Sewage treatment plant sludge treatment

Sludge treatment in sewage treatment plants refers to a series of processes for reducing, stabilizing, harmlessly treating and recycling sludge generated during sewage treatment. Sludge is an inevitable product of sewage treatment, and is mainly derived from solid or semi-solid substances formed by precipitation, concentration or separation of suspended solids, microorganisms and organic matter in sewage during biological and chemical treatment. The following are typical processes and common methods for sludge treatment in general sewage treatment plants: 1. Sludge concentration - Gravity concentration: Utilize the density difference between sludge and water to initially concentrate the sludge and reduce its water content through natural sedimentation or inclined plate/inclined tube sedimentation. - Flotation concentration: Utilize the adhesion of tiny bubbles to sludge particles to make the sludge particles float to the water surface and achieve solid-liquid separation. - Centrifugal concentration: Use a centrifuge to make the sludge rotate at high speed to achieve solid-liquid separation and obtain concentrated sludge. 2. Sludge digestion - Anaerobic digestion: Under anaerobic or anoxic conditions, anaerobic microorganisms are used to decompose organic matter in sludge to produce biogas (which can be recovered as energy), carbon dioxide and stable sludge residues. Anaerobic digestion can significantly reduce sludge volume, stabilize organic matter, kill pathogens, and recover energy. - Aerobic digestion: Under aerobic conditions, the organic matter in sludge is converted into carbon dioxide, water and microbial cells through the biological oxidation of aerobic microorganisms, further reducing the organic matter content, and also has a certain pathogen killing effect. Aerobic digestion usually does not reduce sludge volume as much as anaerobic digestion, but the required residence time is shorter. 3. Sludge dehydration - Mechanical dehydration: Including belt filter press, plate and frame filter press, centrifugal dehydrator, etc., further removes water from sludge through physical pressure or centrifugal force, so that the sludge moisture content is reduced to about 60% to 80%, forming a relatively dry and hard mud cake, which is convenient for subsequent treatment or disposal. - Chemical conditioning: Before dehydration, coagulants (such as polyacrylamide) or flocculants (such as polyaluminium chloride) are sometimes added to condition the sludge to improve the dehydration performance of the sludge and increase the dehydration efficiency. 4. Deep dehydration - Thermal drying: The dehydrated sludge is further dried by heating methods such as hot air and steam to reduce the moisture content to 10% to 40%, significantly reducing the volume, increasing the calorific value, and facilitating subsequent incineration or resource utilization. - Low-temperature heat pump drying: Using low-temperature heat pump technology, deep dehydration of sludge is achieved with lower energy consumption, which is especially suitable for occasions with high requirements for energy recovery and environmental friendliness. 5. Sludge stabilization - Composting: Through the aerobic fermentation process, the organic matter in the sludge is converted into stable humus under the action of microorganisms to make organic fertilizer, which is suitable for sludge containing more plant matter. - Thermochemical treatment: Such as thermal hydrolysis, wet oxidation, incineration, etc., through high temperature or chemical oxidation, the organic matter is completely decomposed, pathogens are killed, and the sludge is harmless and reduced. 6. Final disposal and resource utilization - Land use: Sludge that has been harmless and stabilized, such as compost products, can be directly used for soil improvement or farmland fertilization, but it must comply with strict agricultural standards and supervision. - Landfill: For sludge that is not suitable for land use, it can be sent to a landfill that meets environmental protection requirements for safe landfill, but the occupation of landfill space should be minimized. - Incineration: The sludge is completely burned through a sludge incinerator to achieve maximum reduction, and heat energy is recovered for power generation or heating. The amount of ash after incineration is small, stable and harmless, and can be used as a raw material for building materials or safely landfilled. - Building material utilization: For example, in brick making and ceramsite making, sludge is used as a raw material or additive to produce various building materials products. 7. Environmental monitoring and management - Recording and supervision of the entire process of sludge generation, treatment and disposal: Ensure that sludge treatment complies with relevant national and local laws, regulations and standards. - Regular testing: monitor various indicators of treated sludge (such as moisture content, organic matter content, heavy metal content, number of pathogens, etc.) to ensure that they meet the discharge or utilization standards. - Emergency treatment plan: formulate emergency treatment plans to deal with emergencies such as sludge treatment facility failure and sludge leakage to reduce the impact on the environment. Sludge treatment in sewage treatment plants is a comprehensive process. It is necessary to select an appropriate combination of treatment technologies based on the characteristics of the sludge and the actual local conditions, taking into account economic benefits, environmental benefits and social benefits. At the same time, with the advancement of technology and the improvement of environmental protection requirements, sludge treatment processes are also being continuously optimized and innovated to achieve more efficient and environmentally friendly sludge disposal goals.