Sewage sludge, the stabilized and digested solid waste product of the wastewater treatment process, can be disposed of by landfilling, incineration, composting, or ocean dumping. Nature returns organic material to the soil as fertilizer. Organic material becomes waste when it is not returned to the soil but instead is burned, buried, or dumped in the ocean. These unhealthy practices began when chemical fertilizers took the market away from sludge-based compost and when industrial waste began to contaminate sewage sludge with toxic metals (lead and cadmium), making it unusable for agricultural purposes. Until recently, the bulk of the sewage sludge generated by metropolitan areas has been either landfilled or dumped in the ocean. These options are gradually disappearing and as a result municipalities will have to make some hard decisions. (See Sections 7.31 to 7.56).
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