presentation at the 9th world aqua congress on 26th-27th nov 15

Presentation at IX World Aqua Congress WAC-IC 2015

IMPROVING WATER QUALITY BY CONSTRUCTING AN EFFLUENT TREATMENT PLANT

Prabhash Gokarn*, Pankaj Satija and Arijit Mondal, FA&MD, Tata Steel

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Proposed Title


Full Name of Author : PRABHASH GOKARN, Head (Engineering Projects & Town), Tata Steel Full Name of Co-Author 1 : PANKAJ SATIJA, General Manager(Operations), FAM, Tata Steel Full Name of Co-Author 2 : ARIJIT MONDAL, Manager(Projects & Construction), FAM, Tata Steel Full contact address of corresponding author :

Prabhash Gokarn Head (Engineering Projects & Town) Ferro Alloys & Mineral Division Tata Steel Limited Administrative Building | Sukinda Chromite Mine | PO Kalarangiatta | Jajpur | Odisha 755028 Mobile : +91 - 77 5200 4399 e mail : [email protected] [email protected]

Identification of the Congress theme most closely related to the paper

Water Quality & Treatment Techniques & Practices

Five keywords of the paper

Effluent Chromium+6

Water-treatment Technology Construction

Category of their presentation format : Oral




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Title

IMPROVING WATER QUALITY BY CONSTRUCTING AN EFFLUENT

TREATMENT PLANT

ABSTRACT

Tata Steel operates chromite mines at the Sukinda Valley in Odisha producing chrome ore which is subsequently

converted it to Ferro Chrome and sold to customers across the world. A large quantity of water, pumped out from the

mining pit and due to rainfall, needs to be handled during the mining operations. Chrome Ore mainly contains tri-valent

Chromic 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 0.005 mg/l for human consumption; requiring all water to be treated

before its release from the mines. Thus, Tata Steel is setting up an additional state of art effluent treatment plant at

Sukinda with a capacity of 108 million litres / day; one of the largest in the region; which will be completed by Sept 2015.

This paper discusses how the technology for the Effluent Treatment Plant was chosen amongst various alternatives, how

the capacity of the plant was decided, the challenges during construction of the said Effluent Treatment Plant that were

faced, and how these were successfully tackled. The paper also describes how, because the outlet water is of a better

quality than the water from the local water body, the outlet water will be used as the input to the Water Treatment Plant,

aiding water consumption and lowering operating cost.




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Title

IMPROVING WATER QUALITY BY CONSTRUCTING AN EFFLUENT

TREATMENT PLANT

INTRODUCTION

Describing Sukinda and importance to FAM

Sukinda Valley, in Odisha is known for its high grade chromite deposits. The deposit was first proved by geologists of

Tata Steel in 1949. TSL’s Sukinda Chromite Mines is the one of the largest chrome mines in India enabling Tata Steel to

be one of the larger chrome alloy players in India.

Chrome Ore

Chrome ore occurs as Chromite, which is chromium oxide, and as friable or lumpy rocks(Fig-1). Chromite contains mainly

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

Fig - 1 : 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 and can cause irritation and

ulcers in the stomach and the intestines, eyes and the nose; and allergic skin reactions. There is no evidence of elevated




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levels of these diseases (compared to the national and the state average) in the valley. This is probably due to the low

levels of Cr+6

found naturally (and in Sukinda).

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. 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-2)

Fig – 2 : Map showing water discharge circuit, garland drains and ETP Locations

IMPETUS TO UPGRADE

Tata Steel set up Effluent Treatment Plants in the early 2000s. There was need to upgrade the (over ten year old) ETPs

due to the following reasons:

1. Tata Steel has been conducting a very successful afforestation program around the Sukinda resulting in good

rainfall.

2. Tata Steel’s Sukinda Chromite Mine is already one of the deepest Open Cast Chromite Mines in India and we are

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, facilities are now available for

automation, online monitoring etc., with an increased understanding of water treatment methods.




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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 1) :

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

Electrolytic

oxidation of the

‘sacrificial

electrode’.

Wide pH range

Tolerant to

suspended solids

Cost (sacrificial

electrode & electricity)

High sludge

Moderate kinetics

Unsuitable due to cost,

moderate speed of

treatment in low

concentration

3

Osmosis/Me

mbrane

separation

Using ultra-filtration

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 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 – 1 : Selection of Right Technology from the Available Options for Remediation of Hexavalent Chromium

Effluent.




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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)

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 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.

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 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. Fig. 3 gives the capacity and guaranteed output water parameters of the Effluent Treatment Plant at Sukinda

(Fig-3)




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Fig - 3 : 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-4).

Fig - 4 : Block Diagram of the Modular Effluent Treatment Plant at Sukinda (1500 m3/hr X 3 modules)




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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.

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 2) :

Many facilities were set up to ease construction and improve construction quality as shown in table below (Table 3) :

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 – 2 : Summary of Quality Checks during the Construction of the ETP




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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 – 3 : 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.

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.

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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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 ≤ 35

o . 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.

UNIQUE FEATURES OF THE EFFLUENT TREATMENT PLANT

The Effluent Treatment Plant under construction at Sukinda has many unique features(Table-4) :

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 – 4 : 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 transmit the data thus captured automatically to

OPCB/ CPCB server on real time basis. The schematic of data transmission is shown in Fig-5 and the output screen in

Fig-6.




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Fig - 5 : Schematic Diagram of Capturing & Transmitting Data for Real Time Monitoring

Fig - 6 : Result of Online Monitoring of Treated Effluent - the effluent is well within the specified limits




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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.

A photograph of the Effluent Treatment Plant is shown in Fig-7.

Fig - 7 : The Effluent Treatment Plant (View of Clariflocculator #1)

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-8). 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 - 8 : Schematic Diagram of our plan to use the ETP discharge as an input to our WTP

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.

presentation at the 9th world aqua congress on 26th-27th nov 15

Environment