With the arrival of summer, a thorny problem often arises in the water treatment process of the water plant: the turbidity of the raw water is not high, only a few NTU. After a series of treatments, a large amount of scum floats on the surface of the sedimentation tank, and the turbidity of the water leaving the factory cannot be reduced to the ideal level. This situation seriously affects the water quality of the water supply.
Algae outbreak is one of the key causes. In a high algae environment, the special properties of algae interfere with the normal coagulation and sedimentation process. At the same time, there is room for optimization of factors such as the addition of reagents in the treatment process and the operating conditions of the sedimentation tank.
Characteristics and changes of algae impact in summer
1. Characteristics of algae: When algae bloom, the extracellular organic matter on the surface of algae cells protects the algae cells, making the flocs produced during the coagulation process loose, low in density and poor in sedimentation, resulting in some algae failing to settle effectively, forming scum floating on the surface of the sedimentation tank.
Changes in pH value: Algae absorb carbon dioxide during growth, causing the pH value of water to increase, and high pH value reduces the hydrolysis effect of coagulants, affects the formation and precipitation of alum flocs, and thus makes the turbidity of the effluent higher.
Various agents and dosing issues
1. Insufficient or improper coagulant dosing: Insufficient PAC dosing may lead to poor coagulation effect, and impurities such as suspended matter and algae in the water cannot be fully flocculated to form large alum flowers, thereby affecting the sedimentation effect, causing scum and increased turbidity. In addition, if the quality of PAC is poor or the dosing method is unreasonable, it may also affect the coagulation effect.
Oxidant dosing issues: Although potassium permanganate pre-oxidation and chlorine dioxide sterilization are used, if the dosing amount is insufficient or the dosing ratio is unreasonable, it may not be able to effectively oxidize and decompose organic matter and algae in the water, leaving some organic matter and algae, affecting the sedimentation effect and causing scum. If the oxidant is added in excess, the pH value of the water may increase, which is not conducive to coagulation and sedimentation.
Factors related to sedimentation tanks
1. Unstable water flow: The flow velocity distribution in the sedimentation tank inlet area is uneven, and there are short-flow or vortex phenomena, which may cause the alum flowers to be destroyed or fail to settle fully during the sedimentation process, and some alum flowers rise with the water flow to form scum. The design of the outlet area is unreasonable, such as the load of the outlet weir is too high, which will also cause the settled alum flowers to float again.
Insufficient sedimentation time: If the residence time of the sedimentation tank is too short, impurities such as flocs and algae in the water that have not been completely settled will flow out with the water flow, affecting the water quality of the outlet water.
Optimize the pretreatment process
1. Adjust the dosage of oxidant: According to the changes in raw water quality, accurately adjust the dosage of potassium permanganate and chlorine dioxide to ensure that the oxidant can effectively oxidize and decompose organic matter and algae in the water, while avoiding excessive addition leading to an increase in pH. The water quality indicators of raw water can be monitored in real time, and the optimal dosage and dosage ratio can be determined in combination with experiments.
2. Combined use of oxidants and algaecides: On the basis of oxidant pre-oxidation, consider adding an appropriate amount of algaecides such as copper sulfate when the raw water algae density is high to enhance the algae removal effect.
Improve coagulation and sedimentation process
1. Add coagulants: Add activated silica and other coagulants to increase the density and strength of alum flocs, improve their sedimentation performance, and help reduce scum and reduce the turbidity of factory water.
2. Optimize coagulant addition: timely adjust the amount of PAC added according to water quality changes, and ensure that the quality of PAC meets the requirements. At the same time, optimize the coagulant addition method, such as multiple additions or point additions, so that the coagulant and water are fully mixed to improve the coagulation effect.
Improve the operating conditions of the sedimentation tank: hydraulic simulation and optimization of the sedimentation tank, adjust the design of the water inlet and outlet areas, improve the flow state of the water, and reduce short-flow and vortex phenomena. The sedimentation time can be appropriately extended according to the actual situation to ensure that impurities in the water have enough time to settle.
Strengthen flotation treatment process and water quality monitoring
1. Add flotation device: Change the sedimentation tank to a flotation tank, or add a flotation process to the existing process, and use bubbles to adhere algae particles and flocs, so that they float and remove, which can effectively reduce the content of algae and suspended matter in the water.
2. Optimize flotation operation parameters: According to water quality and water temperature, adjust the operating parameters of the flotation tank such as dissolved air pressure, flotation time, and dosage to improve the flotation effect.
3. Strengthen water quality monitoring: Establish a sound water quality monitoring system to monitor the water quality changes of raw water, treatment process water and effluent in real time, including turbidity, algae density, pH value and other indicators, timely discover water quality problems and adjust process parameters.
4. Regularly maintain equipment: Regularly maintain and maintain the equipment of the water plant to ensure its normal operation. For example, check and repair the mixer, dosing system, mud discharge equipment of the sedimentation tank, etc., to ensure that the reagents are mixed evenly, the dosage is accurate, and the mud discharge of the sedimentation tank is smooth.