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Explora: Environment
and Resource Air pollution mitigation technologies

Table 1. Summary of techniques for air pollution control 5
Techniques SO (%) NO (%) Mercury (%) Particulate matter (%) Cost ($/kW) Applicability
2 2
Advanced dry scrubber 90–95 – 0–90 – 50–150 Pilot to commercial scale; it
depends on the type of coal
Activated carbon injection with an – – 50–90 99 3–8 Pilot scale; retrofit and new
electrostatic spray adsorption process plants with FF and ESP
Combined mercury and SO sorbents 40–85 – Up to 90 – 30–60 Pilot scale; integrated with
2
ESP or FF unit
WFGD with mercury oxidation 95 – >80 90% for>10 µm 160–275 Pilot scale testing
process (up to 39.6% for PM )
2.5
Wet scrubbers with a wet electrostatic 99 – 80 90–99 10–20 Commercial level; integrated
precipitator with existing wet scrubbers
Activated coke 90–98 15–80 90–99 80–85 150–200 New plants and retrofits
SCR with WFGD 95 90–95 40–90 90% for>10 µm SCR: 50–140; Commercial level
(up to 39.6% for PM ) WFGD: 160–275
2.5
Electrocatalytic oxidation 98 90 90 86 200 (for 500 Demonstration level: new
MW) plants and retrofits
Abbreviations: SO : Sulfur dioxide; NO : Nitrogen dioxide; WFGD: Wet flue gas desulfurization; SCR: Selective catalytic reduction; FF: Fabric filter;
2
2
ESP: Electrostatic precipitator; PM: Particulate matter.
Table 2. Factors influencing photocatalyst immobilization Advantages include simplicity, scalability, and
method selection 6 potential good adhesion depending on the substrate.
Limitations are the difficulty in controlling coating
Criteria Consideration thickness and the need for multiple application cycles
Substrate type Porous ceramics, glass, metals • Spin coating: A small amount of catalyst suspension is
Operating environment Indoor versus outdoor, ultraviolet versus dropped onto a substrate, which is then rapidly spun
visible light to distribute the liquid uniformly. Advantages include
Pollutant target Nitrogen oxides, volatile organic compounds, high uniformity and production of thin films ideal for
and particulate matter optical applications. Limitations are its restriction to
Durability requirements Resistance to weathering, abrasion flat, small substrates and the poor mechanical strength
Reactor design Batch versus continuous flow of the resulting film
• Chemical vapor deposition: Volatile precursors
embeds the photocatalyst onto a substrate (e.g., glass decompose or react on a heated substrate to form a
or ceramics). Advantages include excellent coating thin film. Advantages include strong adhesion, high
uniformity, strong substrate adhesion, and pore purity, and good crystallinity. Limitations are high
structure control that enables high surface area. The cost, operational complexity, and potential substrate
highest reported NO removal rate using this method damage from elevated temperatures
x
is 16 mg/m min. Limitations include the potential • Electrophoretic deposition: Charged photocatalyst
6
2
for cracking during drying and the complexity of its particles are deposited onto a conductive substrate
multi-step process under an electric field. Advantages are rapid, efficient
• Thermal spraying: The photocatalyst is deposited onto deposition and suitability for complex geometries.
a surface by spraying at high temperatures, causing Limitations include the requirement for a conductive
partial melting and strong adhesion. Variants include substrate and the need for post-deposition sintering.
plasma spraying, flame spraying, and high-velocity
oxy-fuel. Advantages are high durability and suitability 3.3. Radical-induced oxidation
for coating large and irregular surfaces. The highest To remediate air pollutants present in flue gas, additional
reported VOCs removal rate is 107 mg/m •min. oxidants can be introduced as radical precursors. Various
2
Limitations include possible thermal degradation of types of reactive radicals are used in this process, such
photocatalyst (especially TiO ) and reduced surface as hydroxyl radicals, sulfate radicals, chlorine radicals,
2
area and porosity and ozone. These radicals can be generated and applied
• Dip coating: The substrate is immersed in a suspension through different catalytic and photochemical pathways,
of photocatalyst, then withdrawn, dried, and calcined. such as homogeneous catalysis, heterogeneous catalysis,

Volume 2 Issue 3 (2025) 4 doi: 10.36922/EER025210041