The paper and board industry is a key sector in the production chain for paper, board, board packaging, and pulp products. These industries not only consume wood and energy but also pose significant environmental problems. One of the most significant is wastewater treatment, i.e., the disposal of the resulting liquid waste. This wastewater has a complex chemical composition and contains large amounts of organic pollutants, suspended solids, chlorides, and various chemical elements. Untreated wastewater can have negative impacts on surface waters, soils, vital ecosystems, and human health.
1. Wastewater sources from the paper and board industry
1. Pulp processing:
In this step, wood or cellulose is converted into cellulose. Lignin is chemically separated from the cellulose. The resulting wastewater contains suspended solids, organic compounds, and chemicals. One of the most important pollutants is black liquor, which contains high concentrations of organic matter and salts.
2. Pulp washing:
The pulp is washed to remove excess material. The water in this process contains organic matter and salt compounds.
3. Bleaching:
In the production of white paper, pulp must be bleached using oxidizing agents. This process produces persistent organic compounds and chlorides that harm the environment.
4. Paper production and processing:
In this phase, drinking and washing water, so-called “white water,” is produced, which contains microfibers, fillers, dyes, and resins.
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Equipment cleaning and general cleaning:
As in other industries, cleaning equipment and conveyor belts generates a certain amount of wastewater.
2. Properties of wastewater from companies in the paper and cardboard industry
2.1 Physical properties
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Suspended solids: Most wastewater consists of fibers and filler particles.
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Color: Wastewater is typically dark brown in color due to the presence of lignin and organic compounds.
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Temperature: The temperature of the outflowing water is usually high.
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pH value: Depending on the production stage, it can be acidic or alkaline.
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Odor: Sulfur compounds or anaerobic conditions can cause unpleasant odors.
2.2 Chemical properties
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BOD and COD: The values are very high due to the presence of dissolved and suspended organic substances.
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Ions and salts: including sodium, chloride, sulfate, calcium, etc.
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Phenols and chlorinated compounds: are used, among other things, for bleaching .
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Addition of chemicals: resins, dyes, adhesives.
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Heavy metals: sometimes present in very small quantities.
2.3 Environmental impacts
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The content of dissolved oxygen in the receiving water decreases.
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Chlorides and phenol compounds are toxic to aquatic organisms.
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Long-term consequences such as mutations and cancer.
3. Methods of wastewater treatment in the paper and board industry
3.1 Pretreatment
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Sieving: Removing coarse material.
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Preliminary clarification: separation of suspended solids.
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Coagulation and agglomeration: Conversion of fine particles into sedimentable clumps.
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Dissolved air flotation (DAF): Removes light particles.
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Homogenizer: regulates fluctuations in the quality and flow of wastewater .
3.2 Biological treatment (secondary)
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Aerobic processes: such as activated sludge processes, mobile biofilm reactors, etc.
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Anaerobic methods: such as UASB reactors or anaerobic ponds for high organic loads.
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Combined anaerobic and aerobic process: the most common method for reducing pollutant loads.
3.3 Additional treatments
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Membranes (UV, NF, RO): are used to separate salts and organic compounds.
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Activated carbon adsorption: removes organic residues.
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Advanced oxidation: e.g. ozone, UV/H₂O₂.
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Sand and carbon filtration: removes particles and reduces color.
3.4 Sludge management
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Condensation and drying of water: Use a filter press or belt filter to reduce the sediment volume.
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Anaerobic digestion: produces biogas and reduces sludge volume.
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Incineration or landfilling of waste: depends on local conditions.
4. Problems and limitations
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There are compounds that are resistant to decomposition.
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Fluctuations in wastewater quality and wastewater flow .
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Energy and chemical costs are high.
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Problem with clogged diaphragm.
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Produces large amounts of sludge.
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Strict environmental standards.
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Economic issues of small businesses.
5. Innovations and new approaches
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Purified water is reused in the production line.
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Improve process design to reduce water consumption.
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Modern membrane applications and hybrid systems.
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The use of specialized fungi and microorganisms to degrade complex compounds.
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Removes dyes and toxic compounds through deep oxidation.
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Implementation of intelligent control and real-time monitoring .
6. Practical examples (cases)
Factory specifications:
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Production capacity: 10,000 tons/year
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Wastewater volume: 5000 m3/day
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Properties of the incoming substances: COD = 1200 mg/l, BOD = 600 mg/l, SS = 1200 mg/l
Treatment options:
1. Homogenization and pH adjustment
2. DAF pretreatment
3. Anaerobic treatment (UASB)
4. Aerobic treatment (MBBR or activated sludge)
5. Filtration or ozone decolorization
6. Sludge drying in a filter press
Result: The BCD of the final wastewater was below 25, the PHD below 150 and the salinity below 20 mg/l, which complies with the standards.
7. Suggested solutions
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Continuous monitoring and automation of the system.
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Improve the chemicals used.
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Reuse of part of the purified water.
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Use biogas energy.
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Efficient sludge management.
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Professional training of staff.
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Follow the rules and keep your equipment up to date.
Finally
Due to its high content of organic matter, suspended solids, and hazardous chemicals, wastewater from the paper and board industry requires multi-stage treatment. Wastewater quality can be improved through a combination of physical, chemical, biological, and complementary processes. Innovative technologies such as water reuse, membrane technology, and advanced oxidation also contribute to the sustainable development of this industry. Proper wastewater management not only protects the environment but also saves costs and improves resource efficiency.