How to use recycled water well?

What is recycled water?
Regenerated water refers to water that, after appropriate treatment, meets certain water quality indicators, meets certain usage requirements, and can be used for beneficial purposes. Compared with seawater desalination and cross basin water transfer, recycled water has significant advantages. From an economic perspective, the cost of recycled water is the lowest. From an environmental perspective, wastewater recycling and utilization can help improve the ecological environment and achieve a virtuous cycle of water ecology. Regenerated water, also known as "reclaimed water", is a Japanese term used. Usually, tap water is called "upper water" and sewage is called "lower water". The quality of recycled water is between upper water and lower water, hence the name "reclaimed water".

What are the uses of recycled water?
There are many uses for recycled water: it can be used for groundwater recharge, industrial water, agricultural, forestry, and animal husbandry water, urban non drinking water, and landscape environment water. Regenerated water can be reused for groundwater recharge, which can be used for groundwater source replenishment, prevention and control of seawater intrusion, and prevention and control of ground subsidence; Regenerated water can be reused in industries as cooling water, washing water, and boiler water; Regenerated water can be reused for agriculture, forestry, and animal husbandry as water for irrigation, planting, and seedling cultivation of food and economic crops, irrigation and planting of trees and ornamental plants, as well as water for livestock and poultry.
3. What is the current situation of renewable water utilization in China?
Since 1986, China has been exploring and investing human and material resources to deeply treat sewage and reuse it for urban life and industrial production. The investment and demand for renewable water resources have been increasing year by year. Beijing, Tianjin, Xi'an and other places actively carry out urban sewage recycling and utilization, and have accumulated good experience in formulating local sewage recycling plans and management measures, and developing recycled water users. The Tianjin Economic Development Zone Comprehensive Research and Demonstration Project for Wastewater Recycling and Utilization has formulated a series of policy measures based on local actual needs and water environment characteristics to expand the water use channels for recycled water, as well as technical regulations to ensure water supply safety, effectively alleviating the local water shortage situation. However, the lack of sewage treatment facilities and supporting pipelines in our country, as well as people's biases towards the understanding of recycled water, have caused great difficulties in the development of recycled water utilization channels. At present, the utilization of recycled water is still in its early stages, and the production and utilization capacity of recycled water in most provinces and regions in China is limited, with an average utilization rate of less than 10%.
In March 2007, the Ministry of Water Resources issued the "Water Quality Standards for Regenerated Water", which strictly required the classification, water quality management, and water quality monitoring of recycled water. Regenerated water replenishes groundwater mainly through surface infiltration and groundwater injection, artificially recharging recycled water into groundwater aquifers, allowing recycled water to participate in groundwater circulation. The quality of recycled water will directly affect groundwater bodies and aquifers, and its adverse effects often have lag and long-term effects. For groundwater recharge, key factors to consider include: pollution of water bodies by organic and toxic substances in the water; No blockage is caused during the recharge process. Therefore, the control items for groundwater quality in recharge mainly include: 1) conventional indicators: chromaticity, turbidity, odor, and pH value; 2) Organic pollutant indicators: dissolved oxygen, five day biochemical oxygen demand (BOD5) and chemical oxygen demand (CODCr); 3) Inorganic pollutant indicators: total hardness, ammonia nitrogen, nitrite nitrogen, total dissolved solids, mercury, cadmium, arsenic, chromium, lead, iron, manganese, fluoride, and cyanide; 4) Biological indicators: fecal coliform group. When reclaimed water is used for industrial water, the key factors to be considered include scale, corrosion, biological growth, blockage, foam and workers' health. Therefore, the control projects for industrial water quality using recycled water mainly include: 1) water quality indicators to prevent equipment blockage: turbidity and suspended solids (SS); 2) Water quality indicators to prevent equipment corrosion: chromaticity, pH value, total hardness, five day biochemical oxygen demand (BOD5), chemical oxygen demand (CODCr), total dissolved solids, ammonia nitrogen, total phosphorus, iron and manganese; 3) Biological indicators: fecal coliform group. The use of recycled water for agriculture, forestry, and animal husbandry focuses on factors such as its impact on soil properties, crop growth, and irrigation systems. Therefore, the indicators used for agricultural, forestry, and animal husbandry water quality mainly include: 1) indicators that affect soil and plant growth: chromaticity, pH value, total hardness, five day biochemical oxygen demand (BOD5), chemical oxygen demand (CODCr), total dissolved solids, mercury, cadmium, arsenic, chromium, lead, and cyanide; 2) Indicators to prevent blockages in irrigation systems: turbidity and suspended solids (SS); 3) Biological indicators that affect environmental hygiene: fecal coliforms. The key factors to consider when using recycled water for non drinking water in cities include the requirements of water environment, human health, and water supply network. Therefore, the control projects for urban non drinking water quality mainly include: 1) biochemical indicators that affect the ecological environment: five day biochemical oxygen demand (BOD5), ammonia nitrogen, and total dissolved solids; 2) Sensory indicators: chromaticity, turbidity, odor, and anionic surfactants (LAS); 3) Indicators that affect pipeline equipment: pH value, dissolved oxygen, iron and manganese; 4) Biological indicators that affect environmental hygiene: fecal coliforms. The key factors to consider when using recycled water for landscape use include the requirements for human perception and the growth requirements of aquatic organisms. Therefore, the control projects for landscape water quality mainly include: 1) indicators that affect human perception: chromaticity, turbidity, odor, suspended solids (SS), anionic surfactants (LAS), and petroleum; 2) Indicators that affect the growth of aquatic organisms: pH value, dissolved oxygen, five day biochemical oxygen demand (BOD5), chemical oxygen demand (CODCr), ammonia nitrogen, and total phosphorus; 3) Biological indicators that affect environmental hygiene: fecal coliforms.
What are the functions of recycled water?
1. Effective ways to alleviate water scarcity According to relevant data statistics, 80% of urban water supply is converted into sewage. After collection and treatment, 70% of the recycled water can be reused. This means that by reusing sewage, the available water in the city can be increased by at least 50% while the existing water supply remains unchanged. Regenerated water, as a legitimate alternative water source, is being increasingly utilized and has become an important component of urban water resources. 2. Promoting advanced sewage treatment and promoting the use of recycled water are important measures to achieve sustainable utilization of water resources, promote coordinated development between humans and nature, create a good water environment, and promote the development of circular cities. Internationally, there has been a significant change in the management goals of water resources, shifting from controlling, developing, and utilizing water to a focus on water recycling and ecological restoration, fundamentally achieving a virtuous cycle of water ecology and ensuring sustainable utilization of water resources. 3. It can bring considerable benefits. The rational utilization of recycled water not only has good economic benefits, but also has enormous social and ecological benefits. Firstly, with the increase in urban tap water prices, further reduction in operating costs of recycled water, and an increase in reused water, economic benefits will become increasingly prominent; Secondly, the rational utilization of recycled water can maintain ecological balance, effectively protect water resources, change the traditional mode of "exploitation, utilization, and discharge", achieve a virtuous cycle of water resources, and play a positive role in alleviating the shortage of water resources in cities, with long-term social benefits; Thirdly, the ecological benefits of rational utilization of recycled water are reflected in not only removing the adverse effects of wastewater on the urban environment, but also further purifying and beautifying the environment.
6. Foreign cases of recycled water utilization and reuse
United States: In Florida, based on its urban water concentration, the basic model proposed is non drinking water reuse, with a large-scale implementation of a dual pipe water supply system that supplies urban sewage treatment water to golf courses, urban greenery, buildings, and residential areas for around 40% of the price of tap water; In Texas, based on its traditional water usage and hydrogeological characteristics, it adopts an "indirect reuse" model and conducts large-scale underground recharge of sewage treatment water.
Japan: The term "recycled water" originated in Japan and began using recycled water as early as 1955. The dual pipe water supply system is quite common in large cities in Japan, one is the drinking water system, and the other is the recycled water system, also known as the 'recycled waterway' system. Regenerated waterways are known for transporting recycled water for daily use, accounting for approximately 40% of the recycled water usage. Recycled water in Japan is mainly used for urban miscellaneous use, industry, agricultural irrigation, etc., and the management system is very strict. The reinjection of recycled water in Japan is mainly carried out by supplying groundwater through rivers, and in recent years, an underground capillary filtration system has been developed to supplement groundwater through leakage reinjection. Most areas use sewage treatment to clean and revive water, and the restoration and protection of the water environment is the focus of reuse.
Israel: Israel is one of the earliest countries to use recycled water for crop irrigation. Its remarkable achievements in industrial agriculture and national economic development are not only due to the vigorous development of high-tech, but also the implementation of sewage reuse policies, which provide reliable guarantees for the survival and development of the country. Israel is the country with the highest proportion (approximately two-thirds of the total sewage) of using recycled water for irrigation in the world. The sewage discharge reached approximately 500 million cubic meters per year in 2010, and the amount of recycled water used reached approximately 350 million cubic meters per year. Currently, one-third of Israel's agricultural irrigation uses recycled water.