Why are they harmful to the environment?

Landfills pose a significant problem for the environment, especially relating to how they affect the decomposition of natural material.  Food in landfills is subjected to anaerobic composting which is significantly worse for the environment.  This rotting food produces large quantities of methane emissions, which could be avoided by using sustainable aerobic composting.  Waste disposal in landfills is already harmful because it often causes pollutants to seep into soil beds, contaminating air and water and negatively affecting communities.  This is sadly unavoidable for most waste that cannot be recycled or composted, but the mass of landfills with compostable food waste is unnecessary and harmful to ecosystems and the Earth as a whole.