Accelerate the construction of a technical system for pollution reduction and carbon reduction in the whole process of sewage treatment
The sewage treatment industry is one of the top ten greenhouse gas emitting industries in the world, and its carbon emissions account for 2%-3% of the total global carbon emissions, and it is still increasing year by year. In June 2022, the Ministry of Ecology and Environment (MEE) and other departments issued the Implementation Plan for Synergy in Pollution Reduction and Carbon Reduction, which for the first time put forward relevant requirements for pollution reduction and carbon reduction in sewage treatment plants.
In order to thoroughly implement Xi Jinping's thought on ecological civilization and implement the requirements of the National Conference on Ecological and Environmental Protection, the National Development and Reform Commission, the Ministry of Housing and Urban-Rural Development, and the Ministry of Ecology and Environment recently jointly issued the "Implementation Opinions on Promoting the Synergy of Pollution Reduction and Carbon Reduction in Sewage Treatment" (hereinafter referred to as the "Implementation Opinions") also made further clear arrangements for the synergy of sewage treatment, pollution reduction and carbon reduction.
Adhere to carbon reduction at the source, and grasp the "bull's nose" of water conservation and efficiency improvement
Huang Runqiu, Minister of Ecology and Environment, pointed out in his keynote speech at the 2022 June Five-Year Environment Day National Main Event that carbon reduction can reduce pollutant emissions at the source. Therefore, adhering to the concept of "saving water is pollution control, saving water is carbon reduction", and grasping the "bull's nose" of water saving and efficiency increase, can we effectively play the traction role of carbon reduction at the source on carbon emission reduction in the sewage treatment process.
For industrial parks, water conservation and efficiency enhancement are mainly through the integration and optimization of the water system in the industrial park, saving the utilization of water resources, reducing the amount of water used in production and living and sewage discharge, and promoting the recycling of wastewater in industrial enterprises and parks through the quality and recycling of wastewater in industrial enterprises, so as to realize the series of water use, quality water, multi-purpose and cascade utilization, so as to maximize the realization of water conservation and emission reduction at the source. In addition, the "Implementation Opinions" also put forward new requirements for standardizing the drainage management of industrial parks, pointing out that the wastewater that cannot be effectively treated by urban sewage treatment plants or may affect the stability of the effluent of sewage treatment plants is strictly restricted from entering the municipal sewage collection and treatment system. The Three-Year Action Plan for Improving the Quality and Efficiency of Urban Sewage Treatment (2019-2021) issued in 2019 proposes to withdraw from the management enterprises that are assessed as pollutants that cannot be effectively treated by sewage treatment plants or may affect the stability and compliance of sewage treatment plants. The Ministry of Ecology and Environment's Notice on Further Standardizing the Environmental Management of Urban (Park) Sewage Treatment (Huanban Memo [2020] No. 290) also has similar instructions. Therefore, the purpose of this opinion is to further strengthen the classified collection and quality treatment of industrial wastewater and domestic sewage, and to accelerate the construction of centralized industrial sewage treatment facilities.
For urban sewage treatment plants, the main purpose of water saving and efficiency improvement is to improve the efficiency of sewage collection, by carrying out the diagnosis and repair of the old pipe network in built-up areas, accelerating the elimination of blank areas of urban sewage collection pipe network, realizing the full coverage of urban sewage pipe network, and orderly promoting the transformation of rain and sewage diversion. These aspects are mainly proposed to solve the sequelae of "heavy factories and light networks" that have existed for a long time in the construction of sewage treatment and collection facilities in some areas. Although the sewage treatment plant has been completed, due to the poor operation quality of the pipe network, a large amount of groundwater and rainwater have entered the sewage collection pipe network, resulting in the phenomenon that the water concentration in the sewage treatment plant is not high, and the water enters and exits, so the construction and improvement of the sewage collection pipe network is of great significance to the water saving and efficiency of the urban sewage treatment plant. In addition, the "Implementation Opinions" also put forward new management and control requirements for areas where the construction and renovation of sewage collection pipe networks are not in place. When the biochemical oxygen demand concentration of influent water in a regional sewage treatment plant is less than 100 mg/L, the requirements for new sewage treatment capacity in the area will be strictly approved, and the "one plant, one policy" remediation plan will be implemented, which reflects the relevant requirements of plant-network linkage.
Strengthen process carbon reduction, and innovate new paths to reduce consumption and increase efficiency
The carbon emissions of the wastewater treatment process include direct carbon emissions and indirect carbon emissions. In terms of reducing greenhouse gas emissions in the treatment process, the Implementation Opinions put forward new requirements for both aspects. Indirect carbon emissions are the ectopic carbon emissions caused by energy and power consumption caused by the operation of equipment, accounting for about 50%-70% of the total carbon emissions of sewage treatment plants. At the same time, through the development and application of advanced low-carbon sludge treatment processes, such as deep sludge dewatering, efficient drying, pyrolysis, etc., the indirect carbon emissions of the sludge treatment process can also be reduced. These are the only ways to achieve carbon reduction in the wastewater treatment industry.
The direct carbon emissions of the wastewater treatment industry, i.e., fugitive greenhouse gas emissions, mainly include CH in the process of conveying sewage pipe networks4Emissions, CO in aerobic biological treatment processes2CH during discharge, anaerobic and sludge treatment4as well as the denitrification process N2Emissions of O. The "Implementation Opinions" proposes to support the use of biodegradable wastewater from upstream production enterprises as a carbon source supplement for downstream sewage treatment plants in accordance with laws and regulations, as a substitute for carbon sources, strengthen the application of low-carbon technologies such as efficient nitrogen and phosphorus removal, and reduce the escape of nitrous oxide in the denitrification process. Escaping CH from sewage treatment plants across the country in 20154 and N2The direct carbon emissions generated by O are 2512.2 t, which is estimated to increase to 56.8867 million tons in 2030 based on an average annual growth rate of 5.57%. Therefore, the management of fugitive greenhouse gas emissions in the sewage treatment industry is the most direct means to reduce the greenhouse gas emissions in the sewage treatment industry.
Strengthen end-of-line carbon substitution to help green and low-carbon cycles
In terms of increasing the use of reclaimed water energy and reclaimed water, the "Implementation Opinions" put forward plans such as photovoltaic power generation and reclaimed water recycling, in fact, whether it is photovoltaic power generation instead of electric energy, or reclaimed water recycling is a new end of the "carbon replacement" way, which can not only reduce the use of fresh energy and carbon emissions, but also help the green and low-carbon cycle of resources and energy. In 2021, the Ministry of Ecology and Environment and other four ministries and commissions jointly issued the "Regional Reclaimed Water Recycling Pilot Implementation Plan", which proposed to include reclaimed water in the unified allocation of water resources to promote the balance between reclaimed water production and utilization. Therefore, in order to further promote the utilization of sewage resources, it is necessary to build a regional reclaimed water recycling system and a rural sewage community-based on-site treatment and reuse system, make full use of the natural purification and transportation capacity of the ecosystem, and realize the carbon substitution of sewage operation and treatment process.
Secondly, in terms of sludge resource utilization, it is necessary to strengthen the recycling of sludge and biogas, promote biogas cogeneration, make full use of the organic matter and heat energy in sludge, carry out sludge gasification, fermentation and gas production technologies, improve the recovery rate of energy, and reduce the use of traditional carbon sources. By actively promoting sludge land use, we will explore ways to utilize sludge resources, such as biomass fuel, organic fertilizer, agricultural land improvement materials, etc., to achieve carbon substitution in sludge process. Therefore, to carry out the synergy of sewage treatment and carbon reduction, it is necessary to fully explore the resource and energy attributes of sewage and sludge, realize the terminal carbon replacement through the efficient recycling of resources and energy, and build a new green and low-carbon cycle model of sewage treatment industry.
The "Implementation Opinions" also proposed that by 2025, the synergy of pollution reduction and carbon reduction in the sewage treatment industry will make positive progress, 100 green and low-carbon benchmark plants for sewage treatment with efficient recycling of energy and resources will be built, and it is proposed to accelerate the formulation of the national standard of "Collaborative Carbon Reduction Performance Evaluation - Urban Sewage Treatment" to help the screening of green and low-carbon benchmark plants, which provide action guidance for us to carry out sewage treatment pollution reduction and carbon reduction.
Author Affilications:Institute of Water Ecology and Environment, Chinese Academy of Environmental Sciences
