Pulp Mill Effluent Electrodialysis for Water Reuse and Chemical Recovery
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Solution Overview
Problem
Current effluent treatment systems in pulp and paper mills are limited by high organic matter and salt content, leading to scaling, corrosion, and inefficient water recirculation, which fails to meet environmental discharge standards and increases chemical consumption.
Innovation Solution
A multi-step process combining pulsed electrodialysis reversal (pEDR) with secondary treatments like electrocoagulation and post-treatment systems such as crystallization or spray drying to separate and recover inorganic salts and chemicals, achieving 'zero liquid discharge'.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If effluent is recirculated in the pulp and paper mill, then water recovery is improved, but organic matter modifies product characteristics and increases bleaching chemical consumption
Solution Approach 1:
The patent extracts and removes organic matter from the effluent through advanced treatment systems including activated sludge digestion, anaerobic treatment, and chemical oxidation processes. This extraction allows the water to be recirculated without the harmful effects of organic matter modification and increased chemical consumption
Solution Approach 2:
The patent changes the physical and chemical parameters of the effluent through multiple treatment stages including pH adjustment, oxidation-reduction potential modification, and temperature control. These parameter changes enable the effluent to meet product quality requirements for recirculation while maintaining water recovery benefits
2Quantity of substance
If effluent is recirculated in the pulp and paper mill, then water recovery is improved, but salts accumulate as non-processable elements causing scaling and corrosion
Solution Approach 1:
The patent extracts and removes salts from the effluent through electrodialysis processes and crystallization units. These systems separate salts from the water stream, allowing purified water to be recirculated while concentrating and removing salts through evaporation and crystallization, preventing scaling and corrosion
Solution Approach 2:
The patent utilizes phase transitions including evaporation and crystallization to remove salts from the effluent. By evaporating water and allowing salts to crystallize, the system separates and removes non-processable elements, enabling water recirculation without salt accumulation problems
3Object-generated harmful factors
If conventional effluent treatment is used, then organic matter removal is achieved, but water cannot be fully recovered and discharged effluent remains
Solution Approach 1:
The patent applies preliminary treatment actions including mechanical screening, sedimentation, and preliminary biological treatment to prepare the effluent for advanced treatment. These preliminary actions remove bulk organic matter and prepare the stream for subsequent advanced treatment processes that enable full water recovery
Solution Approach 2:
The patent utilizes evaporation and crystallization phase transitions to recover water from the effluent. By evaporating the effluent and condensing the vapor, the system recovers pure water while leaving salts and non-processable elements behind as solids, achieving full water recovery
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Achieves high water recovery (up to 90%) and chemical reuse, preventing effluent discharge and reducing water consumption, while meeting environmental standards.
Implementation Method 1
a first dialysis system (4), which is selected from a pulsed electrodialysis reversal or a electrodialysis reversal for separation of a concentrate (7) and recovery of the water as a dialyzed effluent (13)
Implementation Method 2
pass the re-concentrated rejection stream (10) obtained in step (d), through a drying system (11), obtaining a condensate (14) and a solid by-product (12)
Data Source
AI summary
Described herein is a process for upgrading effluent treatment plants for pulp and paper production processes, where salts are removed from the effluent for water reuse and chemical recovery. The process comprises a first dialysis system for salt removal, a second treatment system for recovery or re-concentration, and optionally a post-treatment of the re-concentrate preventing liquid discharges to the environment. In the first system, a reversible electrodialysis or reversible pulsed step is carried out, separating the salts from the effluent, which are sent to the second treatment system to concentrate the salts (re-concentrate) or transform them into useful chemicals for the same process (recovery). Chemical recovery is achieved by electrodialysis with bipolar membranes or metathesis, to reduce the re-concentrate stream, which cannot be reused in the same plant. Lastly, this stream may be treated by spray drying, crystallization or evaporation.