Acute shortage of freshwater resources coupled with population surge has contributed to the growing demand for freshwater supply across the world. To prevail over the problem of water scarcity several governments, notably those in the Arabian Peninsula, have resorted to desalination to generate freshwater from seawater. In the last two decades, there has been a substantial increase in desalination facilities across the shores of the Red Sea and the Arabian Gulf, which host to roughly half of the installed global production capacity of desalinated water. Over the years, the most common desalination technology included thermal processes such as multi-effect distillation (MED), multi-stage flash (MSF) desalination, and mechanical vapor compression. However, considering the substantial negative impacts of thermal facilities on the environment in terms of carbon emissions from fossil fuel, and waste heat in the brine, there has been increasing focus on reverse osmosis (RO), where saltwater is transferred through a series of semi-permeable membranes. Despite growing technological advancement in this field, RO-based plants still have many environmental concerns associated with their operation, including energy and chemical use, reject brine disposal, and sludge generation. A detailed assessment of plant operation and configuration is required to quantify relevant impacts and determine the optimum operational regimes to ensure desalination technologies are more viable, sustainable, and optimized.
The purpose of this study was to investigate the impacts of seawater quality, intake system, pretreatment, chemicals and energy source on the overall environmental footprint associated with SWRO processes, and identify possible solutions to existing challenges for future facility improvement and optimization. A secondary objective was to determine the relative impacts of brine and sludge disposal, which are frequently ignored from the life-cycle analysis. Life cycle studies were conducted to investigate the potential environmental impacts of different seawater RO operation processes. Various impact categories were used to evaluate the environmental impacts associated with operating desalination plants in the Arabian Gulf such as abiotic depletion potential elements (ADP-e), acidification potential (AP), eutrophication potential (EP), global warming potential (GWP), ozone layer depletion (ODP), human toxicity potential (HTP), marine aquatic eco-toxicity potential (MAETP), terrestrial eco-toxicity potential (TETP) and photochemical oxidation potential (POCP). Data collected from different sites from the Arabian Gulf were analyzed through AqMB® software (water process modeling), Hydranautics® and AWCProton® (chemical dosage optimization), and ThinkStep’s GaBi® platform (environmental analysis).
Results showed that although energy is a major contributor, chemicals involved with pretreatment have significant impacts in certain categories. When those impacts are normalized by total per capita emissions, MAETP is the greatest concern. The emission solely from consuming SWRO produced water over a year are five times higher than the total typical per capita contribution to this impact category. GWP also had a large per capita contribution. Energy plays a large role in the relative environmental impacts. Wind power is the lowest impact energy source, reducing normalized environmental impacts investigated to less than 1% of a typical per capita burden with the exception of MAETP. Photovoltaics, in contrast, reduce GWP but greatly increase MAETP, making natural gas more desirable if wind power is not feasible. Subsurface intakes are one way to reduce chemical requirements and therefore environmental burdens including reduction of MAETP by up to one third compared to open intake systems. Water feed quality can also realize large reductions in pretreatment and chemical usage through optimized plant location, achieving reductions of at least 25% in certain environmental impact categories. The selection of chemicals for various pretreatment units can have significant impacts, due to the burdens associated in their production – particularly those from the Chlor-Alkali process. The effects of brine and sludge need to be considered more carefully, but in general, are relatively small compared to the overall operational impacts from chemical production and electricity consumption.
Increasing demand for freshwater across the Arabian Gulf implies that desalination capacity will continue to grow to meet those demands. Considering this and the large normalized impacts associated with desalinated water consumption, greener operational processes within seawater RO plants need to be considered to reduce their potential environmental footprint. While the traditional focus on reducing energy and GWP is important, this research highlights significant impacts from pretreatment and chemical consumption that can be reduced through increased careful site selection, intake and process designs, chemical selection, and effective recycling processes for the major desalination wastes.
| Date of Award | 2021 |
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| Original language | American English |
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| Awarding Institution | - HBKU College of Science and Engineering
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