Environmental and Social Impact of Desalination
Environmental Impact
In water-stressed countries, freshwater supplies often fall short of meeting high demand, making saltwater desalination a viable solution. Desalination has become a reliable non-conventional water source, especially for producing drinking water. However, it has significant environmental impacts that need to be addressed.
The primary environmental concerns include the discharge of brine, a salt-saturated solution loaded with chemicals, and the emission of greenhouse gases (GHGs). These impacts vary depending on the desalination process and the plant's location. Coastal plants primarily face water pollution issues, while inland plants, generally using brackish water, must manage concentrated brine discharge.
Brine Discharge and Marine Impact
Brine discharge affects marine environments by altering salinity and temperature and creating water currents. Brine from desalination plants increases sea salinity and turbidity, elevates water temperature, and induces thermal pollution. Additionally, the use of various chemicals in pre- and post-treatment processes adds toxic substances to the discharge. Brine's high salinity (65-85 g/l) and temperature (45-50°C) significantly impact marine ecosystems, causing fish migration and promoting algae, nematodes, and small mollusks.
The chemical composition of brine includes residual chemicals and heavy metals like copper, chromium, nickel, and iron, which originate from pre-treatment processes. Coagulants, such as aluminum sulfate and ferric chloride, and antiscalants used to control scaling contribute to the presence of these contaminants in the brine. These substances pose ecotoxicological risks to marine life.
Air Pollution and Health Impact
Desalination plants, particularly thermal plants like multi-stage flash (MSF) distillation, contribute to air pollution. These plants burn significant amounts of fuel, releasing pollutants such as carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons, and sulfur oxides (SOx). CO is a toxic gas that impairs oxygen transport in the body, causing dizziness, headaches, and potentially fatal effects at high concentrations. NOx, including nitric oxide (NO) and nitrogen dioxide (NO2), react with unburned hydrocarbons to form photochemical smog, producing harmful oxidants like ozone and peroxyacetyl nitrate (PAN). SO2 is an irritant gas that affects the respiratory system.
Energy Consumption and Carbon Footprint
Membrane desalination techniques, such as reverse osmosis (RO), are characterized by high pretreatment requirements, higher conversion rates, and lower energy consumption compared to thermal processes. However, they produce brine with higher salinity, increasing environmental impacts. Heishel et al. reported that 96% of emissions from RO desalination originate from the electrical sector. The carbon footprint varies depending on fuel type and plant efficiency, ranging from 0.4 to 6.7 kg CO2 equivalent per cubic meter for seawater desalination and 0.1 to 2.4 kg CO2 equivalent per cubic meter for brackish water desalination.
Beery et al. conducted a detailed analysis of the carbon footprint of an RO seawater desalination plant, including ultrafiltration pretreatment. They found that 74% of emissions came from the high-pressure pump, with backwash pumps contributing 7%. Thermal desalination has a higher carbon footprint due to greater energy demand, both thermal and electrical.
Mitigation and Control Strategies
Effective environmental impact assessment (EIA) and mitigation strategies are essential for sustainable desalination. Best practices for brine management and emissions reduction are implemented in regions with extensive desalination use. For example, California's desalination amendment, passed in 2016, tightens regulations on water intake and brine disposal, requiring new plants to use best available measures to minimize marine life mortality.
In terms of reducing the carbon footprint, the desalination plant in Perth, Australia, serves as a model. The plant offsets its energy consumption with 100% renewable electricity from a nearby wind farm, achieving carbon neutrality.
领英推荐
Social Impact
Desalination plants also have significant social impacts, particularly on aesthetics, noise levels, and land use. The visual impact varies with the technology used; RO plants have a lower visual impact compared to thermal plants, which have large units, extensive piping, and tall chimneys. These structures permanently alter landscapes, especially in coastal areas where tourism is significant.
Noise pollution is another concern, with noise levels in RO plants reaching up to 100 decibels due to high-pressure pumps and energy recovery devices. Additionally, the construction of desalination plants can lead to biodiversity loss and changes in soil characteristics, negatively affecting the value of nearby real estate.
Recommendations
Algeria is planning to increase seawater desalination to address water shortages. It is crucial to involve stakeholders, including leading academics and various ministries, in the site selection for new plants to protect the environment and fishery resources from the adverse effects of desalination. The collaboration of experts from universities, along with the Ministry of Water Resources and Water Security, and the Ministry of Tourism, Fisheries, the Environment, and Energy, is essential for ensuring sustainable desalination development. Comprehensive Environmental Impact Assessments (EIA) and the implementation of best practices in brine management, emissions reduction, and social impact mitigation are vital for achieving sustainable desalination outcomes.
?Références
Khaled Elsaid, Mohammed Kamil, Enas TahaSayed, Mohammad Ali Abdelkareem, TabbiWilberforcefA.Olabi.Environmental impact of desalination technologies: A review. Science of The Total Environment Volume 748, 15 December 2020, 141528
?
Khaled Elsaid, Enas Taha Sayed, Mohammad Ali Abdelkareem, Ahmad Baroutaji, A.G.Olabi. Environmental impact of desalination processes: Mitigation and control strategies. Science of The Total Environment. Volume 740, 20 October 2020, 140125
?
Heihsel, M., Lenzen, M., Malik, A., Geschke, A., 2019. The carbon footprint of desalination: An input-output analysis of seawater reverse osmosis desalination in Australia for 2005–2015. Desalination 454, 71–81. https://doi.org/10.1016/j.desal.2018.12.008
Matan Beery, Frans Knops, Jens-Uwe Repke.Calculating the Carbon Footprint of SWRO Desalination: A Computational Tool. IDA Journal of Desalination and Water Reuse. Volume 4, 2012 pp.22-29 - Issue 2
Werner, M.; Sch?fer, A.; Richards, B.; Broeckmann, A. PV Powered Desalination in Australia: Technology Development and Application, Presentation by University of Wollongong Researach Group, 2005.
?
Professor-Dr. of Chemistry- Senior Researcher- Djillali Liabès University, Sidi Bel Abbès, Algeria
5 个月Thanks for sharing. Indeed, for the success of this important water challenge, the contribution of all skills in this field is crucial. In particular, for the management of the quantities of brine produced, after desalination