Ever wondered what happens to that water you use after you flush, do a load of laundry, or wash a sink full of dishes? You're about to!
From showering to brushing, cooking, and basic hygiene to industrial processes that employ copious amounts of water, we use tons of water in our daily life. While some of it can be safely disposed off in the environment, heavily polluted water needs a system to treat, restore, and, if possible, recycle it.
Enter wastewater treatment.
Wastewater treatment refers to the process in which a combination of various processes (e.g., physical, chemical and biological) are used to treat wastewater - water that is no longer needed or is no longer suitable for use. The process entails a series of steps that remove pollutants and sediment before and convert the wastewater into an effluent that can be safely discharged back into the environment or directly reused.
In the olden days, when sewage was simply dumped into the nearest available body of water, wastewater underwent a natural treatment process. First, the sheer volume of clean water in the stream or lake diluted wastes. Next, bacteria and other small organisms in the water consumed the sewage and other organic matter, turning it into new bacterial cells, carbon dioxide and other products. The 'cleaned' water was then reused by people in the neighbouring areas, completing the recycling process. While natural wastewater treatment still occurs today, we can't rely on it as our sole method of water purification. Our higher populations and a greater volume of domestic and industrial wastewater means that we can't wait for nature to take its course and need man-made processes to keep up with the increased supply of wastewater.
Wasterwater is collect via sewers and drains from homes, businesses and industries where it is then directed to a central point. From there, underground drainage systems or by exhauster tracks owned and operated by business people deliver the water to specialised plants for treatment. The basic function of wastewater treatment is to speed up the natural processes by which water is purified, via two basic stages - primary and secondary - which are outlined below:
Full of pollutants and foul substances, wastewater is first treated for odor by the use of chemicals that neutralise the foul smells. Next, the water is screened. Screening involves the removal of large objects for example nappies, cotton buds, plastics, diapers, rags, sanitary items, nappies, face wipes, broken bottles or bottle tops that in one way or another may damage the equipment. Failure to observe this step, results in constant machine and equipment problems. Specially designed equipment is used to get rid of grit that is usually washed down into the sewer lines by rainwater. The solid wastes removed from the wastewater are then transported and disposed off in landfills.
Wastewater then moves onto the primary stage, where solids are allowed to settle and removed from it. This process involves the separation of macrobiotic solid matter from the wastewater. Primary treatment is done by pouring the wastewater into big tanks for the solid matter to settle at the surface of the tanks. The sludge, the solid waste that settles at the surface of the tanks, is removed by large scrappers and is pushed to the center of the cylindrical tanks and later pumped out of the tanks for further treatment. The remaining water is then pumped for secondary treatment.
Over the years, primary treatment alone has been unable to meet many communities’ demands for higher water quality. To meet them, cities and industries normally treat to a secondary treatment level, and in some cases, also use advanced treatment to remove nutrients and other contaminants.
In the secondary treatment stage, seed sludge is added to the wastewater to ensure that is broken down further. Air is first pumped into huge aeration tanks which mix the wastewater with the seed sludge which is basically small amount of sludge, which fuels the growth of bacteria that uses oxygen and the growth of other small microorganisms that consume the remaining organic matter. This process leads to the production of large particles that settle down at the bottom of huge sedmentation tanks. The wastewater passes through the large tanks for a period of 3-6 hours, and results about 85 percent of the organic matter in sewage being removed. To complete secondary treatment, effluent from the sedimentation tank is usually disinfected with chlorine and sodium hypochlorite for at least 20-25 before being discharged into receiving waters. The disinfection process is an integral part of the treatment process because it guards the health of the animals and the local people who use the water for other purposes. The effluent (treated waste water) is later released into the environment through the local water ways.
The solid matter that settle out after the primary and secondary treatment stages are directed to digesters. The digesters are heated at room temperature. The solid wastes are then treated for a month where they undergo anaerobic digestion. During this process, methane gases are produced and there is a formation of nutrient rich bio-solids which are recycled and dewatered into local firms. The methane gas formed is usually used as a source of energy at the treatment plants. It can be used to produce electricity in engines or to simply drive plant equipment. This gas can also be used in boilers to generate heat for digesters.
The filtered wastewater finally enters into the tertiary stage of treatment, where most impurities are removed from the supply. During this stage, as much as 99% of the impurities are eliminated, making water that is close to drinking water quality. For this stage, wastewater facilities need special equipment and chemical feed stations powered by system automation to effectively sanitize the water. After the combination of equipment and system automation has successfully sanitized wastewater, it is released into the environment through local waterways.
The final byproduct of this process - the sludge that is produced and collected during the primary and secondary treatments - is then concentrated in thickening tanks that allow it to settle down and later separates from the water. This process can take up to 24 hours, after which the remaining water is collected and sent back to the huge aeration tanks for further treatment. The sludge is then treated and sent back into the environment and can be used for agricultural use.
Purified wastewater is can also be used to combat the scarcity of water in urban developments. Reclaimed water can supply needed water for irrigation and industrial purposes, while freeing up fresh water that can be used somewhere else, such as for drinking water. A lot of wastewater goes toward municipal uses like watering golf courses, public parks, sporting facilities, private gardens, roadsides; Street cleaning; Fire protection systems; Vehicle washing; Toilet flushing; Air conditioners; Dust control, and for landscaping alongside public roads.