Function and Settings

Due to the presence of large particles such as sand in urban wastewater, a sand settling tank must be installed before the primary sedimentation tank in urban wastewater treatment. Industrial wastewater treatment with less sand content may not require a sand settling tank.

The particulates removed by the grit chamber in urban sewage treatment include sand particles, coal slag, fruit kernels, etc. The requirements for the grit chamber's setup are to remove sand particles (density 2.65g/cm³) with a particle size of 0.2mm, and to minimize the organic matter attached or carried away in the transported grit to avoid excessive decomposition of the sand渣 in the grit chamber waste disposal process.

General provisions for sedimentation tank setting and design calculations include:

The sand settling pond is designed to remove sand particles with a relative density of 2.65 and a particle size of 0.2mm or greater.

2. Wastewater flow should be considered in phases of construction: When wastewater flows in naturally, calculate based on the designed flow rate of each phase; when lifted in by wastewater pumps, calculate based on the combined flow rate of the pump sets of each phase; in a combined sewerage treatment system, the designed flow rate during rainfall should be calculated.

The number or compartment of the sedimentation pond should not be less than two, arranged in parallel, so that only one pond can be operated when the wastewater volume is low.

4. The sand content in urban wastewater can be calculated at 0.03L/m3 (wastewater), with the sand渣 moisture content at 60% and density of 1500kg/m3; the sand content in combined wastewater systems should be determined based on actual conditions.

The sand hopper volume is calculated based on the 2d sediment quantity, with the angle between the hopper wall and the horizontal plane being no less than 55 degrees.

6. Typically, mechanical sand removal is employed, and a sand storage pond is set up. The diameter of the sand discharge pipe should not be less than 200mm.

When gravity desanding, the sand settling pond and sand storage pond should be as close as possible.

8. Before transporting sand waste, it is advisable to process it with a sand washing machine to remove the adhered organic matter from the sand.

The sedimentation pond can be categorized into three main types: horizontal flow, aeration, and vortex sedimentation ponds.