Shenbin Cao

Biological nitrogen removal from sewage via anammox: Recent advances.

Biological nitrogen removal from sewage via anammox is a promising and feasible technology to make sewage treatment energy-neutral or energy-positive. Good retention of anammox bacteria is the premise of achieving sewage treatment via anammox. Therefore the anammox metabolism and its factors were critically reviewed so as to form biofilm/granules for retaining anammox bacteria. A stable supply of nitrite for anammox bacteria is a real bottleneck for applying anammox in sewage treatment. Nitritation and partial-denitrification are two promising methods of offering nitrite. As such, the strategies for achieving nitritation in sewage treatment were summarized by reviewing the factors affecting nitrite oxidation bacteria growth. Meanwhile, the methods of achieving partial-denitrification have been developed through understanding the microorganisms related with nitrite accumulation and their factors. Furthermore, two cases of applying anammox in the mainstream sewage treatment plants were documented.

Advanced nitrogen removal with simultaneous Anammox and denitrification in sequencing batch reactor

In this study, a sequencing batch reactor (SBR) was used to achieve advanced nitrogen removal by simultaneous Anammox and denitrification processes. During the entire experiment, the Anammox microorganisms aggregated in the reactor as wall growth. Nitrogen removal was improved due to the reduction of nitrate, and the maximum total nitrogen (TN, including ammonia, nitrite and nitrate nitrogen) removal efficiency of 97.47% was obtained at C/N of 2. However, the sequentially increased organic matter resulted in a poor TN removal performance due to the suppression of Anammox. Fortunately, the Anammox activity completely resumed quickly after stopping dosing organic matter. PCR analysis results revealed that the Anammox bacteria gene copy number was not significantly reduced during the inhibition, which might explain the quick recover.

Performance and microbial community analysis of a novel DEAMOX based on partial-denitrification and anammox treating ammonia and nitrate wastewaters

In this study, a novel DEAMOX (DEnitrifying AMmonium OXidation) process coupling anammox with partial-denitrification generated nitrite (NO2--N) from nitrate (NO3--N) was developed for simultaneously treating ammonia (NH4+-N) and NO3--N containing wastewaters. The performance was evaluated in sequencing batch reactors (SBRs) with different carbon sources for partial-denitrification: acetate (R1) and ethanol (R2). Long-term operation (180 days) suggested that desirable nitrogen removal was achieved in both reactors. The performance maintained stably in R1 despite the seasonal decrease of temperature (29.2xa0°C-12.7xa0°C), and high nitrogen removal efficiency (NRE) of 93.6% on average was obtained with influent NO3--N to NH4+-N ratio (NO3--N/NH4+-N) of 1.0. The anammox process contributed above 95% to total nitrogen (TN) removal in R1 with the nitrate-to-nitrite transformation ratio (NTR) of 95.8% in partial-denitrification. A little lower NRE was observed in R2 with temperature dropped from 90.0% at 22.7xa0°C to 85.2% at 16.6xa0°C due to the reduced NTR (87.0%-67.0%). High-throughput sequencing analysis revealed that Thauera genera were dominant in both SBRs (accounted for 61.53% in R1 and 45.17% in R2) and possibly played a key role for partial-denitrification with high NO2--N accumulation. The Denitratisoma capable of complete denitrification (NO3--N→N2) was found in R2 that might lead to lower NTR. Furthermore, different anammox species was detected with Candidatus Brocadia and Candidatus Kuenenia in R1, and only Candidatus Kuenenia in R2.

Advanced nitrogen removal from wastewater by combining anammox with partial denitrification.

The anammox (anaerobic ammonium oxidation) process has attracted much attention for its cost-saving. However, excess nitrate is usually produced which should be further treated. In this study, an innovative process combined anammox with partial denitrification (nitrate→nitrite) was proposed for advanced nitrogen removal in two sequencing batch reactors (SBRs). The nitrate produced in anammox-SBR (ASBR) was fed into partial denitrification-SBR (DSBR), in which the nitrate was reduced to nitrite, and then removed by backflow of the nitrite to ASBR for secondary anammox process. Results showed that ∼80% nitrate in the effluent of previous anammox was converted to nitrite in DSBR. And the maximum nitrogen removal efficiency (NRE) of 94.06% was obtained with total nitrogen (TN) in the effluent of 10.98 mg/L in average. It indicated that desired effluent quality could be achieved, and the advanced nitrogen removal performance was attributed to the successful achievement of partial denitrification.

Achieving partial denitrification with sludge fermentation liquid as carbon source: The effect of seeding sludge

The partial denitrification (nitrate to nitrite) has been a promising way for nitrate wastewater treatment combined with ANAMMOX system subsequently. This work investigated the effect of seeding sludge on partial denitrification by using sludge fermentation liquid as carbon source, with the sludge taken from: anoxic/oxic reactor (SA), anaerobic-anoxic-oxic reactor (SA-A-O) and alternately anaerobic sludge fermentation coupling anoxic denitrification reactor (SA-A). The results showed that transient accumulation of nitrite was observed in SA and SA-A-O. However, at the initial nitrate concentration of 30 mg/L, a high nitrite of 20.91 ± 0.52 mg/L was accumulated under complete nitrate reduction in the SA-A system, which indicated that partial denitrification could be realized. Furthermore, as much as 80% nitrate-to-nitrite transformation ratio (NTR) was achieved in a 108-day operation with inoculating SA-A, which illustrated the stability of partial denitrification under long-term operation.

High-throughput profiling of microbial community structures in an ANAMMOX-UASB reactor treating high-strength wastewater

In this study, the microbial community structure was assessed in an anaerobic ammonium oxidation–upflow anaerobic sludge blanket (ANAMMOX-UASB) reactor treating high-strength wastewater (approximately 700xa0mgxa0Nxa0L−1 in total nitrogen) by employing Illumina high-throughput sequencing analysis. The reactor was started up and reached a steady state in 26xa0days by seeding mature ANAMMOX granules, and a high nitrogen removal rate (NRR) of 2.96xa0kgxa0Nxa0m−3xa0day−1 was obtained at 13.2∼17.6xa0°C. Results revealed that the abundance of ANAMMOX bacteria increased during the operation, though it occupied a low proportion in the system. The phylum Planctomycetes was only 8.39xa0% on day 148 and Candidatus Brocadia was identified as the dominant ANAMMOX species with a percentage of 2.70xa0%. The phylum of Chloroflexi, Bacteroidetes, and Proteobacteria constituted a percentage up to 70xa0% in the community, of which the Chloroflexi and Bacteroidetes were likely to be related to the sludge granulation. In addition, it was found that heterotrophic denitrifying bacteria of Denitratisoma belonging to Proteobacteria phylum occupied a large proportion (22.1∼23.58xa0%), which was likely caused by the bacteria lysis and decay with the internal carbon source production. The SEM images also showed that plenty of other microorganisms existed in the ANAMMOX-UASB reactor.

Mechanisms and microbial structure of partial denitrification with high nitrite accumulation

Nitrite (NO2−-N) accumulation in denitrification can provide the substrate for anammox, an efficient and cost-saving process for nitrogen removal from wastewater. This batch-mode study aimed at achieving high NO2−-N accumulation over long-term operation with the acetate as sole organic carbon source and elucidating the mechanisms of NO2−-N accumulation. The results showed that the specific nitrate (NO3−-N) reduction rate (59.61xa0mg N VSS−1xa0h−1 at NO3−-N of 20xa0mg/L) was much higher than specific NO2−-N reduction rate (7.30xa0mg N VSS−1xa0h−1 at NO3−-N of 20xa0mg/L), and the NO2−-N accumulation proceeded well at the NO3−-N to NO2−-N transformation ratio (NTR) as high as 90xa0%. NO2−-N accumulation was barely affected by the ratio of chemical oxygen demand (COD) to NO3−-N concentration (C/N). With the addition of NO3−-N, NO2−-N accumulation occurred and the specific NO2−-N reduction rate declined to a much lower level compared with the value in the absence of NO3−-N. This indicated that the denitrifying bacteria in the system preferred to use NO3−-N as electron acceptor rather than use NO2−-N. In addition, the Illumina high-throughput sequencing analysis revealed that the genus of Thauera bacteria was dominant in the denitrifying community with high NO2−-N accumulation and account for 67.25xa0% of total microorganism. This bacterium might be functional for high NO2−-N accumulation in the presence of NO3−-N.

Nitrite production in a partial denitrifying upflow sludge bed (USB) reactor equipped with gas automatic circulation (GAC)

Nitrite production in a partial denitrifying (NO3(-)-N→NO2(-)-N) upflow sludge bed (USB) reactor equipped with gas automatic circulation (GAC) was investigated at ambient temperature (28.8-14.1xa0°C). The nitrite production rate (NPR) increased with the nitrate loading rate (NLR). Average NPR of 6.63xa0kgNxa0m(-3)xa0d(-1) was obtained at 28.0xa0°C with the organic loading rate (OLR) and NLR of 25.38 KgCOD∙m(-3)∙d(-1) and 10.82xa0kgNxa0m(-3)xa0d(-1), respectively. However, serious sludge floatation was observed when the NLR increased to 13.18xa0kgNxa0m(-3)xa0d(-1), which might be attributed to sludge bulking at high NLR. The USB reactor recovered rapidly when seeded with the sludge discharged before the deteriorated period, and a stable NPR of ∼4.35xa0kgNxa0m(-3)xa0d(-1) was achieved at 14.1-15.7xa0°C in the following 100-day operation, during which the maximum nitrate-to-nitrite transformation ratio (NTR) of 81.4% was achieved at the GAC rate of 1.08xa0Lxa0h(-1). The application of GAC in the partial denitrifying USB reactor enhanced mass transfer, which effectively avoided the channel and dead space, and improved the nitrate transform to nitrite. Moreover, it was found that the GAC system played an important role in promoting the stability of the USB reactor by preventing the sludge floatation. The Illumina high-throughput sequencing analysis revealed that the genus of Thauera was dominate in the USB reactor (67.2-50.2%), which may be responsible for the high nitrite accumulation. Results in this study have an important application in treating nitrate wastewater with an economic and efficient way by combining with ANAMMOX process.

Integrated anaerobic ammonium oxidization with partial denitrification process for advanced nitrogen removal from high-strength wastewater

In this study, a novel integrated anaerobic ammonium oxidization with partial denitrification process (termed as ANAMMOX-PD) was developed for advanced nitrogen removal from high-strength wastewater, which excess NO3--N produced by ANAMMOX was fed into PD reactor for NO2--N production and then refluxing to ANAMMOX reactor for further removal. Results showed that total nitrogen (TN) removal efficiency as high as 97.8% was achieved and effluent TN-N was below 20mg/L at influent TN-N of 820mg/L. Furthermore, the feasibility of simultaneously treating domestic wastewater was demonstrated in ANAMMOX-PD process, and NH4+-N removal efficiency of 96.7% was obtained. The nitrogen removal was mainly carried out through ANAMMOX pathway, and high-throughput sequencing revealed that Candidatus_Brocadia was the major ANAMMOX species. The presented process could effectively solve the problem of excess nitrate residual in ANAMMOX effluent, which hold a great potential in application of currently ANAMMOX treating high-strength wastewater (e.g. sludge digestion supernatant).

Performance of partial denitrification (PD)-ANAMMOX process in simultaneously treating nitrate and low C/N domestic wastewater at low temperature

The simultaneous treatment of nitrate (NO3(-)-N∼50mgL(-1)) and domestic wastewater (ammonia (NH4(+)-N)∼60.6mgL(-1), COD∼166.3mgL(-1)) via a novel partial denitrification (PD)-ANaerobic AMMonium OXidation (ANAMMOX) process was investigated at low temperature (12.9∼15.1°C). Results showed that desirable performance was achieved with average NO3(-)-N, NH4(+)-N and COD removal efficiencies of 89.5%, 97.6% and 78.7%, respectively. However, deteriorated sludge settleability in PD reactor was observed during operation, which bulked with serious sludge wash-out, leading to excess NO3(-)-N remaining in PD effluent. Fortunately, a satisfactory nitrogen removal was still achieved due to the occurrence of partial denitrification in ANAMMOX reactor. This was demonstrated by high-throughput sequencing, which revealed that the high nitrite (NO2(-)-N) production denitrifying bacteria of Thauera was detected (6.1%). ANAMMOX (above 70%) maintained the dominant pathway for nitrogen removal, and Candidatus Jettenia was identified as the major ANAMMOX species accounted for 2.7%.