Nitrite has been commonly recognized as an important factor causing N(2)O production, which weakened the advantages of nitrogen removal via nitrite. To reduce and control N(2)O production from wastewater treatment plants, both long-term and batch tests were carried out to investigate main sources and pathways of N(2)O production during nitrogen removal via nitrite from real domestic wastewater. The obtained results showed that N(2)O production during nitrogen removal via nitrite was 1.5 times as much as that during nitrogen removal via nitrate. It was further demonstrated that ammonia oxidization were main source of N(2)O production during nitrogen removal from domestic wastewater; whereas, almost no N(2)O was produced during nitrite oxidization and anoxic denitrification. N(2)O production during nitrogen removal via nitrite decreased about 50% by applying the step-feed SBR, due to the effective control of nitrite and ammonia, the precursors of N(2)O production. Therefore, the step-feed system is recommended as an effective method to reduce N(2)O production during nitrogen removal via nitrite from domestic wastewater.

The feasibility of obtaining and keeping stable nitrite accumulation in Sequencing Batch Reactors (SBRs) treating domestic wastewater is studied. The final product of ammonium oxidation is either reproducible nitrate or nitrite depending on the aeration strategy. With the aerobic-anoxic sequence, two SBRs fed with domestic wastewater are operated in parallel. One SBR (SBR1) is controlled by the aeration control strategy, and the other SBR (SBR2) by alternate aeration control strategy. Based on the on-line indirect measurements of DO and pH, the relationship between pH (or DO) and nitrogen concentration (NH4+-N, NO3−-N and NO2−-N) is investigated. The result indicates that pH and DO can be used as control parameters for the real-time aeration control strategy to obtain nitritation in SBR treating domestic wastewater. The result of SBR1 indicates that long-term stable nitritation is possible at 32 ± 1°C. The result of SBR2 indicates that the aeration control strategy is necessary for nitritation during the acclimation period, because the nitrite accumulation disappears when the aeration is extended.

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Since the application of fiber-reinforced polymer continues to expand, the demands of product quality for secondary cutting process are becoming increasingly higher to ensure the accurate coordination, connection, and assembly. There are some defects such as tearing, burr, delamination, and thermal damage after secondary cutting process, which limit the further applications of the materials. It is urgent to carry out comprehensive research on the secondary processing technology. In this paper, the fiber-reinforced composites' category, characteristics, and their applications were first described. Then the cutting performances, the causes of machining defects, and machining mechanisms have been analyzed. Finally, different compound processing methods, their characteristics, and applications have been elaborated. The most common forms of compound processing method including combined machining of cutting and grinding, ultrasonic vibration–assisted machining, and low-temperature–assisted machining have been covered in this paper. Results show that the compound processing method is the most effective way for improving the second processing quality of fiber-reinforced polymer. More machining mechanisms and applications of compound processing method need further experimental research. The barriers and future in the fields of research on machining of fiber-reinforced composites have been analyzed in this paper.