Reverse Osmosis Concentrate Treatment via Calcium Sulfate Crystallization
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Solution Overview
Problem
Current methods for treating reverse-osmosis concentrated water containing calcium sulfate are inefficient, leading to environmental pollution and high energy consumption, with limited water recycling and increased costs due to the use of foreign materials and energy-intensive crystallization processes.
Innovation Solution
A system comprising a sequence of crystallization units, reverse osmosis units, and a lime softening unit, which includes crystallizers, thickeners, centrifugal dehydrators, multi-media filters, and reverse osmosis membrane devices, allowing for the cascade filtration and recycling of calcium sulfate without additional agents, achieving high purity and reduced water hardness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional crystallization method is used to treat calcium sulfate in reverse osmosis concentrated water, then calcium sulfate can be converted to calcium carbonate, but foreign materials are introduced and downstream treatment burden increases
Solution Approach 1:
The invention extracts and removes calcium sulfate directly from the concentrated water through crystallization, eliminating the need to convert it to calcium carbonate with foreign materials. The calcium sulfate is separated as pure crystals, avoiding introduction of additional substances that would complicate downstream treatment.
Solution Approach 2:
The invention converts the harmful calcium sulfate directly into beneficial pure calcium sulfate crystals that can be回收利用, rather than converting it into calcium carbonate which requires additional treatment. The crystallization process transforms the problematic scale-forming substance into a recoverable resource.
2Reliability
If strongly evaporative crystallization is used to achieve zero emission, then calcium sulfate can be removed, but energy consumption increases significantly
Solution Approach 1:
The invention changes the crystallization parameters by using a lower temperature range (40-80°C) compared to strong evaporation methods, and controls supersaturation degree to achieve efficient calcium sulfate crystallization without requiring high energy input for evaporation.
Solution Approach 2:
The invention replaces the thermal-mechanical evaporation system with a controlled crystallization system that uses supersaturation control and seed crystals to induce precipitation, substituting high-energy thermal processes with lower-energy crystallization kinetics control.
3Reliability
If carbonate is introduced as a softener, then temporary hardness can be removed, but treatment cost increases
Solution Approach 1:
The invention directly extracts and removes calcium sulfate through crystallization, eliminating the need to introduce carbonate as a softener. By targeting calcium sulfate specifically through controlled crystallization, the process avoids the cost of additional chemical softeners while achieving the same hardness removal effect.
4Productivity
If reverse osmosis water production rate is only 75%, then water recycling is limited, but concentrated salt water production is high
Solution Approach 1:
The invention recovers calcium sulfate from the concentrated salt water through crystallization, transforming the waste stream into a recoverable resource. The crystallized calcium sulfate can be disposed of as a solid or potentially reused, while the treated water can be recycled, thereby recovering value from what would otherwise be waste.
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
The system effectively recycles over 90% of calcium sulfate with purity greater than 97%, reducing water hardness to less than 50 mg/L, eliminating the need for additional agents and enhancing water resource recovery, while minimizing energy consumption and treatment costs.
Implementation Method 1
a first reverse osmosis membrane device; an inlet of the first multi-media filter is connected to a water outlet of the first crystallizer, a water outlet of the first thickener and a water outlet of the first centrifugal dehydrator; an outlet of the first multi-media filter is connected to an inlet of the first reverse osmosis membrane device
Implementation Method 2
The first crystallization unit includes a first crystallizer, a first thickener and a first centrifugal dehydrator; an inlet of the first crystallizer is connected to a concentrated brine inlet pipe
Implementation Method 3
an outlet of the first thickener is connected to an inlet of the first centrifugal dehydrator
Data Source
Figure 1~2
AI summary
The invention relates to sewage treatment, and more particularly to a system for treating reverse-osmosis concentrated water with permanent hardness. The system includes a first crystallization unit, a first reverse osmosis unit, a second crystallization unit, a lime softening unit and a second reverse osmosis unit, which are connected in sequence. The system of the invention is able to eliminate the permanent hardness and the temporary hardness of the concentrated brine, and the hardness can be reduced to equal to or less than 50 mg/L.