How to achieve green and low-carbon development of sewage treatment?



Carbon neutrality means the total amount of carbon dioxide emissions directly or indirectly generated by an enterprise, group or individual over a certain period of time, offset by afforestation, energy conservation and emissions reduction to achieve "zero emissions".

01 What changes will carbon neutrality make?

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

At the industrial end, energy processing industry, steel industry and chemical raw material manufacturing and other related high-energy industries are not only the key industries of coal consumption, but also the main industries of carbon dioxide emissions.

As a result, China's energy system will be revolutionized over the next 40 years as its carbon-neutral strategy is in full swing.

At the same time, due to the industrial chain effect, the transformation of the energy system will certainly promote the all-round change of the national economy.

Li Junfeng, executive director of the China Energy Research Society and researcher of the National Center for Strategic Research and International Cooperation on Climate Change, pointed out that "carbon neutrality is not only about energy, it is related to all aspects of the industrial chain." The goal of carbon neutrality will profoundly influence the restructuring and reorganization of the industrial chain and the new international standards."

Achieving carbon peak by 2030 will require some regions and some industries to peak first.

According to China's carbon peak, carbon neutral target node, the Ministry of Industry and Information Technology this year will implement industrial low-carbon action and green manufacturing engineering, and formulate steel, cement and other key industries carbon peak action plan and road map.

The 14th Five-Year Plan, which is being formulated, also regards carbon peaking and carbon neutrality as the main targets of the battle against pollution. It is expected that special plans for departments, localities and industries will be introduced this autumn and winter.

From January 1, 2021, the first compliance cycle of the national carbon market (until December 31, 2021) was officially launched, involving 2,225 key emission units in the power generation industry.

This is the first time that China has consolidated the responsibility for carbon dioxide control and emission to enterprises at the national level, and promoted industrial technology upgrading through the market forcing mechanism. The prelude to change has quietly begun!

02 Sewage treatment industry is a big energy consumer

In contrast, although the energy consumption of the sewage treatment industry is not as high as that of the 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, in 2014, China's sewage treatment plant power consumption accounted for 0.26% of the country's total power consumption, including industrial wastewater treatment and sludge treatment, the proportion will exceed 2%.

There are more than 16,000 wastewater treatment plants in the United States, which account for 1% of society's total electricity consumption. In Denmark, water and wastewater treatment processes consume 25 to 40 percent of municipal electricity.

In addition, sewage treatment needs to consume a lot of fuel and chemicals, indirectly emit a lot of greenhouse gases, the treatment process itself will also directly emit greenhouse gases.

According to United Nations data, the global water treatment industry, such as sewage treatment, accounts for about 2% of global carbon emissions. About 2 percent of U.S. energy consumption in 2017 was used in drinking water and wastewater treatment systems, generating about 41 million tons of greenhouse gases.

In addition, the pump is also one of the main sources of energy consumption for sewage treatment. According to Grundfos, pumps account for 10% of all water-related energy consumption.

From the perspective of energy conversion, the traditional sewage treatment model is essentially energy consumption in exchange for water quality. In order to reduce water pollution, we use a lot of electricity, which indirectly produces a lot of carbon dioxide emissions, causing a negative impact on the global ecological environment.

Therefore, in order to reduce carbon emissions, reducing energy consumption and material consumption of sewage treatment is the inevitable goal of industry upgrading.

At present, many countries in the world have issued a carbon neutral technology roadmap for sewage plants, and the United States has proposed that all sewage treatment plants should achieve carbon neutrality by 2030.

However, as an important public utility, China's sewage treatment rate has not reached 100%, and reducing water pollution is still the top priority of ecological and environmental protection work.

It can be predicted that the sewage treatment industry does not have the objective conditions to undertake large-scale emission reduction tasks in the short term.

However, from the level of enhancing 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 enterprises can start low-carbon change early, they will win greater initiative and broader space for development.

03 How to achieve green and low-carbon development?

So, how can the sewage treatment industry achieve green and low-carbon development? In general, it can be considered from the two aspects of open source and throttle. Combing the advanced experience at home and abroad can be specifically started 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. It is estimated that the energy contained in sewage is 9-10 times as much as the energy consumed by the sewage treatment itself. Carbon neutrality can be achieved by optimizing wastewater treatment process, recovering organic energy and utilizing biogas thermal cogeneration.

Austria's Strass sewage treatment plant continues to optimize and improve the process, as early as 2005 to achieve production capacity greater than energy consumption (108% energy self-sufficiency rate), has reached 200% energy self-sufficiency rate, exceeding the standard to achieve carbon neutrality.

The Sheboygan Wastewater Treatment plant in the United States uses methane produced by anaerobic co-digestion of high-concentration food waste and sludge for cogeneration, and adopts energy-saving measures to achieve a ratio of 90% to 115% of electricity consumption, which has approached the goal of carbon neutrality.

In the field of sludge disposal, the domestic Xiaohongmen and Gaobeidian sludge treatment centers have successfully operated, and the sludge gas production rate has exceeded the expected target, in addition to meeting the needs of thermal hydrolysis energy balance, there is still a surplus.

This fully shows that the advanced anaerobic digestion technology of sludge has been 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 wastewater treatment plant in Austria has spent more than 10 years continuously optimizing the treatment process to reach the current level of treatment.

In addition, the influent COD concentration of China's urban sewage treatment plant is low, only 40%-70% of that of European and American countries, resulting in insufficient carbon sources. This requires that the sewage treatment process suitable for China's national conditions must be developed according to local conditions.

2. China's sewage treatment concept plant practice

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

In 2014, Qu Jiuhui, academician of the Chinese Academy of Engineering, and six other experts proposed the idea of "building a future-oriented Chinese sewage treatment concept plant". In 2018, Henan Water Resources Investment Group and Zhongshou Water Company built the third sewage treatment plant in Suixian County, Shangqiu, Henan, based on the earlier version of the concept plant.

Suixian project comprehensively uses straw, livestock manure, aquatic grass and sludge and other materials for collaborative high-dry anaerobic digestion. DANAS dry anaerobic fermentation technology is adopted to significantly improve the efficiency of organic matter treatment and realize the virtuous circulation and resource operation of materials. The biogas produced is used to generate electricity, which can meet 20-30% of the plant's energy consumption.

At the same time, the difficulty of sludge treatment is reduced, and the organic fertilizer produced after sludge treatment has been used for experimental crop planting in the factory.

The project has been widely recognized and has made local residents and the government feel the charm of innovative and green development.

If the Suixian project is the 1.0 version of the concept plant, then the Jiangsu Yixing city water resources concept plant, which will be started in April 2020, is the 2.0 version.

The project is the first sewage treatment plant to fully follow the concept of the concept plant. In addition to the basic function of pollutant reduction, it also has new functions such as urban energy plant, water plant and fertilizer plant, and will further develop into a new environmental infrastructure with all-round integration and mutual benefit between urban and rural areas.

The project was completed in the middle of this year, and if it can continue to operate steadily, it will have a far-reaching impact on the green and low-carbon development and industrial upgrading of China's sewage treatment industry.

3. Upgrade the aeration system

Secondly, taking various measures to achieve energy throttling according to local conditions is also an important part of green and low-carbon development.

Data show that the power consumption per unit volume of sewage treatment plant in China is about 0.15 ~ 0.28kW·h/m3.

Among them, the proportion of power consumption of aeration blower is 56.2%. Although the energy consumption of different treatment processes is different, it is a fact that the overall energy consumption of the aeration system is the largest. Therefore, the key point of energy saving and consumption reduction in sewage treatment plants is to upgrade the aeration system.

The core of the energy saving of 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 the balance between supply and demand and avoid the waste of aeration energy consumption.

This requires accurate control of the microbial activity process, while accurately controlling the operation process of the blower. It is necessary to prevent both over-aeration and under-aeration. This puts forward high requirements for the stability, reliability and accuracy of hardware equipment and control systems.

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 accurate control of aeration systems, there are not only technical requirements, but also requirements for the selection and brand of equipment, and even strict requirements for the installation location of metering equipment such as flow meters and liquid level meters.

In general, upgrading the aeration system requires comprehensive consideration of various elements from a system perspective, which is a complex systematic project.

Some domestic cases show that through the energy-saving transformation of the blower, the average daily power consumption is reduced from 32,990 to 29,835, a decrease of 3155, a decrease of 11.4%. Roughly, it 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 costs 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 the input of raw materials

There are various wastewater treatment processes, but the essence is to remove pollutants from the water through biochemical reactions.

Therefore, carbon sources and a variety of chemical agents need to be added in the treatment process. These raw materials consume energy during production and transportation, and also consume a certain amount of energy during the dosing process.

Therefore, optimizing the feeding link helps to save energy and reduce carbon emissions.

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

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

The second is to use AI technology for big data analysis of sewage water quantity, water quality and other parameters and dosing system operation data to form an optimal algorithm model, so as to achieve fine control of the dosing system and effectively reduce drug consumption and equipment operation energy consumption.

5. Optimize the 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 minimize this energy consumption, various measures must be taken to optimize the performance of the pipe network.

Among them, the most basic is to transform and upgrade the operation and management mode of the pipe network, and the key work includes the investigation, positioning, maintenance and prevention of potential leakage risks.

Realize real-time monitoring of the operation status of the drainage network, and can quickly analyze whether leakage, blockage, and the severity, specific location, etc., to provide accurate support for managers to quickly maintain.

To improve the water transmission performance of the drainage network, the most fundamental solution is to improve the coverage rate of the drainage network, achieve 100% sewage collection, and carry out the rain and pollution diversion transformation to significantly increase the carbon nitrogen ratio of the sewage treatment plant.

In this way, it can solve the problem of insufficient carbon sources, effectively improve the organic matter - methane conversion rate of the sewage treatment plant, turn the sewage treatment plant into a power plant, fundamentally solve the problem of energy consumption, and achieve carbon neutrality.

6. Energy saving and consumption reduction of drainage pumping station

Drainage pumping stations are also big energy users. Some data show that drainage pumping stations account for 35% of the total energy consumption of urban water. Therefore, upgrading the drainage pumping station or adopting 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 pump stations, or new projects directly use digital pumps and other new equipment and facilities, in order to reduce the energy consumption of pump stations.

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

04 General junction

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, it is necessary to systematically plan the whole process of "user control - source separation - pipe network storage - purification treatment".

In this process, the relevant government departments and enterprises need to comprehensively upgrade the management and operation mode, upgrade from management-driven to data-driven, build a new digital management model, and realize the intelligent upgrade of the entire operation model.

To fundamentally solve this problem, we need to jump out of the sewage treatment industry, stand in the ecological civilization construction, urban and rural integration development, sewage resources, energy self-sufficiency, environmental friendliness and other aspects of comprehensive consideration, need to carry out top-level planning, system design and overall arrangement from the different levels of "point-line-face-body".

This is not only a technological and conceptual renewal of the entire industry, but also a revolution in the thinking and cognition of the entire society.

It will be a long and tortuous process. It is encouraging that the proposal and practice of the wastewater treatment concept plant has taken a critical first step, and we have reason to believe that China's wastewater treatment industry will soon make a positive contribution to the carbon neutral strategy.