Achieving mainstream nitrogen removal through simultaneous partial nitrification, anammox and denitrification process in an integrated fixed film activated sludge reactor

Enhanced nitrogen removal of the simultaneous partial nitrification, anammox and denitrification (SNAD) biofilm reactor for treating mainstream wastewater under low dissolved oxygen (DO) concentration

The simultaneous partial nitrification, anammox and denitrification (SNAD) process for treating mainstream wastewater was investigated under different intermittent aeration modes. By controlling the aeration time of 20, 60 and 180 min during the intermittent modes, the oxygen concentration remained 3.50, 1.45 and 0.70 mg·L^-1. Correspondingly, the reactor achieved the nitrogen removal rate of 0.17, 0.29 and 0.30 kg N·m^-3·d^-1. Meanwhile, the average total inorganic nitrogen (TIN) removal efficiency reached 93.4%, 87.5% and 92.7%. The effluent NO₃^--N concentration was very low. High-throughput sequencing analysis indicated that the proportion of nitrite oxidization bacteria (NOB), anammox bacteria and denitrification bacteria was 0.15%, 0.33% and 8.78%. Candidatus Anammoxoglobus was the abundant anammox bacteria genus. Further study on the unclassified sequences revealed the possibility of the high relative abundance of Nitrosomonas-related genus and Candidatus Kuenenia-related genus on the SNAD biofilm.

Inhibition of nitrite oxidizing bacterial activity based on low nitrite concentration exposure in an auto-recycling PN-Anammox process under mainstream conditions

For municipal wastewater with low temperature and ammonium, conventional oxygen-limited have difficulty achieving long-term stable inhibition of nitrite oxidizing bacteria (NOB) and stable nitritation. So a partial nitrification-anaerobic ammonium oxidation integrated reactor with independent partitions was used to investigate the feasibility of adding an auto-recycling system to promote low exposure of nitrite in the aerobic zone and to inhibit the NOB activity. The results showed that nitrite produced in the aerobic zone could be timely transported to the anaerobic zone for Anammox utilization, and the nitrite nitrogen concentration was diluted to keep within 1 mg/L in the aerobic zone by the effluent recycling. NOB growth was inhibited by nitrite deficiency. The maximum nitrogen removal rate of the reactor was 0.29 kg/(m³·d), and the nitrate nitrogen production rate of NOB was controlled within 0.04 kg/(m³·d). Nitrosomonas and Candidatus Kuenenia were found as functional species of ammonia-oxidizing bacteria and Anammox bacteria, respectively.

Enhancing mainstream nitrogen removal by employing nitrate/nitrite-dependent anaerobic methane oxidation processes

Due to serious eutrophication in water bodies, nitrogen removal has become a critical stage for wastewater treatment plants (WWTPs) over past decades. Conventional biological nitrogen removal processes are based on nitrification and denitrification (N/DN), and are suffering from several major drawbacks, including substantial aeration consumption, high fugitive greenhouse gas emissions, a requirement for external carbon sources, excessive sludge production and low energy recovery efficiency, and thus unable to satisfy the escalating public needs. Recently, the discovery of anaerobic ammonium oxidation (anammox) bacteria has promoted an update of conventional N/DN-based processes to autotrophic nitrogen removal. However, the application of anammox to treat domestic wastewater has been hindered mainly by unsatisfactory effluent quality with nitrogen removal efficiency below 80%. The discovery of nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) during the last decade has provided new opportunities to remove this barrier and to achieve a robust system with high-level nitrogen removal from municipal wastewater, by utilizing methane as an alternative carbon source. In the present review, opportunities and challenges for nitrate/nitrite-dependent anaerobic methane oxidation are discussed. Particularly, the prospective technologies driven by the cooperation of anammox and n-DAMO microorganisms are put forward based on previous experimental and modeling studies. Finally, a novel WWTP system acting as an energy exporter is delineated.

Achieving efficient nitrogen removal and nutrient recovery from wastewater in a combining simultaneous partial nitrification, anammox and denitrification (SNAD) process with a photobioreactor (PBR) for biomass production and generated dissolved oxygen (DO) recycling

This study presents a new way to achieve energy neutral wastewater treatment based on a combined nitrification, anammox, and denitrification (SNAD) process and photobioreactor (PBR) configuration with external recycling instead of aeration, and without an additional carbon source, using fixed-film-activated sludge technology (IFAS). The SNAD-PBR process achieved total nitrogen (TN) and phosphorus removal efficiencies of 90 and 100%, respectively. In addition, dissolved oxygen (DO) was controlled in the range 0.4-1.2 mg/L by the introduction of an external recycling system. The presence of microalgae to serve as a carbon source in the SNAD reactor enabled the denitrifiers to survive. When the reflux ratio was 1:3, the lower COD/N protected the activity of the anammox bacteria, not suppressed by the heterotrophic denitrifiers. Microbial community analysis by Illumina MiSeq sequencing revealed that the new environment was more suitable for Candidatus Brocadia when a reflux system was introduced.

Nitric oxide removal from flue gas with ammonium using AnammoxDeNOx process and its application in municipal sewage treatment

A novel AnammoxDeNOx process was designed to simultaneously remove NOx in flue gas and ammonium wastewater, with the aim of exploring the possibility of using NO as a long-term and stable electron acceptor for anammox bacteria. The performance of the AnammoxDeNOx process indicated a NOx removal efficiency from simulated flue gas (including CO₂, SO₂, O₂ and NO₂) of 87-96% using simulated ammonium wastewater. With municipal wastewater, the removal efficiencies for NOx were 70-90%, total nitrogen 40-70%, and COD 80-90% (NO concentration: 100-500 ppm). The anammox genus underwent considerable changes from the dominant Candidatus Kuenenia in the stage of domestication to the predominant Candidatus Brocadia, which then became the dominant species in the simulated flue gas and actual municipal wastewater stages.

Role of cyclic diguanylate in affecting microbial community shifts at different pH during the operation of simultaneous partial nitrification, anammox and denitrification process

The intracellular cyclic diguanylate acid (c-di-GMP) has emerged as a prominent second signal molecule that coordinates sessile-motile transition and biofilm formation in many bacteria. Herein, we study the role of c-di-GMP in affecting microbial community shifts at different pH levels during simultaneous partial nitrification, anammox and denitrification process (SNAD) in integrated fixed film activated sludge (IFAS) reactor. The results demonstrated that the contents of c-di-GMP notably decreased in suspended sludge, whereas the contents of c-di-GMP in biofilm had no significant change as pH gradually increased from 7.5 to 8.5. Most of the bacteria (Blastocatella, Brevundimonas) with flagella that have been reported to be regulated by c-di-GMP were present in suspended sludge, and the microbial community structure of suspended sludge had obvious change than biofilm. The increased alkaline pH reduced intracellular c-di-GMP content for increasing the motility of bacteria to be washed out from the reactor, causing the microbial community shifts in suspended sludge. This change would lead to the increase of nitrite-oxidizing bacteria which would inhibit anammox activity. Overall, this study provided more comprehensive information regarding the shifts of microbial community induced by c-di-GMP in SNAD-IFAS reactor.