Development of a Membrane Desalination and Coprecipitation System for Enhanced Reclamation of Cooling Tower Water: Mechanism Evaluation and Pilot-Scale StudySource: Journal of Environmental Engineering:;2025:;Volume ( 151 ):;issue: 006::page 04025028-1Author:Jin-Min Li
,
Bo-Ming Yang
,
Chathura Dhanasinghe
,
Rao Y. Surampalli
,
Tian C. Zhang
,
Chih-Ming Kao
DOI: 10.1061/JOEEDU.EEENG-8006Publisher: American Society of Civil Engineers
Abstract: The raw water in southern Taiwan has high hardness and high silica (SiO2) characteristics. If the high SiO2-content water is used as a makeup water source for cooling towers (CT), the SiO2 concentration in the tower blowdown (BD) would exceed the saturation level (120 mg/L) within a short operational period. The objective of this study was to develop a combined coprecipitation (first stage) and membrane desalination [ultrafiltration (UF)/reverse osmosis (RO) (second stage)] system to enhance the water reclamation efficiency of cooling tower (CT) in the petrochemical industry. Flue gas desulfurization (FGD) wastewater containing magnesium ions (Mg2+) and cooling tower blowdown (CTBD) were mixed, and Mg2+ and silica (SiO2) were removed through the coprecipitation process (core mechanism). The supernatant was directed to the UF/RO for reclamation. Results show that alkaline environments promoted the creation of Mg2+─SiO2 coprecipitates [Mg3Si2O5(OH)4, Mg2SiO4 and MgSiO3], which allowed for the effective removal of SiO2. Under alkaline conditions, when the molar ratio of Mg2+/calcium ions (Ca2+)∶SiO2 was 1∶1, Mg2+ exhibited more pronounced advantages for SiO2 removal. The maximum SiO2 removal rate reached 99% in the Mg2+∶SiO2 group, compared to 75% in the Ca2+∶SiO2 group. Mg2+ showed a stronger correlation (R2=0.95) with SiO2 removal than Ca2+ (R2=0.61355). Following the coprecipitation process, the supernatant was transferred to the UF/RO for desalination. The pilot-scale study results indicate that up to 92% of SiO2 in CTBD could be removed. When the volume ratio of FGD wastewater to CTBD was 1∶5 (pH=10.5), the SiO2 concentration was reduced to below 25 mg/L. The UF/RO treatment results show that the conductivity, alkalinity, and Mg2+ concentrations were reduced to 179 μS/cm, 15 mg as CaCO3/L, and not detectable, respectively. The regenerated water is suitable for reuse as makeup water for CT.
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contributor author | Jin-Min Li | |
contributor author | Bo-Ming Yang | |
contributor author | Chathura Dhanasinghe | |
contributor author | Rao Y. Surampalli | |
contributor author | Tian C. Zhang | |
contributor author | Chih-Ming Kao | |
date accessioned | 2025-08-17T23:01:40Z | |
date available | 2025-08-17T23:01:40Z | |
date copyright | 6/1/2025 12:00:00 AM | |
date issued | 2025 | |
identifier other | JOEEDU.EEENG-8006.pdf | |
identifier uri | http://yetl.yabesh.ir/yetl1/handle/yetl/4307798 | |
description abstract | The raw water in southern Taiwan has high hardness and high silica (SiO2) characteristics. If the high SiO2-content water is used as a makeup water source for cooling towers (CT), the SiO2 concentration in the tower blowdown (BD) would exceed the saturation level (120 mg/L) within a short operational period. The objective of this study was to develop a combined coprecipitation (first stage) and membrane desalination [ultrafiltration (UF)/reverse osmosis (RO) (second stage)] system to enhance the water reclamation efficiency of cooling tower (CT) in the petrochemical industry. Flue gas desulfurization (FGD) wastewater containing magnesium ions (Mg2+) and cooling tower blowdown (CTBD) were mixed, and Mg2+ and silica (SiO2) were removed through the coprecipitation process (core mechanism). The supernatant was directed to the UF/RO for reclamation. Results show that alkaline environments promoted the creation of Mg2+─SiO2 coprecipitates [Mg3Si2O5(OH)4, Mg2SiO4 and MgSiO3], which allowed for the effective removal of SiO2. Under alkaline conditions, when the molar ratio of Mg2+/calcium ions (Ca2+)∶SiO2 was 1∶1, Mg2+ exhibited more pronounced advantages for SiO2 removal. The maximum SiO2 removal rate reached 99% in the Mg2+∶SiO2 group, compared to 75% in the Ca2+∶SiO2 group. Mg2+ showed a stronger correlation (R2=0.95) with SiO2 removal than Ca2+ (R2=0.61355). Following the coprecipitation process, the supernatant was transferred to the UF/RO for desalination. The pilot-scale study results indicate that up to 92% of SiO2 in CTBD could be removed. When the volume ratio of FGD wastewater to CTBD was 1∶5 (pH=10.5), the SiO2 concentration was reduced to below 25 mg/L. The UF/RO treatment results show that the conductivity, alkalinity, and Mg2+ concentrations were reduced to 179 μS/cm, 15 mg as CaCO3/L, and not detectable, respectively. The regenerated water is suitable for reuse as makeup water for CT. | |
publisher | American Society of Civil Engineers | |
title | Development of a Membrane Desalination and Coprecipitation System for Enhanced Reclamation of Cooling Tower Water: Mechanism Evaluation and Pilot-Scale Study | |
type | Journal Article | |
journal volume | 151 | |
journal issue | 6 | |
journal title | Journal of Environmental Engineering | |
identifier doi | 10.1061/JOEEDU.EEENG-8006 | |
journal fristpage | 04025028-1 | |
journal lastpage | 04025028-12 | |
page | 12 | |
tree | Journal of Environmental Engineering:;2025:;Volume ( 151 ):;issue: 006 | |
contenttype | Fulltext |