Wastewater treatment in the paper industry: processes, limit values and solutions
Sector overview
Paper and pulp production generates large volumes of polluted wastewater containing organic substances, fibres and salts. High COD levels, deposits and increasing requirements for water reuse present companies with technical and economic challenges, for which ClearFox provides suitable solutions for efficient wastewater treatment.
Wastewater treatment in the paper industry: processes, limit values and solutions
Sector overview
Contents
Sources of paper and pulp mill wastewater
In wastewater treatment for the paper industry, the largest wastewater loads do not originate at the paper machine. Pulp production, groundwood, recovered paper processing and bleaching stages determine volume and pollution levels even before sheet formation. In integrated mills, dissolved organic substances from these stages enter the paper production water circuit directly.
In the paper process, water performs several functions at once. It serves as a suspension medium, transport medium and solvent. Depending on the grade, 250 to 1,000 l of water per unit of product are required for fibre preparation and sheet formation. This process water forms the basis of wastewater in the paper mill. Wastewater is generated primarily as excess recirculated water that displaces fresh water.
| Production step | Production component | Substances in the wastewater |
|---|---|---|
| Pulp production, kraft process | Wood, sodium hydroxide, sodium sulfide | dissolved wood constituents, especially lignin and hemicelluloses, as well as contaminated cooking liquor streams |
| Pulp production, sulfite process | Wood, bisulfite solution with SO₂ | vapour condensates, dissolved organic substances and contaminated wash streams |
| Bleaching processes | Pulp | coloured compounds, residual lignin and other dissolved organic substances |
| Groundwood production | mechanically defibrated wood | dissolved organic compounds from the groundwood suspension |
| Recovered paper processing and deinking | Recovered paper, printing inks, auxiliaries | ink residues, other impurities, fibre residues and flotation rejects |
| Paper machine and stock circuit | Fibres, fillers, auxiliaries | fines, kaolin, calcium carbonate, talc, sizing agents, resins, polymers and recirculated water with COD load |
In addition to fibres, fillers and auxiliaries also shape the wastewater profile. Kaolin, calcium carbonate, talc, sizing agents, resins and mixed polymers significantly influence subsequent wastewater treatment. These substances largely determine the requirements for industrial wastewater treatment.
Composition of wastewater in the paper industry
In their typical form, paper mill wastewaters are considered to be low in concentration, non-toxic and readily biodegradable. Nevertheless, wastewater treatment in the paper industry remains a key challenge due to the organic load.
The organic load originates mainly from carbohydrates and lignin. The average BOD5/COD ratio for mechanically pre-treated paper mill wastewater is around 0.5. Sulfate typically reaches up to 600 mg/l. For recovered paper, values above 1,000 mg/l also occur.
Typical COD and BOD values in paper industry wastewater
| Category | Product range | BOD5 (mg/l) | COD (mg/l) | Specific wastewater volume (l/kg) |
|---|---|---|---|---|
| Woodfree | Tissue | 50 – 100 | 95 – 270 | 9 – 25 |
| wf’ specialty | 40 – 550 | 90 – 1,100 | 15 – 60 | |
| Wood-containing | SC | 125 – 480 | 450 – 1,020 | 13 – 20 |
| wc’ printing | 220 – 500 | 500 – 1,160 | 8 – 30 | |
| Recovered paper | Newspaper | 460 – 1,270 | 960 – 2,400 | 7 – 20 |
| Corrugating medium | 1,280 – 2,840 | 2,190 – 5,680 | 0 – 10 | |
| Board (RP) | 530 – 3,000 | 1,140 – 5,500 | 0 – 15 | |
| Recycled paper | 250 – 400 | 540 – 790 | 10 – 20 |
The values refer to mechanically pre-treated wastewater. The range clearly shows how strongly the requirements for wastewater treatment vary depending on the paper grade. The overall range therefore extends from 10 to 3,000 mg/l BOD5 and from 20 to 5,680 mg/l COD.
Why is wastewater treatment beneficial for a company?
Wastewater treatment in the paper industry is a key prerequisite for complying with statutory discharge limit values.
At the same time, wastewater treatment reduces costs and production risks through:
- lower wastewater volumes through recirculation
- recovery of fibres as a raw material
- avoidance of operational issues such as deposits
In addition, optimised industrial wastewater treatment improves resource efficiency and sustainably reduces operating costs.
Tighter water circuit closure reduces fresh water demand and wastewater volume. However, overly closed circuits promote salinisation, limescale deposits and odours. These effects show that targeted wastewater treatment in the paper mill is indispensable.
Processes for wastewater treatment in the paper industry
Wastewater treatment in the paper industry is carried out in several coordinated process stages. Each stage addresses specific loads and prepares the water specifically for the next step.
Mechanical pre-treatment
The wastewater contains large quantities of fibres and mineral fillers. These substances lead to deposits and significantly burden downstream biological processes.
To separate coarse solids, the ClearFox® screen screw can be used. It compacts the discharge within the unit and significantly reduces the solids volume.
Physico-chemical treatment
Fine particles, deinking residues and colloidal substances remain in the water after sedimentation. These substances continue to increase the COD value and impair water quality.
Flotation is often used to remove these substances. The ClearFox DAF System operates with dissolved air flotation, in which air bubbles transport the particles to the surface. There, the contaminated sludge phase is separated in a targeted manner.
Aerobic biological processes
The remaining load consists predominantly of dissolved organic substances such as carbohydrates and lignin. These increase oxygen demand and must be biologically degraded.
Biological processes using microorganisms are employed for this step. One possible system is the ClearFox® FBBR. Microorganisms colonise carrier media and specifically break down the organic load. This significantly reduces the COD value.
Water reuse in operations
Biologically fully treated water often still contains calcium carbonate, salts, colour or residual COD, which promotes deposits in the production process.
For water reuse in the paper industry, additional processes such as reverse osmosis, ultrafiltration or ozonation are therefore often required. These improve water quality for closed-loop circuits.
Which wastewater treatment is suitable for which paper production?
In practice, requirements for wastewater treatment vary depending on the paper grade.
- Woodfree papers: lower organic load; predominantly biological treatment is sufficient
- Wood-containing papers: medium load due to lignin; a combination of pre-treatment and biological treatment is required
- Recovered-paper-based papers: high COD values and foreign matter; a combination of flotation, sedimentation and biological treatment is necessary
Use of residual materials from wastewater treatment
Wastewater treatment generates various by-products:
- Fibre sludge: can be returned to the production process
- Excess sludge: dewatering using belt filter presses
- Lime-containing sludge: targeted separation to prevent deposits
These by-products play an important role in resource efficiency in the paper industry.
To reduce the high water content of the sludge, the ClearFox® thickener is used for sludge thickening. Depending on the sludge composition, it increases the dry solids content from 0.5–3% to 5–15%.
For final dewatering, the ClearFox® sludge screw press is used for sludge treatment. It significantly reduces volume and lowers disposal costs.
Planning and purchasing a wastewater treatment plant for paper and pulp mills
Planning a wastewater treatment plant for the paper industry requires a precise analysis of the wastewater parameters. Key factors are target quality, inflow, COD load and load fluctuations.
A typical plant configuration includes:
- Mechanical pre-treatment
- Sedimentation and primary clarification
- Chemically assisted flotation
- If required, neutralisation and cooling
- Biological treatment
- Secondary clarification
- If required, tertiary treatment (e.g. filtration, ozonation)
Selecting the right wastewater technology for paper mills depends heavily on the product range. Recovered-paper-based processes generate higher loads and require more intensive treatment.
Conclusion
Wastewater treatment in the paper industry requires a coordinated combination of modern processes. Mechanical, physico-chemical and aerobic biological stages ensure compliance with statutory limit values.
The use of specialised solutions such as ClearFox systems for industrial wastewater treatment enables efficient treatment and cost-effective water reuse.
Your benefits at a glance
With our integrated solutions and process guarantees, ClearFox® is one of the market leaders in Europe. With our modular, container-based systems, we can flexibly adapt your wastewater treatment to your specific requirements. This creates a customised and cost-effective solution for every application.
Our focus is on:
✔ Compact design – saves valuable space
✔ Automated operation with optional remote monitoring
✔ Low operating costs through energy-efficient process technologies
✔ Seamless on-site integration into existing systems
✔ Simple solutions for complex treatment challenges
✔ Budget-conscious design without compromising on quality
✔ Customer-focused approach for support and satisfaction
Reliable technology with clear results
Our fixed-bed process (FBR) has been independently tested and certified by PIA GmbH.
✔ Lowest operating costs on the market
✔ Modular & scalable systems
✔ Leasing options available for short-term or pilot projects
We understand wastewater from the sugar industry
Every processing plant generates a unique wastewater profile. That is why it is crucial to work with a partner who understands the specific processes and challenges of wastewater treatment in the sugar industry.
We have worked with various European plants to implement efficient, cost-effective and compliant treatment systems that are precisely tailored to the respective operating conditions.
Global support, local expertise
ClearFox®’s internationally positioned service team provides continuous support throughout the entire project duration to ensure smooth, reliable operation. This applies both during planning and after commissioning.
Project kick-off
Have we sparked your interest? We would be pleased to offer you a non-binding site analysis including a preliminary design. Loads, boundary conditions and process objectives are assessed in order to find a suitable solution for you and develop an initial cost estimate.
Reference projects
FAQs
Which wastewater treatment is suitable for which paper production?
- Woodfree → lower load → simple biological treatment
- Wood-containing → medium load → pre-treatment required
- Recovered paper → high load → combination of flotation + biological treatment
What is wastewater treatment in the paper industry?
Wastewater treatment in the paper industry includes mechanical, physico-chemical and biological processes for treating process water. The aim is to comply with limit values and reuse water.
How is COD reduced in paper industry wastewater?
COD is mainly reduced through biological processes. Microorganisms break down organic substances such as carbohydrates and lignin, thereby reducing the load in the wastewater.
When is flotation used in wastewater treatment?
Flotation is used when fine particles, fats or colloidal substances remain in the wastewater. The ClearFox DAF System uses dissolved air to transport these substances to the surface and separate them. This process is particularly suitable for heavily polluted industrial wastewaters.
Is water reuse possible in the paper industry?
Water reuse is generally possible, but requires further treatment. In addition to biological treatment, processes such as filtration or membrane technology are used to remove dissolved substances and salts. This allows the treated water to be returned to the production cycle.
What advantages do ClearFox systems offer compared to conventional wastewater treatment plant solutions?
ClearFox systems are compact and can be combined modularly. This makes them particularly suitable for industrial applications with limited space or fluctuating wastewater loads. They also enable targeted adaptation of individual process stages to the respective wastewater.
How is sewage sludge treated with ClearFox systems?
The resulting sewage sludge is treated in several steps. The ClearFox® thickener first reduces the water content and increases the dry solids content. The ClearFox® sludge screw press then performs dewatering and significantly reduces sludge volume, lowering transport and disposal costs.
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