In view of the better economy of seawater desalination on the island, some people recently called for the desalination of seawater as a new water source into the national water network project. During the "14th Five-Year Plan" period, China plans to add desalination scale of more than 200,000t/d in the island area alone. It is necessary to improve the relevant policy requirements for the real problems of desalination scale utilization.
The contradiction between supply and demand of water resources in China's coastal areas is outstanding, which restricts the economic and social development. The total water resources of the 11 coastal provinces (autonomous regions and municipalities directly under the central government) account for only 27% of the country's total water resources, but create 55% of the gross domestic product. Fifty-one of the 55 coastal cities above the prefecture level in the region are water-scarce cities, and all 12 island counties are water-scarce counties. Desalination is an important incremental water source, which is of great significance to alleviate water shortage in coastal areas and islands and ensure water security.
Desalination Development Overview
Since 2010, China's desalination industry has set up the "12th Five-Year Plan" to "14th Five-Year Plan" three stages of development goals, the introduction of a number of support policies to vigorously promote the development of the industry.
During the "12th Five-Year Plan" period, China's seawater desalination industry was still in the initial development stage, and the national policy started from the basic planning and successively issued the "Opinions on Accelerating the Development of Seawater Desalination Industry", "Seawater Desalination Industry Development "12th Five-Year Plan", "Seawater Desalination Science and Technology Development "Twelfth Five-Year Plan" and other documents to guide the establishment of seawater desalination technology innovation system.
During the "Thirteenth Five-Year Plan" period, in order to promote the development of seawater desalination industry in the direction of scale and integration, the National Development and Reform Commission and the State Oceanic Administration jointly issued the "Thirteenth Five-Year Plan for National Seawater Utilization", and seawater desalination became a strategic emerging industry in China.
"Since the 14th Five-Year Plan, the national policy has focused more on application, and the National Development and Reform Commission and the Ministry of Natural Resources jointly issued the Action Plan for the Development of Seawater Desalination Utilization (2021-2025) to promote the large-scale utilization of seawater desalination.
Desalination has been utilized on a large scale around the world. Desalinated water has been used for municipal water supply for more than 60 years, and about 300 million people in more than 160 countries have been drinking desalinated water for a long time. Global desalination capacity has grown from less than 30 million t/d in 2000 to 100 million t/d by 2020, an average annual increase of more than 7%. Desalination costs have fallen from US$10/t in the 1970s to less than US$1/t today and are becoming economically viable.
China has built 123 desalination projects, with a desalination capacity of more than 1.6 million t/d. According to the "Action Plan for the Development of Desalination Utilization (2021-2025)", by 2025, the total scale of desalination in China will reach more than 2.9 million t/d, with a new desalination scale of more than 1.25 million t/d, of which the coastal cities will add Desalination scale of 1.05 million t / d or more, the island area new desalination scale of 200,000 t / d or more. The plan requires coastal water-scarce areas to desalinate water as a supplemental source of water for life, new municipal water supply and important emergency backup water, and increase the proportion of desalinated water in the allocation of water resources year by year; on the basis of the protective development of the island, the construction of seawater desalination facilities on the island is moderately advanced layout to meet the demand for water for production and living ecology.
Potential risks of seawater desalination scale utilization
At present, China has not yet built a national standard system related to seawater desalination. Due to the special nature of seawater, it is difficult for the existing national standards to solve various health and safety problems that arise in the process of production, transportation and drinking. Some of the existing desalination industry standards have not yet been recognized by the health and water conservancy departments.
Water quality standards are not sound
First, there are no clear standards for seawater quality as a source of desalinated water. The current national standard "drinking water hygiene standards" (GB 5749-2006) covers 106 indicators, only provides for the use of surface water or groundwater as a source of drinking water water quality health requirements, does not involve other water sources. 2022) was released, will be April 1, 2023 all instead of GB 5749-2006, the new standard covers a total of 97 indicators did not desalinated water as a source of drinking water. The "Seawater Quality Standard" also does not specify the water quality requirements for desalination water sources, resulting in the lack of water quality standards for desalinated water used for drinking water.
Second, drinking water quality standards can not clearly determine the health and safety of desalinated water. In 2011, the World Health Organization (WHO) in the "Guidelines for Drinking Water Quality" (fourth edition, water quality indicators 237), especially pointed out that the current In 2006, WHO issued the "desalinated drinking water development guidelines" to introduce the possible problems of desalination, and in 2007 and 2011 published a more detailed guide, a comprehensive introduction to desalination may bring health problems and environmental issues. 2021 On September 29, 2012, the International Organization for Standardization (ISO) released "Marine Technology - Reverse Osmosis Desalination Product Water Quality - Guidelines for Municipal Water Supply", which is the first China-led ISO international standard in the field of desalination, and the guidelines regulate key water quality parameters for drinking reverse osmosis desalinated water and their scope, monitoring frequency and Test methods. But the standard can be recognized by the water quality health authorities, but also need to test the practice.
Third, the existing radioactive indicators can only play a primary screening role, and the domestic standard is low. The current "drinking water health standards" in the radioactive indicators only total alpha radioactivity, total beta radioactivity two, only as a primary screening indicators of drinking water radioactivity, that is, below this value of water can be considered suitable for drinking, higher than the value does not mean unsuitable for drinking, radionuclide analysis should be carried out to estimate the resulting dose, to make a hygienic evaluation. The WHO recommended value is 0.1Bq/L for total alpha radioactivity and 1Bq/L for total beta radioactivity, while China's current Sanitary Standard for Drinking Water stipulates the limit value of total alpha radioactivity as 0.5Bq/L and total beta radioactivity as 1Bq/L. The limit value of total alpha radioactivity is obviously higher than the WHO recommended value.
Fourth, there is no lower limit value for the water quality index in the Sanitary Standard for Drinking Water, which cannot be directly applied to desalinated water and cannot meet the quality control requirements needed for large-scale production. 2010, the European Parliament and the European Council analyzed the health, environmental and policy issues of desalination in the Guidelines on Desalination Regulations, pointing out that the water quality guidelines for desalinated water should set the minimum content of calcium and magnesium ions. Since China's current domestic drinking water health standards with surface water or groundwater as raw water do not set lower limits for water hardness and all minerals and chemical elements, it is impossible to evaluate and supervise the water quality and hygiene of desalinated water, which makes it difficult to guarantee the water quality and hygiene safety of desalinated water and limits the scale production.
Long-term consumption has potential risks
Desalination can remove some harmful substances, regardless of raw water quality, treatment, product water quality, and traditional surface water or groundwater as a source of drinking water are very different, there are potential risks of long-term drinking.
First, the harmful components are high, and the beneficial components are too low. On the one hand, the island and ship reverse osmosis desalination for boron retention rate efficiency is limited, the water boron concentration is often relatively high, usually higher than 0.5mg / L. 0.5mg / L is the "drinking water sanitation standards" (GB 5749-2006) boron concentration limit, "drinking water sanitation standards" (GB 5749 -But in most countries and regions of the world, the concentration of boron in drinking water is less than 0.5mg/L. But for some places, even after secondary reverse osmosis treatment, the content of boron in water is still 1~2mg/L. L, long-term consumption of high boron water may have adverse effects. On the other hand, the concentration of calcium, magnesium, sulfate, bicarbonate, fluorine and other components are often lower than the concentration range required by the "Low Mineralization Drinking Water Mineralization Health Standards" (GJB 1335-92), which is typical of soft water, long-term drinking is not good for human health.
Second, residents of the islands who drink desalinated water for a long time are at greater risk of certain chronic diseases. The Center for Disease Control and Prevention of Zhoushan City, Zhejiang Province and the Center for Disease Control and Prevention of Shengsi County had used residents who drank desalinated water as the desalinated water observation group, residents who drank desalinated water and other water sources as the mixed water source observation group, and residents who drank reservoir water and water from other sources as the fresh water observation group to investigate and analyze the current situation of chronic disease incidence through the chronic disease network reporting and resident health record system, and found that residents' long-term It was found that there was a correlation between residents' long-term consumption of desalinated water and malignant tumor, coronary heart disease and stroke.
Third, the scale inhibitor required for reverse osmosis desalination process may be genotoxic.In 2018, the Chinese Center for Disease Control and Prevention had tested the genotoxic effects of different desalination scale inhibitors on Chinese hamster ovary cells using in vitro comet test and flow cytometry in vitro micronucleus test, and found that modified polycarboxylic acid scale inhibitor, polyacrylic acid scale inhibitor and maleic acid scale inhibitor were genotoxic. However, in contrast, the Center for Disease Control and Prevention of Zhoushan City collected 18 copies of raw seawater and discharge water of each process of desalination plant in Caiyuan Town, Shengsi County, from December 2011 to September 2012, and 5 copies of raw surface water and discharge water of each process, and conducted genotoxicity test according to the international standard method recommended by ISO-13829. Genotoxicity is significantly lower than that of surface water as the source of drinking water.
Fukushima nuclear wastewater discharged into the sea, raising concerns about the potential risks of desalinated water
One is that Japan does not drink desalinated water directly on a large scale. The Drinking Water Sanitation Standards in the Watercourse Law of Japan do not set radioactive indicators. Water supply to the main island is generally based on surface water and groundwater, and desalinated water accounts for a small percentage. For the outlying islands close to the main island, most of them use direct water supply by laying submarine pipelines. For the outlying islands that are far from the main island, small desalination plants are used to supply water and mix it with conventional water for drinking. Japan's desalination project only a few as a municipal company facilities, about 94% of desalination plants are used for industrial experiments. This point should draw our country's attention.
Second, radionuclides cannot be completely removed by the desalination process and are at risk of enrichment. on April 13, 2021, the Japanese government approved a plan that anticipates that all of the nuclear-contaminated water from the Fukushima Daiichi nuclear power plant will be discharged into the Pacific Ocean within 30 years, sparking global concern. Its emissions of tritium, carbon 14, xenon, strontium, cesium, iodine and other radionuclides are difficult to remove completely by desalination, especially desalination has no effect on tritium removal.
Policy recommendations for scientifically promoting desalination on a large scale
To promote seawater desalination on a large scale, it is still necessary to make scientific proof, improve standards, carry out health risk assessment, and strengthen monitoring and evaluation and international cooperation.
Improve the desalination of seawater and desalinated water health standards to ensure large-scale production and utilization
First, with reference to the "surface water environmental quality standards" (GB 3838-2002), revise the "seawater quality standards", adding "seawater supplementation for centralized drinking water / specific project standard restrictions.
Second, accelerate the development of "desalinated water drinking health standards". To "drinking water hygiene standards" as a guide, according to the characteristics of seawater itself and its desalination process to choose the appropriate sanitary indicators, such as desalination pretreatment process should be incorporated into the corresponding microbial indicators and general chemical indicators; desalination of seawater can not be completely removed and the new generation of various substances harmful to human health, the human body necessary calcium, magnesium, iron, zinc, selenium and other nutrients, and disinfection by-products In addition, the Government should set reasonable limits or ranges for desalinated water; set the necessary organoleptic indicators, radioactive indicators and toxicological indicators for desalinated water.
Desalinated water mainly as a backup water source into the unified management of water resources
First, desalinated water should be incorporated into the unified management of water resources. It is proposed to amend the water law to include desalinated water and other non-conventional water sources into water resources and enjoy relevant policies; for coastal areas and islands, clarify the status of desalinated water as a strategic backup water source and include it in the unified water resources allocation system.
Second, desalinated water is mainly used as a backup water source for domestic water. By the end of 2019, the main uses of desalinated water in China accounted for 66.6% of industrial water and 33.1% of domestic water. In the existing water allocation plan for coastal cities, desalinated water should be used only as a strategic backup or supplementary water source. However, in special places such as islands and ships, it can be used as the main source of drinking water for a short period of time.
Third, the full demonstration, and steadily promote. From the point of view of the built projects, seawater desalination project utilization rate is generally low, the energy consumption per unit of water production, high operating costs. It is recommended to fully demonstrate the project water demand, policy conditions and construction conditions before the project construction, and strive to sign the water supply intention agreement first to protect the project utilization rate; coordinate the planning of desalinated water and traditional tap water for mixed drinking. Strengthen the reverse osmosis process to further remove harmful elements such as boron and minimize the residue of scale inhibitor; when food-grade calcium carbonate is used in the desalination water conditioning process, the stability of water quality should be enhanced
Strengthen seawater and desalinated water health monitoring and research, and carry out risk assessment
First, strengthen desalinated water quality monitoring and epidemiological studies. Given that the applicability of drinking water hygiene standards for desalinated water needs further assessment, a long-term desalinated water quality monitoring system should be established to monitor boron, disinfection by-products, heavy metals, etc. in product water and end-of-pipe water, continue to strengthen relevant epidemiological studies, and carry out in-depth investigations on the relationship between population health and drinking desalinated water.
Second, the establishment of health risk level standards. For desalinated water mineral deficiency, low hardness, low fluorine content and other human health risks, reference can be made to the appropriate concentration of calcium, magnesium and fluorine in drinking water at home and abroad to establish risk level standards, and then compare the monitoring results with the standards to qualitatively analyze the risk of desalinated water to human health.
Third, the degree of water quality risk evaluation. The whole process of desalinated water supply for desalinated water - post-treatment - pipe network - users, the risk assessment of the whole process can refer to the hazard analysis and critical control point (HACCP) system of food production, the degree of risk of desalinated water quality evaluation and analysis.
Fourthly, marine radioactivity monitoring and assessment and international cooperation should be carried out. The next 30 years or even a longer period, it is recommended to establish long-term cooperation and research exchange mechanisms with relevant international institutions and countries, and the monitoring area should not only cover the coastal areas of Japan, especially the Fukushima waters, but also the North Pacific Ocean waters and the marginal sea waters, in order to carry out a comprehensive marine radioactivity and seawater quality health forecast - monitoring - assessment work, and Early detection of risks to ensure the health and safety of desalinated water in China.
