Hydrogen peroxide will naturally decompose into water and oxygen when exposed to sunlight, but it can also be rendered inert by adding oxalic acid, active carbon or many other mild acids. Hydrogen peroxide is more basic than acidic, so if it is necessary to neutralize it faster than it would automatically neutralize in sunlight, one must add some type of acid to bring its pH level value closer to 7.
The standard hydrogen peroxide solution that can be bought at the store is actually only about 3 percent hydrogen peroxide and the rest is water. This solution is a very mild base that will not cause any harm. It is sold in an opaque bottle because it will decompose very quickly when exposed to sunlight. If this solution needs to be disposed of, it can simply be poured down the drain due to how mild of a base it is.
Some hydrogen peroxide solutions can contain up to 30 percent hydrogen peroxide. These solutions should be handled with care and must be disposed of properly, and definitely should not just be poured down the drain. The solution can be diluted with water and left out to naturally decompose, or it can be neutralized by adding certain acids such as oxalic acid or active carbon. It should be noted that neutralization with an acid will produce an exothermic reaction, which means it will produce heat.