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.
Maximum life span (or, for humans, maximum reported age at death) is a measure of the maximum amount of time one or more members of a population have been observed to survive between birth and death. The term can also denote an estimate of the maximum amount of time that a member of a given species could survive between birth and death, provided circumstances that are optimal to that member's longevity.