Impact of instrumentation reliability on mainstream suspended partial denitrification-anammox (PdNA).

This study successfully revealed the importance of probe reliability and sensitivity with ion sensitive electrode (ISE) probes on achieving high partial denitrification (PdN) efficiency; and decreasing carbon overdosing events that cause the decline of microbial populations and performance of PdNA. In a mainstream integrated hybrid granule-floc system, an average PdN efficiency of 76% was achieved with acetate as the carbon source. Thauera was identified as the dominant PdN species; its presence in the system was analogous to instrumentation reliability and PdN selection and was not a consequence of bioaugmentation. Up to 27-121 mg total inorganic nitrogen/L/d, an equivalent of 18-48% of the overall total inorganic nitrogen removed, was achieved through the PdNA pathway. Candidatus Brocadia was the main anoxic ammonium oxidizing bacteria species that was seeded from sidestream and enriched and retained in the mainstream system with observed growth rates of 0.04-0.13 day-1 . Moreover, there was no direct negative impact of methanol's use for post-polishing on anoxic ammonium oxidizing bacteria activity and growth. PRACTITIONER POINTS: Stress testing with ISE sensors revealed the importance of probe reliability and sensitivity on PdN selection and PdNA performance. Up to 121 mg TIN/L/d was achieved via PdNA in a mainstream suspended hybrid granule-floc partial denitrification-anammox (PdNA) system. Candidatus Brocadia was the dominant AnAOB species with observed growth rates of 0.04-0.13 day-1. There was no direct negative impact of methanol's use for post-polishing on AnAOB activity and growth.

Comparative assessment of energy generation from ammonia oxidation by different functional bacterial communities.

Bioelectrochemical ammonia oxidation (BEAO) in a microbial fuel cell (MFC) is a recently discovered process that has the potential to reduce energy consumption in wastewater treatment. However, level of energy and limiting factors of this process in different microbial groups are not fully understood. This study comparatively investigated the BEAO in wastewater treatment by MFCs enriched with different functional groups of bacteria (confirmed by 16S rRNA gene sequencing): electroactive bacteria (EAB), ammonia oxidizing bacteria (AOB), and anammox bacteria (AnAOB). Ammonia oxidation rates of 0.066, 0.083 and 0.082 g NH4+-N L-1 d-1 were achieved by biofilms enriched with EAB, AOB, and AnAOB, respectively. With influent 444 ± 65 mg NH4+-N d-1, nitrite accumulation between 84 and 105 mg N d-1 was observed independently of the biofilm type. The AnAOB-enriched biofilm released electrons at higher potential energy levels (anode potential of 0.253 V vs. SHE) but had high internal resistance (Rint) of 299 Ω, which limits its power density (0.2 W m-3). For AnAOB enriched biofilm, accumulation of nitrite was a limiting factor for power output by allowing conventional anammox activity without current generation. AOB enriched biofilm had Rint of 18 ± 1 Ω and yielded power density of up to 1.4 W m-3. The activity of the AOB-enriched biofilm was not dependent on the accumulation of dissolved oxygen and achieved 1.5 fold higher coulombic efficiency when sulfate was not available. The EAB-enriched biofilm adapted to oxidize ammonia without organic carbon, with Rint of 19 ± 1 Ω and achieved the highest power density of 11 W m-3. Based on lab-scale experiments (scaling-up factors not considered) energy savings of up to 7 % (AnAOB), 44 % (AOB) and 475 % (EAB) (positive energy balance), compared to conventional nitrification, are projected from the applications of BEAO in wastewater treatment plants.

Nitrogen removal capacity and carbon demand requirements of partial denitrification/anammox MBBR and IFAS processes.

A pilot study was conducted to investigate the carbon demand requirements and nitrogen removal capabilities of two mainstream partial denitrification/anammox (PdNA) processes: a two-zone, moving bed biofilm reactor (MBBR) process and an integrated fixed-film activated sludge (IFAS) process. The first MBBR zone conducted PdNA, while the second operated as an anammox zone. Operation of the IFAS process was conducted in two phases. The first phase of the operation involved minor external carbon addition, while the second phase of the operation involved controlled external carbon addition. The MBBR process produced an average effluent TIN concentration and chemical oxygen demand (COD)/TIN ratio of 2.81 ± 1.21 mg/L and 2.42 ± 0.77 g/g. The average effluent TIN concentrations and COD/TIN ratios for the IFAS process were 4.07 ± 1.66 mg/L and 1.08 ± 0.38 g/g during phase 1 and 3.30 ± 0.96 mg/L and 2.18 ± 0.99 g/g during phase 2. Despite having relatively low and unstable partial denitrification (PdN) efficiencies, both mainstream PdNA processes exhibited low effluent TIN concentrations and carbon requirements compared to nitrification/denitrification. Successful operation of the PdNA IFAS process indicates that mainstream PdNA can be implemented with minimal capital costs in a water resource recovery facility's second anoxic zone. PRACTITIONER POINTS: Low effluent TIN concentrations can be maintained in mainstream PdNA MBBR and IFAS processes with low external carbon demand. MBBR and IFAS PdNA processes do not require consistent or high PdN efficiencies to maintain low effluent TIN concentrations. IFAS and MBBR PdNA processes exhibit similar TIN and NH3 removal efficiencies. PdNA can be implemented in a second anoxic zone, using IFAS technology for anammox retention, with minimal capital costs.

Startup strategies for mainstream anammox polishing in moving bed biofilm reactors.

This study evaluated startup strategies for mainstream polishing anammox moving bed biofilm reactors (MBBRs) without anammox bacterial (AMX) biomass inoculation. Two types of startups were tested: anammox only (no external carbon addition) and partial denitrification/anammox (PdNA) with glycerol addition. Reactors were started with either virgin carriers or carriers with a preliminary biofilm from a mainstream aerobic integrated fixed-film activated sludge (IFAS) process. Three pilot-scale startups were completed under the following conditions: anammox-only with preliminary biofilm carriers, PdNA with preliminary biofilm carriers, and PdNA with virgin carriers. AMX presence was confirmed via quantitative polymerase chain reaction (qPCR) after 57, 57, and 77 days, respectively. Prior to AMX detection, average influent concentrations of ammonia and nitrite ranged from 1.7-2.7 mg/L and 0.98-1.8 mg/L, respectively. This study demonstrated that AMX can be grown on carriers without AMX seeding under mainstream conditions (temperature 17-29°C, low ammonia and nitrite), regardless of whether nitrite came from upstream or partial denitrification within the reactor. This study also showed that using preliminary biofilm carriers can decrease startup time by approximately 1 month. These results address critical questions for moving mainstream anammox processes to full-scale implementation, and suggest that PdNA MBBRs are feasible and sustainable for full-scale ammonia, nitrate, and nitrite polishing to meet stringent total nitrogen requirements. PRACTITIONER POINTS: This research will help utilities develop methods for starting up mainstream anammox MBBRs without the barrier of anammox biomass seeding. Preliminary biofilm carriers accelerated startup time in a PdNA MBBR, but a virgin carrier reactor started up in a similar timeframe, contrary to expectations. Also, contrary to expectations, high concentrations of ammonia and nitrite are not necessary for startup of an anammox or PdNA MBBR.

Mainstream partial denitrification-anammox in sand and expanded clay deep-bed polishing filters under practical loading rates and backwashing conditions.

This study focused on evaluating the feasibility of expanded clay and sand as media types for mainstream partial denitrification-anammox (PdNA) in deep-bed single-media polishing filters under nitrogen and solids loading rates as well as backwash conditions similar to conventional denitrification filters. The surface roughness and iron content of the expanded clay were hypothesized to allow for enhanced anammox retention, nitrogen removal rates, and runtimes. However, under the tested loading rates and backwash conditions, no clear benefit of expanded clay was observed compared with conventional sand. This study showed the feasibility of PdNA in filters with both sand and expanded clay with PdN efficiencies of 76% and 77%, PdNA rates of 840 and 843 g N/m3 /d and TIN removal rates of 960 and 964 g N/m3 /d, respectively. Glycerol demands were 1.5-1.6 g COD added per g TIN removed , thus indicating potential carbon savings up to 75% compared with conventional denitrification. Overall, this study showed for the first time PdNA filters performing at nitrogen removal rates double that of previous PdNA studies under realistic conditions while providing insights into the media choice and backwashing conditions. Future research on expanded clay backwash conditions is needed to provide its full potential in PdNA filters. PRACTITIONER POINTS: Hydraulic and TSS loading rates similar to conventional denitrification can be applied in PdNA filters. Conventional sand can be used when retrofitting conventional denitrification filters into PdNA filters. Carbon savings up to 75% can be achieved with glycerol when retrofitting conventional filters into PdNA filters.

Full-scale transition from denitrification to partial denitrification-anammox (PdNA) in deep-bed filters: Operational strategies for and benefits of PdNA implementation.

This study shows for the first time more than 2 years of operation of a mainstream anammox application at full-scale under temperate climate. This implementation of partial denitrification-anammox (PdNA) in deep bed filters at the HRSD York River treatment plant was demonstrated to achieve the benefits of shortcut nitrogen removal without nitrite oxidizing bacteria (NOB) out-selection. The transition from denitrification to PdNA filters required bleeding ammonium to the filters using an optimized ammonium versus NOx (AvN) control in the upstream aeration tanks and maintaining a nitrate residual in the filter effluent through feedforward/feedback control. The latter actions led to savings of 85% in methanol, 100% in alkalinity, and 35% in capacity enhancement. Up to 6 mg NH4 + -N/L with an average of 2.2 ± 0.98 mg NH4 + -N/L was removed through the anammox pathway, which accounted for about 15% of the overall plant nitrogen removal. Anammox enrichment was confirmed by activity testing and molecular analysis. The large excess of AnAOB capacity present in the filters (5-10 times more than normal operation) resulted in stable and reliable operation through winter conditions and showed potential for further intensification. PRACTITIONER POINTS: For the first time, long-term mainstream anammox was established full-scale through PdNA implementation in deep-bed filters. PdNA implementation required upstream aeration control optimization to provide a blend of ammonium and nitrate to the filters. Efficient anammox enrichment and retention resulted in reliable PdNA performance under different seasonal and influent conditions. PdNA implementation resulted in significant methanol and alkalinity savings and upstream capacity enhancement as ammonia removal depended less on aerobic nitrification. In the event of NOB out-selection and presence of nitrite, carbon savings in PdNA polishing filters can be enhanced via partial nitritation-anammox.

Enrichment of a denitratating microbial community through kinetic limitation.

Denitratation, or the intentionally engineered accumulation of nitrite (NO2-) from selective reduction of nitrate (NO3-), can be combined with downstream anammox to reduce chemical and energy use associated with conventional nitrification and denitrification. This study aimed to enrich a denitratating microbial community capable of significant NO2- accumulation by applying added kinetic limitation to an already stoichiometrically-limited, glycerol-driven denitratation process. Operation at solids residence time, SRT=3.0 d, resulted in optimal denitratation performance and a microbial community dominated by NO3--respirers, noted by one order of magnitude lower total copy numbers of nirS and nirK gene transcripts compared to longer SRTs. Selective NO3- reduction to NO2- was achieved at all SRTs although longer SRTs (less kinetic limitation) supported microbial communities more capable of full denitrification as described by a lower NO2- accumulation ratio (NAR=42±5%) and higher steady-state nitrous oxide (1.5 mg/L N2O-N) accumulation. Shorter SRTs (more kinetic limitation) led to higher observed yields (Y=0.63 mg-COD/mg-COD) with more electrons dedicated for cell synthesis (fs=0.56±0.10), which potentially contributed to the accumulation of NO3-. Enrichment of a denitratating-dominant microbial community by optimizing kinetic limitation operating parameters could support significant NO2- accumulation and reduce chemical and energy use for biological nitrogen removal when combined with downstream anammox.

Size dependent impacts of a model microplastic on nitrification induced by interaction with nitrifying bacteria.

Two sizes of polystyrene (PS) were compared to investigate their impact on nitrification. The smaller PS (50 nm) had a higher impact than the larger PS (500 nm). Lower NO2- and NO3- accumulation was observed in the 50 nm PS treatment. There was no significant difference in DIN concentration between the control and 500 nm PS treatments. PS treatment did not have a significant influence on the specific ammonia oxidation rate, but the specific nitrite utilization rate was the lowest in the 50 nm PS treatment. The changes in transcript levels of amoA gene did not correspond well with the observed changes in DIN concentrations, suggesting that the effects of 50 nm PS treatment might be unrelated to biological phenomena, for which an actual uptake of PS is needed. The fluorescent images revealed that the smaller PS can easily access bacterial cells, which corroborated the results of inhibition of nitrification by the smaller PS. Notably, most of the PS particles did not penetrate bacterial cells, suggesting that the observed effects of 50 nm PS on nitrification might be due to disruption of the membrane potential of the cells.