How to deal with printing ink waste water in response to environmental protection

[China Packaging Network News] During the production and application of water-based inks, a certain amount of waste water will be generated due to the cleaning of the equipment. The ever-changing water-based ink color causes the chemical composition of its waste water to be quite complex, with high COD, high chroma, and hard to biodegrade. Once it enters the water, it will cause serious pollution to the water environment. Wastewater treatment processes have a very close relationship with the type and characteristics of aqueous inks. At present, the research and application of water-based ink wastewater treatment mainly focuses on chemical coagulation, electrolysis, coagulation air flotation, coagulation air floatation-microelectrolysis, chemical oxidation-coagulation and other pretreatment methods combined with biochemical processes.

1 electrolytic method

In some pretreatment methods, electrolysis shows good performance, and domestic research and application have a certain basis; the advantages of electrolysis are: (1) The OH generated in the process is directly and selectively organically contaminated in wastewater. The material reacts and degrades into carbon dioxide, water and simple organic matter, with little or no secondary pollution; (2) The electrolytic process is accompanied by the function of generating air flotation; (3) The energy efficiency is high, and the electrochemical process is generally at room temperature. Pressing can be carried out; (4) can be used as a separate treatment, but can also be combined with other treatments. For example, as a pretreatment, the biodegradability of wastewater can be improved, and the biodegradability of wastewater after pretreatment can be greatly improved; (5 Electrolysis equipment and its operation are generally relatively simple. The environmental engineering design center of Maoming City Environmental Protection Bureau applied in the wastewater treatment system of Maoming Sakata Ink Co., Ltd. It was proved that the pretreatment by electrolysis, followed by biochemical treatment, the treated sewage could reach the standard emission.

Electrolysis decontamination mechanism

Electrolysis method is a kind of method that is adaptable to various sewage treatment, high efficiency, short time, and no secondary pollution treatment. It uses iron plate as anode and aluminum plate as cathode, and conducts electrochemical treatment of sewage under the action of strong current. The main chemical reaction formula is:

Anode: Fe----Fe2++2e

Cathode: 2H++2e----H2

The iron plate as an anode slowly dissolves during the electrolysis process and enters the wastewater as it is, and hydrolyzes to form Fe(OH)2. These Fe(OH)2 have a high agglomeration effect and generate new ecological hydrogen at the cathode. The reduction ability is very strong, and it reacts with the pollutants in the waste water. At the same time, the macromolecular pollutants are decomposed into small molecules. The electrolysis process contains oxidation, reduction, agglomeration, and air flotation.

1) Oxidation. Oxidation in electrolysis can be divided into direct oxidation (ie, the contaminants lose their electrons directly at the anode and oxidize) and indirect oxidation. Indirect oxidation refers to the use of anion (eg, OH-, Cl-) with lower electrode potential in solution. Loss of electrons at the anode generates new strong oxidizing agent active substances [O], Cl2, etc., and these active substances make the contaminants lose electrons and act as oxidative decomposition to reduce BOD5, COD, NH3-N, etc. in the original liquid.

2) reduction. Reduction in the electrolysis process can also be divided into two categories. One is the direct reduction, that is, the contaminants get electrons directly on the cathode and the reduction takes place; the other is the indirect reduction, and the cations in the contaminants first get electrons at the cathode, making the electrolyte high or low in metal cations. From the cathode, electrons are directly reduced to lower cations or metal precipitates.

3) Cohesion. Soluble anodes such as iron, aluminum and other anodes, through direct current, after the anode loses electrons, the formation of metal cations Fe2+, Al3+, and OH- in solution to generate metal hydroxide colloidal flocculants, its adsorption capacity is extremely strong, can be contaminants Adsorption forms flocculates.

4) Air flotation. In the electrolysis of waste water, when the voltage reaches the decomposition voltage of water, hydrogen and oxygen respectively precipitate on the cathode and the anode. On the other hand, the OH- produced in the electrolysis process reacts with the organic matter to produce carbon dioxide. The gas bubbles of these gases are small in size and have a high degree of dispersion and can float as a carrier to adhere suspended solids in water, so that it is easy to remove contaminants. Electrical float can remove both hydrophobic and hydrophilic contaminants in wastewater.

2 UASB process

The UASB (Up-flow Anaerobic Sludge Bed) process has the dual characteristics of anaerobic filtration and anaerobic activated sludge process, which can convert pollutants in sewage into Renewable clean energy - a technology of biogas. In 1971, Professor Lettinga of Wageningen Agricultural University in the Netherlands invented a three-phase separator by designing physical structures and using the effect of gravity field on different density materials. The activated sludge residence time was separated from the wastewater residence time to form a prototype of an upflow anaerobic sludge blanket (UASB) reactor. In 1974, when CSM Co., Ltd. of the Netherlands processed sugar beet sugar wastewater in its 6m3 reactor, it discovered a biopolymer structure formed by the self-immobilization mechanism of activated sludge, that is, granular sludge. The emergence of granular sludge not only promoted the application and development of the second-generation anaerobic reactor represented by UASB, but also laid the foundation for the birth of the third-generation anaerobic reactor.

UASB process is also adaptable to different solids-contaminated wastewater, and its structure, operation and maintenance management is relatively simple, the cost is relatively low, and the technology is mature. It is increasingly being taken seriously by the sewage treatment industry and widely welcomed and applied. .

3 Air floatation

The dispersed tiny air gown serves as a carrier to adhere suspended contaminants in the waste water, making its buoyancy greater than gravity and resistance, so that the contaminants float to the surface of the water to form a foam, and then scrape the foam from the water surface with a scraping device to achieve solidification. The process of liquid or liquid separation is called air floatation.

The principle of air-flotation and degreasing is mainly to use the characteristics that the surface tension between oil and water is greater than the surface tension between oil and gas, the oil is hydrophobic and the gas is relatively hydrophilic, and the air is introduced into the sewage, and at the same time, the flotation agent is added to make the oil particles adhere to the air bubbles. Bubbles absorb oil and suspended solids to the surface of the water to achieve the purpose of separation. The air floatation method mainly removes the residual oil and the dispersion oil without surfactant. The disadvantage is that there are many rotating parts in the equipment, and the oily sewage contains high salinity and is corrosive. Therefore, the stability of the process operation is poor.

4 Coagulation

Coagulation method is to add a certain amount of pharmaceuticals to the sewage, through the destabilization, bridging and other reaction processes, so that the water pollutants condensed and settled. Colloidal contaminants in the water are usually negatively charged, and the colloidal particles repel each other to form a stable mixture. If the oppositely charged dielectric (ie, coagulant) is used in the water, the colloidal particles in the waste water can be changed to be electrically charged. Neutral, and condensed under the action of molecular gravity into large particles sink.

This method is used to treat oily wastewater, dyeing wastewater, and hair washing wastewater. This method can be used independently or in combination with other methods, generally as pretreatment, intermediate treatment and advanced treatment. Commonly used coagulants include aluminum sulfate, basic aluminum chloride, ferrous sulfate, and ferric chloride.

5 Biological Contact Oxidation

Biological contact oxidation is one of the main facilities of the biofilm method. The biofilm method is a general term for a large class of biological treatment methods. It mainly uses microorganisms (ie, biofilms) attached to the surface of certain solid materials for organic sewage treatment. method. Biofilm is an ecosystem composed of highly dense aerobic bacteria, anaerobic bacteria, facultative bacteria, fungi, protozoa, and algae. The attached solid media is called filter media or carrier. The biofilm can be divided into the celebration gas layer, aerobic layer, adhesion water layer and sports water layer from the filter material. The principle is that the biofilm firstly adsorbs organic matter attached to the water layer, is decomposed by the aerobic bacteria in the aerobic layer, enters the anaerobic layer for anaerobic decomposition, and the flowing water layer flushes out the aged biofilm to grow a new biofilm. , so to achieve the purpose of purifying sewage. The aged biofilm continuously falls off and is removed by precipitation as the water flows into the secondary precipitate.

The biological contact oxidation treatment structure is an immersed aeration biological filter, also called biological contact oxidation tank.

The biological contact oxidation tank is provided with a filler, the filler is submerged in the wastewater, and the filler is covered with a biofilm. During the contact of the wastewater with the biofilm, the organic matter in the water is adsorbed, oxidized and decomposed by the microorganism and converted into a new biofilm. The biofilm that has fallen off the filler is removed after the water flows to the secondary sedimentation tank, and the wastewater is purified. In the contact oxidation tank, the oxygen needed by the microorganisms comes from the water, and the waste water continuously supplements the lost dissolved oxygen from the drummer's air. The air enters the water stream through a perforated pipe provided at the bottom of the pool. When air bubbles rise, it supplies oxygen to the waste water, sometimes to return the pool water.

Biological contact oxidation method features:

(1) Due to the large specific surface area of ​​the filler, the oxygenation conditions in the cell are good. The bio-solids in the biological contact oxidation tank is higher than the activated sludge aeration tank and the biological filter. Therefore, the biological contact oxidation tank has a higher volumetric load.

(2) The biological contact oxidation method does not require sludge recirculation, there is no problem of sludge expansion, and the operation and management are simple;

(3) Due to the large amount of biosolids, the water flow is completely mixed, so the biological contact oxidation tank has a strong adaptability to sudden change of water quality and water quantity;

(4) When the organic volume load of the biological contact oxidation tank is relatively high, the F/M is kept at a low level and the sludge yield is less.

6 Membrane Bioreactors

Membrance Bioreactor Reactor (abbreviated as MBR) is a new wastewater biological treatment process combined with membrane separation and biological treatment technology. Compared with traditional biochemical treatment technologies, MBR has the following main features: high treatment efficiency and effluent quality Good; compact equipment, small footprint; easy to achieve automatic control, simple operation and management. Since the 1980s, the technology has received more and more attention and become a hot topic in water treatment technology research. At present, membrane bioreactors have been used in more than 10 countries such as the United States, Germany, France, Japan, and Egypt, with a treatment scale of 6 to 13,000 m3/d.

In the past two years, membrane bioreactors have entered a practical stage in China. The MBR system will be expanded from domestic sewage to high-concentration organic wastewater and hard-to-degrade industrial wastewater, such as pharmaceutical wastewater, chemical wastewater, food wastewater, slaughter wastewater, tobacco wastewater, soy bean wastewater, fecal wastewater, and astragalus wastewater. Judging from the current trends, the reuse of water will be the main direction for the promotion and application of MBR in China. Table 1 lists the application of MBR in China and the processing results. These application examples show that MBR has a good treatment effect on domestic sewage, high-concentration organic wastewater and refractory industrial wastewater.