The purpose of this thesis is to provide a combined theoretical and experimental approach to solve several enduring questions in wastewater chemistry. Firstly, the sulfate radical has been proposed as an alternative oxidant in advanced oxidation processes (AOPs). Its reactivity with dissolved organic matter (DOM) has not yet been studied and will be quantied in this work using electron pulse radiolysis. Next, it has been shown that DOM present in wastewater can act to impede the remediation of harmful pharmaceutical contaminants in the AOP. Using a new binding model presented here, this association was quantied in terms of equilibrium constants. Lastly, due to the use of bleach to prevent biofouling of the membrane bioreactor in wastewater treatment facilities, chlorine atom chemistry is becoming increasingly important to study regarding AOPs. A numerical system is provided in this thesis to understand the reactivity of chlorine atoms in the presence of wastewater constituents.