Investigation of nitrite accumulation by hydrogenotrophic denitrification in a moving bed biofilm reactor for partial denitrification and anammox process.

The partial denitrification and anammox (PDA) process has received attention for its ability to optimize treatment of wastewater containing a low NH4+-N concentration. This study investigated the suitable operational conditions for NO2--N accumulation by hydrogenotrophic denitrification (HD) in operation of a laboratory-scale moving bed biofilm reactor, for future application in the PDA process. NO2--N accumulation was achieved by minimizing the H2 flow rate under optimized conditions (i.e., 15 mL/min H2 flow rate, 40 mg-N/L influent NO3--N, 7.0 h hydraulic retention time, and 2 L working volume). Hydrogenophaga comprised 39.2% of the bacterial abundance after NO2--N accumulated, indicating its contribution to the NO2--N accumulation. In addition, an intermittent H2 supply maintained the NO2--N accumulation rate (NAR) and maximized the nitrite accumulation efficiency (NAE). A H2 supply ratio of 0.7 (i.e., ON: 7 min, OFF: 3 min) was optimal, which induced increases in NAR, NAE, and the NO3--N removal efficiency that reached 0.07±0.01 kg-N/m3/d, 64.4±14.5%, and 89.2±8.9%, respectively. The ratio of H2 supply rate to the NO3--N loading rate was calculated as 4.3 in this experiment, which may represent the optimal balance for maximization of NO2--N accumulation by HD.

Newly established process combining partial hydrogenotrophic denitrification and anammox for nitrogen removal.

The anaerobic ammonium oxidation (anammox) process holds great promise for treating nitrogen-contaminated water; stable nitrite-nitrogen (NO2 --N) production is significant to anammox performance. In this study, partial hydrogenotrophic denitrification (PHD) was used to stably and efficiently produce NO2 --N from nitrate-nitrogen (NO3 --N). An investigation of the effects of initial pH on the PHD process revealed that a high NO2 --N production efficiency (77.9%) could be ensured by setting an initial pH of 10.5. A combined PHD-anammox process was run for more than three months with maximal ammonium-nitrogen (NH4 +-N), NO3 --N, and total dissolved inorganic nitrogen removal efficiencies of 93.4, 98.0, and 86.9%, respectively. The NO2 --N to NH4 +-N and NO3 --N to NH4 +-N ratios indicated that various bioprocesses were involved in nitrogen removal during the anammox stage, and a 16S rRNA gene amplicon sequencing was performed to further clarify the composition of microbial communities and mechanisms involved in the nitrogen removal process.

Coupled anaerobic ammonium oxidation and hydrogenotrophic denitrification for simultaneous NH4-N and NO3-N removal.

Nitrate removal during anaerobic ammonium oxidation (anammox) treatment is a concern for optimization of the anammox process. This study demonstrated the applicability and long-term stability of the coupled anammox and hydrogenotrophic denitrification (CAHD) process as an alternative method for nitrate removal. Laboratory-scale fixed bed anammox reactors (FBR) supplied with H2 to support denitrification were operated under two types of synthetic water. The FBRs showed simultaneous NH4-N and NO3-N removal, indicating that the CAHD process can support NO3-N removal during the anammox process. Intermittent H2 supply (e.g. 5 mL/min for a 1-L reactor, 14/6-min on/off cycle) helped maintain the CAHD process without deteriorating its performance under long-term operation and resulted in a nitrogen removal rate of 0.21 kg-N/m3/d and ammonium, nitrate, and dissolved inorganic nitrogen removal efficiencies of 73.4%, 80.4%, and 77%, respectively. The microbial community structure related to the CAHD process was not influenced by changes in influent water quality, and included the anammox bacteria 'Candidatus Jettenia' and a Sulfuritalea hydrogenivorans-like species as the dominant bacteria even after long-term reactor operation, suggesting that these bacteria are key to the CAHD process. These results indicate that the CAHD process is a promising method for enhancing the efficiency of anammox process.

Characterization of microbial communities distributed in the groundwater pumped from deep tube wells in the Kathmandu Valley of Nepal.

Although groundwater is a major water supply source in the Kathmandu Valley of Nepal, it is known that the groundwater has significant microbial contamination exceeding the drinking water quality standard recommended by the World Health Organization (WHO), and that this has been implicated in causing a variety of diseases among people living in the valley. However, little is known about the distribution of pathogenic microbes in the groundwater. Here, we analysed the microbial communities of the six water samples from deep tube wells by using the 16S rRNA gene sequences based culture-independent method. The analysis showed that the groundwater has been contaminated with various types of opportunistic microbes in addition to fecal microbes. Particularly, the clonal sequences related to the opportunistic microbes within the genus Acinetobacter were detected in all samples. As many strains of Acinetobacter are known as multi-drug resistant microbes that are currently spreading in the world, we conducted a molecular-based survey for detection of the gene encoding carbapenem-hydrolysing ß-lactamase (bla(oxa-23-like) gene), which is a key enzyme responsible for multi-drug resistance, in the groundwater samples. Nested polymerase chain reaction (PCR) using two specific primer sets for amplifying bla(oxa-23-like) gene indicated that two of six groundwater samples contain multi-drug resistant Acinetobacter.

Development of an attached growth reactor for NH4-N removal at a drinking water supply system in Kathmandu Valley, Nepal.

Higher concentrations of ammonium (NH(4)-N) and iron (Fe) than a standard for drinking are typical characteristics of groundwater in the study area. To remove NH(4)-N and Fe, the drinking water supply system in this study consists of a series of treatment units (i.e., aeration and sedimentation, filtration, and chlorination); however, NH(4)-N in treated water is higher than a standard for drinking (i.e., <1.5 mg NH(4)-N/L). The objective of this study, therefore, is to develop an attached growth system containing a fiber carrier for reducing NH(4)-N concentration within a safe level in the treated water. To avoid the need of air supply for nitrification, groundwater was continuously dripped through the reactor. It made the system simple operation and energy efficient. Effects of reactor design (reactor length and carrier area) were studied to achieve a high NH(4)-N removal efficiency. In accordance with raw groundwater characteristics in the area, effects of low inorganic carbon (IC) and phosphate (PO(4)-P) and high Fe on the removal efficiency were also investigated. The results showed a significant increase in NH(4)-N removal efficiency with reactor length and carrier area. A low IC and PO(4)-P had no effect on NH(4)-N removal, whereas a high Fe decreased the efficiency significantly. The first 550 days operation of a pilot-scale reactor installed in the drinking water supply system showed a gradual increase in the efficiency, reaching to 95-100%, and stability in the performance even with increased flow rate from 210 to 860 L/day. The high efficiency of the present work was indicated because only less than 1 mg of NH(4)-N/L was left over in the treated water.

Distribution and Community Composition of Anammox Bacteria in Shallow Groundwater of the Kathmandu Valley, Nepal.

The abundance and diversity of anaerobic ammonium oxidation (anammox) bacteria were assessed in 152 groundwater samples in the Kathmandu Valley, Nepal. Anammox bacterial 16S rRNA genes were detected in 54% (37/68) of samples collected in the dry season at 1.6×105-8.8×106 copies L-1, and in 60% (50/84) of samples collected in the wet season at 4.3×104-1.2×107 copies L-1. The 16S rRNA genes of "Candidatus Brocadia", "Candidatus Anammoxoglobus", and five new deduced anammox bacterial phylotypes were detected in the shallow groundwater samples. Diverse anammox bacteria were broadly distributed in the shallow groundwater aquifer of the Kathmandu Valley.

Effects of nitrite inhibition on anaerobic ammonium oxidation.

In order to assess the stability of nitrogen removal systems utilizing anaerobic ammonium oxidation (anammox), it is necessary to study the toxic effects of nitrite on these biochemical reactions. In this study, the effects of nitrite on anammox bacteria entrapped in gel carriers were investigated using batch and continuous feeding tests. The results showed that the nitrite concentration in a reactor must be less than 274-mg N/L in order to prevent a decrease in the anammox activity, which occurred when the gel carriers were soaked in nitrite solutions with concentrations greater than 274-mg N/L in a batch test. In a continuous feeding test, nitrite inhibition was not observed at low concentrations of nitrite. However, the anammox activity decreased to 10% when the nitrite concentration increased to 750-mg N/L over a 7-day period in the reactor. In addition, it was shown that the effects of nitrogen on the anammox reaction were reversible because the anammox activity completely recovered within 3 days when the influent nitrite concentration was decreased to less than 274-mg N/L.

Presence and activity of anammox and denitrification process in low ammonium-fed bioreactors.

A combination of anammox and denitrification process was studied for 300 days in low ammonium-fed bioreactors under the support of organic carbon. Nutrient profiles, (15)N-labelling techniques and qualitative fluorescence in situ hybridization (FISH) probes were used to confirm the nitrogen removal pathways and intercompetition among different bacteria populations. About 80% of nitrogen removal was achieved throughout the study period. The results confirmed that anammox bacteria were absent in the bioreactor inoculated with anaerobic granules only but they were present and active in the central anoxic parts of biopellets in the bioreactor inoculated with mixed microbial consortium from activated sludge and anaerobic granules. It also showed that the anammox bacteria were successfully enriched in the low ammonium-fed bioreactors. Results of this study clearly demonstrated that anammox and denitrification processes could coexist in same environment and anammox bacteria were less competitive than denitrifying bacteria.

Ferrates (iron(VI) and iron(V)): environmentally friendly oxidants and disinfectants.

Iron(VI) and iron(v), known as ferrates, are powerful oxidants and their reactions with pollutants are typically fast with the formation of non-toxic by-products. Oxidations performed by Fe(VI) and Fe(V) show pH dependence; faster rates are observed at lower pH. Fe(VI) shows excellent disinfectant properties and can inactivate a wide variety of microorganisms at low Fe(VI) doses. Fe(VI) also possesses efficient coagulation properties and enhanced coagulation can also be achieved using Fe(VI) as a preoxidant. The reactivity of Fe(V) with pollutants is approximately 3-5 orders of magnitude faster than that of Fe(VI). Fe(V) can thus be used to oxidize pollutants and inactivate microorganisms that have resistance to Fe(VI). The final product of Fe(VI) and Fe(V) reduction is Fe(III), a non-toxic compound. Moreover, treatments by Fe(VI) do not give any mutagenic/carcinogenic by-products, which make ferrates environmentally friendly ions. This paper reviews the potential role of iron(VI) and iron(V) as oxidants and disinfectants in water and wastewater treatment processes. Examples are given to demonstrate the multifunctional properties of ferrates to purify water and wastewater.

Effects of inorganic carbon limitation on anaerobic ammonium oxidation (anammox) activity.

Anammox bacteria are chemoautotrophic bacteria that oxidize ammonium with nitrite as the electron acceptor and with CO(2) as the main carbon source. The effects of inorganic carbon (IC) limitation on anammox bacteria were investigated using continuous feeding tests. In this study, a gel carrier with entrapped anammox sludge was used. It was clearly shown that the anammox activity deteriorated with a decrease in the influent IC concentration. The relationship between the influent IC concentration and the anammox activity was analyzed using Michaelis-Menten kinetics, and the apparent K(m) was determined to be 1.2mg-C/L. The activity could be recovered by adding IC to the influent. The consumption ratio of IC to ammonium was not constant and mainly depended on the influent ratio of the IC to ammonium concentrations (inf.IC/inf.NH(4)-N). The results indicated that an inf.IC/inf.NH(4)-N ratio of 0.2 in the anammox reactor was ideal for the anammox process using gel cubes.

Long-term dynamics of freshwater red tide in shallow lake in central Japan.

OBJECTIVE: The aim of this study is to clarify the long-term dynamics of the red tide occurring in Lake Kawaguchi. METHODS: The measurement of environmental factors and water sampling were carried out monthly at a fixed station in Lake Kawaguchi's center basin from April 1993 to March 2004. On June 26, 1995, the horizontal distribution ofPeridinium bipes was investigated using a plastic pipe, obtaining 0∼1-m layers of water column samples at 68 locations across the entire lake. RESULTS: P. bipes showed an explosive growth and formed a freshwater red tide in the early summer of 1995, when the nutrient level was higher than those in the other years, particularly the phosphate concentration in the surface layer. The dissolved total phosphorus (DTP) concentration was sufficient forP. bipes growth in that year. In the study of its horizontal distribution,P. bipes was found at all the locations. The numbers of cells per milliliter ranged from 67 to 5360, averaging 1094±987 cells/ml, with particularly high densities along the northern shore. Since then,P. bipes has annually averaged about 25 cells/ml in Lake Kawaguchi. CONCLUSION: We observed that the red tide caused byP. bipes correlates with a high DTP concentration in Lake Kawaguchi.

Quantification of anammox populations enriched in an immobilized microbial consortium with low levels of ammonium nitrogen and at low temperature.

Anaerobic ammonium oxidizing (anammox) bacteria present in microbial communities in two laboratory-scale upflow anoxic reactors supplied with small amounts of ammonium (<3 mg/l) at low temperature were detected and quantified. The reactors, operated at 20 degrees C, were seeded with an immobilized microbial consortium (IMC) and anaerobic granules (AG) from an upflow anaerobic sludge blanket (UASB) treating brewery wastewater. Our results showed that complete ammonium and nitrite removal with greater than 92% total nitrogen removal efficiency was achieved in the reactor inoculated with both the IMC and AG, while that of the reactor inoculated with only the IMC was lower than 40%; enrichment was successful after the addition of AG. Quantitative fluorescence in situ hybridization (FISH) analysis confirmed that anammox bacteria were present only in the reactor inoculated with an IMC and AG. The copy number of the 16S-rRNA gene of the anammox bacteria calculated by most probable number-polymerase chain reaction (MPN-PCR) from the total DNA extracted from both reactors (2.5 x 10(4) copies/mug of DNA) was two orders lower than that of the domain bacteria (2.5 x 10(6) copies/mug of DNA). The results revealed that immobilized multiple seed sludges were optimal for anammox enrichment at low temperature and ammonium concentrations.