Influence and mechanisms of humic substances on distinct anammox-based systems: A critical review

Anaerobic ammonia oxidation (anammox) is an effective nitrogen removal process with numerous advantages for NH4+-N-rich wastewater treatment. Humic substances (HSs), primarily fulvic acid (FA) and humic acid (HA) are abundant in actual wastewater (landfill leachate, etc.) and may hinder the activity of anammox bacteria despite their beneficial effect on the anammox process at (sub) optimal dosages; reports of process inhibition at excessively elevated levels have also been corroborated. This article therefore examines the influence of HSs on the performance and mechanism of anammox process. In general, low concentrations of HSs (<150 mg/L) stimulate anammox activity, whereas high concentrations (>150 mg/L) reportedly cause inhibition. Hence, previous anammox studies employing HSs have thoroughly been discussed to expound on their stimulatory or inhibitory mechanisms. Furthermore, the use of anammox for the treatment of actual wastewater with HSs and the microscopic mechanisms by which additional HSs affect anammox need to be further investigated. This paper is aimed at offering a reference for the efficient treatment of wastewater containing HSs via anammox process.