Making a scale model of a waster water treatment plant is a great way to illustrate to your children the complex infrastructure that is responsible for modern cities. Waste water treatment plants have to process polluted water through several steps before it is OK to put back into the water supply. Furthermore the waste water treatment plants requires a lot of space for the open air treatment tanks and the pumps to move all the waste water.
First lay down a 1- by 1-foot long piece of cardboard for the base of the model. Use a piece of cardboard with out any moisture damage or large seams that may bend and break the model.
Cut out a 4 inch by 4 inch by 4-inch square to represent the water pump building. Glue that block on to the cardboard, 1 inch from a corner. Label this building the pump room with a black marker. Glue a straw to the pump room so that the straw hangs off the side of the cardboard. Label this the intake pipe. Cut two 2-inch wide and 2-inch deep disks from the Styrofoam and label them settling tanks. Connect these models with straws to the pump building and glue them all to the cardboard.
Cut out two 6 inch by 4 inch by 2-inch rectangles for the aeration basins. Connect each basin to a settling tank with a straw and then super glue to the cardboard. Make another two settling tans and connect these to the aeration basins with straw. Glue to the cardboard. Affix a line of straws from the final settling basins to a green patch on the cardboard to represent the return of the water to the soil.