01 What changes will carbon neutrality bring?

From the current situation in China, the power generation, industrial and transportation sectors are the main sources of carbon emissions, and the carbon emissions of agriculture, residential, commercial and public services are relatively low.

On the industrial side, energy-intensive industries such as the energy processing industry, the steel industry, and the chemical raw material manufacturing industry are not only key industries for coal consumption, but also major industries for carbon dioxide emissions. Therefore, with the full implementation of the carbon neutral strategy, China's energy system will undergo disruptive changes in the next 40 years.

At the same time, due to the effects of the industrial chain, the transformation of the energy system will surely promote all-round changes in the national economy. Li Junfeng, executive director of the China Energy Research Society and a researcher at the National Center for Climate Change Strategy Research and International Cooperation, pointed out that "carbon neutrality is not just about energy, it is related to all aspects of the industrial chain. The goal of carbon neutrality will have a profound impact. One-step industrial chain reconstruction, reorganization and new international standards."

To achieve a carbon peak before 2030, this requires some regions and some industries to take the lead. According to my country's carbon peak and carbon neutral target nodes, the Ministry of Industry and Information Technology will implement industrial low-carbon actions and green manufacturing projects this year, and formulate carbon peak action plans and roadmaps for key industries such as steel and cement. The "14th Five-Year Plan" that is being formulated also regards carbon peaking and carbon neutrality as the main targets in the battle for pollution prevention and control. It is expected that special plans for departments, localities and industries will be issued this autumn and winter.

From January 1, 2021, the first compliance cycle of the national carbon market (as of December 31 this year) was officially launched, involving 2,225 key emission units in the power generation industry. This is the first time that my country has consolidated the responsibility for carbon dioxide control and emissions from the national level to enterprises, and promoted the upgrading of industrial technology through the market force mechanism. The prelude to the change has been quietly opened!

02The sewage treatment industry is a big energy consumer

In contrast, although the energy consumption of the sewage treatment industry is not as high as power generation, steel, chemical and other industries, the total energy consumption is not small, and it is also a large energy consumer.

According to statistics, the electricity consumption of sewage treatment plants in my country in 2014 accounted for 0.26% of the country's total electricity consumption, including industrial wastewater treatment and sludge treatment, the proportion will exceed 2%. There are more than 16,000 sewage treatment plants in the United States, and electricity consumption accounts for 1% of the total electricity consumption of the whole society. In Denmark, water and wastewater treatment processes consume 25% to 40% of municipal electricity.

In addition, sewage treatment requires a large amount of fuel and chemicals, which indirectly emits a large amount of greenhouse gases, and the treatment process itself will also directly emit greenhouse gases. United Nations data shows that the global carbon emissions of sewage treatment and other water treatment industries account for about 2% of global carbon emissions. Approximately 2% of the US energy consumption in 2017 was used in drinking water and sewage treatment systems, generating approximately 41 million tons of greenhouse gases.

In addition, water pumps are also one of the main sources of energy consumption for sewage treatment. Grundfos data shows that the energy consumed by water pumps accounts for 10% of the energy consumption of all water-related facilities.

From the perspective of energy conversion, the essence of traditional sewage treatment mode is to exchange energy for water quality. In order to reduce water pollution, we use a lot of electricity, which indirectly generates a large amount of carbon dioxide emissions, which has a negative impact on the global ecological environment.

Therefore, in order to reduce carbon emissions, reducing the energy and material consumption of sewage treatment is an inevitable goal of industry upgrading. At present, many countries in the world have issued carbon neutral technology roadmaps for wastewater treatment plants. The United States has proposed that all wastewater treatment plants should be carbon neutral by 2030.

However, as an important public utility, China's sewage treatment rate has not yet reached 100%, and reducing water pollution is still the top priority of ecological and environmental protection. It is foreseeable that the sewage treatment industry does not yet have the objective conditions to undertake large-scale emission reduction tasks in the short term.

However, in terms of improving the core competitiveness of enterprises, green and low-carbon development is also the way to go. At the same time, as a policy-driven industry, if companies can initiate low-carbon reforms earlier, they will surely win greater initiative and broader development space.

03How to achieve green and low-carbon development?

So, how does the sewage treatment industry achieve green and low-carbon development? Generally speaking, it can be considered from two aspects: increasing revenue and reducing expenditure. To sort out the advanced experience at home and abroad, we can start from the following aspects.

1 Optimize the process to recover organic energy

First of all, to achieve energy self-sufficiency through open source is to fundamentally solve the problem of green and low-carbon development. According to calculations, the energy contained in sewage is 9-10 times as much as the energy consumed by sewage treatment itself. Carbon neutrality can be achieved by optimizing the sewage treatment process, recovering organic energy, and using biogas to generate electricity.

The Strass Sewage Treatment Plant in Austria continued to optimize and improve the process. As early as 2005, the production capacity was greater than the energy consumption (108% energy self-sufficiency rate), and it has now reached 200% energy self-sufficiency rate, exceeding the standard to achieve carbon neutrality.

The U.S. Sheboygan Sewage Treatment Plant uses high-concentration food waste and sludge anaerobic co-digestion of methane for cogeneration, and at the same time adopts energy-saving measures to achieve a ratio of electricity to electricity consumption of 90% to 115%. Approaching the goal of carbon neutrality.

In the field of sludge disposal, the domestic Xiaohongmen and Gaobeidian sludge treatment centers have been successfully operated. The sludge gas production rate has exceeded the expected target. In addition to meeting the needs of thermal hydrolysis energy balance, there is a margin. This fully shows that the advanced anaerobic digestion technology of sludge is relatively reliable and stable, which not only explores new ideas for domestic sludge treatment, but also provides strong support for achieving carbon neutrality.

Of course, wastewater treatment process optimization is a long-term process. The strass sewage treatment plant in Austria has spent more than ten years continuously optimizing the treatment process to reach the current treatment level.

In addition, the influent COD concentration of urban sewage treatment plants in my country is low, only 40%-70% of those in European and American countries, resulting in insufficient carbon sources. This requires the development of a sewage treatment process suitable for China's national conditions in accordance with local conditions.

2 China's sewage treatment concept plant practice

While in-depth research and understanding of the concepts, processes, technologies and engineering practices of advanced foreign sewage treatment plants, Chinese academia and industry are also actively exploring new sewage treatment models.

In 2014, six experts including Qu Jiuhui, an academician of the Chinese Academy of Engineering, put forward the idea of ​​"building a future-oriented China sewage treatment concept plant". In 2018, Henan Water Conservancy Investment Group and Zhongchi Water Company built the third sewage treatment plant in Shangqiu Sui County, Henan Province based on the early version of the concept plant.

The Suixian project comprehensively uses various materials such as straw, livestock manure, aquatic plants and sludge for collaborative high-dry anaerobic digestion, and adopts DANAS dry anaerobic fermentation technology to significantly improve the efficiency of organic matter treatment and realize a virtuous cycle of substances And resource-based operations. The biogas produced is used for power generation, which can meet 20-30% of the energy consumption of the plant.

At the same time, to reduce the difficulty of sludge treatment, the organic fertilizer produced after sludge treatment has been used for experimental planting of crops in the factory. The project has been widely recognized, and local residents and the government can feel the charm of innovative development and green development.

If the Suixian project is a version 1.0 concept factory, then the Jiangsu Yixing Urban Water Resources Concept Factory, which started construction in April 2020, is version 2.0. This project is the first sewage treatment plant to fully follow the concept of the concept plant. In addition to the basic functions of pollutant reduction, it also has new functions such as urban energy plants, water source plants, and fertilizer plants. It will further develop into an all-round integration and mutual benefit between urban and rural areas. Symbiotic new environmental infrastructure. The project was completed in the middle of this year. If it can continue to operate stably, it will have a profound impact on the green and low-carbon development and industrial upgrading of China's sewage treatment industry.

3 Transform and upgrade the aeration system

Secondly, actively adopting various measures to reduce energy consumption according to local conditions is also an important part of green and low-carbon development.

Data shows that the power consumption per unit volume of sewage treatment in my country's sewage treatment plants is about 0.15 to 0.28 kW·h/m3. Among them, the proportion of aeration blower power consumption is 56.2%. Although different treatment processes have different energy consumption, it is a fact that the overall energy consumption of the aeration system accounts for the largest proportion. Therefore, the key point of energy saving and consumption reduction in sewage treatment plants is to upgrade the aeration system.

The core of energy saving in aeration system is to provide dissolved oxygen required by microorganisms on demand under the premise of ensuring that the effluent reaches the standard, so as to achieve a balance between supply and demand and avoid waste of aeration energy consumption. This requires precise control of the activity process of microorganisms and precise control of the operation process of the blower. It is necessary to prevent both over-aeration and under-aeration. This puts high demands on the stability, reliability and accuracy of hardware equipment and control systems.

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According to a domestic enterprise that has been engaged in the research of energy saving and consumption reduction technology for aeration systems for many years, in order to achieve precise control of aeration systems, there are not only requirements for technology, but also for equipment selection and brand, and even for flow meters. There are also strict requirements for the installation location of metering equipment such as liquid level gauges. In general, the transformation and upgrading of aeration system requires comprehensive consideration of various elements from a system perspective, which is a complex systematic project.

There are cases in China that show that through energy-saving renovation of the blower, the average daily power consumption has been reduced from 32990 to 29835, a reduction of 3155, a drop of 11.4%. A rough estimate can reduce carbon dioxide emissions by 1,148 tons per year. For small and medium-sized sewage treatment plants, at least hundreds of thousands or even millions of electricity bills can be saved every year. At the same time, the unit total nitrogen was reduced by 10.8%, and the unit ammonia nitrogen was reduced by 13.1%.

4 Optimize raw material input links

Sewage treatment processes are diverse, but the essence is to remove pollutants in water through biochemical reactions. Therefore, it is necessary to add a carbon source and a variety of chemicals in the treatment process. These raw materials consume energy in the process of production and transportation, and also consume a certain amount of energy in the process of adding. Therefore, optimizing the feeding process will help save energy and reduce consumption and reduce carbon emissions.

How to optimize the input of raw materials? Currently, there are two main ways in the market.

The first type is to upgrade the configuration of the dosing system, from the commonly used frequency conversion metering pump to a digital pump, and the amount of dosing is reduced to varying degrees.

The second type is to use AI technology to perform big data analysis on sewage water volume, water quality and other parameters and dosing system operating data to form an optimal algorithm model to achieve fine control of the dosing system and effectively reduce drug consumption And the energy consumption of equipment operation.

5 Optimize the water delivery performance of the drainage network

In the urban sewage treatment system, the collection and transportation of sewage involves large-scale pipe network laying and long-distance transportation, which requires a lot of energy consumption to support daily operation and maintenance. In order to reduce this part of the energy consumption as much as possible, various measures must be taken to optimize the water delivery performance of the pipe network.

Among them, the most basic is the transformation and upgrading of the pipeline network operation and management model. The key tasks include leakage point survey, location, repair and prevention of potential leakage risks. Realize real-time monitoring of the operating status of the drainage network, and can quickly analyze whether leakage, blockage, and severity, specific locations, etc. have occurred, so as to provide accurate support for rapid maintenance of management personnel.

The most fundamental solution to improve the water delivery performance of the drainage pipe network is to increase the coverage of the drainage pipe network, realize 100% collection of sewage, and carry out rain and sewage diversion reforms to greatly increase the carbon-nitrogen ratio of the sewage treatment plant influent. In this way, the problem of insufficient carbon sources can be solved, the organic matter-methane conversion rate of sewage treatment plants can be effectively improved, and the sewage treatment plants can be turned into power plants, which can fundamentally solve the problem of energy consumption and achieve carbon neutrality.

6 Drainage pumping station energy saving and consumption reduction

The drainage pumping station is also a big energy consumer. Data shows that drainage pumping stations account for 35% of the total energy consumption of urban water services. Therefore, upgrading the drainage pumping station or adopting an intelligent operation mode can effectively reduce energy consumption.

At present, there are two main methods. One is to use frequency conversion technology to transform old drainage pumping stations, or to directly use digital pumps and other new equipment and facilities in new projects to reduce the energy consumption of pumping stations.

Secondly, from the perspective of the system, optimize the operation mode of the drainage pumping station from a higher level. On this basis, the Internet of Things and mobile Internet technologies are used to create an intelligent management platform to realize remote control, centralized management and digital operation of drainage pumping stations to achieve the purpose of energy saving and consumption reduction.

04 Summary

In general, achieving carbon neutrality in the wastewater treatment industry is a long-term systematic project. Only from the perspective of the sewage treatment plant industry, systematic planning needs to be carried out from the entire process of "user control-source separation-pipe network storage-purification treatment". In this process, relevant government departments and enterprises are required to comprehensively upgrade their management and operation models, from management-driven to data-driven, build a new digital management model, and realize the intelligent upgrade of the entire operation model.

To solve this problem fundamentally, we need to step out of the sewage treatment industry and take comprehensive considerations from the perspective of ecological civilization construction, urban-rural integration development, sewage recycling, energy self-sufficiency, and environmental friendliness. Top-level planning, system design and overall planning are carried out at different levels of "face-body". This is not only an update of the entire industry's technology and ideas, but also a revolution in the thinking and cognition of the entire society.

This will be a long and tortuous process. What is gratifying is that the proposal and implementation of the wastewater treatment concept plant has taken a critical first step. We have reason to believe that the Chinese wastewater treatment industry will soon make positive contributions to the carbon neutral strategy.