In our daily life, a large amount of waste alkali water comes from pulp and paper industry, petrochemical industry, textile and dyeing, oil-out cleaning, recycling waste water from ion exchange and other industries. According to incomplete statistics,the annual treatment of alkali-containing waste water in the field of black liquor of paper-making, viscose fiber waste water, beer bottle washing waste water and ion-exchange resin elution waste water reaches 404 million tons in China.
Alkali recovery refers to the process of recovering the used chemicals from alkali pulping effluent liquor.
The ceramic membrane system independently developed and produced by JIUWU HI-TECH can treat desizing wastewater and viscose fiber wastewater respectively. Through the recovery of alkali liquor, the water and alkali can be reused.
A. Desizing wastewater
The dyeing industry is an important part of textile industry and the main source of wastewater in the textile industry. A large amount of pollutants in the wastewater comes from the slurry used in the sizing process, which is mainly polyvinyl alcohol (PVA) slurry. The wastewater is alkaline and has a pH of about 12.
According to the characteristics of desizing wastewater containing high concentration of caustic soda and high COD,JIUWU HI-TECH adopts the process of coarse filter filtration integrated with membrane concentration . The coarse filter mainly intercepts the large particles in the effluent.
The sizing wastewater also contains a higher concentration of caustic soda (0.5% ~ 7%) and a certain amount of refining agent, with a high recovery value.
The membrane concentration system uses ceramic membranes to concentrate desizing wastewater. The ceramic membrane can retain most of PVA slurry, while most of caustic soda and some additives can pass through ceramic membrane together with clear liquid. The clear liquid of ceramic membrane system is stored in the clear liquid storage tank, which is used by the external supply pump for reduction and other processes so as to achieve the recovery alkali.
However, the amount of concentration of ceramic membrane containing PVA slurry only accounts for 10% of total inflow, which is convenient for centralized treatment and reduces the difficulty of subsequent treatment. The reuse rate of water and caustic soda in this process system is more than 90%, which reduces the influence of desizing wastewater on wastewater treatment process of printing and dyeing enterprises.
B. Viscose wastewater
The waste alkali solution containing semi fiber is produced in the pressing section. The content of semi fiber is about 35g/L and the content of alkali is about 200g/L.
The process of ceramic membrane combined with alkali resistant organic membrane can be used to recycle the waste alkali liquor and effectively reduce the production cost of the enterprise.
This lye is pre-treated with ceramic membrane to reduce the fiber content in the waste lye, effectively reduce the processing load of organic membrane system,and effectively extend the life of organic membrane. The permeate produced by ceramic membrane is further filtered with an alkali-resistant organic membrane, and final filtrate half fiber content of the system is less than 5g/L. By recycling lye, resources can be reused. The purpose of recovering alkali is realized.
C. Process features
Wastewater can achieve a reuse rate of more than 90%, and the reuse rate of caustic soda is higher than 90%;
PLC control, which can realize fully automatic operation without manual intervention;
Stable permeate which can be returned to front-end dyeing process to recover alkali ;
The process has been verified by long-term operation with high reliability.