No abstract

Dissolved organic nitrogen (DON) is ubiquitously present in the environment and its presence in drinking water has been related to the formation of nitrogenous disinfection byproducts recently. Therefore, a better understanding of the occurrence and control of DON is important. However, conventional DON method calculates DON as the difference between total dissolved nitrogen (TDN) and dissolved organic nitrogen (DIN), in which the subtraction process is likely to be subject to accumulated analytical errors and therefore sometimes results in unreliable DON data. Electrodialysis (ED) as a pretreatment tool may separate completely DON from DIN and enable direct and improved DON analysis. However, the important factors affecting the efficiency of ED process are unknown now. So, this study investigates a series of operational and instrumental options on the removal efficiency of ED for DON measurement. These factors include the type and concentration of electrolyte(s) in the sample and electrolyte media, flowrate, power input, specific area of ion exchange membrane (IEM), and electrode materials, etc. Ultimately, we have developed an ED unit capable of separating DON from DIN by 99% within 90 minutes with a consumption of sample of only 50 ml. The main purpose is to optimize the ED process while avoiding potential problems. The information may help optimize the ED process to provide automatic tools for DON analysis in the future.

This study evaluated electrodialysis (ED) for direct, accurate, and precise dissolved organic nitrogen (DON) analysis in water. Unlike conventional methods that calculate DON as the difference between total dissolved nitrogen (TDN) and dissolved inorganic nitrogen (DIN), we designed a compact ED reactor as a pretreatment tool that completely separates DIN from DON in water and then measures DON by equating DON to TDN. The experiments confirmed that the ED pretreatment process can achieve 99% removal of all three major DIN species (i.e., ammonia, nitrite, and nitrate) and an average recovery rate of 88% for an array of model DON compounds of varying characteristics (e.g., urea, amino acids, tripeptide, protein, and humic substances). Variations in nitrogen removal and recovery might be explained by a combined effect of molecular weight, acid dissociation ability (pK(a)), aromaticity, and ED reactor configurations. For model solutions with DIN/DON ratios varying from 1 to 10 mg-N/mg-N, the relative standard deviations in DON concentrations were considerably lower with ED pretreatment (<10%) than without pretreatment (47%). A survey of seven field samples, including lake water, tap water, and treated wastewater, also demonstrated the benefits of using ED pretreatment as compared with a conventional DON analysis method. Overall, this study provides evidence and mechanistic insight for a new DON detection method that uses ED pretreatment. The ED unit is robust for separating DIN and DON, and thus it may facilitate more frequent detection of DON and ultimately enhances understanding of DON issues in the environmental studies.

Reducing pressure has become a major topic for recent Chinese education. New policies aimed to further relieve students from schoolwork burden were enacted and implemented in 2021. After one year of implementation, the result is yet to be calculated. Contrary to traditional Chinese education ideologies, the policy imposes uniform and strict regulations on school actions. Some of the controversial terms stated in the policy may obstruct students from improving grades with extensive extra effort. Subsequently, school conditions are different and the policy is confronted with potential reluctance. The research mainly adopts questionnaire studies on primary school students in Wuxi, China. The result has revealed the uneven implementation of the regulation among different schools and the common negligence of high-grade students in pressure-reduction activities. Further, from students' responses, it is suggested that school actions require specified regulations.

Two years after the initial breakout, the COVID-19 epidemic is still spreading worldwide. As the virus mutates and becomes more contagious, several epidemic outbreaks in China led to serious public health crises in 2022. The government has adopted the Zero-COVID Policy, a draconian measure aiming to lockdown cities with infected people as a means to combat the contagion.  Cities are vigilant and cautious of the pandemic, implementing lockdowns whenever COVID-19 cases emerged. Learning has fundamentally changed. Schools need to comply with unpredictable lockdown policies and transition to online teaching. Students, on the other hand, need to overcome new difficulties and make adaptations to the sudden shift in teaching mode. Previous studies have indicated evidence suggesting that online study has the potential to bring anxiety and pressure. Under such erratic circumstances, the challenge of retaining study progress has been perceived as arduous by the general public, requiring students to finish all study tasks in the changing environment. Through questionnaire studies and interviews with students who underwent different policies in different regions, the main goal of the research is to investigate how stress differently affects students and trace the reasons for the tension of studying online.