Paper making equipment-method for wastewater treatment

The Paper industry is an industry with significant water consumption and severe pollution. High quality Papermaking equipment can effective avoid environments Pollution, Due to the high concentration of pollutants in papermaking wastewater and the difficulty of treatment, all countries have listed papermaking wastewater as one of the significant public hazards. Japan has listed it as one of the five significant public hazards. According to the United Nations Environmental Planning Group, the world's paper industry discharges 27.4 billion tons of wastewater every year. The total amount of pollutants in papermaking wastewater is 10.8 million tons. The total amount of suspended solids is 5.94 million tons, and the sulfide is 1 million tons.

China's paper industry has the following characteristics: First, small and medium-sized enterprises with an annual output of fewer than 10,000 tons account for a large proportion, accounting for about 82%; second, my country's papermaking is dominated by straw pulp raw materials. Wood pulp papermaking accounts for about 14% of the total production, non-wood pulp accounts for about 86%, and about 60% of non-wood pulp production is straw pulp paper. Straw pulp papermaking makes my country's paper industry wastewater pollutant concentration higher than the foreign paper industry.

Paper industry wastewater is divided into black liquor, middle water, and white water. Black liquor; from cooking waste liquor, about 10t of black liquor is produced to produce 1t of pulp. The concentration of pollutants in black liquor is related to the type of papermaking raw materials used and the internal production process. Generally, impurities in black liquor account for about 10-20%, of which 1/3 is inorganic, mainly various sodium salts; 2/3 is organic, mainly alkali lignin, hemicellulose, fatty acid, and resin acid.

The water in the middle section comes from the papermaking process's washing, screening, and bleaching sections. The indicators of the middle water: COD=800～2000mg/L, BOD=200～500 mg/L, lignin=50～200 mg/L, PH=7～8, the color of this kind of wastewater is higher, and the water contains complicated organisms degraded substances. White water comes from paper machines and pulpers in the papermaking process, and the concentration of pollutants in white water is low, and the BOD is usually only tens of mg/L.

The recycling pulp industry using waste paper has developed rapidly in recent years. Still, deinking wastewater will be produced during waste paper recycling, and its water quality is characterized by a high content of ink and short fibers. Recovering alkali from black liquor is difficult for small and medium-sized paper mills. Some small and medium-sized pulp mills use acid precipitation to recover lignin, turning waste into treasure. After the lignin is extracted from the black liquor, the coagulation and biochemical treatment process is used to achieve the discharge standard.

My country's treatment technology for middle-stage wastewater has been gradually improved through research, and practical application, such as coagulation air flotation-biochemical treatment process, anaerobic fluidized bed-aerobic treatment process, stabilization pond treatment process, hydrolysis acidification-SBR treatment process have all been obtained. It has been widely used and achieved good processing results.

Due to the low concentration of pollutants in white water, the focus of treatment is to realize water reuse. The commonly used processes are air flotation-filtration or membrane treatment.

The papermaking deinking wastewater treatment process is based on the needs of the waste paper for the pulping process. The primary pollutants in waste paper pulping wastewater are ink, porcelain clay, and short fibers. The two-stage air flotation-filtration process was successfully used in the experiment. After treatment, it can be used in the production process and achieve good environmental and economic benefits.

The process flow mainly includes the following methods:

(1) Deinking wastewater: wastewater→regulating tank→mixing reaction tank→first-level air flotation→mixed reaction tank→second-level air flotation→valveless filter→standard discharge

(2) White water wastewater: white water → collection tank → air flotation tank → cleaning tank → to production slurry tank

(3) Papermaking black liquor: black liquor→silicon removal reaction tank→coagulation reaction tank-mixed liquid separation equipment→clear liquid tank→discharge into middle water treatment station

(4) Wastewater in the middle section: sewage → sand settling tank → first settling tank → oxidation tank (dosing) → oxidation tank → secondary settling tank → effluent