Recently, the second round of the Sixth Batch of ecological and environmental protection supervision teams respectively fed back the supervision information to five provinces (autonomous regions) of Hebei, Jiangsu, Inner Mongolia, Tibet and Xinjiang and the Xinjiang production and Construction Corps.

In the feedback report to Hebei, it was pointed out that the problem of illegal disposal of sludge was serious. Since 2017, Zhengxiang animal husbandry company in Longyao County, Xingtai City has illegally received more than 88000 tons of sludge, and nearly 13000 tons have been dumped on 226 mu of arable land, without taking any prevention and control measures. Since 2018, wanong organic fertilizer plant in Guye District of Tangshan City has illegally received 156000 tons of sludge, and the whereabouts of more than 50000 tons are unknown. The sludge temporary storage sites of 11 leather enterprises in Xinji City store about 1.27 million cubic meters of sludge.

After combing the second round of inspectors, the reporter found that in addition to Hebei, the inspectors also pointed out the improper disposal of sludge in many places.

The second batch of inspectors in the second round have pointed out that there are sludge disposal violations in Beijing, Tianjin, Zhejiang and other three provinces and cities. The third batch of inspectors in the second round once pointed out that Chaoyang, Liaoning, has long illegally and temporarily stockpiled more than 400000 tons of sludge, which has prominent potential environmental risks. The fourth batch of inspectors in the second round once pointed out that Suining, Sichuan, has allowed relevant enterprises to illegally dispose of sludge in the name of "soil improvement" for a long time, which has seriously polluted the surrounding environment.

Similar problems have been pointed out many times. Why is there still a chaotic situation of illegal disposal of sludge after the second round of inspections? Where should sludge disposal go?

Sludge reduction has been initially realized, but the "four modernizations" have not been realized

Sludge contains a large amount of organic matter, bacteria and inorganic particles, which are easy to decay and stink. Some industrial sludge also contains heavy metals, and improper disposal will cause serious pollution to the environment. But at the same time, the sludge is also rich in nutrients, such as carbon, nitrogen and phosphorus. Therefore, sludge has dual attributes of "pollution" and "resource".

Dai Xiaohu, Professor of the school of environmental science and engineering of Tongji University and director of the urban pollution control * Engineering Research Center, introduced that "with the increasing scale of urban sewage treatment in China, the output of municipal sludge has also increased correspondingly, and the sludge problem has not been properly solved, which has greatly reduced the benefits of sewage treatment infrastructure. The comprehensive treatment and disposal of sludge is still a short board of sewage treatment in China." According to statistics, in 2020, the output of sludge with 80% water content in China has exceeded 65 million tons, and it is expected that the annual output of sludge in China will exceed 90 million tons in 2025.

"Due to the long-term 'heavy water and light mud' in China, the sludge treatment and disposal technology has not been improved synchronously with the sewage treatment." At present, sludge treatment and disposal are facing many challenges.

In 2016, the development and Reform Commission and the Ministry of housing and urban rural development jointly issued the "13th five year plan" for the construction of national urban sewage treatment and recycling facilities, which pointed out that the construction and transformation of urban sewage treatment facilities and pipe networks should be accelerated, and the harmless treatment of sludge should be promoted, and the transformation from "heavy water and light mud" to "mud and water".

"We have been making continuous efforts to promote the construction of the technical system and standard system for sludge an total treatment and disposal. At present, we have made phased progress, but there is still a long way to go before high-quality development." Dai Xiaohu pointed out that the sludge treated by the sewage treatment plant needs to be fully disposed of at the terminal. There are three disposal methods commonly adopted in China: sanitary landfill, building materials utilization after thermochemical treatment, and land utilization after biological stabilization treatment.

However, these methods have encountered obstacles in varying degrees: where to bury them, how to burn them, and who will use them?

Landfilling is better than random dumping, but there are fewer and fewer sites available for landfilling, and the embarrassing situation of "no land to bury" is often encountered; Incineration is better than landfill, but the water content of sludge is high, the energy consumption of incineration is too high, and the neighbor avoidance effect is serious; Land use is better than incineration, but it has higher requirements on sludge quality, so it is necessary to carry out stabilization treatment of sludge. The stabilization treatment of sludge is the short board of sludge treatment and treatment in China at present. Meanwhile, due to the doping of industrial wastewater, heavy metals and other toxic and harmful substances in sludge often exceed the standard, and land use is restricted.


According to incomplete statistics, at present, only a small part of the sludge from urban sewage treatment plants in China is subject to stabilization treatment, land utilization, incineration and building materials utilization, and most of the sludge is not subject to standardized treatment and disposal.

Professor Dai Xiaohu pointed out that at present, due to the lack of relevant laws and regulations on sludge treatment and disposal, China's urban sewage treatment plants have basically realized the initial reduction of sludge, but have not really realized the stabilization, harmless and resource-based treatment, and there is a serious risk of secondary pollution.

How is the sludge treated?

Sludge treatment and disposal includes two stages: treatment and disposal. Treatment mainly refers to the process of stabilization, reduction and harmless treatment of sludge. Disposal refers to the process of absorbing the treated sludge.

Compared with the developed countries, the sludge of urban sewage treatment plants in China has the characteristics of low organic matter content, high sand content and large output. Therefore, the selection of sludge treatment and disposal technology route should be combined with the specific characteristics of sludge of urban sewage treatment plants in China, and the dual attributes of "resource" and "pollution" of sludge should be fully considered to achieve greater environmental, economic and social benefits.

According to Dai Xiaohu, after many years of exploration, China has formed four mainstream technical routes for sludge treatment and disposal: deep dehydration landfill, anaerobic digestion land utilization, aerobic fermentation land utilization, dry incineration landfill or building materials utilization.

The figure shows the mainstream technical route of sludge treatment and disposal (provided by Dai Xiaohu)

According to Dai Xiaohu's analysis, sludge is a kind of organic solid waste with high water content and easy to decay. Improper treatment will cause secondary pollution to the environment. The treatment process should include two important links, namely "stabilization" and "reduction". In China, the sludge of sewage treatment plants has basically realized dehydration and reduction, while the sludge stabilization and harmless treatment is a short board. The investment in sludge stabilization and harmless treatment during the construction of sewage plants is seriously insufficient, Anaerobic digestion technology is one of the main technologies for sludge stabilization at home and abroad. Anaerobic digestion can simultaneously realize the stabilization and sanitation of high water content perishable organic matter and the recovery of biomass energy. How to realize the standardized treatment of sludge stabilization and sanitation of sewage treatment plants in China is an important task for realizing sludge treatment and disposal and recycling in China. After the stabilization and reduction of sludge in the sewage treatment plant, the quality of sludge has been significantly improved, which provides a basic guarantee for the subsequent full resource treatment of an.

As for the disposal path, sludge is rich in nutrients such as carbon, nitrogen and phosphorus. Land use can improve the soil and realize the recycling of nutrients. Therefore, for the sludge that does not exceed the standard of heavy metals, priority should be given to encourage the use of land after anaerobic or aerobic stabilization treatment, including landscaping, soil remediation and agriculture; When the heavy metal exceeds the standard, the land use is limited, or the land use cost is high and the local economic level is high, the treatment and disposal process of anaerobic stabilization coupled with terminal drying and incineration can be adopted. At present, China generally adopts the "deep dehydration landfill" technical route, which causes serious secondary pollution, occupies land, wastes resources and is unsustainable.

According to the data, the reporter found that the five sludge treatment and disposal centers of beipai group, including Gaobeidian, Xiaohongmen and Qinghe, and the Changsha black Mi peak sludge anaerobic digestion demonstration project all adopted the "sludge thermal hydrolysis anaerobic digestion" technology to improve the anaerobic digestion performance of sludge, kill pathogenic bacteria through thermochemical pretreatment, reduce resistance genes, and achieve the transformation of perishable organic matter through anaerobic stabilization treatment, It reduces the risk of secondary pollution and improves the quality of sludge. Finally, the stabilization and harmlessness of sludge are realized, which provides a guarantee for the subsequent disposal of an.

In addition, according to Professor Dai Xiaohu's analysis, "With years of exploration on sludge treatment and disposal in China, there has been a great breakthrough in sludge treatment and disposal technology and equipment, and two full chain demonstration modes of sludge treatment and disposal have been formed: anaerobic digestion land utilization mode in Beijing and dry incineration ash residue building materials utilization mode in Shanghai, laying a foundation for the green, low-carbon and healthy development of subsequent sludge treatment and disposal. However, the stabilized sludge The path of land utilization has not been opened, and relevant policies still need to be further *

What is the future of sludge under the "double carbon" target?

According to the development plan for urban sewage treatment and resource utilization during the 14th Five Year Plan period, the harmless disposal rate of urban sludge should reach more than 90% by 2025, and the harmless disposal of sludge will be realized by 2035, and the level of sewage and sludge resource utilization will be significantly improved.

Dai Xiaohu told reporters, "At present, many places are relying on scientific and technological innovation to improve the capacity of sludge harmless disposal. Some places pay for cement plants or power plants to carry out collaborative incineration disposal; some places carry out sanitary landfilling, and some economically developed areas are planning separate incineration or other thermochemical treatment methods of sludge. In addition, for the bottleneck of limited land use, it is necessary to * introduce corresponding management policies."

In July 2020, the national development and Reform Commission and the Ministry of housing and urban rural development jointly formulated the implementation plan for strengthening the weak points of urban domestic sewage treatment facilities. In large and medium-sized cities that are short of land resources, the disposal mode of "biomass utilization + incineration" is encouraged to be adopted, and incineration ash is used as building materials. Anaerobic digestion and aerobic fermentation are encouraged to treat sludge.

"Sludge biomass utilization mainly includes anaerobic digestion technology to realize the stabilization and sanitation of sludge perishable organic matter and recover biomass energy in sludge. It is an important link in the whole chain treatment of sludge." From the perspective of future development, anaerobic digestion land utilization, aerobic fermentation land utilization, low consumption drying clean incineration building materials utilization and other technical routes are important development directions of sludge treatment and disposal in China in the future.

Dai Xiaohu said that under the "double carbon" target, the ultimate goal of sludge treatment and disposal should be pollution control. Through recycling means such as biomass energy recovery of organic matter and recycling of nutrients, the energy and resources in sludge can be recovered, which is an important link to achieve carbon emission reduction in the sewage treatment process. Therefore, from the perspective of reducing pollution and carbon, the sludge treatment and recycling process has important potential and significance for carbon reduction of sewage treatment.

He believes that the proposal of the "double carbon" target is a good promotion for the treatment and disposal of sludge. In the past, the evaluation of energy saving, consumption reduction and resource recovery and utilization in the sludge treatment and disposal process was mainly reflected in the economic benefits. After the carbon emission index is available, the carbon emission level of the sludge treatment and disposal technology can be quantitatively evaluated, which will actively promote the sludge treatment and disposal towards low-carbon, green The direction of sustainable development.

In the future, energy consumption and drug consumption should be reduced as much as possible in the sludge treatment process, and how to recycle materials should be considered in the sludge treatment process.

Among them, from the perspective of "waste free city" construction, sludge landfill will be gradually banned, mainly due to the disorderly emission of a large number of greenhouse gases and the waste of carbon, nitrogen, phosphorus and other resources.

With the attention paid by the ecological and environmental protection inspectors to the sludge problem, it is helpful to promote the local government to accelerate the planning, construction, operation and management of sludge treatment and disposal facilities and financial support, and improve the level of sludge harmless treatment and resource utilization.

Dai Xiaohu suggested that, first of all, the standardized treatment of sludge in sewage treatment plants should be well controlled at the front end. All localities should adjust measures according to local conditions and establish sludge treatment facilities and systems to improve the stabilization and sanitary treatment capacity and level of perishable substances in sludge. Secondly, solve the problem of blocking points in land use, carry out harmless treatment of sludge, and encourage land use after meeting the relevant standards, which can be preferentially used for land improvement, afforestation of wasteland, mine restoration, nursery stock breeding, landscaping, etc.

"The terminal is the king of sludge disposal. Realizing sludge reduction, stabilization and harmless treatment and disposal, and steadily promoting resource utilization are important measures to promote the synergy of sewage treatment, pollution reduction and carbon reduction. It is necessary to establish a systematic view of sewage and sludge treatment and disposal, scientifically plan and implement it according to local conditions, actively and steadily promote it, give play to the role of the government and the decisive role of the market in resource allocation, and clarify the responsibility subjects, so as to save energy and reduce carbon Technology and path to promote sludge reduction, stabilization, harmless treatment and resource utilization. " He said.

Editor: Shang yu