELECTION AND CHARACTERISTICS

3.2.1 Selection of Wastewater

Based on a preliminary survey covering the various industries located around 25-50

km radius from this region (ie. Puducherry and its environs), a few types of process

industries which produce pharmaceutical and surfactant wastewaters, which are

considered to be potentially polluting and whose impact on the environment needs

constant monitoring were identified. Further, critical review of literature has also

revealed that studies on the effect of certain type of wastewaters, such as, surfactant

and pharmaceutical wastewaters, etc., on soils are rather rare or scarce . In view of the

above, the two types of wastewaters, namely, pharmaceutical and surfactant were

selected for the present study, which are referred to as WW1 and WW2 respectively,

in this Thesis. WWl is an antibiotic molecules based pharmaceutical effluent.

Surfactants or surface active agents are amphipathic of polar/ hydrophilic head and a

non-polar/hydrophilic 'tail'. When added to water, a surfactant molecule may dissolve

as a monomer, and/or absorbed to an interface with its hydrophilic end pointing away

from the water. Surfactants are of ionic and non- ionic type. The surfactant

wastewater (WW2) used in this study belongs to "ionic" type. Synthetic detergents

have been increasingly used in recent years due to their extensive applications in

domestic life, agriculture and industry. Synthetic detergents when released

inadvertently/indiscriminately either into the aquatic system or on soil affecting the

ecosystem drastically. Thus the chosen wastewaters WWl and WW2 are not only

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significant from an Engineering point of view, but also, from the point of view of

society at large, for studying and understanding their effect on various types of soils.

3.2.2 Source and Collection of Wastewaters

The wastewater-WW1 was collected from a private process industry located in and around Puducherry region of Union Territory of Puducherry, South India, manufacturing Penicillin – G, a base derivative for manufacturing a host of antibiotics. The above untreated wastewater was manually collected continuously for a period of one year, at intervals of every 3 months, from the equalization unit (ie before treatment) of the respective industries in 40 litres plastic cans ( air tight containers) and then brought to the laboratory where they were stored in a deep freezer. The temperature of the deep freezer was maintained at 4°C, to avoid degradation and subsequent change of concentration of pollutants present in the samples. WW1 thus collected and stored, was diluted to get the required concentrations for characterizing it and for carrying out the experimental investigations contemplated in the present study. Wastewater characteristics in general are known to vary with time (ie day/season etc), which has to be realized in obtaining their characteristics and in using them for various investigations. Therefore, one year period adopted for collection of WW1 is expected to cover a full cycle of operation and realize the various operating conditions of a typical process industry and also serve as a representative sample reflecting the characteristics of the chosen process industry, namely the pharmaceutical industry manufacturing Penicillin - G

As surfactant wastewater from an industrial source in this part of the region is found to

be a mixture of oil, grease, scum and undigested organic / inorganic residues, they are

likely to interfere with the behaviour of surfactant alone, it is decided to use a synthetic

wastewater prepared using a common detergent. The above wastewater (referred to as

WW2) is expected to offer an “interference – free” behaviour with the chosen soils.

3.2.3 Wastewater Parameters Estimated

The experimental parameters considered for the study are: pH, electrical conductivity, chloride, sulphate, total solids (TS), total dissolved solids (TDS) and chemical oxygen demand (COD). The above parameters are used to characterize the wastewaters based on the Standard Methods for the Examination of Water and Wastewater (APHA,

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2005), and for the outflow from the experimental set-up i.e. soil-column, at specified intervals. The above parameters are comprehensive and sufficient to characterize the wastewaters and to understand their effect on chosen soils. Apart from pH (which is measured immediately on collection), all other parameters are determined only in the laboratory.

3.2.4 Analytical Procedure

The analytical procedures adopted for the estimation of various wastewater parameters

and the instruments used in this study, are very briefly described in Appendix A.

3.2.5 Characteristics of Wastewater

The characteristics of the sample of wastewaters (namely, pharmaceutical and surfactant) were analyzed adopting the standard test procedure and the results obtained are given in Tables 3.1 and 3.2 respectively. The values indicated are based on a few trials and for each trial the standard acceptance criteria was applied. The range indicated cover the characteristics of wastewater collected/used over the stipulated period of time.

Comparing the characteristics of the sample of pharmaceutical effluent (Table 3.1)

with that of the stipulations in Indian standards i.e. IS: 249O, IS: 33O7 and IS: 3306

and on critical analysis of salient characteristics, following inferences are drawn:

(i) The above wastewater is very highly acidic (pH 3-4);

(ii) TDS present in the above wastewater is very high ie. about 10 times

higher than the prescribed limit set in IS 3306 for disposal onto a water

body and

(iii) The COD values present are extremely high indicating the presence of

high organic content in the wastewater. Moreover, the WW1 is highly

toxic due to the accepted presence of antibiotics and its various

intermediates (recalcitrant in nature ie. not easily degradable), which will

completely destroy the nutrients and the beneficial microbes present in a

soil mass, if it is indiscriminately disposed on land. Further, natural

degradation of the toxic elements will take a very long duration of time to

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attain a stable state due to the absence of supporting nutrients required for

initiation and completion anaerobic reactions.

Similarly, based on the analysis of the characteristics of WW2, following inferences

are drawn:

(i) The above wastewater is medium alkaline (pH:6-12) in nature;

(ii) TDS present is about 4 times higher than the permissible value as stipulated

in IS 3306;

(iii) Chlorides and sulphates present is about 3-4 times higher than the

permissible values as stipulated in IS 3306;

(iv) COD values present are extremely high, indicating the presence of very

high organic content in the wastewater and

(V) The uniqueness of the above wastewater is the accepted presence if linear

alkyl benzene sulphonate (LABS) a predominant constituent of surfactant,

which is reported to form a 'layer of scum' and 'impart imperviousness' on

the soil mass, if it is indiscriminately disposed on land. The scum

formation will render the soil mass super-saturated and will also lead to a

rapid spreading of the polluted area.

Comparing the various characteristics of the two wastewaters the uniqueness of the

WW1 and WW2 can be summarised as: (i) pharmaceutical - toxic and organically

recalcitrant and (ii) surfactant - highly organic and imparts imperviousness. Salient

extract of values from IS: 2490, IS: 3307, IS: 3306 are given in Appendix B.

The chemical characteristics of wet mycelium fibres present in WW1, dry mycelium

fibres and mycelium fibres with soil obtained from the dumping site were determined

by standard methods and results are presented in Tables 3.4 to 3.6. It can be seen that

the COD, TS and TDS are very high in the wet mycelium fibres when compared to

that of other fibres. The above characteristics are expected to have unique interaction

with fine-grained soils. Further, even after exposing to the atmospheric conditions for

several years. There is substantial COD, TS & TDS in the fibres obtained from the

dumping site. This proves the recalcitrant nature of WW1 and the fibres present in it.

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3.3 CHARACTERISTICS OF SOILS

3.3.1 Selection and Source

Based on a preliminary survey of existing soil types of this region (ie., Puducherry,

South India) and based on the reported results in literature that the influence of

effluents are generally predominant only in fine-grained soils, soil samples were

collected from two different locations from the region. Representative soil samples

from the identified locations were collected in 50 kg capacity air tight polythene bags

and brought to the laboratory and stored in air tight containers under normal laboratory

temperature until actual use. The natural soils thus collected are henceforth referred to

as S1 and S2.

3.3.2 Analyses of Soil Samples

(A) Tests Conducted Generally, tests are conducted on soils to determine their index properties, strength and deformation characteristics. However, as the primary process of the present study is to understand the basic behavior of soils when they are artificially contaminated with industrial wastewaters, only index properties and salient strength characteristics were evaluated for all types of soils, before and after they were artificially contaminated with wastewaters. Accordingly, following tests were conducted on the soil samples for charactering the soils and for understanding their behaviour after artificially contaminating them with industrialwastewaters:

(1) Visual observations (2) Specific gravity (3) Grain size analysis (including hydrometer method for grain sizes smaller

than 75microns) (4) Atterberg's limits (liquid limit, plastic limit, shrinkage limit) (5) Proctor compaction test (6) Unconfined compressive strength test (UCC test) (7) Sophisticated method of analysis : (a) GC-MS Spectrometer analysis (b) SEM & EDXA (c) XRD - Analysis

Brief description of the above tests are given in Appendix C, E, F and G.

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(B) Characteristics of Soil Samples Results of the various tests on the chosen soils are summarized in Table 3.3. Based on

the above results and on comparing with the IC code stipulations for classification of

soils (IS: 1498-1970) following inferences are drawn:

(i) Both soils S1 and S2 belong to silt and clays of high compressibility and

exhibit medium to low shrinkage.

(ii) S1 is classified as a silty clay, where as S2 is a clayey silt soil, based on

grain size distribution.

(iii) The chosen two soils have distinct characteristics. As the clay content is

the highest in S2, it is expected to be affected to a larger extent than S1,

which contains least amount of clay content.

The soils were evaluated for its chemical characteristics, adopting standard methods of

tests and the salient characteristics are given in Tables 3.7 and 3.8. It can be seen that

S2 has larger concentration of inorganic pollutants in its native form than S1.

3.4 EXPERIMENTAL PROGRAMME

3.4.1 Choice of Experimental Set-up

Several investigators have studied the soil-pollutant interactions by a few methodologies as summarized in Table 3.9. It is seen that the flooding method has been widely used for studying the effect of wastewaters on different types of soils. On the other hand, one-dimensional column method is best suited to understand the soil-pollutant interactions. Further, the above method permits investigation of soil-pollutant interactions under various flow rates and retention times. Hence, in the present study one-dimensional soil-column method was selected and adopted. Of the several investigators who have adopted one-dimensional soil- column, only Drewes and Fox (1999) have investigated the variation of flow rate and concentration of pollutant/(s) with respect to hydraulic travel times. As one of the objectives of the present study is to understand the physico-chemical behaviour of soil-pollutant interactions under various modes of operations, the methodology adopted for Drewes and Fox was selected from among the various approaches reported in literature.

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The expenmental set-up adopted by Drewes and Fox was for study of the

characteristics of recalcitrant compounds (DOC- Dissolved Organic Carbon ) in

ground water (i.e. raw water) through a soil-column. The above soil- column system

simulates aquifer conditions in a series four 1 meter columns (diameter 140mm) and

was operated under saturated, anoxic- redox conditions. Soil samples were collected

twice a week after flow through each 1 meter column corresponding to hydraulic

travel times of approximately 5,10,15 and 21 days. In fact the experiment conducted

by Drewes and Fox (1999) was only under a batch mode of operation and the

hydraulic travel times adopted were found to be too large. Hence, the above

methodology cannot be considered as true representation of field conditions. It was

therefore decided to consider the methodology of Drewes and Fox (1999) as a

conceptual model and modify it to suit the present investigations and to represent

field conditions.

3.4.2 Description of Experimental Set-up

The experimental setup consisted of eighteen laboratory soil columns (identical in

shape and size) fabricated and mounted on a steel frame work as shown in Figs. 3.1.

Each soil column of Perspex material was made by joining 90 mm diameter and 600

mm height Perspex pipe with a hopper portion made of brass material and having a

flange. The hopper portion was fitted with an outlet control valve to regulate the flow,

which in turn was connected to the drain outlet. The hopper portion was also provided

with a stainless steel wire mesh to prevent the soil particles from being washed away.

A drain pipe was provided to collect the effluent from the drain outlet. The effluent to

the soil columns was fed through a feed tank made of PVC, fitted with an inlet control

valve for maintaining the flow rate. Fig. 3.2 shows a schematic view of a single soil

column.

The soil columns are graduated in cm from bottom to top. The soil columns are

marked as CT (chemical column) and as ST (soil column). Samples of effluents were

collected through the drain valve and from two lateral probes connected to the soil

column at 20 cm and 40 cm from the bottom of the soil column marked as CT, and

were used to obtain various monitoring parameters by standard tests/methods. Soil

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samples were collected from columns marked as ST at regular intervals of 15 days and

also around the point of attainment of peak accumulation of chlorides, sulphates and

COD in the soils, for determining the soil parameters like liquid limit, plastic limit,

shrinkage limit and UCC values.

3.4.3 Experimental Scheme

(A) Modes of operation

The fabricated experimental set - up was used for two modes of study, namely (i)

batch - mode and (ii) continuous - mode, with varying hydraulic retention times

(HRTs). 'HRT' is defined as time taken by the first droplet of the effluent to flow from

inlet to outlet of soil column. The batch-mode was operated to study the chemical

equilibrium that gets established between various types of soils and the pollutants of

the wastewaters, whereas, continuous-mode of operation was aimed at analyzing and

reporting" soil-pollutant interactions (with respect to HRT) as applicable to field

conditions (i.e. discharge of wastewater on soil is continuous with varying flow rate

and concentration of pollutants). It (i.e. continuous mode) is intended to explain the

mechanism involved and suggest possible measures for the remediation of

contaminated site.

In fact comprehensive review of literature reveals that only a few attempts have been

made so far to conduct experiments under continuous-mode and hence to understand

the effect on soil- pollutant interactions simulating field conditions. Hence, both the

modes of operation were employed in the comprehensive experimental investigations

reported in this study. 48 hours was assumed as the empty bed dry period between the

two-modes of operation, which is the minimum period stipulated in the literature.

( B ) Preparation of Soil Specimen and Operating Scheme

Soil samples (weighing about 3.6kg) were loaded in the soil columns and light

compaction was done with wooden rammer. Wastewater were added to the effluent

feed tank and were allowed on to the soil columns containing soils using flow control

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valve. Chemical analysis was carried out for the outlet effluent collected from the soil-

columns marked as CT and soil analysis was performed for the soil samples collected

from soil-column marked as ST for the respective soils. Soil samples weighing about

300 gm were collected at intervals of 15 days both in batch-mode and in continuous-

mode of operation and around the point of peak accumulation of chlorides, sulphates

and COD in the soils during continuous mode. Effluent samples from the drain outlet

were collected at an interval of 24 hrs during batch-mode and at intervals of 8 hr and

16hr during continuous mode of operation.

The basis of selection of the various HRTs are :

(i) Any process industry is operated in shifts of 8 hours duration. Hence, 8 hours HRT can represent one shift and it also represents a shock-load imparted to soil (sample ) at maximum flow rate and concentration of pollutants.

(ii) On the other hand, 16 hours HRT represents a situation where in the flow and the concentration of pollutants are likely to be minimum.

Wastewater of volume 1.2 liters was used to fill the feed tanks for batch-mode of

operation. However, for continuous-mode of operation, flow rates for the various soils

and for the various HRTs considered were calculated based on the porosity of the soil

samples at the end of the batch mode. The flow rates thus arrived at for various types

of soils are summarized in Table 3.10. The methodology adopted to arrive at the flow

rates for the various HRTs are outlined in Appendix D.

3.5 SUMMARY

The natural soils (S1 to S2) were specifically selected to study the effect of two chosen

industrial wastewaters (pharmaceutical and surfactant) on them due to their artificial

contamination. The various soils and wastewaters selected were characterized by

standard methods and their uniqueness identified. An experimental set-up of one

dimensional soil-column, based on the experimental study by Drewes and Fox was

selected and slightly modified to suit the objectives and certain uniqueness of the

present study. The salient features of the experimental set-up chosen and adopted and

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the experimental scheme proposed for the present study have also been briefly

described.

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Table 3.1 Salient characteristics of pharmaceutical wastewater (WW1)

Sl.No.

Parameter

Pharmaceutical (E1)

1 pH 3.0 – 4.5

2 Electrical conductivity (µS/cm)

800 - 1350

3 Chloride

1000 - 3000

4 Sulphate 200 - 4000

5 Chemical oxygen demand

15000 - 22000

6 Total solids

20000 - 40000

7 Total dissolved solids

8000 – 20000

8 Total suspended solids 12000 - 20000

Table 3.2 Salient characteristics of surfactant wastewater (WW2)

Sl.No.

Parameter

Detergent (E2)

1 pH 6.0 – 12.0


12 - 40

3 Chloride

1500 -2100

4 Sulphate 150 – 3500


8000 – 11200

6 Total solids

8000 – 15000


5000 – 10000

8 Total suspended solids 3000 - 5000

Note: (*) – All values in mg/L, except pH and electrical conductivity.

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Table 3. 3 Characteristics of soils (S1 & S2)

Sl. No.

Soil Properties S1 S2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

(A) Visual classification Colour Odour Texture (B) Index properties Liquid Limit (%) Plastic Limit (%) Shrinkage Limit (%) Specific gravity (C) Sieve analysis % of sand (D) Hydrometer analysis % of clay % of silt (E) Proctor compaction test Maximum Dry Density (kN/m2) Optimum Moisture Content (%) (E) Unconfined compressive strength (qu) (N/mm2) (F) Classification Compressibility Swell

Black Organic Mixed grained fraction of fine grained soil 60.80 30.00 15.20 2.95 11.0 09.3 90.70 15.8 29.0 0.184 CH High High

Grey Organic Mixed grained fraction of fine grained soil 71.50 25.40 15.60 2.39 02.0 57.6 42.4 14.2 33.5 0.192 CH High High

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Table 3.4 Salient chemical characteristics of wet Mycelium fibres

Sl.No.

Parameter

Values

(average)

1 pH 3.8


1320

3 Chloride

1324

4 Sulphate 1040


14340

6 Total solids

18300


11000

Table 3.5 Salient chemical characteristics of dry Mycelium fibres

Sl.No.

Parameter

Values

(average)

1 pH 4.1


1286

3 Chloride

965

4 Sulphate 896


3220

6 Total solids

8100


7900

Note: (*) all values in mg/L, except pH and electrical conductivity

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Table 3.6 Salient chemical characteristics of soil affected by Mycelium fibres (5 yrs contact period)

Sl.No.

Parameter

Values

(average)

1 pH 5.2


1074

3 Chloride

782

4 Sulphate 702


2640

6 Total solids

5100


1100

Table 3.7 Salient chemical characteristics of Soil S1

Sl.No.

Parameter

Values

(average)

1 pH 6.50


550

3 Chloride

456

4 Sulphate 365


1180

6 Total solids

3400


300


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Table 3.8 Salient chemical characteristics of Soil S2

Sl.No.

Parameter

Values

(average)

1 pH 6.42


1006

3 Chloride

615

4 Sulphate 520


6040

6 Total solids

5700


4700


Table 3.9 Overview of methodology for soil – pollutant interaction studies

Sl. No.

Methodology Investigator/(s) Year

1

2

3

Flooding condition

1-advective-diffusive-dispersive Mixing of sand with oil

Sridharan & Rao

Rowe &Badv

Al-Sanand et al

1979

1996

1995

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Table 3.10 Flow rate for continuous mode of operation

Flow rate (ml/min) Sl. No.

1 2

Wastewater

Pharmaceutical

Surfactant

HRT (hr)

8

16

8

16

S1

1.073

0.84

1.94

0.97

S2

0.76

0.34

1.62

0.81

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Fig. 3.1 Photograph showing the fabricated experimental set-up

1 400 1. Feed Tank (140mm Ø X 450mm)

2. Inlet Control Valve 3. Inlet Feed Tube(8mm Ø)

4. Soil Column (90mm Ø X 600mm) 3 2 120 5. Wire Mesh 6. Hopper Portion

7. Control Valve 8. Drain Outlet (8mm Ø) 9. Drain Pipe (50mm Ø)

4 600

(All dimensions are in mm) 5 6 135 7

8 200 9

Fig. 3.2 Schematic diagram of a single soil-column

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