Biomass segregation between biofilm and flocs improves the control of nitrite-oxidizing bacteria in mainstream partial nitritation and anammox processes. (1st May 2019)

• Record Type: Journal Article
• Authors: Laureni, Michele; Weissbrodt, David G.; Villez, Kris; Robin, Orlane; de Jonge, Nadieh; Rosenthal, Alex; Wells, George; Nielsen, Jeppe Lund; Morgenroth, Eberhard; Joss, Adriano
• Is Part Of: Water research. Volume 154(2019)
• Page Start: 104
• Page End: 116
• Publication Date: 2019-05-01
• Subjects: Mainstream anammox -- Partial nitritation/anammox -- Hybrid system -- IFAS -- Biomass segregation -- NOB washout -- Mathematical modelling -- Nitrite sink; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2018.12.051
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: The control of nitrite-oxidizing bacteria (NOB) challenges the implementation of partial nitritation and anammox (PN/A) processes under mainstream conditions. The aim of the present study was to understand how operating conditions impact microbial competition and the control of NOB in hybrid PN/A systems, where biofilm and flocs coexist. A hybrid PN/A moving-bed biofilm reactor (MBBR; also referred to as integrated fixed film activated sludge or IFAS) was operated at 15 °C on aerobically pre-treated municipal wastewater (23 mgNH4-N L −1 ). Ammonium-oxidizing bacteria (AOB) and NOB were enriched primarily in the flocs, and anammox bacteria (AMX) in the biofilm. After decreasing the dissolved oxygen concentration (DO) from 1.2 to 0.17 mgO2 L −1 - with all other operating conditions unchanged - washout of NOB from the flocs was observed. The activity of the minor NOB fraction remaining in the biofilm was suppressed at low DO. As a result, low effluent NO3 − concentrations (0.5 mgN L −1 ) were consistently achieved at aerobic nitrogen removal rates (80 mgN L −1 d −1 ) comparable to those of conventional treatment plants. A simple dynamic mathematical model, assuming perfect biomass segregation with AOB and NOB in the flocs and AMX in the biofilm, was able to qualitatively reproduce the selective washout of NOB from the flocs in response to the decrease in DO-setpoint. Similarly, numerical simulations indicated that flocs removal is an effective operational strategy to achieve the selective washout of NOB. The direct competition for NO2 − between NOB and AMX - the latter retained in the biofilm and acting as a "NO2 -sink" - was identified by the model as key mechanism leading to a difference in the actual growth rates of AOB and NOB ( i.e., μNOB < μAOB in flocs) and allowing for the selective NOB washout over a broad range of simulated sludge retention times (SRT = 6.8–24.5 d). Experimental results and model predictions demonstrate the increased operational flexibility, in terms of variables that can be easily controlled by operators, offered by hybrid systems as compared to solely biofilm systems for the control of NOB in mainstream PN/A applications. Graphical abstract: Image 1 Highlights: Hybrid PN/A systems provide increased operational flexibility for NOB control AOB and NOB enrich primarily in the flocs, and AMX in the biofilm ("NO2 -sink") AMX use NO2 − allowing to differentiate AOB and NOB growth rates A decrease in DO or an increase in floc removal leads to selective NOB washout from flocs The activity of the minor NOB fraction in the biofilm is suppressed at limiting DO