A by-product of sewage treatment is usually a semi-solid waste or slurry, called sewage sludge, that has to undergo further treatment before being suitable for disposal or land application.
Life expectancy is defined statistically as the average number of years remaining for an individual or a group of people at a given age.Longevity refers to the characteristics of the relatively long life span of some members of a population.athematically, life expectancy is the mean number of years of life remaining at a given age, assuming constant mortality rates. It is denoted by, which means the average number of subsequent years of life for someone now aged, according to a particular mortality experience.
life expectancy, n the probable number of years a person will live after a given age, as determined by the mortality rate in a specific geographic area. This number may be individually qualified by the person's condition, race, sex, age, and other demographic factors.