constructing on of india's largest single location effluent treatment plants

Project Management Challenges during the Construction of an Effluent Treatment Plant at Sukinda

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ABSTRACT

Tata Steel operates one of the largest chromite mines in India at the Sukinda Valley in Odisha. The

chrome ore produced is subsequently converted it to Ferro Chrome and sold to customers across the

world, making Tata Steel one of the top ten Chrome players in the world. A large quantity of water,

generated during mining and due to rainfall, needs to be handled during the mining operations.

Chrome Ore mainly contains tri-valent chromium oxide and a very small fraction of hexavalent di-

chromate. Water coming in contact with chromium ore preferentially leaches out soluble hexavalent

chromium from the ore body, as a result, water from the mine contains 0.2 – 4 mg/l of hexavalent

chromium against a safe limit of 0.05 mg/l for human consumption; requiring all water to be treated

before its release from the mines. Thus, Tata Steel has set up an Effluent Treatment Plant at Sukinda

with a capacity of ~108 million litres/day, the largest in the region, and possibly one of the largest

single location ETPs in India. This paper discusses how the challenges faced during construction of

this Effluent Treatment Plant were successfully tackled.

KEY WORDS

Chromite or Chromium Ore

Hexavalent Chromium

Effluent Treatment

Project Management

Construction

Optimization

Safety Management

Real Time Monitoring


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INTRODUCTION

Describing Sukinda and its importance to India

Sukinda Valley, known for its high grade chromite deposits, is located in eastern state of Odisha,

India. This valley contains 99% of India’s chromite deposit. The ultramafic mass occurs sporadically

over an area of 420 sq. km around Sukinda(Fig-1). The deposit was first proved by geologists of Tata

Steel in 1949, followed by intensive exploration. TSL’s Sukinda Chromite Mines, with a mine

extending over 406 Ha, is the one of the largest chrome mines in India. The Chrome ore mined at

Sukinda has enabled Tata Steel to be the largest chrome alloy players in India and among the top ten

globally.

Fig – 1 : Tata Steel’s Chromite Mine at Sukinda

Chrome Ore

Chrome ore occurs as Chromite, which is chromium oxide, and is essentially in the form of un-

weathered, hard, compact, fine grained dark grey lumpy ore or as a weathered, and loosely bonded,

brown-black, friable ore in ultra-basic host rock(Fig-2). Chromite contains mainly stable trivalent

oxide of Chromium with a small fraction in the unstable hexavalent state.


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Fig - 2 : Weathered Friable Ore and Massive, Un-weathered Lumpy Ore

Hexavalent Chromium

While trivalent compounds of chromium are not soluble in water, hexavalent chromium compounds

are. Water coming in contact with chromium ore leaches out soluble hexavalent chromium from ore

body. Both mine water and surface runoff have 0.2-4 mg/l of hexavalent chromium against the safe

limit of 0.05 mg/l for human consumption.

Hexavalent chromium (Cr+6) is considered a human carcinogen with geno-toxic properties.

Hexavalent chromium can cause the following diseases:

Ingestion of hexavalent chromium contaminated water causes irritation and ulcers in the

stomach and the intestines

Contact with hexavalent chromium (in the form of dust or dissolved in water) with soft

mucous tissues of the eyes and the nose can lead to irritation and ulceration

Exposure to liquids/water contaminated with hexavalent chromium causes allergic skin

reactions

There is no evidence of elevated levels of these diseases (compared to the national and the state

average) in the valley. Another study, by Utkal Polyclinic, has also showed a lower incidence of skin

diseases in the Sukinda Valley, which, due to the allergic effects of Cr+6 on skin, is contrary to

expectations. This is probably due to the low levels of Cr+6 found naturally (and in Sukinda).


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Water Management at Sukinda Mines

The Sukinda Valley experiences about 110 cm to 180 cm of rainfall annually, of which eighty per-cent

(80%) occurs during the monsoon season i.e. between June and September. Owing to this highly

uneven distribution of rain, the weather in the Sukinda Valley ranges from extremely dry to

extremely wet.

The major portion of the rain goes as surface runoff, and flows through the garland drains, that have

been made around the quarries and dumps. The flow carries silt and dry vegetation with it, apart

from picking up hexavalent chromium as it trickles down the chrome rich quarries and dumps. These

drains also channel the water pumped out during mining operations. (Fig-3)

Fig – 3 : Map showing water discharge circuit, garland drains and ETP Locations

History of Hexavalent Chromium Management at Sukinda Mines

Hexavalent Chromium in the Sukinda Valley water was first detected in the mid-1990s. Tata Steel

pioneered the efforts to mitigate the ill effects of hexavalent chromium by collaborating with India’s

premier environmental research institute, NEERI, Nagpur and set up three Effluent Treatment Plants

(ETPs) based on technology co-developed with NEERI. Initially, spent pickled liquor, from Tata Steel’s

old Sheet Mills was used to reduce hexavalent chromium; and later a process using FeSO4 was

established. (Table – 1)


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Sl.

No.

Effluent

Treatment Plant

Year

Established

Capacity To Treat Process Used

1 Pilot ETP with

NEERI

1998 200 m3/hr Mine

Water

Reduction of Cr+6 using spent

pickle liquor.

2 Up-graded ETP-1 2002 715 m3/hr Mine

Water

FeSO4 based treatment with

gravity sand filters

3 ETP-2 and ETP-3 2003 3000

m3/hr

Surface

Run-off

FeSO4 based treatment with

baffles and roughing filters

Table – 1 : History of Effluent Treatment Plants at Sukinda Chromite Mines, Tata Steel

IMPETUS TO UPGRADE

While the pioneering efforts of Tata Steel in setting up Effluent Treatment Plants were well

acknowledged, there was a growing pressure to upgrade the (over ten year old) ETPs, both internally

and from the Government agencies, due to the following reasons :

1. Partly in order to mitigate environmental effects due to its mining operations and partly to

meet statutory obligations, Tata Steel has been conducting a very successful afforestation

program around the Sukinda and Kalarangiatta areas. Other miners at Sukinda too have

made some efforts in afforestation which has resulted in good rainfall.

2. Tata Steel’s Sukinda Chromite Mine is already one of the deepest Open Cast Chromite Mines

in India. As open cast mining is reaching the ultimate pit bottom, Tata Steel has long been

contemplating starting Underground Mining at Sukinda. This will further increase the

quantity of water that needs to be handled.

3. The ETPs set up in early 2000’s were possibly state of art at that time. However, with

facilities available for automation, online monitoring etc., and an increased understanding of

water treatment methods, the ETPs seem to be extremely maintenance and manpower

intensive today, and technologically obsolete.

4. The State Pollution Control Board, Odisha (OSPCB), hired IIT Kharagpur to conduct a study

on possible solutions to the issue of water pollution. The study recommended that a

common Effluent Treatment Plant be set up by OSPCB treating all water before reaching the

Damsala River.

However, the common ETP proposal was a non-starter because :

a. It was complicated, and not easy to execute on the ground; primarily due to requirement

of channelling all the water from the valley to one location, which would be challenging

due to (i) the large undulating contour of the Sukinda Valley and (ii) the vast area to be

covered.

b. The common ETP would require a large amount of capital expenditure. Sharing of the

capital expenditure between different mine owners was an extremely contentious issue.

Also, land for the ETP and right of way for the drainage would have been bottlenecks.

c. Operations of the Common ETP would be challenging too, given the different operating

philosophies, that different mine owners have.


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Due to the above issues, it was decided that all the mines would set up their own ETPs individually

based on the conceptual design provided by IIT, Kharagpur to treat water generated from their

mines (including surface runoff) inside their leases.


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CHOOSING THE RIGHT TECHNOLOGY AND EXECUTION STRATEGY

1. Evaluation of various techniques to treat Cr+6 and why we chose FeSO4 technology

There are many solutions to eliminate hexavalent chromium from water. Some technologies are well

established and in use commercially for specific situations. There are also some innovative solutions

that have been proven experimentally. A summary of the available technologies, and the reasons for

the selection of the FeSO4 technology is summarized in the table below (Table 2) :

Sl

No Technology Process Details Advantages Disadvantages

Suitability to treatment of

mine water

1

Physical

Adsorption of

soluble

chromium

ions(Cr+6)

Use of active

absorbents like

activated charcoal,

zeolites etc.

Fast Kinetics – able to

deal with large volume

of water

Low Cost

Narrow pH range,

Fouled by suspended

solids,

tolerance

Unsuitable due to TSS &

pH

2

Electro

chemical

treatment

Electro-coagulation by

electrolytic oxidation

of the ‘sacrificial

electrode’.

Wide pH range

Tolerant to suspended

solids

Cost (sacrificial

electrode & electricity)

High sludge

Moderate kinetics in low

concentration

Unsuitable due to cost,

moderate speed of

treatment in low

concentration

3

Osmosis/Mem

brane

separation

Using ultra-filtration

membrane to remove

Cr+6 ions based on

size exclusion

High removal efficiency

(>85%)

Low solid generation,

Low chemical

consumption

Narrow pH range,

Fouled by suspended

solids,

High Cost of membrane

Unsuitable due to high cost,

Low speed of treatment

4

Bio-

remediation

Using Microbes,

especially bacteria

capable of Chromium

(VI) reduction

Eco-friendly

Highly selective

Operational

flexibility(can be grown

in existing drains)

Low operational cost

Narrow pH &

temperature range,

Fouled by suspended

solids, oil & other

contaminants,

Effect of bacteria on

animals & humans not

known fully.

Unsuitable due to

intolerance to variations in

pH, temperature,

contaminants

& possible ill effects of

bacteria

5 Phyto-

remediation

Using plants which

accumulate toxic

compounds i.e.

Chromium (VI)

Very cost effective Has

aesthetic advantages&

long term applicability

Eco-friendly

Tolerant to pH &

suspended solids

Very slow process,

Phytotoxic at high

concentration

High space requirement

Plant waste needs to be

buried

Unsuitable due to the very

low process kinetics

Large space requirements

& possible ill effects of plant

bio-mass

6 Chemical

Precipitation

Chemical Reduction of

soluble Cr+6 to

insoluble Cr+3

Fast reaction

Time tested

Tolerant to variations in

pH and to high TSS

Medium Capex

Simple well understood

operation

High Sludge generation,

Extra operational cost

for sludge disposal

Method chosen due to prior

experience, fast reaction

time, low space

requirement. Tolerance to

TSS, pH, temperature

variations, very well

understood process

* Ref : IFA/ABP/389/2013 – Dr Y Rama Murthy et al, Jun-14(ref. 1)

Table – 2 : Selection of Right Technology from the Available Options for Remediation of

Hexavalent Chromium Effluent.

Tata Steel, along with CLRI, has also developed a Herbal Treatment process using Terminalia

Chebula, an organic product, for Cr(VI) removal in chromite concentrates; but the process is not

suitable for treatment of Cr+6 in mine effluent, given the volume of water to be treated, the slow

reaction rate & the cost of Terminalia Chebula(ref. 2)


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2. ETP Process Design : Optimization of the treatment

Before designing the process, extensive jar tests were carried out on the effluent water to allow for :

a) Highly efficient and fast reaction for the reduction of hexavalent chromium Cr+6 to Cr+3 .

b) Rapid flocculation of precipitated Cr+3 compounds to reduce residence time in the Clariflocculator,

while enabling control of TSS within statutory limits.

Both the above are necessary to increase the throughput of the ETP and enable treatment of a large

volume of water in a short time. As a result of the jar tests, we have included three more facilities in

the ETP, which were not in the original design, namely :

i. Acid Dozing of the raw effluent in a flash mixer to bring down the pH before reaction with FeSO4

since the FeSO4 reaction is most efficient at a low pH. Also, because of the efficient reaction at

low pH, the consumption of FeSO4 and the amount of sludge generated can be substantially

reduced.

ii. Stirring arrangement in the flash mixer and a reaction channel to allow for complete reduction of

hexavalent chromium.

iii. pH correction using an alkali before dozing with a polyelectrolyte, to ensure complete reaction, as

polyelectrolyte reaction needs a neutral pH, along with a stirring arrangement. The alkali

recommended for pH reduction is NaOH but for various reasons we are using Ca(OH)2.

3. Sizing of the Effluent Treatment Plant

To determine the most suitable size for the effluent treatment plant, we needed to determine

the volume of both mine water (water pumped out from the mines during operation) and the

surface run off. The determination of mine water volume was simpler, due to ready data

available from which a correlation between mine production and water volume could be

obtained(ref. 3). The volume of mine water then was approximated from the long term plan for

mining, inclusive of the planned shift to Underground Mining. Determining the surface run-off

was more difficult. For this, we studied the water flow pattern and the meteorological data over

the last seven years for the region. The maximum rainfall over 24 hours in the last ten years

formed the basis for the calculation of surface run-off volume. The most likely maximum volume

of water that would need to be treated, thus determined, became the basis of determining the

size of the Effluent Treatment Plant. This resulted in us recommending the setting up of an ETP

capable of treating 4500 m3/hr; by far the largest ETP in the region. Other miner owners arrived

at far smaller ETPs, but subsequent events proved that we were correct. A year(and a rainy

season) later, many of the neighbouring mines are already expanding the capacities of their much

smaller ETPs.

4. Specifications for the Effluent Plant Output

We took a decision that the Effluent Treatment Plant output would not only meet the current

specifications for treated effluents in non-urbanized areas, but in order to be future ready, meet


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the specifications for treated effluents in both urban areas and the likely stricter norms for

treated effluent that are likely to be imposed in the future. Thus the plant has been designed

such that the output has less than 0.01 mg/l of Cr+6 against a norm of 0.05 mg/l and meets the

stricter TSS standard of < 10mg/l (drinking water specifications) against a norm of < 100 mg/l

(norms for treated effluents in non-urbanized areas). We also took a decision to treat both

surface run off water and mine water in same way, which none of the other mines in Sukinda

planned to do. This decision proved to be fortuitous, as the Pollution Control Board has now

asked all mine owners to treat both surface run off and mine water and many mine owners have

had to look at augmenting the capacity of their ETPs.

Fig. 4 gives the capacity and guaranteed output water parameters of the Effluent Treatment Plant

at Sukinda (Fig 4)

Fig - 4 : Capacity and Guaranteed Output Water Parameters of the Effluent Treatment Plant at

Sukinda

5. Modular ETP

The wide variation in the quantity of surface water to be treated between the monsoon months

of June-Sept (where over eighty per-cent of the rainfall takes place) and the very dry months in

winter (Nov-Dec) and peak summer(Apr-May) posed its own challenges. Instead of making a

single large 4500m3/hr Effluent Treatment Plant, which would unnecessarily increase operations

cost in the dry period, we decided to make the ETP in three modules of 1500m3/hr capacity each

(Fig 5).


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Fig - 5 : Block Diagram of the Modular Effluent Treatment Plant at Sukinda (1500 m3/hr X 3

modules)

6. Locating the ETP

Building an ETP of 108 million litres/day capacity is a huge challenge due to lack of sufficient

available space in Tata Steel’s Sukinda Chromite Mines leasehold area. The site for the ETP was

selected considering two main aspects, namely

a. The selected location would have to be at the lowest point of the mine so that all the water

(mine water and surface run-off) could be channelized at the minimum cost using gravity.

b. There would need to be adequate space at the site so that a 108 million litres / day ETP can

be constructed at the site.

The best candidate (though with many shortcomings) for location of the said ETP was at the south-

west boundary of the lease, the area used for despatches and truck parking. Also, the main despatch

road ran through almost the middle of the selected area. Thus we needed to first relocate the truck

parking yard and re-route the main despatch road, a big task by itself.

Due to the topography of the mine, some of the water would naturally flow to the north east

extremity of the mine, near the temple. Initially it was decided that we would need to construct one

of the ETP modules (1,500m3/hr) at the temple end and two ETP modules (2 x 1,500 m3/hr) at the

south west end(also known as the main site).


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In a measure of further optimization, along with our Engineering Consultants, TCE, Jamshedpur and

execution partners, M/s EFFWA Infra and Research, Mumbai, the Engineering & Projects team at

Sukinda redesigned the layout of the modular ETPs such that all three clariflocculators could be

located next to each other at the main site with two collection tanks, one at the temple end and the

other at the main site; connected by a system of pumps and underground piping(Fig 6).

Fig - 6 : 3D View of the Modular Effluent Treatment Plant at Sukinda (1500 m3/hr X 3 modules)

7. Project Cost Optimization

In line with our tradition and philosophy of implementing the best environmental protection

measures and to remain a benchmark in the industry, we increased the capacity of the Effluent

Treatment Plant, with a concomitant increase in capital cost. We brainstormed to lower the cost

of the project, resulting in many innovative solutions, such as :

i. ETP at a Single Location : We had initially proposed construction of two separate ETPs at both

extremities of the mine. Every unit (pumps, motors, transformers, RCC tanks, clariflocculators

etc) would thus need to be constructed in both locations(albeit of a smaller capacity). Making

the ETP at one location, and the pumping of the effluent collected to the main ETP site; resulted

in substantial savings of about Rs XXX crores.


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ii. Free supply of steel : We changed the terms of the contract to include free supply of re-bars,

which, being a product made by Tata Steel, was available to us at transfer prices (lower than

market prices due to lower taxes) and also gave us the advantage of assured quality, By this we

saved over Rs XXX crores in the project cost.

iii. Transmission of raw effluent partly through existing drains instead of through a underground

steel pipe : Initially we had planned to send the pumped raw effluent through a steel pipe.

However, on examination of the topography we found a natural slope from mid-way enabling

us to use the existing network of garland drains(after repairing them and increasing their

carrying capacity) to transmit the raw effluent. This resulted in a saving of Rs XX crores.

iv. Optimization of the steel structures, by evaluating the soil bearing capacity, for each location :

Initially we had taken a single measurement of the soil bearing capacity(SBC) at the centre of

the proposed ETP location. Because the SBC value was low, the structures were designed with

higher reinforcement. However, during excavation, it was found that the area, being partly

refilled, had widely varying SBCs. SBC values for each structure were measured and the

structures were re-designed, resulting in a substantial saving in construction cost, about Rs XX

crores.

v. Changing the sludge disposal method : Initially we had planned to handle dry sludge (less than

30% moisture) from the centrifuge using a conveyor to the sludge yard from where it would be

re-handled. However, the conveyor was taking up a large amount of space that we could be ill

afford. To optimize space and improve subsequent operations, we re-designed the sludge

handling system so that the dry sludge falls directly into buckets from which it will be lifted by

the Placer Dumper for disposal. This has led to a reduction in cost by Rs XX crores.

These cost reduction measures, taken up through a DMAIC project(ref. 5), resulted in lowering the cost

by Rs XXX crores.

CHALLENGES DURING THE EXECUTION

The State Pollution Control board had given us a deadline of 31-Dec-2014 for setting up facilities to

treat mine water and 30-Jun-2015 for setting up of the complete ETP. This was a seemingly

impossible deadline, considering that we had to start from scratch, from choosing the technology,

the execution partner, the engineering consultants, getting capex approvals and executing the

project within the stiff timeline of one and a half years.

Getting the capex approval and post techno-commercial negotiations to choose the execution

partner and engineering consultants, took close to six months. To meet the challenge of meeting the

almost impossible deadlines, we decided to :

a) Initially concentrate on meeting the target of treating mine water by completing one module

of the ETP by 31-Dec-2014.

b) Completion of the second module of the ETP by 30-Jun-2015 to treat the surface run off.

c) Completion of the third module (to treat water from underground mining/increased capacity in

open cast) and other finishing jobs post meeting the above deadlines.


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1. Keeping the Project within timelines

To keep the progress on track, we used the CCPM method along with Weekly Review Meetings at

the local level, a weekly report which was circulated right up to the VP(Raw Materials), and a

detailed monthly review with the design team.

A major challenge has been working through two very heavy monsoon periods, one at the start of

the project, where a lot of excavation was involved, and one towards the end, where the heavy rains

have notched up the difficulty of safe and timely work by several degrees.

To address the issue of the almost impossible timelines, we also had to start civil construction before

completion of detailed design and engineering. To ensure that this did not affect the project,

sequencing of drawing approvals, accuracy in design and detailed engineering etc. were ensured by

close coordination between the Project Team, the Engineering Consultants and the Execution

Partners.

2. Quality Checks

A system of field quality audits during project execution was established, along with the help of the

engineering consultants, for various parameters, as shown in the table below (Table 4) :

Soil Tests Tests for Concrete Strength Tests for structural Integrity

Soil Bearing

Capacity – SBC

Sieve analysis for

coarse and fine

aggregate

Water absorption and

compressive strength

tests for fly ash brick

Water

tightness test

for RCC tanks

Holiday test for

wrapping and

coating of MS

pipe

Soil compaction

test for plinth

filling

Compressive

strength tests for

concrete (cube test)

Slump test for

concrete

Dye Penetrant

test for

welding joints

The tests were done at the laboratory established at the construction site or through a Government

Accredited laboratory at Bhubaneswar

Table – 4 : Summary of Quality Checks during the Construction of the ETP


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Many facilities were set up to ease construction and improve construction quality as shown in table

below (Table 5) :

Sl No Detail of Facilities Set Up Description & Purpose of Facility

1 Batching Plant for concreting 6500 m3 of concreting jobs are to be done with desired quality of

M30 & M25 grade concrete.

2 Laboratory for site test Site laboratory set up for conducting Site tests as described in

Table 3.

3 Construction material storage

spaces

Space management was a challenge, in order to accommodate

1. Sand of Zone- III,

2. Aggregates of various sizes (10 mm -40 mm) in different

piles,

3. Covered cement storage area

4. 10,000m3 of excavated earth.

4 Equipment storage sheds Storage shed for equipment :

1. Electro-mechanical,

2. Cables (HT, LT, Control etc.),

3. Transformers, VCB, Panels etc,

4. Other equipment(pumps and Motors) etc.

5 Material fabrication & storage

yard

For various jobs like :-

1. Rod cutting, bending (640 tonnes of steel)

2. Scaffolding material storage yard

3. Scrap material yard etc.

6 Inside road for material handling For material handling we had to also provide a 4m wide road in

the constrained area.

Table – 5 : Various facilities set up during the construction of the ETP

3. Safety Challenges during Execution

a) Making the Site Safe from Normal Operations The best candidate (though with many short-

comings) for the location of the ETP was at the south-west boundary of the lease, the area used for

despatches and truck parking. However, the main despatch road ran almost through the middle of

the selected area. Thus we needed to first relocate the truck parking yard and re-route the main

despatch road, a big task in itself. This helped in ensuring that the construction site was kept

separate from normal operations and greatly increased safety during construction.

b) Weather Proofing : A major challenge has been working through two very heavy monsoon

periods, where the heavy rains notched up the difficulty of safe and timely working by several

degrees. To ensure safe working we ensured that no foundation work (excavation, making of

columns etc), electrical work (HT cabling etc.) or erection work was scheduled during the monsoon

period.

Safety is not a bolt-on program that can be managed after the project begins; safety should

be integrated into how work is performed, as are cost, schedule and quality


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Similarly, we ensured that during the very hot period from mid-March to mid-June, when heat

induced incidents are common, we scheduled all heavy work for the early mornings and late

evenings, and by taking precautions of ensuring adequate lighting and separate gangs of workmen

and supervisors, sometimes, working through the night, instead of during the day.

c) Lack of space, mentioned earlier, has also meant that the work that could have been carried out

in parallel at any other site, per-force has had to be sequenced because of safety and other

execution concerns.

4. Site Safety

Safety is not negotiable, and we at Tata Steel, through years of training, efforts and learning from

incidents have made safe working almost second nature. This is also true for most of our contractors

and partners. However, our execution partner M/s Effwa Infra & Research and their sub-contractors

were working with Tata Steel for the very first time. We were also unable to ensure adequate

training on construction activities, since the training program at Sukinda is tuned more to sae

working in mines. Hence, we had to jointly develop safe working SOPs, HIRA and training of

workmen during the execution of the job. Inadequate planning and sequencing of jobs is a major

cause for onsite incidents. Timely and regular safety audit in the initial stages by external teams,

helped us greatly in identifying hazards(ref 4) Post the audits, we developed many safety protocols

which were implemented in letter & spirit.

Adopting Safe Construction Practices : The severe restriction in space and other difficulties led us to

adopt safe and at times unique construction practices, a few examples being highlighted below :

a) Pump House area– This area is highly space constrained. Drawings for pump house were

approved after the completion of construction of the Clariflocculator-1. Due to the pump

house being almost 3 meters lower than the Clariflocculator, an almost vertical cut needed

to be made for the raft of the pump house, where the shear resistance angle of the soil was

~ 10o < Φ ≤ 35o . Hence, we made sheet piles to stabilize the slope before excavation of the

pump house structure.

b) Deep Excavation– The tank structures involved very deep excavation, of over 4 meters

below the ground. Due to constraints of space the slope angle was greater than the angle of

shear of the soil. We used slope stabilizing nets and shoring to stabilize the slopes.

c) Ground Water Seepage– The deep excavation resulted in constant ingress of ground water

in the excavated pits. Thus constant pumping of the water while casting needed to be done,

which was risky as well as complex. Protocols developed especially for such situations

ensured close coordination between the pumping and casting gangs and safe working in

these risky situations.

d) As there was a High Tension Line running close to the project site, we shifted the 11kV line

with proper shutdown planning with the help of CESU to ensure that we could work safely.

The safety performance achieved during the period of construction is shown in the following table.


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UNIQUE FEATURES OF THE EFFLUENT TREATMENT PLANT

The Effluent Treatment Plant under construction at Sukinda has many unique features(Table-6) :

a. 24/7 real-time monitoring of the input raw effluent and output treated water for Cr+6, pH and

TSS through online monitors installed at both input (raw effluent) and output (treated water).

This will prevent any inadequately treated effluent from leaving the mine and give warning

signals if the treated output water quality is not up to the mark.

b. The ETP is highly automated, with a feedback mechanism. Thus the dozing of chemicals (acid,

FeSO4, alkali, and flocculants) is automated through a system of PLC based controllers, based on

the input raw effluent and the output water quality.

c. Automated backwash arrangements for the pressure sand filters to ensure that the filters do

not choke.


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b) ETP Technology Additional Facilities

Technology chosen is

- Highly efficient & rapidly reduces hexavalent chromium to trivalent chromium

- Causes rapid flocculation of precipitated Cr+3

compounds - Reduces residence time in the

Clariflocculator, while enabling control of TSS within statutory limits

This has increased the throughput of the ETP and enables treatment of a large volume of water in a short time

i. Acid Dozing of the raw effluent in a flash mixer to bring down the pH before reaction with FeSO4 since the FeSO4 reaction is most efficient at a low pH. Also, because of the efficient reaction at low pH, the consumption of FeSO4 and the amount of sludge generated is substantially reduced.

ii. Stirring arrangement in the flash mixer and a reaction channel to allow for complete reduction of hexavalent chromium.

iii. pH correction using an alkali before dozing with a polyelectrolyte, to ensure complete reaction, as polyelectrolyte reaction needs a neutral pH, along with a stirring arrangement.

These facilities have not been installed by other players

Design Elements Online Monitoring & Automation

The Effluent Treatment Plant is so designed that:

- the output not only meets current specifications for treated effluents in non-urbanized areas, but in order to be future ready, meet the specifications for treated effluents in both urban areas and the likely stricter norms for treated effluent that are likely to be imposed in the future.

- the plant has been designed such that the output has less than 0.01 mg/l of Cr+6 against a norm of 0.05 mg/l and meets the stricter TSS standard of < 10mg/l (drinking water specifications) against a norm of < 100 mg/l (norms for treated effluents in non-urbanized areas)

- treat both surface run off water and mine water in same way, which none of the other mines in Sukinda planned to do

The ETP has state of art online monitoring & automation systems :

a. 24/7 real-time monitoring of the input raw effluent and output treated water for Cr+6, pH and TSS through online monitors installed at both input (raw effluent) and output (treated water) to prevent any inadequately treated effluent from leaving the mine and give warning signals if the treated output water quality is not up to the mark.

b. The ETP is highly automated, with a feedback mechanism. Thus the dozing of chemicals (acid, FeSO4, alkali, and flocculants) is automated through a system of PLC based controllers, based on the input raw effluent and the output water quality.

c. Automated backwash arrangements for the pressure sand filters to ensure that the filters do not choke.

Table – 6 : Unique Features of the Effluent Treatment Plant at Tata Steel Sukinda Chromite Mines

Real Time Monitoring of Data

For real-time monitoring of data, we have set up a data communication system that captures real-

time information from the analysers for Cr+6, TSS and pH installed at the outlet in a server and


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transmit the data thus captured automatically to OPCB/ CPCB server on real time basis. The

schematic of data transmission is shown in Fig-7 and the output screen in Fig-8.

Fig - 7 : Schematic Diagram of Capturing & Transmitting Data for Real Time Monitoring


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Fig - 8 : Result of Online Monitoring of Treated Effluent - the effluent is well within the specified limits

Thus the output water quality data are available both internally through a dedicated web page and

can be transmitted to the Pollution Control Board on a real time basis.

Photographs of the Effluent Treatment Plant are shown at the end of the article.

CONCLUSIONS

The success of the ETP Project can be summarized to be as a result of the following :

i. Vendor selection only after an intense technical evaluation of the capability of the vendor

and not on commercial considerations alone.

ii. A strict focus on time lines and cost at all levels with frequent high level reviews and support

to the project team

iii. Over-riding concerns of safety and quality with mechanisms for frequent checks (preferably

external to project team)

iv. Deep understanding and cooperation between all agencies working on the project, which

developed during the course of the execution and was necessary to cope up with

unforeseen challenges that can crop up at any time : and need to be resolved

collaboratively.


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WAY FORWARD

The output water quality post treatment at the Effluent Treatment Plant is better than the water

available in the local Nullah, giving us the opportunity to use it as an input for our Water Treatment

Plant(WTP) and in various other places, like dust suppression, gardening etc.(Fig-10). The benefits of

this are:

a. Good Quality Water: During the monsoon season water flowing through Domsala river has very

high TSS. The output water from the ETP is already treated and thus a better input to the WTP

than the water from the Nallah.

b. Cost Saving : Apart from substantial cost saving in pumping from the Nallah which is over 3 km

away, the chemical consumption at the WTP will substantially reduce, due to the consistent and

better input water quality, reducing the cost of treatment as well.

c. Towards Zero Discharge : As per the Pollution Control Act, an industry should ideally have ZERO

discharge. Thus reusing the water from the ETP is one step towards achieving zero discharge.

Fig - 10 : Schematic Diagram of our plan to use the ETP discharge as an input to our WTP


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PHOTOGRAPHS

The Effluent Treatment Plant (View of Clariflocculator #1)

Panaromic View of the ETP showing the centrifuge building,

the chemical building and the power sub station


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Filter Beds and Raw Water Tank

Three Clariflocculators of 38m diameter


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Filter Gallery and Treated Water Tank

Inauguration by MD, Tata Steel and other Senior Officials


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References

1. Rama Murthy Y (Dr) et.al, IFA/ABP/389/2013, Development of Process for Water Treatment

at Chrome Ore Beneficiation Plant, Sukinda, Jun-14.

2. Kapure, Gajanan et.al., Application of Terminalia Chebula for Removal of Hexavalent. ISIJ

International, Vol. 48. 2008.

3. Internal Report on Water Quality & Runoff Management at Sukinda Chromite Mine, 2012.

4. Internal Safety Audit Report, Pravin Srivastava & Anirban Mukherjee, Sept-2014.

5. ASPIRE/DMAIC/2829 “Reducing Cost of Construction of Effluent Treatment Plant at Sukinda

Chromite Mines”, Apr-15.

ACKNOWLEDGEMENTS

Acknowledgements

The authors would like to place on record their gratitude to their colleagues at FA&MD – Sukinda

Chromite Mines – without whose help making the ETP would have been impossible; in particular, we

would like to thank the Mine Planning team for their help at all stages of the project. We would also

like to thank the Mining team, for the help during execution, and, RMPP, for the help in the initial

stages of the project.

constructing on of india's largest single location effluent treatment plants

Environment