Progress and Prospects of the Research of Complete Ammonia Oxidizers in Biological Wastewater Treatment

Abstract

Comammox collapses the textbook two-step nitrification into a one-cell reaction: the same bug converts NH₃ straight to NO₃⁻, upending the dogma that ammonia and nitrite oxidation must be split between different microbes. These single-step nitrifiers reset the playbook for microbial nitrogen turnover, global N-cycling and engineered denitrogenation. Here we chart their discovery trail, then condense what is known about their physiology, ecology and environmental footprints.We also map where comammox cells hide in treatment plants and how they can sway nitrogen conversions. Their edge under low O₂ and modest NH₃ hints at threats to partial nitritation and anammox stability. Closing sections flag open questions for future plant-focused work.