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Pulp and Paper Industry Wastewater Treatment: How We Restored Performance After COD and Foam Problems
Updated: 3 days ago
Overview
Pulp and paper industry wastewater treatment can be difficult when COD remains high and foam keeps returning. Paper mill wastewater may contain cellulose, lignin, fibres, colour-causing materials, sizing agents and surfactants. Some of these materials can be hard for microorganisms to break down. This article explains how we checked the causes of repeated COD and foam problems, reviewed the biological tank and supported microbial activity. It also covers common treatment problems, ways to reduce COD, and the checks that paper mill operators can make before changing their treatment process.
Table of Contents
Why Is Pulp and Paper Wastewater Difficult to Treat?
Pulp and paper wastewater can contain several types of organic and inorganic material. Cellulose fibres, lignin, suspended solids, sizing agents and surfactants may all enter the treatment plant.
The amount and type of these materials can change with production. Pulping, bleaching, washing, recycling and paper-making can all affect the wastewater reaching the ETP.
This makes pulp and paper wastewater treatment different from treating wastewater with a more consistent composition.
High COD paper mill wastewater can also place a heavy load on the biological tank. Sudden changes in pH, temperature, chemicals or organic load can affect the microorganisms that break down organic matter.
These are some of the common challenges in pulp and paper industry wastewater treatment.
What We Checked First
We did not begin by changing the treatment programme. We first checked the plant readings.
The checks included:
COD and BOD
pH
Temperature
Dissolved oxygen
MLSS
Sludge settling
Foam
Incoming wastewater load
Changes in paper production
These readings gave us a clearer picture of what was happening inside the plant.
Sludge settling is another important indicator, and our guide to sludge bulking and MLSS control explains how poor settling can affect biological treatment performance.
Paper industry wastewater management is closely linked with mill operations. A change in production can change the wastewater entering the treatment plant. So the ETP team needs to know what happened upstream before making changes downstream.
This is also a useful starting point when asking, how is wastewater treated in the pulp and paper industry?
Why Was Foam Appearing?
Foam can have several causes.
Surfactants and other process chemicals can contribute to foam. Certain types of microbial growth can also produce or increase foam in an aeration tank.
We did not treat foam as an isolated problem. We checked it along with COD, dissolved oxygen, sludge condition and other plant readings.
This matters because foam can sometimes point towards a change in the biological tank. For a broader troubleshooting guide, see how sludge bulking and foaming in STP and ETP systems can be linked to microbial imbalance and operating conditions.
For a pulp and paper ETP, regular observation can help operators spot changes before they become larger treatment problems.
Supporting the Biological Treatment Stage
Biological treatment depends on microorganisms that consume biodegradable organic matter in wastewater.
Understanding how aerobic bioculture works in wastewater treatment can help operators assess how microbial activity supports organic matter and COD removal.
For an activated sludge paper industry plant, microorganisms need suitable conditions to remain active. Dissolved oxygen, pH, temperature, food supply and sludge levels all matter.
Biological treatment methods for pulp and paper wastewater can include activated sludge, extended aeration, SBR, MBBR and MBR. The choice depends on wastewater quality, plant design and discharge requirements.
The same principle applies to biological treatment for paper industry plants using different biological reactors. If microorganisms face sudden chemical shocks or large changes in organic load, COD removal may fall.
What Role Do Cellulose and Lignin Play?
Cellulose mainly comes from paper fibres and plant material. Lignin comes from wood and is associated with the pulping process.
Both can add organic matter to wastewater.
Cellulose wastewater treatment depends on microorganisms being able to break down the available organic material. Lignin can be harder to break down because of its complex structure.
This is why biological treatment of pulp mill effluent needs suitable microbial activity and stable operating conditions.
Lignin degradation wastewater treatment may require particular microbial populations that can act on these compounds.
We used BactaServe Pulp & Paper as microbial support for the biological stage. The manufacturer states that it contains selected microorganisms intended to act on lignin, cellulose, sizing agents, surfactants and fibrous solids found in paper mill wastewater.
The manufacturer also states that the amount used should be based on wastewater volume and organic load rather than one fixed amount for every plant.
How to Reduce COD in Paper Mill Wastewater
If you are asking how to reduce COD in paper mill wastewater, start by finding where the COD is coming from.
First, check the incoming wastewater. Then check the equalisation tank, primary treatment and biological stage.
If the COD is largely biodegradable, biological treatment can remove a significant part of the organic load when the microorganisms have suitable conditions.
For a closer look at the treatment stages used to address high organic loads, see our guide to the pulp and paper wastewater treatment process.
If the wastewater contains compounds that are difficult for microorganisms to break down, the plant may need other treatment steps or better control of the source.
Good paper mill effluent treatment starts with knowing the wastewater entering the plant.
The same approach applies to pulp and paper wastewater treatment. Operators should check pH, temperature, oxygen, sludge levels and incoming loads before making major changes.
What Changed After We Reviewed the Plant?
We stopped looking at COD and foam as two separate problems.
Instead, we looked at the biological stage as a whole. We checked the wastewater entering the tank, the condition of the sludge and the readings that showed whether the microorganisms were working under suitable conditions.
This gave us a better way to understand the repeated problems.
For paper industry wastewater management, this type of regular checking can help operators find changes in wastewater quality before they cause longer treatment problems.
It also shows why biological treatment for paper industry plants needs regular testing rather than occasional checks.
Regular monitoring can also help identify micronutrient deficiency in wastewater treatment, which may weaken microbial activity even when the main operating parameters appear acceptable.
A Simple Checklist for Paper Mill Operators
Before changing the treatment programme, check:
COD and BOD at important points in the plant.
pH and temperature.
Dissolved oxygen in the aeration tank.
MLSS and sludge settling.
The type and amount of foam.
TSS entering the biological stage.
Recent changes in production.
Changes in process chemicals.
Sudden organic loads.
Return sludge and sludge wasting.
These checks can help answer why is pulp and paper wastewater difficult to treat?
If poor sludge settling or filamentous growth is also affecting the plant, BactaServe MLSS Debulking can provide targeted microbial support for sludge bulking control.
They can also show whether the problem is coming from the incoming wastewater or from conditions inside the biological tank.
Common Problems in Pulp and Paper ETPs
The common challenges in pulp and paper industry wastewater treatment include high COD, changing organic loads, fibres, colour, surfactants, foam, poor sludge settling and sudden chemical loads.
A paper mill effluent treatment plant has to deal with these changes while keeping the biological stage in suitable condition.
This is why biological treatment methods for pulp and paper wastewater should be selected according to the actual wastewater and plant design.
For how to reduce COD in paper mill wastewater, the first step is to identify the COD source. The next step is to check the biological stage and its operating conditions.
For biological treatment of pulp mill effluent, microbial activity, oxygen, pH, temperature and sludge condition all need attention.
Conclusion
Repeated COD and foam problems do not always mean that the whole ETP needs to be replaced.
Start with the basics. Check the wastewater. Check the plant readings. Check the biological tank. Look for changes in production and chemicals.
Pulp and paper industry wastewater treatment works best when the treatment process matches the wastewater entering the plant.
A careful review can also help operators decide whether they need changes to operation, biological support or another treatment stage.
For other complex industrial effluents, industrial wastewater treatment biocultures are available for different wastewater characteristics and biological treatment requirements.
Good paper industry wastewater management begins with understanding what the mill is sending to the ETP and how the treatment plant responds to it.
For mills dealing with high COD paper mill wastewater, regular testing can make it easier to spot problems early and decide what needs attention.
Frequently Asked Questions
Why is pulp and paper wastewater difficult to treat?
Pulp and paper wastewater can contain cellulose, lignin, fibres, surfactants, colour and suspended solids. Some of these materials can be difficult for microorganisms to break down.
What are the common challenges in pulp and paper industry wastewater treatment?
Common problems include high COD, changing organic loads, fibres, colour, surfactants, foam, poor sludge settling and sudden changes in wastewater quality.
What biological treatment methods for pulp and paper wastewater are commonly used?
Common methods include activated sludge, extended aeration, SBR, MBBR and MBR. The right method depends on the wastewater, plant design and discharge requirements.
How to reduce COD in paper mill wastewater?
Start by finding the source of the COD. Then check pH, temperature, dissolved oxygen, MLSS, sludge settling and incoming wastewater loads. If the COD is biodegradable, a properly operated biological stage can remove much of the organic load.
How is wastewater treated in the pulp and paper industry?
Treatment may include screening, equalisation, primary solids removal, biological treatment, clarification and final treatment. The exact process depends on the wastewater quality and the discharge requirements.
