Efficient Removal of Hardness and Silica from Wastewater Using a Coupled Electrochemical Crystallization-Electrocoagulation-Flocculation Process

Published on: 7/7/2025 | By: YASA ET

Introduction

In recent years, dealing with high hardness and silica content in industrial wastewater has been a major challenge especially for reverse osmosis concentrate (ROC) generated in zero liquid discharge (ZLD) systems. A new scientific study published in Desalination (2024) presents an energy-efficient and scalable solution through a coupled electrochemical crystallization-electrocoagulation-flocculation system.

What Is This Process?

The researchers developed a membrane-free electrochemical crystallization system that:

• Extracts acidic anolyte to spatially separate H⁺ and OH⁻ ions

• Promotes homogeneous crystallization of hardness ions (Ca²⁺, Mg²⁺) and silica

• Enhances sedimentation using electrocoagulation and a common flocculant (PAM)

Key Performance Highlights

Parameter	Removal Rate
Total Hardness	90%
Magnesium Hardness	76%
Silica	82%
Energy Use	2.4 kWh/m³

• Optimal pH separation allows efficient crystallization of CaCO₃ and silicate compounds.

• The presence of silica even helps reduce magnesium interference, forming sepiolite (Mg₄Si₆O₁₅(OH)₂·6H₂O).

• Flocs from Fe or Al electrodes enhance crystal growth and accelerate sedimentation up to 18x faster than natural settling.

Real Results from PREDEST Electrocoagulation

Real-World Application Potential

This hybrid system is especially suited for:

• RO brine (ROC) treatment in power plants, chemical factories, semiconductor, and cooling tower circuits

• Industries targeting low-energy ZLD operation

• Cases with high concentrations of hardness ions + silica in a compact footprint

Scientific Innovation

Key innovations in the process include:

1. Membrane-free crystallization with acid-layer extraction

2. Integrated electrocoagulation and flocculation to improve sedimentation

3. PAM-assisted settling for fast removal of fine crystalline particles

4. Low operating cost: Only ~$0.26/m³ in energy at 0.108 USD/kWh

Read the Full Research

Title: Coupled electrochemical crystallization-electrocoagulation-flocculation process for efficient removal of hardness and silica from reverse osmosis concentrate Authors: Xuesong Wang, et al.Published in: Desalination, 2024 Click here to read the full article

Want to Implement Similar Technology?

At YASA ET, we develop electrochemical solutions for advanced water treatment including:

• Lab-scale crystallization test kits

• Full-scale electrocoagulation pilot units

• BDD-based electro-oxidation cells

👉 Contact us today to learn how we can help optimize your ZLD system with integrated electrochemical processes.