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Partial oxidation of ammonium to nitrite is a pre- and crucial step to achieve shortcut biological nitrogen removal from ammonium-rich wastewater. In the present study, a nitritation granular reactor using activated sludge as inoculum was started up in a sequencing batch reactor (SBR) at a fixed influent C/N ratio of 2:1. Variations in the reactor performance, functional bacteria activities, sludge morphology and bacterial community structure were investigated. Results showed the formation of compact granules was achieved in 55 days, and a stable nitrite accumulation rate of 0.68 kg N·m−3·d−1 was maintained in the following period. With a rapid growth of granular size, the total nitrogen removal by simultaneous nitritation/denitritation was progressively increased to 50%. In sludge granulation, the significant enrichment of r-strategist ammonium oxidizing bacteria (Nitrosomonas) was identified. Additionally, both high free ammonia concentration and extra nitrite competition by heterotrophic denitrifiers were critical to suppress nitrite oxidizing bacteria effectively.

In this study, a high-rate CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) process was started up successfully by enhancing the in-situ enrichment of anammox bacteria in aerobic granules at conditions relevant for mainstream wastewater treatment. Firstly, to provide nitrite for anammox bacteria growth efficient nitrite-oxidizing bacteria (NOB) repression was rapidly achieved and stably maintained. Both low dissolved oxygen (DO) and ammonium concentrations ratio (DO/NH4+

To elucidate how high dissolved oxygen (DO) favors the startup of nitritation with aerobic granular sludge, two granular reactors were operated under low (1–2 mg O2·L−1) and high DO (3–5 mg O2·L−1) conditions with similar effluent ammonium concentrations (>20 mg N·L−1). The results showed that though nitritation with an average nitrite accumulation ratio of above 95% was finally achieved in both reactors, a five-fold start-up time (eleven weeks) was required for the low DO reactor compared to the high DO reactor. Moreover, the nitritation performance was positively correlated with the extent of nitrifiers stratification in granules. The faster startup of nitritation under high DO conditions mainly resulted from the faster formation of well-stratified nitrifiers, with ammonium oxidizing bacteria (AOB) dominating granule surface. High DO operation combined with sufficient ammonium supply ensured the faster growth of AOB, which should provide a competitive advantage to AOB in competing for habitable space (i.e., granule surface). Besides, the lower porosity, larger size, and more active extracellular polymeric substances (particularly proteins) production of granules was observed under the high DO condition. Overall, these findings supported the proposition that the switch from mixed to stratified distribution of nitrifiers in granule was primarily driven by their competition for habitable space rather than by oxygen-limitation.

The start-up of completely autotrophic nitrogen removal over nitrite (CANON) process was investigated by seeding nitritation granular sludge in a continuous stirred tank reactor with typical geometry. Nitrogen loading rate (NLR) was increased from 1.5 to 3.3 kg N m−3 d−1, by shortening hydraulic retention time from 2.0 to 0.9 h under oxygen-limiting conditions. An extremely high nitrogen removal rate (NRR) of 2.83 kg N m−3 d−1 was achieved, due to the high specific NRR of huge biomass in the reactor. With the improvement of granular structure compactness, it was believed that the EPS accumulation could be beneficial to enhance nitrogen removal performance of granules. In addition, high-throughput pyrosequencing analysis revealed that a co-culture of aerobic and anaerobic ammonium oxidizing bacteria, affiliated to genera Nitrosomonas and Candidatus Kuenenia respectively, had been established in mature CANON granules, while the growth of nitrite oxidizing bacteria (Nitrospira spp.) was effectively suppressed through substrate competitions between three groups of bacteria. Therefore, a single continuous reactor with granules is applicable to achieve high performance CANON process for treating ammonium-rich wastewater.

The Ag/TiO2 and Ag2O/TiO2 films were deposited by magnetron sputtering on the polyester fabrics. The Kelvin probe system was simply developed and used to investigate the photoelectric properties of Ag/TiO2 and Ag2O/TiO2 junctions. The measured work functions of the deposited Ag, Ag2O and TiO2 are 4.65 e V , 5.53 e V and 5.03 e V , respectively. Ag2O/TiO2 junction has a 0.12 e V larger E F difference than Ag/TiO2 junction, indicating that Ag2O/TiO2 junction has a higher ability of charge separation than Ag/TiO2 junction. The photocatalytic activities of samples towards RB solution under 365 nm UV light were investigated. The results show that the Ag/TiO2 and Ag2O/TiO2 coated polyester fabrics have a far better photocatalytic performance than TiO2 coated polyester fabrics. And the photocatalytic activity of Ag2O/TiO2 coated sample is prominently higher than that of Ag/TiO2 coated sample, which is attributed to the larger E F difference and the wider space charge region of Ag2O/TiO2 junction compared with that of Ag/TiO2 junction.

Biomass segregation between granules/biofilm and flocs is widespread in anammox-based processes. The segregation of biomass allows for easy control of processes stability. The goal of this study is to understand the biomass segregation in two anoxic anammox reactors respectively operated in nitrite-limited (RNO2) and ammonium-limited (RNH4) modes treating low-strength wastewater at 20 °C. Results showed that size-based biomass segregation was developed in both reactors. But the functional and population heterogeneity was more significant in the ammonium-limited anammox reactor. The activity and abundance of anammox bacteria in large granules were significantly higher than that in flocs under the ammonium-limited conditions. The large granules played a major role in nitrogen removal in RNH4. By contrast, both large granules and small flocs contributed significantly to the nitrogen loss in the nitrite-limited anammox reactor, since a large number of anammox bacteria existed in both granules and flocs. Besides, a number of Nitrospira-like NOB were also detected in both anoxic anammox reactors, which primarily inhabited in flocs seemingly droved by the availability of oxygen. But the abundance of Nitrospira in RNH4 was much higher than that in RNO2. All these results suggested that selective flocs removal would be necessary for RNH4 to improve its anammox performance but non-essential for RNO2. The two anammox reactors shared the predominant anammox species with the closest relative to Ca. Brocadia sp. 40 (98%). Unexpectedly, the anammox species grew faster in RNH4. But the microbial diversity and evenness was much greater in RNO2, suggesting its higher functional stability.

The polyester fabrics were modified with Ag-Ag2O-TiO2 coating. The TiO2 layer was prepared by DC magnetron sputtering and oxidation in air: a method which avoids the problem of Ti target poisoning in reactive sputtering. The Ag2O layer was deposited by DC reactive sputtering. As a contrast, the TiO2 layer of Ag-Ag2O-TiO2 coating was also prepared using radio frequency (RF) reactive sputtering in Ar/O2 gas mixture. The surface photovoltage (SPV) spectrum and the measured work functions of samples indicate that a built-in electric field was formed at the interface between Ag2O layer and TiO2 layer. The photocatalytic efficiency was analyzed through monitoring the degradation of Rhodamine B (RB) under UV illumination. Compared to the polyester merely coated with TiO2, the polyester fabrics coated with Ag-Ag2O-TiO2 showed the superior performance of photocatalysis, indicating the Ag2O/TiO2 heterojunction contributes to photocatalytic degradation of RB. Results also show that the TiO2 layer in Ag-Ag2O-TiO2 coating prepared by DC magnetron sputtering and then natural oxidation had comparable photocatalytic activities with that prepared by RF reactive sputtering.

In order to reduce the external nutrient loads in Lake Taihu, it was found that controlling nutrient input is the most effective way of reducing the risk of blooms. In this regard, nutrient removal by using a combined process consisting of an anaerobic baffled reactor and an aerobic membrane bioreactor for municipal wastewater treatment was investigated. The results demonstrated that hydraulic retention time, recycle ratio and dissolved oxygen had a negligible effect on the removal efficiencies of chemical oxygen demand and ammonia. Optimal operation conditions with a hydraulic retention time of 7.5 h at a recycle ratio of 200% and dissolved oxygen of 3 mg/L was shown to achieve higher quality effluent with chemical oxygen demand, ammonium, total nitrogen and total phosphorus of 26, 0.5, 10.5 and 0.4 mg/L, respectively. Analysis of fluorescence in situ hybridization showed that the specialized microorganisms, including nitrifying bacteria (ammonia-oxidizing bacteria and nitrite-oxidizing bacteria), and phosphorus accumulating organisms, were enriched in this process. The profile of nitrite-oxidizing bacteria was similar to that of ammonia-oxidizing bacteria. The nitrifying bacterial population had a good correlation with nitrogen removal efficiency. A good correlation was also observed between phosphorus removal performance and the percentage of phosphorus accumulating organisms present in the sludge.