6.2 Risks
6.2.1 Environmental Impacts
There are multiple ways in which a desalination facility can negatively impact the surrounding
environment; therefore, particular attention should be paid to each potential site prior to
construction in order to minimize these risks. One of the most significant impacts of seawater
desalination activities can be on the marine habitat adjacent to the desalination plant. Brine
discharge released as effluent in the waste from the facility can potentially harm marine organisms
by raising the salinity to unhealthy or even fatal levels. In addition to brine discharge, intake
facilities, the disposal of pre-treatment chemicals and the production of energy through the use of
fossil fuels are also potential threats to the environment. The environmental risks of desalination
are presented below in the sequential order of the treatment process.
Intake Facilities
Seawater intakes often receive scrutiny during siting, primarily because the impact these facilities
have on marine life. Marine organisms can be harmed through the intake and during the
desalination process. Large marine organisms, such as fish, birds, invertebrates and mammals, can
be killed on a desalination plant’s intake screen (impingement). Those organisms that are small
enough to pass through the intake screen, are destroyed during the desalination process
(entrainment) reducing the available food supply for larger organisms and disturbing the overall
ecological balance of the marine environment. Additionally impacts occur during the construction
of each type of seawater intake. Usually these impacts are temporary if construction is completed
responsibly; however long-term impacts to be avoided are the destruction of reefs or rocky habitat
areas as well as permanent structures that will affect wildlife.
Pre-Treatment
Chemicals used in pre-treatment and for membrane cleaning and storage are potentially harmful to
the environment and are usually discharged with the brine in the waste stream. Pre-treatment
chemicals such as acids (anti-scalants) or biocides released to the marine environment can kill fish
and degrade marine habitats in proximity to the discharge location. The discharge of these
chemicals to wastewater treatment facilities can also be problematic. To minimize this risk
ultrafiltration can be used to pre-treat source water. Post-treatment is often necessary prior to
disposal, however this can be difficult to accomplish because of the increased density and salinity of
the waste stream.
Brine
The waste from the desalination process or brine disposal can provide a significant challenge when
siting and designing a desalination facility. The high salinity of brine can have serious negative
effects on marine resources surrounding the discharge structure. While some marine life can adapt
to the increase in salinity, there are some species, such as sea urchins that are extremely sensitive to
salinity changes (RBF Consulting 2004). Any shift or negative impact to specific species in any
marine environment is detrimental to the ecosystem. This is particularly true in the Loreto region
with the presence of a National Marine Park.
Brine discharge to existing sewer facilities is usually not a viable option unless the sewer system has
the capacity to handle the large volume of additional loading. In addition, large amounts of brine
discharged to the sewer system can change the treatment scheme of a plant and require the plant to
undergo retrofit or operational changes. Based on an assessment performed by SAPAL, the existing
sewer system in Loreto is already strained and would not be able to handle the large volumes of
brine expected from a desalination facility (Quintero 2006). Additionally, the conventional
wastewater treatment system that exists in Loreto has limited ability to reduce the dissolved solid
content of water; therefore the only benefit would be dilution. Ultimately, a significant retrofit
effort would be likely to accommodate brine waste in the existing sewer system.
Product Water
The product water produced from desalination is often corrosive because reverse osmosis and
distillation alter the chemical composition of the product water, increasing the pH. Post-treatment
of the product water is often required to avoid corrosion to the distribution system or the leaching
of toxic metals from the distribution system's piping. Product water can be further treated to
increase the pH or diluted with an existing potable water resource to reduce this effect. |
