Pollutant control

Pollutant control is crucial in the modern world as human activities result in worldwide air, water, and soil pollution. You can help with the world's pollution problem by recycling waste instead of putting it in the rubbish bin. This may seem insignificant, but the combined effects of regional recycling initiatives help limit environmental pollution. Today we shall briefly cover the principles of pollution control and then cover some of the methods used to control the release of a variety of dangerous pollutants.

The meaning of pollution control

The removal of dangerous substances can be considered pollutant control as well. Pollutant control only tackles waste and emissions released by human activity rather than emissions from natural sources. Harmful substances include greenhouse gases, metal particulates, smoke, carbon monoxide (CO), and oil.

Effects of pollutants

Polluting substances can damage the environment, ecosystems, and human health. Here are some key examples of how pollution affects our planet:

Principles of pollution control

These are the three principles of pollutant control that are used to varying degrees around the world:

1. Accountability: This principle stresses that whichever individual or company is responsible for releasing pollutants into the environment should be accountable for these.

   Therefore, they should be the ones to implement removal methods and mitigate any further release of pollutants.

2. Prevention: This principle suggests that any potential pollution released from an operation or activity should be stringently considered before commencing.

   This means considering any pollutant removal, storage, or neutralising methods and having them ready.

3. Individual responsibility: This principle is more of a widespread plea as it is more challenging to implement strictly. It argues that the Earth is our home and we are lucky enough to have a habitable planet, so we should try our best to protect it.

   This means recycling, reducing vehicle use, and reducing mass consumption.

The importance of pollutant control

Let's take a look at some of the reasons pollutant control is important:

• Sustainable future: controlling emissions and waste is essential for reducing the degradation of the biologically productive land we depend on.

• Climate change: greenhouse gases (GHG) contribute to the greenhouse effect in the atmosphere and warm the planet's system.

  Limiting GHG emissions is pivotal in preventing global warming.

• Human health: many pollutants, such as smoke, carbon monoxide, and metal particulates, threaten human health.

• Economic pressure: post-pollution control methods are often expensive and complicated to carry out, so preventing pollution from the source is important in relieving the financial stress of countries.

Methods of pollution control

So now we know what pollution control is and the principles behind it, let's have a look at the methods individuals and companies use to control specific pollutants:

Smoke (PM10)

Often shrouded in black smog, smoke can contain carbon (C), tar, and ash and causes respiratory problems and even cancer in animals and humans.

Here are some of the methods used to reduce smoke pollution:

• Clean Air Act 1956: this legislation was passed by the UK government due to London's 1952 'Great Smog'. This included the transition to smoke-free fuels and measures to reduce chimney smoke.

• Coal treatment: the application of heat to coal removes the majority of tar.

• Electrostatic precipitators: these devices apply a small electrostatic charge to gas to remove fine particulates like smoke and dust.

• Cyclone separators: these work much like a centrifuge and spin air particles at high speeds to separate particles of heavier densities.

Figure 1: Smoke in Cape Town, South Africa, Wikimedia Commons.

Acid precipitation

Acid rain is precipitation exhibiting a pH of 5.2 or less. Nitrous oxide and sulphur dioxide emissions will react with water vapour in clouds to form nitric acid (HNO₃) and sulphuric acid (H₂SO₄), which then fall as acid rain. Nitrous oxide will also initiate the formation of ground-level ozone (O₃), which is a greenhouse gas.

Acid rain is limited in the following ways:

• Sulphur dioxide:

  • Wet flue gas desulphurisation (FDL): this involves the wet scrubbing of gases using an alkaline slurry (made of limestone or seawater).

  • Dry FDL: dry desulphurisation involves spray towers and injection systems that inundate the gas with the alkaline sorbent to remove sulphur (S) molecules.

• Nitrous oxide:

  • Catalytic converters: catalytic converters are attached to vehicle exhaust pipes and form a ceramic honeycomb made up of platinum (Pt), palladium (Pd), and rhodium (Rh). They will reduce nitrous oxides to harmless nitrogen (N) and oxygen (O₂) gas.

Carbon monoxide and hydrocarbons

Carbon monoxide is a dangerous gas released from the incomplete combustion of fossil fuels and can cause fatal respiratory problems by binding to haemoglobin molecules. Hydrocarbons are released in the same way and can sometimes form volatile organic compounds (VOCs) in the air, which contribute to the formation of ground-level ozone. Oxidative catalysts in catalytic converters will oxidise carbon monoxide and hydrocarbons to carbon dioxide and water.

Oil pollution

Oil spills from tanker accidents, pipeline leaks, and waste lubricating oil can pollute oceans and lakes. This can be very dangerous for marine organisms because they can become trapped and suffer hypothermia. The migration and reproduction of wildlife are affected, as well as sunlight availability for aquatic producers.

Oil pollution can be reduced in the following ways:

• Recycling oil: lubricants and other recyclable oils must not be disposed of carelessly because they are tough to remove from the environment and can devastate aquatic ecosystems.

• Tanker design: tankers with spill-proof designs must be used. This could be the implementation of a double hull, twin engines, and containment booms to limit the effects of leaks.

• Improved navigation: any potentially environmentally endangering spots must be identified and avoided on oil tanker routes.

• Oil spill clean-up: skimmers can manually remove oil from the surface, so can absorbent and polymerising materials.

Figure 2: Oil pollution in wetlands, Wikimedia Commons.

Polluting pesticides are synthetic mixtures sprayed directly on crops or over a general area to deter or exterminate 'pests' (e.g. locusts, aphids, caterpillars). These substances often contain toxic chemicals that can negatively affect non-target organisms and bioaccumulate in the ecosystem.

Pesticide pollution is reduced by introducing regulations on the quantities and types (most poisonous) of pesticides that farmers can use. Shifting to sustainable agricultural methods is essential in improving the gene pool in the agroecosystem and slowing the spread of disease.

Nutrients

The overuse of fertilisers in agriculture can result in soils becoming overloaded with nitrates and phosphates, which can leach into nearby waters. Sewage treatment plants focus on removing toxic substances, so masses of nutrients may be flushed into water sources. Urban waste contains lots of nutrients as well and is often improperly disposed of.

Polluted waters can undergo eutrophication, which involves the formation of 'algal blooms' from an excess of nutrients. When these algal blooms are decomposed, the ecosystem will be starved of oxygen, and life cannot survive.

Here are some ways to reduce nutrient pollution:

• Regenerative agriculture: innovative farming methods such as intercropping, under-sowing, and cover cropping will improve soil fertility and reduce the need for fertilisers.

• Primary sedimentation: removes settleable organic solids from the slurry.

• Secondary sedimentation: separates the waste into organic sludge and effluent after aerobic decomposition by microorganisms.

• Tertiary sedimentation: involves anaerobic sludge digestion and phosphate materials.

Heavy metals

Lead (Pb) can pollute waters through the corrosion of old lead pipes and the improper disposal of waste containing cosmetics and paints.

Human activities like oil refineries, cement production, and incomplete fossil fuel combustion release dangerous mercury (Hg) particulates into the atmosphere. These particulates can be inhaled by humans or make their way into aquatic ecosystems and be consumed by fish.

Pollution control type: transitioning to non-release pollution

Many of the types of control covered in this article are reactionary - meaning that they are only implemented once the pollution has been released/emitted. In order to make significant reductions in the amount of pollution we release, we need to shift to pollution prevention methods.

It is straightforward: if we do not release pollution in the first place, it will not damage the environment, and we will not have to expend energy and resources to remove it.