Paper Mill Effluent Treatment

Characteristics of paper mill effluent treatment

Paper mill effluent contains a large amount of fiber, alkaline substance, pigment and inorganic salt, and has a special malodor. The BOD can be as high as 5000~40000g/L.

Paper mill effluent comes from three parts of water discharged by paper mills according to the process:

1. Pulping and cooking waste liquid, which is generally called papermaking black liquor;

2. The water from washing, sorting and rinsing of pulp after separation of black liquor, which is also called middle water;

3. The white water on paper machine, it can be treated and reused.

The main pollutions in paper mill effluent are as follows:

1. Suspended solids include settleable suspended solids and non-settable suspended solids, mainly fiber and fiber fines (broken fiber fragments and hybrid cells)

2. Organic substances that are easily biodegradable include low molecular weight hemicellulose, methanol, acetic acid, formic acid, sugars, and the like.

3. Biodegradable organic matter mainly derived from lignin and macromolecular carbohydrates contained in fiber raw materials.

4. Toxic substances: Rosin acid and unsaturated fatty acids in black liquor.

5. Acid-base poisoning: The pH value of alkaline pulping wastewater is 9~10; the pH value of acid pulping wastewater is 1.2~2.0.

6. Chroma: The residual lignin contained in the pulping wastewater is highly colore

Treatment Process:

Production raw waste water — go through Mechanical bar screen to remove bigger solids — flow to EQ Tank by gravity to store, equalize, and buffer the waste water being fed to treatment system — Lift to two side fine screen to collect useful fibers — Flow to DAF to remove tiny suspended matters and heavy particles — Flow to hydrolysis acidification tank by gravity in which the molecular organic can degrade to biodegradable micro molecular organic — Flow to Aerobic Biologic Selector by gravity to recycle activated sludge — Flow to aeration basin by gravity to remove major COD and BOD — Flow to secondary clarifiers by gravity to sediment activated sludge created in aeration basin — Flow into a water storage tank by gravity — Lift up to Fenton reactor to degrade refractory organic — Flow to stripping basin by gravity to oxidize these refractory organics more completely and consume the rest oxidizing agent — Flow to flocculation basin by gravity to add(PAM), making the suspended matters settleable — Flow to tertiary clarifiers by gravity for final setting — Flow out water by gravity or reuse or discharge.