ZLD with High pH RO

Solutions for Industrial Field

ZLD with High pH RO


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


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
ZLD Process

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.

Four problems in ZLD system with conventional RO
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>

Process description
composition of equipment image
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.

Comparison between ZLD with conventional RO and ZLD with High pH RO
  ZLD with conventional RO ZLD with High pH RO
Recovery rate Low
  • Normal water recovery rate: 70 to 80%
  • More than 90% recovery rate (depending on water conditions)
Initial cost Moderate
  • The larger the evaporator size, the higher the initial cost
  • Cost increase due to additional pre-treatment systems (ion exchange, degasser) and high pressure RO system
  • Cost reduction through downsizing of the evaporator and boiler
Running cost High
  • The higher the steam consumption, the higher the running costs
Much lower
  • Significantly lower than normal RO system
  • Short-term recovery of initial investment
Daily inspection Good Moderate
Compared to conventional RO,
  • More equipment in need of checking
  • No special equipment in need of great care
Periodical maintenance Moderate
  • More frequent RO CIP(*5) for scaling and fouling
  • Frequent evaporator cleaning due to rich-hardness RO reject
  • Less frequent RO CIP and longer membrane life through prevention of scaling and fouling in High pH RO
  • Stable evaporator operation with low-hardness reject
  • (*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.

case study of operational cost

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.

treatment water image
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  • 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

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%.
An Automotive Factory photo1
An Automotive Factory photo2
  • (*6) MBR: Membrane Bioreactor

Treatment Process

Treatment Process image

Leaflet of ZLD with High pH RO

Please download the leaflet of ZLD with High pH RO.

Zero Liquid Discharge(ZLD) with High pH RO System Leaflet


  1. Overview
  2. ZLD
  3. Highlights of High pH RO
  4. Reference Project (High pH RO)

ZLD with High pH RO (PDF)(555KB)

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