Laughing gas is a common name for the gaseous chemical substance nitrous oxide, (N₂O).

Nowadays, it has come into focus of discussions about greenhouse gases. It´s global warming potential is about 300 times stronger than carbon dioxide, (CO₂)! Laughing gas is produced during combustion processes in power plants and combustion motors, but mainly also in natural decomposi-tion processes. These are processes where ammonium is converted to nitrate and further to elemental nitrogen. In sewage treatment plants this is nitrification/denitrification. In particular, the step to nitrate takes place in several sub-steps, where nitrous oxide is one of the intermediate products.

Sub-steps of nitrification: NH₃ → NH₂OH → N₂O → NO → NO₂^- → NO₃^-

Various causes can disrupt this process chain. Intermediate products, such as nitrous oxide, can then be released before they are further converted. This release of the greenhouse gas can become increasing-ly relevant if the concentrations are high, as in centrate or process water. Therefore, in biological treatment of process water, it is particularly advantageous with regard to low emission of greenhouse gases to use a continuous single-stage process such as the EssDe^®-process . High partial concentrations cannot occur as in two-stage processes or in batch processes like SBR. This considerably reduces the emission of greenhouse gas.

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