[China Packaging Network News] During the production and application of water-based inks, a certain amount of wastewater is generated due to equipment cleaning. The frequent color changes in these inks result in complex chemical compositions in the wastewater, characterized by high COD (Chemical Oxygen Demand), intense color, and poor biodegradability. Once released into water bodies, this wastewater can cause severe environmental pollution. Therefore, the treatment of such wastewater is closely related to the type and properties of the aqueous inks used. Currently, research and practical applications in treating water-based ink wastewater mainly focus on pretreatment methods such as chemical coagulation, electrolysis, coagulation flotation, coagulation flotation-microelectrolysis, and chemical oxidation-coagulation, combined with biochemical processes.
**1. Electrolytic Method**
Electrolysis has shown promising performance in some pretreatment techniques, with a solid foundation for domestic research and application. Its advantages include: (1) The hydroxyl radicals (OH) produced during the process directly react with organic pollutants, degrading them into carbon dioxide, water, and simple organic compounds, with minimal or no secondary pollution; (2) The electrolytic process also facilitates air flotation; (3) It operates at high energy efficiency and can be carried out at room temperature; (4) It can function as a standalone treatment or in combination with other methods. For instance, it can improve the biodegradability of wastewater before biological treatment. A case study from Maoming City Environmental Protection Bureau’s Environmental Engineering Design Center showed that after electrolytic pretreatment followed by biochemical treatment, the effluent met discharge standards.
**Electrolysis Decontamination Mechanism**
The electrolysis method is efficient, fast, and environmentally friendly, suitable for various types of wastewater. Using iron plates as anodes and aluminum plates as cathodes, electrochemical treatment occurs under strong current. Key reactions are:
- **Anode:** Fe → Fe²⺠+ 2eâ»
- **Cathode:** 2H⺠+ 2e⻠→ H₂
As the iron anode dissolves, it forms Fe(OH)â‚‚, which acts as a flocculant. Simultaneously, hydrogen gas is released, aiding in the removal of contaminants. The process involves oxidation, reduction, flocculation, and flotation.
**Oxidation:** Direct oxidation occurs when contaminants lose electrons at the anode. Indirect oxidation involves the formation of reactive species like [O], Clâ‚‚, which further degrade pollutants.
**Reduction:** This includes direct reduction at the cathode and indirect reduction through cations reacting with electrons.
**Flocculation:** Metal ions like Fe²⺠and Al³⺠form colloidal flocs that adsorb pollutants.
**Flotation:** Gas bubbles created during electrolysis help lift suspended particles to the surface for removal.
**2. UASB Process**
The Upflow Anaerobic Sludge Blanket (UASB) process combines anaerobic filtration and activated sludge techniques. It converts organic matter into biogas, a renewable energy source. Developed in the 1970s, the UASB reactor uses a three-phase separator to separate sludge from wastewater. The discovery of granular sludge improved the efficiency of anaerobic treatment, leading to the development of advanced reactors.
**3. Air Flotation**
Air flotation involves introducing fine air bubbles into wastewater, which attach to contaminants, increasing their buoyancy so they float to the surface. This method is effective for removing oils and suspended solids but faces challenges like equipment wear and corrosion in high-salinity environments.
**4. Coagulation**
Coagulation involves adding chemicals to destabilize colloids, causing them to aggregate and settle. Common coagulants include alum, ferric chloride, and others. This method is often used as a pretreatment step for oily, dyeing, and washing wastewater.
**5. Biological Contact Oxidation**
This method uses biofilms attached to media to treat organic pollutants. Microorganisms break down contaminants, forming new biofilm layers. Advantages include high volumetric load, no sludge recirculation, and good adaptability to fluctuating conditions.
**6. Membrane Bioreactors (MBR)**
MBR combines membrane filtration with biological treatment, offering high-efficiency, compact systems with excellent effluent quality. Since the 1980s, MBR technology has gained popularity globally, with applications in treating domestic and industrial wastewater. In China, MBR is increasingly used for high-concentration and refractory wastewaters, showing great potential for reuse and sustainable water management.
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