The performance of high-loading composite anammox reactor and its long-term recovery from extreme substrates inhibition

Responses of anammox and sulfur/pyrite autotrophic denitrification in one-stage system to high nitrogen load: Performance, metabolic and bacterial community

To remove residual nitrate from anammox process and achieve efficient nitrogen removal, a two-stage system (TAS) with the two individual reactors and a one-stage system (OAS) with the spatial functional areas in one reactor were established via anammox coupling sulfur autotrophic denitrification. The total nitrogen removal efficiency (TNRE) of OAS system (97.85 ± 1.92%) was higher than that of TAS system (93.63 ± 1.87%) under the influent NH₄⁺-N and NO₂^--N of 227 and 300 mg/L. Meanwhile, the responses of microbial metabolism to high nitrogen load were investigated in term of microbial metabolites, electron transfer and metabolic activity. Microbial metabolites characteristics demonstrated that the OAS system secreted more EPS with lower protein (PN)/polysaccharide (PS) ratio than that in the TAS system, which was beneficial to protect bacteria from high nitrogen load. Electrochemical analysis suggested that the secretion of electron conductive substance (such as PN, PS) and redox active substances (such as flavin mononucleotide, the binding of flavins and cytochrome c on the outer membrane) were increased in the OAS system, which promoted the electron transfer efficiency. Moreover, the electron transport system activity (ETSA) values and ATP contents in OAS system were higher than that in the TAS system, which indicated that metabolic activity was improved in OAS system under the stimulation of high nitrogen load. Additionally, the bacterial community analysis indicated that the functional bacteria of Candidatus_Kuenenia and Armatimonadetes_gp5 had higher abundance in the OAS system than that in the TAS system, which was beneficial to realize the stable nitrogen removal performance. Overall, the responses mechanism of the OAS system was established to explain the resistant to high nitrogen load.

Recovery of anammox process performance after substrate inhibition: Reactor performance, sludge morphology, and microbial community

Most of the current studies have focused on the inhibition of anaerobic ammonium oxidation (anammox) by substrates, however, little attention has been paid to the recovery process of the reactor after inhibition. Therefore, we investigated the changes in reactor performance, granular sludge structure, and microbial community during the recovery phase after being inhibited by a high nitrogen load for 15 d. The nitrogen removal rate of the reactorwasrestored to pre-inhibition levels after 75 d of recovery, and the stoichiometric ratio converged to the theoretical value. The surface of the granular sludge developed into a broccoli-like structure, and the Ca and P contents of the granules increased from 6.88% and 4.39% to 24.42% and 13.88%, respectively. The abundance of the anammox bacterium Candidatus brocadia increased from 5.86% to 12.10%, and network analysis indicated that SMA102 and SBR1031 were positively correlated with the occurrence of Candidatus brocadia.

Responses of simultaneous anammox and denitrification (SAD) process to nitrogen loading variation: Start-up, performance, sludge morphology and microbial community dynamics

The effects of loading variation on the efficiency, EPS, sludge morphology and microbial population of simultaneous anammox and denitrification (SAD) were thoroughly investigated with the low-abundance SAD sludge. Results indicated that the first stage lasted the longest (33d), and the average removal rate of TN can be maintained above 95%. The specific anammox activity (SAA), specific denitrification activity and PN/PS continued to increase, but the excessive loading caused the effluent to deteriorate rapidly, and SAA and PN/PS also decreased slightly, but it could be recovered quickly. The contribution rate of anammox and denitrification to N removal reached 87.6% and 12.4% eventually, respectively. The abundance of AnAOB was 10.68%-18.01%, 9.01%-15.54%, 5.74%-12.88% in the upper, middle and lower layers, respectively. Candidatus Kuenenia was always the dominant AnAOB, especially after high loading inhibition. The abundance of denitrifying bacteria (mainly Bacillus, Comamonas and Denitratisoma) gradually became the highest.

Realizing stable operation of anaerobic ammonia oxidation at low temperatures treating low strength synthetic wastewater

The low activity of Anammox bacteria at low temperatures and competition from nitrite oxidation bacteria (NOB) when treating low strength wastewater have been major bottlenecks in implementing Anammox in mainstream wastewater treatment. By intermittent high strength feeding (IHSF) and stepwise temperature reduction, stable operation of a granular Anammox reactor was realized at low temperatures (down to 15°C) for 28days when treating low strength synthetic wastewater. The nitrogen loading rate reached 1.23-1.34kgN/m³/day, and the total nitrogen removal rate reached 0.71-0.98kgN/m³/day. The IHSF enriched the Anammox sludge in high strength cycles and compensated for sludge loss in low strength cycles, and the high concentration of ammonium in high strength cycles inhibited NOB. The 16SrRNA gene sequencing results revealed that Candidatus Kuenenia was predominant in the reactor at low temperatures.