The various unit operations of pulp bleaching are as follows.

1. Chipping: In this operation the wood logs are cut into chips of the desired size in rotary chippers.
2. Cooking: The chips are transported into the digestors which are large pressure vessels where the chips are treated with white liquor (a combination of sodium hydroxide and sodium sulphate) .The cooked chips are blown into a blow tank .Cooking is the first stage where removal of lignin from cellulose takes place.
3. Washing and screening: The blown pulp is washed and screened before it enters into oxygen delignification.
4. Oxygen delignification: The washed and screened pulp is treated with oxygen in 2 stages for removing the residual lignin .
5. Bleaching: The primary bleaching agent used in ECF process is chlorine di oxide .ClO₂ is added in the first and last stage of the bleaching process. After the first stage of ClO₂ the pulp is treated with Sodium Hydroxide ,oxygen and Hydrogen peroxide before it enters the final stage of ClO₂ bleaching.

The final pulp brightness achieved is 88%. The ECF process results in considerable reduction in Adsorbable Organic Halides (AOX) .Further the Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) reduces by 15% on the final effluent. The end result is a brighter and whiter paperboard which can be used for direct food contact!!