On October 24, 2021, the State Council issued the "Action Plan for Carbon Peaking by 2030" (Guo Fa [2021] No. 23). "Ten Actions for Carbon Peaking" in all aspects, and carry out the work of "Carbon Peaking" as a whole. One of the goals clearly stated in the document is to "basically form a low-carbon development model". The "Implementation Plan for Synergistic Efficiency of Pollution Reduction and Carbon Reduction" (Huan Comprehensive [2022] No. 42) issued on June 13, 2022 clarifies the contribution of sewage resource utilization to carbon reduction, and encourages sewage treatment plants to actively implement energy saving, consumption reduction, Utilization of clean energy, promoting carbon emission calculations for urban sewage treatment and resource utilization, reducing energy consumption of sewage treatment facilities and optimizing carbon emission management. For my country's urban water system, with population growth and improvement of living standards, both water consumption and sewage volume will continue to increase. In addition, due to the increase in extreme weather, the burden of urban stormwater control and transfer is also increasing. Only by reducing the carbon emission intensity of the urban water system through the implementation of carbon emission reduction, can the "carbon peak" goal be achieved under the condition of continuous increase in the amount of treated water, that is, carbon emission accounting is not the goal and the end, but carbon emission accounting is used as a tool. Guide the urban water system to gradually integrate the concept of pollution reduction and carbon reduction, and promote the sustainable and optimized development of the urban water system.
This article is divided into three parts to describe the emission reduction path
1. Water supply and reclaimed water system
2. Sewage system
3. Rainwater system
1.1 Carbon emission reduction path analysis
Based on the carbon emission accounting of the water supply system and literature research and analysis, the greenhouse gas emitted by the operation and maintenance of the water supply system mainly comes from the consumption of electric energy, and other possible emission sources include the consumption of various materials and chemicals, which are all classified as indirect carbon emissions. Among them, nearly 100% of the greenhouse gases in long-distance water transmission facilities, water intake facilities, and water transmission and distribution pipe networks come from the power consumption of lifting water pumps; while water supply treatment plants that use groundwater and surface water as water sources and seawater desalination plants that use seawater as water sources (reverse Infiltration and other processes) in the total greenhouse gas emissions, electricity consumption also accounted for 95%, 82% and 98% respectively. Therefore, the key to formulating carbon emission reduction plans for water supply systems is to improve management levels and optimize treatment technologies to reduce power consumption. From the perspective of the 4 types of action strategies in the carbon emission reduction plan (Figure 7-4), the locations where the water supply system can be optimized for emission reduction and the available emission reduction technical solutions are summarized, as shown in Figure 1-1.
Figure 1-1 Roadmap for Carbon Emission Reduction in Water Supply System
In terms of source control, measures such as water conservation by users, enhanced water consumption measurement, gradient pricing, and water source protection can reduce water demand and reduce the workload (water volume and pollutant treatment) of water intake facilities, water transmission and distribution network, and water supply treatment. thereby reducing greenhouse gas emissions. In fact, the reclaimed water system can equally reduce the workload of long-distance water delivery and water intake facilities by reusing sewage to irrigate crops, water green areas, or flush toilets. In fact, it is a source control at the system level. carbon reduction strategies.
In terms of process optimization, water supply system operators can also take a variety of technical measures to reduce carbon emissions, focusing on the application of technologies such as source efficiency package network technology and filter backwash optimization.
In terms of process upgrading, it mainly refers to the water supply system information water supply mode and the development of advanced treatment process technology, such as regional water pressure control mode, as well as innovative technologies such as low-energy seawater treatment, which can significantly reduce energy consumption and carbon emissions. emission level.
In terms of low-carbon energy, the water supply system also has action strategies that can be implemented, including heat energy extraction, potential energy recovery, etc. However, the formulation and implementation of carbon plans that need to be paid attention to should avoid affecting water safety (water quality) and water comfort (water pressure). The content and implementation characteristics of the actionable strategies are shown in Table 1-2.
Technical Action Strategy for Carbon Emission Reduction in Water Supply System
1.2 Carbon reduction path
1.2.1 Pipe network leakage detection
According to relevant standards and regulations, the average leakage rate of urban water supply pipe network should not be higher than 10%. According to the "China Urban and Rural Construction Statistical Yearbook" (2020), the comprehensive leakage rate of water supply pipe networks in cities and counties across the country in 2020 is 13.26%, and the leakage rate in some cities even exceeds 25%. This not only caused a huge waste of water resources, but also increased energy consumption and carbon emissions of the water supply system. Undoubtedly, the implementation of effective pipeline network leakage detection technology will help to monitor leakage accidents in a timely manner, locate leakage points and repair them in time, thereby reducing the carbon emission intensity of water supply systems by improving water resource utilization efficiency. In fact, the exploration and development of pipeline network leakage technology has always been an important topic in the water industry, and it has been applied in practice. Carry out real-time monitoring and timely repair of water pressure, water volume and water leakage in the water transmission and distribution pipeline network, and complete the synchronous transmission and feedback of the current operation status and real-time data. Engineering experience shows that 6 water distribution systems have been built through detection and control methods such as intelligent flow detection, leakage sensing and repair, and 1.2×105m3 water has been supplied to 150,000 users. In 12 years, a total of 4.7×104tCO2-eq emissions have been reduced, avoiding 2.0 ×108m3 water leakage. According to the intelligent monitoring and feedback of pipeline network leakage, timely implement measures such as sub-regional supply pressure control and renovation of old facilities, and accelerate the intelligent construction of water supply pipeline network, so as to promote the pilot work of national construction of water supply pipeline network leakage control in 2025.
1.2.1 New seawater desalination technology
As a non-traditional method, seawaterization can solve the problem of water shortage. However, whether it is distillation or process, fossil fuels such as coal or carbon are often required in the production process. Some new marine technology developments can reduce the total carbon emissions. Among them, deep-sea technology and high-efficiency absorption steam The compression system (AB) process has obvious advantages in carbon emission reduction. The former installs the seawater desalination device on the seabed and uses the natural hydrostatic pressure as the "pre-membrane pressure. The desalination unit establishes a connection with the coast through a pipe gallery. desalinated water, which can reduce indirect carbon emissions by more than 40% in the operation and maintenance phase; the latter reduces the need for externally heated steam by reusing the final steam generated, thereby reducing coal consumption and reducing the indirect carbon emissions in the operation and maintenance phase by about 73%. indirect carbon emissions.
1.3 Carbon Replacement Pathway
1.3.1 Water energy recovery technology
As an energy carrier, water contains various forms of abundant energy, including potential energy from pressurization and heat energy contained in itself. If the potential can be recovered, it can feed back the energy consumption of the water supply system, thereby reducing the consumption of fossil fuels and achieving the purpose of carbon replacement and emission reduction. The potential energy of water in the pipe network can be recovered by micro-turbine power generation technology. Under the premise of not increasing the loss of water head, a micro-turbine is installed in the water flow pipeline to generate power. The annual power generation can reach up to millions of kWh, which can be used for system intelligent monitoring Alternative power source for the device.
In addition, because the temperature of the water in the pipe network is low and relatively constant, it can undertake excessive heat energy in the room, and has great potential for building cooling, which can be fully realized with the help of water source heat pump technology. Moreover, urban buildings are connected to the water transmission and distribution network, and can guarantee 24h supply, ensuring the stability as a cooling source. With the help of water source heat pump technology, it should be an effective means to increase the value of water resources and contribute to the carbon neutrality of urban water system by utilizing the water exchange cooling capacity of water treatment plants for cooling in summer. The cold energy exchanged belongs to clean energy, and the output to the society can form a negative carbon effect.
1.3.2 New seawater desalination technology
Based on the principle of carbon replacement, some new seawater desalination technologies using clean energy have been developed to replace the original fossil fuels and reduce carbon emissions. For example, large-scale concentrating solar seawater desalination technology builds a huge glass dome to heat seawater by concentrating light to make the seawater boil, and it is equipped with energy storage equipment (over 4GW energy storage) for night or cloudy production. The huge glass dome is equipped with heat-conducting steel rails, which makes the heat distribution more uniform and improves the utilization rate of heat energy. Its operation and maintenance do not require additional energy input at all, so it will not cause carbon emissions.