It is bio toilets, which are fitted underneath the lavatories. The human waste discharged into them is acted upon by a particular kind of bacteria that converts human waste into non-corrosive neutral water.
But to my surprise there was no water in the my boogie on 1 side. so people had to use only 2 toilets and 1 washbasin in the morning. there were passengers coming from next boogie also to use toilets . this is very very bad expirence.