Rapid enrichment of anammox bacteria and transformation to partial denitrification/anammox with nitrification/denitrification sludge

Improving anammox activity and reactor start-up speed by using CO2/NaHCO3 buffer

Anammox bacteria grow slowly and can be affected by large pH fluctuations. Using suitable buffers could make the start-up of anammox reactors easy and rapid. In this study, the effects of three kinds of buffers on the nitrogen removal and growth characteristics of anammox sludge were investigated. Reactors with CO2/NaHCO3 buffer solution (CCBS) performed the best in nitrogen removal, while 4-(2-hydroxyerhyl)piperazine-1-ethanesulfonic acid (HEPES) and phosphate buffer solution (PBS) inhibited the anammox activity. Reactors with 50 mmol/L CCBS could start up in 20 days, showing the specific anammox activity and anammox activity of 1.01±0.10 gN/(gVSS·day) and 0.83±0.06 kgN/(m3·day), respectively. Candidatus Kuenenia was the dominant anammox bacteria, with a relative abundance of 71.8%. Notably, anammox reactors could also start quickly by using 50 mmol/L CCBS under non-strict anaerobic conditions. These findings are meaningful for the quick start-up of engineered anammox reactors and prompt enrichment of anammox bacteria.

Novel and innovative approaches to partial denitrification coupled with anammox: A critical review

The partial denitrification (PD) coupled with anaerobic ammonium oxidation (Anammox) (PD/A) process is a unique biological denitrification method for sewage that concurrently removes nitrate (NO3--N) and ammonium (NH4+-N) in sewage. Comparing PD/A to conventional nitrification and denitrification technologies, noticeable improvements are shown in energy consumption, carbon source demand, sludge generation and emissions of greenhouse gasses. The PD is vital to obtaining nitrites (NO2--N) in the Anammox process. This paper provided valuable insight by introduced the basic principles and characteristics of the process and then summarized the strengthening strategies. The functional microorganisms and microbial competition have been discussed in details, the S-dependent denitrification-anammox has been analyzed in this review paper. Important factors affecting the PD/A process were examined from different aspects, and finally, the paper pointed out the shortcomings of the coupling process in experimental research and engineering applications. Thus, this research provided insightful information for the PD/A process's optimization technique in later treating many types of real and nitrate-based wastewater. The review paper also provided the prospective economic and environmental position for the actual design implementation of the PD/A process in the years to come.

Simultaneous ammonia and nitrate removal by novel integrated partial denitrification-anaerobic ammonium oxidation-bioelectrochemical system

The current study explored the performance of an integrated partial denitrification-anaerobic ammonium oxidation (anammox)-bioelectrochemical system on simultaneous removal of ammonia nitrogen and nitrate nitrogen. Different operational conditions were selected to optimize critical parameters of the process for improving nitrogen removal. The results indicated that more than 90 % of total inorganic nitrogen removal efficiency was achieved under the optimal conditions: ammonia nitrogen/nitrate nitrogen ratio of 1:2, external resistance of 200 Ω and inoculation volume ratio of anammox bacteria/denitrifying at 2:1. Improved nitrogen removal under the optimal conditions were confirmed by microbial community changes (Candidatus Brocadia and Thiobacillus) and enhanced of nitrogen metabolism-related genes (hao, hzsA/C and hdh). Increases of Limnobacter indicated an enhanced electron transfer efficiency. Overall, high-efficiency and stable nitrogen removal efficiency without nitrite nitrogen accumulation could be achieved by the integrated system under the optimal conditions, providing novel insights for simultaneous treatment of domestic wastewater and groundwater.

Enrichment of anammox biomass during mainstream wastewater treatment driven by achievement of partial denitrification through the addition of bio-carriers

Anammox is widely considered as the most cost-effective and sustainable process for nitrogen removal. However, how to achieve the enrichment of anammox biomass remains a challenge for its large-scale application, especially in mainstream wastewater treatment. In this study, the feasibility of enrichment of anammox biomass was explored through the realization of partial denitrification and the addition of bio-carriers. By using ordinary activated sludge, a sequencing batch reactor (SBR) followed by an up-flow anaerobic sludge bed (UASB) was operated at 25 ± 2°C for 214 days. The long-term operation was divided into five phases, in which SBR and UASB were started-up in Phases I and II, respectively. By eliminating oxygen and adjusting the inflow ratios in Phases III-V, advanced nitrogen removal was achieved with the effluent total nitrogen being 4.7 mg/L and the nitrogen removal efficiency being 90.5% in Phase V. Both in-situ and ex-situ activity tests demonstrated the occurrence of partial denitrification and anammox. Moreover, 16S rRNA high-throughput sequencing analysis revealed that Candidatus Brocadia was enriched from below the detection limit to in biofilms (0.4% in SBR, 2.2% in UASB) and the floc sludge (0.2% in SBR, 1.3% in UASB), while Thauera was mainly detected in the floc sludge (8.1% in SBR, 8.8% in UASB), which might play a key role in partial denitrification. Overall, this study provides a novel strategy to enrich anammox biomass driven by rapid achievement of partial denitrification through the addition of bio-carriers, which will improve large-scale application of anammox processes in mainstream wastewater treatment.

Tracing and utilizing nitrogen loss in wastewater treatment: The trade-off between performance improvement, energy saving, and carbon footprint reduction

Biological nitrogen removal is widely applied to reduce the discharge of inorganic nitrogen and mitigate the eutrophication of receiving water. However, nitrogen loss is frequently observed in wastewater treatment systems, yet the underlying principle and potential enlightenment is still lacking a comprehensive discussion. With the development and application of novel biological technologies, there are increasing achievement in the deep understanding and mechanisms of nitrogen loss processes. This article reviews the potential and novel pathways of nitrogen loss, occurrence mechanisms, influential factors, and control strategies. A survey of recent literature showed that 3%∼73% of nitrogen loss beyond the nitrogen budget can be ascribed to the unintentional presence of simultaneous nitrification/denitrification, partial nitrification/anammox, and endogenous denitrification processes, under low dissolved oxygen (DO) and limited available organic carbon source at aerobic conditions. Key influential parameters, including DO, aeration strategies, solid retention time (SRT), hydraulic retention time (HRT), temperature and pH, significantly affect both the potential pathways of nitrogen loss and its quantitative contribution. Notably, the widespread and spontaneous growth of anammox bacteria is an important reason for ammonia escape at anaerobic/anoxic conditions, leading to 7%∼78% of nitrogen loss through anammox pathway. Moreover, the unwanted nitrous oxide (N2O) emission should also be considered as a key pathway in nitrogen loss. Future development of new nitrogen removal technologies is proposed to suppress the generation of harmful nitrogen losses and reduce the carbon footprint of wastewater treatment by controlling key influential parameters. Transforming "unintentional observation" to "intentional action" as high-efficiency and energy-efficient nitrogen removal process provides a new approach for the development of wastewater treatment.

Pilot-scale demonstration of self-enrichment of anammox bacteria in a two-stage nitrification-denitrification suspended sludge system treating municipal wastewater under extremely low nitrogen loading rate

In suspended sludge system, efficient enrichment and retention of anammox bacteria are crucial obstacles in mainstream wastewater treatment by anammox process. In this study, anammox bacteria was self-enriched in a pilot-scale suspended sludge system of two-stage nitrification-denitrification process serving municipal wastewater treatment. With the low ammonia (NH4+-N) of 9.3 mg/L, nitrate (NO3--N) of 15.6 mg/L and COD/NO3--N of 2.2 under extremely low nitrogen loading rate of 0.012 kg N/m3/d, anammox activity bloomed after its abundance increasing from 5.9 × 107 to 4.6 × 109 copies/g dry sludge. Significant NH4+-N removal was occurred and maintained stably in the denitrification reactor with anammox bacteria accounting for 1.13%, even under temperature decreasing to 20.0℃. The adequately anoxic environment, efficient retention with the static settlement, and NO2- production via NO3- reduction provided favorable environment for anammox bacteria. This study demonstrated the feasibility and great potential in mainstream anammox application without seeding specific sludge.

Nitrite soaking pretreatment induced initial denitrifying nitrite accumulation

Partial denitrification (PD) could be another method for obtaining nitrite. However, PD startup takes a long time limiting its investigation and application. This study proposed nitrite soaking as a pretreatment method for starting PD. Results showed that denitrifying nitrite accumulation (4.20 mg/L) emerged after previously soaking by 10 mg/L nitrite for 9 h. When the duration was 6 h, comparing different soaked nitrite concentrations, the highest denitrifying nitrite accumulation amount (4.92 mg/L) was obtained in the 20 mg/L group. Nevertheless, high pH of 9 and frequent feeding could further advantage denitrifying nitrite accumulation. Pretreatment as a disturbance would impel the microbial community to change from complete denitrification towards PD.

Response of nitrite accumulation, sludge characteristic and microbial transition to carbon source during the partial denitrification (PD) process

Partial denitrification (PD, nitrate (NO3--N) → nitrite (NO2--N)) as a novel pathway for NO2--N production has been widely concerned, but the specific conditions for highly efficient and stable nitrite maintenance are not yet fully understood. In this study, the effects of carbon sources (acetate, R1; propionate, R2; glucose, R3) on NO2--N accumulation was discussed without seeding PD sludge and the mechanism analysis related to sludge characteristic and microbial evolution were elucidated. The optimal NO2--N, nitrate-to-nitrite transformation ratio (NTR) and nitrite removal efficiency (NRE) reached up to 32.10 mg/L, 98.01 %, and 86.95 % in R1. However, due to the complex metabolic pathway of glucose, the peak time of NO2--N production delayed from 30 min to 60 min. The sludge particle size decreased from 154.2 μm (R1), 130.8 μm (R2) to 112.6 μm (R3) with the increasing extracellular polymeric substances (EPS) from 80.75-85.44 mg/gVSS, 82.68-92.75 mg/gVSS to 106.31-110.25 mg/gVSS, where the ratio of proteins/polysaccharides (PN/PS) was proved to be closely associated with NO2--N generation. For the microbial evolution, Saccharimonadales (70.42 %) dominated the glucose system, while Bacillus (7.42-21.63 %) and Terrimonas (4.24-5.71 %) were the main contributors for NO2--N accumulation in the acetate and propionate systems. The achievement of PD showed many advantages of lower carbon demand, minimal sludge production, lesser greenhouse gas emission and prominent nutrient removal, offering an economically and technically attractive alternative for NO3--N containing wastewater treatment.