ZLD with High pH RO
Solutions for Industrial Field
Overview
Water scarcity and pollution are persistent global issues. The most prudent solution is to recycle and reuse wastewater. Therefore, environmental authorities all over the world introduce ZLD (*1) systems to industrial processes.
We, Toshiba, have a state of the art ZLD system based on High pH RO technology, which offers more efficient and superior treatment at lower life cycle cost than conventional systems.
- *1 ZLD: Zero Liquid Discharge
ZLD
The ZLD system can be introduced in cases where water resources are limited and environmental sustainability is prioritized.
The recycling system with RO (*2) membrane generates reject water containing highly concentrated wastewater with TDS (*3). In most cases, reject water cannot be discharged, thus an evaporator is installed after RO, to evaporate reject water and concentrate salts to dryness. Also due to the high cost of evaporators, it is a prerequisite to integrate a high efficiency RO system in the ZLD process so as to minimize the RO reject volume and optimize the size of the evaporator to be installed. This can be achieved by increasing the recovery across the RO system in the ZLD system based on High pH RO technology.
- (*2) RO: Reverse Osmosis
- (*3) TDS: Total Dissolved Solids
Four problems in ZLD system with conventional RO
There are scaling and fouling problems in the ZLD system with conventional RO, causing an increase in feed pressure, a decrease in permeate flow, lower permeate quality, frequent RO cleaning, longer downtime, and eventually frequent replacement of RO membranes.
| 1. Hardness scaling | Settlement of saturated calcium or magnesium salts, heavy metal sulfates, phosphates or carbonates on the membrane surface |
|---|---|
| 2. Silica scaling | Settlement of reactive silica exceeding the solubility limit on the RO membrane surface while conventional RO is operated at neutral or slightly acidic pH |
| 3. Organic fouling | Result of the deposition of organic matter on the membrane surface, usually on the feed/concentrate side |
| 4. Biofouling | Growth of microbes on the RO membrane surface, causing permanent irreversible damage |
For a conventional RO system, pH of feed water is lowered and antiscalant is dosed to prevent hardness scaling. But it does not work for higher recovery rates. In addition, lower pH decreases silica solubility, resulting in silica scaling. Some of the COD(*4) remain in industrial wastewater even after biological treatment. In many cases, the conventional RO fails to operate in a sustainable manner at 80%+ recovery due to silica and residual COD in the feed water.
- (*4) COD: Chemical Oxygen Demand
Solution for ZLD: High pH RO
High pH RO is a technology to eliminate all scaling and fouling factors (hardness, alkalinity, silica precipitation, organic fouling and bio-fouling) by ion exchange, degassing and RO system operation at high pH by maximizing recovery through the RO system.
In the High pH RO system, scaling and fouling are eliminated; therefore, the system can increase the RO water recovery rate to the maximum extent possible.
＜Process description＞
| Equipment composition |
 |
||
|---|---|---|---|
| Lime/caustic clarifier and/or ion exchange system | Degassing tower or membrane | High pH RO operation | |
| Purpose | Hardness removal (Softening) | Alkalinity removal | Prevention of RO filter fouling Increase in water recovery rate |
| To remove Ca, Mg and other heavy metals, which can potentially cause scaling in RO | To remove carbonic acid, which can cause carbonate scaling in RO | To improve silica solubility, prevent the adsorption of organic matter by RO, inactivate bacteria, and enhance the zeta potential between membrane and particles | |
| Solution for 1. Hardness scaling |
Solution for 1. Hardness scaling |
Solutions for 2. Silica scaling 3. Organic fouling 4. Biofouling |
|
Comparison between ZLD with conventional RO and ZLD with High pH RO
By virtue of high efficiency, low generation of reject and downsizing of the evaporator, the High pH RO system can reduce operation costs, compared to conventional RO systems.
| ZLD with conventional RO | ZLD with High pH RO | |
|---|---|---|
| Recovery rate | Low
|
High
|
| Initial cost | Moderate
|
Moderate
|
| Running cost | High
|
Much lower
|
| Daily inspection | Good |
Moderate Compared to conventional RO,
|
| Periodical maintenance | Moderate
|
Good
|
- (*5) CIP: Clean in Place
Highlights of High pH RO
More than 95 % water recovery rate
The recovery rate of conventional RO systems is limited to 70% to 80% depending on inlet water quality.
We offer the High pH RO system for ZLD, which can operate at a recovery rate of more than 95% in most cases.
Compared to conventional RO systems, the High pH RO system can reduce the volume of reject water to 1/4 and provide significant operational savings.
Extension of reverse osmosis membrane life
Scaling and fouling factors are eliminated, leading to an extension of the RO membrane life, a reduction of the system shutdown time, and eventually a significant reduction in the life cycle cost of the system.
- All products, services and company names mentioned herein may be trademarks or registered trademarks of their respective companies.
- The information contained herein is presented only as a guide for the applications of our products. No responsibility is assumed by Toshiba for any infringements of patents or other rights of the third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Toshiba or others.
- Our products should not be embedded into other products of which production or sale is prohibited by law.
- Toshiba does not take any responsibility for incidental damage (including loss of business profit, business interruption, loss of business information, and other pecuniary damage) arising out of the use or disability to use Toshiba products.
- All information including specifications herein are subject to change without notice.
- The products described in this document include products subject to foreign exchange and foreign trade laws.
- The products described in this document contain components made in the United States and subject to export control of the U.S. authorities. Diversion contrary to U.S. law is prohibited.
Reference Project (High pH RO)
Automotive Factory
| Location | India |
|---|---|
| Launch | 2017 |
| Capacity | 350 m3/day |
| Project Description | Wastewater treatment plant for automotive industry was built. ZLD was adopted in order to meet strict wastewater treatment requirements in India. |
| Scope | Design, engineering, supply, erection, installation, testing and commissioning |
| Solutions | We constructed ETP - ZLD system. The system consists of pre-treatment, anoxic - aerobic - MBR(*6) based treatment, High pH RO thermal based evaporator to provide treated water suitable for reuse in the production plant. The High pH RO evaporator is less than 1/4 of the conventional RO system in size. Accordingly, steam consumption can be saved by 75% and water recovery can reach 95%. |
- (*6) MBR: Membrane Bioreactor
Treatment Process
Leaflet of ZLD with High pH RO
Please download the leaflet of ZLD with High pH RO.
Contents
- Overview
- ZLD
- Highlights of High pH RO
- Reference Project (High pH RO)
ZLD with High pH RO (PDF)(555KB)
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