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Abstract
Reverse osmosis (RO) membranes are now core to modern desalination processes and
are widely used around the world. Based on the increasing number of desalination
plants, and the finite lifespan of the membranes, the resulting number of used RO
modules to be discarded is becoming a critical challenge. The overall aim of this study
is to identify, develop and assess alternative end-of-life options for used RO elements
and investigate the associated technical readiness, environmental impact, financial
considerations and legislative challenges. The assessed end-of-life alternatives include,
direct reuse of the old membranes within lower throughput systems; chemical conversion
into porous, ultrafiltration (UF) like filters; direct reuse or recycling of the various module
components; various energy recovery techniques, and landfill disposal. The results show
that direct reuse is a promising application that can be utilised with minimal additional
treatment or infrastructure; however, module storage techniques are a critical
consideration, particularly as membrane drying has a significant and irreversible impact
on membrane performance due to pore collapse in the polysulfone support layer. The
method for chemical conversion with controlled exposure to NaOCl has been optimised,
resulting in promising organic and virus removal properties, comparable to commercially
available 10 – 30 kDa molecular weight cut off UF membranes; however, there was
significant variation in hydraulic performance, ranging from 8 – 400 L.m-2.h-1.bar-1. A
detailed life cycle assessment was completed and demonstrated that module fabrication
contributed less than 1% of the CO2-e emissions for the production of potable water from
seawater desalination, and that direct reuse over one year is more environmentally
favourable than landfill disposal, regardless of the transportation distance required.
However, in terms of direct reduction of waste to landfill, incineration provided the
greatest benefit, at the expense of increased greenhouse gas emissions. Applying the
knowledge generated within this study, an interactive online educational tool has been
developed using a dynamic multi criteria decision analysis system, providing information
on end-of-life options to membrane users. Overall, this study provides detailed
quantitative information for membrane users and manufacturers to enhance their
decision making process when it comes to end-of-life membrane options.