The paper business consumes a lot of process water for bleaching and pulp preparation, among other things. Paper pulp is created by combining fibres like cellulose, wood, or recycled paper with water. When recycled paper is used, an additional step is necessary to remove the ink. These procedures generate a sizable amount of contaminated wastewater and sludge.
Do you know that an average of 17,000 gallons of industrial process water is needed, for every tonne of pulp used in the production of paper. This places the paper and pulp sector at the top of the list for energy, and fresh water consumption in industry.
How is wastewater treated in the paper making industry?
The term "wastewater from papermaking" mostly refers to liquid produced by the pulp and paper sector that is above standard.
Primary, secondary, and tertiary treatment, cooling, precision filtration, acid-base neutralisation, anaerobic treatment, aeration, and discharge are the main steps in the wastewater treatment process.
· Primary treatment process
The effluent is discharged into the primary filter tank, where it passes through three layers of filter mesh with diminishing filtration precision from top to bottom, to remove the majority of the suspended particulates.
The residual suspended solids in the effluent are filtered out in the secondary filter tank. Three sets of strainers are fitted symmetrically on either side of the stirring shaft.
· Cooling
After secondary filtering, the effluent is then routed into the cooling tower, where it is chilled to 50°C.
· Precision filtering
The cooling tower's wastewater is sent to the flocculation tank for sedimentation. Here, the flocculating agent is introduced, and an hour later the sediment is formed. The silt is then removed. It should be noted that the effluent must be filtered before being released into the neutralising pool.
· Neutralisation of Acid-Base
Adding the neutralising agent will bring the effluent's pH value in the neutralisation pool down to 7.
· Anaerobic treatment
An anaerobic tank is used for anaerobic treatment after the effluent has been neutralised.
· Aeration
The effluent is released into the aeration tank in this stage, where it is given oxygen in the form of air by specialised aeration apparatus, such as the blast blower and jet aerator.
· Advanced treatment
The specific components of wastewater that cannot be removed by secondary treatment, such as nitrogen, phosphorus, extra suspended solids, refractory organics, or dissolved solids, are removed in the advanced treatment process using a shallow air flotation machine, or RO Plants.
But, the water cannot be released until it meets a certain standard!
Conclusion
There is a critical need for the treatment process to be optimised given this excessive usage of water and energy. Sediments, effluent solids, absorbable organic halides (AOX), chlorinated organic compounds, chemical oxygen demand (COD), and biological oxygen demand (BOD) pollutants, are all present in the wastewater generated during the production of paper.
On-site main and secondary treatment systems are needed for the treatment of this effluent. When properly constructed, these systems can significantly lower a plant's water use by reusing treated water. The next significant problem to address is post-wastewater treatment sludge, because it is produced in such large quantities. Clarifiers and dissolved air flotation are two treatments for effluent from paper and pulp production. The best way to handle sludge is using a sludge dewatering system, which dries the sludge.
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