Abstract
A sensor‐mediated strategy was applied to a laboratory‐scale granular sludge reactor (GSR) to demonstrate that energy‐efficient inorganic nitrogen removal is possible with a dilute mainstream wastewater. The GSR was fed a dilute wastewater designed to simulate an A‐stage mainstream anaerobic treatment process. DO, pH, and ammonia/nitrate sensors measured water quality as part of a real‐time control strategy that resulted in low‐energy nitrogen removal. At a low COD (0.2 kg m−3 day−1) and ammonia (0.1 kg‐N m−3 day−1) load, the average degree of ammonia oxidation was 86.2 ± 3.2% and total inorganic nitrogen removal was 56.7 ± 2.9% over the entire reactor operation. Aeration was controlled using a DO setpoint, with and without residual ammonia control. Under both strategies, maintaining a low bulk oxygen level (0.5 mg/L) and alternating aerobic/anoxic cycles resulted in a higher level of nitrite accumulation and supported shortcut inorganic nitrogen removal by suppressing nitrite oxidizing bacteria. Furthermore, coupling a DO setpoint aeration strategy with residual ammonia control resulted in more stable nitritation and improved aeration efficiency. The results show that sensor‐mediated controls, especially coupled with a DO setpoint and residual ammonia controls, are beneficial for maintaining stable aerobic granular sludge.Practitioner points Tight sensor‐mediated aeration control is need for better PN/A.Low DO intermittent aeration with minimum ammonium residual results in a stable N removal.Low DO aeration results in a stable NOB suppression.Using sensor‐mediated aeration control in a granular sludge reactor reduces aeration cost.
Highlights
There is great interest in wastewater systems that are energy neutral or positive to achieve resource recovery using means that meet stringent effluent standards
We propose the use of real-time sensor-mediated control (SMC) for robust aeration control to suppress NOB
Phase 1: Granule formation The initial phase of granule development took about 60 days (Figure 2), which is relatively rapid compared to other granular systems (Ni et al, 2009)
Summary
There is great interest in wastewater systems that are energy neutral or positive to achieve resource recovery using means that meet stringent effluent standards. The anaerobic membrane biofilm reactor (AnMBR) has been proposed as a viable A-stage technology that could become an energy-efficient option (Smith et al, 2014). The B-stage is focused on energy-efficient nutrient (commonly nitrogen) management (Jetten, Horn, & van Loosdrecht, 1997; Wan, Gu, Zhao, & Liu, 2016). Most of the energy expense in an A-B process occurs due to aeration in the B-stage, where the remaining carbon and nitrogen (N) are removed. In some cases, it is possible for the energy expense in the B-stage to negate the energy gained in the A-stage, making A-B process inefficient for energy recovery (Zhou et al, 2013)
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