with oxygen; the term usually applies to microbial decomposition processes that take place where air is present (5)

ability to pay for a product or service (13)

without oxygen; the term usually applies to microbial decomposition that takes place in the absence of air (5)

decomposition of organic material by micro-organisms in the absence of oxygen to produce biogas (5)

first stage in a waste stabilisation pond system that consists of a deep pond  where anaerobic decomposition takes place (6)

a type of composting latrine that does not require emptying. When the pit is full, a tree is planted in it and a new pit is dug (5)

percentage of solid material remaining when all the combustible material in a waste has been burned (7)