Wastewater treatment of pulp and paper making industries

The pulp and paper industry was one of the biggest sources of environmental pollution from long time ago, so the issue of paper and cardboard wastewater treatment is very important. Paper industry and the paper production process requires a lot of water and is considered one of the industries with a lot of wastewater. In paper factories, pulp is usually used as paper feed, and cellulose sources such as wood and bamboo are also used to produce pulp. In general, three different raw materials are used in the pulp and paper industry as non-wood fibers and wood materials. Waste and effluents are generated from both pulping and dyeing processes, and it is estimated that around 100 million kilograms of toxic pollutants are released from this industry each year. In addition to the large volume, the waste water of the paper industry has a high concentration of waste water pollutants, especially COD. In this article, there is a discussion about paper mill wastewater treatment and also the method of wastewater treatment in these industries.

The importance of paper and cardboard wastewater treatment:

Wastewater pollutants from pulp and paper industries are very diverse and have complex structures that require wastewater treatment before disposal in the environment. Due to the following reasons, the discharge of untreated wastewater from the paper mill can bring many risks to the environment:

• Due to the presence of fine fibers that exist as suspended solids in wastewater, it is possible to clog valves, pumps and channels.
• Untreated wastewater from the pulp and paper industry can pollute the downstream water up to 80 km.
• Complex chemical compounds and a lot of color present in papermaking wastewater have caused their destruction process to be done very slowly.
• Due to the fact that many chemicals and dyes enter the water flow, the possibility that the oxygen consumption in the water will increase greatly is high.

Description of the main pulp and paper production process:

The pulping process is the first step in production. The main stages of this section include forming, crushing, digestion and chemical purification, pulp screening, thickening and washing. Throughout the world, mechanical and chemical processes are mostly used in pulping. Mechanical processes include mechanical pressure, disc refining, heating to produce pulp and the use of light chemical processes to increase pulp performance. The process of pulping and pulp production is the main source of waste water pollution in the paper industry. In this process, which is carried out after the crushing stage (production of wood chips), we have chemical purification, which is done to break down the tissue and cellulose fibers and separate the black liquor (Black Liquor), and finally, the effluent and wastewater that is rich in lignin, It produces fats, carbohydrates and chemicals. In the next stage of paper pulp production, we have dyeing so that the produced pulp turns into an almost white color suitable for paper. In the dyeing stage, chemical treatment is done in three stages by three different chemicals and colored effluent is produced.

Finally, after pulp production, we have three stages of chemical treatment, straightening and drying to produce paper. Chemicals such as alum, talc, and glue are used as fillers in the dough, and then this dough is passed through a series of rollers arranged from large to small in the smoothing process to remove possible stains and make it completely smooth. After drying the product, cuts are made in different sizes and finally paper is produced.

Pulp and paper making factory waste water:

As mentioned in the previous section, the majority of waste water produced by the paper factory is related to pulping or pulp production. Different pulp production processes use different amounts of water and all these processes have a high consumption of water. The quality of wastewater from the pulp production and dyeing stage is significantly different due to the different type of process and different types of chemicals used.

Approximately 200 cubic meters of water is used for each ton of pulp produced, and most of it is highly polluted, especially the wastewater from the chemical refining process. The most important sources of wastewater pollution in the pulp and paper industry are related to the screening and washing processes of wood pulp, as well as the dyeing process.

Qualitative characteristics of paper and cardboard industries waste water:

The raw wastewater entering the wastewater treatment plant system from the production line of the paper mill with the capacity to produce 2000 tons of paper per day is roughly stated according to the following table:

Wastewater treatment method of paper and cardboard industries:

In the following, the wastewater treatment methods of the Akhal paper factory are briefly mentioned, taking into account the maximum recycling of water.

Primary treatment:

In the primary treatment, the goal is to remove suspended solids such as skin particles, fiber, fiber waste, fillers and coatings, and consequently organic substances. Primary clarification can also be done without sedimentation and floating. DAF (Dissolved Air Floatation) system is one of the methods of flotation with dissolved air, which is used as primary treatment for paper mills. Dissolved air flotation (DAF) is used for particles that have a density close to water and are difficult to settle. Coagulant materials will also be used after this step to mix the floating materials and separate them easily. It is obvious that the resulting sludge contains moisture, so it will be necessary to dewater it with a filter press to reduce the volume.

Secondary treatment:

In this stage of the target treatment, the pollutant is transferred from the dissolved state to the suspended solid or sludge. A variety of biological or secondary treatment methods are used as widely used methods in the final treatment of paper industry wastewater. Aerobic lagoons, activated sludge systems, anaerobic treatment, and sequential biological treatment (aerobic-anaerobic or anaerobic-aerobic) are the most common biological treatment programs for paper mills.

Given that the design of the waste water treatment system of paper mills is the same in terms of strategy, but in terms of technology, due to the characteristics of the production lines, they can be different, therefore the suggestions of Pasenco Company are presented considering the strategy of maximum water recycling and the technique of reducing operational costs with high performance.

With more than 20 years of successful experience in providing engineering services related to the design, consulting and implementation of industrial wastewater treatment systems, along with the full guarantee of obtaining environmental standards, Pajoohesh Sanat-e-Ab company accompanies you in this important matter. If you need free expert advice, you can contact our experts through the communication methods mentioned on this page.