In polar water cycle monitoring, satellite Earth observation is one of the important tools. The snow and ice in the polar region as a freshwater reservoir have undergone significant changes due to ongoing global warming. These changes are recognized as an urgent global issue due to their contribution to sea-level rise. This paper shows estimation methods for the rapidly decreasing polar sea ice and land snow cover and insights into the mass balance and albedo change of the Antarctic Ice Sheet and Greenland Ice Sheet as topics captured by satellite Earth observation. Additionally, this paper introduces previous efforts related to the polar water cycle, along with field observations as the foundation for capturing polar region changes.

In order to promote healthy water circulation and address urban water issues, the concept of Rainwater Harvesting, to use and slowly drain rainwater instead of eliminating it quickly, becomes important. In addition to introducing the current status of rainwater storage and utilization in Japan and the quality of stored rainwater, the report will focus on efforts in Sumida-ku, Tokyo, noting the progress and challenges of small-scale decentralized rainwater management in urban areas. Future efforts will include appropriate management of water volume in tanks, verification of the effectiveness of runoff control, and formulation of operational rules. In light of global environmental trends such as Green Infrastructure and Nature Positive, the report will also introduce initiatives that citizens can take to realize a sustainable urban environment.

The dye effluents from textile industries have been difficult targets for wastewater treatment. Biological treatment shows a very limited performance for the organic compounds contained in the soluble fraction of the effluent from paint industries, although the particulate matters are efficiently removed by coagulation – flocculation process. The use of advanced oxidation processes is sometimes considered as a treatment option for the organic matters which cannot be removed by biological processes, although the treatment costs by advanced oxidation processes are generally high. This review outlines the key technologies in the treatment of colored wastewater.

The biological nitrogen removal process known as anammox treatment has been gaining attention as an alternative to conventional high-energy consumption and high-carbon nitrification-denitrification method. However, the growth rate of anammox bacteria is extremely slow, and operational instability due to inhibition and sludge loss has been a problem, resulting in limited application. In this paper, new insights into anammox, including the HAP-based one-stage partial nitritation anammox (PNA) process and the one-stage partial denitrification anammox (PDA) process, which can remove nitrogen and phosphorus, simultaneously, are summarized. Additionally, the recent achievements in process development are reviewed, and future research directions are discussed.