Colorful Guizhou Network | National Ecological Day: Homemade Gold! "Turning waste into treasure" in the non factory area of Guiyang domestic sludge

The sludge generated in sewage treatment may cause pollution to the environment. Through technological treatment, soil generates gold and sludge is transformed into high-quality nutrient soil required for landscaping. On August 15th, the first National Ecological Day, a reporter from Colorful Guizhou Network visited the Xinzhuang Sludge Drying Center of China Water Environment Group in Guiyang to explore the process of sludge transforming into nutrient soil.

The Xinzhuang Sludge Drying Center is located on Shuidong Road in Gaoxin Community, Wudang District, Guiyang City, covering an area of about 32 acres. Rows of factory buildings are built against the mountain, and there is no smell when entering the factory area.

After the sludge truck driver poured the sludge into the sludge receiving workshop, the task was completed. The vast factory area rarely sees workers. Zhang Xiaoyu, the manager of the Xinzhuang Sludge Drying Center in the Guizhou business area of China Water Environment Group, immediately solved the confusion of the reporter: currently, their factory's sludge disposal has achieved full process electronic processing. Through the electronic screen in the monitoring room, the staff can have a full view of each process and process.

"Our equipment mainly performs harmless, reduced, and resourceful treatment on sludge," said Zhang Xiaoyu. According to the process, after the sludge enters the receiving workshop, it is conditioned and then sent through pipelines to the sludge drying system for treatment. Throughout the process, the sludge system was closed and the deodorization facilities were activated, so there was almost no odor from the outside.

"There are a total of 34 domestic sewage treatment plants in the central urban area of Guiyang, which produce about 900 tons of sludge every day. Sludge treatment has always been a headache." Cao Xiaoxin, Deputy General Manager of Guizhou Business District of China Water Environment Group, introduced that before 2016, most of the sludge produced by sewage treatment plants in various parts of the country was treated by landfill. This extensive disposal method only transferred the pollution source from sewage to soil, which poses great environmental hazards.

In the research, Cao Xiaoxin found that sludge is not completely useless. "Sludge is both a pollutant and a resource. Through certain technological treatments, sticky sludge can also become a 'treasure'."

So, how to turn sludge into treasure?

"Sludge is a product of sewage treatment, and to talk about sludge, one must first understand the composition of sewage." Cao Xiaoxin explained that urban sewage in Guiyang mainly comes from comprehensive domestic sewage, construction sewage, and initial rainwater. Taking comprehensive domestic sewage as an example, washing dishes, clothes, taking a shower, and flushing the toilet can generate an average of about 180 liters of sewage per person per day.

"Domestic sewage is an important source of pollution generated in the process of urbanization, which contains a large amount of pollutants such as organic matter, ammonia nitrogen, total phosphorus, and total nitrogen, and many pathogenic bacteria. During the sewage treatment process, these pollutants are consumed by microorganisms, producing new bacterial bodies. The excess microorganisms need to be discharged into the system, known as surplus sludge. If the sludge is not effectively treated, it is easy to cause secondary pollution to the environment." Cao Xiaoxin pointed to the sludge workshop and introduced that the factory needs to process 280 tons of domestic sludge every day, accounting for about 1/5 of the city's daily production of domestic sludge, which is over 100000 tons in a year.

Transformed into nutrient soil under high-temperature fermentation

For this reason, from 2021, Guizhou Business Area of China Water Environment Group, Institute of Geochemistry of the Chinese Academy of Sciences, Guizhou University and other units began to carry out research and test on sludge recycling technology, make full use of organic carbon and nutrient elements in sludge, develop efficient sludge compost fermentation and organic nutrient soil preparation technology, and promote sludge recycling.

"The processed nutrient soil can be used for flower cultivation," said Zhang Yong, a staff member of the factory. This process technology involves continuously treating sludge through multiple equipment such as sedimentation tanks, flocculation tanks, sludge pumps, and filter presses, and finally transforming it into organic nutrient soil required for landscaping under high-temperature fermentation. The entire process technology takes about 21 days.

Simply put, it means efficiently breaking down the cell wall of sludge, reducing the water content of sludge to below 60%, and achieving the goal of initial reduction; Through the backend high-temperature fermentation equipment and mixed fermentation with fermentation auxiliary materials, the pathogenic microorganisms and roundworm eggs in the sludge are effectively killed, and the final organic nutrient soil product is produced. After testing by a third-party quality supervision and inspection station, the organic matter and heavy metal indicators fully meet national standards and can be used in fields such as landscaping, mine restoration, and home gardening, truly achieving the reuse of urban organic waste.

"Only the daily sludge generated by the Xinzhuang Sewage Treatment Plant (Phase I) can produce 30-40 tons of organic nutrient soil through aerobic fermentation treatment." Zhang Xiaoyu said that this technology not only makes urban sludge a renewable resource, but also fundamentally solves the secondary pollution caused by improper use of sludge containing inorganic salts, pathogens, etc.

Nowadays, in the green belt of Xinzhuang Sewage Treatment Plant (Phase I), vibrant small daisies and brightly colored triangular plums are displayed in excellent condition. What nourishes them is the domestic sludge that has been successfully transformed into nutrient soil after treatment. And this type of green belt that uses nutrient soil has a soft soil surface, good water retention, and no odor.

Nutrient soil is used to nourish vegetation

"The ultimate goal of sludge is to take the path of resource utilization, integrate into the ecosystem, and form a new economic cycle system." Cao Xiaoxin said that they will gradually promote the process technology pilot in Guizhou based on the needs of downstream customers. They can further process resource products according to the needs of different customers, effectively improve the added value of sludge products, extend the downstream industrial chain, and achieve the goal of "reducing, harmless, and resourceful sludge". At the same time, continuously improving sewage treatment discharge standards and ensuring urban water supply safety, improving the living environment, enhancing urban quality, and contributing to promoting green and circular development.

Although sludge is urban waste, it is also an inexhaustible urban mineral resource. Soil can produce gold.

Through on-site visits, the reporter found that a sewage treatment plant has been built in Guiyang, and most of the main indicators of effluent have reached the Class IV standard for surface water. In the field of sewage treatment, there is a saying that "treating water but not sludge leads to a large transfer of pollution", which indirectly confirms the importance of sludge treatment.

In order to achieve harmless comprehensive utilization of sludge and assist in the construction of low-carbon and waste free cities, the Xinzhuang Sludge Drying Center in Guiyang City has developed efficient sludge composting fermentation and organic nutrient soil preparation technologies to maximize the recycling of sludge and solve the final outlet problem of sewage treatment plant sludge. The application of these technologies can save valuable land resources, effectively protect the water and soil environment, and have good social, environmental, and economic benefits.