The effect of sulfide inhibition on the ANAMMOX process

Step-wise temperature decreasing cultivates a biofilm with high nitrogen removal rates at 9°C in short-term anammox biofilm tests

The anaerobic ammonium oxidation (anammox) and nitritation-anammox (deammonification) processes are widely used for N-rich wastewater treatment. When deammonification applications move towards low temperature applications (mainstream wastewater has low temperature), temperature effect has to be studied. In current research, in a deammonification moving bed biofilm reactor a maximum total nitrogen removal rate (TNRR) of 1.5 g N m(-2 )d(-1) (0.6 kg N m(-3 )d(-1)) was achieved. Temperature was gradually lowered by 0.5°C per week, and a similar TNRR was sustained at 15°C during biofilm cultivation. Statistical analysis confirmed that a temperature decrease from 20°C down to 15° did not cause instabilities. Instead, TNRR rose and treatment efficiency remained stable at lower temperatures as well. Quantitative polymerase chain reaction analyses showed an increase in Candidatus Brocadia quantities from 5 × 10(3) to 1 × 10(7) anammox gene copies g(-1) total suspended solids (TSS) despite temperature lowered to 15°C. Fluctuations in TNRR were rather related to changes in influent [Formula: see text] concentration. To study the short-term effect of temperature on the TNRR, a series of batch-scale experiments were performed which showed sufficient TNRRs even at 9-15°C (1.24-3.43 mg N g(-1 )TSS h(-1), respectively) with anammox temperature constants (Q10) ranging 1.3-1.6. Experiments showed that a biofilm adapted to 15°C can perform N-removal most sufficiently at temperatures down to 9°C as compared with biofilm adapted to higher temperature. After biomass was adapted to 15°C, the decrease in TNRR in batch tests at 9°C was lower (15-20%) than that for biomass adapted to 17-18°C.

Inhibition of the partial nitritation by roxithromycin and Cu(II)

To facilitate the application of partial nitritation (PN) - anaerobic ammonium oxidation process in nitrogen removal from livestock wastewater, the inhibition of roxithromycin (ROX) and Cu(II) on the PN sludge was examined using a respirometric method. The results showed that the IC50 of ROX and Cu(II) on PN sludge were 346 and 74.3mgL(-1), respectively. The relative specific respiration rate (SRR) of ammonia-oxidizing bacteria (AOB) decreased from 87.4% to 17.7% with the ROX concentration increased from 0 to 500mgL(-1). When the concentration of Cu(II) increased from 0 to 160mgL(-1), the SRRs of AOB and nitrite-oxidizing bacteria decreased by 85.5% and 11.2%, respectively. According to the isobole plots analysis, combined suppression by ROX and Cu(II) was synergistic. Fourier transform infrared spectroscopy analyses showed that ROX exposure altered the positions of CO bonds, and the intensity of the absorption peak at 2100cm(-1) changed under Cu(II) exposure.

Integrating landfill bioreactors, partial nitritation and anammox process for methane recovery and nitrogen removal from leachate

A new process consisting of a landfill bioreactor, partial-nitritation (PN) and the anammox process has been developed for landfill leachate treatment. In this study, the landfill bioreactor exhibited excellent performance in methane-rich biogas recovery, with a specific biogas yield of 0.47 L gas g⁻¹ COD and methane percentages of 53–76%. PN was achieved in the aerobic reactor by high free ammonia (101 ± 83 mg NH₃ L⁻¹) inhibition for nitrite-oxidizing bacteria, and the desired PN effluent composition (effluent nitrite: ammonium ratio of 1.1 ± 0.3) was controlled by adjusting the alkalinity concentration per unit of ammonium oxidized to approximately 14.3 mg CaCO₃ mg⁻¹ N in the influent. The startup of anammox process was successfully achieved with a membrane bioreactor in 160 d, and a maximum nitrogen removal rate of 216 mg N L⁻¹ d⁻¹ was attained for real landfill leachate treatment. The quantitative polymerase chain reaction results confirmed that the cell-specific anammox activity was approximately 68–95 fmol N cell⁻¹ d⁻¹, which finally led to the stable operation of the system.

Model-Based Feasibility Assessment of Membrane Biofilm Reactor to Achieve Simultaneous Ammonium, Dissolved Methane, and Sulfide Removal from Anaerobic Digestion Liquor

In this study, the membrane biofilm reactor (MBfR) is proposed to achieve simultaneous removal of ammonium, dissolved methane, and sulfide from main-stream and side-stream anaerobic digestion liquors. To avoid dissolved methane stripping, oxygen is introduced through gas-permeable membranes, which also from the substratum for the growth of a biofilm likely comprising ammonium oxidizing bacteria (AOB), anaerobic ammonium oxidation (Anammox) bacteria, denitrifying anaerobic methane oxidation (DAMO) microorganisms, aerobic methane oxidizing bacteria (MOB), and sulfur oxidizing bacteria (SOB). A mathematical model is developed and applied to assess the feasibility of such a system and the associated microbial community structure under different operational conditions. The simulation studies demonstrate the feasibility of achieving high-level (>97.0%), simultaneous removal of ammonium, dissolved methane, and sulfide in the MBfRs from both main-stream and side-stream anaerobic digestion liquors through adjusting the influent surface loading (or hydraulic retention time (HRT)) and the oxygen surface loading. The optimal HRT was found to be inversely proportional to the corresponding oxygen surface loading. Under the optimal operational conditions, AOB, DAMO bacteria, MOB, and SOB dominate the biofilm of the main-stream MBfR, while AOB, Anammox bacteria, DAMO bacteria, and SOB coexist in the side-stream MBfR to remove ammonium, dissolved methane, and sulfide simultaneously.

Metatranscriptomic evidence of pervasive and diverse chemolithoautotrophy relevant to C, S, N and Fe cycling in a shallow alluvial aquifer

Groundwater ecosystems are conventionally thought to be fueled by surface-derived allochthonous organic matter and dominated by heterotrophic microbes living under often-oligotrophic conditions. However, in a 2-month study of nitrate amendment to a perennially suboxic aquifer in Rifle (CO), strain-resolved metatranscriptomic analysis revealed pervasive and diverse chemolithoautotrophic bacterial activity relevant to C, S, N and Fe cycling. Before nitrate injection, anaerobic ammonia-oxidizing (anammox) bacteria accounted for 16% of overall microbial community gene expression, whereas during the nitrate injection, two other groups of chemolithoautotrophic bacteria collectively accounted for 80% of the metatranscriptome: (1) members of the Fe(II)-oxidizing Gallionellaceae family and (2) strains of the S-oxidizing species, Sulfurimonas denitrificans. Notably, the proportion of the metatranscriptome accounted for by these three groups was considerably greater than the proportion of the metagenome coverage that they represented. Transcriptional analysis revealed some unexpected metabolic couplings, in particular, putative nitrate-dependent Fe(II) and S oxidation among nominally microaerophilic Gallionellaceae strains, including expression of periplasmic (NapAB) and membrane-bound (NarGHI) nitrate reductases. The three most active groups of chemolithoautotrophic bacteria in this study had overlapping metabolisms that allowed them to occupy different yet related metabolic niches throughout the study. Overall, these results highlight the important role that chemolithoautotrophy can have in aquifer biogeochemical cycling, a finding that has broad implications for understanding terrestrial carbon cycling and is supported by recent studies of geochemically diverse aquifers.

Impact of Tannery Effluent on the Self-purification Capacity and Biodiversity Level of a River

The present study investigates the impact of tannery effluents on the self-purification capacity and the local macroinvertebrate community of one natural stream. As the concentration of chromium and sulfide increased from up- to downstream sites, the reduction of suspended solids, 5-days biological oxygen demand (BOD5), chemical oxygen demand and nitrification capacity decreased by 61 %, 21 %, 30 % and 74 %, respectively. Similarly, the share of Ephemeroptera, Plecoptera, and Trichoptera on the macroinvertebrate community decreased from 24 % to 0 %. Also the diversity (Simpson's) index and the correlation between the physicochemical parameters, BOD5 reduction, the macroinvertebrate abundance and the chromium concentration underpin the importance of the contamination by tannery effluents for the degradation of the stream habitat quality. In conclusion, although the physicochemical parameters indicate that the self-purification of the river can be maintained for a certain stream section, the biodiversity of the river is severely compromised.

Effect of cathode electron acceptors on simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell

The current investigation reports the effect of cathode electron acceptors on simultaneous sulfide and nitrate removal in two-chamber microbial fuel cells (MFCs). Potassium permanganate and potassium ferricyanide were common cathode electron acceptors and evaluated for substrate removal and electricity generation. The abiotic MFCs produced electricity through spontaneous electrochemical oxidation of sulfide. In comparison with abiotic MFC, the biotic MFC showed better ability for simultaneous nitrate and sulfide removal along with electricity generation. Keeping external resistance of 1,000 Ω, both MFCs showed good capacities for substrate removal where nitrogen and sulfate were the main end products. The steady voltage with potassium permanganate electrodes was nearly twice that of with potassium ferricyanide. Cyclic voltammetry curves confirmed that the potassium permanganate had higher catalytic activity than potassium ferricyanide. The potassium permanganate may be a suitable choice as cathode electron acceptor for enhanced electricity generation during simultaneous treatment of sulfide and nitrate in MFCs.

Platforms for energy and nutrient recovery from domestic wastewater: A review

Alternative domestic wastewater treatment processes that recover energy and nutrients while achieving acceptable nutrient limits (<5mgNL(-1)) are a key challenge. Major drivers are value and availability of phosphorous, nitrogen, and potassium, and increasing energy costs. The two major platforms that can achieve this are (a) low energy mainline (LEM), with low strength anaerobic treatment, followed by mainline anaerobic nitrogen removal and chemical or adsorptive phosphorous removal and (b) partition-release-recover (PRR), in which carbon and nutrients are partitioned to solids through either heterotrophic or phototrophic microbes, followed by anaerobic digestion of these solids and recovery from the digestate. This paper reviews practical application of these processes, with a focus on energy costs. Compared to conventional processes which require 0.5kWhkL(-1) electricity (500mgCODL(-1) influent concentration), PRR requires only 0.05kWhkL(-1) electricity. LEM offers the possibility to recover 0.1kWhkL(-1) as electricity with net energy generation above 400mgCODL(-1)influent, while PRR becomes energy generating at >650mgCODL(-1). PRR offers the possibility for recovery of nitrogen and other nutrients (including potassium) through assimilative recovery. However, the energetic overhead of this is substantial, requiring 5kWhkgN(-1) as electricity, which compares to ammonia fixation costs. The lower energy costs, and near to market status of LEM treatment make it likely as a recovery platform in the shorter term, while ability to recover other elements such as nitrogen and potassium, as well as enhance favourability on concentrated wastewaters may enhance the desirability of partitioning in the longer term.

Anammox-based technologies for nitrogen removal: Advances in process start-up and remaining issues

Nitrogen removal from wastewater via anaerobic ammonium oxidation (anammox)-based process has been recognized as efficient, cost-effective and low energy alternative to the conventional nitrification and denitrification processes. To date, more than one hundred full-scale anammox plants have been installed and operated for treatment of NH4(+)-rich wastewater streams around the world, and the number is increasing rapidly. Since the discovery of anammox process, extensive researches have been done to develop various anammox-based technologies. However, there are still some challenges in practical application of anammox-based treatment process at full-scale, e.g., longer start-up period, limited application to mainstream municipal wastewater and poor effluent water quality. This paper aimed to summarize recent status of application of anammox process and researches on technological development for solving these remaining problems. In addition, an integrated system of anammox-based process and microbial fuel cell is proposed for sustainable and energy-positive wastewater treatment.

Potential risk and control strategy of biofilm pretreatment process treating raw water

An enhanced lab-scale biofilm pretreatment process treating raw water obtained from eutrophicated water bodies was established and started up with a novel strategy of low-level nutrients addition and effluent recirculation. Results showed that the startup strategy was useful for biofilm formation and pollutants removal, but it had the risks of increasing substrate affinity constant (Ks) and biofilm decay in treating raw water. Fortunately, the increased Ks value did not affected the NH4(+)-N removal performance via keeping the NH4(+)-N loading rate larger than 6.29 mg L(-1)d(-1). In addition, lower hydraulic retention time (HRT) favored the removal of organic matters, and the maximum TOC removal rate of 76.5 mg L(-1)d(-1) were achieved at HRT of 2h. After long-term acclimatization at oligotrophic niche, the decrease of Ks value and increase of biomass, extracellular polymeric substances, bioactivity were achieved. Finally, the stable operation of biofilm pretreatment process was realized in treating polluted raw water.

Elemental sulfur formation and nitrogen removal from wastewaters by autotrophic denitrifiers and anammox bacteria

Elemental sulfur (S(0)) formation from and nitrogen removal on sulfide, nitrate and ammonium-laden wastewaters were achieved by denitrifying ammonium oxidation (DEAMOX) reactor with autotrophic denitrifiers and anaerobic ammonium oxidation (anammox) bacteria. The sulfide to nitrate ratio is a key process parameter for excess accumulation of S(0) and a ratio of 1.31:1 is a proposed optimum. The Alishewanella, Thauera and Candidatus Anammoximicrobium present respectively the autotrophic denitrifiers and anammox bacteria for the reactor. DEAMOX is demonstrated promising biological process for treating organics-deficient (S+N) wastewaters with excess S(0) production.

Performance and enhanced mechanism of a novel bio-diatomite biofilm pretreatment process treating polluted raw water

A lab-scale novel bio-diatomite biofilm process (BDBP) was established for the polluted raw water pretreatment in this study. Results showed that a shorter startup period of BDBP system was achieved under the completely circulated operation mode, and the removal efficiencies of nitrogen and disinfection by-product precursor were effective at low hydraulic retention time of 2-4 h due to high biomass attached to the carrier and diatomite. A maximum NH4(+)-N oxidation potential predicted by modified Stover-Kincannon model was 333.3 mg L(-1) d(-1) in the BDBP system, which was 4.7 times of that in the control reactor. Results demonstrated that the present of bio-diatomite favors the accumulation of functional microbes in the oligotrophic niche, and the pollutants removal performance of this novel process was enhanced for polluted raw water pretreatment.

Start-up of granule-based denitrifying reactors with multiple magnesium supplementation strategies

In the present work, the effect of Mg(2+) supplementation on the start-up of a denitrification process and the granulation of denitrifying sludge was investigated in three upflow anaerobic sludge blanket (UASB) reactors. The reactors R1 and R2 were continuously and intermittently, respectively, supplied with 50 mg L(-1) Mg(2+), whereas R0 was used as the control. The nitrogen loading rate (NLR) and organic loading rate (OLR) gradually increased, and extremely high values were obtained (36.0 kgN m(-3) d(-1) and 216.0 kgCOD m(-3) d(-1), respectively). Granulation occurred in R1 first, but the reactor capacities were comparable. Suffering from starvation, the R0-R2 performances were comparable. At the end of the experiment, the average diameter of the granules in R0, R1, and R2 were 1.67, 1.72 and 1.68 mm, respectively, and the settling velocities of the granules in R1 and R2 were 1.14-fold the speed of R0. The specific denitrifying activity (SDA) of the sludge from the reactors supplied with Mg(2+) was greater than the reactor without Mg(2+). Intermittent Mg(2+) supplementation was identified as the best choice to be utilized to cultivate denitrifying granules, which was consistent with kinetic analysis.

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 [Formula: see text]-, 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(-3)d(-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 ∼2×10(6) 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.

Physiological characterization of anaerobic ammonium oxidizing bacterium 'Candidatus Jettenia caeni'

To date, six candidate genera of anaerobic ammonium-oxidizing (anammox) bacteria have been identified, and numerous studies have been conducted to understand their ecophysiology. In this study, we examined the physiological characteristics of an anammox bacterium in the genus 'Candidatus Jettenia'. Planctomycete KSU-1 was found to be a mesophilic (20-42.5°C) and neutrophilic (pH 6.5-8.5) bacterium with a maximum growth rate of 0.0020 h(-1) . Planctomycete KSU-1 cells showed typical physiological and structural features of anammox bacteria; i.e. (29) N2 gas production by coupling of (15) NH4 (+) and (14) NO2 (-) , accumulation of hydrazine with the consumption of hydroxylamine and the presence of anammoxosome. In addition, the cells were capable of respiratory ammonification with oxidation of acetate. Notably, the cells contained menaquinone-7 as a dominant respiratory quinone. Proteomic analysis was performed to examine underlying core metabolisms, and high expressions of hydrazine synthase, hydrazine dehydrogenase, hydroxylamine dehydrogenase, nitrite/nitrate oxidoreductase and carbon monoxide dehydrogenase/acetyl-CoA synthase were detected. These proteins require iron or copper as a metal cofactor, and both were dominant in planctomycete KSU-1 cells. On the basis of these experimental results, we proposed the name 'Ca. Jettenia caeni' sp. nov. for the bacterial clade of the planctomycete KSU-1.

Effect of high electron donor supply on dissimilatory nitrate reduction pathways in a bioreactor for nitrate removal

The possible shift of a bioreactor for NO3(-) removal from predominantly denitrification (DEN) to dissimilatory nitrate reduction to ammonium (DNRA) by elevated electron donor supply was investigated. By increasing the C/NO3(-) ratio in one of two initially identical reactors, the production of high sulfide concentrations was induced. The response of the dissimilatory NO3(-) reduction processes to the increased availability of organic carbon and sulfide was monitored in a batch incubation system. The expected shift from a DEN- towards a DNRA-dominated bioreactor was not observed, also not under conditions where DNRA would be thermodynamically favorable. Remarkably, the microbial community exposed to a high C/NO3(-) ratio and sulfide concentration did not use the most energy-gaining process.

Floatation of flocculent and granular sludge in a high-loaded anammox reactor

The floatation of flocculent and granular sludge was investigated in this study. An anaerobic ammonium oxidation (anammox) upflow anaerobic sludge blanket (UASB) reactor was operated for 665 days. During this time, the maximum nitrogen removal rate was 52.6 kg Nm(-3) d(-1). Floccule floatation occurred between days 100 and 140, which potentially resulted from the sudden increase in gas yield and the poor settling ability of the floccules. Increasing the shear rate from 0.084 to 0.135 s(-1) was effective at eliminating floccule floatation. In addition, granule floatation occurred between days 572 and 665, which likely resulted from the formation of hollows within the granules. Floatation may be effectively prevented by maintaining a shear rate of more than 0.778 s(-1). Furthermore, the mechanisms of granule floatation and the floatation processes were proposed. Overall, controlling the shear force may effectively overcome sludge floatation.

Impact of inocula and operating conditions on the microbial community structure of two anammox reactors

The microbial community structure of the biomass selected in two distinctly inoculated anaerobic oxidation of ammonium (anammox) reactors was investigated and compared with the help of data obtained from 454-pyrosequencing analyses. The anammox reactors were operated for 550 days and seeded with different sludges: sediment from a constructed wetland (reactor I) and biomass from an aerated lagoon part of the oil-refinery wastewater treatment plant (reactor II). The anammox diversity in the inocula was evaluated by 16S rRNA gene-cloning analysis. The diversity of anammox bacteria was greater in the sludge from the oil-refinery (three of the five known genera of anammox were detected) than in the wetland sludge, in which only Candidatus Brocadia was observed. Pyrosequencing analysis demonstrated that the community enriched in both reactors had differing compositions despite the nearly similar operational conditions applied. The dominant phyla detected in both reactors were Proteobacteria, Chloroflexi, Planctomycetes, and Acidobacteria. The phylum Bacteroidetes, which is frequently observed in anammox reactors, was not detected. However, Acidobacteria and GN04 phyla were observed for the first time, suggesting their importance for this process. Our results suggest that, under similar operational conditions, anammox populations (Ca. Brocadia sinica and Ca. Brocadia sp. 40) were selected in both reactors despite the differences between the two initial inocula. Taken together, these results indicated that the type of inoculum and the culture conditions are key determinants of the general microbial composition of the biomass produced in the reactors. Operational conditions alone might play an important role in anammox selection.

Production of nitrous oxide from anaerobic digester centrate and its use as a co-oxidant of biogas to enhance energy recovery

Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) is a new process for wastewater treatment that removes nitrogen from wastewater and recovers energy from the nitrogen in three steps: (1) NH4(+) oxidation to NO2(-); (2) NO2(-) reduction to N2O gas; and (3) N2O conversion to N2 with energy production. In this work, we optimize Steps 1 and 2 for anaerobic digester centrate, and we evaluate Step 3 for a full-scale biogas-fed internal combustion engine. Using a continuous stirred reactor coupled to a bench-scale sequencing batch reactor, we observed sustained partial oxidation of NH4(+) to NO2(-) and sustained (3 months) partial reduction of NO2(-) to N2O (75-80% conversion, mass basis), with >95% nitrogen removal (Step 2). Alternating pulses of acetate and NO2(-) selected for Comamonas (38%), Ciceribacter (16%), and Clostridium (11%). Some species stored polyhydroxybutyrate (PHB) and coupled oxidation of PHB to reduction of NO2(-) to N2O. Some species also stored phosphorus as polyphosphate granules. Injections of N2O into a biogas-fed engine at flow rates simulating a full-scale system increased power output by 5.7-7.3%. The results underscore the need for more detailed assessment of bioreactor community ecology and justify pilot- and full-scale testing.

Towards energy neutral wastewater treatment: methodology and state of the art

Conventional biological wastewater treatment processes are energy-intensive endeavors that yield little or no recovered resources and often require significant external chemical inputs. However, with embedded energy in both organic carbon and nutrients (N, P), wastewater has the potential for substantial energy recovery from a low-value (or no-value) feedstock. A paradigm shift is thus now underway that is transforming our understanding of necessary energy inputs, and potential energy or resource outputs, from wastewater treatment, and energy neutral or even energy positive treatment is increasingly emphasized in practice. As two energy sources in domestic wastewater, we argue that the most suitable way to maximize energy recovery from wastewater treatment is to separate carbon and nutrient (particularly N) removal processes. Innovative anaerobic treatment technologies and bioelectrochemical processes are now being developed as high efficiency methods for energy recovery from waste COD. Recently, energy savings or even generation from N removal has become a hotspot of research and development activity, and nitritation-anammox, the newly developed CANDO process, and microalgae cultivation are considered promising techniques. In this paper, we critically review these five emerging low energy or energy positive bioprocesses for sustainable wastewater treatment, with a particular focus on energy optimization in management of nitrogenous oxygen demand. Taken together, these technologies are now charting a path towards to a new paradigm of resource and energy recovery from wastewater.

Effect of operating modes on simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell

The effect of operating modes on the simultaneous sulfide and nitrate removal were studied in two-chamber microbial fuel cells (MFCs). The batch and continuous operating modes were compared and evaluated in terms of substrate removal and electricity generation. Upon gradual increase in the influent sulfide concentration from 60 to 1,020 S mg L(-1), and the hydraulic retention time decrease from 17.2 to 6 h, the MFC accomplished a good substrate removal efficiency whereby nitrogen and sulfate were the main end products. The removal efficiency of the MFC in the continuous mode was much higher than that in the batch mode, and its current densities in the continuous mode were more stable and higher than in the batch mode, which could be explained by the linear relationship between electrons released by the substrates and accepted on the electrodes. The electricity output in the continuous mode of the MFC was higher than that in the batch mode. MFC's operation in the continuous mode was a better strategy for the simultaneous treatment of sulfide and nitrate.

Feasibility and interest of the anammox process as treatment alternative for anaerobic digester supernatants in manure processing--an overview

Completely autotrophic nitrogen removal (ANR) is based on the combination of partial nitritation (PN) and anaerobic ammonium oxidation (anammox). It is a promising alternative for the subsequent treatment of biogas digester supernatants in livestock manure processing and nitrogen surplus scenarios. However, as no full-scale experiences in the treatment of manure digestates by ANR have been published to date, future field studies addressing treatment of this kind of effluent would be of great interest. Some topics to be considered in these studies would be coupling anaerobic digestion and ANR, analysis of the factors that affect the process, comparing reactor configurations, microbial ecology, gas emissions, and achieving robust performance. This paper provides an overview of published studies on ANR. Specific issues related to the applicability of the process for treating manure digestates are discussed. The energy requirements of ANR are compared with those of other technological alternatives aimed at recovering nitrogen from digester supernatants. The results of the assessment were shown to depend on the composition of the supernatant. In this regard, the PN-anammox process was shown to be more competitive than other alternatives particularly at concentrations of up to 2 kg NH4(+)-N m(-3).

The increasing interest of ANAMMOX research in China: bacteria, process development, and application

Nitrogen pollution created severe environmental problems and increasingly has become an important issue in China. Since the first discovery of ANAMMOX in the early 1990s, this related technology has become a promising as well as sustainable bioprocess for treating strong nitrogenous wastewater. Many Chinese research groups have concentrated their efforts on the ANAMMOX research including bacteria, process development, and application during the past 20 years. A series of new and outstanding outcomes including the discovery of new ANAMMOX bacterial species (Brocadia sinica), sulfate-dependent ANAMMOX bacteria (Anammoxoglobus sulfate and Bacillus benzoevorans), and the highest nitrogen removal performance (74.3–76.7 kg-N/m³/d) in lab scale granule-based UASB reactors around the world were achieved. The characteristics, structure, packing pattern and floatation mechanism of the high-rate ANAMMOX granules in ANAMMOX reactors were also carefully illustrated by native researchers. Nowadays, some pilot and full-scale ANAMMOX reactors were constructed to treat different types of ammonium-rich wastewater including monosodium glutamate wastewater, pharmaceutical wastewater, and leachate. The prime objective of the present review is to elucidate the ongoing ANAMMOX research in China from lab scale to full scale applications, comparative analysis, and evaluation of significant findings and to set a design to usher ANAMMOX research in culmination.

Performance of the ANAMMOX process using multi- and single-fed upflow anaerobic sludge blanket reactors

The performance of the ANAMMOX process was investigated in two identical laboratory-scale multi- and single-fed upflow anaerobic sludge blanket (UASB) reactors (denoted R1 and R0) at different hydraulic residence times (HRTs) varying from 2.06 to 1.52 h and NH4(+)-N inf concentrations ranging from 70 to 266 mg L(-1). The substrate removal efficiencies of both reactors decreased as HRT decreased and NH4(+)-N inf increased. The kinetics of these reactions were analyzed, and the Stover-Kincannon model was appropriate to describe the process kinetics of the reactors. In addition, an empirical model incorporating the influent substrate concentration and HRT adequately described R1. Shock experiments were conducted in which the reactors were subjected to transient shock loads. The results showed that the operation of R1 was more stable than that of R0, especially in response to the substrate shocks. Subsequently, the properties of the ANAMMOX granules and the effects of the feeding protocol on those properties were investigated.

Presence and diversity of anammox bacteria in cold hydrocarbon-rich seeps and hydrothermal vent sediments of the Guaymas Basin

Hydrothermally active sediments are highly productive, chemosynthetic areas which are characterized by the rapid turnover of particulate organic matter under extreme conditions in which ammonia is liberated. These systems might be suitable habitats for anaerobic ammonium oxidizing (anammox) bacteria but this has not been investigated in detail. Here we report the diversity and abundance of anammox bacteria in sediments that seep cold hydrocarbon-rich fluids and hydrothermal vent areas of the Guaymas Basin in the Cortés Sea using the unique functional anammox marker gene, hydrazine synthase (hzsA). All clones retrieved were closely associated to the “Candidatus Scalindua” genus. Phylogenetic analysis revealed two distinct clusters of hzsA sequences (Ca. Scalindua hzsA cluster I and II). Comparison of individual sequences from both clusters showed that several of these sequences had a similarity as low as 76% on nucleotide level. Based on the analysis of this phylomarker, a very high interspecies diversity within the marine anammox group is apparent. Absolute numbers of anammox bacteria in the sediments samples were determined by amplification of a 257 bp fragment of the hszA gene in a qPCR assay. The results indicate that numbers of anammox bacteria are generally higher in cold hydrocarbon-rich sediments compared to the vent areas and the reference zone. Ladderanes, lipids unique to anammox bacteria were also detected in several of the sediment samples corroborating the hzsA analysis. Due to the high concentrations of reduced sulfur compounds and its potential impact on the cycling of nitrogen we aimed to get an indication about the key players in the oxidation of sulfide in the Guaymas Basin sediments using the alpha subunit of the adenosine-5′-phosphosulfate (APS) reductase (aprA). Amplification of the aprA gene revealed a high number of gammaproteobacterial aprA genes covering the two sulfur-oxidizing bacteria aprA lineages as well as sulfate-reducers.

Evaluating the recovery performance of the ANAMMOX process following inhibition by phenol and sulfide

In this study, the recovery performance of two anaerobic ammonium oxidation (ANAMMOX) reactors (R1, R2) that were previously subjected to phenol and sulfide for nearly 200 days with respective levels of 12.5-50 and 8-40 mg L(-1) and then operated in the absence of these suppressors was investigated. High nitrogen removal rates of greater than 36 kg-Nm(-3)d(-1) were achieved through the 81 and 75 days restoration of R1 and R2, respectively. The recovery performance was determined by specific sludge removal rate, heme c contents, specific ANAMMOX activity, settling properties and morphology of ANAMMOX granules. In addition, the modified Boltzmann model, the modified Gompertz model and the modified Logistic model were applied to simulate recovery performance. The modified Boltzmann model was found to be appropriate for predicting recovery performance of the phenol-inhibited reactor, while the modified Logistic model effectively simulated the recovery performance of the sulfide suppressed reactor.

Mathematical modeling of high-rate Anammox UASB reactor based on granular packing patterns

A novel mathematical model was developed to estimate the volumetric nitrogen conversion rates of a high-rate Anammox UASB reactor based on the packing patterns of granular sludge. A series of relationships among granular packing density, sludge concentration, hydraulic retention time and volumetric conversion rate were constructed to correlate Anammox reactor performance with granular packing patterns. It was suggested that the Anammox granules packed as the equivalent simple cubic pattern in high-rate UASB reactor with packing density of 50-55%, which not only accommodated a high concentration of sludge inside the reactor, but also provided large pore volume, thus prolonging the actual substrate conversion time. Results also indicated that it was necessary to improve Anammox reactor performance by enhancing substrate loading when sludge concentration was higher than 37.8 gVSS/L. The established model was carefully calibrated and verified, and it well simulated the performance of granule-based high-rate Anammox UASB reactor.