When societies were still mostly rural and agricultural, waste disposal was hardly an issue, partly because people tended to make use of everything and partly because there was plenty of space to bury rubbish. It was when societies became predominantly urban and industrial that problems arose - mainly to do with wealth. City authorities had a hard time trying to find efficient ways of getting rid of all the rubbish. One of these was to get people to sort out their rubbish into different types, just as these days we are encouraged to separate our rubbish into different categories for easier removal and recycling. So, for example, kitchen rubbish was set aside and used for feeding animals. However, fears of disease put an end to that. In fact, it wasn't until the 20th century that all waste was simply thrown together and ploughed into landfills.