During the past three years, a new group of water and wastewater treatment technologies, called advanced reduction processes (ARPs), has been developed by combining activation methods with reducing reagents to yield reducing free radicals, including hydrated electron (e_aq^-) and hydrogen atom (H·), etc. The most commonly used activation method is UV, and the reducing agent is usually sulfite (SO₃^2-) or dithionite (S₂O₄^2-). The produced reducing radicals can donate an unpaired electron to a target contaminant and thereby chemically reduce it. Many kinds of stubborn contaminants can be degraded by ARPs, such as chlorinated organic compounds, fluorinated compounds and some inorganic pollutants (perchlorate, nitrate, bromate, etc.). So this novel process has a bright future in control of environmental pollutions. However, the ARPs are short of systematic research now. In order to promote the development of ARPs, the present research situation and prospect are reviewed in this paper. And the existing problems are also presented based on the analysis of its basic principles.

Contents
1 Introduction
2 Reaction mechanism of ARPs
2.1 Production of free radicals
2.2 The reaction between contaminant and free radicals
3 The research progress of ARPs
3.1 Influencial factors
3.2 Mechanism of degradation
3.3 Kinetic model
4 Conclusion and prospection
4.1 A further study of factors
4.2 Making clear of the degradation mechanism
4.3 Evaluating removal efficiency of different senior reduction technology for different pollutants
4.4 The extension of ARPs