Sedimentation Pond
Sedimentation is an important part of water treatment. A sedimentation pond, also known as a settling pond or clarifier, is a surface water treatment facility designed to remove suspended solids from raw water. The sedimentation process often includes the addition of chemicals such as alum, iron salts, lime and polymer. The chemical addition is to improves the solids removal rate of the pond by providing a greater surface area for the solids to attach to and by providing a greater the flocculation rate.
Sedimentation ponds are normally long, narrow and shallow basins, built of concrete or cement blocks, and designed to hold water in the range of 2-3 meters deep. Sedimentation ponds use gravity to separate solids from the water, as the heavier suspended solids settle to the bottom of the pond forming a sludge layer, while the lighter water rises to the top. As water flows into the pond, a portion of the suspended solids settle to the bottom of the pond, while the rest is gradually removed by flocculation processes. Flocculation is the aggregation of suspended particles with different electric charges and the formation of small, compact and movable aggregates.
Sedimentation pond consists of two zones: the sedimentation zone, which is the area for solids-liquid separation, and the flocculation zone, which is the area for chemical addition. The purpose of the chemicals is to form a layer on the surface of the solids, which then stick to each other, further settling out of the water. The flocculation zone can also be used to separate water from sludge, though this is less common. Additionally, the sedimentation ponds are designed to remove plant material, algae and other small particles, but not large industrial particles or metals.
The sedimentation pond is usually lined with an impermeable barrier, such as geomembrane, to prevent inflow of water and any pollutants to the underlying soils, and prevent seepage out of the pond. The water collected in the sedimentation pond is then passed through a filter or a sand filter to further remove any smaller particles. The sediment and filter materials are collected in the bottom of the pond and must be periodically removed.
Sedimentation ponds are an important component of water quality management. They help to improve the quality of water by removing suspended particles, reducing turbidity levels, and decreasing the amount of organic material. Without the use of sedimentation ponds, the organic materials and suspended solids in raw water can create health hazards and reduce the efficacy of treatment. Furthermore, sedimentation ponds also help to reduce water contamination by providing a space for the settling of any harmful substances or particles before they can enter the stream or river.