Reuse of treated water

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Classified by use: Recycled water can be treated in three different ways depending on its intended use. 1. One method involves treating it to drinking water standards so that it can be reused in daily life, thereby enabling direct recycling of water resources. This approach is suitable for areas with severe water shortages, but it requires high investment and complex treatment processes； 　　2. Another approach is to treat the water to meet non-potable water standards; this is mainly used for water that does not come into direct contact with humans, such as flushing toilets, cleaning floors and vehicles, watering gardens, fire fighting, and general industrial use. This is the usual method for treating treated water. 　　3. In industry, reclaimed water reuse technologies can be employed to reprocess industrial wastewater that meets discharge standards; equipment such as mixed-bed systems is typically used to raise its quality to that of softened water, allowing for industrial recycling and thus helping to save costs and protect the environment. Classification by treatment method: Based on the treatment method, wastewater treatment processes are generally divided into 3 types: 1. Physical treatment methods: Membrane filtration is suitable for situations where water quality varies greatly. 　　The advantages of using this process are a compact design, easy operation, and low sensitivity to load variations. 　　In membrane filtration, under the action of external force, the solution to be separated flows along the surface of the membrane at a certain flow rate; the solvent, low-molecular-weight substances, and inorganic ions in the solution pass through the membrane from the high-pressure side to the low-pressure side and are discharged as filtrate ； The polymers, colloidal particles, and microorganisms in the solution are retained by the ultrafiltration membrane, causing the solution to be concentrated and discharged in a concentrated form. 　　2. Physicochemical methods: Suitable for situations where the quality of wastewater varies significantly. Commonly used methods include: sand filtration, activated carbon adsorption, flotation, coagulation sedimentation, etc. This process is characterized by the use of hollow fiber ultrafilters for treatment; it features advanced technology, a compact design, low space requirements, intermittent operation of the system, and simple management. 　　3. Biological treatment method 　　　Applicable to wastewater with a high content of organic matter. Biological treatment methods such as the activated sludge process, contact oxidation, and biological rotating disk are commonly used. It can be used alone or in combination with several biological treatment methods, such as contact oxidation + biological filter ； Biological filter + activated carbon adsorption ； Processes such as rotary drum and sand filtration. This process has advantages such as strong adaptability to changes in hydraulic load, low sludge generation, and easy maintenance. 　　At present, as some **regions are over-exploiting water resources in an unrestrained manner and lack awareness of environmental protection, both surface water and groundwater have been polluted to varying degrees, thereby limiting the supply of fresh water that originally had good quality ； Secondly, the fresh water sources to be developed are located far from the centralized water supply points, resulting in high one-time investment costs; as a result, such water-scarce areas are unable to expand their water supply capacity. To the extent that it is not suitable for drinking, this gives rise to the concept of reclaimed water. Reclaimed water refers to high-quality wastewater from daily life and industrial activities that does not contain feces or kitchen waste, as well as other types of wastewater without fecal contaminants and domestic sewage. After being collected and treated, this water can be reused for purposes such as cleaning surfaces, watering plants, washing cars, cooling air conditioning systems, flushing toilets, and firefighting – in applications where it does not come into direct contact with humans. Since its water quality parameters are below the standards for drinking water in urban supply systems, but above the standards permitted for discharging wastewater into surface water bodies, that is, its water quality falls between the standards for potable drinking water and those for wastewater discharge, it is referred to as \"reclaimed water\". 　　Technologies for the development and reuse of reclaimed water have seen rapid progress recently, and they are widely applied in countries such as the United States, Japan, India, and the United Kingdom (with Japan being particularly prominent). All of these approaches determine, based on the characteristics of each country and region, wastewater recycling technologies that are suitable for those specific national conditions and capabilities, thereby enabling such technologies to become increasingly refined. In China, this technology has received attention from various levels of ** and relevant departments, who have carried out extensive theoretical research and practical work on the reuse of wastewater in construction. Wastewater recycling projects have been implemented in many cities across the country, such as Shenzhen, Beijing, Qingdao, Tianjin, Taiyuan, etc., with significant results achieved. At present, state-owned industrial enterprises in our country, as well as some private enterprises – such as those that cause significant pollution and consume large amounts of water – have established wastewater recycling systems, thereby contributing to the efforts aimed at achieving low-carbon production and energy conservation. Edit this paragraph: The use of ultra-high flux inorganic ceramic membranes in reclaimed water reuse; The development process of inorganic ceramic membranes. Ceramic membranes, also known as GT membranes, are asymmetric membranes made from inorganic ceramic materials through special manufacturing processes, and they come in tubular or multi-channel forms. The wall of the ceramic membrane tube is covered with numerous micropores. Under pressure, the feed liquid flows inside the membrane tube or on the outside of it; small molecules (or liquids) pass through the membrane, while larger molecules (or solid particles, liquid droplets) are retained by the membrane, thereby achieving solid-liquid separation, concentration, and purification. 　　Organic membranes were among the first to be developed and applied in the field of membrane technology. Easy to manufacture, easy to shape, with good performance and low cost, they have become the most widely used type of microfiltration membrane. However, with the development of membrane separation technology and its applications, increasingly stringent requirements have been placed on the operating conditions of membranes. There is a need to develop membrane solid-liquid separation systems capable of functioning under extreme conditions. Compared to organic membranes, inorganic ceramic membranes possess advantages such as high temperature resistance, good chemical stability, resistance to acids, alkalis, and organic solvents, high mechanical strength, the ability to be backwashed, strong antimicrobial properties, easy cleanability, a narrow pore size distribution, high permeability, high flux, excellent separation performance, and a long service life. 　　There are mainly two obstacles to the application of inorganic ceramic membranes in water treatment: firstly, the manufacturing process is complex, resulting in high costs and expensive prices ； The second issue is membrane flux; only by overcoming membrane fouling and increasing the filtration flux of the membranes can they be truly applied across various fields of water treatment. 　　The DEAR inorganic ceramic membrane system developed by the environmental technology company in Seattle, USA, is based on research into conventional ceramic membranes; through high-tech modifications, it reduces membrane fouling and increases membrane flux. It effectively overcomes the main problems associated with the use of inorganic ceramic membranes in water treatment, thereby making it possible to utilize such membranes for this purpose. Features: (1) Unique double-layer membrane structure: The DEAR inorganic ceramic membrane system for membrane filtration prepares TiO2 sol on the surface of the membrane layer using the sol-gel method, and applies nano-TiO2 photocatalytic material to the ceramic membrane via the impregnation and pulling method. This gives the surface of the ceramic membrane a \"self-cleaning\" function, which reduces the accumulation of organic substances on the membrane surface and prevents clogging. As a result, membrane contamination is reduced, while the strength of the ceramic membrane tubes and the membrane filtration flux are increased, along with improved stability of the membrane flux ； Structure of Al2O3—ZrO2 composite membrane: It improves the mechanical properties of the membrane tubes. Due to inherent defects in the material itself or various practical issues that arise during the manufacturing process, single inorganic membrane materials generally cannot meet practical requirements; as a result, research on inorganic-supported composite separation membranes has progressed rapidly. The DEAR inorganic ceramic membrane utilizes an integral composite technology, and the Al2O3—ZrO2 composite membrane is prepared through the sol-gel method. Since ZrO2-containing materials possess better mechanical strength, chemical durability, and resistance to alkali corrosion compared to materials such as Al2O3, SiO2, and TiO2, the DEAR® inorganic ceramic membrane has higher mechanical strength and thermal stability. Moreover, the composite membrane exhibits a narrow pore size distribution with a single peak. 　　(2) Online backflushing is achievable, resulting in stable membrane flux: Thanks to the unique structure and mechanical properties of the composite ceramic membrane, it can effectively withstand backpressure below 0.4 MPa, allowing for online backflushing and thus a stable membrane flux. This overcomes the problems associated with inorganic membrane systems in water treatment, such as high costs, susceptibility to contamination, low membrane flux, and large equipment size, making it possible to utilize inorganic ceramic membrane systems in water treatment applications. The DEAR inorganic ceramic membrane for wastewater treatment is designed specifically for this purpose. Its main advantages include a high flux rate – the operating flux is 10–100 times higher than that of organic membranes, and 50–10 times higher than that of ordinary porous ceramic membranes. It also features high mechanical strength, resistance to contamination, and the ability to undergo online backwashing. Key technical parameters: Film thickness: 50–60 μm; film pore size: 0.01–0.5 μm ； 　　Pore density: 44–46% ； 　　Filter pressure: 1.0 Mpa, backwash pressure: below 0.4 Mpa ； 　　Membrane material: double-layer membrane, outer layer TiO2 ； Main application areas of Al2O3—ZrO2 composite membrane ceramic membranes: reclaimed water reuse ； 　　Detoxification treatment of raw water in industrial aquaculture ； 　　Side filtration systems for large-scale cooling circulating water in power plants, chemical plants, etc ； 　　Reuse treatment of oilfield produced water ； 　　Treatment of steel rolling emulsion waste liquid ； 　　Regeneration treatment of metal surface cleaning solutions. Edit the water quality requirements for recycled water in this section. The quality of recycled water must meet the following conditions: 1. It must satisfy hygiene requirements. Its key indicators include the number of E. coli, total bacterial count, residual chlorine level, suspended solids, COD, BOD5, phosphides, etc. 　　2. Meet people’s sensory requirements, that is, without any unpleasant sensations. Its key measurement indicators include turbidity, color, odor, etc. 　　3. Meet the requirements regarding the design of the equipment, that is, the water quality should not cause severe corrosion or scaling of the equipment and pipelines. Its measurement indicators include pH value, hardness, evaporation residue, soluble substances, etc. 　　In recent years, China has conducted increasingly in-depth research on reclaimed water. To ensure the safe, reliable, and rational use of reclaimed water as water for miscellaneous domestic purposes, the \"Water Quality Standards for Miscellaneous Domestic Water\" (CJ25·1–89) were officially issued in 1989. Edit the classification of water reuse systems in this paragraph. Water treatment and reuse systems can generally be divided into the following four categories based on the scope and scale of their supply: Water reuse systems in individual buildings located in areas with well-developed drainage facilities. In such systems, the water source for reuse comes from non-potable water and high-quality wastewater within the same system. This wastewater is collected and processed before being used for flushing toilets, cleaning vehicles, and maintaining landscaping within the building. Its treatment facilities can be located either inside this building or nearby the exterior, depending on the conditions. For example, the water treatment equipment in the Beijing Xinhuanshou Hotel is located in the basement. Reuse systems for wastewater in individual buildings in areas with inadequate drainage facilities: In regions where the urban drainage system is insufficient and the water treatment facilities do not meet secondary treatment standards, the reuse of wastewater can help reduce the recontamination of local rivers by sewage. In this system, the water source is taken from the building’s wastewater treatment tanks (such as sedimentation tanks, septic tanks, oil removal tanks, etc.), and the water in these tanks constitutes the total domestic wastewater. The processing facilities of this system can be installed indoors or outdoors depending on the conditions. Water reuse system in small-scale building complexes: The source of water for this system is the wastewater generated by various buildings within the complex. Such systems can be used in residential buildings, schools, and compound areas of government agencies and organizations. Its treatment facilities are located within the community. Water reuse systems in regional building complexes: This system features secondary wastewater treatment facilities in small areas. The water source for use in these areas can be water treated by urban wastewater treatment plants or industrial wastewater; this water is then transported to regional water treatment stations, where it undergoes further treatment before being used for tasks such as flushing toilets and watering landscaping within the buildings. Edit this section: Introduction to water reuse technology. Its characteristic lies in the use of various physical, chemical, and biological methods to treat industrial wastewater to varying degrees, so as to achieve a water quality that meets the requirements of the processes involved; thereafter, this treated water is reused in those processes, thereby helping to conserve water resources and reduce environmental pollution. The following introduces the two most common reuse technologies: (1) Cooling water technology. Saving cooling water is the main way to conserve water in industry. 1. Replacing direct cooling with indirect cooling: During the cooling process, especially in the chemical industry, using direct cooling methods often results in the cooling water containing a large amount of pollutants, rendering it unsuitable for reuse. By switching to indirect cooling, this drawback can be overcome. 　　2. Reduce cooling requirements and lower the consumption of cooling water. 　　3. Non-water cooling is used. 　　In certain manufacturing processes, air cooling or oil cooling is used to achieve cooling purposes. 　　4. Use artificial cooling sources or seawater as cooling water to reduce the consumption of groundwater or fresh water. 　　5. Make rational use of cooling water. 　　Used cooling water can be cooled to a certain extent and reused, or it can be used in other applications with lower requirements regarding water quality and temperature after being used as cooling water for the first time. 　　When adopting this method, it is necessary to ensure close coordination among the water supply systems in various workshops, strengthen the management of cooling water, and prevent issues in one area from affecting the water supply to other workshops. 　　6. Recycling of cooling water 　This cooling water utilization technique involves using hot water generated by coolers, and then reducing its temperature through cooling systems to the level suitable for reuse, thereby enabling recycling. 　 　　When cooling water is reused, attention should be paid to issues such as bacterial growth in the water, scale formation, equipment corrosion, and changes in water pressure and flow rate. (II) Multiple uses of water or reuse of treated wastewater: Due to the varying water quality standards required at different stages of the production process, the water from certain stages is appropriately treated and then reused or utilized in other stages where lower water quality requirements apply. In order to achieve water conservation. For example, clean water can be used as cooling water first, and then sent to a water treatment plant where it is softened before being used as water for boilers. Treated municipal wastewater is used for production, daily life, etc. Examples of reclaimed water reuse technology Below is a brief introduction to reclaimed water in daily life. 　　In daily life, water refers mainly to treated domestic wastewater that has met the required standards; it is used for various purposes such as flushing toilets, watering gardens and landscapes, spraying roads, and replenishing cooling water. The quality of reclaimed water should meet the \"Quality Standards for Miscellaneous Domestic Water.\" 　　1. Reclaimed water source: When choosing reclaimed water, high-quality mixed wastewater should be given priority. The order of selection is generally as follows: A. Cooling water; B. Shower wastewater; C. Washing wastewater; D. Laundry wastewater; E. Kitchen wastewater; F. Toilet wastewater.
2. Treatment process: When high-quality mixed wastewater and ordinary mixed wastewater are used as sources of reclaimed water, a treatment process based primarily on physical and chemical methods can be employed, or a process that combines biological treatment with physical and chemical methods can also be used. 　　When domestic wastewater is used as a source of reclaimed water, a two-stage biological treatment process, or a treatment process that combines biological treatment with physical and chemical treatment, can be employed. 　　3. Regulations on the design and construction of reclaimed water systems: All construction projects shall be designed to include reclaimed water facilities in accordance with the relevant regulations. Construction projects falling under the following categories are required to have such facilities designed and installed: A) Buildings such as hotels, restaurants, shops, apartments, comprehensive service buildings, and high-rise residential buildings with a floor area of over 20,000 square meters. B. The building area of government agencies, research institutions, colleges and universities, as well as large-scale comprehensive cultural and sports facilities is over 30,000 square meters. 　　C. The planned population in residential communities is over 30,000 (or the reuse volume of reclaimed water is over 750 cubic meters per day). 　　The management of reclaimed water facilities is carried out in accordance with the Interim Measures for the Management of Urban Reclaimed Water Facilities issued by the Ministry of Construction, while the design of such facilities follows the Code for Design of Building Reclaimed Water Systems prepared by the China Association for Standardization of Engineering Construction.