In the past years sulfate radicals (SO4●─) are increasingly discussed as an oxidizing agent for pollutant degradation in water treatment. Indeed, SO4●─ has some unique features, such as being a very strong electron acceptor enabling the degradation of recalcitrant compounds which are refractory towards the strongest oxidant used in water treatment, i.e., the hydroxyl radical (●OH) which is formed in advanced oxidation processes (AOPs) (e.g., ozonation or photolysis of hydrogen peroxide (UV/H2O2). One example is perfluorinated carboxylic acids (PFCAs), which can, albeit slow, be degraded by SO4●─, but persist in AOPs. However, important aspects related to SO4●─ based water treatment such as energy demand and by-product formation, are hardly discussed in current literature. This point is targeted by the present study. The influence of the water matrix on SO4●─-based oxidation has been investigated by monitoring the behavior of model pollutants in a SO4●─ based process. It could be shown that for two types of natural organic matter (NOM) (humic acids extracted from Leonardith layers and Suwannee River NOM) degradation of pollutants by SO4●─ is ≈ 2-3 fold more effective than by ●OH. This indicates that SO4●─ reveals a smaller reaction rate towards NOM compared with ●OH. However, some pollutants react much faster with ●OH than with SO4●─ (e.g., tert-butanol: k(●OH) ≈ 108 M-1 s-1, k(SO4●─) ≈ 105 M-1 s-1), counterbalancing this effect. In the next step formation of undesired by-products was investigated. One important by-product is the potential cancerogenic compound bromate (BrO3─) (EU- and US-EPA drinking water standard 10 µg L-1), that can be formed in ozonation. It was shown, that BrO3─ is also formed in presence of SO4●─ in pure water containing Br─. However, very little amounts of organic matter effectively inhibit BrO3─ formation. Hence, a SO4●─ based process could principally be used as substitute for ozonation if BrO3─ formation cannot sufficiently be controlled in the ozone based process. The presence of Cl─ and HCO3─/CO32─ has far-reaching consequences on SO4●─ based processes. SO4●─ reacts fast with Cl─ (≈ 108 M-1 s-1). Thus, if Cl─ is present in the mM range a large fraction of SO4●─ is involved in oxidation of Cl─ yielding chlorine atoms (Cl●). In presence of water Cl● rapidly forms ●OH and Cl─. Hence, SO4●─ are converted to ●OH and the SO4●─ based system turns into a conventional AOP. However, the fast reaction of Cl● plus HCO3─ competes with the turnover of Cl● into ●OH, thus diminishing the oxidation strength. The reaction of SO4●─ plus PFCAs has drawn a lot of attention on SO4●─ as a potential water treatment agent. It has been proposed in the literature, that PFCAs are degraded by SO4●─ in a step-wise process, that is, the primary product per radical attack is a PFCA shortened by one CF2-unit, at S2O82─ doses in large excess over PFCAs (≈ 50 fold). This process, finally leads to complete mineralization yielding F─ and CO2. The present study revealed, that at low S2O82─ concentrations (2 fold excess over PFCA) another reaction pathway sets in, leading to simultaneous formation of PFCAs shortened by up to 4 carbons. Interestingly, the fluorine balance (fluoride plus fluorine bond to PFCAs) was not complete in case of PFCAs with carbon chains > C5. That suggests the formation of products which have not been described in the literature yet. However, the rate constants of the reaction SO4●─ plus different PFCAs (C2-C8) are very small (1-4 × 104 M-1 s-1) indicating that large amounts of energy are required for their degradation. Furthermore, perfluorinated sulfonic acids (PFSAs) are not degraded at all. The present work has shown, that SO4●─ can principally be used as an oxidant in water treatment. However, SO4●─ based processes are strongly affected by the presence of main water constituents, i.e., Cl─ and HCO3─, which can largely affect reactions occurring in the water matrix and the efficiency of pollutant degradation. A reasonable application of UV/S2O82─ probably is restricted to boundary conditions such as low Cl─ concentration in the source water. Such kind of source waters can especially be found in areas of low population density and little industrial activities. With regard to perfluorinated compounds, however, it is questionable if a SO4●─ based water treatment process represents a feasible tool for their degradation.