Principal component analysis for interaction of nitrifiers and wastewater environments at a full-scale activated sludge plant

This study investigated the relationship between wastewater environments and the nitrifiers at a full-scale plant using principal component analysis. Ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were detected by florescent in situ hybridization, polymerase chain reaction, phylogenetic analysis, real-time quantitative polymerase chain reaction. Pyrosequencing was also used in profiling the ammonia monooxygenase locus of ammonia-oxidizing bacteria community. It was found that the dominant ammonia-oxidizing bacteria sequences were related to uncultured ammonia-oxidizing bacterium, uncultured Nitrosomonadaceae bacterium, Nitrosomonas sp., and uncultured bacterium. In addition, Nitrobacter clones were related to uncultured alpha proteobacterium, uncultured bacterium, uncultured Nitrobacter sp., and uncultured Bradyrhizobium sp., whereas Nitrospira clones were similar to uncultured bacterium, Candidatus Nitrospira defluvii, uncultured Nitrospira sp., and uncultured Nitrospirae bacterium. The ammonia-oxidizing bacteria and nitrite-oxidizing bacteria ranged 2.83 × 10⁸–1.33 × 10¹⁰ and 1.25 × 10¹⁰–1.13 × 10¹¹ copies L^?1, respectively, equivalent to nitrite-oxidizing bacteria: ammonia-oxidizing bacteria ratio of 10:1. The first three parts of the principal components analysis accounted for 76.8% of the explained variance. The first principal component (44.4%) designated that ammonia-oxidizing bacteria and Nitrospira were mainly influenced by seasonal variations, followed by chemical oxygen demand concentration and nitrogen species (i.e., ammonia, nitrite, and nitrate). The second principal component (19.1%) showed no information about the nitrifiers’ interaction with environmental factors, whereas Nitrobacter demonstrated a high correlation with ammonia on the third principal component (13.3%). These results revealed that the species of Nitrobacter were less influenced by environmental conditions than ammonia-oxidizing bacteria and Nitrospira spp.     

Dynamics of ammonia-oxidizing archaea and bacteria in relation to nitrification along simulated dissolved oxygen gradient in sediment–water interface of the Jiulong river estuarine wetland,China

Dissolved oxygen (DO) is a very important factor controlling the nitrogen cycle in wetlands. However, it is still unclear to what extent the presence of ammonia-oxidizing archaea (AOA) and bacteria (AOB), and related nitrification, are influenced by DO in estuarine wetlands. The aims of this study were to determine changes of nitrification at the sediment–water interface, to examine the abundance and diversity of archaeal and bacterial ammonia oxidizers in estuarine sediments, and to identify the correlation between nitrification and ammonia-oxidizing microorganisms along a simulated dissolved oxygen gradient in a Chinese estuarine wetland. The results showed that the nitrification rate was positively correlated with the diversity and abundance of AOA but not AOB, and the abundance and diversity of AOA can explain 87 % of the total variance of the first axes in the redundancy analysis. This indicates that AOA were primarily involved in ammonia oxidation in this study. Additionally, AOB were much more influenced by DO than AOA inferred from the assessment of dominant species and principal coordinates analysis of AOA and AOB. Higher diversity and abundance of AOA occurred in the mangrove sediments, which explain the higher nitrification rates in the mangrove sediments compared to the bare mudflat sediments. Notably, the trend of nitrification rate in the bare mudflat sediments was different from that in the mangrove sediments, suggesting that the extent of nitrification as impacted by DO depends largely on the sediment biotic and nutrient properties, and its environmental conditions including DO levels.     

Microbial community analysis for aerobic granular sludge reactor treating high-level 4-chloroaniline wastewater

A laboratory-scale sequencing airlift bioreactor continuously treating high-level 4-chloroaniline (4-ClA) wastewater was used for studying the effect of 4-ClA on the characteristics and microbial community of aerobic granular sludge. The granulation of aerobic sludge and efficient pollutant removal performance were developed via shortening sludge settling time and gradually increasing influent 4-ClA concentration to around 400 mg L^?1. However, the granular sludge reactor deteriorated with the 4-ClA loading rate above 0.8 kg m^?3 d^?1. Denaturing gradient gel electrophoresis and real-time quantitative PCR were applied to investigate the microbial community succession during the start-up and recovery of bioreactor. The results showed that the performance of granular reactor was significantly influenced by the microbial community of aerobic granule, and stable aerobic granule was dominated with β-Proteobacteria (61.28 %), Flavobacteriales, Planctomycetales, Clostridiales, and Acidobacteria. Since Thauera (21.55 %) related to the genus β-Proteobacteria was abundant in the stable 4-ClA-degrading granular sludge, it was speculated as the main 4-ClA-degrading bacteria. Under high chloroaniline level, the sludge granulation may maintain the stability of the bioreactor via adjusting the composition of microbial community and abundance of functional microorganism. This paper provided useful information for better understanding the change of microbial community characteristics under high-level toxic organic pollutants and process optimizing.     

Ameliorating nitrite inhibition in a low-temperature nitritation–anammox MBBR using bacterial intermediate nitric oxide

The long-term sustainability of an anaerobic ammonium oxidation (anammox) process in a moving bed biofilm reactor (MBBR) treating highly concentrated (mean of 740 mg NH₄ ⁺-N L^?1) wastewater was demonstrated by 1600 days of efficient operation. A high maximum total nitrogen removal rate (TNRR) of 1.5 g N m^?2 d^?1 was achieved at the low temperature of 20 °C. For nitrogen removal recovery in cases of nitrite inhibition, anammox intermediate nitric oxide (NO) was tested in batch experiments as an N-removal accelerating agent. The effect of the addition of various NO dosages (8–72 mg NO-N L^?1) was studied under inhibitory nitrite concentrations (>100 mg NO₂ ^?-N L^?1) for anammox bacteria. Optimal maintained NO concentration was 58 mg NO-N L^?1 and brought about the highest biofilm-specific anammox activity (SAA). Compared to a blank test, the minimum concentration of added NO of 40 mg NO-N L^?1 showed a statistically significant (p < 0.05) accelerating effect on SAA. No inhibition of SAA by NO was observed, although at NO concentrations exceeding 72 mg NO-N L^?1, the acceleratory effect upon SAA was decreased by 8%. Changes in the bacterial consortia involved in nitrogen conversion were determined concurrently for the different nitrogen removal rates and operational conditions. Quantities of Planctomycetales clone P4 strains, which are the closest (99% similarity) relative to Candidatus Brocadia fulgida, increased from 1 × 10³ to 1 × 10⁶ anammox gene copies per g total suspended solids during reactor operation days 568–1600, which was determined by quantitative polymerase chain reaction. During the operation of the MBBR, the abundance of ammonium-oxidizing bacteria (AOB) increased proportionally (up to 30%). The abundance of nitrite-oxidizing bacteria (NOB) did not increase (remaining below 10%) during days 232–860. AOB became predominant over NOBs owing to the inhibition of free ammonia spiking on NOBs.     

Effect of extracellular polymeric substances on sludge reduction potential of Bacillus licheniformis

The disposal of wastewater sludge generated during the treatment of the various municipal and industrial wastewaters is a major environmental problem. In this study the thermophilic bacterium Bacillus licheniformis, which enhances the efficiency of sludge reduction, was isolated from waste activated sludge acclimated to 55 °C. The resulting suspended solids’ degradation was 12 % and chemical oxygen demand solubilization was 18 %. To further enhance the sludge reduction potential, extra polymeric substances, which play a major role in the formation of flocs, were removed. A chemical extractant, ethylenediaminetetraacetate that is also a cation binding agent, was used to remove the extra polymeric substances. After the removal of extra polymeric substances, the suspended solids’ degradation increased from 12 to 23 % and the chemical oxygen demand solubilization increased from 18 to 25 %. These observations confirm that Bacillus licheniformis enhanced sludge reduction in non-flocculated sludge (with the removal of extra polymeric substances) as compared to flocculated sludge (without the removal of extra polymeric substances).     

吗啉废水的生化处理工艺

以含有吗啉、甲基吗啉的高浓度有机废水为研究对象,提出了曝气吹脱-吸附-生物处理的联合工艺,并在室内进行了小试实验。结果表明：原废水经过2次曝气吹脱后,ρ(NH₃-N)从62 500 mg/L降为431 mg/L,ρ(COD)从50 840 mg/L降为26 051 mg/L。通过吸附实验,ρ(COD)从26 051 mg/L降为2 769 mg/L,ρ(NH₃-N)从412 mg/L降为134 mg/L。在生物处理室内小试实验中,采用了活性污泥反应器与曝气生物滤池相结合的处理工艺。在活性污泥反应系统中,当废水pH为7.5、ρ(DO)为4.3 mg/L、水力停留时间为30 h时,COD的去除率最高,可以达到83.1%。在曝气生物滤池中,当ρ(DO)为3.3 mg/L时,COD去除率最高,达到55.8%。在生物处理的最佳参数条件下进行连续监测,当进水ρ(COD)为2 769 mg/L、出水ρ(COD)平均值为387 mg/L时,COD去除率可达到85.9%。吗啉废水经过此联合工艺的处理,ρ(COD)从50 840 mg/L降为387 mg/L。     

<Emphasis Type="Italic">Inoculum</Emphasis>-free start-up of biofilm- and sludge-based deammonification systems in pilot scale

Undiluted reject water from the dewatering of anaerobic sludge with an average total nitrogen content of 718 ± 117 mg L^?1 (n = 63) was used to start-up autotrophic nitrogen removal in three different pilot-scale (3 m³) deammonification configurations: (1) biofilm; (2) activated sludge sequence batch; and (3) two-staged (nitritation–anammox). Time- and concentration-based aeration control with alternating aerobic/anaerobic phases was applied for all reactor configurations. All reactors were initiated without anammox-specific inoculum, and biofilm was grown onto blank carriers. During the initial start-up period, biological nitrogen removal was found to be inhibited by an excessive free ammonia content (>10 mg-N L^?1), resulting from the use of high-strength reject water as the process feed. After implementation of free ammonia control by pH adjustment to 6.5–7.5, propagation of the deammonification process was observed with increased nitrogen removal with slight accumulation of NO₃ ^?–N. The highest total nitrogen removal rates were achieved with the single-reactor biofilm- and sludge-based deammonification processes (1.04 and 0.30 kg-N m^?3 day^?1, respectively). The critical factors for successful start-up and stable operation of deammonification reactors turned out to be control of pH below 7.5, dissolved oxygen at 0.3–0.8 mg-O₂ L^?1 and influent solids values below 1000 nephelometric turbidity units. Microbial analysis demonstrated that highest anammox enrichment was achieved in the biofilm reactor (9.40 × 10⁸ copies g^?1 total suspended solids). These data demonstrate the potential of an in-situ grown sludge- or biofilm-based concept for the development and propagation of deammonification process.     

On-site treatment of textile yarn dyeing effluents using an integrated biological–chemical oxidation process

This paper reports the results of the treatment of a yarn dyeing effluent using an integrated biological–chemical oxidation process. In particular, the biological unit was based on a sequencing batch biofilter granular sludge reactor (SBBGR), while the chemical treatment consisted of an ozonation step. Biological treatment alone was first performed as a reference for comparison. While biological treatment did not produce an effluent for direct discharge, the integrated process assured good treatment results, with satisfactory removal of chemical oxygen demand (up to 89.8 %), total nitrogen (up to 88.2 %), surfactants (up to 90.7 %) and colour (up to 99 %), with an ozone dose of 110 mg of ozone per litre of wastewater. Biomass characterization by fluorescence in situ hybridization has revealed that filamentous bacteria represented about 20 % of biomass (coherently with high sludge volume index values); thanks to its special design, SBBGR guaranteed, however, stable treatment performances and low effluent suspended solids concentrations, while conventional activated sludge systems suffer from sludge bulking and even treatment failure in such a condition. Furthermore, biomass characterization has evidenced the presence of a shortcut nitrification–denitrification process.     

Mechanism of efficient nutrient removal and microbial analysis of a combined anaerobic baffled reactor–membrane bioreactor process

A combined ABR–MBR process consisting of an anaerobic baffled reactor (ABR) combined with an aerobic membrane bioreactor (MBR) treating municipal wastewater was investigated at controlled pH range 6.5–8.5 and at constant temperature 25 ± 1 °C. Total nitrogen (TN), ammonia (NH₄ ⁺–N), total phosphorus (TP), and chemical oxygen demand (COD) removal performances were evaluated by analyzing the mechanism for efficient nutrient removal. The results showed that the average removal rates of COD, NH₄ ⁺–N, TN, and TP reached 93, 99, 79, and 92 %, respectively, corresponding with the COD, NH₄ ⁺–N, TN, and TP effluent of 24 (18–31), 0.4 (0–0.8), 10.6 (8.8–12.9), and 0.31 (0.1–0.5) mg/L under the operational condition of hydraulic retention time (HRT) 7.5 h, recycle ratio 200 %, and dissolved oxygen 3 mg/L. The MBR enhanced NH₄ ⁺–N, TN, and TP removal rates of 13, 10, and 18 %, respectively, and the membrane retention reduced TP 0.17 mg/L. The process was able to maintain a stable performance with high-quality effluent. Analysis of the results by fluorescence in situ hybridization showed that the abundance of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and phosphorus accumulating organisms as percentages of all bacteria in each compartment was stable. The enriched microorganisms in the system appear to be the main drivers of the process efficient for nutrient removal.     

Effect of vegetation on the performance of horizontal subsurface flow constructed wetlands with lightweight expanded clay aggregates

This research evaluates the effect of both organic and ammonia loading rates and the presence of plants on the removal of chemical oxygen demand and ammonia nitrogen in horizontal subsurface flow constructed wetlands, 2 years after the start-up. Two sets of experiments were carried out in two mesocosms at different organic and ammonia loading rates (the loads were doubled); one without plants (control bed), the other colonized with Phragmites australis. Regardless of the organic loading rate, the organic mass removal rate was improved in the presence of plants (93.4 % higher for the lower loading rate, and 56 % higher for the higher loading rate). Similar results were observed for the ammonia mass removal rate (117 % higher for the lower loading rate, and 61.3 % higher for the higher loading rate). A significant linear relationship was observed between the organic loading rate and the respective removal rates in both beds for loads between 10 and 13 g m^?2 day^?1. The presence of plants markedly increase removal of organic matter and ammonia, as a result of the role of roots and rhizomes in providing oxygen for aerobic removal pathways, a higher surface area for the adhesion and development of biofilm and nitrogen uptake by roots.     

Enhanced control of activated sludge process using predetermined set-points

The performance of activated sludge process (ASP) is evaluated by the effluent quality which is determined by five different variables of the treated wastewater such as ammonia, total nitrogen, COD, BOD₅ and TSS. To keep these five variables within the limits as per environmental regulations, nitrate and nitrite concentration (S _NO) in the second anoxic reactor and the dissolved oxygen concentration (S _O) in the last aerobic reactor of the ASP should be maintained at prescribed levels. To do that, a closed-loop control configuration is required and proper set-points for these closed-loop control configurations are needed. In this paper, the optimal values of controller set-points are determined for nitrogen removal in the activated sludge process. Effluent quality limits have been considered to evaluate the optimal set-points for the Indian climatic conditions. Once the optimal set-points are determined, PI controllers are used to control S _NO in the second anoxic reactor and S _O in the last aerobic reactor of the ASP. Further, feed-forward control is incorporated to minimize the effect of disturbances, which enters along with the influent. No case studies of BSM1 model have been reported in the literature for the Indian wastewater. In this work, the dynamic simulation of an activated sludge process is performed using the data collected from the sewage treatment plant, located in India. The results of the simulation showed that feed-forward with PI control strategy, ASP can be efficiently controlled without any effluent violations, when compared to BSM1.     

Effects of sludge pretreatment on sludge reduction in a lab-scale anaerobic/anoxic/oxic system treating domestic wastewater

Excess sludge disposal is one of the serious challenges in biological wastewater treatment. Reduction of sludge production would be an ideal way to solve sludge-associated problems rather than the post-treatment of the sludge produced. In this study, a new wastewater treatment process combining anaerobic/anoxic/oxic system with thermochemical sludge pretreatment was tested in a laboratory scale experiment. In this study, the effects of the sludge pretreatment on the excess sludge production in anaerobic/anoxic/oxic were investigated. The system was operated in two Runs (1 and 2). In Run 1, the system was operated as a reference and in Run 2, a part of the mixed liquid was pretreated thermochemically and was returned to the bioreactor. The average solubilization efficiency of pretreated sludge was found to be about 35 % during the study period of 220 days. Sludge production rate in Run 2 was less than that in Run 1 by about 52 %. Total phosphorous was removed by enhanced biological phosphorous removal with the removal efficiency of 83–87 % and 81–83 % for Run 1 and Run 2, respectively. Total nitrogen removal in Run 2 (79–82 %) was slightly higher than that in Run 1 (68–75 %). The mixed liquor suspended solids/mixed liquor volatile suspended solids ratio was identical after both runs in the range 78–83 %. The effluent water qualities were not significantly affected when operated with thermochemical pretreatment at pH 11 and 60 °C for 3 h during 7 months. From the present study it is concluded that thermochemical sludge pretreatment of anaerobic/anoxic/oxic process plays an important role in reduction of sludge production.     

Spectrophotometric determination of hydroxylamine in biological wastewater treatment processes

Hydroxylamine, a very important intermediate in nitrification, has a direct relationship with the production of nitrous oxide in biological wastewater treatment processes. The spectrophotometric method taking ferric ammonium sulfate and 1, 10-phenanthroline as the oxidant and the chromogenic agent, respectively, was used to determine the concentration of hydroxylamine in biological wastewater treatment processes. The impacts of nitrite, nitrate, orthophosphate, calcium ion and trace elements on the method were examined. The results indicated that the spectrophotometric method can be used for the determination of hydroxylamine in biological wastewater treatment processes. The correlation was significant in the range of 0.02–1.00 mg N/L (y = 1.5078x ? 0.0132, R ² = 0.9991), and the range varied to 0.05–1.00 mg N/L when nitrite and orthophosphate presented. Nitrate, calcium ion and trace elements did not interfere with the determination of hydroxylamine nitrogen. When the concentrations of nitrite nitrogen in the samples were lower than 15.00 mg/L, nitrite had a minor interference on the method. The impacts of orthophosphate on the method were complex. When the concentrations of hydroxylamine nitrogen were higher than 0.10 mg/L, the interference of orthophosphate on the method can be ignored. However, when the concentrations of hydroxylamine nitrogen in the samples were lower than 0.10 mg/L, orthophosphate had significant impacts on the determination, and a numerical method proposed can eliminate the interference of orthophosphate. The spectrophotometric method can determine the concentration of hydroxylamine in biological wastewater treatment processes quickly and conveniently and was helpful to understand the function of NH₂OH in N₂O production in biological wastewater treatment processes.     

Illumina sequencing for the identification of filamentous bulking and foaming bacteria in industrial activated sludge plants

In this study, Illumina sequencing was used for the identification of bulking and foaming bacteria in industrial wastewater treatment plants. The reliable identification of bulking and foaming bacteria represents the first step in developing effective and specific control strategies to avoid disturbances in activated sludge systems. Illumina sequencing revealed 432 16S rRNA operational taxonomic units, representing phylotypes and including 21 bulking and foaming bacteria in the two investigated industrial wastewater treatment plants. Foaming represents the most severe problem in the cascade biology system. Up to 22.5% of all sequencing reads are bulking and foaming bacteria, including Chryseobacterium, Candidatus Microthrix parvicella and Gordonia sp. as the dominant bulking and foaming bacteria which are known for foam formation. Moreover, Illumina sequencing revealed an increase in Candidatus Microthrix parvicella and Gordonia sp. reads from activated sludge to foam and scum samples, indicating a preferred flotation and/or growth advantages in the foam and scum layers. Analyses of the taxonomic assignment and distribution showed that the phylum Actinobacteria is the most dominant phylum, underlining the key role of Actinobacteria in bulking and foaming. Multivariate data analysis was applied, revealing that the dominant bulking and foaming bacteria are positively correlated with the sludge age and influent flow and negatively correlated with the dissolved oxygen level and the temperature. In terms of developing a specific control strategy, the positive linear relationships to the fatty acid and surfactant sludge loadings are highlighted and the removal of lipid compounds from the wastewater influent could avoid an overgrowth of bulking and foaming bacteria.     

The effects of sea salts on the forms of nitrogen released from estuarine and freshwater sediments: Does ion pairing affect ammonium flux?

In sediments with oxidized surface layers, the percentage of mineralized nitrogen that is nitrified/denitrified, compared with that released directly as ammonium, appears to be affected by the presence of sea salts. In estuarine systems, a significant portion of the nitrogen is released as ammonium, whereas in freshwater systems, most of the mineralized nitrogen is often released from the sediments as nitrogen gas. We hypothesized that this discrepancy is caused by differential competition between physical diffusion and nitrification/denitrification in the two systems. The vertical migration (by Fickian diffusion) of ammonium out of the oxic layer may be hindered by cation exchange (or sorption) interactions with sediment particles to a greater extent in fresh water than in estuarine systems. The resulting relatively long residence time, and potentially high levels of particle-bound ammonium in the freshwater sediments, would favor nitrification as the major ammonium removal process. By contrast, ion pair formation of ammonium with seawater anions and blockage of sediment cation exchange sites with seawater cations may allow a sizable fraction of the ammonium to diffuse out of estuarine sediments before it is nitrified. A salt effect, consistent with this hypothesis, has been demonstrated in experimental systems by changing the ionic composition of water flowing above intact cores of freshwater and estuarine sediments. Steady-state ammonium release from Lake Michigan sediments was substantially enhanced in the presence of 30% seawater over that in the presence of lake water alone. Likewise, steady-state ammonium release, from Ochlockonee River and Bay sediments (Florida) and from Toms River and Barnegat Bay sediments (New Jersey), was usually higher in the presence of diluted synthetic seawater than it was in the presence of fresh water.     

Comparative performance evaluation of physicochemical treatment processes for simulated dairy wastewater

In the present study, the effectiveness of physicochemical treatment processes (coagulation and Fenton’s oxidation) was investigated for simulated dairy wastewater (pH = 7.3, chemical oxygen demand (COD) = 3600 mg/l, 5-day biochemical oxygen demand (BOD₅) = 1950 mg/l, total Kjeldahl nitrogen (TKN) = 87 mg/l, and total phosphorous (TP) = 14 mg/l). Plain and ballasted coagulation runs were carried out in a jar apparatus, while Fenton’s oxidation was performed in a three-neck glass reactor. Ballasted coagulation caused an enhancement in the settling rate of sludge though no significant enhancement in the removal of organics was observed. Individually, coagulation and Fenton’s oxidation processes resulted in ~67 and 80 % COD removals, respectively, from the wastewater. The sequential treatment exploring coagulation followed by Fenton’s oxidation showed overall COD, BOD₅, TKN, and TP reductions of ~93, 97, 84, and 70 %, respectively, from the wastewater. However, a biological post-treatment would be required to achieve the effluent discharge standards. The removal of proteins, fats, and amino acids from wastewater was confirmed from Fourier transform infrared analysis of the settled sludge (obtained after coagulation process). Preliminary cost analysis suggested coagulation and the sequential treatment (i.e. coagulation followed by Fenton’s oxidation) as the preferred options.     

Treatment of septic tank effluent using moving-bed biological reactor: kinetic and biofilm morphology

Septic tanks are very commonly used wastewater collection systems throughout the world, and especially in rural areas. In this study, the use of moving-bed biological reactors (MBBR) for the treatment of septic tank effluent (STE) was examined. The study was conducted in two phases. In Phase I, the performance of septic tanks from four projects working under different operational conditions and with different service lives was followed to determine the parameters that required further treatment. In Phase II, four specially designed continuous flow pilot-plant MBBRs and one laboratory-scale batch reactor were tested for their efficiency in treating STE. Experiments were carried out at various temperatures (8–25 °C) and with different hydraulic retention times (HRTs). MBBR effectively reduced STE’s nutrients and chemical oxygen demand by 90 and 85 %, respectively, over 180 days of operation. The average ammonia removal rate at 25 °C increased from 0.279 to 0.540 kg N/m³ when the reactor HRT changed from 5.7 to 13.3 h. Under these conditions, the ammonia removal kinetics were successfully correlated with a theta model with an average θ value of 1.054. The biofilm morphology showed a stable and global biomass coverage (>70 %) and a high percentage of live cells. A thinner biofilm was observed when the MBBR operated at high temperatures. The results of this study showed that MBBR is a promising technology for post-treatment of septic tank effluent.     

Activity,Abundance, and Diversity of Nitrifying Archaea and Denitrifying Bacteria in Sediments of a Subtropical Estuary: Bahía del Tóbari,Mexico

Fixed nitrogen (N) removal from estuaries via coupled nitrification–denitrification plays a significant role in the global N cycle and the biogeochemistry of individual estuaries. Much of our understanding of these processes is drawn from temperate estuaries, yet tropical and subtropical estuaries may respond differently to N inputs. I tested the hypothesis that nitrification is limited within subtropical estuaries by comparing nitrification and denitrification potentials, and the abundance of archaeal ammonia monooxygenase (amoA) and bacterial nitrite reductase (nirS) genes, across five sites in Bahía del Tóbari, Mexico. Sampling was conducted when agricultural runoff supplied substantial quantities of N (ca. 20–80 μM ammonium), yet nitrification was detected at a single site. Denitrification was measured at four sites, and three displayed nitrate uptake rather than net nitrification—indicating a N sink within these sediments. Bacterial nirS genes uniformly outnumbered archaeal amoA genes (3- to 49-fold) and were more abundant in the northern part of the estuary. Patterns of community similarity among different sites were also different for nirS and archaeal amoA: similarities between sites based on nirS were often greater than for amoA, and sites were more rarely statistically different from each other. While amoA abundance was inversely related to temperature, neither amoA nor nirS was correlated with nitrification or denitrification potentials. My results are broadly consistent with known and proposed patterns of nitrification and denitrification in subtropical estuarine sediments, including the idea that nitrification is limited within subtropical estuarine sediments.     

Correlation between nitrite accumulation and the concentration of AOB in a nitritation reactor

Nitritation is an innovative biological nitrogen removal method in wastewater, and it has the advantages of energy and economy. The correlation between a nitrite conversion rate and the gene copy numbers of ammonia oxidizing bacteria (AOB) in a nitritation reactor was examined to measure the effectiveness of removing a nitrogen content in a biological nitrogen removal process, using a biological process of nitritation. A laboratory scale reactor was prepared and operated for over a year, using digester supernatant to induce a stable nitritation, and to optimize the operational conditions by adjusting various operating factors. The relationship between operational results of nitritation reactor and the AOB gene copies was approximated through identification and quantitative analysis of AOB. A stable nitritation can be artificially led with the control of SRT, while treating anaerobic digester supernatant from MWTPs. And AOB gene copies showed a correlation with free ammonia (FA) inhibition and performance of nitritation, and AOB activity. Thus, AOB gene copies were found important when it comes to analyzing nitritation.     

Cytotoxic and genotoxic evaluation and chemical characterization of sewage treated using activated sludge and a floating emergent-macrophyte filter in a municipal wastewater treatment plant: a case study in Southern Brazil

This study was conducted to evaluate the chemical parameters and the cytotoxic and genotoxic potential of raw domestic sewage and effluents from treatment with activated sludge and a floating emergent-macrophyte filter from a domestic wastewater treatment plant in the city of Novo Hamburgo, Rio Grande do Sul, Brazil. The physicochemical analysis revealed that both treatment systems achieved the legal emission pattern for biochemical oxygen demand, chemical oxygen demand, and suspended solids, but ammoniacal nitrogen and E. coli values were above the limits in the macrophyte treatment effluent. Phosphorous values were above the maximum permitted for both treatments. The results obtained from the Allium cepa test and the micronuclei test in fish did not demonstrate any significant differences in both cytotoxicity (mitotic index) and genotoxicity (chromosome aberration and micronucleus) endpoints between the negative control group and the exposed groups. However, the comet assay in fish revealed a DNA damage increase in animals exposed to the 30 % concentration of the macrophyte effluent and two concentrations of the activated sludge treatment effluent (10 and 75 %), which suggests that these two treatment systems may increase wastewater genotoxicity.