What is AOX in paper mill effluent and why is it regulated?

AOX stands for Adsorbable Organic Halogens, a group of persistent, toxic chlorinated compounds generated primarily by chlorine-based bleaching. They bioaccumulate in aquatic organisms and cause liver damage, immune disruption, and carcinogenesis. CPCB regulates AOX discharge from paper mills with limits of 1.5–2.0 kg/tonne of paper produced for ECF mills.

What is black liquor and what happens to it?

Black liquor is the spent cooking chemical mixture from pulping extremely high in COD (40,000–120,000 mg/L) and containing dissolved lignin. In kraft mills, it is concentrated and burned in a recovery boiler to recover chemicals and generate steam. In small agro-based mills without recovery systems, black liquor must be segregated and managed separately it cannot be treated in a standard biological ETP.

Is ZLD mandatory for all Indian paper mills?

ZLD is mandatory for paper mills in critically polluted areas and in states where the SPCB has extended ZLD requirements. Under CPCB Charter 3.0, specific targets for water consumption and effluent quality are imposed on mills in major river basins. Check your SPCB's specific requirements for your location.

Water Treatment for Paper & Pulp Industry