Food waste has become a critical issue in modern society, especially in the urbanized and fast-growing cities of Asia. The increase in food waste has serious negative impacts on environmental sustainability, water and land resources, and food security, as well as climate and greenhouse gas emissions. Through a specific case study in Da Nang City, Vietnam, this paper examines the extent of food waste generation at the consumption stages, the eating habits of consumers, food waste from households and service establishments, as well as prospects for the reuse of food waste as pig feed. The results of this study indicate that per capita food waste generation in Da Nang has increased from 0.39 to 0.41kg in 2016, 0.46 in 2017, and reached 0.52kg in 2018. According to the results of our consumer survey, 20% of respondents stated that they often generate food waste, 67% stated they sometimes do, and 13% stated they rarely do. Furthermore, 66% of surveyed households stated that their food waste is collected and transported by pig farmers to be used as feed for pigs. The use of food waste as feed for pigs is a typical feature in Da Nang. The study also found that there is a high level of consumer awareness and willingness to participate in the 3Rs (reduce, reuse, recycle) program, which was being initiated by the city government. In service facilities such as resorts and hotels, daily food waste reached 100–200 kg in large facilities and 20–120 kg in small facilities. This waste was also collected for use in pig farming. However, there has been a fall in demand for pig feed in line with a decrease in the number of pig farms due to the African swine fever epidemic that occurred during the implementation of this study. This paper suggests that there is a strong need to take both consumer-oriented waste prevention and waste management measures, such as waste segregation at source and introduction of effective food waste recycling techniques, to ensure that food waste can be safely and sustainably used as a “valuable resource” rather than “wasted.”

Fraction of young water (Fyw) and mean transit time (MTT, $\overline{\tau }$) calculated from water isotope profiles are valuable information for catchment hydrological assessment, especially in anthropogenically impacted region where natural conditions may not be decisive to catchment hydrology. The calculation of Fyw and MTT were performed on three subsets of δ¹⁸O_H₂O data collected at the Hanoi meteo-hydrological station, Red River, in three periods; 2002–2005, 2015, and 2018–2019. The mean (min and max) values of δ¹⁸O_H₂O in rainwater over the three periods are, respectively, −5.3‰ (−11.0 and −1.2‰), −5.4‰ (−10.7 and −1.4‰), and −4.5‰ (−13.9 and 1.7‰). The corresponding values in river water are −8.4‰ (−9.8 and −6.9‰), −8.5‰ (−9.1 and −7.7‰), and −8.4‰ (−9.5 and −7.2‰), respectively. The mean of Fyw calculated from the δ¹⁸O_H₂O data for different periods is 22 ± 9%, 10 ± 5%, and 8 ± 3%. Mean transit time is 4.69 ± 15.57, 1.65 ± 1.53, and 2.06 ± 1.87 years. The calculated Fyw (MTT) is negatively (positively) proportional to change in reservoir volume over the three periods, which is logical, since reservoirs tend to keep more water in the catchment and slower down water flow. The strong variation of Fyw and $\overline{\tau }$, two essential variables characterizing the catchment hydrology, represents an anthropogenic impact in the Red River system.