Preface

Water is the source of life and a clean body of water is the key to human survival. However, the world's water is being polluted by sewage, which, if not treated, will endanger human health and threaten the environment. If we want to live on Earth in a sustainable and healthy way, it is our duty to treat sewage. Although sewage treatment has a long history, it is becoming increasingly difficult due to rapid population growth and the increasing variety of sewage. This requires us to: first, we must master the current situation of sewage, from the generation, discharge, destination and its impact of sewage; second, innovative sewage treatment technology, the generation of sewage is inevitable, we can do is to better solve the problem, innovative sewage treatment technology is a shortcut.

We need to systematically understand the harm brought by sewage, first of all, the harm to the environment, the human living environment if destroyed, the impact will be unbearable. The existence of sewage will lead to a reduction in the number of organisms in the ecosystem or even extinction, resulting in a reduction in the value of various types of environmental resources, and ultimately the ecological balance is destroyed; second, the harm to production, water pollution, industrial water must be invested in more treatment costs, resulting in a waste of resources, energy, food industry water requirements are more stringent, water quality is not qualified, will bring production to a halt. Agricultural use of sewage, so that crop yield reduction, lower quality, and even human and animal victims, large areas of farmland suffer from pollution, reducing the quality of soil; third, the harm to the human body, if people drink polluted water, will cause acute and chronic poisoning, cancer, infectious diseases, and some other bizarre diseases, the sensory deterioration caused by polluted water, will cause inconvenience to human life, emotions are adversely affected.

There are numerous hazards of sewage, so methods of sewage treatment are of great concern. Traditional wastewater treatment methods can no longer meet the existing new types of wastewaters, so it is urgent to explore more novel wastewater treatment methods. In the context of the new crown epidemic, the pollution condition of water bodies by drugs is becoming more and more serious, and we must be more careful in treating these new wastewaters due to the special characteristics of drugs. New wastewater treatment methods are escalating around physical, chemical, and biological methods, such as wastewater treatment using microbial fuel cells, oxidizing electric furnaces for wastewater treatment, and fused physicochemical methods. This manuscript systematically describes the research progress on wastewater, treatment methods, etc., which hopefully can be enlightening to the readers.

> **Tao Zhang** China Agricultural University, Beijing, China

Section 1
