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Steps in the Primary Treatment Of Wastewater

Once the earth’s natural water cycle could no longer meet the demands of its burgeoning population, humans were forced to devise methods to recycle water artificially. In practice, most of that we use to shower, flush toilets, clean our clothes and power innumerable industrial processes will eventually be returned to our taps or reused in some other fashion. However, reuse is only possible after a series of purification processes. During the primary treatment of wastewater, much of the focus is on its visible qualities. This initial phase of the purification process could consist of several steps that vary, depending upon the source and the size and nature of the solids present.

Municipal Water Treatment Solutions

Preliminary Screening and Shredding

The raw source water is often drawn from a stream or storage dam. It is likely to contain large items such as branches, leaves and discarded packages and bottles. Therefore, the first step in the primary treatment of wastewater will generally be to remove such items. The process utilises a coarse filtration procedure known as screening. A closely spaced collection of metal bars forms a screen that traps the larger pieces of debris, which can then be disposed of in a landfill or incinerated. However, this technique will still allow some debris to pass. A grinding device, known as a comminutor, will shred any untrapped solid residue to make it more suitable for removal by alternative techniques.

The Sedimentation Stage

The following requirement in the primary treatment of wastewater will be to remove those remaining large solids. Some of the residual shredded debris may be sufficiently dense to settle out under the effect of gravity. In contrast, materials with low specific gravity will continue to float. The settlement process takes place in large tanks. The source water will continue to stand until the sedimentation phase is complete. It is then possible to skim off the surface material before separating the relatively clear fluid from the sediment, ready for the next step in the purification process.

Chemical Treatment and Filtration

At this stage, some turbidity remains, and residual organic materials will also give rise to odours and discolouration. Subsequent treatments applied during the secondary phase of processing will result in a clear, colourless and odourless fluid ready for the final tertiary phase. After pH testing, sufficient volumes of alkali or acid are added until the effluent’s pH is neutral. Residual colloids in suspension may also be aggregated by adding chemical flocculants before filtering the liquid through layers of sand and gravel.

For more information, quality chemicals and equipment for use in the primary treatment of wastewater, contact the expert team at Watericon.