Single-stage Nitrogen removal using Anammox and Partial nitritation (SNAP) process was newly developed as an economical nitrogen removal process for ammonium rich wastewaters. The experimental studies for the evaluation of SNAP process were carried out using a novel biofilm reactor, in which hydrophilic net-type acryl fiber biomass carrier was applied. This SNAP reactor was operated under operational conditions of pH 7.5–7.7, 35 °C and DO 2–3 mg/L, and 60 to 80% of influent NH₄-N was removed under loading rate of 0.48 kg-N/m³/d. Through the DNA analysis of the attached sludge, it was made clear that ammonium oxidizing bacteria (AOB) and anammox bacteria coexisted in the attach-immobilized sludge on the acryl fiber biomass carrier. Favorable conditions for the growth of anammox bacteria were created inside attach-immobilized nitrifying sludge. Two kinds of anammox bacteria and two kinds of AOB were detected in the SNAP sludge. Existence ratios of anammox and AOB were estimated to be 15% and 8.7%, respectively, based on the obtained clone numbers. This coexisting condition was confirmed by the FISH image of SNAP sludge and its confocal laser scanning microscope.

Diversity and productivity of primary producers are known to be influenced simultaneously by resource availability and resource ratio, but the relative importance of these two factors differed among studies and so far only entire phytoplankton communities were investigated which might ignore specific nutrient requirements and stoichiometric plasticity of different functional groups. We measured nutrient availability (DIN, total N [TN], total P [TP]), nutrient imbalance (TN:TP, DIN:TP, N:P_seston), species richness, and abundance of the whole phytoplankton community, as well as those specific for cyanobacteria, diatoms, and dinoflagellates in Cau Hai lagoon in Vietnam. We determined the correlation among these variables, using structural equation modeling. The models applied to the whole phytoplankton community indicated that the nutrient availability (particularly TP and DIN) drove variation in phytoplankton abundance and richness, and that abundance also depended on species richness. The models applied to different functional groups differed considerably from the entire community and among each other, and only a part of the models was significant. The relationship between nutrient availability (mainly TP) and abundance was driven by cyanobacteria, and the relationship between nutrient imbalance (only with N:P_seston) and species richness was driven by diatoms. Remarkably, the positive relationship between species richness and abundance, as consistently observed for the whole phytoplankton community, was only observed for one of the three functional groups (diatoms), indicating that resource complementarity occurs particularly among species of different functional groups. Our results emphasized that nutrient availability (TP and to a lesser extent DIN) as well as nutrient imbalance (albeit only with N:P_seston as proxy) were driving factors for the phytoplankton community in the Cau Hai lagoon and hence alterations in both of these factors leading to a shift in phytoplankton species composition and productivity.

In the process named SNAP (Single-stage Nitrogen removal using Anammox and Partial Nitritation), influent ammonium was removed as nitrogen gas by the combination of two autotrophic steps, partial nitritation and anammox, in one unit process. The reactors were packed with acryl-resin fiber biomass carriers and gently aerated. The synthetic influent, simulating secondary-treated landfill leachate, contained ammonium concentrations of 240 mg-N/l and 500 mg-N/l for reactors named SN-2 and SN-3, respectively. Data from 300 days of SNAP operation using reactor SN-2 showed ammonium conversions of 47.7∼88.1% with nitrogen removal rates of 0.31∼0.45 kg-N/㎥/d under various operational conditions. The best performance with loading rate of 0.6 kg-N/㎥/d was obtained at 35°C, pH 7.8, and aeration rate of 0.10 vvm (volume per volume per minute), with 88.1% ammonium conversion and 78.5% nitrogen removal. The results of about 100 days of operation for reactor SN-3 confirmed the treatment capability of SNAP process, with about 80% nitrogen removal with loading rates up to 1.0 kg-N/㎥/d. Some important characteristics of the SNAP process are discussed.独立栄養性の窒素変換経路である部分亜硝酸化とanammoxを組み合わせた単一槽での窒素除去法 (SNAP法) で、流入水中のアンモニアを窒素ガスとして除去することができた。SNAPリアクタにはアクリル繊維性生物担体を充填し、緩やかな曝気を行うことでリアクタを混合攪拌した。埋立地浸出水の二次処理水に似せた合成浸出水のNH4-N濃度を240mg-N/l, 500 mg-N/lの二段階に設定し実験を行った。流入水NH4-N濃度を240mg-N/lに設定し300日間SNAP処理した結果、NH4-N変換率47.7～88.1%、T-N除去速度0.31～0.45 kg-N/㎥/dという結果を得た。T-N容積負荷量0.6 kg-N/㎥/d、35℃、pH7.8、曝気量0.10vvmの条件下において、NH4-N変換率88.1%、T-N除去率78.5%の処理成績が得られた。設定NH4-N濃度を500 mg-N/lに設定して約100日間運転し、T-N容積負荷量1.0 kg-N/㎥/dの条件下において、T-N除去率約80%というSNAPの優れた処理能力を確認した。幾つかの重要なSNAPプロセスの特性について論じた

Disease outbreaks attributed to monsoon flood-induced pathogen exposure are frequently reported, especially in developing cities with poor sanitation. Contamination levels have been monitored in past studies, yet the sources, routes, and extents of contamination are not always clear. We evaluated pollution from municipal wastewater (MWW) discharge and investigated fecal contamination by Escherichia coli (E. coli) in three agricultural fields on the outskirts of Hue City, Vietnam. After E. coli concentration was determined in irrigation water (IRW), MWW, soil, vegetables (VEG), and manure, its dispersion from MWW was tracked using multilocus sequence typing (MLST) and phylogenetic analyses during the wet and dry seasons. IRW was severely contaminated; 94% of the samples were positive with E. coli exceeding the stipulated standards, while VEG contamination was very low in both seasons. The confirmed total number of isolates was comparable between the seasons; however, results from MLST and phylogenetic clustering revealed more links between the sites and samples to MWW during the wet season. The wet season had four mixed clusters of E. coli isolates from multiple locations and samples linked to MWW, while only one mixed cluster also linking MWW to IRW was observed during the dry season. The most prevalent sequence type (ST) complex 10 and two others (40 and 155) have been associated with disease outbreaks, while other STs have links to major pathotypes. Irrigation canals are significant routes for E. coli dispersion through direct links to the urban drainage-infested river. This study clarified the genotype of E. coli in Hue city, and the numerous links between the samples and sites revealed MWW discharge as the source of E. coli contamination that was enhanced by flooding.

Anammoxと部分亜硝酸化を活用する単一槽での窒素除去法（SNAP法）の処理の再現性と安定性を連続処理試験にて検討した。35℃，pH7.5～7.8，曝気量0.06～0.10vvm，合成浸出水の流入窒素容積負荷量0.6kg－N/m3/dという条件下において60日間連続運転をおこない，NH4－N変換率89.2±6.2％，T－N除去率76.3±7.2％という結果を得た。汚泥生成速度は0.045 mg－VSS/mg－Nと低い値となった。SNAP汚泥の粒径は主に420～550μmに分布しており，網状アクリル性繊維担体の内部に集合する傾向を示している。汚泥のアンモニア酸化活性は，好気状態で430～610mg－N/g－VSS/d，嫌気状態で32～51mg－N/g－VSS/dだった。アンモニア酸化菌と亜硝酸酸化菌はそれぞれ，107～109MPN/g－VSS，106MPN/g－VSSの割合で検出された。SNAP汚泥のDNA分析によりSNAP汚泥には3種類の細菌が存在し，アンモニア酸化菌はNitrosomonas europaeaに，亜硝酸酸化菌はNitrospira sp.に，anammox菌はKU2，KSU－1にそれぞれ相同性を有していることが明らかになった。これらの細菌は動的平衡状態で存在しており，運転条件を変化させることでその平衡状態が変化することが示唆された。