Priit Vabamäe

Nitrite inhibition and limitation – the effect of nitrite spiking on anammox biofilm, suspended and granular biomass

Anaerobic ammonium oxidation (anammox) has been studied extensively while no widely accepted optimum values for nitrite (both a substance and inhibitor) has been determined. In the current paper, nitrite spiking (abruptly increasing nitrite concentration in reactor over 20 mg NO-2-NL-1) effect on anammox process was studied on three systems: a moving bed biofilm reactor (MBBR), a sequencing batch reactor (SBR) and an upflow anaerobic sludge blanket (UASB). The inhibition thresholds and concentrations causing 50% of biomass activity decrease (IC50) were determined in batch tests. The results showed spiked biomass to be less susceptible to nitrite inhibition. Although the values of inhibition threshold and IC50 concentrations were similar for non-spiked biomass (81 and 98 mg NO-2-NL-1, respectively, for SBR), nitrite spiking increased IC50 considerably (83 and 240 mg NO-2-NL-1, respectively, for UASB). As the highest total nitrogen removal rate was also measured at the aforementioned thresholds, there is basis to suggest stronger limiting effect of nitrite on anammox process than previously reported. The quantitative polymerase chain reaction analysis showed similar number of anammox 16S rRNA copies in all reactors, with the lowest quantity in SBR and the highest in MBBR (3.98 × 108 and 1.04 × 109 copies g-1 TSS, respectively).

Nitric oxide for anammox recovery in a nitrite-inhibited deammonification system.

The anaerobic ammonium oxidation (anammox) process is widely used for N-rich wastewater treatment. In the current research the deammonification reactor in a reverse order (first anammox, then the nitrifying biofilm cultivation) was started up with a high maximum N removal rate (1.4 g N m−2 d−1) in a moving bed biofilm reactor. Cultivated biofilm total nitrogen removal rates were accelerated the most by anammox intermediate – nitric oxide (optimum 58 mg NO-N L−1) addition. Furthermore, NO was added in order to eliminate inhibition caused by nitrite concentrations (>50 mg ) increasing (2/1, respectively) along with a higher ratio of (0.6/1, respectively) than stoichiometrical for this optimal NO amount added during batch tests. Planctomycetales clone P4 sequences, which was the closest (98% and 99% similarity, respectively) relative to Candidatus Brocadia fulgida sequences quantities increase to 1 × 106 anammox gene copies g−1 total suspended solids to till day 650 were determined by quantitative polymerase chain reaction.

Nitritating-anammox biomass tolerant to high dissolved oxygen concentration and C/N ratio in treatment of yeast factory wastewater

Maintaining stability of low concentration (<1 g L−1) floccular biomass in the nitritation-anaerobic ammonium oxidation (anammox) process in the sequencing batch reactor (SBR) system for the treatment of high COD (>15,000 mg O2 L−1) to N (1680 mg N L−1) ratio real wastewater streams coming from the food industry is challenging. The anammox process was suitable for the treatment of yeast factory wastewater containing relatively high and abruptly increased organic C/N ratio and dissolved oxygen (DO) concentrations. Maximum specific total inorganic nitrogen (TIN) loading and removal rates applied were 600 and 280 mg N g−1 VSS d−1, respectively. Average TIN removal efficiency over the operation period of 270 days was 70%. Prior to simultaneous reduction of high organics (total organic carbon>600 mg L−1) and N concentrations>400 mg L−1, hydraulic retention time of 15 h and DO concentrations of 3.18 (±1.73) mg O2 L−1 were applied. Surprisingly, higher DO concentrations did not inhibit the anammox process efficiency demonstrating a wider application of cultivated anammox biomass. The SBR was fed rapidly over 5% of the cycle time at 50% volumetric exchange ratio. It maintained high free ammonia concentration, suppressing growth of nitrite-oxidizing bacteria. Partial least squares and response surface modelling revealed two periods of SBR operation and the SBR performances change at different periods with different total nitrogen (TN) loadings. Anammox activity tests showed yeast factory-specific organic N compound-betaine and inorganic N simultaneous biodegradation. Among other microorganisms determined by pyrosequencing, anammox microorganism (uncultured Planctomycetales bacterium clone P4) was determined by polymerase chain reaction also after applying high TN loading rates.

Start-up of low-temperature anammox in UASB from mesophilic yeast factory anaerobic tank inoculum

Robust start-up of the anaerobic ammonium oxidation (anammox) process from non-anammox-specific seeding material was achieved by using an inoculation with sludge-treating industrial -, organics- and N-rich yeast factory wastewater. N-rich reject water was treated at 20°C, which is significantly lower than optimum treatment temperature. Increasing the frequency of biomass fluidization (from 1–2 times per day to 4–5 times per day) through feeding the reactor with higher flow rate resulted in an improved total nitrogen removal rate (from 100 to 500 g m−3d−1) and increased anammox bacteria activity. As a result of polymerase chain reaction (PCR) tests, uncultured planctomycetes clone 07260064(4)-2-M13-_A01 (GenBank: JX852965) was identified from the biomass taken from the reactor. The presence of anammox bacteria after cultivation in the reactor was confirmed by quantitative PCR (qPCR); an increase in quantity up to ∼2×106 copies g VSS−1 during operation could be seen in qPCR. Statistical modelling of chemical parameters revealed the roles of several optimized parameters needed for a stable process.

Effect of concentration on anammox nitrogen removal rate in a moving bed biofilm reactor

Anammox biomass enriched in a moving bed biofilm reactor (MBBR) fed by actual sewage sludge reject water and synthetically added was used to study the total nitrogen (TN) removal rate of the anammox process depending on bicarbonate ( ) concentration. MBBR performance resulted in the maximum TN removal rate of 1100 g N m−3 d−1 when the optimum concentration (910 mg L−1) was used. The average reaction ratio of removal, production and removal were 1.18/0.20/1. When the concentration was increased to 1760 mg L−1 the TN removal rate diminished to 270 g N m−3 d−1. The process recovered from bicarbonate inhibition within 1 week. The batch tests performed with biomass taken from the MBBR showed that for the concentration of 615 mg L−1 the TN removal rate was 3.3 mg N L−1 h−1, whereas for both lower (120 mg L−1) and higher (5750 mg L−1) concentrations the TN removal rates were 2.3 (±0.15) and 1.6 (±0.12) mg N L−1 d−1, respectively. PCR and DGGE analyses resulted in the detection of uncultured Planctomycetales bacterium clone P4 and, surprisingly, low-oxygen-tolerant aerobic ammonia oxidizers. The ability of anammox bacteria for mixotrophy was established by diminished amounts of nitrate produced when comparing the experiments with an organic carbon source and an inorganic carbon source.

Deammonification process start-up after enrichment of anammox microorganisms from reject water in a moving-bed biofilm reactor

Deammonification via intermittent aeration in biofilm process for the treatment of sewage sludge digester supernatant (reject water) was started up using two opposite strategies. Two moving-bed biofilm reactors were operated for 2.5 years at 26 (±0.5)°C with spiked influent (and hence free ammonia (FA)) addition. In the first start-up strategy, an enrichment of anammox biomass was first established, followed by the development of nitrifying biomass in the system (R1). In contrast, the second strategy aimed at the enrichment of anammox organisms into a nitrifying biofilm (R2). The first strategy was most successful, reaching higher maximum total nitrogen (TN) removal rates over a shorter start-up period. For both reactors, increasing FA spiking frequency and increasing effluent concentrations of the anammox intermediate hydrazine correlated to decreasing aerobic nitrate production (nitritation). The bacterial consortium of aerobic and anaerobic ammonium oxidizing bacteria in the bioreactor was determined via denaturing gel gradient electrophoresis, polymerase chain reaction and pyrosequencing. In addition to a shorter start-up with a better TN removal rate, nitrite oxidizing bacteria (Nitrospira) were outcompeted by spiked ammonium feeding from R1.