Environmental regulations on wastewater COD, BOD, colour, heavy metals, ammonia nitrogen, total phosphorus, specific toxic and hazardous substances and other indicators of the requirements continue to increase, making it difficult to meet the discharge standards continue to increase. Printing plant wastewater treatment wastewater difficulties are mainly due to the dramatic volatility of sewage and the extremely high demand for treatment technology and cost. To solve these difficulties usually need to be adapted to the design of a combination of processes, strengthen the source control and pretreatment.
1. Wastewater composition is extremely complex and variable:
A variety of pollutants coexist: including inks (pigments, resins, solvents), fountain solution (alcohols, surfactants, buffers), cleaning agents (solvents, surfactants), starch solution, adhesives, auxiliaries, and rinse water. Different printing methods (offset printing, gravure printing, flexographic printing, screen printing, digital printing) use different consumables, resulting in a huge difference in the composition of wastewater; frequent changes in ink colours and printing orders, resulting in fluctuations in the quality of wastewater (COD, chromaticity, pollutant type) fluctuations.
2. High concentration of organic matter (COD/BOD) and high chromaticity:
Organic pigments, resin connectors, solvents, etc. in the ink are the main contributors to COD and BOD, and the concentration is usually very high; organic pigments lead to wastewater chromaticity is extremely high and very stubborn, conventional physical-chemical or biological treatment methods are often difficult to effectively decolorise the ink, and strong oxidation or adsorption and other in-depth treatment means are required.
3. Ink and oil substances (especially emulsified oil):
Must add specific emulsion breakers or strong physical and chemical methods (such as flocculation, advanced oxidation) for pretreatment, increasing the difficulty and cost of treatment; ink particles are fine, especially offset printing in the ink - fountain solution emulsion system, the formation of a very stable oil / water emulsion, conventional oil separation, air flotation and other methods are difficult to effectively emulsion separation.
4. Difficult biodegradable substances:
Ink resin, some organic solvents, some surfactants and other large molecules or complex structure of synthetic organic matter, microbial degradation or degradation rate is difficult to slow.
5. Water quantity and quality volatility:
Wastewater discharge and production activities are closely related, such as colour change cleaning, equipment maintenance when a high concentration of wastewater, other times the water volume is small or low concentration.
In the typical printing wastewater treatment process, Lamella Clarifier is often in the core position of physical and chemical treatment, is to achieve effective pretreatment and guarantee the stable operation of subsequent processes one of the key links.
