The dirty water that comes from homes and businesses as a result of laundry, using the bathroom, and all the soapy water that comes from washing dishes and the likes in the kitchen is what we call sewage or wastewater. Rain water entering drains and industrial wastes also appear to fit under this category.Sewage is treated by a variety of methods to make it suitable for its intended use, be it for spraying onto irrigation fields for watering crops or be it for human consumption. Sewage treatment mainly takes place in two main stages: Primary and Secondary treatment. In arid areas, where there is not enough water, sewage also undergoes a tertiary treatment to meet the demands of the drinking water supply.During primary treatment, the suspended solids are separated from the water and the BOD - Biochemical Oxygen Demand of the water is reduced, preparing it for the next stage in waste water treatment.Secondary treatment can be accomplished by a wide variety of means .However, in our project and poster, we will only be concentrating on two of the most commonly used methods: the trickling filter and activated sludge. The activated sludge method uses air and a biological flock that is comprised of bacteria mainly Zoogloea and protozoan’s.
This “aeration” continues for 4-6 hours, after which it is stopped and the contents moved to a settling tank. In the settling tank, the flock settles out and removes much of the organic material with it. This process removes 75-95% of the BOD.In the trickling filter, sewage is passed as a fine spray over a bed of rocks or molded plastic, over which a bio film of aerobic microorganisms grow. This method removes 80 to 85% 0f BOD.The water is then disinfected, mostly by chlorination, and released into flowing streams or oceans .If needed or desired , the sewage water can be treated in such a way as to make it safe for consumption. This is where tertiary treatment appears.The sole purpose of any tertiary treatment is to make sewage water after it has passed through secondary treatment suitable for human consumption, in other words, it gives us potable water.