Mixed-up sentence exercise

Put the parts in order to form a sentence. When you think your answer is correct, click on "Check" to check your answer. If you get stuck, click on "Hint" to find out the next correct part.
   The water has chlorine added to kill any remaining bacteria, and the water is tested before being returned to the lake or river.      Water is screened to remove large objects.      Waste water enters the treatment area from town sewers.      Gases produced by this process are collected and sold as fuel; the remaining sludge is dried and buried, burned, or sold as fertilizer.      The liquid is stored in a settling tank where solids suspended in the water can settle to the bottom.      A final settling tank allows remaining solids to be collected.      Meanwhile the water has chemicals added to remove phosphates and is then moved to aeration tanks, where oxygen is added, and bacteria consume any organic materials.      This sludge is collected, and bacteria are added, which consume organic waste.