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www.GOALias.blogspot.comFig. 18.2 Filtration process Fig. 18.3 Bar screen• Observe carefully the samples in allthe test tubes. Do not taste! Justsmell them!Now answer the following questions:(a) What changes did you observe in theappearance of the liquid afteraeration?(b) Did aeration change the odour?(c) What was removed by the sand filter?(d) Did chlorine remove the colour?(e) Did chlorine have an odour? Was itworse than that of the wastewater?18.4 WASTEWATERTREATMENTPLANT(WWTP)Treatment of wastewater involvesphysical, chemical, and biologicalprocesses, which remove physical,chemical and biological matter thatcontaminates the wastewater.1. Wastewater is passed through barscreens. Large objects like rags,sticks, cans, plastic packets, napkinsare removed (Fig. 18.3).2. Water then goes to a grit and sandremoval tank. The speed of theincoming wastewater is decreased toallow sand, grit and pebbles to settledown (Fig. 18.4).Fig. 18.4 Grit and sand removal tank3. The water is then allowed to settle ina large tank which is sloped towardsthe middle. Solids like faeces settleat the bottom and are removed witha scraper. This is the sludge. Askimmer removes the floatable solidslike oil and grease. Water so clearedis called clarified water (Fig. 18.5).223WASTEWATERSTORY223