Concentrate (when discharged to the ocean) may have chronic/acute impacts on
marine ecosystems, particularly in the mixing zone around outfalls. The environmental
impact of the desalination plant discharges is very site- and volumetric specific, and
depends to a great extent on the salinity tolerance of the specific marine microbial
communities as well as higher order organisms inhabiting the water column in and
around this extreme discharge environment. Scientific studies that aim to grant insight
into possible impacts of concentrate discharge are very important, in order to understand how this may affect different marine species when exposed to elevated salinity levels or
residual chemicals from the treatment process in the discharge site.
The objective of this PhD research was to investigate the potential environmental
effects of the concentrate discharge in the near-field area around the submerged discharge
of the King Abdullah University of Science and Technology (KAUST) seawater reverse
osmosis (SWRO) plant by a combination of biological and hydrological studies.
Possible changes in microbial abundance were assessed by using flow cytometric
(FCM) analysis on a single-cell level in 107 samples, taken from the discharge area, the
feed-water intake area and two control sites. Results indicate that changes in microbial
abundance in the near-field area of the KAUST SWRO outfall are minor and appear to bethe result of a dilution effect rather than a direct impact of the concentrate discharge.
In order to also investigate potential impacts on higher order organisms, a longterm
in-situ salinity tolerance test at the discharge site was conducted on the coral Fungia
granulosa and its photophysiology. The corals were exposed to elevated levels of
salinity as a direct result of concentrate discharge. Their photosynthetic response after
exposure to extreme salinity conditions around the full-scale operating SWRO
desalination discharge was measured. A pulse amplitude modulated (PAM) fluorometer
was used to assess photochemical energy conversion in photosystem II (PSII) measured
under constant concentrate discharge conditions. Based on a literature review, we
anticipated distinct impairment of photosynthetic characteristics as a response to elevated
salinity levels. We also expected particularly quick indications of bleaching for the
specimens exposed to the highest salinity levels. The hypothesis was strongly rejected
as symbiotic dinoflagellates of Fungia granulosa demonstrated high tolerance to hyper
saline stress as measured by effective quantum yield of PSII (ΔF/Fm’) during this study.
A series of propulsion driven autonomous underwater vehicle (AUV) missions
with velocity and salinity measurements were used for possible plume detection and
evaluation of the discharge. The Cornell Mixing Zone Expert System (CORMIX) was
additionally utilized in order to assess discharge performance under different ambient
velocity magnitudes. Results show that AUV missions could provide significant insight
with regards to plume identification and effluent discharge environmental impact studies.
Combined with robust in-situ field measurements, models and expert systems were used
to evaluate possible impacts on the marine environment in comparison with regulatory
mixing zones and dilution criteria.
Based on the findings and existing environmental governance (national and
international), a revised regulatory framework for mixing zones within the Kingdom of
Saudi Arabia is recommended.
|Date of Award||Jun 2014|
- Biological, Environmental Science and Engineering
|Supervisor||Gary Amy (Supervisor)|
- Concentrate Discharge
- Marine Monitoring
- Salinity Tolerance
- Impact Assessment
- Environmetal Management