Policies established in the United States, primarily through its "Part 503" regulations, have been used as the basis for many countries' policies and regulations governing wastewater solids. These U.S. policies were largely based on risk estimates and, thus, an underlying belief that minimizing human risk is paramount. However, some aspects of the U.S. policy (such as nutrient loadings to land) are based on the idea of maintaining or not exceeding a given environmental state. This sustainability paradigm is being more widely adopted internationally, and it is argued here that "risk" and "sustainability" paradigms are not necessarily correlated or consistent. A hybrid approach is desirable and its characteristics will determined by local priorities. Within these constraints, the engineer may be tasked primarily with issues of cost and technical feasibility.
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