https://www.forbes.com/sites/bridaineparnell/2015/09/15/pooping-stars-nasa-reveals-what-happens-to-human-waste-aboard-the-iss/?sh=596dc7982b09

"..Ever wondered what happens to astronaut’s excrement when they’re on the International Space Station? Well, wonder no more! It turns out that the faeces is ejected from the station and burns up in Earth’s atmosphere as rather gross shooting stars, according to NASA ........As well as what happens to his solid toilet output, Kelly will consume around 730 litres of recycled urine and sweat as water over the year......"