External Costs
Economic aspects of sewage sludge management

In environmental economics, an externality is the effect of a private action (producing, consuming, investing) on society that bypasses the price system. When such decisions are made by an individual or a company, they evaluate their private costs and benefits, but the side effects (whether benign or harmful) are external to the market and are not compensated for by either the polluter or the beneficiary.

An externality is negative when the effect is harmful to someone else. This is the case, for example, if a factory pollutes the water, causing pollution that degrades the environment and the health of nearby residents.

An externality is positive when the effect is beneficial or useful...