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 is the most commonly used measure to describe population health and reflects the overall mortality level of a population.Life expectancy measures how long, on average, a person is expected to live based on current age and sex-specific death rates.In summarising mortality patterns, life expectancy is often expressed as the number of years of life a person born today is expected to live.ife expectancy measures how long, on average, a person is expected to live based on current age and sex-specific death rates.