Micro–nanobubbles (MNBs) can generate ·OH in situ, which provides a new idea for the safe and efficient removal of pollutants in water supply systems. However, due to the difficulty in obtaining stable MNBs, the generation efficiency of ·OH is low, and the removal efficiency of pollutants cannot be guaranteed. This paper reviews the application research of MNB technology in water security from three aspects: the generation process of MNBs in water, the generation rule of ·OH during MNB collapse, and the control mechanisms of MNBs on pollutants and biofilms. We found that MNB generation methods are divided into chemical and mechanical (about 10 kinds) categories, and the instability of the bubble size restricts the application of MNB technology. The generation of ·OH by MNBs is affected by the pH, gas source, bubble size, temperature, and external stimulation. And the pH and external stimulus have more influence on ·OH generation in situ than the other factors. Adjusting the pH to alkaline or acidic conditions and selecting ozone or oxygen as the gas source can promote ·OH generation. MNB collapse also releases a large amount of energy, during which the temperature and pressure can reach 3000 K and 5 Gpa, respectively, making it efficient to remove ≈90% of pollutants (i.e., trichloroethylene, benzene, and chlorobenzene). The biofilm can also be removed by physical, chemical, and thermal effects. MNB technology also has great application potential in drinking water, which can be applied to improve water quality, optimize household water purifiers, and enhance the taste of bottled water. Under the premise of safety, after letting people of different ages taste water samples, we found that compared with ordinary drinking water, 85.7% of people think MNB water is softer, and 73.3% of people think MNB water is sweeter. This further proves that MNB water has a great prospect in drinking water applications. This review provides innovative theoretical support for solving the problem of drinking water safety.

Excessive fertilizer application in the cropping industry leads to excessive nitrogen and phosphorus in surrounding water bodies, which causes farmers to increase economic cost and damage the environment. To address the problem, we built a crop-soil runoff soil column test system, setting eight fertilizer application levels for eggplants. Then, crop yield, soil fertility and pollutant concentrations in the receiving water bodies were measured. The process of fertilizer application on the water quality of surrounding receiving water bodies and the rationality of fertilizer application were analyzed. The results showed that crop yield, soil fertility, and pollutant concentrations in the receiving water increased with the increase in fertilizer application. The crop yield stabilized when the fertilizer application amount was higher than 0.12 kg/m²; the concentrations of total nitrogen (TN) and total phosphorus (TP) in the water increased significantly with the increase in fertilizer application, where particulate nitrogen (PN) and organic phosphorus (OP) were the key pollutants. In addition, crop growth had an interception effect on pollutant migration. The concentration of pollutants in the water was significantly lower in the late crop growth period (after flowering) than in the early. The crop had the best interception effect on pollutants when the fertilizer application was 0.12 kg/m². The concentrations of TN and TP in the water were 29.7% and 22.3% after the flowering period, being lower than those before the flowering period. Therefore, a reasonable value of 0.12 kg/m² is recommended for fertilizer application in this article. It can provide a reference for the fertilization system of eggplant planting in North China and theoretical support for the realization of clean production in small rural watershed planting.

The development of wastewater treatment industry has gradually entered the high-standard period and the wastewater treatment technology needs to be refined for different types of wastewater. Traditional water quality indicators are not able to explain new problems encountered in the current wastewater treatment process, especially the potential of removing pollutants via biological methods. This research proposed a new method of evaluating the biological treatment process by measuring the oxygen consumption in the biodegradation of pollutants on-the-go and describing the complete biological oxygen consumption process. The biodegradability of wastewater from an actual textile wastewater treatment plant was quantitatively evaluated by analyzing the proportion of different organic pollutions. Results showed that the hydrolytic acidification can improve the biodegradability of textile wastewater by increasing the content of biodegradable organic matter (growth of 86.4%), and air flotation has little effect on the biodegradability of the wastewater. Moreover, the biodegradability of the textile wastewater could be improved by increasing the nitrogen and phosphorus content, which could come from urea and K₂HPO₄. Concretely, nitrogen source mainly increases organic matter of rapid bio-treated and organic matter of easy bio-treated by 14.94% and 70.79%, and phosphorus source mainly increases the organic matter of easy bio-treated by 143.75%. We found that the optimum concentration of additional N and P to the textile wastewater was 35 mg/L and 45 mg/L, respectively. This approach holds great application prospects such as risk control, optimizing treatment technology, and management, due to its characteristics of being simple, easy to use, and rapid online implement action.