Treatment of Flue Gas Desulfurization Wastewater by an Integrated Membrane-Based Process for Approaching Zero Liquid Discharge.

Carmela Conidi,Pietro Argurio,Alfredo Cassano,Francesca Macedonio,Aamer Ali,Alessandra Criscuoli,Enrico Drioli

doi:10.3390/membranes8040117

Carmela Conidi, Pietro Argurio + Show 5 more

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https://doi.org/10.3390/membranes8040117

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Abstract

An integrated membrane process for the treatment of wastewaters from a flue gas desulfurization (FGD) plant was implemented on a laboratory scale to reduce their salt content and to produce a water stream to be recycled in the power industry. The process is based on a preliminary pretreatment of FGD wastewaters, which includes chemical softening and ultrafiltration (UF) to remove Ca2+ and Mg2+ ions as well as organic compounds. The pretreated wastewaters were submitted to a reverse osmosis (RO) step to separate salts from water. The RO retentate was finally submitted to a membrane distillation (MD) step to extract more water, thus increasing the total water recovery factor while producing a high-purity permeate stream. The performance of RO and MD membranes was evaluated by calculating salts rejection, permeate flux, fouling index, and water recovery. The investigated integrated system allowed a total recovery factor of about 94% to be reached, with a consequent reduction of the volume of FGD wastewater to be disposed, and an MD permeate stream with an electrical conductivity of 80 μS/cm, able to be reused in the power plant, with a saving in fresh water demand.

Highlights

Much research is today focusing on minimizing the scarcity of potable water and the impact of air, water, and solid waste pollutants
Afterwards, the flue gas desulfurization (FGD) wastewaters were treated with an antiscalant (Carboxyline CM supplied by Aquastill B.V., Sittard, The Netherlands) at the recommended concentration (8 mg/L) in order to prevent the precipitation of low soluble salts
Raw waters were characterized by a lower content of Ca2+ and Mg2+ when compared to typical FGD wastewaters sampled by United States Environmental Protection Agency (USEPA)

Summary

Introduction

Much research is today focusing on minimizing the scarcity of potable water and the impact of air, water, and solid waste pollutants. To improve the control of SO2 emissions, various flue gas desulfurization (FGD) technologies have been developed in the last decades. Flue gas desulfurization processes are primarily used to remove SO2 from exhaust flue gases of fossil fuel thermoelectric power plants. In these plants, SO2 is produced during the combustion of coal and oil, and can be further converted (about 1%) into sulfur trioxide (SO3 ) if high contents of oxygen are present [1]. Depending on the coal source, used technology, and operating conditions, FGD processes can give origin to various streams, with a different and complex composition. Sulfate, nitrate, calcium, magnesium as well as various heavy metals and dissolved silica and borate are Membranes 2018, 8, 117; doi:10.3390/membranes8040117 www.mdpi.com/journal/membranes

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