Performance of single PN/A reactor under wide fluctuation of nitrogen load.

Partial nitritation-anammox (PN/A) is a cost-effective technology in high ammonia-nitrogen wastewater treatment. However, PN/A is prone to instability as the ammonia-nitrogen sharply fluctuates. In this study, a packed bed reactor is employed to construct a single-stage PN/A system to investigate the operational characteristics and explore the denitrification mechanism. The effluent NH4+-N concentration, ammonia nitrogen removal rate (ARE), and total nitrogen removal rate (TNR) could be sustained at about 60 mg/L, 80%, and over 70%, respectively, when the influent nitrogen load rate (NLR) is changed from 0.733 to 0.879 kg-N/m3/day. Both ARE and TNR are decreased when NLR continues increasing to 1.026 kg-N/m3/day. The influent NLR decreases from 0.879 to 0.147 kg-N/m3/day, and ARE and TNR reached 98% and 85.4%, respectively. Therefore, the denitrification effect of the reactor could be recovered, and the excellent nitrogen removal capacity could be obtained within a wide range of influent NLR. Moreover, the high-throughput sequencing and metagenomic testing indicate that the Proteobacteria and Planctomycetes that the PN/A functional strains (i.e., ammonia-oxidizing bacteria (AOB) and anammox bacteria (AnAOB)) account for 38.8% in the sludge. The relative abundance of Nitrospira containing the nitrite-oxidizing bacteria (NOB) has dropped to 0.01%, and the functional gene nxr of the nitrite oxidation process is also inhibited. The relative expression of the functional gene is dominated by the short-range nitritation and anammox oxidation, which demonstrates that the nitrogen removal is mainly dominated by nitritation-anammox.

Soil diazotrophs sustain nitrogen fixation under high nitrogen enrichment via adjustment of community composition.

Biological nitrogen (N) fixation, an important pathway of N, inputs from the atmosphere to Earth's ecosystems, is well demonstrated to decline under N input. However, it remains unclear why N fixers sustain N fixation in many forests under high atmospheric N deposition. To address this knowledge gap, we analyzed the response of the diazotroph community to low N loads (short-term and low N addition; 3-year N addition at the rates of 25-50 kg N ha-1 year-1) vs high loads (chronic and high N addition; 9-year N addition at the rate of 150 kg N ha-1 year-1) in forest soils using high-throughput sequencing. Rates of N fixation decreased under low and high N loads (by 13%-27% and 10%-12%, respectively). Richness and alpha diversity (ACE and Chao1) of the soil diazotroph community decreased under low but not high N loads. Approximately 67.1%-74.4% of the nifH gene sequences at the OTU level overlapped between the control and low N loads, but only 52.0%-53.6% of those overlapped between the control and high N loads, indicating a larger shift of diazotroph community composition under high N loads. Low N loads increased soil NH4+ concentrations, which decreased diazotroph community richness, diversity, and N fixation rates, whereas the increased soil NH4+ concentrations under high N loads did not have negative impacts on the structure and function of the diazotroph community. These findings indicate that diazotrophs sustain N fixation under high N deposition via adjustment of their community composition in forest soils. IMPORTANCE: This study examined the changes in soil diazotroph community under different loads of simulated N deposition and analyzed its relationship with N fixation rates in in five forests using high-throughput sequencing. The magnitudes of N fixation rates reduced by low N loads were higher than those by high N loads. Low N loads decreased richness and diversity of diazotroph community, whereas diazotroph community structure remained stable under high N loads. Compared with low N loads, high N loads resulted in a less similarity and overlap of nifH gene sequences among the treatments and a larger adjustment of diazotroph community. Low N loads increased soil NH4+ concentrations, which decreased diazotroph community richness, diversity, and N fixation rates, whereas the increased soil NH4+ under high N loads did not have negative impacts on diazotroph community structure and N fixation. Based on these findings, it is urgently needed to incorporate the loads of N deposition and the composition of diazotroph community into terrestrial N-cycling models for accurate understanding of N inputs in forest ecosystems.

Simulated nitrogen load promoted mineralization of N2P1 compounds and accumulation of N4S2 compounds in soil dissolved organic matter in a typical subtropical estuarine marsh.

Soil dissolved organic matter (DOM) is the most reactive pool in estuarine marshes, playing an important role in the biogeochemical processes of biogenetic elements. To investigate the impacts of enhanced nitrogen (N) load on DOM molecular composition and its interactions with microbes in typical Cyperus malaccensis mashes of the Min River estuary, a field N load experiment with four N levels (0, 37.50, 50 and 100 g exogenous N m-2 yr-1, respectively; applied monthly for a total of seven months) was performed. DOM molecular composition was characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), the microbial community compositions (MCC, including fungi and bacteria) were determined by high-throughput sequencing technique, and their relationships were presented by co-occurrence network analysis. The results indicated that enhanced N load had significant impacts on soil DOM molecular composition, with N/C and P/C of DOM decreasing but S/C increasing markedly. Meanwhile, enhanced N load decreased the percentages of N2P1 compounds (primarily lipids) but increased those of N4S2 compounds (mainly lignins and lipids). The relative abundances of lignins significantly increased with increasing N load levels, whereas the proportions of lipids decreased. The abundance of N2P1 and N4S2 compounds was primarily positively correlated with eutrophic and oligotrophic microorganisms, respectively. Therefore, mineralization of N2P1 compounds might act as a source to replenish inorganic P, while enrichment of N4S2 compounds may make great contribution to organic S accumulation. Overall, enhanced N load promoted P depletion and S enrichment via altering plant growth, litter decomposition and MCC.

Datamining approaches for examining the low prevalence of N-acetylglutamate synthase deficiency and understanding transcriptional regulation of urea cycle genes.

Ammonia, which is toxic to the brain, is converted into non-toxic urea, through a pathway of six enzymatically catalyzed steps known as the urea cycle. In this pathway, N-acetylglutamate synthase (NAGS, EC 2.3.1.1) catalyzes the formation of N-acetylglutamate (NAG) from glutamate and acetyl coenzyme A. NAGS deficiency (NAGSD) is the rarest of the urea cycle disorders, yet is unique in that ureagenesis can be restored with the drug N-carbamylglutamate (NCG). We investigated whether the rarity of NAGSD could be due to low sequence variation in the NAGS genomic region, high NAGS tolerance for amino acid replacements, and alternative sources of NAG and NCG in the body. We also evaluated whether the small genomic footprint of the NAGS catalytic domain might play a role. The small number of patients diagnosed with NAGSD could result from the absence of specific disease biomarkers and/or short NAGS catalytic domain. We screened for sequence variants in NAGS regulatory regions in patients suspected of having NAGSD and found a novel NAGS regulatory element in the first intron of the NAGS gene. We applied the same datamining approach to identify regulatory elements in the remaining urea cycle genes. In addition to the known promoters and enhancers of each gene, we identified several novel regulatory elements in their upstream regions and first introns. The identification of cis-regulatory elements of urea cycle genes and their associated transcription factors holds promise for uncovering shared mechanisms governing urea cycle gene expression and potentially leading to new treatments for urea cycle disorders.

Predicting stormwater nitrogen loads from a cold-region urban catchment in year 2050 under the impacts of climate change and urban densification.

Urban stormwater is a primary source of pollution for receiving water, but there is a shortage of studies on pollutant loads from urban catchments in cold regions. In this study, we coupled a build-up and wash-off model (in Mike Urban) with a climate change model to assess the impacts of climate change and urban densification on stormwater nitrogen loads (TN, TKN, NOx-N, and TAN) in an urban catchment in Canada. We calibrated and validated the Mike Urban model against observed event mean concentrations and nitrogen loads from 2010 to 2016. Results show that the nitrogen loads were mainly governed by rainfall intensity, rainfall duration, and antecedent dry days. Future precipitation data were downscaled using the Global Climate Models (GCMs), and three different Representative Concentration Pathways (RCP 2.5, RCP 4.5, and RCP 8.5) were used. Modeling results show that the TN, TKN, NOx-N, and TAN loads in 2050 will increase by 28.5 - 45.2% from May to September under RCP 2.5 compared to those from 2010 to 2016, by 34.6 - 49.9% under RCP 4.5, and by 39.4 - 53.5% under RCP 8.5. The increase of our projected TN load (from 1.33 to 2.93 kg·N/ha) is similar or slightly higher than the limited studies in other urban catchments. This study provides a reference for predicting stormwater nitrogen loads in urban catchments in cold regions.

Sources and spatiotemporal distribution characteristics of nitrogen and phosphorus loads in the Haihe River Basin, China.

Water quality monitoring stations are crucial for detecting excess pollutants in river sections, but identifying the causes of these exceedances can be challenging, especially in heavily polluted rivers with multiple contamination sources. To address this issue, we used the SWAT model to simulate pollution loads from various sources in the Haihe River Basin, analyzing the spatiotemporal distribution of pollutants from seven nitrogen/phosphorus sources in sub-basins. Our results show that crop production is the primary contributor to nitrogen and phosphorus loads in the Haihe River Basin, with the highest loads occurring in summer, followed by fall, spring, and winter. However, industries, atmospheric deposition, and municipal sewage treatment plants have a greater downstream impact on nitrogen/phosphorus contributions due to land use changes. The study highlights the need for targeted prevention and control policies based on the primary sources of pollution loads in different regions.

Denitrification and N2O Emission in Estuarine Sediments in Response to Ocean Acidification: From Process to Mechanism.

Global estuarine ecosystems are experiencing severe nitrogen pollution and ocean acidification (OA) simultaneously. Sedimentary denitrification is an important way of reactive nitrogen removal but at the same time leads to the emission of large amounts of nitrous oxide (N2O), a potent greenhouse gas. It is known that OA in estuarine regions could impact denitrification and N2O production; however, the underlying mechanism is still underexplored. Here, sediment incubation and pure culture experiments were conducted to explore the OA impacts on microbial denitrification and the associated N2O emissions in estuarine sediments. Under neutral (in situ) conditions, fungal N2O emission dominated in the sediment, while the bacterial and fungal sources had a similar role under acidification. This indicated that acidification decreased the sedimentary fungal denitrification and likely inhibited the activity of fungal denitrifiers. To explore molecular mechanisms, a denitrifying fungal strain of Penicillium janthinellum was isolated from the sediments. By using deuterium-labeled single-cell Raman spectroscopy and isobaric tags for relative and absolute quantitation proteomics, we found that acidification inhibited electron transfers in P. janthinellum and downregulated expressions of the proteins related to energy production and conservation. Two collaborative pathways of energy generation in the P. janthinellum were further revealed, that is, aerobic oxidative phosphorylation and TCA cycle and anoxic pyruvate fermentation. This indicated a distinct energy supply strategy from bacterial denitrification. Our study provides insights into fungi-mediated nitrogen cycle in acidifying aquatic ecosystems.

Crop improvement influences on water quantity and quality processes in an agricultural watershed.

Field crop traits have and are experiencing significant changes due to genetic and agronomic improvements. How these changes affect regional water quantity and quality processes has not been clarified. The St. Joseph River Watershed (SJRW) located in the U.S. Corn Belt was selected as a case study area. Crop (corn and soybean) trait improvements in the past decades were reviewed and summarized and include changes of growing degree days (GDD), leaf area index (LAI), light utilization (LU), drought tolerance (DT), nutrient content (NC), and harvest index (HI). Based on a calibrated 9-year (from 2011 to 2019) SWAT (Soil and Water Assessment Tool) simulation in SJRW, sensitivities of the above crop traits to yield, ETa, stream flow, tile flow, surface runoff, and nutrient loads (NO3N, TN, soluble-P, and TP) were analyzed. Crop traits and their corresponding SWAT parameters for the 2010s were obtained from model calibration and used as the baseline/current scenario; for the 1980s, they were summarized from literature review and used as an historical scenario, while those for the 2040s were determined by assuming crop traits are changing linearly with time and projected as the future scenario. Water quantity and quality changes under the historical and future crop scenarios were compared with the baseline/current simulation. Results showed LU and DT were the most sensitive crop traits to water quantity (i.e., ETa, stream flow, tile flow, and surface runoff), while HI was the most sensitive to nutrient loads. The impacts of crop improvements on nutrient loads were more significant than on water budgets. Compared with the baseline, the historical and future scenarios resulted in 1.5 - 2.0% changes of stream flow, 6.8 - 18.6% changes of nitrogen loads (NO3N and TN) and 2.6 - 3.9% changes of phosphorus loads (soluble-P, and TP) in the stream flow, annually. Moreover, in certain months, these changes can reach about 12% for stream flow, 42% for nitrogen loads, and 12% for phosphorus loads. Nitrogen losses by tile drainage and percolation, and phosphorus losses by surface runoff and tile drainage were most significantly affected by the crop improvements. Future work should consider expected crop improvements when studying long-term hydrology and nutrient cycles in agricultural watersheds.

Denitrification and Nitrogen Burial in Swiss Lakes.

Earth's nitrogen (N) cycle is imbalanced because of excessive anthropogenic inputs. Freshwater lakes efficiently remove N from surface waters by transformation of NO3- to atmospheric N2 and/or N2O (denitrification; DN) and by burial of organic N in sediments (net sedimentation; NS). However, relatively little is known about the controlling environmental conditions, and few long-term measurements on individual lakes are available to quantify conversion rates. We report N-elimination rates in 21 Swiss lakes estimated from whole-lake N budgets covering up to ∼20 years of monitoring. The NO3- concentration in the bottom water was the main predictor of DN. Additionally, DN rates were positively correlated with external N load and the area-specific hydraulic loading rate (mean depth/water residence time; Qs). NS of N was strongly related to total phosphorus (P) concentration. Nitrogen removal efficiency (NRE), the fraction of the load of dissolved N to a lake removed by DN and NS, was strongly negatively related to Qs. This previously unconsidered variable improves the predictability of NRE and does not require knowledge of N and P loading rates or concentrations. We conclude that P management alone intended to oligotrophy lakes only slightly increases N export unless it is accompanied by N management.

Analysis of satellite imagery using a simple algorithm supports evidence that Trichodesmium supplies a significant new nitrogen load to the GBR lagoon.

This work supports previous studies in the Great Barrier Reef lagoon that show the new nitrogen (N) load introduced by Trichodesmium is similar to or greater than that from riverine discharges. However, the current management programs aimed at improving the chronic eutrophic state of the GBR ignore the N load from Trichodesmium. These programs also ignore the evidence that Trichodesmium blooms could promote the bioavailability of heavy metals and be a source of toxins in the ciguatera food chain. Further work is urgently required to better quantify the potential impacts of Trichodesmium and develop management plans to reduce those impacts. A simple algorithm that uses MODIS imagery is developed for not only monitoring the spatial extent of Trichodesmium blooms but also for quantifying the concentration of those blooms. The algorithm is based on the readily available MODIS L2 data. A management plan that includes the harvesting of Trichodesmium is outlined.

Role of weak magnetic strength in the operation of aerobic granular reactor for wastewater treatment containing ammonia nitrogen concentration gradient.

Weak magnetic field (WMF) and aerobic granular sludge (AGS) technology were both robust technologies in wastewater treatments. In this study, the AGS characteristics and nutrient removal performances were all estimated at the load of 20 to 40 mg/L ammonia nitrogen (NH4+-N) and 0 to 40mT magnetic field. Results showed that 10mT was beneficial for keeping stable structure of granules when increasing NH4+-N load, accompanied with increasing protein (PN) secretion in EPS. Besides, all the total nitrogen (TN) removal rate under 10mT reached above 90%, while they were all less than 80% under other WMF strength when loading with 40 mg/L NH4+-N. Moreover, the simultaneous nitrification and denitrification (SND) efficiency could be enhanced by WMF of 10mT. Illumina MiSeq sequencing showed that NH4+-N load changed the bacterial richness and diversity when the magnetic strength was 10mT. And Candidatus_Competibacter was identified as the main functional genes for effective operation in this system.

An improved method used for evaluating potential environmental pollution risk based on spatial distribution and density of farms.

The livestock manure nitrogen load on farmland (LMNLF) is often used to assess the potential environmental pollution risk of livestock manure nitrogen nutrient (LMN) in a target region. First, the LMNLF of Wuhan city is calculated, and the potential environmental pollution risk of LMN is mainly concentrated in Jiangxia District, Xinzhou District, and Huangpi District, but does not exceed the European Union (EU) standards. Heat map results also certificate this conclusion. Therefore, these three districts are the research emphases. Second, considering spatial distribution of farms, an improved LMNLF method is proposed combining the previous LMNLF and density-based spatial clustering of applications with noise (DBSCAN) methods. Several regions with pollution risks including seven regions in Jiangxia District, one in Xinzhou District, and one in Huangpi District are found out using the improved LMNLF method. Third, to evaluate the carrying capacity of the intensive breeding areas more reasonably, 2 km is taken as the farthest transportation distance of manure; there is still one region in Huangpi District which has serious pollution risk on the environment. These above results can help evaluate the pollution degree of livestock manure to the surrounding environment more precisely.

Multi-functional benefits from targeted set-aside land in a Danish catchment.

In this study, we explored how a targeted land use change in a Danish catchment (River Odense) may provide multi-functional benefits through nitrogen (N)-load reductions to obtain good ecological quality in Odense estuary, protection of N-vulnerable groundwater aquifers, protection of Natura2000 sites and carbon sequestration. An N-load model linked to GIS thematic layers of known protected areas (Natura2000 sites and N-vulnerable groundwater aquifers) was utilised targeting high N-load areas to locate set-aside land. The achieved multi-functional benefits within the catchment and estuary were assessed and cost-benefit assessment was performed by dividing the total welfare costs of the set-aside by the total multi-functional benefits gained from each strategy. The results show that obtaining multi-functional benefits at the lowest cost requires a targeted shift of set-aside from the traditional hot-spot N-load areas to designated protected areas.

Nitrogen induced DOC and heavy metals leaching: Effects of nitrogen forms, deposition loads and liming.

Atmospheric nitrogen (N) deposition is believed to accelerate dissolved organic carbon (DOC) production and could lead to increased heavy metal mobility into water resources. We sampled intact soil cores from the Isle of Skye with low background N deposition history and having Serpentine rock known for its higher heavy metal concentrations including zinc (Zn), copper (Cu), nickel (Ni) and lead (Pb). The effects of 16 (16kgN) and 32 kg N ha-1 year-1 (32kgN), and liming with 32kgN (32kgN+Lime) on soil solution chemistry and heavy metal mobilization were investigated over the 15-month study. Nitrogen in deposition load was added at five ammonium (NH4+) to nitrate (NO3-) ratios of 9:1, 5:1, 1:1, 1:5 and 1:9 along NO3-dominance. We found significant effects of load on Cu and NH4+/NO3- ratio on pH, DOC and Zn in soil solution. However, under lime and ratio experimental factors, liming significantly influenced pH, DOC, Cu and Pb, and NH4+/NO3- ratio pH, DOC, Ni and Zn whereas interactions between lime and ratio was significant for Ni and Cu. pH and DOC increased with N load, liming and NO3- dominance, and both correlated significantly positively. Liming under NH4+ dominance enhanced DOC production due to supply of base cations in lime. Mobilization of Cu, Ni and Pb was driven by DOC concentrations and, therefore, increased with load, liming and NO3- dominance in deposition. However, in contrast, low pH and high NH4+ dominance was associated with Zn mobilization in soil solution. On the contrary, despite of some patterns, heavy metals in soil HNO3 extracts were devoid of any load, lime and NH4+/NO3- ratio effects. Our study suggests that the effects of N load and forms in deposition on sites with high accumulated loads of metals need to be better quantified through soil solution partitioning models.

Response of the nitrogen load and its driving forces in estuarine water to dam construction in Taihu Lake, China.

To regulate the water level and minimize the occurrence of water eutrophication in shallow lakes, dams and gates are often constructed in rivers. However, this practice may result in a deterioration of water quality in some estuaries. In the present study, using the correction of Nemerow pollution index (CNPI) and a redundancy analysis (RDA), water samples from different dammed rivers around Taihu Lake were compared to assess the pollution risk and identify the factors responsible for water eutrophication. The average total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC) concentrations, and chemical oxygen demand (CODMn) were 2.45 ± 2.28, 0.08 ± 0.06, 43.01 ± 18.75, and 10.78 ± 4.86 mg L-1, respectively. The CNPI values indicated that approximately 76.47% of the estuarine water was moderately polluted (1 < CNPI < 7.28). A positive correlation was observed between dam construction and nutrient concentrations (e.g., rTN = 0.38, p < 0.05; rTP = 0.89, p < 0.01). Under the effects of dam construction, land use change, estuary shape, and meteorological conditions, there was a clear spatial variation of the TN concentrations. Dams that were closed all year round accelerated the TN accumulation in the water around them. The pollution risk in a trumpet-shaped estuary was higher than that in other regions (t = 2.92, p = 0.02). Endogenous release of pollutants was an important factor that may have a priming effect on algal blooms and should be given more attention. In Wuli Lake, exogenous pollution was the dominant pollutant source. A total of 74.49% of the nitrogen losses with the runoff into the estuarine water in 2018 were derived from urban domestic sewage and constructed land, with the load being 4.40 times higher than in 2000. The RDA results revealed that dam construction was the main factor (43.70%) affecting water quality, while meteorological conditions, land use types, estuary shape, and other factors contributed 56.30%. Scientific regulation and control of dam operation is important to protect the water environment of Taihu Lake.

Nitrate leaching losses from two Baltic Sea catchments under scenarios of changes in land use, land management and climate.

Pollution with excess nutrients deteriorate the water quality of the Baltic Sea. The effect of combined land use and climate scenarios on nitrate leaching and nitrogen (N) loads to surface waters from two Baltic Sea catchments (Norsminde in Denmark and Kocinka in Poland) was explored using different models; the NLES and Daisy models for nitrate leaching, and MIKE SHE or MODFLOW/MT3DMS for N transport. Three Shared Socioeconomic Pathways (SSP1, SSP2 and SSP5) defined change in land use and agricultural activities. The climate change scenarios covered 2041-2060 compared with 1991-2010 under RCP8.5, applying four different climate models. Increases in predicted N-load from climate change vary from 20 to 60% depending on climate model. SSPs moderate these N-load changes with small changes for SSP1 to large increases for SSP5, with greater increases for Norsminde than Kocinka due to land use differences. This stresses needs for new measures and governing schemes to meet sustainability targets.

Atmospheric nitrogen pollution in urban agglomeration and its impact on alpine lake-case study of Tianchi Lake.

The atmospheric pollution caused by human activities has been recognized as an important factor affecting the water quality of freshwater bodies. The process of the human factors' impact on high-altitude lakes in inland regions is not clear up to now. In this research, regions around Tianchi Lake were taken as a case study to explore the relation between the urban air pollution and alpine lake water quality. Multi-scale station observed data were analyzed for the urban NO2 pollution by means of relevance analysis and trend analysis, the field measured data were analyzed for the lake total nitrogen (TN) pollution using multiple methods including the water quantity and quality balance, remote sensing retrieval and nutrient load assessment. The sources and occurrence conditions of atmospheric pollution and lake pollution were identified by a multi-method driving factor analysis. As a result, there is sufficient direct and indirect evidence to prove that the serious air pollution in surrounding cities is an important cause of the nitrogen pollution in Tianchi Lake.

[Adjusting Temperature and Settling Time to Achieve ANAMMOX Particles Rapid Start-up and Stable Operation].

At room temperature (21-25℃), the long start-up time of anaerobic ammonium oxidation (ANAMMOX) granular sludge is the main problem preventing the practical application of this technology. This experiment aimed to cultivate the anaerobic ammonia oxidizing granular sludge in the SBR reactor by adjusting the temperature. After the start-up of the ANAMMOX, stable operation was achieved by changing hydraulic retention time (HRT) and the concentration of the inflow water substrate. The results demonstrated that the anaerobic ammonia oxidation granular sludge could be successfully started-up in 30 d and realized a stable operation at room temperature (21-25℃). The removal rate of ammonia-nitrogen and nitrogen was about 88% and 85%, respectively, and the removal rate of total nitrogen was 75%. At the stable operation stage of the low matrix, the removal rate of ammonia-nitrogen reached 86%, the removal rate of nitrogen was 98%, and the total nitrogen removal rate was over 85%. SVI was stable at 30 mL·g-1, and MLVSS/MLSS was more than 60%. The value of protein/polysaccharide was stable around 1.75. The dissolved oxygen in the influent was not removed. In this case, controlling the temperature could be used to realize the rapid start-up of the anaerobic ammonia oxidation granular sludge at room temperature (21-25℃), and the high biomass content and nitrogen removal rate can be obtained.

Design parameters for nitrogen removal by constructed wetlands treating mine waters and municipal wastewater under Nordic conditions.

Nitrogen (N) loads from municipal and mine wastewater discharges typically increase N concentrations in recipient water bodies which should get more attention especially in cold-climate regions. This study compared N removal efficiency of six constructed wetlands (CWs) treating mine waters and three CWs polishing municipal wastewater. There were clear impacts of point source N loading to recipient water bodies in all cases studied and >300-fold increase in N was seen in some cases. First-order N removal coefficient was determined for seven of these CWs. All CWs studied were observed to remove N efficiently during the warm growing season but the amount of N released increased significantly during the cold season. Although some year-round purification was achieved by both peat-based and pond-type CWs, removal of nitrate + nitrite-N ((NO3- + NO2-)-N) was low during winter. The first-order N removal coefficient varied from 4.9 ·â€¯10-6 to 1.9 ·â€¯10-3 d-1 and showed that peat-based CWs were slightly more efficient in N removal than pond-type CWs. However, purification efficiency was steadier and higher for pond-type CWs, as lower hydraulic load or longer water residence time compensated for purification performance. Pond-type CWs showed mean removal efficiency of 59% and 46% for ammonium-N (NH4+-N) and (NO3- + NO2-)-N, respectively, whereas peatland-type CWs had lower removal efficiency for NH4+-N (mean of 26%) and in many cases negative removal for (NO3- + NO2-)-N. Correlation analysis revealed no clear, systematic relationship between temperature and N removal. However, in some CWs the highest correlation was between temperature and (NO3- + NO2-)-N, reflecting lower denitrification rate at lower temperature. More than 50% removal was found to require a hydraulic load below 10 mm d-1. In order to achieve 70% of NH4+-N removal, Ntot load lower than 75 g m-2 year-1 and a residence time longer than 80 d are needed in CWs in cold-climate regions.

[Effect of Aerobic/Phosphorus Granules on Start-up of Partial Nitrification Granular Sludge].

The different effects of additional aerobic granules (AGs) and phosphorus removal granules (PRGs) on the start-up and stable operation of partial nitrification granular sludge (PNGS) were compared at room temperature(22-28℃). The results showed that in the first stage (days 0-22), partial nitrification was accomplished on day 19 for the three reactors (R1, R2, and R3). In the second stage (days 23-56), 20% AGs and 20% PRGs were added to R2 and R3 to induce PNGS. The start-up of the granules of the three reactors was successfully achieved. The mean particle sizes of R1, R2, and R3 reached 412 µm at day 76, 468 µm at day 42, and 400 µm at day 56. In the third stage (days 57-108), because the influent ammonia load increased from 0.4 kg·(m3·d)-1 to 0.5 kg·(m3·d)-1 and the COD load increased from 0.2 kg·(m3·d)-1 to 0.5 kg·(m3·d)-1, the mean particle sizes of R1 and R2 increased significantly. The average particle sizes of R1 and R2 reached 689 µm and 893 µm by the end of the operation (day 108), but sludge expansion occurred in R3. The inoculation of either AGs or PRGs could quickly achieve granulation, but the PNGS inoculated with the AGs could adapt to higher C/N and be more tolerable to shock loads and long-term stable operation.