Abstract
Wastewater treatment using aerobic granular sludge has gained increasing interest due to its advantages compared to conventional activated sludge. The technology allows simultaneous removal of organic carbon, nitrogen, and phosphorus in a single reactor system and is independent of space-intensive settling tanks. However, due to the microscale, an analysis of processes and microbial population along the radius of granules is challenging. Here, we introduce a model system for aerobic granular sludge on a small scale by using a machine-assisted microfluidic cultivation platform. With an implemented logic module that controls solenoid valves, we realized alternating oxic hunger and anoxic feeding phases for the biofilms growing within. Sampling during ongoing anoxic cultivation directly from the cultivation channel was achieved with a robotic sampling device. Analysis of the biofilms was conducted using optical coherence tomography, fluorescence in situ hybridization, and amplicon sequencing. Using this setup, it was possible to significantly enrich the percentage of polyphosphate-accumulating organisms (PAO) belonging to the family Rhodocyclaceae in the community compared to the starting inoculum. With the aid of this miniature model system, it is now possible to investigate the influence of a multitude of process parameters in a highly parallel way to understand and efficiently optimize aerobic granular sludge-based wastewater treatment systems.Key points• Development of a microfluidic model to study EBPR.• Feast-famine regime enriches polyphosphate-accumulating organisms (PAOs).• Microfluidics replace sequencing batch reactors for aerobic granular sludge research.
Highlights
The activated sludge system is the most common method for conventional wastewater treatment
We grew the S. oneidensis biofilm first under fumarate reducing anoxic conditions and microscopically inspected after 3 days whether we would see fluorescent signals. As this was not the case, we switched to the oxic mode by replacing nitrogen with air overpressure and imaged the biofilm again
As the goal of our study was to establish a platform for the cultivation of polyphosphate-accumulating organisms (PAO), we inspected whether a sample from an aeration tank of a municipal sewage plant would contain the desired organisms
Summary
The activated sludge system is the most common method for conventional wastewater treatment. Still, it is space demanding, which is a major obstacle in the context of a growing world population and simultaneous urbanization. More compact systems for wastewater treatment are preferable. Due to the poor settling velocity of activated sludge flocs, most of the space required for conventional treatment systems is needed for settling tanks. A promising alternative is the utilization of aerobic granular sludge (AGS) instead of activated sludge flocs (Morgenroth et al 1997; de Bruin et al 2004; Adav et al 2008). Increased settling velocities can be achieved due to the physical characteristics of the self-aggregating
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