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CHAPTER 3

MATERIALS AND METHODS

3.1 INTRODUCTION

This chapter explains the hybrid methodology adopted for the

treatment of tannery wastewater. The materials such as the tannery

wastewater and its characterization are detailed. The experimentation was

done in three modules. Electrocoagulation process was optimized with

respect to various parameters so as to be integrated to membrane process.

Then, the dead end filtration mode was selected for preliminary experiments

to check the feasibility of the hybrid process in mitigating fouling and

increasing the performance of the membrane. Then the hybrid process was

extended to submerged membrane system. The various analytical techniques

used for the substantiation is also introduced in this chapter.

3.2 MATERIALS

3.2.1 Tannery Wastewater

Wastewater from the tanneries contains high biochemical oxygen

demand (BOD), chemical oxygen demand (COD), sodium sulphide and

suspended solids (Al-kdasi et al 2004, Vijayaraghavan and Murthy 1997,

Iqbal et al 1998). In Tamilnadu, the ground water regime in upper Palar basin

has been adversely contaminated by the large volume of tannery wastewater

discharged, hence requires effective treatment practice. The tannery

wastewater used in this study was collected from Common Effluent

Treatment Plant (CETP) located at Pallavaram, Chennai. The wastewater

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generated from 150 tannery units were connected to this common effluent

treatment plant (CETP). Figure 3.1 shows the flow diagram of the treatment

process carried out in CETP. This plant uses chemical coagulation as primary

treatment and the supernatant is subjected to secondary treatment by

Activated Sludge Process (ASP). After this the wastewater is finally passed

through an activated carbon filter (tertiary treatment) before disposal. The

wastewater from the equalisation tank, after the initial screening (to remove

the hides and skins) was collected, just before the primary treatment. The

samples of effluents were collected and stored in deep freezer at 40C until

use. The wastewaters were characterized for BOD, COD, pH, solids,

dissolved salts, color and chromium by using the standard methods (Clesceri

et al 1998).

Figure 3.1 Flow diagram of treatment procedure of tannery

wastewater adopted at CETP

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It is suggested that due to the high salt concentration in the

wastewater, electrocoagulation would be more effective than chemical

coagulation and high quality water can be achieved after a membrane

filtration step. The typical characteristics and the discharge guidelines of the

wastewater as per the Tamilnadu Pollution Control Board (TNPCB) are

presented in Table 3.1.

Table 3.1 Tannery effluent characteristics and its standard discharge

norms according to TNPCB

PARAMETERS VALUESSTANDARD

NORMS

1. pH 7.4±0.1 5.5 – 9.0

2. Electrical conductivity 8.46 mmho/cm Not Available

3. Total Solids (TS) 7055± 100mg/L 2200 mg/L

4.Total Dissolved Solids

(TDS)4675± 70mg/L 2100 mg/L

5.Total Suspended Solids

(TSS)2380± 85mg/L 100 mg/L

6.Chemical Oxygen

Demand (COD)1600 ± 60 mg/L 250 mg/L

7. Chromium content 15 mg/L 2.0 mg/L

8. Colour Black colourless

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3.2.2 Synthetic Wastewater

Dead end filtration experiments were carried out in the second phase to

study the removal of heavy metals in model wastewater and its effect on membrane

fouling. The synthetic wastewater was prepared from a stock solution of

1000ppm (1 L) of each metal with sulphate salts of Cadmium, Nickel and

Zinc. Electrocoagulation experiments were conducted with different

concentrations of metals by diluting the stock solution.

3.2.3 Chemicals

All the chemicals used in the study were analytical grade.

3.2.4 Membranes

A membrane is a material that forms a thin wall capable of

selectively resisting the transfer of different constituents of a fluid and thus

effecting a separation. Thus, it should be made with a material of reasonable

mechanical strength that can maintain a high throughput of a desired

permeate with a high degree of selectivity. Membranes are made of either

polymeric or ceramic material. Polymeric membranes are more feasible over

ceramic in low cost production, but are prone to fouling and degradation

because of variations in pore size, which occurs naturally during casting.

Almost all the MBR manufacturers use polymeric microfiltration membranes.

Table 3.2 shows different common materials used to make polymeric

membranes.

The most commonly used polymeric materials are celluloses,

polyamides, polysulphone, charged polysulphone and other polymeric

materials such as polyacrylonitrile (PAN), polyvinylidene difluoride (PVDF),

81

polyethylsulphone (PES), polyethylene (PE), and polypropylene (PP). The

PVDF membrane with meticulous pore-size distribution is renowned for

outstanding chemical durability, high flux ratio and rugged physical stability.

Its low cost and simple chemicals for cleaning compared to other membrane

materials makes it apt for industrial wastewater treatment application.

Table 3.2 Common polymeric membrane materials and its characteristics

(Layson 2004)

Polymeric material

and abbreviationAdvantages Disadvantages

Polypropelene (PP) High range pH tolerance

Low cost

Expensive cleaning

chemical required, no

chlorine tolerance

Polyvinylidene

fluoride (PVDF)

High chlorine tolerance

Low cost

Simple cleaning

chemicals

Cannot withstand pH>10

Polyether sulphone,

polysulphone

(PES/PS)

Chlorine tolerance

Reasonable cost

Brittle material which

requires support

Polyacrilonitrile

(PAN)

Typically used for UF

membranes, low cost

Less chemically resistant

than PVDF

Cellulose Acetate

(CA)

Low cost Narrow pH range and

biologically active

Two forms of membranes of PVDF material (Figure 3.2) were used

in this study. A flat sheet microfiltration membrane of 0.22µm (GVWP14250,

Millipore) was used for dead filtration experiments and a submersible hollow

fibre membrane module rated at 0.1µm with 125 fibres per module was used

for submerged membrane system. The microfiltration membrane fibres were

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hydrophilic and 344mm long with inner diameter of 0.9 mm and outer

diameter of 1.5mm. The membrane porosity was 75-80%.

(a)

(b)

Figure 3.2 Photographs of (a) flat sheet and (b) submersible hollow

fibre membrane module

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Physical cleaning of the membrane was done by removing it from

the reactor and washing it under tap water and then with de-ionised water

to remove the cake layer adhered on to the membrane. Chemical membrane

cleaning was done by soaking it in 0.4% NaOH (w/v) to remove the

organic pollutants adhered into the membrane and 0.3% HCl (v/v) to

remove inorganic materials, for 1 h and then in 1% NaOCl solution overnight

(Meng et al 2006).

3.3 DEAD-END FILTRATION EXPERIMENTS

The most basic form of filtration is dead-end filtration. The

complete feed flow is forced through the membrane and the filtered matter is

accumulated on the surface of the membrane. The dead-end filtration is a

batch process as accumulated matter on the filter decreases the filtration

capacity, due to clogging. A next process step to remove the accumulated

matter is required. Dead-end filtration can be a very useful technique for

concentrating compounds. There are two types of filtration which can be

employed in a dead end cell unit; dead-end microfiltration with constant flux

and dead end microfiltration with constant pressure drop.

The dead end microfiltration with constant flux ensures that the

permeate flux through the filter remains constant, this filtration can be

achieved by positive displacement pump. As the cake build-up increases with

time, the pressure drop must be increased to maintain constant flux. In dead

end microfiltration with constant pressure, as the cake build-up with the time

the permeate flux decreases (Munir 2006).

In this set of experiments, electrocoagulation was first optimized

with respect to various operating parameters and then integrated with dead

end filtration.

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3.3.1 Optimization of Electrocoagulation (EC)

Before integrating electrocoagulation with membrane process, it

was optimized with respect to various operating parameters for the treatment

of tannery wastewater and synthetic wastewater containing heavy metals.

Since tannery effluent contains large amount of salt (NaCl), the effect of

supporting electrolyte was omitted, where as a small amount of NaCl was

added as supporting electrolyte in the case of model wastewater. EC was

operated also to find the increase in the Biodegradability Index (BI) of the

wastewater. Table 3.3 shows the different parameters optimized for both the

wastewater samples and the corresponding pollutant removal.

Batch electrocoagulation process was done in an electrolytic cell

consisting of a glass beaker of 250 ml capacity. Aluminium with a submerged

area of 17.6 cm2 in size was used as sacrificial anode while stainless steel of

same size was used as cathode and was fixed vertically and parallel to each

other with an inter electrode distance of 2.5 cm during electrolysis. A direct

current was supplied by a DC-regulated power source (METRONIC model

ME-305A, 0–5A and 0–30V). The electrodes were cleaned manually by

abrasion with sand paper and by the treatment with dilute hydrochloric acid

followed by washing with distilled water prior to every experimental run. The

pH of the effluent was adjusted by adding hydrochloric acid (HCl) or sodium

hydroxide (NaOH) solution. The uniform concentration condition was

maintained by constantly stirring the effluent at a speed of 150 RPM with a

magnetic stirrer. All the experiments were carried out at room temperature

(30oC).

The samples were collected at regular intervals of time and

analyzed for the removal of COD, BOD and colour as per standard method

(APHA 1999). BOD was analysed to check the change in the biodegradability

index of tannery wastewater during electrolysis. Biodegradability index is the

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ratio of BOD to COD value of the effluent and should be above 0.4 for an

effective biodegradation. A digital calibrated pH-meter was used to measure

the pH of the wastewater samples before and after the treatment.

Table 3.3 Different operational parameters for both the wastewater

samples and the corresponding pollutant removal

Type Electrocoagulation

Tannery

Wastewater

Parameter Condition Removal

Current density (mA/cm2) 10,15, 20

COD & ColourpH 5, 7.4, 9

Anode material Al

Synthetic

Wastewater

Current density (mA/cm2) 5, 10, 15

Heavy metal

removalpH 4, 6.6, 9

Initial concentration (ppm) 50, 100, 150

Anode material Al

The selection of electrodes plays a vital role in using

electrocoagulation for the treatment of wastewater. It uses consumable

electrodes such as Aluminium and Iron to supply ions into the water stream.

The use of electrocoagulation using iron and aluminium electrodes as a

pre-treatment step before microfiltration (MF) has been recently evaluated.

Iron electrodes show various disadvantages like generation of soluble ferrous

ions and accumulation of colloidal precipitates on electrodes for micro- and

ultra-filtrations of wastewater (Timmes et al 2010, Timmes et al 2009,

Bagga et al 2008) and limited work has been done with aluminium as

sacrificial electrodes (Sasson and Adin 2010) for microfiltration

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pre-treatment. Therefore Aluminium electrode was chosen for

electrocoagulation pre-treatment before microfiltration.

These optimized conditions of both the wastewater samples were

scaled up to 1.5 L capacity for integrating with dead end filtration experiment.

The submerged area of electrodes was 125.4 cm2, with all other conditions

maintained same.

3.3.2 Kinetics and Adsorption Isotherms of EC

The adsorption kinetics was studied for the electrocoagulation

batch process for the treatment of the tannery effluent and synthetic heavy

metal effluent with the optimized conditions. Though the mineralization of

organic contaminants by electro coagulation process is complex and involves

number of elementary chemical steps, the overall rate of COD removal can

often be described either by zero order or first order rate expressions. A

Zero-order reaction has a rate that is independent of the concentration of the

reactant(s). The speed of the reaction is unaltered with increase in the

concentration of the reacting species i.e. the amount of substance reacted is

proportional to the time. Zero-order reactions are typically found when a

material that is required for the reaction to proceed, such as a surface or

a catalyst or an adsorbent, is saturated by the reactants. The rate law for a

zero-order reaction is given by,

r k (3.1)

where r is the reaction rate and k is the reaction rate coefficient with units of

concentration/time.

[ ]d Cr k

dt (3.2)

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And the integrated zero order rate law can be obtained by

integrating the above differential equation,

[Ct] = -kt + [C0] (3.3)

where [Ct] represents the concentration of the chemical of interest at a

particular time, and [C0] represents the initial concentration. A reaction is zero

order if concentration data plotted versus time is a straight line with the slope

being the negative of the zero order rate constant k.

A first-order reaction or unimolecular reaction depends on the

concentration of only one reactant. The rate law for an elementary reaction

that is first order with respect to a reactant C is

[ ][ ]

d Cr k C

dt (3.4)

k is the first order rate constant, which has units of 1/s. and the integrated

first-order rate law is

ln[C] = -kt + ln [C0] (3.5)

A plot of ln [C] vs. time t gives a straight line with a slope of -k.

In electrocoagulation, the amount of metal dissolved is dependent

on the quantity of electricity passed through the electrolytic solution. A

simple relationship between current applied (A) and the amount of substances

(M) dissolved (g ) can be derived from Faraday’s law:

Mitw

nF (3.6)

88

where w is the quantity of electrode material dissolved (g ), i the current

density (A), t the time in s; M the relative molar mass of the electrode

concerned, n the number of electrons in oxidation/reduction reaction and F

the Faraday’s constant, 96,500Cmol1. There is usually an agreement between

the calculated amount of substances dissolved as a result of passing a definite

quantity of electricity and the experimental amount determined. Since the

removal of pollutant by adsorption on flocks is very similar to conventional

adsorption and the amount of coagulant can be estimated using Faraday’s

Law for a given time, the pollutant removal can be modeled by adsorption

phenomenon.

The sorption mechanism and the surface properties and affinity of

the sorbent can be determined by the adsorption isotherm models and its

underlying thermodynamic assumptions (Ho et al 2002). The adsorption

capacity of the process was monitored in terms of COD and concentration of

heavy metals. The reaction was carried out to determine the time required for

the adsorption process to reach the equilibrium state. The adsorbent dose in

electrocoagulation can be calculated by knowing the applied current density.

To describe the nature of pollutant removal, the data collected was modeled

using various existing adsorption isotherm like Langmuir, Tempkin and

Freundlich model (Kalyani et al 2009, Vasudevan et al 2009, Chithra and

Balasubramanian 2010). The model constants were calculated and linear

regressions were done for each model.

The amount of pollutant adsorbed at different experimental current

densities was calculated by adsorption equilibrium equation:

m

CCVq eo

e

)( (3.7)

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where qe refers to the amount of pollutant adsorbed after equilibrium (mgg-1

),

m is the weight of electrode dissolved (g), V is the volume of effluent taken

(L), Co initial COD or metal concentration, and Ce is the COD or metal

concentration at equilibrium (mg/l).

The Langmuir isotherm assumes monolayer deposition of adsorbate

on homogenous adsorbent surface (coagulant). The mathematical expression

of Langmuir isotherm can be given as,

eL

eLe

Ca

CKq

1 (3.8)

The linearization of the above equation results

e

L

L

Le

e CK

a

Kq

C 1 (3.9)

The binding constant (KL,) and the sorbent capacity (aL) can be

estimated by plotting Ce/qe against Ce, where qe refers to the amount of

pollutant adsorbed and Ce refers to COD or metal concentration at equilibrium

time.

The Freundlich isotherm is an empirical model which relates the

adsorption intensity of the sorbent towards adsorbent. The isotherm is

adopted to describe reversible adsorption on heterogeneous surfaces and is

not restricted to monolayer formation. The Freundlich model can be

mathematically written as:

Fb

eFe CKq (3.10)

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where KF and bF are the constants which give adsorption capacity and

adsorption intensity respectively. The above equation takes the linear form

and can be written as:

lnqe = ln KF + bF ln Ce

(3.11)

Plot of lnqe versus lnCe gives a straight line with slope KF and

intercept bF.

The effect of adsorbate and adsorbent interactions on adsorption

isotherm is considered in Tempkin Isotherm. It describes the behavior of

adsorption systems on heterogeneous surfaces, and the following equation

was suggested

qe = Bln A + Bln Ce (3.12)

where A and B are Tempkin constants.

3.3.3 Activated Sludge Process

In activated sludge process (ASP) wastewater containing organic

matter and nutrients is aerated in which micro-organisms metabolize the

suspended and soluble organic matter. These microbes live and grow

entrapped in Extra Polymeric Substances (EPS) that bind them into discrete

three-dimensional aggregated microbial structures called flocs. The ability of

microorganisms to form flocs is vital for the activated sludge treatment of

wastewater. These flocs forming micro colonies not only enables the

adsorption of soluble substrates, colloidal matter and macromolecules found

in wastewaters (Michael and Fikret 2002, Liwarska and Bizukojc 2005) but

also uses a part of organic matter to synthesize new cells and a part is

oxidized to CO2 and water to derive energy. The activated sludge contains a

91

consortium of diverse micro organisms with prokaryotes (bacteria),

eukaryotes (protozoa, nematodes, rotifers), and viruses. In this complex

microsystem, bacteria dominate the microbial population and play a key role

in the degradation process (Michael and Fikret 2002).

Biological treatment of the tannery wastewater was also done after

the increase of biodegradability index to 0.4 by electrocoagulation and before

microfiltration. The microbial characterization of activated sludge from CETP

revealed the presence of Escherichia coli, Bacillus species, pseudomonas

species, Achromobacter, Flavobacterium species and Alcaligenes species,

which are resistant to heavy metal environment (Tamilselvi et al 2012) and

also various salt tolerant bacteria predominated by Pseudomonas aeruginosa

(Sivaprakasam et al 2008). The sludge for the process was collected from the

same tannery treatment plant and was acclimatised overnight using fill and

draw method (Chang and Lee 1998). Fill and draw technique consists of

allowing the sludge to settle for 30 min, and the supernatant was withdrawn

and discarded. Then, it was refilled with the fresh feed solution and aeration

restated. These fill and draw processes were repeated every 6 h. Aeration and

mixing were provided through a porous stone diffuser delivering compressed

air. ASP was initiated with the acclimatized sludge as a post treatment at

Mixed Liquor Suspended Solids (MLSS) concentration of 8000 mg/l in dead

end filtration experiments and around 3000 mg/l in the case of submerged

membrane system.

3.3.4 Integration with Dead End Microfiltration

Constant pressure, unstirred dead-end filtration experiments were

conducted using a fabricated methyl acrylate cell, with 0.0143 m2 of effective

filtration area. PVDF membranes rated at 0.22 µm (GVWP14250, Millipore)

with 192 mm diameter were used and were supported over a porous mesh.

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The schematic representation of the experiments carried out is shown in

Figure 3.3.

Figure 3.3 Schematic representation of dead-end hybrid electro

membrane bioreactor

The influent (tannery effluent) was treated by electro coagulation

and activated sludge process before pumping it to the dead end filtration

system. Manometer is used to measure the transmembrane pressure of the

membrane reactor and the experiments were done at a constant pressure and

at room temperature. The treated effluent from the membrane separation is

collected in a permeate collection tank and analyzed for various quality

parameters. The permeate flux was calculated by measuring the volume of

permeate per unit time.

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3.4 SUBMERGED MEMBRANE SYSTEM

The second module of the work consisted of treating the tannery

effluent using submerged membrane system. In submerged MBRs the

membrane separation is carried out with vacuum-driven membranes

immersed directly into the bioreactor and operates in dead-end mode. The

energy consumption required for filtration in submerged MBR is significantly

lower when compared to side stream configuration. Submerged systems are

becoming favourites in industries due to its various associated advantages.

Their reduced capital cost and lesser space requirement makes them more

suitable in wastewater treatment.

3.4.1 Experimental Set Up

The collected tannery effluent was stored in a PVC feed tank. The

effluent was pumped into the submerged membrane bio reactor using a feed

pump. The specifications of the submerged membrane bioreactor are given in

Table 3. The main tank body was made of poly methyl methacrylate material.

The reactor had the dimension of 47cm × 35 cm × 48 cm with effective

volume of 65.8 L, which was maintained by a level sensor inside the reactor

and connected to the feed pump. It was partially divided into two

compartments. In the first compartment, electrodes were dipped (aluminum

and stainless steel) and two set hollow fibre membrane modules were

immersed in the second compartment. Electrocoagulation (EC) was carried

out by immersing stainless steel as cathode and aluminium as anode and by

connecting it to a DC regulated power supply (METRONIC model ME-305A,

0–5A and 0–30V). The submerged area of the electrodes was maintained as

487.5 cm2 with an inter electrode distance of 5 cm. The effluents from the

membrane modules were withdrawn via peristaltic pumps (SZ037DB,

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YUEHUA Company, China) operated at constant suction pressure. The

pressure was measured by a vacuum pressure gauge and regulated by a valve.

Air diffusers were located at the bottom of the reactor (85 l/min) to provide

aeration to the biological system and to produce effective scouring of the

membrane surface. It also provided a uniform mixing of the mixed liquor

suspension in the reactor. The schematic and photograph of the Submerged

Hybrid membrane bioreactor is shown in Figures 3.4 and 3.5 respectively.

Table 3.4 The specifications of submerged membrane bioreactor

Main Tank BodyPolyMethylMethacrylate(PMMA)

Material1 set

Special Blower flow 85 liter/min., pressure 0.04MPa, 1 no

Suction PumpSZD-037 flow 1m

3/hr., suction head

5m, head 25m1 no

MembraneZCM-0.4, PVDF, hollow fiber

submerged type.6 nos

Outlet Flow Meter ~ 1 no

Vacuum Pressure

Gauge~ 1 no

Aeration System ~ 1 set

Pipe & Valve ~ 1 set

Control SystemControl panel, cable, power

acceptable 220V, 50Hz1 set

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Figure 3.4 Schematic representation of Hybrid Submerged Membrane Bioreactor

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Figure 3.5 Hybrid submerged membrane bioreactor set up

3.4.2 Experimental Method and Operation Protocol

Three modes with different combination of treatment techniques;

(a)Electrocoagulation combined with microfiltration (EMR); (b) Membrane

Bioreactor (MBR) and (c) Electrocoagulation integrated with membrane

bioreactor (HMBR) were operated at a constant transmembrane pressure

(TMP) of 5kPa. All the processes were operated at room temperature for 7

days. In order to minimise the drastic initial fouling and to increase the

biodegradability index (BI) above 0.4, which enhances the efficiency of

biological treatment (Solomon et al 2009), 60 minutes of electrocoagulation

pre-treatment was done prior to the start up of filtration. According to

Alshawabkeh et al 2004, aerobic cultures are capable of withstanding and

enhancing pollutant removal in a range of 0.28 to 1.14 V/cm DC supply.

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Therefore, in the case of HMBR the voltage gradient was reduced to 1V/cm

just before the addition of activated sludge, in order not to hinder the

biological process. Fresh membranes were used for each experimental mode.

During the experimental runs no sludge was wasted and the process was

operated at complete sludge retention time (SRT).

3.5 FOULING MODELS

Despite the various advantages of the MBR process, the present

cost of treatment by MBR is unfortunately higher than that of the

conventional treatment. One of the major reasons for this higher cost of

treatment is attributed to membrane fouling. A decrease in process

performance is generally indicated with the term fouling. According to

International Union of Pure and Applied Chemistry fouling is defined as

‘Process resulting in loss of performance of a membrane due to deposition of

suspended or dissolved substances on its external surfaces, at its pore

openings, or within its pores’ (Koros et al 1996). Fouling is encountered at

two levels i.e., the filterability, which is reflected as the loss of ‘process

performance’ during a filtration run. The second level is the reversibility,

which is a measure of the extent to which the membrane performance can be

regained after it was fouled during filtration. Although filterability and

reversibility are linked, they must be separated when discussing membrane

fouling (Roorda 2004). Membrane fouling causes the increase in filtration

resistance resulting in the decline in permeate flux or increase in TMP.

Membrane fouling can result from the formation of a polarization cake layer

and the plugging of membrane pores (Figure 3.6)

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Figure 3.6 Membrane fouling

3.5.1 Percentage Reduction in Permeate Flux

The fouling was evaluated quantitatively by measuring the decline

of permeate flux with time and the comparison was done by percentage

reduction in permeate flux given by:

( )100 (3.13)

i f

i

J JPRPF

J

Where Ji is the initial permeation flux measured during the first

minute and Jf is the permeate flux at the end of each mode of integrated

operation.

99

3.5.2 Resistance In Series

Clear water resistance test (CWRT) was done before each

experiment, by measuring the membrane permeability with distilled water and

it was verified again after membrane cleaning. Effects of membrane fouling

on the decline of permeate flux can be explained using the resistance-in-series

model. It gives information about the reversibility of the different fouling

types and is a practical way to obtain an idea of the predominant type of

fouling that occurs in membranes .According to this model, the relationship

between permeate flux and transmembrane pressure (TMP) is described in by

using Darcy’s law:

RT = Rm + Rc+ Rp (3.15)

Where J is the Membrane flux (Lm-2

h-1

), P is theTrans-membrane

pressure, (Pa), µ is the Viscosity of permeate (Pa.s), RT is the total resistance

(m-1

), Rm is the intrinsic membrane resistance (m-1

), Rc is the cake layer

resistance (m-1

), Rp Pore blocking resistance (m-1

).

The total resistance of the membrane after each experimental run

was found out from the final value of permeate flux using equation 3.14.This

total resistance is a combination of membrane resistance and fouling

resistance. Fouling resistance consists of reversible (cake layer) and

irreversible (pore blocking) resistance. Irreversible fouling resistance was

calculated from the permeate flux obtained with distilled water after physical

(3.14)T

PJ

R

100

and chemical cleaning. The resistance of the cake layer (Rc) was calculated

by subtracting the summation of membrane resistance and the pore blocking

resistance (Rm + Rp) from the total resistance RT. Finally, the pore blocking

resistance was calculated (Melhem and Smith 2012). Physical cleaning of the

membrane was done by removing it from the reactor and washing it under tap

water and then with de-ionised water to remove the cake layer adhered on to

the membrane. Chemical membrane cleaning was done by soaking it in 1%

NaOCl solution overnight (Meng et al 2006).

3.6 ANALYTICAL METHODS AND SOPHISTICATED

INSTRUMENTS

3.6.1 Water Quality Analysis

Influent and effluent were sampled regularly and analyzed for water

quality parameters according to Standard Methods for the Examination of

Water and Wastewater (APHA 1999). Chemical Oxygen Demand (COD) of

the wastewater samples were measured using open reflux method (Standard

methods 5220 B), where an excess of potassium dichromate (strong oxidizing

agent) is added to the sample and the remaining quantity is determined by

titration against ferrous ammonium sulphate using ferroin indicator. A blank

is also run to compensate for any error that may result because of presence of

organic matter in the reagents. Biochemical Oxygen Demand (BOD) by 5-

Day BOD Test (5210 B) which is mainly a bio-assay procedure, involving the

measurement of oxygen consumed by the bacteria while stabilizing the

organic matter under aerobic conditions. A mixed group of organisms should

be present in the sample, if not; the sample has to be seeded artificially.

Temperature is controlled at 200C. The test is conducted for 5 days, as 70 to

80 % of the waste is oxidized during this period. Total dissolved solids

(TDS) and Total suspended solids (TSS) were done by Gravitational Methods

(2540 C and D). Conductivity was measured using conductivity meter

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(Sansel, DCM-200) and colour was monitored by double beam UV-Vis

spectrophotometer (Elico SL 164).The values of pH was measured using a pH

metre (RI 501 A). Heavy metal removal was monitored using AAS

(Shimadzu, Japan, AA6300).

3.6.2 Fouling Analysis

MLSS concentration has a complex interaction with MBR fouling,

and is considered as the main foulant parameter. But controversial findings

about the effect of this parameter on membrane filtration have also been

reported (Chang and Kim 2005, Cicek et al 1999, Brookes et al 2006 Hong et

al 2002, Lesjean et al 2005). Mixed liquor suspended solids (MLSS) and

mixed liquor volatile suspended solids (MLVSS) were also sampled from

inside the reactor and performed according to Standard Methods given by

APHA, 1999 to analyze its impact on membrane fouling. Mixed liquor

suspended solids (MLSS) represents the concentration of non-soluble solids

in the mixed liquor in the bioreactor. The solids are comprised of biomass

(dead and living bacteria as well as debris) and organic and inorganic

contaminants which may be introduced by the wastewater or may be

produced during biomass growth and decay. A mixed liquor sample of 25 ml

was taken from the bioreactor every day. The sample was centrifuged for 15

minutes and the supernatant was discarded and the sludge was transferred to a

pre-weighed crucible. The sample was dried in an oven at 100oC overnight.

The sample was weighed after the crucible cooled down to the room

temperature. Mixed liquor volatile suspended solids (MLVSS) was calculated

by putting the samples in the furnace at 550oC for 30 minutes, during which

the organic fraction evaporated leaving behind the inorganic fraction.

Extra Polymeric Substance (EPS) are the excreta of microbes,

which are known as one of the most predominant fouling agent in activated

102

sludge systems. Analysis of EPS in the mixed liquor was done using the

thermal treatment method. It is said to be one of the best extraction method

among the various procedures because it results in a good release of

exocellular polymer from the flocs and causes less cellular disruption (Foster

1985). The mixed liquor was centrifuged for around 30 minutes. The pellet

(after discarding the supernatant) was washed and resuspended with 0.9%

saline water. The extracted solution was obtained from heat treatment (100°C,

lh) of this resuspended solution. The extracted solution was centrifuged again

and the supernatant obtained in this way was analysed for EPS by measuring

the volatile solids of this solution without further precipitation procedure.

3.6.3 Sophisticated Instrumental Analysis

Sophisticated instruments were also used to study the fouling

and its reduction in the hybrid system. SEM analysis (Carl Zeiss MA 15 /

EVO 18) was done to assess the morphological studies of the membrane. The

sludge formed by the electrocoagulation process was analysed by SEM-EDX

(Oxford Instruments Nano Analysis INCA Energy 250). The increase in the

particle size in the integrated process was monitored by Particle size

distribution analysis which describes the floc size was measured using

dynamic light scattering method (ZEN3600, Zetasizer Ver. 6.20). This was

used to substantiate the mechanism of mitigation of fouling in membranes.