Mechanical mixing clarifier: mixer and sludge scraper

I. Applicable Conditions for Clarifier Mixers:
The clarifier mixer is used in the clarification stage of water supply and wastewater treatment processes and serves as the primary equipment for mechanically stirred clarifiers.
Influent suspended solids concentration: For clarifiers without mechanical sludge scraping, the typical limit is no more than 1,000 mg/L, with a short-term allowance of up to 3,000 mg/L; for those equipped with mechanical sludge scraping, the typical limit is no more than 5,000 mg/L, with a short-term allowance of up to 10,000 mg/L. When the influent concentration frequently exceeds 5,000 mg/L, a preliminary sedimentation basin should be installed upstream of the clarifier. Clarifiers equipped with mixers exhibit high treatment efficiency, large water production per unit area, strong adaptability to variations in flow rate, water temperature, and water quality, and relatively stable treatment performance. With the addition of mechanical sludge-scraping equipment, these clarifiers demonstrate a certain degree of suitability for treating highly turbid water (with suspended solids concentrations exceeding 3,000 mg/L). The clarifier mixer creates two distinct circulating flows within the tank to achieve effective water clarification. Its function is as follows: the impeller blades at the lower part of the lifting impeller carry out mechanical flocculation in the first flocculation chamber, enabling the microflocs formed through chemical dosing and mixing to collide with and adsorb onto the pre-existing alum flocs in the recirculating flow, thereby forming larger floc aggregates; the lifting impeller then conveys the flocculated water from the first flocculation chamber to the second flocculation chamber, after which the flow is redirected into the clarification zone for separation—clear water rises to the surface, while the sludge settles to the bottom of the clarification zone and returns to the first flocculation chamber. In summary, the clarifier mixer, through these two functional components, jointly accomplishes both mechanical flocculation and separation-based clarification within the clarifier.

II. Overall Configuration The clarifier mixer consists of a variable-speed drive, an impeller, blades, and a flow-conditioning device. The mixer can be driven by a continuously variable-speed electric motor, allowing adjustment of the recirculation flow rate and mixing intensity in response to changes in influent water quality and flow. Typically, a YCT-series slip-control electromagnetic speed-regulating induction motor is used; alternatively, a standard constant-speed motor may be employed, coupled with two stages of reduction—first via V-belt pulleys and then via a worm gear set. The worm shaft and the agitator shaft are rigidly connected, usually through a clamp-type coupling. When a sludge scraper is installed:
When the tank diameter is 16.9 m or less, a center-driven sludge scraper is used, with the mixer’s main shaft designed as a hollow shaft to allow the scraper shaft to pass through the center, and the scraper’s variable-speed drive unit is mounted at the top of the mixer.
When the tank diameter exceeds 19.5 m, a split-type configuration is adopted: the mixer is positioned at the center of the tank, with its main shaft rigidly connected to the variable-speed drive and vertically suspended into the tank; meanwhile, the sludge scraper’s main shaft is independently mounted in an eccentric position on one side of the tank, and its reduction gear typically employs a two-stage reduction system consisting of a cycloidal pinwheel reducer and a pin-and-gear transmission. To meet the varying operational requirements for the ratio between lifting and mixing intensities and to ensure that the lift flow rate satisfies the conditions for separation and sedimentation, all mixers shall be equipped with flow-adjusting devices.

III. Table of Main Technical Parameters and Installation Dimensions

IV. Commissioning and Operation
When putting the equipment into operation, add No. 40 gear oil according to the reducer’s instructions; after the initial full fill, replace the oil after 3 months of operation, then replace it again 6 months after the first change, and continue this cycle. The equipment is shipped with two sets of oil already installed. Upon energizing the control cabinet, perform commissioning on the reducer motor; if any abnormal noise is detected from the reducer or motor, carry out timely maintenance to ensure proper operation before putting the equipment into service. Prior to start-up, clean the high points and any debris from the sloped concrete bottom surface inside the tank.
The equipment operates in a clockwise direction;
When starting the speed-regulating motor, gradually increase the speed from the zero position to the high-speed setting, typically to around 350–400 rpm. If the equipment is operated at high speed, the alum flocs formed by chemical dosing in the water may be easily broken up, which can compromise effluent quality and necessitate increased chemical dosage, leading to waste.
The clearance between the agitator impeller and the tank wall is 3 cm, and the clearance between the sludge scraper blades and the tank bottom is 3–8 cm.
Sludge discharge should be carried out 3 hours after inflow begins, and the timing of sludge discharge should be gradually optimized during operation (as the sludge volume depends on the specific water quality of the influent, it is not fixed).
If the clarifier is to be shut down, all settled sludge must be completely discharged before shutdown to prevent the sludge from clumping after prolonged settling, which could damage the equipment upon restart.
When operating the speed-regulating agitator motor, gradually increase the speed from zero to high and, upon shutdown, gradually reduce it from high back to zero; under no circumstances is high-speed startup or abrupt deceleration permitted, as this can lead to wear on the worm gear.

Meticulous Design

- Customized Drainage Treatment Blueprint

Leveraging a highly professional team and extensive experience, we meticulously design water supply and wastewater treatment solutions tailored to the specific needs of each region and project. Our comprehensive offerings include multi-system designs for debris interception, chemical dosing and reaction, and other critical processes, providing scientifically sound, customized engineering design services for wastewater treatment projects.

Diverse Products

- Forging a powerful tool for wastewater treatment

As a specialized manufacturer of water supply and drainage treatment equipment and materials, we offer a comprehensive range of complementary products, including systems for water supply and drainage treatment as well as bio-media and aerators tailored for wastewater treatment projects. Our extensive product portfolio meets a wide variety of application needs.

Professional Installation

- Ensure the drainage system operates smoothly

We boast a professional installation team that provides efficient installation services to customers across more than 20 provinces (including municipalities directly under the central government), as well as Hong Kong, Macao, and Southeast Asia. Adhering rigorously to standardized procedures, we ensure precise and flawless installation of water supply and wastewater treatment equipment, thereby guaranteeing stable system operation.

Keywords: trash-rack equipment, sedimentation equipment, flap-valve filter bed