I. Introduction
The printing and dyeing industry is a critical link in the textile value chain, but it is also a major water consumer and pollutant generator. According to statistics, China's printing and dyeing wastewater annual discharge reaches 1.8 to 2 billion tons, accounting for approximately 11% of the country's total industrial wastewater discharge, making it a typical high-difficulty organic industrial wastewater. The challenge of reducing wastewater volume and enabling resource recovery while maintaining production output is a real-world issue for every water treatment professional.
Membrane separation technology, with its advantages of high efficiency, energy savings, and operational simplicity, has gained increasingly widespread application in printing and dyeing wastewater treatment in recent years. As a professional brand in the membrane technology field, Vontex's reverse osmosis (RO) membranes and ultrafiltration (UF) membranes are playing an important role in wastewater reuse systems within the printing and dyeing industry. This article explores the characteristics of printing and dyeing wastewater and discusses the technical advantages and application value of Vontex membrane products.
II. Pain Points in Printing and Dyeing Wastewater Treatment
Printing and dyeing wastewater is characterized by complex composition, high pollutant concentration, and large flow volumes, making it significantly more difficult to treat than general industrial wastewater. Specific challenges include:
High organic matter concentration. The wastewater contains substantial amounts of dyes, sizing agents, auxiliaries, and other organic substances, with COD values typically ranging from several hundred to several thousand milligrams per liter, and even higher in some high-strength waste streams.
High salinity. The extensive use of inorganic salts such as Glauber's salt and sodium chloride in dyeing processes results in high salt content and electrical conductivity, imposing stringent requirements on the treatment system's salt tolerance and corrosion resistance.
Deep color and high alkalinity. Residual dyes cause extremely high color levels in the wastewater, and the strong alkalinity from alkali-deweighting processes makes conventional biological treatment difficult to apply directly.
Significant fluctuations in water quality and quantity. Variations in production batches and product types lead to intermittent and unstable discharge characteristics, placing high demands on the treatment system's shock-load resistance.
In conventional treatment processes, poor UF membrane performance and rapid RO membrane degradation have long been bottlenecks limiting water reuse rates. Therefore, selecting membrane products with stable performance and strong fouling resistance is the key to enabling wastewater reuse for printing and dyeing enterprises.
III. Technical Advantages of Vontex Membrane Products
Ultrafiltration Membranes: Balancing Precision and Flux
Vontex ultrafiltration membranes operate in a full-flow filtration mode with a typical transmembrane pressure differential of only 0.3 to 0.8 bar, effectively reducing energy consumption. With a membrane pore size of 10 nanometers and a narrow pore size distribution, they provide an absolute barrier against all suspended solids, including bacteria and coliform groups. The treated effluent has suspended solids below 0.5 mg/L, turbidity below 0.1 NTU, bacterial removal exceeding 6 log, and virus removal exceeding 4 log.
Compared to conventional UF membranes, Vontex's combined design of full-flow filtration and periodic backwashing effectively removes solid particles deposited on the membrane surface, preventing continuous pollutant accumulation. This design approach aligns with industry trends toward "fiber armor" reinforcement strategies—enhancing membrane structural strength to extend service life.
Reverse Osmosis Membranes: Dual Assurance of Stability and Fouling Resistance
In the RO stage, Vontex brackish water series RO membrane elements utilize aromatic polyamide composite membrane materials, achieving a salt rejection rate of up to 99%, with an effective membrane area of 400 square feet (approximately 37 square meters), suitable for feed water with total dissolved solids below 10,000 mg/L.
Significantly, advanced RO membrane products in the industry have achieved average membrane flux no less than 45 L/m²·h, with sodium chloride rejection maintained above 97% over three years, membrane fouling rates reduced by more than 20% compared to conventional membranes, and system water reuse rates reaching above 65%. These key performance indicators not only reflect the direction of technological advancement but also provide a benchmark for evaluating Vontex product performance in practical applications.
In real-world applications, frequent membrane cleaning and performance degradation are the primary concerns for end users. Vontex RO membranes address these issues through optimization of both the support layer and separation layer, employing multi-scale structural regulation of the homogeneous polysulfone support membrane and the polyamide separation layer to enhance overall membrane stability and fouling resistance. This makes them particularly well-suited for high-fouling applications such as printing and dyeing wastewater treatment.
IV. Application of Membrane-Based Combined Processes in the Printing and Dyeing Industry
In actual engineering practice, a single membrane product alone cannot achieve compliant printing and dyeing wastewater reuse. A well-designed combined process train is the key to achieving both efficient treatment and resource recovery. The industry-standard approach currently follows the "pretreatment + UF + RO" membrane integration route, typically including the following stages:
Step 1: Pretreatment and Ultrafiltration. Following coagulation and sedimentation pretreatment, the feed water enters the UF system. Vontex UF membranes serve as upstream protection for the RO system, removing suspended solids, colloids, and most microorganisms, thereby reducing the fouling risk for downstream RO membranes.
Step 2: Reverse Osmosis Advanced Treatment. The UF permeate enters the RO system, where Vontex RO membranes efficiently reject dissolved salts and residual organic matter, producing high-quality water that can be recycled back to the production process.
Step 3: Concentrate Treatment and Resource Recovery (optional). For high-salinity concentrate streams, specialized spiral-wound UF membranes combined with RO and desalting processes can be further applied to recover inorganic salts such as Glauber's salt. Industry practice demonstrates that with multi-stage membrane integration, the system salt recovery rate can exceed 75%, and the recovered liquid Glauber's salt concentrate reaches an electrical conductivity of no less than 70,000 μS/cm.
In printing and dyeing industrial parks, the combined process train of "coagulation pre-sedimentation — A/O biological treatment — coagulation decolorization — sand filtration — ultrafiltration — UV disinfection — reverse osmosis" has achieved COD and ammonia nitrogen removal rates of 92.6% and 91.5%, respectively. The membrane separation system alone achieves over 96% conductivity removal, and the reclaimed water quality consistently meets the textile dyeing and finishing industry reuse water standards. This fully validates the feasibility and reliability of membrane-based combined process solutions.