Views: 218 Author: Site Editor Publish Time: 2024-04-28 Origin: Site
Whether it is sewage collection or sewage treatment, environmental protection projects must ensure that all operations comply with local standards and specifications to the greatest extent possible. By implementing sewage treatment work, the harm of sewage to the surrounding environment can be minimized, thereby creating conditions for people's healthy lives and efficient production. Generally, the sewage treatment work carried out by environmental protection projects is divided into four essential steps: pretreatment, primary treatment, secondary treatment, and tertiary treatment.
During the actual pre-treatment work of environmental protection engineering, the main thing is to remove the substances collected from the raw sewage. If this work is not done well, it is straightforward to damage these substances or cause problems such as clogging the primary treatment clarifier pump and sewage pipeline. In this sewage treatment work, there are many types of treatment objects, such as garbage, branches, and large objects.
Sewage pretreatment refers to a series of pretreatment measures for sewage before the formal sewage treatment process. These measures mainly include physical, chemical, and biological methods. Physical methods mainly include sedimentation, filtration, extraction, etc., which are used to remove suspended matter and impurities; chemical methods mainly include neutralization, oxidation-reduction, chemical phosphorus removal, etc., which are used to remove or transform harmful substances; biological methods include biofilters, rotating discs, biofilm reactors, etc., which are used to remove organic matter and nutrients through the action of microorganisms.
Sewage pretreatment is a crucial step in the wastewater treatment process. Its purpose is to create optimal conditions for subsequent treatment processes, especially biochemical treatment. This step is also known as "pretreatment," and it helps to eliminate toxic and harmful substances from wastewater. By doing so, it ensures that the microorganisms in the biochemical pool can function correctly.
Pretreatment has several benefits. It can enhance the biodegradability of sewage and create favorable conditions for further treatment processes. It can also reduce the biological treatment load and alleviate the burden of biological treatment. Therefore, it plays a critical role in treating wastewater effectively and efficiently.
Sewage treatment involves several standard pretreatment processes, including screens, grit chambers, primary sedimentation tanks, flotation tanks, and more.
1. Screens:
Screens are installed before the sewage treatment system or water pump to capture suspended matter and significant solid pollutants in the sewage. This helps to prevent damage to pumps or process pipelines of subsequent treatment units. Typically, two screens are installed in the sewage treatment process. The sewage first passes through the coarse screen and then the fine screen.
2. Grit chamber:
Sewage inevitably gets mixed with mud and sand during migration, flow, and collection. If the sand in the sewage is not pre-sedimented, separated, and removed, it can interfere with the operation of the subsequent treatment equipment. It can cause damage to the pump, block the pipe network, and interfere with or destroy the biochemical treatment process. The grit chamber works on the principle of gravity separation. Therefore, the water inlet flow rate of the grit chamber must be controlled to enable inorganic particles with a large specific gravity to sink, while organic suspended particles can be carried away with the water flow.
3. Primary sedimentation tank:
The primary sedimentation tank serves as a pretreatment facility for the secondary biological treatment structure. It effectively removes suspended matter (SS) in sewage, with a removal rate of around 40% to 50%. Additionally, it can remove about 25% of BOD5, improving the biological treatment structure's operating conditions and reducing its pollutant load. Primary sedimentation tanks can be classified into horizontal flow, radial flow, and vertical flow based on the different water flow directions in the tank.
The primary treatment of sewage involves mechanical treatment which uses various hardware facilities such as screens, regulating tanks, grit chambers, flotation tanks, etc. These facilities serve different functions depending on their supporting methods.
The screen plays a critical role in intercepting floating objects to prevent them from blocking the pipeline. The regulating tank helps regulate water quality and maintain a suitable pH value, which is necessary for the smooth progress of subsequent sewage treatment work. The grit chamber removes inorganic particles, thus improving the purity of water. This helps to reduce impurity content and lessen the interference of impurities on the operation of the water pump, thereby increasing the durability of the water pump.
The air flotation tank causes suspended matter to float upward, and in the process, tiny bubbles of biogas in the sewage are released and effectively stored in the gas collection hood.
After the primary treatment, the secondary treatment stage is initiated. In this stage, various methods are used, each with its unique characteristics. Let's examine some of the standard secondary treatment methods:
(1) Activated Sludge Method:
During the aeration process, the organic matter in the sewage is degraded. Two important processes take place during this stage: adsorption and stabilization. The activated sludge has a large surface area, making it ideal for adsorbing organic matter. Additionally, the sticky polysaccharides present in the sludge help in adsorption. Stabilization occurs when microorganisms combine with organic matter, resulting in an effective sludge adsorption effect.
(2) SBR Process:
The SBR reactor is the main device used in this process. The treatment is relatively simple, and the organic matter in the sewage is cleaned up more effectively. The treatment effect is relatively good, and additional secondary sedimentation tank treatment is not required.
(3) CASS Method:
Derived from the SBR method, the CASS method is known for its ability to optimize the reaction tank and distribute multiple reaction zones along the direction of the reaction tank. A pre-reaction zone and central reaction zone are established, and a water-skimming device that can be raised and lowered for the primary reaction area is provided. The characteristic of the CASS method is that the sewage treatment process can be completed in only one pool, making it more convenient than the activated sludge treatment method. Additionally, it occupies less space on site.
The tertiary treatment of sewage plays a crucial role in removing heavy metals, bacteria, and BOD5. It also prevents sewage eutrophication by using methods like suspended matter cleaning, organic matter dissolution, and inorganic matter removal.
After the secondary treatment, the solid suspended matter (SS) in the water mostly consists of colloids ranging from 1 μm to 1 mm that haven't yet flocculated. This can be treated using the concrete method.
For coagulation and sedimentation, coagulants are the best option. These can separate the colloids and tiny particles of sewage, resulting in relatively independent colloids that can be further condensed to form granular flocs. These flocs can be precipitated more effectively, making the treatment process more efficient. To remove dissolved organic matter from sewage, activated carbon is the most effective method. Its surface contains appropriate pores that increase surface area and effectively adsorb heavy metal ions. O3 can also remove organic matter in sewage and effectively sterilize it.
Soluble inorganic salts in sewage can affect water quality, such as scaling. Ion exchange can be used to treat this problem and remove soluble inorganic salts. If the treated water will be used for agricultural irrigation, it should also be disinfected using a combination of ultraviolet and ozone processes to ensure high-quality water sources.
Artificial wetland-sewage treatment is a typical technical form that has achieved good application results. It uses a synthetic matrix with an appropriate amount of aquatic plants to form an ecosystem that can purify sewage through matrix filtration, precipitation, and adsorption. Microorganisms and aquatic plants interact with each other to give a natural touch to the purification process.
To ensure effective sewage treatment, a treatment mode of pre-treatment, primary, secondary, and tertiary linkage must be established. Various technologies must be jointly applied to improve the quality of sewage treatment. Industry technicians should accurately grasp the critical points of sewage treatment, operate reasonably, and optimize the technology to improve its feasibility as the industry develops. In summary, sewage treatment is a crucial part of environmental protection projects that needs to be reasonably planned and effectively implemented.
