We all have, more or less, a brief idea about what happens inside a water treatment plant – basically, it purifies water and sewage so that clean water can be allowed back into the environment. What many of us don’t know is that the plant actually eliminates contaminants & solids first, then breaks down the organic matter present in the water, and finally performs a complete restoration of oxygen content. And these things, in turn, are achieved through a specific series of operations –
1) Preliminary treatment
2) Primary treatment
3) Secondary treatment
4) Sludge treatment
Let’s take a quick look at these four phases:
During the phase of preliminary treatment, easy pickings such as garbage, leaves, tree branches, plastic bottles, diapers, cans, waste materials, rags, etc. are extracted by bar screens. Some plants have air blowers for whipping fats and grease into froth so that they can be removed easily. Glass, sand and stones are settled out through regulation of water inflow by grit chambers & equalisation basins.
In this stage, water collected within sedimentation tanks and large basins are first separated from small particles by allowing the pollutants to settle out. Mechanical scrapers then gathers the solid matter for directing it to hoppers, which are, in turn connected to sludge treatment chamber. Some plants for water treatment in Cork use surface skimmers to extract oil and grease during the primary phase.
Secondary treatment mainly moves waste water inside secondary basins after aerating it, adding beneficial microbes in the process to initiate breakdown of organic matter. An array of strategies are employed for breaking down sludge as well. Certain facilities construct reed beds and wetlands for decomposing organic materials. Biological aerated filters and membrane bioreactors are the other forms of technologies utilised.
This is the ultimate phase in which the sludge, or biosolids and remnant water are treated. At first, gravity segregates heavy grit from organic matter, so that they can be disposed off in landfill. The residual primary sludge is allowed to pass into a thickener and then fed into digesting tanks with anaerobic bacteria after centrifugation. The remaining impure water is thoroughly treated with nitrogen, phosphorus and various other nutrients, in addition to being disinfected until it can be finally returned to water supply.
Thus, these are the most fundamental processes involved in the purification of water within water treatment plants.