Deammonification for digester supernatant pretreated with thermal hydrolysis: overcoming inhibition through process optimization

Abstract

The thermal hydrolysis process (THP) has been proven to be an excellent pretreatment step for an anaerobic digester (AD), increasing biogas yield and decreasing sludge disposal. The goal of this work was to optimize deammonification for efficient nitrogen removal despite the inhibition effects caused by the organics present in the THP-AD sludge filtrate (digestate). Two sequencing batch reactors were studied treating conventional digestate and THP-AD digestate, respectively. Improved process control based on higher dissolved oxygen set-point (1 mg O2/L) and longer aeration times could achieve successful treatment of THP-AD digestate. This increased set-point could overcome the inhibition effect on aerobic ammonium-oxidizing bacteria (AerAOB), potentially caused by particulate and colloidal organics. Moreover, based on the mass balance, anoxic ammonium-oxidizing bacteria (AnAOB) contribution to the total nitrogen removal decreased from 97 ± 1 % for conventional to 72 ± 5 % for THP-AD digestate treatment, but remained stable by selective AnAOB retention using a vibrating screen. Overall, similar total nitrogen removal rates of 520 ± 28 mg N/L/day at a loading rate of 600 mg N/L/day were achieved in the THP-AD reactor compared to the conventional digestate treatment operating at low dissolved oxygen (DO) (0.38 ± 0.10 mg O2/L).

Impacts of feed dilution and lower solids retention time on performance of thermal hydrolysis/anaerobic digestion

“…Another potential advantage of feed dilution is that the concentration of sCOD leaving the digester is lower, and this could reduce inhibition of sidestream processes. For example, deammonification has been used to treat return liquors from THP‐AD systems and components in the filtrate have been shown to be inhibitory (Figdore et al., ; Zhang et al., ). Figdore et al.…”

“…() suggested that the inhibitory compounds were associated with the sCOD fraction, while Zhang et al. () suggested that colloidal and particulate COD fractions were associated with inhibition. Figdore et al.…”

“…Another potential advantage of feed dilution is that the concentration of sCOD leaving the digester is lower, and this could reduce inhibition of sidestream processes. For example, deammonification has been used to treat return liquors from THP-AD systems and components in the filtrate have been shown to be inhibitory (Figdore et al, 2011;Zhang et al, 2016). Figdore et al (2011) suggested that the inhibitory compounds were associated with the sCOD fraction, while Zhang et al (2016) suggested that colloidal and particulate COD fractions were associated with inhibition.…”

“…For example, deammonification has been used to treat return liquors from THP-AD systems and components in the filtrate have been shown to be inhibitory (Figdore et al, 2011;Zhang et al, 2016). Figdore et al (2011) suggested that the inhibitory compounds were associated with the sCOD fraction, while Zhang et al (2016) suggested that colloidal and particulate COD fractions were associated with inhibition. Figdore et al (2011) suggested dilution of the return liquor could be used to reduce inhibition.…”

Novel Stokesian Metrics that Quantify Collision Efficiency, Floc Strength, and Discrete Settling Behavior

“…This pilot simulated the BNR system at Blue Plains with the difference that an aggressive aerobic SRT (1 to 5 days) was used under transient anoxia and anammox granules were bioaugmented. Therefore, this system can be seen as a hybrid system with a small fraction of anoxic ammoniumoxidizing granules; (4) Sidestream sludge was obtained from a sidestream deammonification pilot at Blue Plains (Zhang et al, 2016). The sidestream pilot plant was a sequencing batch reactor, which was treating centrate from the Alexandria Sanitation Authority.…”