New concepts of microbial treatment processes for the nitrogen removal in wastewater

Stoichiometric and kinetic characterisation ofNitrobacter in mixed culture by decoupling the growth and energy generation processes

The growth, maintenance and lysis processes of Nitrobacter were characterised. A Nitrobacter culture was enriched in a sequencing batch reactor (SBR). Fluorescent in situ hybridisation showed that Nitrobacter constituted 73% of the bacterial population. Batch tests were carried out to measure the oxygen uptake rate and/or nitrite consumption rate when both nitrite and CO2 were in excess, and in the absence of either of these two substrates. The results obtained, along with the SBR performance data, allowed the determination of the maintenance coefficient and in situ cell lysis rate of Nitrobacter. Nitrobacter spends a significant amount of energy for maintenance, which varies considerably with the specific growth rate. At maximum growth, Nitrobacter consume nitrite at a rate of 0.042 mgN/mgCOD(biomass) . h for maintenance purposes, which increases more than threefold to 0.143 mgN/mgCOD(biomass) . h in the absence of growth. In the SBR, where Nitrobacter grew at 40% of its maximum growth rate, a maintenance coefficient of 0.113 mgN/mgCOD . h was found, resulting in 42% of the total amount of nitrite being consumed for maintenance. The above three maintenance coefficient values obtained at different growth rates appear to support the maintenance model proposed in Pirt (1982). The in situ lysis rate of Nitrobacter was determined to be 0.07/day under aerobic conditions at 22 degrees C and pH 7.3. Further, the maximum specific growth rate of Nitrobacter was estimated to be 0.02/h (0.48/day). The affinity constant of Nitrobacter with respect to nitrite was determined to be 1.50 mgNO2(-)-N/L, independent of the presence or absence of CO2.

Phytoremediation of landfill leachate

Leachate emissions from landfill sites are of concern, primarily due to their toxic impact when released unchecked into the environment, and the potential for landfill sites to generate leachate for many hundreds of years following closure. Consequently, economically and environmentally sustainable disposal options are a priority in waste management. One potential option is the use of soil-plant based remediation schemes. In many cases, using either trees (including short rotation coppice) or grassland, phytoremediation of leachate has been successful. However, there are a significant number of examples where phytoremediation has failed. Typically, this failure can be ascribed to excessive leachate application and poor management due to a fundamental lack of understanding of the plant-soil system. On balance, with careful management, phytoremediation can be viewed as a sustainable, cost effective and environmentally sound option which is capable of treating 250m(3)ha(-1)yr(-1). However, these schemes have a requirement for large land areas and must be capable of responding to changes in leachate quality and quantity, problems of scheme establishment and maintenance, continual environmental monitoring and seasonal patterns of plant growth. Although the fundamental underpinning science is well understood, further work is required to create long-term predictive remediation models, full environmental impact assessments, a complete life-cycle analysis and economic analyses for a wide range of landfill scenarios.

Wind-driven surficial oxygen transfer and dinitrogen gas emission from treatment lagoons

Surficial oxygen transfer plays an important role, when analyzing the complex biochemical and physical processes responsible for ammonia and dinitrogen gas emission in animal waste treatment lagoons. This paper analyzes if currently known nitrogen biochemical pathways can explain the enigmatic dinitrogen gas emissions recently observed from the treatment lagoons, based on the amount of wind-driven oxygen that can be transferred through the air-water interface. The stoichiometric amounts of the maximum dinitrogen gas production potential per unit mass of O(2) transferred were calculated according to three most likely biochemical pathways for ammonia removal in the treatment lagoons-classical nitrification-denitrification, partial nitrification-denitrification, and partial nitrification-Anammox. Partial nitrification-Anammox pathway would produce the largest N(2) emission, followed by partial nitrification-denitrification pathway, then by classical nitrification-denitrification pathway. In order to estimate stoichiometric amount (i.e., maximum) of N(2) emission from these pathways, we assumed that heterotrophic respiration was substantially inhibited due to high levels of free ammonia prevalent in treatment lagoons. Most observed N(2) emission data were below the maximum N(2) emission potentials by the classical nitrification-denitrification pathway. However, one value of observed N(2) emission was much higher than that could be produced by even the partial nitrification-Anammox pathway. This finding suggests yet unknown biological processes and/or non-biological nitrogen processes such as chemodenitrification may also be important in these treatment lagoons.

Correlation between anammox activity and microscale distribution of nitrite in a subtropical mangrove sediment

The distribution of anaerobic ammonium oxidation (anammox) in nature has been addressed by only a few environmental studies, and our understanding of how anammox bacteria compete for substrates in natural environments is therefore limited. In this study, we measure the potential anammox rates in sediment from four locations in a subtropical tidal river system. Porewater profiles of NO(x)(-) (NO2- plus NO3-) and NO2- were measured with microscale biosensors, and the availability of NO2- was compared with the potential for anammox activity. The potential rate of anammox increased with increasing distance from the mouth of the river and correlated strongly with the production of nitrite in the sediment and with the average concentration or total pool of nitrite in the suboxic sediment layer. Nitrite accumulated both from nitrification and from NO(x)(-) reduction, though NO(x)(-) reduction was shown to have the greatest impact on the availability of nitrite in the suboxic sediment layer. This finding suggests that denitrification, though using NO2- as a substrate, also provides a substrate for the anammox process, which has been suggested in previous studies where microscale NO2- profiles were not measured.

Aerobic nitrification-denitrification by heterotrophic Bacillus strains

Twenty-four Bacillus strains predominantly outgrown in a night soil treatment system were isolated and characterized. Under various culture conditions, cell interactions took place among them and cell population changed. Maximum removal of NH4+-N and cell production by the isolates occurred under the conditions of 30% DO and C/N ratio of 8. Five dominant isolates were identified to be species of Bacillus cereus, Bacillus subtilis and Bacillus licheniformis with similarities of 78-94%. Additions of 0.8% peptone and 0.3% yeast extract to a basal medium influenced the growth of isolates and the removal of NH4+-N in flask culture. Metal ions such as Ca2+, Fe2+ and Mg2+ had a similar effect. The specific growth rates of the five isolates were found to be in a range of 0.43-0.55 h(-1). During the flask experiment of nitrogen removal under aerobic growth conditions, active nitrification by the isolates occurred largely in 1h with a decrease of COD and alkalinity reduced to only 74.6% of theoretical value. From the nitrogen balance, the percentage of nitrogen lost in the flask culture was estimated to be 33.0%, which was presumed to convert to N2 gas. This conversion of ammonia to N2 without formation of nitrous oxide under aerobic growth conditions was confirmed by GC analysis. From all the results, it has been found that the Bacillus strains were able to occur simultaneously aerobic nitrification/denitrification and the B3 process using the Bacillus strains seemed to possess some economic advantages.

The influence of operational conditions in sequencing batch reactors on removal of nitrogen and organics from municipal landfill leachate

The removal of nitrogen and organics from municipal landfill leachate in sequencing batch reactors (SBR) was investigated in the present study. The influence of hydraulic retention time (HRT), sludge age, manner of leachate dosage (short filling period of SBR and filling during the reaction period), and operational conditions with and without a mixing phase in the SBR cycle was explored. Four series were performed. In each series, the HRT used in the four SBRs was 12, 6, 3 and 2 days, respectively. Series 1 and 2 were characterized by a short leachate filling period, whereas series 3 and 4 were characterized by filling during the 4 h duration of the reaction in the SBR cycle. In series 1-3 SBR reactors worked with mixing and aeration phases, whereas in series 4 they worked only with an aeration phase. The effectiveness of the removal of organics increased with the extension of the HRT of leachate, particularly under operational conditions with the mixing and aeration phases in the SBR cycle. At 12 days HRT, the SBRs with the mixing and aeration phases in the cycle (series 1-3) showed better results than those with only an aeration phase (series 4). However, at 2 days HRT the operational conditions in SBR reactors with leachate filling over the reaction period (series 3 and 4) were more suitable. The highest efficiency of ammonium removal was obtained in series 1 with a short leachate filling period. In this series, at an HRT of 3-12 days, the ammonium concentration in the effluent did not exceed 1 mg NNH4 L(-1). Nitrogen removal proceeded mainly in the aeration phase as a result of ammonium losses and, to a lesser extent, dissimilative nitrate reduction over the mixing phase. The highest percentage of nitrogen removal as a result of ammonium losses was observed in series with a short filling period and long sludge age (series 1) and also in series without a mixing phase and filling over the aeration phase (series 4), whereas the highest nitrogen consumption for biomass production occurred in series 3 with filling during the reaction period and mixing phase of the cycle.

Competition and coexistence of aerobic ammonium- and nitrite-oxidizing bacteria at low oxygen concentrations

In natural and man-made ecosystems nitrifying bacteria experience frequent exposure to oxygen-limited conditions and thus have to compete for oxygen. In several reactor systems (retentostat, chemostat and sequencing batch reactors) it was possible to establish co-cultures of aerobic ammonium- and nitrite-oxidizing bacteria at very low oxygen concentrations (2-8 microM) provided that ammonium was the limiting N compound. When ammonia was in excess of oxygen, the nitrite-oxidizing bacteria were washed out of the reactors, and ammonium was converted to mainly nitrite, nitric oxide and nitrous oxide by Nitrosomonas-related bacteria. The situation could be rapidly reversed by adjusting the oxygen to ammonium ratio in the reactor. In batch and continuous tests, no inhibitory effect of ammonium, nitric oxide or nitrous oxide on nitrite-oxidizing bacteria could be detected in our studies. The recently developed oxygen microsensors may be helpful to determine the kinetic parameters of the nitrifying bacteria, which are needed to make predictive kinetic models of their competition.

Characteristics of ammonium removal by heterotrophic nitrification-aerobic denitrification by Alcaligenes faecalis No. 4

Alcaligenes faecalis no. 4 has heterotrophic nitrification and aerobic denitrification abilities. By taking the nitrogen balance under different culture conditions, 40-50% of removed NH4+-N was denitrified and about one-half of removed NH4+-N was converted to intracellular nitrogen. The maximum ammonium removal rate of no. 4 (28.9 mg-N/l/h) and its denitrification rate at high-strength NH4+-N of about 1200 ppm in aerated batch experiments at a C/N ratio of 10 were 5-40 times higher than those of other bacteria with the same ability. Only a few percent of the removed ammonium was converted to nitrite, and the main denitrification process was speculated to be via hydroxylamine which was produced by ammonium oxidation.

Biphasic behavior of anammox regulated by nitrite and nitrate in an estuarine sediment

The production of N2 gas via anammox was investigated in sediment slurries at in situ NO2- concentrations in the presence and absence of NO3-. With single enrichment above 10 microM 14NO2- or 14NO3- and 15NH4+, anammox activity was always linear (P < 0.05), in agreement with previous findings. In contrast, anammox exhibited a range of activity below 10 microM NO2- or NO3-, including an elevated response at lower concentrations. With 100 microM NO3-, no significant transient accumulation of NO2- could be measured, and the starting concentration of NO2- could therefore be regulated. With dual enrichment (1 to 20 microM NO2- plus 100 microM NO3-), there was a pronounced nonlinear response in anammox activity. Maximal activity occurred between 2 and 5 microM NO2-, but the amplitude of this peak varied across the study (November 2003 to June 2004). Anammox accounted for as much as 82% of the NO2- added at 1 microM in November 2003 but only for 15% in May 2004 and for 26 and 5% of the NO2- added at 5 microM for these two months, respectively. Decreasing the concentration of NO3- but holding NO2- at 5 microM decreased the significance of anammox as a sink for NO2-. The behavior of anammox was explored by use of a simple anammox-denitrification model, and the concept of a biphasic system for anammox in estuarine sediments is proposed. Overall, anammox is likely to be regulated by the availability of NO3- and NO2- and the relative size or activity of the anammox population.

Bacterium-based NO2- biosensor for environmental applications

A sensitive NO2- biosensor that is based on bacterial reduction of NO2- to N2O and subsequent detection of the N2O by a built-in electrochemical N2O sensor was developed. Four different denitrifying organisms lacking NO3- reductase activity were assessed for use in the biosensor. The relevant physiological aspects examined included denitrifying characteristics, growth rate, NO2- tolerance, and temperature and salinity effects on the growth rate. Two organisms were successfully used in the biosensor. The preferred organism was Stenotrophomonas nitritireducens, which is an organism with a denitrifying pathway deficient in both NO3- and N2O reductases. Alternatively Alcaligenes faecalis could be used when acetylene was added to inhibit its N2O reductase. The macroscale biosensors constructed exhibited a linear NO2- response at concentrations up to 1 to 2 mM. The detection limit was around 1 microM NO2-, and the 90% response time was 0.5 to 3 min. The sensor signal was specific for NO2-, and interference was observed only with NH2OH, NO, N2O, and H2S. The sensor signal was affected by changes in temperature and salinity, and calibration had to be performed in a system with a temperature and an ionic strength comparable to those of the medium analyzed. A broad range of water bodies could be analyzed with the biosensor, including freshwater systems, marine systems, and oxic-anoxic wastewaters. The NO2- biosensor was successfully used for long-term online monitoring in wastewater. Microscale versions of the NO2- biosensor were constructed and used to measure NO2- profiles in marine sediment.

Propionate oxidation by and methanol inhibition of anaerobic ammonium-oxidizing bacteria

Anaerobic ammonium oxidation (anammox) is a recently discovered microbial pathway and a cost-effective way to remove ammonium from wastewater. Anammox bacteria have been described as obligate chemolithoautotrophs. However, many chemolithoautotrophs (i.e., nitrifiers) can use organic compounds as a supplementary carbon source. In this study, the effect of organic compounds on anammox bacteria was investigated. It was shown that alcohols inhibited anammox bacteria, while organic acids were converted by them. Methanol was the most potent inhibitor, leading to complete and irreversible loss of activity at concentrations as low as 0.5 mM. Of the organic acids acetate and propionate, propionate was consumed at a higher rate (0.8 nmol min(-1) mg of protein(-1)) by Percoll-purified anammox cells. Glucose, formate, and alanine had no effect on the anammox process. It was shown that propionate was oxidized mainly to CO(2), with nitrate and/or nitrite as the electron acceptor. The anammox bacteria carried out propionate oxidation simultaneously with anaerobic ammonium oxidation. In an anammox enrichment culture fed with propionate for 150 days, the relative amounts of anammox cells and denitrifiers did not change significantly over time, indicating that anammox bacteria could compete successfully with heterotrophic denitrifiers for propionate. In conclusion, this study shows that anammox bacteria have a more versatile metabolism than previously assumed.