Biohazards are widely present in wastewater, and contaminated water can lead to disease. Consequently, effectively removing biohazards from water is a worldwide need. Advanced oxidation processes (AOPs), based on TiO2 photocatalysis, have effectively degraded a wide spectrum of organics and inactivated biohazards. Photoelectrochemical technology with an anode bias has recently emerged in the research as an alternative tool for photocatalytic inactivation of biohazards. The applied cell voltage can greatly accelerate separation and suppresses the recombination of photogenerated electrons and holes, enabling direct holes attack reactions. This chapter provides an overview of current research activities that focus on using TiO2 photocatalysis and photoelectrocatalysis AOPs to remove biohazards and inactivate microorganisms. To understand the full spectrum of inactivation mechanisms of living microorganisms, the chapter uses a bottom-up strategy to review the decomposition of a series of biological contaminants, ranging from small biological compounds, to large biological compounds, to living biohazards. The chapter concludes by discussing the advancements needed to advance our understanding of the photocatalytic and photoelectrocatalytic decomposition of biohazards and the inactivation mechanism of microorganisms.