Paper industry is one of the world's six major industrial pollution sources, accounting for 10% of China's total industrial waste water. Papermaking wastewater is mainly high concentration of organic wastewater, and containing lignin, residual alkali, sulfide, chloride and other pollutants. It is characterized by large amount of waste water, high COD concentration, waste water in the fiber suspended solids, and containing divalent sulfur elements, high color, mercaptans odor.
In the pulping (chemical method) and papermaking production process mainly produces three types of wastewater: black (red) liquid, the middle of the waste water and paper white water. Black (red) liquid is mainly cooking pulp wastewater, the middle of the water, including pulp washing, screening, bleaching wastewater, paper machine white water for the papermaking workshop waste water. Which is the most serious environmental pollution of cooking wastewater, accounting for 90% of the entire paper industry pollution.
The main components of black liquor are lignin, cellulose, hemicellulose, monosaccharide, organic acid and sodium hydroxide, etc., can be a comprehensive recovery of useful substances; the middle of the wastewater pollutants complex, containing a higher concentration of lignin, fiber And the resin is more difficult to biodegradable material composition, and rich in bleaching stage to produce organic chloride, with a deep color and great toxicity, pH 9-11, suspended solids 1000mg / l or so, COD600- 2500mg / 1; papermaking wastewater, also known as "white water", mainly from the beating, pulp purification and wet paper machine wetting. Contaminants in wastewater mainly include suspended solids such as fibers, fillers, coatings, and dissolved wood components, added wetting agents, preservatives and the like.
Hazard of Papermaking Wastewater
Papermaking wastewater is very harmful, of which black water is the most harmful, it contains pollutants accounted for more than 90% of the total pollution of the paper industry pollution, due to the large black water, deep color, heavy smell, And a large number of consumption of dissolved oxygen in water, serious pollution of water, to the environment and human health hazards. While the middle of the water pollution is the most serious bleaching process of chlorine wastewater generated, such as chlorinated bleach wastewater, hypochlorite bleaching wastewater. In addition, bleach waste contains highly toxic carcinogens dioxin, but also on the ecological environment and human health impact. Therefore, we should choose the appropriate treatment process, the papermaking wastewater for reasonable treatment.
Basic Treatment of Papermaking Wastewater
Papermaking wastewater treatment should focus on improving the rate of recycled water, reducing water consumption and waste water emissions, and should also actively explore a variety of reliable, economical and able to make full use of waste water useful waste water treatment methods. For example: flotation wastewater treatment can be recycled in white water fiber solid material, the recovery rate of up to 95%, clear water can be recycled; combustion wastewater treatment can be recycled black water sodium hydroxide, sodium sulfide, sodium sulfate and organic combination Of other sodium salts. Neutralization wastewater treatment method to adjust the pH value of wastewater; coagulation sedimentation or flotation method can remove suspended solids in wastewater; chemical precipitation method can be decolorized; biological treatment can remove BOD, kerosene wastewater is more effective; wet oxidation treatment of sulfite pulp Wastewater is more successful. In addition, domestic and foreign also use reverse osmosis, ultrafiltration, electrodialysis and other papermaking wastewater treatment methods.
Comprehensive treatment of papermaking wastewater
1) Anaerobic-aerobic combination treatment
Anaerobic-aerobic combination process can give full play to the advantages of high concentration, high load and recovery of effective energy for anaerobic microorganisms, but also the advantages of using aerobic microbial growth speed and handling water quality. The combined treatment process has a low operating cost and less residual sludge. It can improve the biodegradability of the wastewater by the modified organic matter. The anaerobic state can inhibit the growth of filamentous bacteria and prevent the sludge from expanding. Treatment of High Concentration Organic Wastewater.
2) the biological law of the main, materialized, supplemented by the base of straw pulp wastewater treatment technology
The first use of physical law (filtration), followed by biochemical method as the main means to significantly reduce the black liquor and the middle of the water in the organic load, only the physical and chemical method as a supplement Means to achieve the discharge of waste water or reuse.
3) two-phase anaerobic membrane - biochemical system
The removal rate of COD was up to 73% on the black liquor wastewater treated by the traditional two - phase anaerobic process (BS) and membrane separation technology. MBS system has a higher stability.
4) physical and chemical and biochemical combination method
Chemical precipitation, aeration, activated sludge, anaerobic treatment can be used to treat papermaking wastewater, and these methods are also combined. The results show that the SBR + chemical treatment method is low in the middle of the papermaking process, the running cost is low, the effluent quality of the paper mills is stable and the treatment cost is within the acceptable range.