Performance and microbial community of completely autotrophic nitrogen removal over nitrite (CANON) process in two membrane bioreactors (MBR) fed with different substrate levels

Performance and nitrogen removal mechanism in a novel aerobic-microaerobic combined process treating manure-free piggery wastewater

A novel combined sequencing batch reactor (SBR) - up-flow microaerobic sludge reactor (UMSR) process was developed to treat manure-free piggery wastewater characterized by low COD/TN ratio and high NH₄⁺-N. The front-end SBR was designed to get an effluent with COD/TN ≤ 1 by removing COD, allowing the back-end UMSR to practice anammox for the simultaneous removal of TN and NH₄⁺-N. Fed with the raw piggery wastewater, the combined SBR-UMSR process was started up at 27℃ with a reflux ratio of 15:1 in the UMSR. After 230-days running, the removal of COD, TN, and NH₄⁺-N in the combined SBR-UMSR process reached 78.41%,85.05%, and 92.21%, respectively. 50.22% of COD in the wastewater was removed in the SBR, while 87.11% of NH₄⁺-N and 79.69% of TN were removed in the UMSR. Stoichiometry and bacterial function analysis revealed that the partial nitrification - anammox process was the dominant nitrogen removal approach in the UMSR.

The Influence of Different Operation Conditions on the Treatment of Mariculture Wastewater by the Combined System of Anoxic Filter and Membrane Bioreactor

The mariculture wastewater treatment performance for the combined system of anoxic filter and membrane bioreactor (AF-MBR) was investigated under different hydraulic retention times (HRTs), influent alkalinity, and influent ammonia nitrogen load. The results showed that the removal efficiencies of TOC and total nitrogen were slightly better at the HRT of 8 h than at other HRTs, and the phosphate removal efficiency decreased with the increase of HRT. With the increase of influent alkalinity, the removal of TOC and phosphate did not change significantly. With the increase of influent alkalinity from 300 mg/L to 500 mg/L, the total nitrogen removal efficiency of AF-MBR was improved, but the change of the removal efficiency was not obvious when the alkalinity increased from 500 mg/L to 600 mg/L. When the influent concentration of ammonia nitrogen varied from 20 mg/L to 50 mg/L, the removal efficiencies of TOC, phosphate, and total nitrogen by AF-MBR were stable. An interesting finding was that in all the different operation conditions examined, the treatment efficiency of AF-MBR was always better than that of the control MBR. The concentrations of NO₃⁻-N in AF-MBR were relatively low, whereas NO₃⁻-N accumulated in the control MBR. The reason was that the microorganisms attached to the carrier and remained fixed in the aerobic and anoxic spaces, so that there was a gradual enrichment of bacteria characterized by slow growth in a high-salt environment. In addition, the microorganisms could gather and grow on the carrier forming a biofilm with higher activity, a richer and more stable population, and enhanced ability to resist a load impact.

Fast start-up strategies of MBBR for mariculture wastewater treatment

Moving bed biofilm reactor (MBBR) is widely used for ammonia removal in saline recirculating aquaculture systems but often faces a slow start-up problem. The aim of this study was to develop a strategy for the rapid start-up of MBBR treating synthetic mariculture wastewater. Changes in nitrification performance, biofilm characteristics and bacterial community were assessed in response to various start-up strategies: R1 as the control; R2 with step-decrease of inlet NH₄⁺-N; R3 with step-increase of inlet salinity; R4 added with particulate organic matter (POM) and R5 inoculated with nitrifying bacteria. Results show that nitrification was completed on day 63 for R3, 16-18 days faster than the other strategies. The highest protein (28.2 ± 5.1 mg/g·VS) and polysaccharide (59.4 ± 0.4 mg/g·VS) contents were observed in R3, likely linked to the faster biofilm formation. Fourier Transform infrared spectroscopy (FTIR) analysis confirmed the typical constituents of carbohydrates, proteins, lipids and DNA in biofilms. Moreover, along with the biofilm development in R3, the intensity of the peak at 1400 cm^-1 (assigned to specific amides) decreased. Pyrosequencing of 16s rRNA revealed that Gammaproteobacteria was the predominating microbial community at class level (35.6%) in R3. qPCR analysis further verified the significantly higher gene copies of amoA (1.57 × 10⁴ copies/μL) and nxrB (5.51 × 10³ copies/μL) in R3. Results obtained make the elevated salinity strategy a promising alternative for the rapid nitrification start-up of saline wastewater.

Insight into the response of anammox granule rheological intensity and size evolution to decreasing temperature and influent substrate concentration

Anammox granules are advantageous because of their relatively higher nitrogen removal rate (NRR) and biomass retention capacity in ammonia-containing wastewater treatment. However, little attention has been paid to granule rheological intensity and size evolution, especially under low temperature and substrate concentration conditions. In this study, the size evolution and variations in rheological properties associated with biochemical characteristics of anammox granules were investigated at decreasing temperatures (35 → 13 °C) and influent substrate concentrations (300 → 50 mg NH₄⁺-N L^-1). Both the specific anammox activities (SAA) and yield stress (τ_c) (or storage modulus (G')), which reflected granules' intensity, decreased with decreasing temperature and influent substrate concentration. An exponential correlation was found between SAA and τ_c (or G'). Granule size strongly decreased at low temperature (13 °C) and influent substrate concentration (50 mg NH₄⁺-N L^-1), despite slight variations in τ_c (or G'). A threshold τ_c (or G') that is closely related to the hydrodynamic shear force in the reactor may exist for the anammox granules. Once the τ_c (or G') of the anammox granules was lower than this threshold value (τ_c^∗ = 10.13-15.63 kPa), granules that could not endure hydrodynamic shear forces would disintegrate and their size would decrease substantially. Candidatus Kuenenia was the dominant genus in the expanded granular sludge bed reactor, reaching a minimum abundance of 14.6% at 16 °C because of the low-temperature shock, but increasing in abundance to 57.0% at 13 °C, indicating it has a competitive advantage at low temperatures. This contributed to achieving a high reactor nitrogen loading rate (>1.0 kg N m^-3 d^-1) even at 13 °C or with 50 mg NH₄⁺-N L^-1 influent. Overall, the results of this study will facilitate management of anammox bioreactors that run at various temperatures and influent substrate concentrations by clarifying the correlation between rheological intensity and anammox granule sludge activity and identifying the τ_c (or G') threshold.

Start-up evaluations and biocarriers transfer from a trickling filter to a moving bed bioreactor for synthetic mariculture wastewater treatment

Mariculture wastewater treatment by nitrification requires a long start-up time due to high salinity stress. This study aimed to verify the faster start-up of a trickling filter (TF) compared to a moving bed bioreactor (MBBR) treating synthetic mariculture wastewater, and to investigate the feasibility of transferring mature biocarriers from the TF to a new MBBR (TF-MBBR). The nitrogen removal performance, biofilm physicochemical properties and microbial communities were investigated. The results obtained showed that, the TF started up 41 days faster than the MBBR, despite the richer microbial diversity in the latter. Lower biofilm roughness and protein content as well as higher adhesive force and polysaccharide content in the TF were obtained compared to the MBBR. Adhesive force was found to be negatively correlated with roughness (r = -0.630, p = 0.069). Transmittance assigned to amide II (1538 cm^-1) and amid III (1243 cm^-1) through Fourier transform infrared spectroscopy (FTIR) determination was only obtained in the TF, which was likely related to the faster start-up. Nitrosomonas and Nitrospira were detected as the predominant nitrifiers in both reactors. In addition, the new MBBR, incubated with the mature biocarriers transferred from the TF, had a satisfactory nitrification performance with no lag time. Interestingly, the transfer action increased the microbial diversity and made the biofilm physicochemical characteristics shift toward those of the MBBR. Taken together, the study confirmed that MBBR nitrification start-up can be accelerated via TF and biocarrier transfer.

Treatment of municipal sewage with low carbon-to-nitrogen ratio via simultaneous partial nitrification, anaerobic ammonia oxidation, and denitrification (SNAD) in a non-woven rotating biological contactor

In this study, a non-woven rotating biological contactor was evaluated for the treatment of municipal sewage via simultaneous partial nitrification, anaerobic ammonia oxidation (anammox), and denitrification (SNAD). Fluorescence in situ hybridization analysis showed that the dominant bacterial group in the aerobic outer layer of the biofilm was ammonia-oxidizing bacteria (65.13%), whereas anammox (47.17%) and denitrifying (38.91%) bacteria were present in the anaerobic inner layer. Response surface methodology was applied to develop mathematical models for the interaction between C/N and dissolved oxygen (DO) for chemical oxygen demand (COD) and total nitrogen (TN) removal. Results showed that the optimum region for SNAD was at C/N = 1.4-2.3 and DO = 0.2-0.8 mg/L. The most optimal operating condition was determined at C/N = 2.3 and DO = 0.2 mg/L, with actual removal rates of COD and TN were 83.12% and 79.13%, respectively, which are in close model consistency with model prediction (84% and 80%).

The effect and biological mechanism of granular sludge size on performance of autotrophic nitrogen removal system

The autotrophic process for nitrogen removal has attracted worldwide attention in the field of wastewater treatment, and the performance of this process is greatly influenced by the size of granular sludge particles present in the system. In this work, the granular sludge was divided into three groups, i.e. large size (> 1.2 mm), medium size (0.6-1.2 mm) and small size (< 0.6 mm). The medium granular sludge was observed to dominate at high volumetric nitrogen loading rates, while offering strong support for good performance. Its indispensable contribution was found to originate from improved settling velocity (0.84 ± 0.10 cm/s), high SOUR-A (specific oxygen uptake rate for ammonia oxidizing bacteria, 25.93 mg O₂/g MLVSS/h), low SOUR-N (specific oxygen uptake rate for nitrite oxidizing bacteria, 3.39 mg O₂/g MLVSS/h), and a reasonable microbial spatial distribution.

Fast start-up of the CANON process with a SABF and the effects of pH and temperature on nitrogen removal and microbial activity

The long start-up time of the completely autotrophic nitrogen removal over nitrite (CANON) process is one of the main disadvantages of this system. In this paper, the CANON process with a submerged aerated biological filter (SABF) was rapidly started up within 26 days. It gave an average ammonium nitrogen removal rate (ANR) and a total nitrogen removal rate (TNR) of 94.2% and 81.3%, respectively. The phyla Proteobacteria and Planctomycetes were confirmed as the ammonia oxidizing bacteria (AOB) and anaerobic ammonium oxidation bacteria (AnAOB). The genus Candidatus Brocadia was the major contributor of nitrogen removal. pH and temperature affect the performance of the CANON process. This experimental results showed that the optimum pH and temperature were 8.0 and 30 °C, respectively, which gave the highest average ANR and TNR values of 94.6% and 85.1%, respectively. This research could promote the nitrogen removal ability of CANON process in the future.

Effect of dissolved oxygen on nitrogen removal and the microbial community of the completely autotrophic nitrogen removal over nitrite process in a submerged aerated biological filter

Dissolved oxygen (DO) is a crucial parameter of the completely autotrophic nitrogen removal over nitrite (CANON) process. This study determined the nitrogen removal performance and microbial community of the CANON process in a laboratory-scale submerged aerated biological filter (SABF) over a DO concentration range from 0 to 1.2 mg·L^-1. The results showed that the optimum DO (0.2-0.3 mg·L^-1) corresponded to an average ammonium nitrogen removal efficiency of 93.4% and a total nitrogen removal efficiency of 81.0%. A 16S rRNA gene high-throughput sequencing technology confirmed that the phyla Proteobacteria and Nitrospirae enriched, whereas the phylum Planctomycetes was inhibited with increasing DO concentration. At the genus level, the increase of DO concentration resulted in the enrichment of genera Dok59 and Nitrospira, but restrained the genus Candidatus Brocadia. This research can be used to improve the nitrogen removal ability of the CANON process in an SABF in the future.

Quantitative dynamics of ammonia-oxidizers during biological stabilization of municipal landfill leachate pretreated by Fenton's reagent at neutral pH

The application of multi-stage systems including biological step, for the treatment of leachate from municipal landfills, is economically and technologically justified. When microbial activity is utilized as 2nd stage of treatment, the task of 1st stage is to increase the bioavailability of organic matter. In this work, the effect of advanced oxidation process by Fenton's reagent for treatment efficiency of landfill leachate in the sequencing batch reactor was assessed. The quantitative dynamics of bacteria taking a part in ammonia removal process was evaluated by determination of number of DNA copies of 16S rRNA and amoA. Products of neutral pH chemical oxidation, had a definite positive impact on the quantity of β-proteobacteria 16S rRNA, whereas the same gene specified for Nitrospira sp. as well as amoA did not show a significant increase during the process of biological treatment, regardless of whether the reactor was fed with raw leachate or chemically pre-treated.

Achieving nitritation in a continuous moving bed biofilm reactor at different temperatures through ratio control

A ratio control strategy was implemented in a continuous moving bed biofilm reactor (MBBR) to investigate the response to different temperatures. The control strategy was designed to maintain a constant ratio between dissolved oxygen (DO) and total ammonia nitrogen (TAN) concentrations. The results revealed that a stable nitritation in a biofilm reactor could be achieved via ratio control, which compensated the negative influence of low temperatures by stronger oxygen-limiting conditions. Even with a temperature as low as 6°C, stable nitritation could be achieved when the controlling ratio did not exceed 0.17. Oxygen-limiting conditions in the biofilm reactor were determined by the DO/TAN concentrations ratio, instead of the mere DO concentration. This ratio control strategy allowed the achievement of stable nitritation without complete wash-out of NOB from the reactor. Through the ratio control strategy full nitritation of sidestream wastewater was allowed; however, for mainstream wastewater, only partial nitritation was recommended.

Forward osmosis membrane bioreactor for wastewater treatment with phosphorus recovery

A forward osmosis membrane bioreactor (OMBR) with a thin film composite membrane was seeded with flocculated sludge and aerobic granules to treat a synthetic wastewater with 1M NaCl as draw solution. The tested OMBR showed 96%, 43% and 100% removal of PO4(3-)-P, NH4(+)-N, and total organic carbon. Salinity was accumulated in OMBR principally owing to membrane rejection and salt leakage from draw solution. At high salinity level membrane fouling could be induced. Intermittent withdrawal and replenishment of supernatant from OMBR maintained its operation stability, while phosphorus in withdrawn supernatant was recovered by pH adjustment. The OMBR enriched phosphorus concentration from 156 mg/L in feed solution to 890-990 mg/L. At pH 8.5 with 2.65-2.71 g 3 M NaOH/g-P, 814-817 mg-P/L was recovered in the form of sodium hydrogen phosphite hydrate. The OMBR is a volatile wastewater treatment unit with capability for enrichment and recovery of phosphorus at reduced chemical costs.

Effect of trace hydrazine addition on the functional bacterial community of a sequencing batch reactor performing completely autotrophic nitrogen removal over nitrite

A sequencing batch reactor (SBR) was conducted to perform completely autotrophic nitrogen removal over nitrite (CANON). The effect of long-term trace N2H4 addition on ammonium oxidizing bacteria (AOB) and anaerobic AOB (AnAOB) in the CANON system was investigated. AOB and AnAOB primarily related to Nitrosococcus, Nitrosomonas and Candidatus scalindua, respectively. Before and after trace N2H4 addition, the estimates of AOB population decreased from 1.03×10(7) to 6.25×10(4)copies/g (dry sludge), but that of AnAOB increased from 3.14×10(9) to 5.86×10(10)copies/g (dry sludge). Despite there was a partially negative impact on AOB growth, the trace N2H4 addition exerted a stronger inhibition on nitrite oxidizing bacteria (NOB) and promoted AnAOB growth, which improved the nitrogen removal of the CANON system. Sludge granules enriched under long-term trace N2H4 addition were spherical and ellipsoidal, and the aerobic AOB were mainly located on the outer layers while AnAOB occupied most of the interior parts.

Nitrogen removal and microbial characteristics in CANON biofilters fed with different ammonia levels

The nitrogen removal performance and microbial characteristics of four completely autotrophic nitrogen removal over nitrite (CANON) biofilters were investigated. These four reactors were simultaneously seeded from a stable CANON biofilter with a seeding ratio of 1:1, which were fed with different ammonia levels. Results suggested that with the ammonia of 200-400 mg L(-1), aerobic ammonia-oxidizing bacteria (AerAOB) and anaerobic ammonia-oxidizing bacteria (AnAOB) could perform harmonious work. The bioactivity and population of the two groups of bacteria were both high, which then resulted in excellent nitrogen removal, while too low or too high ammonia would both lead to worse performance. When ammonia was too high, the bioactivity, biodiversity and population of AerAOB all decreased and then resulted in the lowest nitrogen removal. Nitrosomonas and Candidatus Brocadia were detected as predominant functional microbes in all the four reactors. Finally, strategies for treating sewage with different ammonia levels were proposed.