Available online sensors can be used to create fingerprints for MABRs that characterize biofilm limiting conditions and serve as soft sensors

Abstract

Membrane aerated biofilm reactors (MABRs) are a promising biological wastewater treatment technology, whose industrial applications have dramatically accelerated in the recent five years. Increasing popularity and fast industrial adaptation are coupled with increased needs to monitor, optimize and control MABRs with available online sensors. Observations of commercial scale MABR installations have shown a distinctive and repetitive pattern relating oxygen purity in MABR exhaust gas to reactor ammonia concentrations. This provides an obvious opportunity for process monitoring and control which this paper investigates with the help of modelling. The relationship plots between the bulk ammonia concentration and the oxygen purity are defined as MABR fingerprint plots, which are described in the form of steady-state curves and dynamic trajectories. This study systematically investigated, analyzed and explained the behaviors and connections of steady-state curves and dynamic trajectories with a MABR model in SUMO®, and proposed a hypothesis about utilizing the MABR fingerprint plots to characterize MABR system performance, identify the limiting factor of biofilms and possibly develop a soft senor for MABR biofilm thickness monitoring and control.

Monitoring biofilm thickness using the membrane aerated biofilm reactor (MABR) fingerprint soft sensor to optimize nitrogen removal

“…There is little change in the slope for biofilm thickness greater than 200 μm, averaging 0.21 with variation less than 10% of the mean. Both ammonia and oxygen are limited (dual‐substrate limitation) when the biofilm is thicker than 200 μm as higher mass transfer resistance builds, which has negative impacts on diffusion of ammonia from the bulk liquid and the resulting bulk ammonia concentration (Casey et al, 2000; Pérez‐Calleja et al, 2022; Yang et al, 2022).…”

“…The MABR unit volume was set at 16 m 3 with tank depth of 3.5 m and membrane area of 1,920 m 2 to reflect the size of a typical commercial cassette (Zeelung 2.0). The MABR media wall thickness was 160 μm, the median of the tested range in the previous study from our group (Yang et al, 2022). The biofilm thickness was varied from 20 to 1,000 μm (50 thicknesses), and the biofilm specific mass was varied from 2 to 100 g TSS/m 2 correspondingly.…”

“…The fingerprint plot for biofilm thicknesses of 60, 80, 100, or 200 μm is essentially a flat line with slopes close to zero. The flat lines represent the oxygen limitation condition where increasing the bulk ammonia concentration will not lower the exhaust oxygen purity (Yang et al, 2022). In such high ammonia loading condition, the MABR system is overloaded, and oxygen demand is higher than the fixed oxygen supply typically used in practice.…”

“…A previous study from our group illustrated a method to monitor nitrification performance and biofilm development in MABRs using a soft sensor called the MABR fingerprint, which is a plot of exhaust oxygen purity in the gas phase versus the bulk liquid ammonia concentration (Yang et al, 2022). The results presented there indicated that biofilm thickness can be evaluated indirectly by analyzing the slope of the inclined linear segment of this plot, referred to as representing ammonia-limited conditions in the MABR biofilm.…”