Temperature Effects of MD on Municipal Wastewater Treatment in an Integrated Forward Osmosis and Membrane Distillation Process

Khaled Almoalimi,Yong-Qiang Liu,Seongbong Heo,Alexander Booth

doi:10.3390/pr10020355

Abstract

An integrated forward osmosis (FO)-membrane distillation (MD) process is promising for the treatment and resource recovery from municipal wastewater. As higher temperature is applied in MD, it could affect the performance of both FO and MD units. This study aimed to investigate the effects of the type of draw solution (DS) and feed solution (FS) such as ammonium solution or municipal wastewater containing ammonium at higher temperatures on membrane treatment performance. It is found that higher FS and DS temperatures resulted in a higher water flux and a higher RSF with either NaCl or glucose as DS due to the increased diffusivity and reduced viscosity of DS. However, the water flux increased by 23–35% at elevated temperatures with glucose as DS, higher than that with NaCl as DS (8–19%), while the reverse solute flux (RSF) increase rate with NaCl as DS was two times higher than that with glucose as DS. In addition, the use of NaCl as DS at higher temperatures such as 50 and FS at 42 °C resulted in increased forward ammonium permeation from the FS to the DS, whereas ammonium was completely rejected with glucose as DS at all operating temperatures. Reducing pH or lowering the temperature of DS could improve ammonium rejection and minimize ammonia escape to the recovered water, but extra cost or reduced MD performance could be led to. Therefore, the results suggest that in an integrated FO-MD process with DS at higher temperatures such as 50 °C, glucose is better than NaCl as DS. Furthermore, a simplified heat balance estimation suggests that internal heat recovery in the FO-MD system is very necessary for treating municipal wastewater treatment. This study sheds light on the selection of DS in an integrated FO-MD process with elevated temperature of both FS and DS for the treatment of wastewater containing ammonium. In addition, this study highlights the necessity of internal heat recovery in the integrated FO-MD system.

Highlights

Introduction published maps and institutional affilThe increasing demand for fresh water with the growth of the world’s population and industrialisation means that around 1.8 billion people would be in water shortage by 2025 [1]
We found that the use of non-ionic draw solution (DS), such as glucose, improved ammonium rejection to almost 100% at 20 ◦ C
The feed solution (FS) temperature was controlled by going through a helical polyvinylchloride (PVC) tube coil immersed into a water bath with a pre-set temperature (Julabo, Stamford, UK) before recirculating, while the DS temperature

Summary

Introduction

The increasing demand for fresh water with the growth of the world’s population and industrialisation means that around 1.8 billion people would be in water shortage by 2025 [1]. To address this issue, alternative water sources such as seawater or treated wastewater are being explored. RO usually demands high energy because it is a pressure-driven membrane filtration process [3]. Forward osmosis (FO) as a osmotic pressure driven process is attractive with the potential to replace conventional energy-intensive processes [4]. FO has been reported to have the high rejection rates of iations

Objectives

Methods

Results

Conclusion