Rui Du

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.

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.

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%.

Characteristic of nitrous oxide production in partial denitrification process with high nitrite accumulation.

Nitrous oxide (N2O) production during the partial denitrification process with nitrate (NO3(-)-N) to nitrite (NO2(-)-N) transformation ratio of 80% was investigated in this study. Results showed that N2O was seldom observed before complete depletion of NO3(-)-N, but it was closely related to the reduction of NO2(-)-N rather than NO3(-)-N. High COD/NO3(-)-N was in favor of N2O production in partial denitrification with high NO2(-)-N accumulation. It was seriously enhanced at constant acidic pH due to the free nitrous acid (FNA) inhibition. However, the N2O production was much lower at initial pH of 5.5 and 6.5 due to the pH increase during denitrification process. Significantly, the pH turning point could be chosen as a controlled parameter to denote the end of NO3(-)-N reduction, which could not only achieve high NO2(-)-N accumulation but also decrease the N2O production significantly for practical application.

Feasibility of enhancing the DEnitrifying AMmonium OXidation (DEAMOX) process for nitrogen removal by seeding partial denitrification sludge

The recently proposed DEnitrifying AMmonium OXidation (DEAMOX) process combined anaerobic ammonia oxidation (ANAMMOX) with denitrification to convert nitrate to nitrite, which was a promising way for treating wastewater containing nitrate and ammonia. This study investigated the feasibility of establishing DEAMOX process by seeding partial denitrification sludge (NO3(-) → NO2(-)) using sodium acetate as an electron donor in a sequencing batch reactor. Results showed that the DEAMOX process was established successfully and operated stably in 114-days operation. The average effluent total nitrogen concentration was below 5 mg L(-1) and TN removal efficiency reached up to 97% at COD/NO3(-) ratio of 3.0 under initial NH4(+) concentration of 25 mg L(-1) and NO3(-) of 30 mg L(-1). It suggested that the presence of NO2(-) in the system supplied for ANAMMOX and the relatively long sludge retention time (SRT) for denitrifiers were attributed to commendable coexistence of ANAMMOX and denitrifying bacteria.