How to Treat Wastewater from Paper Industry?
Features
Paper-making wastewater is very harmful, of which black water is the most harmful, and the pollutants it contains account for more than 90% of the total pollution discharge of the papermaking industry. It also consumes a large amount of dissolved oxygen in water, seriously pollutes water sources, and brings harm to the environment and human health.
The most serious environmental pollution of the middle water is the chlorine-containing wastewater generated during the bleaching process, such as chlorinated bleaching wastewater, hypochlorite bleaching wastewater, etc. In addition, bleaching waste liquor contains highly toxic carcinogen dioxin, which also poses a serious threat to the ecological environment and human health.
Composition
Pulp and papermaking wastewater is mainly divided into three types: black liquor, intermediate wastewater and white water.
Black liquor: cook plant fiber with alkaline agent containing NaOH or NaOH+sodium sulfate to dissolve lignin, and the discharged cooking liquor is "black liquor" (alkali cooking is black liquor, acid cooking is red liquor, most of which use alkali cooking ). Black liquor contains lignin, polypentose and total alkali, and is a high-concentration refractory wastewater.
Mid-stage wastewater: wastewater produced in the process of washing, screening and bleaching of pulp made by alkaline cooking, the COD load per ton of pulp is about 310kg. The BOD/COD is between 0.20 and 0.35, and the biodegradability is poor. The pollutants are mainly soluble COD such as lignin, cellulose, organic acids, etc. The most serious pollution is the chlorine-containing wastewater produced by bleaching.
White water: a large amount of water, mainly containing fine fibers, fillers, coatings and dissolved wood components, mainly insoluble COD, poor biodegradability, and the added preservatives are toxic.
Processing technology
- Black liquor, middle-stage wastewater: alkali recovery, acid precipitation, LB-1 alkali precipitation, membrane separation, flocculation sedimentation, biofilm method, anaerobic biological treatment, mesh microfiltration, air flotation, advanced oxidation.
- White water: filtration, flotation, sedimentation, sieving.
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