Dear Sebastián ,

Upon treating with acids such as HNO3, H2SO4 or H3PO4, a decomposition reactions of the carbonaceous material found in the landfill  with the acid occurs and produce a wide range of other materials including methane, carbon dioxide and a complex mixture of organic acids, aldehydes, alcohols and simple sugars. The foam is the result of the gases formed during this decomposition.

For more details please use the following link: https://en.wikipedia.org/wiki/Leachate

Hoping this will be helpful,

Rafik

The problem could not be happening if the acidic waste was properly stabilized with soil and neutralizing agents before disposing in the land fill reduce or increase the pH to the range between 6.5 and 8.5

Dear Peter,

You are absolutely right.

Pretreatment would have prevented the solve the problem before it occurs.

Rafik