Single-stage MBBR as post-treatment step for upgrading large WWTPs – Experiences of one-year pilot plant operation

• Published in: Journal of water process engineering 2022-04, Vol.46, p.102570, Article 102570
• Main Authors: Leonhard, S., Schreff, D., Thoma, K., Gander, W., Wichern, M., Hilliges, R.
• Format: Article
• Language: English
• Subjects: Bypass operation; Denitrification; MBBR; Nitrate‑nitrogen; Nitrogen removal; Polishing process
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2022.102570

In growing urban areas, increasing nitrogen loads to large WWTPs can be problematic for the existing nitrification/denitrification stage and necessitate the enlargement of the entire wastewater treatment system. Nitrogen removal is usually the most critical process in overload situations, often limited by the hydraulic capacities for recirculation. A simple and cost-effective way to meet low nitrogen effluent requirements is the proposed single-stage MBBR. This system can be implemented additionally as a bypass in the effluent. To investigate the practicability of the proposed concept, a pilot plant was operated to polish treated wastewater with an MBBR. The process is designed for post-treatment denitrification to eliminate the remaining nitrate‑nitrogen in the already treated wastewater. The paper extends the current knowledge of low concentration gradients, since no information is available on the post-treatment of nitrate‑nitrogen to 2.5 mg/L or below. In addition, the tested hydraulic retention time (HRT) of only 60 min is exceptional, allowing future single-stage MBBRs to be sized smaller. The first results of one year of operation showed a stable nitrate‑nitrogen reduction from 10.0 mgNO3-N/L to ≪5.0 mgNO3-N/L to comply with required effluent concentrations for total nitrogen. A maximum removal rate of 2.07 gNOx-N/(m2·d) at T = 20 °C was reached. Average NOx-N removal of 71% could be achieved at a minimal HRT of only 1 h. Following a two-month start-up phase, the process proved to be robust: after carbon dosage interruptions, full performance was regained after only three days in summer. [Display omitted] •Existing nitrification/denitrification stage of large WWTPs runs to its limits•Necessity of a cost-effective way to comply with low nitrogen effluent requirements•Implementation of a single-stage MBBR post treatment step•Reducing low nitrate nitrogen of 10 mg/L to ≪5 mg/L with a biofilm system•Experiences of one-year pilot plant operation to clarify the MBBR technology