Research progress on solid-phase electron donors for the denitrification of wastewater: A review

Abstract

Electron donor-mediated biological denitrification, the most extensively employed method for the treatment of nitrate nitrogen (NO₃⁻-N), involves NO₃⁻-N directly or indirectly by acquiring electrons provided by electron donors and converting them into N₂. Currently, the most widely researched electron donors are gaseous, liquid, and solid forms. Owing to the difficulties in storing and transporting gaseous and liquid electron donors, and their potential for causing secondary pollution, solid-phase electron donors (SPEDs), which can be slowly utilized by microorganisms, have gradually gained attention. SPEDs not only serve as a carrier for microbial attachment, but most SPEDs are also low-cost and readily available, making them advantageous for practical applications. In this review, the different types of SPEDs are classified and their microbial utilization mechanisms in the biological denitrification process discussed based on their classification. Their denitrification performance, influencing factors, practical applications, and existing issues are summarized. This review provides a reference for future research on SPED and its applications. It also provides an outlook on SPED-mediated mixotrophic denitrification and SPED-coupled electrochemical technology for enhanced nitrogen removal processes, in view of this hot direction in SPED research.