Pollution from Industries - Clarity Desk Hub IAS

When we study environmental regulation in India, a major focus is on industries that have a disproportionately large impact on air and water quality. The government identifies these industries, categorises them, and then monitors them through specialised systems. Let’s understand this:

Highly Polluting Industries (HPIs)

The Ministry of Environment, Forest and Climate Change (MoEFCC) has identified 17 categories of industries that are considered “Highly Polluting Industries.”

These include:
Iron and steel, thermal power plants, sugar, cement, distillery, dyes & dyestuff, petrochemicals, refineries, pulp & paper, pharmaceuticals, fertilisers, pesticides, tanneries, copper smelter, zinc smelter, aluminium, and caustic soda.

Why are these classified as HPIs?

Because these sectors:

Use large volumes of chemicals,
Release high-strength effluents,
Generate toxic and persistent pollutants that can remain in the environment for long periods.

Industries like pesticides, pharmaceuticals, and dyes/dyestuff are especially harmful because the chemicals they use often do not break down easily and can contaminate water bodies for years.

Think of it this way:
These industries are not just polluting—they produce pollution that stays.

Grossly Polluting Industries (GPIs)

Here we shift from category-based classification to a performance-based classification.

A Grossly Polluting Industry (GPI) is defined based on how much wastewater it discharges and what type of hazardous chemicals it uses.

Official Definition (Environment Protection Act Rules, 1989):

An industry is considered a GPI if:

It discharges more than 100 kilolitres/day of wastewater, and/or
Uses hazardous chemicals listed in Schedule I, Part II of the Manufacture, Storage and Import of Hazardous Chemical Rules, 1989.

Examples of GPIs

They include a wide range of industries:
Fertilisers, petrochemicals, pesticides, pharmaceuticals, distilleries, dairies, food & beverages, pulp & paper, sugar mills, tanneries, textiles, dyeing units, thermal power plants, slaughterhouses, cement, electroplating, metallurgical units, automobile sector, etc.

So while HPIs are identified by category, GPIs are identified by actual pollution load.

Water Guzzlers

Certain industries consume massive quantities of water, which has major implications for India—a country with growing water stress.

Sector-wise Water Consumption Share

Thermal Power Plants: 70–80% (by far the largest users)
Engineering: 5%
Paper & Pulp: 2.2%
Textiles: 2%
Iron & Steel: 1.3%
Sugar Industry: 0.5%
Cement & Fertilisers: also significant users

Where does this water go?

Mainly for
→ Cooling,
→ Filtration,
→ Cleaning,
→ Wet scrubbing,
→ Effluent discharge processes.

Thus, these sectors not only pollute but also strain freshwater resources.

Monitoring Industrial Emissions & Effluents

To ensure that industries follow environmental norms, their emissions and effluents must be continuously monitored.

Online Continuous Emissions/Effluents Monitoring Systems (OCEMS)

Since 2014, all 17 categories of HPIs are required to install OCEMS.

These systems:

Continuously collect pollution data,
Send it in real time to State Pollution Control Boards (SPCBs) and CPCB.

Every Effluent Treatment Plant (ETP) outlet is connected to this monitoring network.

Key Parameters Monitored (Water/Effluents):

BOD — Biological Oxygen Demand
COD — Chemical Oxygen Demand
TDS — Total Dissolved Solids
TSS — Total Suspended Solids
pH value

Key Parameters Monitored (Air Emissions):

Particulate Matter (PM)
Carbon Monoxide (CO)
Nitrogen Oxides (NOx)
Sulfur Dioxide (SO₂)
Fluoride

If any value exceeds the permissible limit, SPCB/CPCB issues a notice and initiates action—this can include fines, orders for corrective measures, or even closure notices.

Issues and Concerns with OCEMS

While the system looks strong on paper, there are gaps in practice.

Major Issues:

(1) Data opacity

The pollution data collected through OCEMS is not easily accessible to the public.
Transparency is limited, weakening accountability.

(2) Conflict of interest (“The thieves have the keys!”)

This is the most crucial issue:

Industries themselves operate and maintain their own monitoring equipment.
Essentially, the polluter is in charge of measuring its own pollution.

This creates a situation where manipulation of data becomes easier, and enforcement becomes weaker.

In contrast, CAAQMS (ambient air quality) is directly operated by CPCB/state agencies.
But OCEMS relies on industries to monitor themselves.

Thus, while technology exists, the governance and credibility of the system remain questionable.

Pollutants from Highly Polluting Industries (HPIs)

Now, we explore how major industries generate different types of pollution. Understanding this helps link industrial processes with environmental impacts.

Thermal Power Plants (TPPs)

How a TPP Works

A Thermal Power Plant is essentially a heat engine. The chain of operations is:
🔹Burning fossil fuels (mainly coal in India; also, oil and natural gas) to produce heat.
🔹Heat converts water into high-pressure steam.
🔹Steam rotates a turbine.
🔹A generator attached to the turbine produces electricity.

Key issue:

India primarily uses COAL-based TPPs. Coal contains many toxic elements, and most plants operate at low efficiency (20–45%).

To make matters worse, pollution-control technologies such as
→ Flue Gas Desulphurisation (FGD),
→ Electrostatic Precipitators (ESPs),
are often outdated or poorly maintained.

Pollution from TPPs

Fly Ash

Fly ash is the fine residue left after coal combustion. Types include:
→ Dry fly ash
→ ESP ash
→ Pond ash
→ Mound ash

It is disposed into the atmosphere or stored in ash ponds. If these ponds collapse or leak, the toxic elements seep into:
→ Nearby farms
→ Surface water
→ Groundwater
→ Residential areas

Toxic Heavy Metals in Fly Ash

Coal naturally contains trace elements, which become concentrated in fly ash:

These metals contaminate soil and water and can enter the food chain.

Other toxic Elements in Fly Ash

Fluoride | Sulphur compounds

These add to long-term environmental and health risks.

Gaseous Pollutants from TPPs

TPPs release a cocktail of gases:
➡️Carbon Dioxide (CO₂) – a major greenhouse gas.
➡️Sulphur Dioxide (SO₂) – causes acid rain.
➡️Nitrogen Oxides (NOx) – leads to smog and ozone.
➡️Particulate Matter (PM) – PM₂.₅ and PM₁₀ impact lungs and heart.
➡️Methane (CH₄)
➡️Carbon Monoxide (CO) – from incomplete combustion.
➡️Volatile Organic Compounds (VOCs)

Together, these gases degrade air quality drastically around TPP belts like Singrauli, Korba, Talcher, and Chandrapur.

Water Pollution from TPPs

The water footprint of TPPs is massive. Pollution occurs via:
➡️Acid Mine Drainage (AMD) from coal mines (open-cast & underground). This releases metals like iron, aluminium, manganese into rivers.
➡️Effluents from the plant, including:
✅Cooling tower blowdown
✅Ash handling wastewater
✅Wet FGD system effluents

These effluents are often acidic and heavy-metal-rich.

Iron and Steel Industry

This industry forms the backbone of industrial development—yet it is one of the most environmentally damaging. You can read more about this here.

Byproduct of steel making process: Slag

Slag contains impurities removed from the iron, such as:
→ Calcium sulphide (CaS)
→ Oxides of silica, alumina, magnesia, and calcium (CaO)

Environmental and Economic Use of Slag

Cement Manufacturing
Blast furnace slag cement is more durable and less permeable than ordinary Portland cement.
Construction Material
Used in: Concrete, Asphalt, Road bases
Wastewater Treatment
Slag alkalinity helps remove: Metals, Sulfates, Excess nutrients (N, P, K)
Soil Conditioner
Ferrous slags help rebalance soil pH and provide calcium & magnesium.

Thus, slag, though a byproduct, has valuable uses when properly processed.

Air Pollution from the Iron & Steel Industry

This sector burns large quantities of coal—both for generating heat and for coke production.

Key Air Pollutants

PM₂.₅ and PM₁₀
CO₂
SO₂ (sulphur is converted to SO₂ in the blast furnace)
NOx
CO
Hydrogen Sulphide (H₂S)
Non-Methane VOCs (NMVOCs)

Coke Ovens and Naphthalene

Coke ovens release naphthalene, a toxic, carcinogenic compound.
This poses severe health hazards to workers and nearby communities.

Magnetite Pollution

A unique form of pollution seen around iron & steel zones.

What is Magnetite?

Magnetite (Fe₃O₄) is a magnetic mineral released during:
→ Mining
→ Steel processing
→ Industrial grinding operations

Why is it harmful?

Affects birds
Magnetic particles interfere with birds’ natural navigation systems.
Affects electronics
Sensitive instruments such as compasses, communication equipment, and navigation systems can malfunction.

Water Pollution from Iron & Steel Industry

Acid Mine Drainage (AMD)
Slag dumps and coal mines generate acidic water, which leaches heavy metals into groundwater and rivers.
Toxic Coking Wastewater
Coking—heating coal without oxygen—produces wastewater containing:➡️Carcinogenic organic compounds➡️Cyanide
➡️Ammonia
➡️Sulfides
These are extremely harmful if discharged untreated.
Alkaline Groundwater
Slag contains oxides that react with water to increase hydroxide ions (OH⁻), making groundwater highly alkaline.

Cement Industry

Cement is one of the most widely used construction materials in the world, but its production is also one of the largest industrial contributors to CO₂ emissions. You can read about cement manufacturing process here.

Why Cement Produces So Much CO₂

Limestone is mostly calcium carbonate (CaCO₃).

When heated, it breaks into:

Calcium oxide (CaO) → used to form cement
Carbon dioxide (CO₂) → released into the atmosphere

Important insight:
✔ For every 1 ton of cement, at least 0.5 tons of CO₂ is released.
This comes from the chemical breakdown itself, not just the burning of coal.

To reduce emissions, industries increasingly replace part of the limestone with:
→ Blast furnace slag (from steel industry)
→ Fly ash (from thermal power plants)

This reduces both resource use and CO₂ emissions.

Water Use in Cement Production

Water is required for:
➡️Cooling equipment and exhaust gases
➡️Wet scrubbers (pollution control)
➡️Preparing slurry in older wet-process kilns

Pollutants Released

Because cement kilns burn coal, the emissions resemble those from Thermal Power Plants:
➡️CO₂, SO₂, NOx, PM, CO, VOCs
➡️Heavy metals (if present in raw materials or fuel)
➡️Wastewater containing suspended solids, high pH, and heat

Thus, the cement industry is energy-intensive, water-intensive, and emission-intensive.

Copper Smelting Industry

Copper smelting is a multi-step process that transforms a low-grade ore into 99.99% pure copper.

The journey from rock to refined metal involves mining, roasting, smelting, converting, and refining. You can read the processes in details here.

Copper Slag: Uses and Concerns

Copper slag is used for:

Abrasive blasting (cleaning metal surfaces)
Road construction
Making cement, mortar, and concrete

It can replace natural sand or aggregates—reducing mining pressure.

Pollutants from Copper Smelting

Copper ores contain many impurities that can leach into soil and water, including:
➡️Arsenic, antimony, cadmium, lead, mercury
➡️Iron, manganese, aluminium
➡️Selenium, nitrates, fluorides
➡️Radon, due to radioactive decay of uranium in ores

SO₂ Emissions

Almost all copper ores are sulphide-based.
Roasting and smelting release large amounts of Sulphur Dioxide (SO₂).

If not captured properly, this causes:
→ Acid rain
→ Lung irritation
→ Damage to vegetation and water bodies

To control excess SO₂, industries convert it to sulphuric acid—but only if the system is well-maintained.

Thoothukudi Sterlite Copper Plant Controversy (2018)

This is one of the most important environmental case studies for UPSC. Read it here.

Zinc/Lead Smelting Industry

Zinc and lead frequently occur together in nature, usually in sulphide form.
Zinc is crucial for galvanisation (protecting steel from corrosion), while lead is primarily used in lead-acid batteries.

Read about Lead Smelting Process here.

Read about Zinc Smelting Process here.

Pollution from Zinc/Lead Smelting

Air Pollution

Wastewater Sources

Spent electrolytic baths
Slime recovery plants
Spent acid
Cooling water
Air scrubbers

These carry heavy metals and acidic residues.

Heavy Metal Leaching from Slag

These contaminate groundwater and soil.

Aluminium Smelting Industry

Aluminium production is extremely energy-intensive, requiring electricity at massive scales.
This is why aluminium smelters are often located close to a dedicated power station.

You can read about Aluminium Production process here.

Pollution from Aluminium Smelting

Emissions come from both thermal power used to run the plant and electrolysis, including:
→ NOx
→ SO₂
→ Ammonia (NH₃)
→ Polycyclic Aromatic Hydrocarbons (PAHs) — formed from incomplete combustion of carbon anodes

These pollutants are harmful to health and ecosystems.

Red Mud — A Major Environmental Challenge

Red Mud (Bauxite Residue) is:
➡️Highly alkaline
➡️Rich in: iron oxides, aluminium oxides, titanium, rare earths, and other heavy metals
➡️Produced in large quantities during the Bayer Process

Problems

Historically dumped in landfills
Risk of groundwater contamination
Very difficult to neutralize due to high alkalinity

Modern Utilisation

Red mud is now used for:
👉Road construction
👉Iron-rich cement
👉Low-cost concrete
👉Soil improvement (ameliorating acidity)
👉Phosphorus cycling
👉Carbon sequestration

This aligns with circular economy principles.

Petroleum Refining and Petrochemicals

The petroleum sector is enormous and divided into:

Upstream → Exploration & drilling
Midstream → Storage & transportation
Downstream → Refining & petrochemical manufacturing

All about Petrochemical industry: Read Here.

Pollution from Petroleum Refineries

Air Pollutants

Includes: PM | CO₂ | NOx | CO | SO₂ | Hydrogen sulfide (H₂S) | Methane | Lead | VOCs (including benzene, a potent carcinogen)

Water Pollution

Refineries frequently use: Deep injection wells and Coastal discharge to dispose wastewater and oily residues, leading to contamination of:
→ Groundwater
→ Aquifers
→ Coastal ecosystems

Pollution from Petrochemicals

Air Pollution

Emissions include complex Polycyclic Aromatic Hydrocarbons (PAHs), many of which are carcinogenic.

Water Pollution

Wastewater contains:
→ Phenols (toxic organic compounds)
→ Cyanide
→ Formaldehyde

These can severely harm aquatic life and human health.

Fertiliser Industry

The fertiliser industry produces ammonia, urea, DAP, NPK fertilisers, etc. While essential for agriculture, it is also a major polluter.

Air Pollution

Key emissions include:
→ Particulate matter (PM)
→ Ammonia (NH₃)
→ Nitrogen oxides (NOx)
→ Sulphur compounds
→ Carbon dioxide (CO₂)

Prilling Towers

A major emission source in urea plants.
These towers spray molten urea from the top to form small pellets called urea prills.
→ This generates urea dust, a significant form of particulate pollution.

Water Pollution

Fertiliser wastewater contains:

Ammoniacal nitrogen
Phosphates
Heavy metals like:
- Vanadium & Arsenic (used in CO₂ removal systems)
- Chromium (used as corrosion inhibitor in cooling towers)
Fluorides

These contaminants can cause eutrophication, toxicity to aquatic species, and groundwater contamination.

Distillery Industry

Distilleries use molasses, cereals, fruits, sugar beet, etc., to ferment and distill alcohol.
Alcohol is essential for pharmaceuticals, cosmetics, beverages, perfumery, and various chemicals.

Why Distilleries Are Highly Polluting

The fermentation process generates high-strength liquid effluents known as:

Spent Wash (extremely pollutant-rich)

Characteristics of distillery wastewater:

Very high Biological Oxygen Demand (BOD)
→ Indicates massive organic load
High nitrogen content → causes eutrophication
Low pH (acidic)
High temperature
High turbidity
High salinity

This makes distilleries one of the top water-polluting industries in India.

Paper and Pulp Industry

Paper manufacturing begins with creating pulp by separating cellulose fibers from:
→ Wood
→ Bagasse
→ Crop residues
→ Wastepaper

This industry is both energy-intensive and water-intensive.

A. Chemicals Used

For pulping (removing lignin) and bleaching, industries use:
➡️Sulfite salts
➡️Caustic soda (NaOH)
➡️Sodium sulfide
➡️Hydrogen peroxide
➡️Sulphonic acid
➡️Chlorine dioxide

These chemicals help produce paper of different finishes and brightness.

B. Water Pollution

The wastewater contains:

Organic pollutants → Very high BOD
Inorganic chemicals such as NaOH, sodium carbonate, sodium sulfide
Chlorinated compounds (from bleaching)
Acids like HCl

These effluents are toxic, persistent, and difficult to treat.

C. Air Pollution

Key gaseous pollutants:

Hydrogen sulfide (H₂S)
Methyl mercaptan
Sodium sulfide fumes
Sulfur vapors

These gases give pulp mills their characteristic foul odor.

Caustic Soda (Chlor-Alkali) Industry

Caustic soda (NaOH) is produced by the chlor-alkali process using electrolysis of brine (saltwater).

Two major routes:

Mercury Cell Process
Membrane Cell Process (environmentally safer)

These plants also produce:

Soda ash
Chlorine gas
Hydrogen gas → used as fuel or converted to HCl

These chemicals feed multiple industries: detergents, textiles, pulp & paper, PVC, water treatment, etc.

Why It Is Classified as a Polluting Industry

The mercury cell process risks mercury contamination
Handling chlorine gas, its vapors, and hydrogen is dangerous
High probability of toxic leaks

Wastewater Pollution

Comes from:

Chlorine drying (using sulphuric acid)
Scrapped cell parts (membranes, anodes, cathodes) → heavy metal leaching

Tannery Industry

Tanneries process raw animal hides into leather. This involves multiple chemical-intensive steps.

A. Beamhouse Operations

Soaking → removes dirt
Liming → removes hair using lime + sulphide
Deliming → neutralises alkalinity using ammonium salts
Bating → enzymatic/protein degradation
Pickling → reduces pH to allow chromium tannins to penetrate the hide

B. Chrome Tanning

Here, chromium ions cross-link with collagen fibers → stabilises the hide.

This makes leather:
→ More durable
→ Resistant to heat
→ Resistant to microbial degradation

C. Main Environmental Concerns

1. Water Pollution

Chrome tanning discharges chromium-rich wastewater
Beamhouse operations generate high BOD loads

2. Air Pollution

Emissions of:
- Hydrogen sulfide (H₂S)
- Ammonia (NH₃)
- Fumes from dyes & solvents

3. Solid Waste

Hair, flesh scrapings, trimmings, chromium-containing solids

Tanneries worldwide are strictly regulated because of these hazards.

Sugar Industry

Sugar mills process sugarcane or sugar beet into sugar crystals.

Read more about sugar industry here.

Air Pollution

Pollutants released due to burning of:
→ Cane trash
→ Bagasse
→ Residues

Include: Fly ash | SO₂ | CO | NOx | Nitrates | Sulfates | Other carbon compounds

Process-Related Emissions

Sulphitation → introduces SO₂ into cane juice
Carbonation → uses CO₂ & lime to purify juice

Both processes generate SO₂ and CO₂ gases.

Greenhouse Gas Emissions

Major emissions arise from:
→ Crop residue burning (→ CO₂, CH₄, N₂O)
→ Fertiliser use
→ Fossil fuel combustion

Residue burning also emits:
→ CO
→ NMVOCs
→ Other precursors of tropospheric ozone

Water Usage

A highly water-intensive sector:
✅1 kg of sugarcane requires 1,500–2,000 L of water
✅Processing 1 tonne of cane requires another 1,500–2,000 L
✅Generates ~1,000 L of wastewater per tonne

Water Pollution

The sugar industry ranks third in wastewater generation (after pulp & paper and chemicals).

Wastewater contains:
➡️High BOD (due to organic matter)
➡️Suspended solids
➡️Press mud & bagasse residues
➡️High TDS (calcium, magnesium, sodium, nitrates, etc.)
➡️Coliform bacteria (indicator of pathogen presence)

This effluent, if untreated, severely depletes dissolved oxygen in water bodies, killing aquatic life.