What goes down your toilet and drain can end up on farm fields across the United States. Biosolids, or sewage sludge, are the solid byproducts of the wastewater treatment process. So how does this nutrient-rich residue come about? At most sewage treatment plants, the process starts when wastewater arrives and screens are used to filter out large debris such as toilet paper and trash. After that, a sedimentation tank uses gravity to separate more of the solids from the liquid. Other steps use microbes to aid in decomposition, centrifuges to thicken the solids, more microbes, and then heat to kill off most pathogens. One more thickening step and the material is ready to apply on a farm field. What goes down your toilet and drain can end up on farm fields across the United States. Biosolids, or sewage sludge, are the solid byproducts of the wastewater treatment process. So how does this nutrient-rich residue come about? At most sewage treatment plants, the process starts when wastewater arrives and screens are used to filter out large debris such as toilet paper and trash. After that, a sedimentation tank uses gravity to separate more of the solids from the liquid. Other steps use microbes to aid in decomposition, centrifuges to thicken the solids, more microbes, and then heat to kill off most pathogens. One more thickening step and the material is ready to apply on a farm field. AP Technology and Science
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