Chapters

CHAPTER 1.0

INTRODUCTION

1.1 General

Sewage is created by residential, institutional, and commercial and industrial establishments and

includes household waste liquid from toilets, baths, showers, kitchens, sinks and so forth that

is disposed of via sewers. In many areas, sewage also includes liquid waste from industry and

commercial establishments. The separation and draining of household waste into greywater

and blackwater is becoming more common in the developed world, with greywater being

permitted to be used for watering plants or recycled for flushing toilets. Most sewage also

includes some surface water from roofs or hard-standing areas and may include storm water

runoff.

Sewerage systems capable of handling storm water are known as combined systems or

combined sewers. Such systems are usually avoided since they complicate and thereby

reduce the efficiency of sewage treatment plants owing to their seasonality. The variability in

flows also leads to often larger than necessary, and subsequently more expensive, treatment

facilities. In addition, heavy storms that contribute more flows than the treatment plant may

overwhelm the sewage treatment system, causing a spill or overflow. Modern sewered

developments tend to be provided with separate storm drain systems for rainwater.

As rainfall travels over roofs and the ground, it may pick up various contaminants

including soil particles and other sediment, heavy metals, organic compounds, animal waste,

and oil and grease. Some jurisdictions require storm water to receive some level of treatment

before being discharged directly into waterways. Examples of treatment processes used for

storm water include retention basins, wetlands, and buried vaults with various kinds of media

filters, and vortex separators (to remove coarse solids). Sanitary sewers are typically much

smaller than storm sewers, and they are not designed to transport storm water. In areas with

basements, backups of raw sewage can occur if excessive storm water is allowed into a

sanitary sewer system.

Sewage treatment, or domestic wastewater treatment, is the process of removing

contaminants from wastewater and household sewage, both runoff (effluents) and domestic.

It includes physical, chemical, and biological processes to remove physical, chemical and

biological contaminants. Its objective is to produce a waste stream (or treated effluent) and a

1

solid waste or sludge suitable for discharge or reuse back into the environment. This material

is often inadvertently contaminated with many toxic organic and inorganic compounds.

1.2 Wastewater Treatment Plants

Wastewater Treatment Plants are engineered systems planned, designed and constructed

for management of wastewater (domestic, industrial or commercial wastewaters) with

application of principles Environmental Engineering to protect natural systems from

pollution. Sewage can be treated close to where it is created (in septic tanks, bio filters or

aerobic treatment systems), or collected and transported via a network of pipes and pump

stations to a municipal treatment plant. Sewage collection and treatment is typically subject to

local, state and federal regulations and standards. Industrial sources of wastewater often

require specialized treatment processes.

Many processes in a wastewater treatment plant are designed to mimic the natural

treatment processes that occur in the environment, whether that environment is a natural

water body or the ground. If not overloaded, bacteria in the environment will consume

organic contaminants, although this will reduce the levels of oxygen in the water and may

significantly change the overall ecology of the receiving water. Native bacterial populations

feed on the organic contaminants, and the numbers of disease-causing microorganisms are

reduced by natural environmental conditions such as predation or exposure to ultraviolet

radiation. Consequently, in cases where the receiving environment provides a high level of

dilution, a high degree of wastewater treatment may not be required. However, recent

evidence has demonstrated that very low levels of specific contaminants in wastewater,

including hormones (from animal husbandry and residue from human hormonal

contraception methods) and synthetic materials such as phthalates that mimic hormones in

their action, can have an unpredictable adverse impact on the natural biota and potentially on

humans if the water is re-used for drinking water. A significant threat in the coming decades

will be the increasing uncontrolled discharges of wastewater within rapidly developing

countries.

Methods of treatment in which the application of physical forces predominates are known

as unit operations and the removal of contaminants is brought by chemical or biological

reactions are known as unit processes. At present these two categories of treatment methods

are grouped together to provide what is known as primary, secondary, and tertiary treatment.

In primary treatment, physical operations such as screening and sedimentation are used to

2

remove the floating and settleable solids found in wastewater. In secondary treatment,

biological and chemical processes are used to remove most of the organic matter. The

additional combinations of unit operations and processes form tertiary treatment which are

used to remove other constituents, such as nitrogen and phosphorus, that are not reduces

significantly by secondary treatment.

1.3 About Bangalore Water Supply and Sewerage Board (BWSSB)

Bangalore is located on the watershed of two principal river basins, Arkavathi to the west

and South, Pennar to the East. The local topography is characterized by a series of well

defined valleys which radiate from a ridge of High Ground to the north of the city and fall in

a gradual manner towards wide belt of flat land extending beyond the limits of the

metropolitan area to the South.

The Three principal valleys are known as Vrishabhavathi, Koramangala and Challaghatta

and three valleys run generally in a north to the south direction and divide the greater part of

the metropolitan area which lies to the south of the ridge into three separate and distinct

drainage zones. A fourth valley system referred to as the Hebbal series forms drainage zone

to the north of the ridge and runs in north easterly direction.

Five minor valleys, the Kathriguppa and Tavarekere to the south, the Arkavathi and

Kethamaranahally to the north west and Marathhally to the east, lie outside the tributary area

of the major valleys and they drain independently to the fringe areas which form the

remainder of the metropolitan area.

The configurations of valleys in well graded side slopes of their tributary areas have

provided Bangalore with a natural system of drainage without recourse to pumping. Both

sewerage and storm water flow by gravity beyond the city.

The system of sewers for the conveyance of domestic and industrial waste water through

underground drainage system was introduced in the year 1922. The system introduced

initially was confined to heavily populated area in the heart of the city and although a gradual

extension took place then onwards it was not until 1950 that a major programme of sewer

construction was commenced. With the formation of the Board (BWSSB) in 1964, the

programme to provide Sewerage system in the unsewered areas was taken up in a phased

manner and the treatment of sewage before it is led into the natural valleys was also tackled.

3

At present, Bangalore city has a well designed and regularly maintained underground

sewerage system. Stoneware pipes are used up to 300 mm dia. Sizes and RCC hume pipes

varying in Dia. from 300 mm to 2000 mm for sub-mains/mains/outfall sewers.

In order to facilitate easy cleaning in sewer lines whenever blockage occurs in sewer line,

adequate numbers of manholes are provided at regular intervals’. Manholes with cast iron

frames and covers are provided in heavy traffic roads, on small lanes and cross roads with

less traffic with RCC frames and covers for the manholes.

This report discusses the training undergone during June-July ’10 as a part of the M.Tech

course work at 180 MLD Sewage Treatment Plant, Vrishabhavathi Valley maintained by

Bangalore Water Supply and Sewerage Board.

1.4 Objectives

The main aim of undergoing practical training, which is a part of our course, is to study

the processes adopted in the Sewage Treatment Plant. The specific objectives of this study

are:

To gain knowledge of the treatment processes adopted in the plant.

To study the Operation & Maintenance procedures of the plant in brief.

To analyse the performance criteria of the treatment units by conducting analyses at

plant laboratory.

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CHAPTER 2.0

LITERATURE REVIEW

2.1 Sewage Treatment Facilities

There has been a change every now and then, since the concept of wastewater

management or treatment was started. The methods of treatment that were predominant in

late 1980’s and 1990’s are now seen as conventional or outdated at some places. Researchers

and Engineers have always found new ways to treat the polluted waters and curb pollution to

greater extent. These facilities or methods or processes what we use now are the greatest

contribution of those most dedicated and eminent people who have our lives so easy now. In

this section, the salient features of treatment facilities that are been adopted since decades

will be discussed in brief.

Wastewater treatment methods have been classified into well established categories

like physical unit operations, chemical unit processes and biological unit processes. The

objectives of these methods are briefed in section 1.2. The application of treatment methods

is the major part in designing any treatment facilities. Having known the treatment methods

available and the benefits of them, designing of treatment units does not become difficult

provided one has understood the objectives that has to be met. The principal methods now

used for wastewater treatment and sludge are identified here.

2.2 Wastewater Processing

As noted in chap. 1 that unit operations and processes are grouped together to provide

various levels of treatment. The term “preliminary” and/or “primary” referred to physical unit

operations; “secondary” referred to chemical and biological unit processes; and “tertiary” or

“advanced” referred to combinations of all three. The unit operations and processes necessary

to achieve that required level of treatment are grouped together on the basis of fundamental

considerations. Application of these operations, processes, and methods to perform specific

functions is described in the following sections.

2.2.1 Preliminary Wastewater Treatment

This is defined as the removal of wastewater constituents that may cause maintenance

or operational problems with the treatment operations, processes, and ancillary systems.

Examples of preliminary operations are screening and comminution for the removal of debris

5

and rags, grit removal for the elimination of coarse suspended matter that may cause wear or

clogging of the equipment, and floatation for the removal of large quantities of oil and grease.

2.2.2 Primary Wastewater Treatment

In primary treatment, a portion of the suspended solids and organic matter is removed

from the wastewater. This removal is usually accomplished with physical operations such as

screening and sedimentation. The effluent from primary treatment will ordinarily contain

considerable organic matter and will have a relatively high BOD. The principal function of

primary treatment will continue to be as a precursor to secondary treatment.

2.2.3 Conventional Secondary Wastewater Treatment

Secondary treatment is directed towards the removal of biodegradable organics and

suspended solids. Disinfection is included frequently in the definition of conventional

secondary treatment. This is defined as the combination of processes customarily used for the

removal of theses constituents and includes biological treatment by activated sludge, fixed-

film reactors, or lagoon systems and sedimentation.

2.2.4 Advanced Wastewater Treatment/Wastewater Reclamation

Advanced wastewater is defined as the level of treatment required beyond

conventional secondary treatment to remove constituents of concern including nutrients, toxic

compounds, and increased amounts of organic material and suspended solids. In addition to

the nutrient removal processes, unit operations or processes frequently employed in advanced

wastewater treatment are chemical coagulation, flocculation, and sedimentation followed by

filtration and activated carbon. These are used in variety of reuse applications where high

quality water is required.

2.2.5 Sludge Processing

Sludge processing and disposal methods play an important role in waste management

that arise from treatment plants itself. The sludge contains high concentrations of organic

matter and other trace pollutants which are of both highly beneficial and detrimental

characteristics. Sludge being liquid portion of the wastewater is easy to handle and process.

Unlike wastewater treatment sludge processing also has unit operations and processes for

final disposal of sludge. Examples of these include thickening, stabilization, conditioning,

dewatering, heat drying etc, and are employed to prepare sludge for final disposal.

6

2.3 Conventional Trickling Filters

Trickling filters are used for the biological treatment of domestic sewage and

industrial wastes which are amenable to aerobic biological processes. Trickling filters possess

a unique capacity to handle shock loads and provide dependable performance with a

minimum of supervision.

The trickling filter consists of a permeable bed of medium through the sewage or

liquid waste is allowed to percolate. The materials used as filter medium include crushed or

broken rock, gravel, blast furnace slag or inert synthetic materials such as plastics and

ceramics. Randomly packed solid media like rock, gravel and slag are characterised by lower

porosities (40-60%), lower specific surface areas (40-70 m2/m3) and lower depths of 0.9 to

2.5 m. Plastic media of various shapes possess very high porosities (94-97%) and higher

specific surface areas (80-200 m2/m3). While conventional filters usually employ rocks,

gravel and slag as filter medium, plastic media are generally used in super rate filters which

operate at much higher hydraulic and organic loading rates and are much deeper (up to 12 m)

compared to conventional filters. The deep filters containing plastic media are referred to as

biotowers and have been used for both domestic and strong industrial wastewaters. The

trickling filters may be generally circular but square or rectangular shapes may also be used.

The sewage is evenly distributed on the surface of filter medium and the treated effluent is

collected by the underdrains.

The trickling filter is preceeded by primary sedimentation so that the settleable solids

in the sewage may not clog the filter. The sedimentation tanks should have skimmers to

remove the scum. The filter is always followed by a final settling tank to remove from the

filter effluent the settleable organic solids produced in the filtration process. In some cases, it

may be advantageous to provide skimming devices for the final settling tanks also. The

trickling serves both to oxidise and bioflocculate the organic material in sewage and their

efficiency is assessed on the total reduction in BOD affected through the filter and the

subsequent settling tank, since the effluent quality is reckoned after the settlement of the

bioflocculated solids.

2.4 Tertiary Treatment Systems

Advanced wastewater treatment is defined as the additional treatment needed to

remove suspended, colloidal and dissolved constituents remaining after conventional second-

7

ary treatment. Dissolved constituents may range from relatively simple inorganic ions, such

as calcium, potassium; sulphate, nitrate, and phosphate, to an ever-increasing number of

highly complex synthetic organic compounds, in recent years, the effects of many of these

substances on the environment have become understood more clearly.

Research is ongoing to determine (1) the environmental effects of potential toxic and

biologically active substances found in wastewater and (2) how these substances can be

removed by both conventional and advanced wastewater-treatment processes. As a result,

wastewater-treatment requirements are becoming more stringent in terms of both limiting

concentrations of many of these substances in the treatment plant effluent and establishing

whole effluent toxicity limits. To meet these new requirements, many of the existing

secondary Treatment facilities will have to be retrofitted and new advanced wastewater

treatment facilities will have to be constructed.

The need for advanced wastewater treatment is based on a consideration of one or more

of the following factors.

1. The need to remove organic matter and total suspended solids beyond what can be

accomplished by conventional secondary treatment processes- to meet more stringent

discharge and reuse requirements.

2. The need to remove residual total suspended solids to condition the treated wastewater

for more effective disinfection.

3. The need to remove nutrients beyond what can be accomplished by conventional

secondary treatment processes to limit eutrophication of sensitive water bodies.

4. The need to remove specific inorganic (e.g., heavy metals) and organic constituents

(e.g., MBTF and MDMA) to meet more stringent discharge and reuse requirements for

both surface water and land-based effluent dispersal and for indirect potable reuse

applications (e.g., groundwater recharge).

5. The need to remove specific inorganic (e.g., heavy metals, silica) and organic

constituents for industrial reuse (e.g.. cooling water, process water, low-pressure boiler

makeup water, and high-pressure boiler water).

With increased scientific knowledge derived from laboratory studies and environmental

monitoring concerning the impacts of the residual constituents found in secondary effluent, it

is anticipated that many of the methods now classified as advanced will become conventional

within the next 5 to 10 years.

8

CHAPTER 3.0

PRACTICAL TRAINING

3.1 Vrishabhavathi Valley (V-Valley) 180 MLD Sewage Treatment Plant

The Vrishabhavathi valley STP treatment plant has been constructed to treat sewage

generated in the western part of the city. This plant is situated near Nayandahalli in

Bangalore-Mysore road. Capacity of the treatment plant is 180 MLD with Secondary

treatment facilities and 60 MLD of the treated sewage is sent for tertiary treatment.

Initially plant was designed for Primary treatment of 27 MGD (123 MLD) in the year

1974 for the same drainage area. Wastewater generated from 6 areas, Malleshwaram,

Vijayanagar, Attiguppe, Chamrajapete, Market, and Hanumanthnagar is collected and

transported to STP through well designed sewer system. Due to rapid increase in population

and industrial activities, the plant was expanded to treat 180 MLD & upgraded the treatment

upto secondary levels in the year 1999.

The existing secondary treatment plant was commissioned in year 1999 and is spread

over 93 acres next to the state highway connecting Bangalore & Mysore. The sewage from

drainage area of 9910 acres has been brought to the plant by an inlet pipe (outfall sewer) of

diameter 1800 mm. The plant was designed to treat sewage characteristics with BOD 350

mg/L and suspended solids 460 mg/L. The plant is expected to remove 60% solids and 65%

of BOD.

The treatment process adopted in this plant is “Conventional two stage trickling filter

(bio-filters) process” which consists of the following units. The general flow diagram of

units in STP is given in the Fig 3.1.

1. Primary Treatment Units:

a. Screening b. Grittingc. Primary clarifier d. Primary Bio-filters e. Recirculation pump housef. Sludge pumping

2. Secondary Treatment:

a. Secondary Bio-filtersb. Secondary clarifier

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c. Sludge pumpingd. Sludge drying beds

10

30%

INLET

MS

CS

FS

GT3 GT 1 GT 2

PC 1 PC 2 PC 3

PBF 4PBF 1 PBF 2 PBF 3

SBF 1 SBF 2 SBF 3SBF 4

SC 1 SC 2 SC 3SC 4

OUT CHANNEL60 MLD TO TTP

PC 5PC 4

V. VALLEY

Fig 3.1: General flow diagram of 180 MLD STP at V-Valley

11

Manure WW to V.Valley

WW to Inlet

WET WELL

SD 1 SD 2 SD 3 SD 4 SD 5

Sludge from pc & SC

SDBS

Fig 3.2: Flow diagram for sludge handling in 180 MLD STP at V-Valley

Abbreviations of the Flow chart 3.1 & 3.2

CS- Coarse Screen SD- Sludge Digester

MS- Medium Screen DBS- Sludge Drying Beds

FS- Fine Screen Sludge flow

GT- Grit Chamber Supernated Liquid from Digester

PC- Primary Clarifier Flow of wastewater

SC- Secondary Clarifier

PBF- Primary Biofilter

SBF- Secondary Biofilter

SC- Secondary Clarifier

Flow of wastewater

Recirculation

12

3.2 Detailed Description of the Units

3.2.1 Screens

The main purpose of installation of screens is to remove the floating matter of

comparatively large size. This reduces the problem of choking of pumps and pipes by

removing floating materials which are usually wooden pieces, plants, dead animals, plastic

materials, etc which are hindrance to free flow in pipes. Screening is done in three stages i.e.,

Coarse screens, medium screens and fine screens. The specifications of these screens are

given below.

Existing Screens at V-Valley STP

Coarse Screens:

Number of screens : 1 Type : Bar Screen Dimensions : 2.65 m x 4.25 m Clear opening between bars : 75 mm Type of cleaning : Manual Inclination of screens : 45°

Medium Screens:

Number of screens : 2 Type : Bar Screen Dimensions : 1.8 m x 2.1 m Clear opening between bars : 40 mm Type of cleaning : Manual Inclination of screens : 45°

Fine Screens: Number of screens : 3 (2W+1S) Type : Bar Screen Dimensions : 1.8 m x 2.1 m Clear opening between bars : 20 mm Type of cleaning : Manual Inclination of screens : 60°

3.2.2 Grit Chambers

Grit chambers are designed to remove grit, consisting sand, gravel, cinders, or other

heavy solid materials that have subsiding velocities or specific gravities substantially greater

than those of the organic putrescible solids in wastewater. Girt chambers are most commonly

located after the bar racks and before the primary sedimentation tanks.

13

Grit chambers are provided to (1) protect moving mechanical equipment from

abrasion and accompanying abnormal wear; (2) reduce formation of heavy deposits in

pipelines, channels, and conduits; and (3) reduce the frequency of digester cleaning caused by

excessive accumulations of grit. The removal of grit is essential ahead of centrifuges, heat

exchangers, and high-pressure diaphragm pumps.

There are three general types of grit chambers: horizontal-flow, of either a rectangular

or a square configuration; or vortex type. The plant has horizontal-flow type grit chambers,

where flow passes through the channel in a horizontal direction and the straight line flow

velocity is controlled by the dimension of the unit, an influent distribution gates and a weir at

the effluent end.

Existing Grit Chambers at V-Valley STP

Grit chambers:

Type : Detritors with classifiers Number of Units : 3 (2+1)

a. 2 units with dimensions 11.80 m x 11.80 m x 2 m (SWD)b. 1 unit with dimension 7.50 m x 7.50 m x 0.75 m (SWD)

Number of classifier : 3 Over flow rate : 1090 m3/m2/d Detention time : 60-80 seconds

The grit is generally used to reclaim the low lying land. It can also be mixed with poor

soil to condition it. The soil mixed with grit works as good manure for the garden crops.

3.2.3 Primary Clarifiers & Secondary Clarifiers

Primary clarifiers are located just after the grit chambers and they are thus provided to

treat raw sewage. The main objective of providing primary clarifiers is to hold the sewage in

the tank for about 2.5 hours, which allow for about 65% or more, suspended solids to settle to

the bottom and removed by mechanical scraper as primary sludge. Here the Degritted sewage

is fed at the centre of the clarifier.

The wastewater from secondary trickling filters is pumped to secondary clarifier for

settling of organic matter and to oxidise it. After the settlement of organic matter the water is

pumped for tertiary treatment and remaining effluent is let in to the nearby valley.

14

Clarifier has various parts which perform specific functions. Scum baffles are

provided near the outlet channel to prevent the entry of floating substances in to the outlet

channel. Scum removal devices to collect all the scum that has been removed by scum baffles

and is further sent either for further treatment or for final disposal. Sludge accumulated at the

bottom of the tank should be removed periodically.

Existing Primary Clarifiers & Secondary Clarifiers at V-Valley STP

Primary Clarifiers:

Number of tanks : 5 Type : Circular Diameter

a. 1&2 units - 47.26 mb. 3, 4 & 5 - 52 m

Volumea. 1&2 units – 6665 m3

b. 3, 4 & 5 units – 10542 m3

Detention timea. 1&2 units – 2.6 hoursb. 3, 4 & 5 units – 3-5 hours

Side water deptha. 1&2 units – 3.80 mb. 3, 4 & 5 units – 3.99 m

Surface loading rate : 32 m3/m2-d Weir loading : 220 m3/m2-d Primary effluent quality : BOD – 200 mg/L & SS – 210 mg/L

Primary clarified water is sent to primary bio-filters for removal of organic matter.

There are 4 primary bio-filters in the plant, 3 working and 1 standby. The sludge from

clarifiers is removed hydraulically, every 2-3 hour and collected in wet wells for pumping it

to sludge drying beds.

Secondary Clarifiers:

Number of tanks : 4 Type : Circular Diameter : 59 m Volume : 5681 m3

Detention time : 4 hours Side water depth : 2.08 m Surface loading rate : 20 m3/m2-d

15

Weir loading : 160 m3/m2-d Final effluent quality : BOD – 20 mg/L & SS – 30 mg/L

Solids (sludge) produced is pumped to wet wells and then to sludge drying beds.

3.2.4 Primary and Secondary Bio-filters

The main objective of providing trickling filters is to reduce BOD content. By using

trickling filters 90% of the BOD will be reduced. Trickling filters contain permeable bed of

coarse filtering media through which the sewage or liquid waste is allowed to sprinkle or

trickle down through rotary distributors. The percolating sewage is collected at the bottom of

the tank through a well designed under drainage system. The purification of the sewage is

brought about mainly by the aerobic bacteria, which forms a bacterial film around particles of

the filtering media. In order to ensure the large-scale growth of the aerobic bacteria, sufficient

quantity of oxygen is supplied by providing suitable ventilation facilities in the body of the

filter, and also to some extent by the intermittent functioning of the filter.

Existing Primary Trickling filters & Secondary Trickling filters at V-Valley STP

Primary Trickling filters:

Number of filters : 4 Type : Circular Diameter : 61.8 m Depth : 1.67 m Hydraulic loading rate : 30 m3/m2-d Organic loading : 1.8 Kg BOD/ m3-d Recirculation ratio : 1.0 Filter media : Granite Filter media nominal size : 150-200 mm

The effluent from primary trickling filter is allowed in to secondary trickling filter.

Secondary Trickling filters:

Number of filters : 4 Type : Circular Diameter : 61.8 m Depth : 1.17 m Hydraulic loading rate : 30 m3/m2-d Organic loading : 1.8 Kg BOD/ m3-d Recirculation ratio : 1.0

16

Filter media : Granite Filter media nominal size : 150-200 mm

3.2.5 Sludge Pumping

The sludge withdrawn from the clarifiers is collected in sludge wet wells and pumped

to drying beds from there. Pumps with the help of float switches start automatically to pump

it to sludge drying beds. The existing sludge digesters are not in working condition hence the

sludge id pumped directly to drying beds. The sludge pumps are non-clog pumps type with a

pumping capacity of 900 lpm of raw sludge.

3.2.6 Sludge Drying Beds

The collected sludge from wet wells is pumped to drying beds. The deposition is done

evenly upon the beds of size 20 m x 30 m up to a depth of 20 cm. The dissolved gas tries to

come up and float leaving a clear liquid at the bottom, which drains through the sand rapidly.

The evaporation process takes place about 15-20 days. The liquid from under drains is

disposed of by discharging in to valley. The dries cake becomes compact, impervious and in

dark colour is removed by shovels and is used as fertilizer. The details of sludge, grit and

other wastes produced in STP are tabulated in the Table 3.1.

Table 3.1: Details of wastes produced and disposal of the wastes

Sl. No Unit Waste generated Quantity kg/day Disposal

1 Screen Screens 72 Open dumping

2 Grit chamber Grit 150 manure

3 Primary clarifier Sludge 150 manure after drying

4 Secondary clarifier Sludge 75 manure after drying

5 Clarifiers scum 50 Open dumping

Existing Sludge drying beds at V-Valley STP

Sludge Drying Beds:

Number of beds : 30

Length of the beds : 40.85 m

Width of beds : 11.40 m

17

Total area of drying beds : 466 m2

Depth of sludge to beds : 0.2 m

Time to dry sludge : 15 days

3.3 Observations and Data Collected with Interpretation

Observations made during period of training i.e., from 1st June –15th July and the

technical data collected with plots and tables are presented in this section. The detailed list of

working and standby units in STP is given in Table 3.2 below.

Table 3.2: Units in STP

Units No. of Units Unit No.

Total Working Standby Working Standby

Screens

a. Coarse

b. Medium

c. Fine

1 1 - 1 -

4 3 1 1, 2, 3 4

3 2 1 1 & 3 2

Grit chambers 3 2 1 2 & 3 1

Primary Clarifier 5 2 1 1, 2 & 3 4 & 5

Primary Bio-filter 4 1 3 1 2, 3 & 4

Secondary Clarifier 4 1 3 4 1, 2 & 3

Secondary bio-filter 4 2 2 2 & 3 1 & 4

The table above gives the details of units that were operated during the training

period. As the flow was less compared to designed value, only required units were in

operation keeping other units as standby. The flow details are given in the following section.

3.3.1 Flow Measurement

The daily flow patterns were measured every hour using graduated scale. The over

flow depth at the weirs of grit chambers 1, 2, & 3 are measured with the scale and the flow

(calculated using rectangular weir over flow) corresponding to the depth is noted. The details

of flow for the month June-July is given in the following Table 3.3.

18

The flow expected was less to the plant because of the dry season. The flow varied

from a minimum of 27 MLD to a maximum of 117 MLD.

Table 3.3: Flow in MLD corresponding to the depth noted at time of measurement

Sl. No Depth in cmGrit tank 1& 2 flow in MLD

Grit tank 3flow in MLD

1 1 1.03 1.47

2 2 2.93 3.99

3 3 5.39 7.34

4 4 8.3 11.13

5 5 11.6 15.19

6 6 15.26 20.76

7 7 19.23 26.16

8 8 23.49 31.96

9 9 28.04 38.14

10 10 32.84 44.67

11 11 37.88 51.53

12 12 43.17 58.72

13 13 48.67 66.21

14 14 54.4 74.6

15 15 60.33 82.06

16 16 66.46 90.41

17 17 72.79 99.01

18 18 79.3 111.53

19 19 86 114.05

20 20 92.88 117.07

21 21 99.84 125.14

19

1 2 3 4 5 6 7 8 9 10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

0

20

40

60

80

100

120

140

Daily Flow Variation June 2010

Minimum Flow

maximum Flow

Average Flow

Days

Flo

w M

LD

Fig 3.3: Plot of daily flow variation for the month June 2010

1 2 3 4 5 6 7 8 9 10 11 120

20

40

60

80

100

120

140

Daily Flow Variation July 2010

Minimum Flow

maximum Flow

Average Flow

Days

Flo

w M

LD

Fig 3.4: Plot of daily flow variation for the month July 2010

3.3.2 Sampling

The laboratory facility at the STP was well equipped for the required analysis to be

carried out to determine the effluent quality before discharging into the valley. Sampling was

done every hour which formed the grab samples and mixed after 6 hours to make a composite

sample before analysis.

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Sampling points

Sample point 1: Outlet of Grit chamber Sample point 2: Clarified water from primary clarifier Sample point 3: Clarified water from secondary clarifier

After mixing of samples at each point separately, samples were brought to the

laboratory for analysis. The parameters analyzed are given in the Table 3.4 with the methods

of determination. A log book is maintained to keep a record of analysis results and is dully

signed daily by the Assistant Executive Engineer of the plant.

Table 3.4 Parameters and methods used for the analysis of samples

Parameter Method

Temperature Direct measurement

pH Litmus colour comparison with standard pH scale

Dissolved Oxygen (DO) Modified Winkler’s method

Chemical oxygen demand (COD) Closed Reflux method

Bio-chemical oxygen demand (BOD) Modified Winkler’s method

Suspended solids ODYSSEY HACH, Spectrophotometry method

3.3.3 Analysis Data

The results of analyses for the month of June-July are given in the figures below. The

data tabulated is given in the Annexure-I.

1 2 3 4 5 6 7 8 9 10

11

12

13

14

15

16

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35Temperature June - July 2010

InletIntermediateOutlet

Days

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per

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Fig 3.5: Plot of Temperature for the month June-July 2010

21

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7.8pH June - July 2010

Inlet

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Fig 3.6: Plot of pH for the month June-July 2010

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Dissolved Oxygen June- July 2010

Inlet

Days

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mg/

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Fig 3.7: Plot of Dissolved Oxygen for the month June-July 2010

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Inlet

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Fig 3.8: Plot of COD for the month June-July 2010

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Inlet

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Fig 3.9: Plot of 5 Day BOD for the month June-July 2010

23

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Inlet

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Fig 3.10: Plot of Suspended Solids for the month June-July 2010

1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526272829300

10

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Percentage reduction in COD @ STP June 2010

Days

% r

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OD

Fig 3.11: Plot of % reduction in COD

24

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Days

% r

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Fig 3.12: Plot of % reduction in BOD

1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293070

75

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95Percentage SS reduction @ STP in June 2010

Days

% r

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of S

S

Fig 3.13: Plot of % reduction in SS

25

3.4 Operation & Maintenance

Since STP units have various moving mechanical and electrical equipments and

machineries, problems are more often to occur. The problems that occurred in operation of

units in STP are given in the Table 3.5. An operation and maintenance log book is maintained

to record the problems that occur and maintenance measures taken.

Table 3.5: Operational Problems encountered in STP during June-July 2010

UnitUnit No Problems

Screen Screens No problem encountered

Grit Chamber Grit no 2 Breakage of chain due to heavy silt collection in the tank

Primary Clarifier PC 1 Stop due to wheel track problem

Stop due to chain problem

Stopped due to fuse failure & gear box problem

PC 2 Stop due to coupling rubber damage

PC 3 Stop due to wheel track problem

Primary Sludge Pump PSP 1 Stop due to fuse burnt

Stop due to motor problem not able to pump the sludge

PSP 2 Stopped due to electrical problem

Primary bio-filter PBF 1 Not rotating due to less flow

PBF 2 Not rotating due to less flow

PBF 4 Stop due to arm box problem

26

Recirculation pumps RCP Stop due to repair of non return valve

Secondary bio-filter SBF2 Stop due to tie rod problem

SBF3 Stop due to less flow

Secondary Clarifier SC3 Stop due to roller wheel rubber breakdown

Secondary Sludge pump SSP 1 Stop due to bearing problem

Stop due to gland cup problem

SSP 2 Stop due to impeller problem

Other maintenance measures in the plant are as follows:

During heavy rains the bypass gate is opened by closing the gate valves of grit

chamber, clarifier and the water is allowed to the valley.

The units are cleaned for 3 days once in a year followed by painting of all units.

Regular lubrication, valves rotation, moving mechanical parts are checked and

replacement of worn parts is done.

Grit chambers, Clarifiers are cleaned when the moving arms give jerk, the water

during cleaning is diverted to standby unit and complete cleaning is done.

Oil levels and alignment of moving parts are checked regularly.

The flow is regularly diverted to standby units to ensure frequent use so as to

minimise load on working units and corrosion of standby units.

Pumps and motors are run in rotation basis for efficient use and high performance.

Screenings are manual removed continuously from the screens to avoid clogging.

Once a problem is reported, concerned personnel are intimated and corrective

measures are taken immediately.

3.5 Vrishabhavathi Valley (V-Valley) 60 MLD Tertiary Treatment Plant (TTP)

3.5.1 Purpose of the plant

Bangalore Water Supply and Sewerage Board (BWSSB) are having an 180MLD

secondary sewage treatment plant at Vrishabhavathi Valley, Mysore road. Bangalore city is

located 100km away and 0.5km above its only dependable source of drinking water, River

Cauvery. With high energy cost involved in pumping of water coupled with extremely finite

27

source of raw water and facing ever growing needs of an increasing population, BWSSB was

prompted to conserve potable water and to take a serious look at ventures in recycling and

reuse of wastewater. Hence, BWSSB decided to build a 60MLD tertiary wastewater

treatment plant to meet the demands of the proposed new power generation plant at Bidadi by

M/s Karnataka Power Corporation Limited and other plants near Bangalore city. This would

save usage of potable water in these industries which is a depleting source.

This project was implemented under ‘Improvement of Water Supply and Sewerage

System in Bangalore’ under INDO-FRENCH Protocol. BWSSB awarded this project to

Degremont Consortium consisting ONDEO Degremont SA, France and ONDEO Degremont

Limited India.

SECONDARY TREATED SEWAGE

28

PUMPING STATION

REPARTITION

TRICKLING FILTER A TRICKLING FILTER B

COAGULANT

DENSADEG DENSADEGPOLYMER

BELT PRESS FILTRATE WATER

Fig 3.14: Flow diagram of 60MLD Tertiary Wastewater Treatment Plant

3.5.2 Treatment scheme

The design of the plant is based on the following principles:

1. Since the plant is getting the effluent from the existing 180MLD secondary sewage

treatment plant, the plant is assured of a constant flow of 60MLD.

2. For the optimization of the design, cost and operation & maintenance, the plant is

constructed in two modules of 30MLD each.

3.6 Detailed Description of units

3.6.1 Trickling Filter

The pumped secondary treated sewage from the inlet pump house is split into two

modules of 30MLD each in a repartition chamber. This chamber is built at a higher elevation

so that further flow could be a gravity flow.

From the repartition chamber, the sewage flows into a trickling filter unit. The

hydraulic head differences between the sewage level in the repartition chamber and the holes

in the sprinkler mechanism is sufficient enough to rotate the hydraulically. In the trickling

29

PRE-AERATION TANKDIRTY WASH

WATER TANK

FLOPACFLOPAC

FLOPAC FLOPAC

FILTERED WATER TANK TREATED WATER RESERVOIR

filter, the sewage trickles from the top to the bottom through a plastic media, wherein BOD

level of the inlet sewage is reduced. The sewage is collected in a common trickling filter

outlet channel and is fed into DENSADEG clarifier.

Existing Trickling Filters in V-Valley TTP

Repartition chamber

Construction : Concrete

Length : 6.2 m

Width : 3.2 m

Liquid depth : 1.22 m

Tank depth : 1.92 m

Trickling filters

Construction : Concrete with hollow block masonry

Nos : 2

Shape : Orthogonal

Diameter : 20.4 m

Height : 7.36m

Sprinkler mechanism

Nos : 2

Size : 20.4m

Type : Hydraulic sprinkler

Trickling filter media

Nos : 2

Volume : 1620 m³ for each TF

Type : Cross pack 22

Trickling filter outlet penstock

Nos : 1 Type : Manual Size : 750 mm x 750 mm

3.6.2 High Rate Clarifier

It is based on the following five principles:

30

1. Coagulation in a mixing chamber equipped with a flash mixer, where ferric

chloride is added.

2. Flocculation in a reactor equipped with a turbine type flocculator and a tube

intended for rapid dispersion of the injected polymer.

3. Slow velocity transfer from the reactor to the settling zone to preserve floc

cohesion.

4. External recirculation of sludge from the thickening zone to the reactor.

5. Optimized lamellar settling.

The Densadeg is complemented by two chemical units (ferric chloride and polymer)

and a sludge dewatering unit. There are two no’s of Densadeg clarifiers in this plant and each

consist of two flash mixers, one flocculator, and one clarification unit containing scum pipe

and scrapper mechanism.

Operating principle

Flash mixer: The flash mixer receives a dose of ferric chloride as determined by jar

test in order to provide pre-coagulation before the sewage enters the flocculator.

Turbine reactor: One of the original features of the process is the physico-chemical

reaction such as crystal flocculation or precipitation or any other specific precipitation

reaction takes place in the reactor. The reactor is made up of two-series reactor, an agitated

reactor which performs rapid flocculation, and a plug-flow reactor where slow flocculation

takes place.

Agitated reactor: The raw water, which has been pre-coagulated in the flash mixer,

flows into the centre and the base of the reactor. An axial-flow turbine inside the duct

performs homogenous stirring of the reactor, provides the necessary energy and ensures

mixing of the polymer. Inside the agitated reactor, suspended solids concentration levels (floc

or precipitate) are optimized for the type of treatment by external recirculation of the

concentrated sludge from the thickening zone.

Plug-flow reactor: The upflow reactor serves for slow flocculation producing

enlarged floc. The innovative design of this reactor delivers a particularly dense and

homogenous floc of considerable size. As a result of floc densification, the flow enters the

settling zone at far greater speeds than in earlier systems.

31

Existing High Rate Clarifier (DENSADEG) in V-Valley TTP

Flash mixer chamber


Length : 1.4 m

Breadth : 1.4 m

Depth : 3.575 m

Nos : 2

Volume : 5.8 m³

Flocculator


Length : 5.15 m

Breadth : 5.15 m

Depth : 6 m

Nos : 1

Volume : 151 m³

Lamellar modules

No of sheets : (DH 1500*1000) - 632 and (DH 500*1000) - 158

Material : High compact polystyrene food grade

Colour : White

Width (1module) : 1 m

Inclined length : 1.5 m

Thickness of sheet : 1 mm

3.6.3 FLOPAC

The trapped suspended solids gradually block the interstices between the consistent

elements of the filtering media. This phenomenon is known as ‘filter clogging’. As the

clogging increases, the head loss increases which affects the flow of water. When head loss

has reached a figure close to 1.5m of water column, the filter must be cleaned. The rate of

clogging depends on turbidity in the water, settling process, and grain size of the media. The

FLOPAC has four units:

1. Pre aeration tank

32

2. Filters

3. Filtered water tank

4. Dirty wash water tank

Pre aeration tank: Pre aeration tank is provided with an air pipe network with

VIBRAIRS GM type air diffusers for the aeration of water. The air diffuser network supplies

the required amount of air with the help of a set of air blowers. The air blowers are installed

inside FLOPAC blower room. The blower is operated in required speed depending on the

required dissolved oxygen level. Dissolved oxygen meter is installed at the outlet of pre

aeration tank which helps in measuring dissolved oxygen.

Whenever the inlet parameter exceeds the design parameter, a post coagulation

system is provided to improve the efficiency of filtration. Characteristics of the filter are

detailed below.

1. A filtration process involving a thick layer of sand.

2. A large water depth, which provides suitable positive pressure in all parts of the filter.

3. An equal distribution among the filters of the total water flow to be filtered.

4. A simultaneous air and water backwashing followed by water rising, without

expansion of the filter bed. Cross wash ensures the discharge of dirty water of all

impurities by eliminating any zero horizontal total velocity area in which the detached

particles might be allowed to settle again.

Filtration: Water flows equally into all chambers running along the whole length of

the chamber. After filtration, water will be collected under the false floor and then moves to

filtered water outlet channel which is below the filter feed channel.

Washing: A simultaneous scour air backflow and filtered water backflow is followed

by a rinsing stage with filtered water. During washing, the air is distributed by the long-stem

nozzles and water. The frequency of washing cycle depends on the characteristics of water.

Washing is done when the head loss reaches 1.5m. The various sequences of filtration and

washing are as follows:

1. Lowering the water level to the upper edges of the wastewater outlet by sloping the

filtration and opening the wastewater outlet.

Duration : 1 minute

Air flow rate : 60 m³/hr/m²

33

2. Injecting air and water

Duration : 10-15 minutes

Air flow rate : 60 m³/hr/m²

Water flow rate : 10 m³/hr/m²

3. Rinsing with water until the water is discharged into the sewer

Duration : 10 minutes

Water flow rate : 20m³/hr/m²

Existing FLOPAC Units in V-Valley TTP

Pre aeration tank


Length : 7.5 m

Width : 5.5 m


Tank depth : 7 m

Pre aeration blowers

Nos : 2

Capacity : 750/375 Nm³/hr

Pressure : 0.8 bar

FLOPAC filter design

Nominal input : 2500-2740 m³/hr

No of filters : 4

Length : 7.95 m

Width : 9.08 m

Unit filter bed area : 72 m²

Media depth : 1.5 m

Media type : Biolite

Wash water rate : 10 m³/m²/hr

Air scour rate : 60 m³/m²/hr

Backwash air blower

Nos : 2

Capacity : 5000Nm³/hr

34

Discharge pressure : 0.6bar

Dirty water tank


Length : 27.16 m Width : 9.8 m Liquid depth : 3.69 m Tank depth : 4.19 m

Filtered water tank


Length : 7.5 m

Width : 5.5 m


Tank Depth : 7.64 m

3.6.4 Sludge Treatment

The sludge extracted from the DENSADEG is stored in a sludge storage tank and then

sent by sludge feed pumps to the dewatering machine, Superpress after addition of an organic

polymer.

The polymer is prepared in the poly preparation tank and is feed into the flocculator

of Superpress through poly dosing pumps. The dewatered sludge is transported through

conveyor belts to the sludge lime mixer and the filtrate is collected into a filtrate sump and is

pumped to the flocculator of densadeg.

The superpress belts are washed with filtered water pumped from filtered water tank

through belt wash pumps at a pressure of about 8bars after passing through on-line strainer to

remove any particles, if any.

In the sludge lime mixer, the dewatered sludge is conditioned with quick lime for

increasing the pH up to 12 for stability over extended storage and dryness up to 25%.

SUPERPRESS Principle

The superpress is designed for the removal of most of the water contained in sludge

by continuous filtration, under pressure, of a layer of sludge placed between two filter belts

35

after appropriate chemical conditioning that promotes the formation of a bulky floc well

separated from the water. However, the principle of continuous pressure filtration has its

limits; in particular there is a risk of side flow of sludge under the effect of the pressure

applied.

Sludge flow as a function of:

Its rheological characteristics

The water content in the sludge at the inlet of the pressing zone.

Therefore, it is necessary to remove a great part of the water contained in the sludge

before applying the dewatering pressure.

The preliminary drainage phase is essential as it makes it possible to quickly obtain

thicker and much denser sludge than originally present thus increasing the pressing capacity.

The sludge should be evenly distributed over the entire width of the belt to optimize the

production capacity of the unit and the dry solids content of the cake produced.

SUPERPRESS Operation

The lower filter belt is defined as the one receiving the sludge from the flocculator

and the other filter belt is referred to as the upper belt. The sludge to which a polyelectrolyte

has been added is fed to a flocculator equipped with a vertical variable speed stirrer and flows

onto the first belt in the drainage zone. Here the sludge goes through two fences and is

distributed over the belt width by an equalizing roller. Sludge drainage is improved by the

furrowing effect of the fences and slight compacting by the roller help free drainage of the

sludge. After drainage, the sludge is squeezed between the two belts and undergoes

progressive compression in a wedge-shaped inlet and a large diameter perforated drainage

drum until it undergoes the final pressure determined by the degree of tensioning of the belts.

The two filter belts then run between a set of small-diameter return rollers that

increase the drainage pressure and at the same time exert shearing stress, which breaks up the

sludge structure, opens cake drainage grooves and improves final dewatering.

At the end of the line, the two belts part from one another after the drive roller and the

cake is removed by two scraper blades for discharge on the conveyor belt. Tracking of each

belt is automatically centred by a pneumatically controlled angular displacement roller. Both

36

belts are washed continuously by pressurized water sprayers in closed chambers. The filtrate

and wash water are discharged by gravity through launders.

Maximum performance of the filter for each type of sludge can be obtained through

simple settings:

Height of equalizing roller

Filter belt tensioning from pneumatic cylinders.

Belt drive speed adjustable through a manually controlled, mechanical, variable speed

drive.

Rotation speed of flocculator adjustable through a manually controlled, mechanical,

variable speed drive.

The fitter is fitted with fail-safe controls for immediate shutdown in the following cases:

Excessive belt over travel resulting from a malfunction in the tracking device.

Insufficient belt tensioning compressed air or wash water.

A manually operated emergency stop button.

Existing SUPERPRESS Units in V-Valley TTP

Sludge storage tank


Length : 9 m

Width : 6.25 m

Depth : 4.06 m

No of tanks : 1

Volume : 200 m³

Sludge mixers : 2

Polymer dosing system


Length : 1.95 m

Width : 1.7 m

Depth : 2.8 m

Volume : 8 m³

Polymer dose in tank : 1g/L

37

Dewatering machine

Nos : 2

Type : Twin belt pass filter

Width : 2 m

Supplier : Degremont

Belt conveyor

No : 1

Belt width : 0.5 m

Belt length :13.925 m

Speed : 0.5 m/s

Capacity : 1tonne/h

3.7 Plant Automation System

3.7.1 SCADA (Supervisory Control and Data Acquisitions)

The plant has been provided with Programmable Logic Controllers (PLC) based

control system for continuous operation and monitoring the plant. Operation of key unit

processes is totally automated like pulsators, filters, and sludge handling system. Plant can be

operated with little manual intervention.

Automation system consists of various instruments like flow measuring, level sensing,

Dissolved oxygen analysers, pressure sensing etc. There are three PLCs as mentioned above.

These PLCs are connected through three different networks that are as follows:

1. ETHWAY

2. FIPWAY

3. MODBUS

One number panel view operator station is installed at all control panels and filter

desks (LCPs). Telemechanique controllers at each location have been envisaged. The panel

view provides operator interface capabilities in saving space and flat panel designs. The

38

input/output modules are mounted in the I/O racks. The modular family of PLC and rack

based I/O consists of processor, I/Os and peripheral devices. This processor family delivers

power and flexibility with a wide range of communication configurations, features and

memory option. The inputs and outputs for the control system is handled by the following I/O

modules:

32-channel 24V Digital Input module

32-channel 24V DC Digital Output modules

8-channel Analog Input module

8-channel Analog Output Modules

The processor and I/O modules have LED type diagnostics indicating numbers.

3.7.2 Supervision system located in the Main Control Room (SCADA)

Operation

Start/stop from SCADA when switch on MCC is in ‘Auto’ mode indication

Indication on the screen ‘ON/TRIP’ for drives

All process events (levels, pressure, flow meter)

In case of the failure of supervision or the communication network, each PLC cabinet

continue to work with the last data transmitted. The operator can modify data when needed

directly on the operator interface in front of PLC cabinet. Operator is also informed of all the

process events through this operator interface (level, pressure, flow etc).

3.8 Maintenance of the Tertiary Treatment Plant

3.8.1 Mechanical Task Schedule

FLOPAC

Daily maintenance:

Oil level, vibration and noise check for belt wash pump, pre aeration air blowers,

backwash air blowers and air compressor.

Weekly maintenance:

Cleaning of equipment, stainer, and lubrication for belt wash pump.

39

Cleaning of equipment and lubrication for pre-aeration air blower, backwash air

blower air compressor.

Cleaning of equipment, filter and lubrication for EOT crane.

Monthly maintenance:

Check the alignment, tightness of all nuts, bolts for belt wash pump, pre-aeration air

blower and backwash air blower.

Check the alignment, belt tension, tightness of all nuts, bolts etc for air compressor.

Check all nuts, bolts, wire rope condition, limit switches, lubrication if required.

DENSADEG Clarifier

Daily maintenance

Check oil level of gear box, vibration and noise for flash mixer, flocculator and

scrapper mechanism.

Weekly maintenance

Cleaning of equipment and lubrication for flash mixer, flocculator, and scrapper

mechanism.


Check the alignment, tightness of all nuts and bolts; lubricate all bearing for flash

mixer, flocculator and scrapper mechanism.

Dewatering building

Daily maintenance:

Check oil level, vibration and noise for air compressor.

Check oil level, vibration and noise, and belt condition for Super press.

Check oil level, vibration and noise for screw conveyor, belt conveyor, flocculator

and booster pump.

Weekly maintenance:

Cleaning of equipment, belt tension, and filter for air compressor.

Flushing and operation of limit switches for Super press.

Cleaning of equipment, and lubrication for screw conveyor, belt conveyor and

flocculator.

Cleaning of equipment and stainer for booster pump.

Check the smooth operation of EOT crane.

40


Check the alignment of belt and tightness of all nuts bolts for air compressor, super

press, screw conveyor, belt conveyor, and flocculator.

Pipeline maintenance, tightness of all nuts, bolts for booster pump.

Check all nuts, bolts, wire rope condition, limit switches, lubrication if required.

CHAPTER 4.0

DISCUSSIONS

4.1 Recommendations

The screenings of raw sewage mainly consist of plastic materials which are

not supposed to be coming in sewage. The reason for this may be present due

to open channels that carry sewage to STP. Measure has to be taken to prevent

entry of such things into sewer channels.

The influent characteristics of raw sewage flow to STP vary widely, which has

direct …….on the quality of treatment.

The screens provided are efficient and efforts can be made to make them

100% efficient with adopting mechanical cleaning devices. The disposal of

screenings has to be done in an environmental friendly manner.

The breakdown of supporting arms in assembly in Primary clarifiers 2s has to

be replaced completely which reduces frequent repair charges.

Care has to be taken to avoid entry of the airborne wastes into clarifier and

bio-filters. Open channels can be covered with mesh to avoid such entry into

treated waters.

41

Bio-filters have to be replaced with new sprinkler mechanism (Rotary Arms)

for uniform and efficient distribution of wastewater on media. Proper

ventilation has to be made sure to overcome operational problems which lead

to lower efficiency.

The clearance between filter media and rotary arm over it should be not less

than 15 cm as per CPHHEO guild lines and proper alignment of rotary arm

can make sure of this parameter.

Recirculation of treated wastewater completely back into STP units during the

periods of lean flow helps efficient use of units and reduces load on receiving

valley, it is important to decrease load on valley so as to reclaim its naturally

stream quality.

Extension of laboratory facilities with advanced and required instruments is

necessary for regular analysis to check the performance of STP.

180 MLD STP is very old and obsolete technology hence authorities can think

of alternative/advanced methods of wastewater treatment , as in coming days

the load on plants will increase enormously there is a need for new, modified

and advanced treatment technique so as to curb the increasing pollution in the

natural valley stream.

Water reclamation and reuse goals can improve the conditions of valley which

has been polluted even though presence of sufficient treatment plants.

Stringent regulations by the authorities have to be laid before industries

around, to control the pollution through illegal discharges.

Institutional people are academics can be encouraged to know the best

possible treatment methods through research and projects helpful for

authorities.

42

References

G. Tchobanglous, F. Burton, (1991). “Wastewater Engineering, Treatment, Disposal and Reuse, 3rd edition, McGraw Hill Publications.

Joseph A. Salvato, Nelson L. Nemerow, Franklin J. Agardy, (2003). “EnvironmentalEngineering”, fifth edition, Published by John Wiley & Sons, Inc., Hoboken, New Jersey.

The expert committee, (1993), “Manual on Sewerage and Sewage Treatment”, second edition, Ministry of Urban Development, New Delhi.

http://www.wikipedia.org/Sewage_treatment.html

43

http://www.wikipedia.org/Sewage_treatment.html

COD mg/l

44

DateFlow MLD Temperature 0 C pH

DO mg/l

Inlet Intermediate Outlet Inlet Intermediate Outlet Inlet1/6/2010 61 28 24 24 7.7 7.2 7.3 0.62/6/2010 63 27 24 24 7 7.1 7.3 0.33/6/2010 69 28 24 24 7.2 7.3 7.4 0.74/6/2010 68 27 24 24 7.2 7.2 7.3 0.55/6/2010 61 28 25 24 6.9 7.1 7.3 0.36/6/2010 62 27 24 25 7 7.3 7.4 07/6/2010 77 28 24 24 7.1 7.1 7.2 08/6/2010 77 27 25 25 6.9 7.2 7.3 09/6/2010 77 28 24 23 7 7.1 7.2 0

10/6/2010 67 27 24 23 6.9 7.3 7.3 011/6/2010 64 28 24 23 7 7 7.2 012/6/2010 60 27 25 23 7.2 7.1 7.3 0.313/6/2010 54 28 24 24 7.1 7 7.4 0.614/6/2010 51 27 26 24 6.9 7.2 7.3 0.515/6/2010 54 27 25 24 7.1 7 7.3 0.916/6/2010 47 27 25 24 6.9 7.2 7.5 0.817/6/2010 74 28 24 23 7.1 7.1 7.4 0.318/6/2010 90 27 24 24 7.2 7.3 7.2 0.719/6/2010 71 28 25 25 7.1 7.3 7.3 0.320/6/2010 66 27 25 25 6.9 7.2 7.2 0.521/6/2010 66 29 26 24 7 7.1 7.4 0.622/6/2010 66 28 23 22 6.9 7.2 7.3 0.823/6/2010 66 27 24 24 7.1 7.1 7.4 0.224/6/2010 72 29 25 24 7 7.3 7.4 0.325/6/2010 83 28 25 24 7.1 7.2 7.4 0.526/6/2010 81 28 25 24 7.1 7.3 7.4 0.627/6/2010 75 27 24 24 7.2 7.3 7.4 0.728/6/2010 73 28 25 24 6.9 7.3 7.4 0.629/6/2010 78 27 24 23 7.1 7.1 7.3 0.830/6/2010 81 27 24 24 7 7.3 7.5 0.31/7/2010 66 27 24 24 6.9 7.2 7.3 0.72/7/2010 66 28 25 24 7 7 7.2 0.33/7/2010 66 27 26 24 6.9 7.1 7.3 0.54/7/2010 72 28 26 24 7 7 7.3 0.65/7/2010 83 27 26 25 7.2 7.2 7.4 0.86/7/2010 81 29 25 25 7.1 7.3 7.6 07/7/2010 75 28 24 24 6.9 7.2 7.4 08/7/2010 73 27 24 23 7.1 7.1 7.3 0.19/7/2010 78 29 24 24 6.9 7.3 7.5 0

10/7/2010 90 28 24 24 7.1 7.3 7.4 0.211/7/2010 72 27 24 24 7.2 7.3 7.5 0.312/7/2010 83 27 25 25 7.1 7.2 7.4 0.5

Date

Inlet Intermediate Reduction % OutletReduction %

1/6/2010 738 286 61 176 762/6/2010 628 248 61 148 763/6/2010 714 239 67 168 774/6/2010 688 214 69 137 805/6/2010 714 258 64 181 756/6/2010 781 286 63 266 657/6/2010 681 246 64 210 698/6/2010 721 278 61 236 679/6/2010 664 241 63 173 74

10/6/2010 778 287 63 189 7611/6/2010 681 237 65 108 8412/6/2010 704 256 64 126 8213/6/2010 653 194 70 106 8414/6/2010 578 186 68 91 8415/6/2010 667 249 63 140 7916/6/2010 714 263 63 161 7717/6/2010 768 281 63 172 7518/6/2010 781 276 65 168 7819/6/2010 678 238 64 141 7920/6/2010 738 256 65 176 7621/6/2010 761 281 63 189 7522/6/2010 681 244 64 138 8023/6/2010 721 230 68 161 7824/6/2010 814 281 65 190 7725/6/2010 781 273 65 181 7626/6/2010 714 241 66 148 7927/6/2010 781 286 65 168 7928/6/2010 681 246 64 138 8029/6/2010 721 278 65 161 6730/6/2010 664 241 63 173 741/7/2010 778 287 64 189 762/7/2010 681 238 64 108 843/7/2010 704 256 68 126 824/7/2010 653 281 65 106 845/7/2010 578 244 65 91 846/7/2010 667 230 63 176 857/7/2010 768 281 63 176 758/7/2010 781 286 65 181 789/7/2010 678 246 64 141 79

10/7/2010 714 230 66 148 7911/7/2010 721 278 68 161 7812/7/2010 664 241 63 173 79

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Date SS mg/l Inlet Intermediate Reduction % Outlet Reduction %

1/6/2010 608 121 80 58 902/6/2010 437 107 76 49 893/6/2010 481 108 78 52 894/6/2010 518 119 77 58 885/6/2010 524 120 77 62 886/6/2010 558 116 79 110 807/6/2010 574 121 79 126 788/6/2010 536 110 79 116 789/6/2010 428 95 78 96 7810/6/201

0 573 113 75 74 8711/6/201

0 431 109 75 53 8812/6/201

0 478 98 79 59 8813/6/201

0 502 102 80 60 8914/6/201

0 436 92 79 47 8915/6/201

0 482 108 78 47 8916/6/201

0 510 104 80 51 8917/6/201

0 568 118 79 54 8918/6/201

0 537 107 80 58 9019/6/201

0 487 98 79 53 9020/6/201

0 581 108 81 54 9021/6/201

0 610 136 78 63 8922/6/201

0 571 116 80 58 8923/6/201

0 538 108 80 56 9024/6/201

0 622 123 80 62 9025/6/201

0 639 118 81 67 8926/6/201

0 571 108 81 52 9127/6/201

0 621 102 83 60 9028/6/201

0 600 98 84 50 92

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29/6/2010 510 112 78 48 91

30/6/2010 438 96 78 44 90

1/7/2010 589 100 83 46 922/7/2010 639 134 79 65 903/7/2010 571 115 80 60 894/7/2010 449 108 76 59 875/7/2010 426 103 76 55 876/7/2010 538 111 79 50 917/7/2010 539 99 82 47 918/7/2010 555 98 82 52 919/7/2010 488 91 81 69 8610/7/201

0 512 112 78 50 9011/7/201

0 469 111 76 49 9012/7/201

0 499 110 78 56 89

Date BOD3 mg/l

Inlet IntermediateReduction % Outlet Reduction %

1/6/2010 389 124 68 49 872/6/2010 362 109 70 47 883/6/2010 338 107 68 42 854/6/2010 372 118 68 57 865/6/2010 336 106 68 48 846/6/2010 356 141 60 54 707/6/2010 341 179 48 102 638/6/2010 378 188 50 139 699/6/2010 310 160 48 97 76

10/6/2010 336 106 68 79 8511/6/2010 326 94 48 48 8512/6/2010 342 106 50 52 8713/6/2010 321 93 48 46 8614/6/2010 310 98 68 42 8615/6/2010 339 106 71 47 8616/6/2010 356 119 68 55 8417/6/2010 379 128 71 62 8418/6/2010 346 110 68 58 8319/6/2010 321 106 69 51 8420/6/2010 371 118 68 56 8521/6/2010 410 127 69 63 8522/6/2010 341 118 65 54 8423/6/2010 381 113 70 51 87

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24/6/2010 357 109 69 46 8725/6/2010 389 121 69 62 8426/6/2010 378 103 73 48 8727/6/2010 356 128 64 49 8628/6/2010 341 108 68 55 8429/6/2010 321 106 67 53 8330/6/2010 312 101 68 68 781/7/2010 356 109 69 41 882/7/2010 399 122 69 43 893/7/2010 356 119 67 59 834/7/2010 358 110 69 47 875/7/2010 346 109 68 42 886/7/2010 325 107 67 57 827/7/2010 390 140 64 102 748/7/2010 366 123 66 49 879/7/2010 348 110 68 62 82

10/7/2010 331 105 68 51 8511/7/2010 369 141 62 102 7212/7/2010 356 107 70 51 86

The analysis results and flow data collected from the plant for the month June-July is presented in the tables above.

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