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Chapter-5

Bioreactor System and Nanotechnology for Water Treatment


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5.1 INTRODUCTION

Water is one of the essential enablers of life on earth. Beginning with the

origin of the earliest form of life in seawater, it has been central to the evolution of

human civilizations. Years of intense research have contributed significant

breakthroughs in the treatment of polluted water systems. Bioreactor systems and

application of nanotechnology are recently developed options for the better

treatment of the contaminated water. Bioreactor offers platform for the laboratory

evaluation of large scale systems for industrial applications. Once designed, the

system can be optimised for significant parameters and scale up can be done to

greater level of precision. Noble metals have been similarly associated with the

prosperity of human civilizations through their prominent use in jewellery and

medical applications. The most important reason for the use of noble metals is the

minimal reactivity at the bulk scale, which can be explained by a number of

concepts such as electrochemical potential, relativistic contraction, molecular orbital

theory, etc. Recently, water quality has been associated with the development index

of society. A number of chemical and biological contaminants have endangered the

quality of drinking water. The present work includes novel approaches in the area of

the application of bioreactor systems and noble metal nano particle in the treatment

of contaminated river water system

Reactor systems generally offer effective and promising output for online

applications. Reactor systems can be designed to incorporate multiple stages which

can be sequentially put into operation according to the requirement. This added

advantage is a huge benefit in water treatment processes as it requires multiple

methodologies at various level of treatment.

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The polluting factors of contaminated water belong to various categories and

specific treatment strategies are required to tackle each polluting factor. The most

significant polluting aspect of contaminated water system is the presence of high

amount of suspended particles. These particles may be of dissolved or suspended

type, The removal of the total suspended matter is mostly effected by physical or

chemical methods The physical methods are not so cost effective and often result in

the replacement and frequent service requirement of the tangential screens. However

subjecting to natural sedimentation is a cost effective process. But this is a very slow

process and requires more time. Hence additional process aids are required when it

is a matter of large volume of water and particularly when the suspended solids are

relatively high.

The incorporation of additional coagulation and flocculation process to

facilitate better removal of suspended natter contribute to better performance of

subsequent treatment strategies.

Bioreactor may refer to any manufactured or engineered device or system

that supports a biologically active environment. A bioreactor may also refer to a

device or system meant to grow cells or tissues in the context of cell culture. These

devices are being developed for use in tissue engineering or biochemical

engineering or waste management. On the basis of mode of operation, a bioreactor

may be classified as batch, fed batch or continuous. The present bioreactor system

offers multiple treatment strategies contributing to effective removal of suspended

solids, removal of coliforms and hence facilitating chlorination at low dose. This

treatment strategy can be applied online effectively and can be easily scaledup.


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The application of noble metal nanoparticle based chemistry for drinking

water purification is summarized for three major types of contaminants: halogenated

organics including pesticides, heavy metals and microorganisms. Realizing the

molecular nature of contamination in drinking water, significant progress has been

made to utilize the chemistry of nanomaterials for water purification. Scientist

working in the field of environmental nanotechnology view that working at the

nanoscale is not detrimental to the environment. Studies have shown that

nanotechnologies can be used not only to prevent pollution, but also to clean up

pollutants once they have made their way in to the environment. Automatically

precise manufacturing at nanoscale should be able to eliminate chemical pollution

entirely by giving control of processes at the molecular level

Today most of the countries are facing drinking water problems and

conditions are very severe, especially in developing countries. The world is facing

formidable challenges in meeting rising demands of clean water as the available

supplies of freshwater are depleting due to (i) extended droughts, (ii) population

growth, (iii) more stringent health based regulations and (iv) competing demands

from a variety of users USBRSNL (2003), USEPA (1998b), USEPA (1999).Clean

water (i.e., water that is free of toxic chemicals and pathogens) is essential to human

health. In countries such as India, 80% of the diseases are due to bacterial

contamination of drinking water. The World Health Organization (1996)

recommended that any water intended for drinking should contain faecal and total

coliform counts of 0, in any 100 ml sample. When either of these groups of bacteria

is encountered in a sample, immediate investigative action should be taken. The

removal or inactivation of pathogenic microorganisms is the last step in the

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treatment of wastewater. USEPA (1998b). The protection of water treatment

systems against potential chemical and biological acts is also becoming a critical

issue in water resources planning (USEPA, 1999; USEPA, 1998).

Despite the modern success of nanotechnology, the potential health and

environmental risks associated with these applications remain unknown. Prompted

by the discovery that nanoparticles can enter the human body and accumulate in the

environment, government agencies have begun to manage research of

‘nanotoxicology.’ In September 2006, the National Nanotechnology Initiative

reported the intent to research methods to evaluate the toxicity of nanoparticles in

the environment and the human body. This critical information needed is also the

primary focus of the USEPA with regard to nanotechnology. Due to the

overabundance of silver nanoparticles in the consumer market, ‘nanosilver’ has

become a specific area of interest among research scientists. The concerns and

potential consequences related to exposing nanosilver to our water environment

through consumer products are tremendous. If exposed to the environment, silver

nanoparticles may induce the death of bacteria that are surrogate environmental

organisms and vital to all ecosystems. Moreover, in the 1980s, silver ion pollution

from a processing plant endangered the native population of Macoma balthica clams

in the South San Francisco Bay. Since nanosilver is a derivative of silver and silver

ions, the effects of a silver ion pollution in the 1980s may foreshadow a similar and

possibly even worse consequence with nanosilver pollution. Furthermore, the

accumulation of nanosilver in the water environment may have an adverse effect on

the aquatic organisms that inhabit the polluted areas. Current research has shown

that zebrafish embryos exposed to nanosilver result in delayed development,


195

defective fetal maturation and death. The most detrimental effect of silver

nanoparticles would be our efforts in recycling water in the wastewater industry.

Several strains of bacteria are implemented in wastewater treatment to digest the

organic substances present in the sludge. Later these organisms can be destroyed

with nanosilver particle. It is clear that the potential consequences of direct or

indirect exposure of nanosilver to the environment are detrimental. As a result, it is

necessary to develop a systematic technique to quantify and analyze the bacterial

toxicity of silver nanoparticles in environmental conditions. In addition, the

abundance of silver nanoparticles in consumer products increases the possibility of

environmental exposure; thus, it is necessary to analyze the toxicity of silver

nanoparticles in such products.

A water filter with 0.3 nm pores (on left) would clean water down to the

atomic level with minimal pressure drop due to drag. Silver coated Nanofilters are

used in many industrial applications for water purification. They are being evaluated

because of their ability to reduce the coliform content and reduce clogging compared

to traditional filtration methods

Nanofilters can help to tackle decontamination of groundwater from

industrial and natural sources. Semi - permeable membrane can act as a molecular

sieve allowing water to pass through while rejecting impurities such as viruses,

spores, bacteria, heavy metals, and other health threats. Nanoscale filters will be able

to actively screen out items matching certain criteria.

Desalination is an area, where nanotechnology could cut costs, save energy,

and improve the lifetime and efficiency of membranes. Today seawater is most

often turned in to drinking water through a 40-year old process called reverse

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osmosis, which is slow ,expensive and energy intensive. If nanotechnology can

make the process cheaper and efficient.it could have a large impact and is the need

of the hour in most of the developing countries including India

5.2 REVIEW OF LITERATURE

Bioreactors for treating sewage and wastewater are considered as the most

efficient of these systems. Among the advanced wastewater treatment technologies

the Membrane Bioreactor (MBR) process is an emerging area. It involves a

suspended growth activated sludge system that utilises microporous membranes for

solid/liquid separation in lieu of secondary clarifiers. In addition, it provides a

barrier to certain chlorine resistant pathogens such as Cryptosporidium and Giardia

Membrane Bioreactor systems essentially consists of a combination of

membrane and biological reactor systems. These are used for a wide spectrum of

advanced wastewater treatment processes. In general, MBR applications for

wastewater treatment can be classified into four groups (Stephenson et al., 2000)

namely:

Silver and silver compounds have been used as antimicrobial compounds for

coliform found in waste water (Jain, and Pradeep. 2005). Silver nanoparticles,

nanodots or nanopowder are spherical or flake high surface area metal particles

having high antibacterial activity. Furno (2004) and Moran (2005), have used

Nanoscale silver particles of 1-40 nanometers (nm) with an average particle size of

2-10 micron range, specific surface area of approximately 1m2 g-1 for various water

treatment strategies. Applications for silver nanocrystals include as an anti-

microbial, anti-biotic and anti-fungal agent when incorporated in coatings,

nanofiber, first aid bandages, plastics, soap and textiles, in treatment of certain


197

viruses, in self cleaning fabrics, as conductive filler and in nanowire and certain

catalyst applications. It has been reported that Ag nanoparticles were active biocides

against Gram positive Gram-negative bacteria including Escherichia coli,

Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas aeruginosa. (Jain,

and Pradeep, 2005; Sons, et al., 2004). Sondi (2004) and Ping Li et al., (2005

studied that the Ag nanoparticle of narrow size shows enhanced antibacterial effect

against E. coli.

More recently, it has been demonstrated that the bactericidal effect of silver

was caused by silver chelation preventing DNA from unwinding. The anti-microbial

effects of silver, in zerovalent and ionic form, have been widely studied in great

detail. (Jain and Pradeep, 2005., Sondi, and Sondi 2004., Aymonier, 2002). It has

also been used widely as a common disinfectant for surgical masks (Lia et al.,

2006), textile fibers (Dubas et al., 2006), wound dressing (Maneerung et al., 2008),

etc. Significant efforts have been devoted to study the toxic effects of silver

nanoparticles on a broad spectrum of micro-organisms including E. coli (Jain and

Pradeep, 2005, Sondi, and Sondi 2004, Morones, et al., 2005, Pal et al., 2007 and

Lok, et al., 2007). Pseudomonas aeruginosa (Pal, et al., (2007). Vibrio cholera (Pal,

et al., 2007). Bacillus subtilis and HIV-1 (Elechiguerra, 2005). Prior to discussing

the chemistry behind the biocidal activity of silver nanoparticles, it is useful to

understand how silver ions act against micro-organisms. While the precise details

are not yet elucidated, protein inactivation and loss of replication ability of DNA are

suggested. A few important observations are highlighted. It was pointed out that

cells protect the DNA by forming a defense around the nucleus, when the cells are

subjected to external stimuli such as heat. Under severe external stimulus, the

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defense mechanism fails leading to the denaturation of the DNA (loss of replication

ability). A similar observation was found in the case of silver ions with E. coli and

Staphylococcus aureus. (Feng, 2000). The formation of protective layers around

DNA and DNA's condensation was clearly evident in the study (Feng. 2000). The

large-scale movement in the cellular components in the presence of silver ions is

indeed surprising and reflects the ability of the cell to protect itself against external

stimuli. It was also found that the interaction of silver ions with sulfur present in

many proteins, leads to protein inactivation (Liau, 1997). While the external addition

of sulfur-containing compounds led to the neutralization of anti-bacterial activity of

silver ions, the presence of sulfur in silver-rich regions confirmed the interaction

between sulfur and silver.

The nature of the charge on the cell surface (due to presence of different

functional groups) and the anti-bacterial composition plays a key role in determining

the effectiveness. It was found that the same nature of charge on the antimicrobial

composition and cell surface (negative charge) leads to repulsion and decreased

contact (Hamouda 2000). The ability of silver to absorb oxygen in atomic form has

been widely utilized immensely for many organic reactions such as conversion of

methanol to formaldehyde. It is revealed that bulk silver in an oxygen charged

aqueous medium catalyzes the complete destructive oxidation of microorganisms

(Davies 1997).

It is largely understood that cellular membranes play a critical role in

maintaining the viability of cells. The cellular permeability in the case of gram-

negative bacteria such as E. coli is largely controlled by the presence of a

lipopolysaccharide (LPS) layer on the outer surface of the cellular membrane. The


199

heavily saturated fatty acids on LPS links it to the membrane backbone, which itself

contains many negative ions. Thus, LPS binds cations, which is also confirmed by

the presence of Mg2+/Ca2+ as an electrostatic linker to bind adjacent LPS chains. The

affinity of LPS towards cations has been utilized for permeation of polycationic

antibiotics in the cytoplasm. It is also suggested that the binding of even simple

cations to LPS weakens the membrane backbone which may lead to the

disintegration of the membrane. On the contrary, negatively charged ions have been

reported to bind with Mg2+/Ca2+, which also leads to loss of cellular viability. In the

context of observations for silver ions, it is appropriate to understand the

observations for silver nanoparticles. Silver nanoparticles cause irreparable damage

to the cellular membrane (Sondi, 2004, Pal et al., 2007, Gorgoi, 2006) which enables

the accumulation of nanoparticles in the cytoplasm. It is suggested that action of

silver nanoparticle arises due to this damage and not its toxicity (Pal et al., 2007).

The pits in the cell wall, post-treatment, are quite significant. An important aspect of

the biocidal action of silver nanoparticles is the requirement of supported

nanoparticles for anti-bacterial effects. As explained in an earlier section on

biosynthesis of metal nanoparticles, cells protect themselves from metal toxicity

through the action of cellular proteins which bind to the nanoparticle surface leading

to nanoparticle aggregation and thus rendering nanoparticles immobile. This was

suggested by the studies of nanoparticle solutions with bacteria. It is therefore

expected that small size nanoparticles are able to easily penetrate across membranes

(Morones, et al., 2005., Pal et al., 2007). Similarly, antibacterial activity of

nanocrystals is found to have a dependence on crystal shape. The activity is found to

be higher for truncated triangular nanoplates when compared with nanorods and

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spherical particles. The interaction of bacteria with high atom density crystal plane

has been proposed (Morones, et al., 2005) exhibiting higher anti-bacterial activity

was reported (Pal et al., 2007). Recently, it has been proposed that the activity of

silver nanoparticle arises due to the formation of superoxide, which has been

detected by the dismutation activity of superoxide dismutase. The addition of

dismutase leads to reduction in anti-bacterial activity (Chang 2007). It is also

suggested that the chemistry of silver ions is important in the anti-bacterial effect of

silver nanoparticles. That chemisorbed Ag+ ions is important in determining the

silver nanoparticle toxicity was confirmed by the non-toxicity of oxidized

nanoparticles to silver-resistant E. coli strains (Lok, 2007).

5.3 MATERIALS AND METHODS

5.3.1 Designing of the Reactor

This bioreactor consists of a reservoir and three specially designed treatment

units. The reservoir is a rectangular tank made up of polyacrylic material with a

capacity of 10 liters. The tank measures about 30cm in length, 35cm in width and 50

cm in height (Fig.5.1).


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Fig. 5.1

The reservoir unit of 35cm X 30cm X50cm with 5l capacity carrying the polluted water for treatment

The reservoir unit is connected to two pipe lines. Of the two pipelines, one

line offers flow of untreated water as the control from reservoir and the other line

carries the three in line water treatment units (Fig.5.2).

Fig. 5.2

The three single treatment units connected in series contributing to multistage treatment system for the treatment of polluted water along with

the control flow unit

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The treatment units comprises of three Units. The units are same in

dimension and each extends upto 100 cm. Each unit is designed with provisions for

adding the coagulant/ flocculant and also for filtering out the coagulated fraction

(Fig.5.3).

Fig. 5.3

A single treatment unit of 100 cm length in the multistage treatment system for polluted water.

Each of these units is also connected to a sedimentation/ filtration device.

The container for adding flocculent is attached to a funnel that drops down to the

water (Fig.5.4). The sedimentation unit, which is attached to the treatment units, is a

removable device. After each treatment, the sedimentation unit is detached, cleaned

and refitted for future use.


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Fig. No.5.4

A single unit showing the provision for adding coagulants or flocculants for inline treatment

The diameter of pipe fitted between the flocculation unit and sedimentation unit

is comparatively reduced. This reduction in size helps in the effective mixing of

flocculants and water. The funnel of the flocculation unit is 5.5 cm in diameter and 8cm

in height. The sedimentation device is 6cm in diameter and 18 cm in height (Fig.5.5).

Fig. 5.5

The sedimentation and filtration unit in a single unit of multistage treatment system for polluted water

(diameter 6 cm, height 18 cm, No of pores 10/cm2)

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The first unit assigned as the coagulation unit for alum, the second unit is

assigned for flocculation with Moringaseed powder and the third unit for mild

chlorination.

The whole device, except the reservoir unit, is supported by adjustable

metallic stands (Fig.5.6). The reservoir unit is kept high above all the treatment units

(fig.5.1).

Fig. 5.6

The metallic supporting stand of adjustable height to support the inline treatment units and supporting line

5.3.2 Working of the Bioreactor

The contaminated water is first collected in the reservoir unit. Water from

this reservoir unit is allowed to flow through the coagulation unit I, Flocculation

UnitII, Unit, Mild Chlorination unit III and the nanofilter unit towards the end. The


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specially designed control units and outflow units aids in collecting water from

every stages of treatment (Fig.5.7).

Finally provisions are given for attaching nanofilters also. The nano particles

used are silver nano particles (Fig.5.8). The water is allowed to passes through the

coagulation unit at first and then into the flocculation unit, chlorination unit and

finally into the nanofilter (Fig.5.9).

Fig 5.7

The complete multistage inline water treatment system supported by the metallic stands

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Fig. 5.8

The silver particle coated nano filter connected to the inline multistage water treatment system.

Fig. 5.9

The complete multistage inline water treatment stage with nano filter connected at the end.

After the completion of the three stages of treatment, water flows out from

the pipe line. Samples of treated water can be collected after each stage and can be

verified for any qualitative change that can occur in the water sample after the

treatments. The untreated water makes a continuous flow through the control tube


207

and samples can be withdrawn at uniform intervals for comparison of the efficiency

of the treatment strategies.

5.3.3 Alum and Moringa seed powder treatment

Alum and moringa seed powder treatment was done as mentioned in the

section 4.3. The alum at 30mg/l dose was packed in the first stage of the reactor

followed by morinda seed powder at (30 mg/l) in the second stage. The water was

circulated through the packed reactor system under constant reservoir head.

Chlorination was done the last stage at the minimum concentration to get complete

(.1-.75 mg/l) elimination of total coliform.

5.3.4 Silver Nano particle treatment for waste water treatment.

The nano particle was synthesized and it was adhered to the nano filter of

pore size 45 to 47 nm. The water was allowed to pass through the filter with

pressure. The coated filter was incorporated at the end of the reactor system.

5.4 RESULTS

The bioreactor systems offer rapid and efficient treatment system for the

complete purification of the contaminated water. Bioreactor system contributes

multiple strategies for the integrated treatment of the polluted water.

In the present study complete treatment of the polluted water was attempted

with a three stage reactor system. The reactor system could offer facility for alum

coagulation Moringa seed flocculation, mild chlorination and finally nanofilter

treatment.

The treatment was carried out with and without nanofilter treatment. On

treating the polluted water with alum, Moringa seed powder followed by mild

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chlorination the COD, BOD and the MPN were considerably reduced. The BOD

was reduced from 80± mg/l to 24± mg/l. Similarly the COD was reduced from 142±

mg/l to 132± mg/l. The MPN was also brought to minimum from 1200 It is most

striking that after the treatment with the alum and moringa seed powder much of the

coliforms were eliminated. Finally mild chlorination (0.75 mg/L) could bring the

MPN to minimum value. On treating the water with alum, moringa seed powder,

mild chlorination followed by nano treatment the coliform content was completely

eliminated with much reduced BOD and COD at the same low dose of chlorination.

(Table 5.1 and 5.2)

Table 5.1

Effect of various combinations of water treatment without nano filter

Parameters Control Combinations of Alum(1mg/L)Muringa( 2mg/l),Chlorination(0.75 mg/L)

BOD (mg/L) 80±0.04 24±0.81

COD ( mg/L) 142±1.4 132±1.21

MPN 1200±1.06 0

Table 5.2

Effect of various combinations of water treatment with nanofilter

Parameters Control Combinations of Alum(1mg/L)Muringa ( 2mg/l),Chlorination(0.75 mg/L) Nano filter

BOD(mg/L) 80±0.04 12±0.31

COD(mg/L) 132±1.27 38±0.12

MPN 1200±1.06 0


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The FT/IR analysis done for the treated water with alum, Moringa seed

powder and low dose chlorination there was no indication of chlorination derived

byproducts. (Fig.5.10) Even the GC/MS analysis could not bring any evidences of

chlorination derived byproducts. (Fig.5.11)

cm-1

Fig. 5.10

FT/IR analysis of the polluted water sample after integrated treatment of the water sample with the combinations of Alum, Muringa seed powder followed

by low dose chlorination in the multistage reactor system.

% T

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210

10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.50.0

0.5

1.0

1.5

2.0

2.5(x10,000,000)

TIC

50.0 75.0 100.0 125.0 150.0 175.0 200.0 225.0 250.0 275.0 300.0 325.0 350.0 375.0 400.0 425.0 450.0 475.0 500.00.0

25.0

50.0

75.0

100.0

%

7343

12983

115 213157 256185

228 356 480284 342 429403 504325

25.0 50.0 75.0 100.0 125.0 150.0 175.0 200.0 225.0 250.0 275.0 300.0 325.0 350.0 375.0 400.0 425.0 450.0 475.0 500.0 525.0 550.00.0

25.0

50.0

75.0

100.0

%

43

73

41

129

213157115 256185

281 429 503355327 462401314 550534

Fig. 5.11

MS of the peak obtained at 12.5 min in the analysis of the polluted river sample with the combinations of Alum, Muringa seed powder followed by chlorination

at low dose in the multistage reactor system


211

The situation was even better in the case of nanotreated water where there

was no evidence of chlorination derived by products through FT/IR and GC/MS

analysis. But there was complete elimination of coliforms at a low dosage of

chlorination. (Fig.5.12 and Fig. 5.13)

Fig. 5.12

FT/IR analysis of the polluted water sample after integrated treatment of water sample with the combinations of Alum, Muringa seed powder, mild chlorination and followed by nanofilter treatment in the multistage

reactor system.

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212

10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 15.5 16.00.0

1.0

2.0

3.0

4.0(x1,000,000)

TIC

50.0 75.0 100.0 125.0 150.0 175.0 200.0 225.0 250.0 275.0 300.0 325.0 350.0 375.0 400.0 425.0 450.0 475.0 500.00.0

25.0

50.0

75.0

100.0

%

55

41

83

111

264125 180 222166303282 380341 490443402

Fig. 5.13

GC/MS analysis of the of the peak obtained at 11, 25 min of water sample after integrated treatment of water sample with the combinations of Alum, Muringa

seed powder followed by chlorination at low dose in the multistage reactor system.

5.5 DISCUSSION

The presence of chemical contaminants in the aquatic environment is of

significant concern to the society due to the possible health risks to humans, wild

life and domestic animals, The source of chemical contamination of surface waters

includes waste from industrial and domestic waste water plants, runoff from


213

agricultural land and leachates from landfills and storage lagoons. The source of

water pollution of Pamba river water is also from similar sources. During the pilgrim

season there is huge inflow of human waste from partially treated sources besides

direct disposals. The river is also acting as a sink for a variety of organic pollutants

during the pilgrim season.

Water is used for several purposes by humans but the level of purity of the

water being consumed is very critical since it has a direct effect on human health.

Excessive turbidity in drinking water may represent a health concern as it can

provide food and shelter for pathogens and possibly promote excess growth of

pathogens in the distribution system. Although turbidity is not a direct indicator of

health risk, there is strong relationship between turbidity and coliform content.

Turbidity could be effectively removed by coagulation and flocculation followed by

sedimentation. This could also eliminate much of the suspended coliform from the

contaminated water and hence could also reduce the requirement of high dose of

chlorination.

Concern over the negative aspects of chlorination especially super

chlorination had emerged in the early 1970s. This came mostly as result of the

toxicity of residual chlorine to fish and other sensitive aquatic organisms and also

due to the accumulation of cancer causing trihalomethanes and other chlorinated

organics. Despite these environmental concerns, superchlorination of contaminated

drinking water system is still practised in many communities with and without

dechlorination. Chlorine is a strong oxidising agent and its application in water

treatment is likely to modify the chemical and biological nature of treated water.

Hence extreme care should be taken in chlorinating drinking water and every

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possibility should be evaluated for low dose chlorination minimising the formation

of chlorination derived byproducts. Hence in the present study an attempt was made

to evaluate the performance of an integrated treatment system using an online multi

stage reactor system.

The designing of the bioreactor itself was truly novel as it offered provision

for coagulation followed by filtration for the online treatment of the contaminated

water. The reservoir by its high water head offered good flow rate. Both the

control system and the treatment system were connected serially and offered

regulation for the flow of the water. At any time comparison could be made for the

effectiveness offered by the individual or the integrated system in treating the

water (Fig 5.1 to 5.9).

The length of the individual treatment unit and the diameter of the pipe

connecting the mixing and sedimentation unit were taken with a view to offer

maximum mixing inbetween. The designed system carried three such units offering

coagulation and sedimentation separately. Any type of treatment orienting

coagulation followed by sedimentation could be carried out with this system. In the

present attempt, the treatment strategies selected were low dose alum treatment, low

dose moringa seed treatment, low dose chlorination followed by nanofilter

treatment.

The effectiveness of aluminum and iron coagulants arises principally from

their ability to form multi-charged polynuclear complexes with enhanced adsorption

characteristics. The seed kernels of M. oleifera contain significant quantities of low

molecular-weight water soluble proteins that carry a positive charge. When the

crushed seeds are added to raw water, the proteins produce positive charges acting


215

like magnets and attracting the predominantly negatively charged bacteria and

thereby sediments them. When the contaminated water was put into treatment with

alum, moringa seed powder followed by chlorination at low dose of 0.75 mg/l there

was reduction in both BOD and COD. The coliform count was also nil .But when

the strategies were repeated along with the introduction of nanofilter treatment at the

end, the reduction of both BOD and COD were enhanced much at the same dosage

of chlorination. The coliform count was also nil. Therefore the introduction of a

nanofilter treatment offered better treatment facility at the same dose of low

chlorination (Table 5.1 and 5.2).

The mechanism of the antimicrobial action of silver ions is not completely

known. However, the effect of silver ions on bacteria is linked with its interaction

with thiol group compounds found in the respiratory enzymes of the bacterial cells.

Silver binds to the bacterial cell wall and cell membrane and inhibits the respiration

process. In case of E-coli, silver acts by inhibiting the uptake of phosphate and

releasing phosphate, mannitol, succinate, proline and glutamine from the E-coli cell .

In addition, it was shown that Ag+ ions prevent DNA replication by binding to the

polynucleotide molecules, hence resulting in bacterial death. When all these positive

strategies were taken together for water treatment the results obtained were truly

encouraging. The complete removal of coliforms could be effected at a very low

dosage of 0.75 mg/l chlorination whereas the chlorination requirement was 30 mg/l

when taken as a single treatment strategy. 2 mg/l was strong enough to produce the

toxic chlorination derived products. Chlorination at a dosage of 0.75 was incapable

of producing any toxic halogenated compound which was evidenced by the

spectroscopic analysis (Fig. 5.10 to Fig. 5.13).

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In the FT/IR spectra of Fig. 5.10 and Fig. 5.12 there were no peaks at 2880

cm-1, 1258 cm-1 indicating the presence of aliphatic CH3, there was no peak at 1100

cm-1 representing CCl and there was no peak at 700 cm-1 representing residual

chlorine. All these representations were there when the contaminated water was

treated with chlorination alone at high rate of 30 mg/l (Fig.3.7 to 3.18). In the

GC/MS analysis also (Fig.5.11 and Fig.513) there was no representations

corresponding to halogenated alkanes.

The spectroscopic analysis and the values obtained in the analysis of BOD,

COD and MPN strongly suggested that the present treatment strategy adopted was

effective and was bringing coliform count to nil without affecting the organic load.

This strategy was highly useful as it could be applied online during the flow of

contaminated water; it could be scaled up easily and could be implemented

successfully in field trials.

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Bioreactor System and Nanotechnology for Water Treatmentshodhganga.inflibnet.ac.in/bitstream/10603/19613/15/15_chapter5.pdf · Bioreactor System and Nanotechnology for Water Treatment