The paper industry is one of the sectors that contributes significantly to the economy, but at the same time, it is also a source of severe environmental pollution if not properly managed. Wastewater from the paper production process contains many organic and toxic substances, which seriously affect the ecosystem and human health. Therefore, paper industry wastewater treatment is an urgent requirement to protect the environment and comply with environmental protection regulations. Learn more with Tan Thanh.
1. Characteristics of wastewater in the paper production industry
Wastewater from the paper production industry contains many harmful components, which can seriously affect the environment if not properly treated. Below are the main characteristics of wastewater in each production stage:
- Wood to pulp stage: The wastewater at this stage is also called “black liquor,” containing lignin and bleaching chemicals. This is highly toxic wastewater and needs to be treated rigorously.
- Ink removal and bleaching stage: The wastewater contains many chemicals that can cause environmental pollution if directly discharged.
- Paper forming stage: This is the stage that generates the largest volume of wastewater. Despite the reuse of water, a significant amount of wastewater is still produced.
Characteristics of paper industry wastewater:
- High pH, alkaline: The wastewater has a high pH, which can alter the properties of river water, causing ecological imbalance.
- Black color, foam, and characteristic odor: Due to the presence of organic compounds like lignin and its derivatives.
- Suspended solids from pulp: The wastewater contains many solids from the pulp production process, affecting water quality.
- High COD & BOD: These two indices represent the levels of organic and chemical pollution. High values indicate that wastewater needs treatment to avoid negative environmental impacts.
- Dark color: Due to organic compounds involved in paper production.
- Contains toxic chemicals: Some chemicals like halogens and dioxins from the bleaching process can have serious impacts on the ecosystem.
Since January 1, 2020, the regulatory values for new facilities have been applied to all paper and pulp industrial facilities. The maximum allowed value for pH is C max = C (without applying Kq and Kf coefficients). Paper and pulp wastewater discharged into receiving water bodies (urban drainage systems, residential areas without centralized wastewater treatment plants) will apply the value C max = C.
- Kq is the coefficient of the wastewater receiving source corresponding to the flow rate of rivers, streams, creeks, canals, ditches, the volume of lakes, ponds, and swamps; and the intended use of coastal waters.
- Kf is the coefficient of the wastewater flow source corresponding to the total flow of untreated natural rubber wastewater when discharged into a receiving water body.
2. Wastewater treatment methods in paper production
Wastewater from the paper production industry contains many pollutants that need to be treated before being discharged into the environment. Common wastewater treatment methods in paper production include sedimentation, chemical coagulation, and biological treatment.
Sedimentation method
The sedimentation method is used to remove solid particles like pulp and fiber from the grinding and paper forming process. To recover these substances, a funnel-shaped settling tank is often used. However, sedimentation time must be calculated appropriately, as prolonged settling may lead to anaerobic decomposition of sludge, causing odor and secondary pollution. The efficiency of sedimentation can be improved by adjusting the surface load between 1 and 2 m³/m².h. Furthermore, to reduce residence time and increase sedimentation efficiency, compressed air can be injected into the tank at a pressure of 4 to 6 bars, creating flotation with a surface load between 5 and 10 m³/m².h.
Chemical coagulation method
The chemical coagulation method helps remove suspended solids, dissolved organic substances, phosphorous compounds, and some toxic substances in the wastewater. This treatment process uses coagulants like iron sulfate, aluminum sulfate, and lime to bind small particles and form flocs that settle at the bottom of the tank. To speed up the sedimentation process, polymer coagulants may be added. Treatment effectiveness depends on the pH of the wastewater; for example, aluminum sulfate works best in a pH range of 5 to 7, iron sulfate works from 5 to 11, and lime requires a pH above 11.
Biological treatment method
The biological treatment method is applied to remove dissolved organic compounds in wastewater. However, a major challenge in treating paper production wastewater is the high lignin content, especially in the discharge from the pulp production process. Lignin is a very difficult-to-degrade organic compound, particularly under aerobic conditions, and anaerobic decomposition occurs very slowly. Therefore, before wastewater enters the biological treatment system, a preliminary treatment step is necessary to remove lignin from black liquor, reducing pollution load and improving treatment efficiency.
3. Standard wastewater treatment process in paper production
Here is the standard wastewater treatment process for paper production plants, ensuring treatment effectiveness and compliance with environmental protection regulations.
Grille – Removes large debris initially
The first step is for the wastewater to pass through a grille to trap large solid objects like plastic bags, wood scraps, and cardboard, protecting the subsequent treatment equipment.
Note: Regular cleaning of the grille is necessary to prevent clogging and ensure stable flow.
Sand Settling Tank – Efficiently separates heavy sludge
After filtration, wastewater is directed to the sand settling tank. Here, heavy particles such as sand, gravel, and soil settle at the bottom, which are then collected for separate treatment, helping to remove heavy sludge and prevent blockages in later stages.
Collection Pit – Stabilizes the input flow
The collection pit temporarily stores and regulates the flow of wastewater before it enters the main treatment tanks, ensuring stable and continuous operation of the wastewater treatment system.
Equalization Tank – Stabilizes pollutant concentrations
The equalization tank stabilizes the flow and concentration of pollutants (BOD, COD) before the wastewater enters chemical and biological treatment.
- Equipped with air blowers to prevent anaerobic decomposition and odor.
- Reduces BOD and COD by about 10%.
Coagulation Tank – Forms easily settling flocs
In the coagulation tank, chemicals are added to bind suspended particles, forming larger flocs that settle more easily. This step improves the efficiency of subsequent settling tanks.
Settling Tank 1 – Removes primary sludge
The flocs from the coagulation tank settle at the bottom in Settling Tank 1. The clear water is transferred, while the sludge is sent to the sludge storage tank for separate processing.
Biological Tank – Treats dissolved organic matter
Anaerobic Tank: Used to treat BOD and COD with microorganisms in the absence of oxygen. Suitable for wastewater with high organic content.
Aerobic Tank: Follows the anaerobic tank, where microorganisms degrade dissolved organic matter under continuous aeration. Air diffusers maintain dissolved oxygen for optimal microorganism activity.
Settling Tank 2 – Separates activated sludge post-treatment
After biological treatment, the wastewater contains a significant amount of activated sludge and suspended solids. Settling Tank 2 helps to separate this sludge from the water. The settled water is then collected and directed to the disinfection step.
Disinfection Tank – Kills bacteria, ensuring safety
In the final step, the wastewater passes through the disinfection tank, where chemicals like chlorine are used to kill bacteria, viruses, and remaining pathogens. The treated water meets the national technical standard QCVN 12-MT:2015/BTNMT for industrial paper and pulp wastewater.
4. Tan Thanh – Provider of industrial wastewater treatment solutions for paper production
The paper and pulp production industries consume large amounts of water and discharge polluted water containing organic compounds and toxic chemicals. To ensure that wastewater is treated to standard before being discharged, companies must invest in efficient filtration systems and treatment equipment.
Tan Thanh is a specialist in providing liquid filter bags—important equipment that helps remove impurities and solids from pulp wastewater, enhancing treatment efficiency and reducing pollution load.
With over 14 years of experience in manufacturing and distributing dust filtration equipment, exhaust gas treatment systems, and wastewater treatment systems, Tan Thanh is committed to providing high-quality, durable products that meet stringent environmental standards. We not only provide products but also offer optimal solutions to help businesses operate wastewater treatment systems effectively and cost-effectively.
In summary, paper industry wastewater treatment is a critical and necessary task to protect the environment. With modern technologies and efficient treatment processes, we can reduce the negative impacts of paper industry wastewater and move towards a more sustainable future. Contact Tan Thanh for specific consultation.
Contact Info:
- Hotline: 0917 531 007
- Email: kelvin@tatafilter.com
- Address: 50 Road No.1 Cu Xa Dien Luc, Truong Tho Ward, Thu Duc City, Ho Chi Minh City, Vietnam.
