The application of membrane separation technology in wastewater alkali recovery

In daily life, a large amount of waste alkali water comes from pulp and paper industry, petrochemical industry, textile printing and dyeing industry, washing and degreasing industry, separation and regeneration wastewater and other industries. According to incomplete statistics, only black liquor treatment, viscose fiber wastewater, beer bottle washing wastewater and separation resin elution wastewater are treated by 404 million tons of alkali wastewater annually. Alkali recovery refers to the process of recovering chemicals from the waste liquor of alkali pulping and cooking. The inorganic membrane system independently developed and produced by Nanomem®, which can treat desizing wastewater and viscose fiber wastewater respectively, and realize the recycling of resources by recycling alkali liquor.

Printing and dyeing industry is an important part of textile industry, and also the main waste water source of textile industry. A large number of pollutants come from the size used in the sizing process, mainly polyvinyl alcohol (PVA) size. The wastewater is alkaline and the pH is about 12. Nanomem® adopts the process of "coarse filtration + membrane concentration" according to the characteristics of high caustic concentration and high COD in desizing wastewater. The coarse filtration mainly intercepts the large particles in the incoming water. The membrane concentration system uses inorganic membrane to concentrate the desizing wastewater. Inorganic membrane can retain most of PVA size, while most of caustic soda and some additives can pass through inorganic membrane together with clear liquid. The clear solution of the inorganic membrane system is stored in the clear solution storage tank, which is used by the external supply pump for the reduction process, so as to form the alkali recovery. However, the amount of concentrated water of inorganic membrane containing PVA slurry only accounts for 10% of the total water inflow, which is convenient for centralized treatment and reduces the difficulty of subsequent treatment. The reuse rate of water and caustic soda is more than 90% in this process system, reducing the influence of desizing wastewater on the wastewater treatment process of printing and dyeing enterprises.

Viscose fiber wastewater

In the process of viscose production, the waste alkali liquor containing half fiber is produced in the press section, the half fiber content is about 35g / L, and the alkali content is about 200g / L. The process of "inorganic membrane + alkali resistant organic membrane" can be used to recycle the waste alkali liquor and effectively reduce the production cost of the enterprise. The alkali liquor is pretreated by Nanomem® small pore inorganic membrane, which can reduce the fiber content in waste alkali liquor, effectively reduce the treatment load of organic membrane, and effectively extend the service life of organic membrane. The inorganic membrane clear liquid is further filtered by alkali resistant organic membrane, and the final half fiber content of the filtrate is less than 5g / L. Through the recovery of alkali liquor, the recycling of resources can be realized.

Process description

(1) Waste water can achieve more than 90% recycling rate, and the recycling rate of caustic soda is more than 90%;

(2) The membrane system realizes PLC control, which can realize full-automatic operation without manual intervention;

(3) The water quality of the membrane clear liquid is stable, which can be returned to the front-end printing and dyeing process to form alkali recovery;

(4) The adopted process route has been verified by long-term operation, and the system has high reliability.