Environmental Problems With Desalination Plants

[Jacint Kosack]

Oceanscover 70 per cent of the planet. They provide nourishment for over three billion people and absorb 30 per cent of carbon dioxide released into the atmosphere and 90 per cent of the heat from climate change. Increasingly, they are also providing freshwater for a burgeoning population.

In most desalination processes, for every litre of potable water produced, about 1.5 litres of liquid polluted with chlorine and copper are created. When pumped back into the ocean, the toxic brine depletes oxygen and impacts organisms along the food chain.

This can harm organisms living on or in the bottom of a water body and translate into observable effects throughout the food chain. In addition, certain compounds (e.g. copper, chloride) used in the desalination pre-treatment process can be toxic to organisms in the receiving water, according to Qadir.

A 2018 United Nations study says there are now almost 16,000 desalination plants operating in 177 countries, producing a volume of freshwater equivalent to almost half the average flow over the Niagara Falls. However, the toxic brine which is usually dumped in the sea, risks contaminating food chains if left untreated.

Rising water demands associated with population growth, increased water consumption per capita and economic growth, coupled with diminishing water supplies due to climate change and contamination, are exacerbating water scarcity in most world regions.

The study says unconventional water resources, such as those resulting from desalination, are key to support Sustainable Development Goal 6 (to ensure availability and sustainable management of water and sanitation for all), but that innovation in brine management and disposal is required: seawater desalination can extend water supplies beyond what is available from the hydrological cycle.

Desalination is currently concentrated in high-income and developed countries. For affordable and environmentally friendly systems to be rolled out in low-income and lower middle-income countries, technological innovations are necessary, along with innovative financial mechanisms to support the sustainability of desalination schemes, says the study produced by the United Nations University Institute for Water, Environment and Health (UNU-INWEH) Canada project on Unconventional Water Resources.

Globally, 80 per cent of wastewater ends up in our seas, rivers, lakes, and wetlands. Under the Global Programme of Action for the Protection of the Marine Environment from Land-based Activities, UN Environment is working to prevent degradation from land-based activities, such as the operation of desalination plants. The Global Programme also hosts and acts as the secretariat for the Global Wastewater Initiative.

This Initiative is getting people to move away from waste removal and towards resource recovery. It focuses on capacity-building and training, promotion of best practices and technologies, awareness raising and communication, and addressing data gaps.

A better understanding of the long-term ecological impacts of desalination intake methods and discharged brine will allow managers to adequately protect Monterey Bay National Marine Sanctuary (MBNMS) ecosystems from threats associated with planned desalination plants.

Public works agencies, Moss Landing Marine Labs, NOAA Fisheries, California Coastal Commission, Southern California Coastal Water Research Project, Central Coast Regional Water Quality Control Board, State Water Resources Control Board, California State Lands Commission, California Public Utilities Commission

The desalination process involves taking seawater and forcing it through reverse osmosis membranes to clean it (Figure 1 and 3). This process can negatively impact community land use, increase erosion, cause visual and acoustic disturbances, and spread emissions into the water and atmosphere.2 Coastal ecosystems around desalination plants are being threatened by large decreases in primary and secondary consumers as well as the destruction of their fragile environment. When a desalination plant is taking in seawater it also draws in numerous species of aquatic life. The screens contained within the plants will kill these vital microorganisms, which are needed for consumption by larger species.3 A commission staff residing in San Diego estimates that the desalination plants will intake more than 80 million fish larvae, eggs, and invertebrates annually along the 160 kilometers (100 miles) of the Southern California coast.1 These desalination plants cause severe harm to coastal ecosystems, especially considering that the plants are drawing in seawater that is part of the National Marine Sanctuary (Figure 4).

Environmental ScienceBites Copyright 2015 by Kylienne A. Clark, Travis R. Shaul, and Brian H. Lower is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

After decades of slow progress, desalination is increasingly being used to provide drinking water around the globe. Costs for processing salt water for drinking water have dropped, but it remains an expensive option and one that creates environmental problems that must be addressed.

Each day 100 million gallons of seawater are pushed through semi-permeable membranes to create 50 million gallons of water that is piped to municipal users. Carlsbad, which became fully operational in 2015, creates about 10 percent of the fresh water the 3.1 million people in the region use, at about twice the cost of the other main source of water.

A second plant, similar to Carlsbad, is being built in Huntington Beach, California with the same 50-million-gallon-a-day capability. Currently there are 11 desalination plants in California, and 10 more are proposed.

San Diego is one of those places. With just 12 inches of rain a year in the Mediterranean climate of Southern California and no groundwater, the region gets half of its water from the distant Colorado River. The amount of snow that falls in the Rocky Mountains and keeps that mighty river flowing, however, has greatly diminished over the last two decades and according to some researchers may be part of a permanent aridification of the West. Climate change is a very real phenomenon for water managers throughout the Southwest and elsewhere.

Meanwhile, the cost of desalinated water has been coming down as the technology evolves and the cost of other sources increases. In the last three decades, the cost of desalination has dropped by more than half.

A study by the UN Institute for Water, Environment and Health published earlier this year contends that the problem of brine waste has been underestimated by 50 percent and that, when mixed with the chemicals meant to keep systems from fouling, the brine is toxic and causes serious pollution.

Another problem comes from the sucking in of sea water for processing. When a fish or other large organism gets stuck on the intake screen, it dies or is injured; in addition, fish larvae, eggs and plankton get sucked into the system and are killed.

In 2016, California passed the Desalination Amendment, which tightened regulations for intake and brine disposal. Proponents of desalination contend the changes have been onerous and are slowing the march toward a de-sal future.

Because of the cost of seawater processing and the impacts on the ocean, much of the recent desalination growth has involved the use of brackish water. The solids in brackish water are one-tenth the amount in ocean water, and that makes the process much cheaper.

Correction, July 8, 2019: An earlier version of this article incorrectly stated that a desalination plant is being built in Huntington, California. It is being built in Huntington Beach, California.

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Enormous amounts of seawater are desalted everyday worldwide. The total world production of fresh water from the sea is about 2621 mgd (9.92 million m(3) day(-1) 1985 figures). Desalting processes are normally associated with the rejection of high concentration waste brine from the plant itself or from the pretreatment units as well as during the cleaning period. In thermal processes, mainly multistage flash (MSF) thermal pollution occurs. These pollutants increase the seawater temperature, salinity, water current and turbidity. They also harm the marine environment, causing fish to migrate while enhancing the presence of algae, nematods and tiny molluscus. Sometimes micro-elements and toxic materials appear in the discharged brine.This paper will discuss the impact of the effluents from the desalination plants on the seawater environment with particular reference to the Saudi desalination plants, since they account for about 50% of the world desalination capacity.

Desalination of seawater is an increasingly common means by which nations satisfy demand for water. Desalination has a long history in the Middle East and Mediterranean, but expanding capacities can be found in the United States, Europe and Australia. There is therefore increasing global interest in understanding the environmental impacts of desalination plants and their discharges on the marine environment. Here we review environmental, ecological and toxicological research in this arena including monitoring and assessment of water quality and ecological attributes in receiving environments. The greatest environmental and ecological impacts have occurred around older multi-stage flash (MSF) plants discharging to water bodies with little flushing. These discharge scenarios can lead to substantial increases in salinity and temperature, and the accumulation of metals, hydrocarbons and toxic anti-fouling compounds in receiving waters. Experiments in the field and laboratory clearly demonstrate the potential for acute and chronic toxicity, and small-scale alterations to community structure following exposures to environmentally realistic concentrations of desalination brines. A clear consensus across many of the reviewed articles is that discharge site selection is the primary factor that determines the extent of ecological impacts of desalination plants. Ecological monitoring studies have found variable effects ranging from no significant impacts to benthic communities, through to widespread alterations to community structure in seagrass, coral reef and soft-sediment ecosystems when discharges are released to poorly flushed environments. In most other cases environmental effects appear to be limited to within 10s of meters of outfalls. It must be noted that a large proportion of the published work is descriptive and provides little quantitative data that we could assess independently. Many of the monitoring studies lacked sufficient detail with respect to study design and statistical analyses, making conclusive interpretation of results difficult. It is clear that greater clarity and improved methodologies are required in the assessment of the ecological impacts of desalination plants. It is imperative to employ Before-After, Control-Impact monitoring designs with adequate replication, and multiple independent reference locations to assess potential impacts adequately.

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