VOCs (VOCs)

Volatile Organic Compounds (VOCs) are carbon-containing chemicals with high vapour pressure at room temperature, meaning they evaporate readily from solid or liquid form into the surrounding atmosphere. The class includes hundreds of substances — benzene, toluene, xylene, formaldehyde, methanol, ethanol, acetone, terpenes — released from solvents, paints, adhesives, fuels, and many natural and industrial processes. In recycling and waste-processing contexts, VOCs are emitted from biogas (siloxanes and aromatics from landfill or sewage), pyrolysis oil handling, plastic shredding, solvent degreasing in e-waste, and storage of recovered fuels.

VOCs are regulated in India under several frameworks:

• Environment (Protection) Rules, 1986 — Schedule I prescribes industry-specific emission limits including for VOC-emitting sectors
• NAAQS — sets ambient benzene limit at 5 µg/m³ annual average
• CPCB stack norms — typical industrial stack VOC limit is 20–150 mg/Nm³ depending on category, measured as total non-methane hydrocarbons
• SPCB consent conditions — VOC monitoring is now standard in CTOs for solvent-intensive industries

The environmental concern is twofold. At ground level, VOCs react with nitrogen oxides under sunlight to form ozone and photochemical smog — Delhi-NCR's summer ozone problem is partly driven by industrial VOC emissions. Many individual VOCs are also direct health hazards: benzene is a known human carcinogen, formaldehyde is a respiratory irritant, and chronic exposure to xylene damages the central nervous system.

Control technologies fall into three categories: thermal/catalytic oxidation (most effective, but high opex), activated carbon adsorption (good for low concentrations, requires regeneration or disposal), and bio-filtration (suitable for odorous low-concentration streams). For an Indian CBG plant, VOC emissions are usually managed by ensuring all gas vents pass through activated carbon or by routing them back into the digester or flare, rather than venting raw to atmosphere.