Municipal sludge produced in municipal facilities and municipal activities related to operational and maintenance processes, municipal sludge has a distinctive municipal character. According to the characteristics of municipal sludge, municipal sludge can be divided into the following five types.
1. Municipal sewage sludge
There are innumerable water use links in the municipal logistics system, and most of the water after use is converted into sewage sludge containing different types and concentrations of pollutants. The sewage sludge generated by the city can be divided into two categories according to the source: 1. industrial sewage sludge: from the industrial sector of the city, the pollution characteristics are determined by the corresponding industrial technology and process; 2. municipal sewage sludge: residential areas from the city, commercial service areas, etc. In the industrial sector, the pollution characteristics are less related to specific sources (such as commercial and residential areas), that is, the commonality of municipal sewage sludge from different sources is its main aspect.
The purification of municipal sewage sludge is also arranged separately by source. The main treatment target of municipal sewage treatment plants is municipal sewage sludge. In cities or regions where municipal drainage is implemented, runoff drainage from rainfall in some cities is also treated in municipal sewage treatment plants; at the same time, industrial sewage from some cities is also treated in municipal sewage treatment plants, but there are The requirements for industrial wastewater pretreatment make the pollution characteristics of industrial sewage entering municipal sewage treatment plants close to municipal sewage sludge (for example, for heavy metal industrial wastewater, it should be pretreated to remove most of the heavy metal pollution before it can be remitted to municipal sewage treatment plant.)
In the treatment of sewage in municipal sewage treatment plants, part of the pollutants in the sewage are converted into sedimentable substances, and the discharged objects are municipal sewage sludge characterized by solid-liquid mixing.
2. Municipal water supply sludge
Most of the water used in modern cities is tap water supply in the form of pipe network distribution. At present, most of the city’s water supply sources (raw water) can only meet the water quality requirements of the water supply after necessary purification treatment. The purification of raw water is carried out in a special water treatment plant (waterworks). The main treatment process is coagulation and sedimentation (transformation of particulate matter, colloids and partially soluble impurities in raw water into particles or colloidal substances that can be settled or filtered. And filtration (to complete the final removal of the above particles and colloids together with the precipitation), the removed particles and colloids constitute the solid phase portion of the municipal feed water sludge for the removal of these solid phase from the sedimentation tank and the filter Water constitutes the liquid phase portion of the sludge.
3. Municipal water dredged sludge
Municipal water bodies refer to natural or artificial water bodies (rivers, lakes, ponds, etc.) where the main catchment area is a built-up area of the city. In addition to the functions of landscape and shipping, the main function of municipal water bodies is the components of municipal drainage channels and storage capacity. Due to the characteristics of the catchment area, municipal water bodies may receive water flows including municipal surface runoff, municipal sewage and industrial sewage. The particles and colloids entrained in these streams become sediments of municipal water bodies under certain hydraulic and hydrological conditions, and the soluble substances in the above-mentioned water streams will also form sedimentable substances in certain biological and chemical processes, which will be converted into Water sediments. The accumulation of water sediments will threaten the maintenance of the normal function of municipal water bodies. Therefore, municipal water bodies have the need for continuous conservation (dredging), and the water sediments after the flooding are the municipal water bodies that are mixed with solid water (bottom) and mud.
Even if the accelerated impact of municipal sewage and industrial sewage into municipal waters on the formation of sediments is not considered, the surface of the municipal catchment area is different from that of agriculture or natural ecosystems, and the surface with low water impermeability and roughness is Mainly, the ground sediments are easily entrained by runoff, and the impermeability of the underlying surface amplifies the intensity of runoff. In addition, the runoff mainly flows into the water body by means of pipeline flow, and the lack of non-urban river channel vegetation zone removes particulate matter from runoff. Buffering, therefore, the rate of sediment formation in municipal water bodies is higher than that in agricultural or natural ecosystems. The demand for dredging and maintenance of municipal water bodies has obvious municipal characteristics, and its sludge becomes one of the components of municipal sludge.
4. Municipal drainage channel sludge
Modern municipal drainage methods are characterized by pipelines. According to the principle of drainage objects and drainage system (drainage system), municipal drainage channels can be divided into three types: sewage channel, rain channel and combined drainage channel. According to the different choices of water flow in the channel, the drainage channel can also be divided into two types: gravity type and pressure type. No matter what kind of municipal drainage objects, they can contain sedimentable particles and colloids to varying degrees. At the same time, some soluble substances in the drainage also have the possibility of generating sedimentable substances under the environmental conditions and biological action in the drainage channel. Under certain channel hydraulic conditions, it will deposit in the channel and become a factor affecting the normal drainage function of the channel. In order to maintain the normal function of the urban drainage channel, the channel system needs to be regularly maintained, and the channel sludge produced in this process also becomes one of the municipal sludges.
5. Municipal construction site mud
Municipal construction site mud is a type of municipal construction waste, mainly generated during the foundation construction of municipal construction projects (such as concrete pouring pile foundation construction) and building geological exploration (exploration well drilling). Although in a strict sense, construction activity is an industrial production activity, the regional distribution of urban construction activities (randomly appearing throughout the urban area) and the characteristics of waste discharge (the characteristics of waste generated by different construction sites are basically the same). ), all have more commonalities in the city. Therefore, municipal construction waste is generally used as a kind of municipal waste (solid waste). Of course, municipal construction site mud should also be a part of municipal sludge.