**Preface to "Catalytic Processes for Water and Wastewater Treatment"**

Water and wastewater treatment are still facing significant challenges today. Due to climate change, water shortages are already noticeable in many regions of the world. To overcome these problems, alternative water sources must be generated and used; for example, treated wastewater, rainwater, surface water, etc. These water sources have to be treated before use since the development of highly sensitive methods reveals the presence of hazardous compounds in low concentrations. These pollutants should be removed, and many processes have been proposed for their degradation/removal, among them catalytic methods.

Those where catalysts are in solid form in particular exhibit significant advantages.

Catalytic oxidation or reduction processes are among the most efficient processes. These include photocatalysis, sulfate and hydroxyl-radical-based advanced oxidation processes.

This Special Issue contains the contributions of different research groups and discusses the recent progress and advances in catalytic processes in water and wastewater treatment.

> **John Vakros** *Editor*
