Start-up and nitrogen removal performance of CANON and SNAD processes in a pilot-scale oxidation ditch reactor

Anammox-based technologies: A review of recent advances, mechanism, and bottlenecks

The removal of nitrogen via the ANAMMOX process is a promising green wastewater treatment technology, with numerous benefits. The incessant studies on the ANAMMOX process over the years due to its long start-up and high operational cost has positively influenced its technological advancement, even though at a rather slow pace. At the moment, relatively new ANAMMOX technologies are being developed with the goal of treating low carbon wastewater at low temperatures, tackling nitrite and nitrate accumulation and methane utilization from digestates while also recovering resources (phosphorus) in a sustainable manner. This review compares and contrasts the handful of ANAMMOX -based processes developed thus far with plausible solutions for addressing their respective bottlenecks hindering full-scale implementation. Ultimately, future prospects for advancing understanding of mechanisms and engineering application of ANAMMOX process are posited. As a whole, technological advances in process design and patents have greatly contributed to better understanding of the ANAMMOX process, which has greatly aided in the optimization and industrialization of the ANAMMOX process. This review is intended to provide researchers with an overview of the present state of research and technological development of the ANAMMOX process, thus serving as a guide for realizing energy autarkic future practical applications.

Implementing a completely autotrophic nitrogen removal over nitrite process using a novel umbrella basalt fiber carrier

The completely autotrophic nitrogen removal over nitrite (CANON) process is significantly hindered by prolonged start-up periods and unstable nitrogen removal efficiency. In this study, a novel umbrella basalt fiber (BF) carrier with good biological affinity and adsorption performance was used to initiate the CANON process. The CANON process was initiated on day 64 in a sequencing batch reactor equipped with umbrella BF carriers. During this period, the influent NH4+-N concentration gradually increased from 100 to 200 mg·L-1, and the dissolved oxygen was controlled below 0.8 mg L-1. Consequently, an average ammonia nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (TNRE) of ∼90 and 80% were achieved, respectively. After 130 days, ARE and TNRE remained stable at 92 and 81.1%, respectively. This indicates a reliable method for achieving rapid start-up and stable operation of the CANON process. Moreover, Candidatus Kuenenia and Candidatus Brocadia were identified as dominant anammox genera on the carrier. Nitrosomonas was the predominant genus among ammonia-oxidizing bacteria. Spatial differences were observed in the microbial population of umbrella BF carriers. This arrangement facilitated autotrophic nitrogen removal in a single reactor. This study indicates that the novel umbrella BF carrier is a highly suitable biocarrier for the CANON process.

Insights into a novel nitrogen removal process based on simultaneous anammox and denitrification (SAD) following nitritation with in-situ NOB elimination

Simultaneous anammox and denitrification (SAD) is an efficient approach to treat wastewater having a low C/N ratio; however, few studies have investigated a combination of SAD and partial nitritation (PN). In this study, a lab-scale up-flow blanket filter (UBF) and zeolite sequence batch reactor (ZSBR) were continuously operated to implement SAD and PN advantages, respectively. The UBF achieved a high total nitrogen (TN) removal efficiency of over 70% during the start-up stage (days 1-50), and reached a TN removal efficiency of 96% in the following 90 days (days 51-140) at COD/NH₄⁺-N ratio of 2.5. The absolute abundance of anammox bateria increased to the highest value of 1.58 × 10⁷ copies/µL DNA; Comamonadaceae was predominant in the UBF at the optimal ratio. Meanwhile, ZSBR was initiated on day 115 as fast nitritation process to satisfy the influent requirement for the UBF. The combined process was started on day 140 and then lasted for 30 days, during the combined process, between the two reactors, the UBF was the main contributor for TN (66.5% ± 4.5%) and COD (71.8% ± 4.9%) removal. These results demonstrated that strong SAD occurred in the UBF when following a ZSBR with in-situ NOB elimination. This research presents insights into a novel biological nitrogen removal process for low C/N ratio wastewater treatment.

Integrated effects of operational temperature, HRT, and influent ammonium concentration on a CANON coupling with denitrification process treating for digested piggery wastewater: performance and microbial community

In this study, an improved system called the completely autotrophic nitrogen removal over nitrite (CANON) process was presented and coupled with denitrification for the treatment of digested piggery wastewater (DPW). The effects of operating parameters, including hydraulic retention time (HRT) (1.6 d → 1.0 d), influent NH₄⁺-N concentration (350 mg L^-1 → 600 mg L^-1), and temperature (41 ℃ → 17 ℃), on the nitrogen removal performance and response characteristics of microbial population were investigated. Results showed that all considered parameters caused a remarkable effect on NH₄⁺-N and total nitrogen removal efficiencies, and the chemical oxygen demand was more markedly affected by temperature. Candidatus_Kuenenia, Candidatus_Brocadia, Denitratisoma, norank_o_Xanthmonadales, norank_p_WWE3, and SM1A02 were the dominant genera influencing nitrogen removal in the improved CANON system for treating DPW. Redundancy discriminant analysis showed that the biological structure was positively correlated with the influent ammonium concentration, temperature, and HRT. The relative abundance of Candidatus_Kuenenia was perfectly correlated with HRT and temperature. However, environmental factors did not affect Candidatus_Brocadia and norank_p_WWE3. norank_c_Ardenticatenia, SM1A02, and norank_f_SJA-28 were all positively correlated with influent ammonium nitrogen concentration, but not correlated with HRT and temperature. The improved CANON process realized the nitrogen removal under high ammonium (NH₄⁺-N) concentration and low C/N wastewater.

Simultaneous partial nitritation, anammox, and denitrification process for the treatment of simulated municipal sewage in a single-stage biofilter reactor

This study provides a feasible scheme for the treatment of municipal sewage through simultaneous partial nitritation, anammox, and denitrification (SNAD) process, which was realized in a single-stage biofilter reactor (BFR). First, the BFR was started up to enrich the anaerobic ammonium-oxidizing bacteria (AnAOB) in the upper part of the reactor through the operation mode of the top influent and bottom effluent. Then, the BFR was inoculated with activated sludge and aerated continuously at the bottom to realize the coupling of SNAD, which was accompanied by a two-point influent from the bottom and top effluent. Results indicated that the high removal efficiency of NH₄⁺-N (93.40%), total nitrogen (TN, 89.95%), and soluble chemical oxygen demand (SCOD, 92.68%) were achieved with an air-water ratio of 4.29 and hydraulic retention time (HRT) of 6 h. During the SNAD steady phase for the treatment of simulated municipal sewage with a soluble chemical organic demand to nitrogen (C/N) ratio of 2.31, low concentrations of NH₄⁺-N (4.13 mg/L), TN (6.44 mg/L), and SCOD (11.29 mg/L) were attained in the effluent. High-throughput sequencing analysis indicated that the relative abundance of Nitrosomonas, Candidatus Brocadia, and Denitratisoma were 0.77%, 0.43%, and 4.07% in the biofilm at the 0-12.5 cm zone, respectively, suggesting successful implementation of the SNAD process.

Organic carbon bioavailability: Is it a good driver to choose the best biological nitrogen removal process?

Organic carbon can affect the biological nitrogen removal process since the Anammox, heterotrophic and denitrifying bacteria have different affinities and feedback in relation to carbon/nitrogen ratio. Therefore, we reviewed the wastewater carbon concentration, its biodegradability and bioavailability to choose the appropriate nitrogen removal process between conventional (nitrification-denitrification) and Anammox-based process (i.e. integrated with the partial nitritation, nitritation, simultaneous partial nitrification and denitrification or partial-denitrification). This review will cover: (i) strategies to choose the best nitrogen removal route according to the wastewater characteristics in relation to the organic matter bioavailability and biodegradability; (ii) strategies to efficiently remove nitrogen and the remaining carbon from effluent in anammox-based process and its operating cost; (iii) an economic analysis to determine the operational costs of two-units Anammox-based process when compared with the commonly applied one-unit Anammox system (partial-nitritation-Anammox). On this review, a list of alternatives are summarized and explained for different nitrogen and biodegradable organic carbon concentrations, which are the main factors to determine the best treatment process, based on operational and economic terms. In summary, it depends on the wastewater carbon biodegradability, which implies in the wastewater treatment cost. Thus, to apply the conventional nitrification/denitrification process a COD_b/N ratio higher than 3.5 is required to achieve full nitrogen removal efficiency. For an economic point of view, according to the analysis the minimum COD_b/gN for successful nitrogen removal by nitrification/denitrification is 5.8 g. If ratios lower than 3.5 are applied, for successfully higher nitrogen removal rates and the economic feasibility of the treatment, Anammox-based routes can be applied to the wastewater treatment plant.

A novel integrated single-stage anaerobic co-digestion and oxidation ditch-membrane bioreactor system for food waste management and building wastewater recycling

This study is to develop a novel integrated single-stage anaerobic co-digestion and oxidation ditch membrane bioreactor (SAC/OD-MBR) for food waste and building wastewater recycling. The co-digestion of food waste (FW) from a canteen with waste sludge (WS) from OD-MBR was performed with the proportion of FW:WS at 10:1 by weight. The liquid digestate from the co-digestion process was further co-treated with building wastewater in the OD-MBR system for water reuse purpose. Maximum methane content of 65.2% in biogas as well as average specific methane yield of 0.24 gCH₄/gVS could be obtained with anaerobic co-digestion of food waste and waste sludge from OD-MBR with HRT of 24 h and horizontal flow velocity of 0.3 m/s. The observed main methanogen species in this co-digestion process were Methanoculleus bourgensis and Methanoculleus palmolei. For co-treatment of liquid digestate and building wastewater with the OD-MBR, it was found that HRT of 24 h and horizontal flow velocity of 0.3 m/s could achieve highest COD and nitrogen removal efficiencies. HRT can be considered as a main key parameter to promote nitrification activity inside the OD-MBR system. Moreover, treated effluent from the SAC/OD-MBR could comply with the water reuse standard for garden and landscape application in the university campus. Furthermore, the techno-economic analysis indicates that this proposed system has a high potential of total cost savings and other indirect benefits. Therefore, the prototype SAC/OD-MBR can be an alternative system for food waste management and wastewater recycling for building application.

Characteristics of rapid-biofiltering anammox reactor (RBAR) for low nitrogen wastewater treatment

This research provides an important approach for rapid treatment of low nitrogen wastewater through anaerobic ammonium oxidation (anammox), which was realized in a rapid-biofiltering anammox reactor (RBAR). The operation mode of continuous upward flow and gradually shortened hydraulic retention time (HRT) accumulated anammox bacteria effectively in RBAR, where carmine anammox granular sludge and thick biofilm were co-existed, leading the biomass concentration and the specific anammox activity to reach 21.61 gSS/L and 0.82 gN/gVSS·d in the main functional zone. Moreover, the relative abundance of anammox bacteria in the whole reactor was more than 50%, and the relative abundance of Candidatus Brocadia in the biofilm of 20-47 cm zone reached 71.10%. Results showed that the removal rate and effluent concentration of total nitrogen remained stable at 86.24% and 14.20 mg/L (below 15 mg/L) averagely, under HRT of 32 min when the the nitrogen loading rate was 4.86 kgN/m³·d.

Response and Adaptation of Microbial Community in a CANON Reactor Exposed to an Extreme Alkaline Shock

Responses of a microbial community in the completely autotrophic nitrogen removal over nitrite (CANON) process, which was shocked by a pH of 11.0 for 12 h, were investigated. During the recovery phase, the performance, anaerobic ammonia oxidation (anammox) activity, microbial community, and correlation of bacteria as well as the influencing factors were evaluated synchronously. The performance of the CANON process deteriorated rapidly with a nitrogen removal rate (NRR) of 0.13 kg·m^-3·d^-1, and Firmicutes, spore-forming bacteria, were the dominant phyla after alkaline shock. However, it could self-restore within 107 days after undergoing four stages, at which Planctomycetes became dominant with a relative abundance of 64.62%. Network analysis showed that anammox bacteria (Candidatus Jettenia, Kuenenia, and Brocadia) were positively related to some functional bacteria such as Nitrosomonas, SM1A02, and Calorithrix. Canonical correspondence analysis presented a strong correlation between the microbial community and influencing factors during the recovery phase. With the increase of nitrogen loading rate, the decrease of free nitrous acid and the synergistic effects, heme c content, specific anammox activity (SAA), NRR, and the abundance of dominant genus increased correspondingly. The increase of heme c content regulates the quorum sensing system, promotes the secretion of extracellular polymeric substances, and further improves SAA, NRR, and the relative abundance of the dominant genus. This study highlights some implications for the recovery of the CANON reactor after being exposed to an alkaline shock.

Domestic Sewage Treatment Using a One-Stage ANAMMOX Process

A one-stage anaerobic ammonium oxidation (ANAMMOX) reactor can be quickly started within 40 days by mixing partial nitrifying sludge with ANAMMOX granular sludge with an average temperature of 30 °C. After 70 days of nitrogen load acclimation, Acinetobacter, including Candidatus Kuenenia, became the dominant strain of the system within the reactor, which exhibited high efficiency and a stable nitrogen removal performance. At an influent chemical oxygen demand (COD), NH₄⁺-N content, total nitrogen (TN) content, hydraulic retention time (HRT), temperature, and reactor dissolved oxygen (DO) content of 100, 60, and 70 mg/L, 6 h, 30 ± 1 °C, and below 0.6 mg/L, respectively, the one-stage ANAMMOX reactor could effectively treat domestic sewage on campus. The removal rates of COD, NH₄⁺-N, and TN were approximately 89%, 96.7%, and 70%, respectively.

Exploring the effect of plant substrates on bacterial community structure in termite fungus-combs

Fungus-cultivating termites are successful herbivores largely rely on the external symbiotic fungus-combs to decompose plant polysaccharides. The comb harbors both fungi and bacteria. However, the complementary roles and functions of the bacteria are out of the box. To this purpose, we look into different decomposition stages of fungus-combs using high-throughput sequencing of the 16S rRNA gene to examine bacterial community structure. We also explored the bacterial response to physicochemical indexes (such as moisture, ash content and organic matter) and plant substrates (leaves or branches or mix food). Some specific families such as Lachnospiraceae, Ruminococcaceae, and Peptostreptococcaceae may be involved in lignocellulose degradation, whereas Burkholderiaceae may be associated with aromatic compounds degradation. We observed that as the comb mature there is a shift of community composition which may be an adjustment of specific bacteria to deal with different lignocellulosic material. Our results indicated that threshold amount of physicochemical indexes are beneficial for bacterial diversity but too high moisture, low organic matter and high ash content may reduce their diversity. Furthermore, the average highest bacterial diversity was recorded from the comb built by branches followed by mix food and leaves. Besides, this study could help in the use of bacteria from the comb of fungus-cultivating termites in forestry and agricultural residues making them easier to digest as fodder.

Application of the Anammox in China-A Review

Anaerobic ammonia oxidation (anammox) has been one of the most innovative discoveries for the treatment of wastewater with high ammonia nitrogen concentrations. The process has significant advantages for energy saving and sludge reduction, also capital costs and greenhouse gases emissions are reduced. Recently, the use of anammox has rapidly become mainstream in China. This study reviews the engineering applications of the anammox process in China, including various anammox-based technologies, selection of anammox reactors and attempts to apply them to different wastewater treatment plants. This review discusses the control and implementation of stable reactor operation and analyzes challenges facing mainstream anammox applications. Finally, a unique and novel perspective on the development and application of anammox in China is presented.

Study on Propellers Distribution and Flow Field in the Oxidation Ditch Based on Two-Phase CFD Model

The oxidation ditch (OD) plays an important role in wastewater treatment plants. With increasing demand and production costs, the energy consumption and sludge deposition occurring in the OD must be diminished to enhance its development. In this paper, a two-phase computational fluid dynamics (CFD) model of water and activated sludge examined the flow field characteristics of an OD, consisting of two side-by-side propellers. The system was studied under five configurations, where the spacing between the propellers was set equal to −0.2, −0.1, 0, 0.1, 0.2 times the length of the OD. The viscosity and settling rate of activated sludge was imported in the numerical simulation through a user defined function (UDF). The optimal scheme of the propeller’s power consumption, velocity distribution, and sludge concentration distribution was obtained. The result shows that sludge concentrations are linked with dead zone velocity but not necessarily with low velocities. Experiments confirmed the validity of the velocity flow field simulated by the two-phase CFD model. Overall, these findings form the basis for the propellers distribution optimization and allow a deeper insight into the flow field of OD systems.

Particular internal recirculation frequency scope for enhancing denitrifying phosphorus removal in an oxidation ditch

This study investigated the influence of the unique internal recirculation characteristics of an oxidation ditch (OD) system, namely, the internal recirculation frequency (IRF) on denitrifying phosphorus removal (DNPR). The ratios of denitrifying polyphosphate-accumulating organisms (DPAOs) to polyphosphate-accumulating organisms (PAOs) under different IRF conditions were measured using a batch experiment. On this basis, the variation of nutrient transformations was studied using the IRF changes by the mass balance method. The results showed that, for the OD system that had an anaerobic zone upstream from the circular corridor and set anoxic and aerobic zones along the circular corridor, when the IRF was between 3.4 h^-1 and 7.5 h^-1, the DPAOs/PAOs ratio reached about 50%. Approximately 20% of the total phosphorus (TP) was removed and over 11% of the total nitrogen (TN) was transformed into nitrogen gas by the DNPR process, and meanwhile the total removal efficiencies of the TP and TN were over 93% and 80%. When the IRF was greater than 11.5 h^-1, the TN removal efficiency decreased significantly, and this was not conducive to simultaneous nitrogen and phosphorus removal. The results indicated that the OD process would possess a better DNPR potential if the IRF were controlled within the proper scope.