الملخص الإنجليزي
Reverse osmosis (RO) membrane technique is considered as the most widely used
desalination technology around the world. Based on the continuing growth in RO
desalination plants, and the finite lifespan of the RO membranes (due to many factors
including irreversible fouling and physical and chemical damage), large stocks of the endof-life (EoL) RO membranes that are no longer suitable to be used in seawater desalination
have been accumulated over the years. It is estimated that more than 840,000 modules of
the EoL SWRO membranes are discharged annually worldwide, mostly in landfills, which
is becoming a critical challenge in RO desalination industry. The overall objective of this
work is to validate the possibility of direct reuse of the end-of-life seawater reverse
osmosis membranes for brackish water treatment in order to limit the environmental
impacts of their direct disposal, as well as reducing costs of purchasing new filtration
membranes. In this study, membrane performance and surface characterization (including;
TGA, FTIR, SEM/EDS and WCA analyses) were assessed using four end-of-life seawater
reverse osmosis (EoL SWRO) modules. These end-of-life modules are classified as
follows; EoL-M1, EoL-M2, EoL-M3 and EoL-M4, and were cleaned prior to be analyzed
using a combined acid-base cleaning (6% w/v sodium hydroxide and 6% w/v citric acid).
The hydraulic performance of old membranes was assessed using 2 feeds; deionized water
and 5,000 mg/L synthetic NaCl solution, and was compared to the performance of 2
commercial membranes (BW30 and NF90) aiming their reuse in different lower-grade
applications. Removal of common salts represent in natural water sources (Na2SO4,
Mg2SO4 and MgCl2) and humic substances was also investigated using EoL membranes.
As a third part of the experimental work, the direct reuse of end-of-life RO membranes
was evaluated using natural brackish water (5,000 mg/L) in order to validate the direct
reuse of end-of-life SWRO membranes for brackish water filtration with little or no
treatment. Cross flow RO system with an active membrane area of 55.4 cm2 was used to
conduct all tests at around 10 bars. It was shown that 84.1-92.0% NaCl rejection was
achieved by direct reuse of end-of-life seawater RO membranes, which was higher than
the rejection characteristics obtained using commercial BW30 membrane. Additionally,
it has been shown that rejection of Na2SO4, MgSO4 and MgCl2 salt solutions was in the
range of (50.0-85.8%) with a highest rejection value was obtained for Na2SO4 and the
lowest rejection was observed for MgCl2 solution, while a complete rejection was
achieved for humic acid. These results showed a great promise of the direct reuse of the
EoL SWRO membranes within lower throughput systems (i.e. seawater pretreatment and
brackish water treatment). The direct reuse of the EoL SWRO membranes for brackish
water filtration showed that salt rejection performance of the EoL-M1, EoL-M3 and EoLM4 membranes presented NF-like properties. While salt rejection observed using EoLM2 was intermediate between the commercial NF and BW30 membranes. Overall, all
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reused membranes showed lower permeate flux and higher salt rejection values than the
aforementioned commercial membranes. Additionally, the permeate water quality
observed by using seawater EoL reverse osmosis membranes for brackish water filtration
showed TDS values in the range of 800-1300 mg/L, which was within the permissible
limit of irrigation water. Therefore, this product water could be used to cover some of the
agricultural water demands. However, in some cases, this water is required to be
remineralized by blending with raw water to adopt the chemical characteristics as a
function of crops requirements
